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Ca molar ratios as a proxy of precipitation in the northern Yucatan Peninsula, Mexico
Applied Geochemistry 27 (2012) 1579–1586
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Coral Ba/Ca molar ratios as a proxy of precipitation in the northern Yucatan Peninsula, Mexico Guillermo Horta-Puga a,1, José D. Carriquiry a,⇑ a
Instituto de Investigaciones Oceanológicas, Universidad Autónoma de Baja California, Apdo. Postal #453, Ensenada, Baja California 22800, Mexico
a r t i c l e
i n f o
Article history: Received 4 October 2011 Accepted 14 May 2012 Available online 22 May 2012 Editorial handling by R. Fuge
a b s t r a c t The Yucatan Peninsula consists of a karstic terrain that allows the aquifer to directly recharge from rainfall. Due to the various dissolution/precipitation reactions occurring during groundwater flow, the groundwater discharge in the coastal zone becomes a source of trace elements including Ba. The aim of this study was to use the coralline Ba/Ca record as a proxy of precipitation under the consideration that rainfall rates vary at inter-annual time scales. Annual Ba/Ca ratios, both the total content (Ba/CaTC) and the Ca-substitutive fraction (Ba/CaCaF), were quantified in a 52-a old coral colony of Montastraea annularis from the Punta Nizuc Reef, Mexican Caribbean. Average Ba/CaTC (5.90 ± 0.56 lmol/mol) was 20% higher than Ba/CaCaF (4.85 ± 0.33 lmol/mol) indicating that Ba is also incorporated in other fractions. Correlation between annual precipitation and Ba/CaTC time-series is significant (r = 0.77, p < 0.05), allowing the use of the Ba/CaTC ratio as a proxy of precipitation, and hence, enabling the reconstruction of precipitation patterns through time. Likewise, the Ba/CaCaF ratio can be used for the reconstruction of dissolved Ba in coastal seawater. Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction The geochemical record contained in annually banded hermatypic corals has been extensively used as a reliable tool for the reconstruction of recent climate variability at weekly, seasonal, inter-annual, decadal, and even secular time-scales; and has been especially important in tropical areas where there are no available instrumental meteorological/oceanographical data (Druffel, 1997; Gagan et al., 2000; Evans et al., 2001; Mann, 2002). Sea surface temperature (SST) from tropical reef areas has been reconstructed using the coralline ratios of: Sr/Ca (Smith et al., 1979; Beck et al., 1992; de Villiers et al., 1994; McCulloch et al., 1994; Corrège et al., 2000; Marshall and McCulloch, 2002), Mg/Ca (Mitsuguchi et al., 1996; Sinclair et al., 1998; Fallon et al., 1999; Wei et al., 2000), U/Ca (Min et al., 1995), and Ba/Ca (Allison and Finch, 2007). The O stable isotopic record (d18O) has also been used for the reconstruction of SST, salinity and the hydrological regime (precipitation and evaporation) (Cole et al., 1993; Carriquiry et al., 1994; McCulloch et al., 1994; Gagan et al., 2000). As previously suggested by Shen and Sanford (1990), the variability of the coralline Ba/Ca molar ratio from corals growing near coastal areas has been successfully used to infer: salinity and sediment load changes associated with river runoff and soil erosion; volume
⇑ Corresponding author. Tel.: +52 646 1744601; fax: +52 646 1745303. E-mail address: [email protected] (J.D. Carriquiry). Present address: UBIPRO, FES Iztacala, Universidad Nacional Autónoma de México, Av. de los Barrios 1, Los Reyes Iztacala, Tlalnepantla, México 54090, Mexico. 1
0883-2927/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.apgeochem.2012.05.008
of fluvial discharge; and even to calculate the concentration of Ba in river water (dissolved + desorbed from particulate phases) using the effective river’s end-member concentration (Alibert et al., 2003; McCulloch et al., 2003; Sinclair and McCulloch, 2004; Ramos et al., 2004; Sinclair, 2005; Fleitmann et al., 2007; Lewis et al., 2007; Jupiter et al., 2008; Carrilli et al., 2010; Carriquiry and Horta-Puga, 2010; Prouty et al., 2010). Because the volume of freshwater flow from mainland to coastal areas is highly dependent on rainfall, and the levels of coastal Ba increase with increases in river outflow, the coralline Ba/Ca geochemical record could be used as a tracer of precipitation. The northeastern part of the Yucatan Peninsula (NYP) is a relatively flat, low-lying platform consisting of Cretaceous-Tertiary carbonate rocks, predominantly limestone that has evolved into a highly permeable and complex karstic system; hence, surface flow and streams are absent (Ward, 1985; Morán, 1985). Rainwater infiltrates through the porous limestone framework forming groundwater aquifers that flow into the coastal zone and discharge as submarine springs (Back and Hanshaw, 1970; Back et al., 1986; Perry et al., 1989, 2002; Crook et al., 2011). By reacting with atmospheric CO2, rainwater becomes slightly acidified enhancing the dissolution of limestone (Hanshaw and Back, 1980; Back et al., 1986; Beach, 1998), and during the process different minerals (mainly carbonates and sulfates) and trace elements released from the dissociation of these minerals reach the coastal ocean, both in solution or adsorbed to particles (Reeve and Perry, 1994; Carruthers et al., 2005; Young et al., 2008). Also, as freshwater approaches the continental margin, the mixing with seawater generates a highly reactive geochemical zone that enhances dissolution of the carbonate rock
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(Back et al., 1986; Perry et al., 2002) and the desorption of Ba from sedimentary particles, as occurs in an estuarine environment (Hanor and Chan, 1977; Horowitz et al., 2001); in fact, the zone where these reactions take place has been called a ‘subterranean estuary’ (Moore, 1999). Despite that Ba minerals like BaSO4 and BaCO3 are not very water-soluble (Chow and Goldberg, 1960; Church and Wolgemuth, 1972), it has been reported that the contribution of groundwater to the Ba-pool in some coastal areas is very important, accounting for up to 3.5 times the Ba delivered via river flow (Moore, 1997; Shaw et al., 1998). In Florida, consisting of carbonate rock that has developed into a karstic terrain like the NYP, groundwater collected in submarine springs contain up to 4.5 times more Ba than ambient seawater (Swarenski et al., 2001). Therefore, it is hypothesize that as coastal seawater becomes enriched with trace elements, including Ba, especially during high rainfall years, corals should record those events as geochemical records in their growth bands. The Mesoamerican Barrier Reef System (MBRS) is the largest coral reef system in the Caribbean Sea. It lies at the eastern margin of the Yucatan Peninsula, extending from the northeastern tip of the peninsula to the south, as far as Islas de la Bahía, in Honduras. It is a unique reef ecosystem due to its length, reef types, and diverse assemblage of corals and reef-related species. The Punta Nizuc Reef (PNR), which is part of the MBRS, is located 13 km to the south of Cancun, one of the most important resort destinations in the Caribbean, and near the entrance channel that communicates with the Nichupte coastal lagoon. Because of its location in the NYP, the PNR does not receive surface runoff (Granel-Castro and Gález-Hita, 2002; Carruthers et al., 2005). Hence, most terrigenous materials arrive at the coastal zone via groundwater discharge. It is hypothesizee that hermatypic corals growing in the PNR may record annual rainfall variability of the adjacent land, as variations of the Ba/Ca molar ratio in the annual density bands of the skeleton, in a similar way as occurs in areas influenced by river discharge (Alibert et al., 2003; McCulloch et al., 2003; Sinclair and McCulloch, 2004; Carriquiry and Horta-Puga, 2010). Hence, an annual time-scale sampling resolution is enough for reconstructing the environmental molar ratios (Metal/Ca) from the coral growth bands (Shen and Boyle, 1988; Lea et al., 1989; Linn et al., 1990; Reuer et al., 2003). It has been shown that some trace elements, like Cd, Cu, Pb and Ba, that are divalent cations with a ionic radius similar to that of Ca, may enter the CaCO3 molecule ‘‘camouflaging’’ for Ca in the skeleton of hermatypic corals, and the proportion of the substitution varies concomitantly with the element concentration in the dissolved phase in the water column (Shen and Sanford, 1990). However, since the isolation of the Ca-substitutive fraction requires a thorough and timeconsuming cleaning protocol of large samples, usually >0.5 g, as an alternative but simultaneous protocol, the quantification of the total Ba content in addition to the Ca-substitutive molar ratios, on an annual basis, was considered in order to assess its reliability for reconstructing annual precipitation rates.
Fig. 1. Punta Nizuc Reef, Mexican Caribbean.
2. Materials and methods 2.1. Study area and coral collection A living and healthy colony of the hermatypic scleractinian coral Montastraea annularis was collected in August 1998 on the outer slope of the PNR (21°010 3300 N, 86°460 3100 W), near the Nizuc channel that connects with the Nichupte Lagoon. The site is located south of the city of Cancun, in the Mexican Caribbean (Figs. 1 and 2). 2.2. Sample treatment The coral colony was cut into a slab and X-rayed at a local commercial X-ray medical facility (Picker X-ray unit G850S: 31–35 kV,
Fig. 2. Northeastern Yucatan Peninsula. The quadrat centered at 21°N, 87°W depicts the area where precipitation data were obtain.
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200 mA, 0.05 s). The position of annual density bands (low + high) were determined using the X-ray images in order to reconstruct the chronology or age model of the coral colony by assigning calendar years to each band couplet when counting backwards from the band-couplet/year of collection (Fig.3). As the interest was in determining the correlation between rainfall and the Ba/Ca coral record at an inter-annual scale, two replicate samples (1 g blocks) were obtained with a rotary tool equipped with a diamond-cutting wheel from each annual skeletal band. Samples were crushed in an agate mortar, sieved to retain the 280–700 lm fraction, and thoroughly cleaned in 0.2 M HNO3 with ultrasonic agitation to remove contamination associated with the cutting and crushing processes. The two replicates were later processed for separate Ba/Ca molar ratio analysis (i.e., the total content and the Ca-substitutive fractions). For the determination of the total content of Ba, samples were only cleaned several times with a 5 mM HNO3 solution with ultrasonic agitation (Guzmán and Jarvis, 1996). However, for the extraction of the Casubstituting fraction, Shen and Boyle (1988) developed an intense cleaning protocol consisting of a series of oxidation, reduction and weak acid treatments, in order to eliminate trace elements, including Ba, associated with the interchangeable, organic, and authigenic fractions. Thus, the only trace elements that remained in samples were those that substituted for Ca in the coral skeletal carbonate (Shen and Boyle, 1988; Linn et al., 1990). In summary, for the extraction of the Ca-substituting fraction: (1) samples were cleaned with a 1:1 oxidant solution mixture of 30% H2O2: and 0.2 M NaOH, to oxidize the organic matter; (2) samples were cleaned with a reducting solution (1:6:3) of hydrazine (H2NNH2), 2 M NH4OH, and 0.3 M citric acid in 7 M NH4OH, to eliminate oxide coatings, and finally, (3) samples were rinsed several times with a 5 mM HNO3 solution under ultrasonic agitation to remove any persistent metal contamination on the sample surfaces. Once samples were treated following both separate protocols, 200 mg from each thoroughly cleaned annual sample were digested in 2 mL of 2.5 M HNO3. For measuring the annual Ba/Ca molar ratios, an aliquot of 10 lL was obtained from each resulting digested solution and diluted to a final volume of 5 mL with 2% HNO3; hence, the final solution had a Ca concentration of 76 lg/L ([CaCO3]coral 0.2 mg/mL), which is adequate to avoid interferences during instrumental analysis (de Villiers et al., 2002). 2.3. Instrumental analysis The Ba/Ca molar ratios were determined using an ICP-OES (Thermo Jarrell Ash, IRIS/APÒ) with a charge injection solid-state detector, coupled to an ultrasonic nebulizer (CETAC U-5000AT+Ò). All instrumental parameters were adjusted for the highest sensitivity and stability. The instrument was calibrated by the intensity ratio method (de Villiers et al., 1994; Villaescusa-Celaya and Carriquiry, 2004) using the spectral lines with the best stability (i.e., Ba 455.4 and Ca 373.6 nm), and with standard solutions prepared with a known Ba/Ca molar ratio of 2.5–9.0 lmol/mol. To improve the accuracy of the Ba/Ca measurements a standard solution was measured every five samples and a correction factor was calculated for each sample bracketed between measured standard solutions in order to eliminate the effects of instrumental drift, similar to the method proposed by Schrag (1999). Routine instrument precision during the analysis was 4.0%.
Fig. 3. X-radiograph (positive image) of the M. annularis colony from the Punta Nizuc Reef showing annual density bands.
3. Results
2.4. Precipitation data
3.1. Growth rates of M. annularis
Annual precipitation data for the period 1950–1998 was calculated from a 0.5° 0.5° (lat long) cell centered at 21°N, 87°W (UNAM, CMC, 2008), in the adjacent mainland area near the collection site (Fig. 2).
The growth record of the M. annularis colony from the PNR spans 52 a, encompassing the period from 1946 to 1997 (Fig. 3). Average annual growth rate (linear extension) was 9.2 ± 1.1 mm/ a. This growth rate is higher than the 8.2 mm/a reported for this
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species in Puerto Morelos (Carricart-Ganivet, 2004), 25 km south of PNR (see Fig. 1), suggesting that the coral colony was growing healthily.
Raw Ba/Ca time-series of both fractions (Ba/CaCaF and Ba/CaTC) in M. annularis from the PNR are shown in Fig. 4. Annual molar ratios in the Ba/CaCaF ranged from 4.26 lmol/mol (in 1956) to 5.59 lmol/mol (in 1983), with an annual average of 4.85 ± 0.33 lmol/mol. The Ba/ CaTC values ranged from 4.66 lmol/mol (in 1975) to 7.52 lmol/mol (in 1959), with an annual average of 5.90 ± 0.56 lmol/mol. It is interesting to note that the Ba/CaTC average is 20% higher than that for the Ba/CaCaF, this being a statistically significant difference (paired T-test, p < 000.1). The average proportion of non-lattice bound Ba in M. annularis is 0.17 ± 0.09. Correlation between both time-series is low (r = 0.31, p = 0.0213), suggesting that different processes could be influencing coral Ba concentrations in the different geochemical fractions. 3.3. Coral Ba/Ca and precipitation The relationship between raw coral annual Ba/Ca in M. annularis and annual precipitation rates in the land adjacent to the PNR was low for the Ba/CaCaF (r = 0.28, p = 0.044), but for the Ba/CaTC was higher and statistically significant (r = 0.70, p < 0.0001). The correlation between variables did not increase when applying a time lag of 1 or 2 years, hence no lag-time correction was applied while developing a predictive model. Considering that this study was aimed at reconstructing annual precipitation rates using the coral Ba/Ca record as a proxy, in order to filter high-frequency variability, the Ba/CaTC and precipitation time-series were smoothed using a five-a running average following the standard procedure in climate time-series analysis, particularly for developing predictive models (von Storch and Zwiers, 1999; Mann, 2004). The correlation of the filtered time-series increased to r = 0.77, p < 0.0001 (Fig. 5). The predictive model (equation, Fig. 7) obtained from the linear regression analysis of the filtered time-series data relating annual Ba/CaTC versus precipitation (R2 = 0.59, p < 0.001) is presented in Fig. 8.
Precipitation (mm/year)
3.2. Coralline Ba/Ca molar ratios
7.0
1500 1400
6.5
1300 1200
6.0
1100 1000
5.5
900
Ba /Ca ( µm ol/m ol)
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5.0
800 700 600 1950
1955
1960
1965
1970
1975
Years
1980
1985
1990
1995
4.5 2000
Fig. 5. Ba/CaTC molar ratio in the annual bands of M. annularis from PNR (gray line), and annual precipitation rates for a 0.5° 0.5° (lat. long.) cell, centered at 21°N, 87°W (black line). Both time-series were filtered using a 5-a running average.
than those measured in areas directly influenced by river discharge with a high input of terrigenous sedimentary particles, such as the Flower Garden Banks in the Northwestern Gulf of Mexico (Deslarzes et al., 1995) and Montastrea faveolata from the Veracruz Reef System in the Southern Gulf of Mexico (Carriquiry and HortaPuga, 2010), both sites averaging 7.8 lmol/mol. However, the mean Ba/Ca molar ratios from the PNR are slightly above the coral records from other species and geographical areas characterized by carbonate sedimentary environments, like in Pavona clavus from Galapagos (Lea et al., 1989), Porites spp. from the Great Barrier Reef (Alibert et al., 2003; McCulloch et al., 2003; Sinclair and McCulloch, 2004; Jupiter et al., 2008), M. annularis from the Venezuelan Caribbean (Reuer et al., 2003), and M. faveolata from the Southern MBRS (Prouty et al., 2008; Carrilli et al., 2010), which suggests the existence of an additional source of Ba in the NYP area. Merino (1997) has shown that, on a seasonal basis, waters from a depth of 220–250 m upwell in the NYP margin during spring and summer; therefore, it cannot be ruled out that some of the Ba in surface waters, released from remineralization processes in the water column, could be transported from deep water by upwellings in the NYP margin. This also contributes to explain the higher coral Ba/Ca molar ratios observed in the PNR area.
4. Discussion 4.1. Ba/Ca molar ratios in corals from non-terrigenous sedimentary environments The average Ba/Ca ratios observed in M. annularis (Ba/ CaTC = 5.90 lmol/mol, Ba/CaCaF = 4.85 lmol/mol) of PNR are lower
8.0
Ba/Ca (µ µmol/mol)
7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 1945 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000
Years
Fig. 4. Ba/Ca molar ratio in the annual bands of M. annularis from PNR. Ba/CaTC = dark line. Ba/CaCaF = gray line.
4.2. Ba incorporation into the aragonite lattice in M. annularis from the PNR Although Carriquiry and Horta-Puga (2010) reported that almost all Ba contained in the skeleton of M. faveolata from the Southern Gulf of Mexico is incorporated as a Ca-substituting element in the aragonite structure, the present study with M. annularis from the Mexican Caribbean shows that the Ba/CaTC average is 20% higher than the Ba/CaCaF. This indicates that at least in M. annularis from the Mexican Caribbean, an important proportion of Ba is incorporated not as a Ca-substitutive element in the aragonite lattice, but in different geochemical fractions occluded in the skeleton, like particulate, organic and/or authigenic phases that also contain trace elements, as has been widely documented for scleractinian corals (Amiel et al., 1973; Glover and Owen, 1978; Shen and Boyle, 1988; Allison, 1996; Sinclair and McCulloch, 2004). To date the geochemical/biochemical processes involved in the incorporation of Ba into the coral skeleton are not well known. Hence, the process of partition among the different geochemical fractions that differentiates M. annularis from M. faveolata, as well as the sources of Ba for each of the geochemical fractions in the coral skeleton, are also not known. Nonetheless, the geochemical record of annually-banded corals has been shown
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Fig. 6. Annual precipitation rates (dark line), and the relative proportion of lattice-bound Ba (1 Ba/CaCaF/Ba/CaTC) in annual bands of the coral M. annularis from the PNR (gray line).
4.3. Relationship between precipitation and coral Ba/Ca
Ba/Ca ( µ mol/mol)
7.0 6.5 6.0 5.5 Ba/Ca = 0.001(P) + 4.010 R = 0.59 p< 0.001
5.0 4.5
700
800
900
1000
1100
1200
Precipitation (mm/year)
1300
1400
1500
Fig. 7. Regression analysis between the filtered time-series of the Ba/CaTC molar ratio in the annual bands of M. annularis from the PNR and the annual average precipitation. Correlation coefficient between time-series is r = 0.77, p < 0.0001.
Precipitation (mm/year)
2000 1750 1500 1250 1000 750 500 1945 1950 1955 1960 1965 1970 1975
1980 1985 1990 1995 2000
Years Fig. 8. Comparative annual precipitation rates in the NYP. Reported raw precipitation data (black line), and reconstructed using the M. annularis Ba/CaTC record (raw data) from the PNR (gray line).
to reliably record past environmental conditions (McCulloch et al., 2003; Fleitmann et al., 2007; Carriquiry and Horta-Puga, 2010; Prouty et al., 2010), and in this study the use the Ba/Ca record from the PNR is proposed as a proxy for reconstructing historical precipitation, and the dissolved Ba concentrations in the seawater, of the NYP area.
In order to assess the effect of groundwater outflows from karstic terrains into reef areas, which should be influenced by inter-annual variations in rainfall, the annual Ba/Ca coralline record was plotted versus the annual precipitation in the PNR continental adjacent area. Fig. 5 shows that the filtered time-series of Ba/CaTC closely follows the inter-annual variation in rainfall. The correlation is statistically significant (r = 0.77, p < 0.001), supporting the hypothesis that as Ba is transported by groundwater flow into the coastal environment it gets incorporated into the Ba/CaTC of the coral skeletons. It is important to observe that the time-series showed a high correlation with no time lag, a fact that could be explained by the high permeability (j > 1 m2) of the karst in the continental area near the Nichupte Lagoon (Granel-Castro and Gález-Hita, 2002; Crook et al., 2011), which permits groundwater to outflow to the coastal zone almost immediately after precipitation, due to higher hydraulic pressures that are generated in the aquifer (Santos et al., 2012). However, as there are no data on the aquifer’s extent and the average Ba concentration in the limestone of the NYP, it becomes very difficult to assess the residence times and the contribution of the dissolution products of limestone to the coastal seawater pool of Ba. The same analysis was also applied to the Ba/CaCaF timeseries and the correlation was lower (r = 0.28, p < 0.05), which suggest that the coralline Ba-signal in the Ca-substitutive geochemical fraction is not responding entirely to precipitation. Furthermore, the correlation between the proportion of annual non-latticebound Ba relative to the total Ba content (1 Ba/CaCaF/Ba/CaTC) versus precipitation is positive (Fig. 6) with a moderate correlation (r = 0.48, p < 0.001). It is worth noting that during dry years with low precipitation rates (<1000 mm/a), the proportion of nonlattice-bound Ba decreased, on average, down to 10% of the total content in the annual band; but during the years of higher precipitation (>1000 mm/) this proportion increased to >20%. This suggests that, as annual precipitation rates increase, the proportion of Ba that is incorporated into the coral skeleton other than the Ca-substitutive fraction also increases, and vice versa. Therefore, it appears that in the years/periods with low precipitation rates, groundwater does not carry sufficient dissolved/suspended terrigenous materials; hence, the background levels of dissolved-Ba in seawater nearby the collection site comprise the main source of Ba for Ca-substitution. But, when groundwater flow (and/or precipitation) exceeds some threshold, it enhances the delivery of higher amounts
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of particulate material, to the coastal zone which are added to the background levels of Ba in the PNR area, therefore, imprinting its signal in the coral geochemical record through its incorporation into the skeleton, mainly in the non-lattice-bound fraction, as is empirically evidenced by the results obtained here. A similar situation has been reported for the coral Porites spp., which is influenced by the fluvial plume of the Burdekin River in the Great Barrier Reef (Alibert et al., 2003; Sinclair, 2005). Likewise, it has been observed in Porites lobata from Hawaii, wherein episodic releases of higher amounts of Ba-bearing sediments from a nearby mangrove forest, are the source/cause of higher coral Ba/Ca molar ratios (Prouty et al., 2010). Hence, it may not be necessary to isolate the Ca-substituting geochemical fraction, since the Ba/CaTC is the geochemical signal in the coral skeletons that responds to precipitation, and concomitantly to groundwater supply of Ba to the fringing reefs of the NYP. Fig. 7 shows the regression analysis between the filtered Ba/ CaTC and precipitation time-series data, which suggests that the variability in the coral Ba/Ca ratios could be explained by rainfall (R2 = 0.59, p < 0.05). Fluid-rock interaction rates in coastal karstic aquifers seem to be controlled by rainfall rates in which the dissolution products are transported into reef waters to ultimately become encoded in the coral skeletal records. This reveals that the coralline Ba/CaTC record of the hermatypic coral M. annularis can be reliably used as a proxy of precipitation in the NYP. The probable explanations for not finding a higher correlation may be: (1) the annual precipitation data were obtained from a very large quadrant (2830 km2) that may not be entirely representative of the local rainfall rates around the PNR, wherein there are no available long-term records, and the actual extent of the karstic aquifer that flushes freshwater into the coastal zone is unknown (GranelCastro and Gález-Hita, 2002); (2) the variability of the groundwater outflow volume into any specific coastal area due to the karstic nature of the terrain (Hanshaw and Back, 1980; Steinich and Marín, 1997), and although several submarine springs have been located in the adjacent Nichupte Lagoon, none of them has been studied, hindering the ability to calculate the freshwater discharge volume and rates (Granel-Castro and Gález-Hita, 2002); (3) quantitatively undetermined diagenetic and/or dolomitization rates that release or capture unknown quantities of trace elements in the groundwater mixing zone (Ward and Halley, 1984; Moore, 1999); (4) unquantified amounts of dissolved and/or particulate materials carried by groundwater to the coastal area released by the varying hydrogeochemical conditions that yield differential dissolution rates of carbonate soils and rocks (Back et al., 1979, 1986); and (5) the unknown contribution of upwelling waters in the NYP area (Merino, 1997). Equivalent processes have been identified in karstic caves in which, from initial fluid-rock interactions and the transport of the dissolution products, yield the formation of speleothems containing highly reliable geochemical records of environmental and/or climatic change (e.g., Wang et al., 2001; Frappier et al., 2002). 4.4. Reconstructed precipitation in the NYP As coralline Ba/CaTC correlates well with precipitation (Fig. 5), this relationship was used for reconstructing the historical annual precipitation rates in the NYP. The calibration line, obtained from the linear regression analysis of the parameters (Fig. 8), is:
Precipitationðmm=aÞ ¼ 347:3½Ba=CaTC ðlmol=molÞ 939:2 Observed and reconstructed precipitation rate times-series for the 1946–1997 period are shown in Fig. 7. As expected both time series show the same pattern through time with some departures due to the uncertain role or weight of each of the factors considered in the previous section. Considering these uncertainties, this
45 44 43 42
Ba (nmol/kg)
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41 40 39 38 37 36 35 34 33 1945
1950 1955 1960 1965
1970 1975
1980 1985
1990 1995
2000
Years Fig. 9. Reconstructed dissolved Ba concentration in seawater in the NYP coastal zone.
equation is the first attempt to use the coralline Ba/Ca record as a proxy for reconstructing precipitation rates in coastal areas not influenced by significant fluvial discharge, at least in the study area. 4.5. Reconstructed seawater Ba concentrations Considering that: (1) the CaF in corals is responding directly to the concentration of Ba in the dissolved phase in seawater (Shen and Boyle, 1988; Shen and Sanford, 1990), (2) that the empirical distribution coefficient reported for Ba/Ca molar ratios in Montastraea and other coral species is Ba/Cacoral/Ba/Caseawater 1.3 (Lea et al., 1989; Reuer et al., 2003), and (3) that the concentration of Ca in seawater is conservative: [Ca]seawater = 0.412 g/kg (Bruland, 1983), the significance of the Ba/CaCaF in the annual bands of coral as a proxy for the dissolved concentration of Ba in seawater in PNR was investigated. Assuming that salinity is constant (35 PSU), then, the concentration of dissolved Ba in seawater varied from 33.7 nmol/kg in 1957, to 44.3 nmol/kg in 1984, with an average concentration of 38.4 ± 2.7 nmol/kg (Fig. 9). These values are slightly higher than the average concentration of Ba of 34 nmol/kg in oceanic surface waters in the Atlantic (Chan et al., 1977; Lea and Boyle, 1991), but agree well with those expected for coastal surface seawater influenced by groundwater discharge (Swarenski et al., 2001). Hence, the Ca-substituting geochemical fraction of Ba in the coral skeleton (i.e., the Ba/CaCaF ratio) from the PNR seems to coherently record the inter-annual variability of Ba concentration in the coastal zone of the NYP. 5. Conclusions Varying rainfall rates at inter-annual to decadal timescales on the coastal karstic terrain of the NYP is directly related to the groundwater recharge variability of the aquifer of this area. Concomitantly, the changes occurring during groundwater recharge promote fluid-rock interactions, such as carbonate dissolution. The products of dissolution, such as trace elements, are delivered into reef waters via submarine springs to ultimately become incorporated in the coral skeletal records. This study provides evidence that the coralline Ba/CaTC record of the hermatypic coral M. annularis can be reliably used as a long term proxy for precipitation in the NYP. The analytical protocol followed here reveals that it is not necessary to isolate the Ca-substituting fraction, in order to use it as a proxy for rainfall. However, when following a more exhaustive cleaning protocol to isolate the Ca-substituting levels
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of Ba incorporated in the coral skeleton (the Ba/CaCaF ratio) an adequate reconstruction of dissolved Ba concentrations in coastal seawater can be achieved. Hence, the Ba/CaCaF ratio can be used as a proxy for dissolved Ba in seawater in the NYP. However, the exact mechanisms explaining the cause-effect relationship between seawater (dissolved or particulate) and coral Ba concentrations, in any or all geochemical fractions, are still not known. This is a research issue that should be properly addressed in the future, in order to fully understand the processes involved in the geochemistry of the skeleton of M. annularis. Acknowledgements We thank Julio Villaescusa and Pedro Castro (UABC, IIO) for their collaboration in all stages of laboratory work. Also thanks for the comments and suggestions of two anonymous reviewers, which notably improved this manuscript. This study was financed in part by a grant from the National Science and Technology Council of Mexico to J.D. Carriquiry (CONACYT: 46814). References Alibert, C., Kinsley, L., Fallon, S.J., McCulloch, M.T., Berkelmans, R., McAllister, F., 2003. Source of trace element variability in Great Barrier Reef corals affected by the Burdekin flood plums. Geochim. Cosmochim. Acta 67, 231–246. Allison, N., 1996. Geochemical anomalies in coral skeletons and their possible implications for palaeoenvironmental analyses. Mar. Chem. 55, 367–379. Allison, N., Finch, A.A., 2007. High temporal resolution Mg/Ca and Ba/Ca records in modern Porites lobata corals. Geochem. Geophys. Geosys. 8, Q05001. http:// dx.doi.org/10.1029/2006GC001477. Amiel, A.J., Friedman, G.M., Miller, D.S., 1973. Distribution and nature of incorporation of trace elements in modern aragonitic corals. Sedimentology 20, 47–64. Back, W., Hanshaw, W., 1970. Comparison of chemical hydrogeology of the carbonate peninsulas of Florida and Yucatan. J. Hydrol. 10, 330–368. Back, W., Hanshaw, B., Herman, J.S., van Driel, J.N., 1986. Differential dissolution of a Pleistocene reef in the ground-water mixing zone of coastal Yucatan, Mexico. Geology 14, 137–140. Back, W., Hanshaw, B., Pyle, T.E., Plummer, L.N., Wedie, A.E., 1979. Geochemical significance of groundwater discharge and carbonate dissolution to the formation of Caleta Xel-Ha, Quintana Roo, Mexico. Water Resour. Res. 15, 1521–1535. Beach, T., 1998. Soil constraints on Northwest Yucatan, Mexico: Pedoarchaeology and Maya subsistence at Chunchucmil. Geoarchaeology 13, 759–791. Beck, J.W., Edwards, R.L., Ito, E., Taylor, F.W., Recy, J., Rougerie, F., Joannot, P., Henin, C., 1992. Seasurface temperature from coral skeletal strontium/calcium ratios. Science 257, 644–647. Bruland, K., 1983. Trace elements in seawater. In: Riley, J.P., Chester, R. (Eds.), Chemical Oceanography, vol. 8. Academic Press, London, pp. 147–220. Carricart-Ganivet, J.P., 2004. Sea surface temperature and the growth of the West Atlantic reef-building coral Montastraea annularis. J. Exp. Mar. Biol. Ecol. 302, 249–260. Carrilli, J.E., Prouty, N.G., Hughen, K.A., Norris, R.D., 2010. Century-scale records of land-based activities recorde in Mesoamerican coral cores. Mar. Pollut. Bull. 58, 1835–1842. Carriquiry, J.D., Horta-Puga, G., 2010. The Ba/Ca record of corals from the Southern Gulf of Mexico: contributions from land-use changes, fluvial discharge and oildrilling muds. Mar. Pollut. Bull. 60, 1625–1630. Carriquiry, J.D., Risk, M.J., Schwarcz, H.P., 1994. Stable isotope geochemistry of corals from Costa Rica as proxy indicator of the El Niño/Southern Oscillation (ENSO). Geochim. Cosmochim. Acta 58, 335–351. Carruthers, T.J.B., van Tussenbroek, B.I., Dennison, W.C., 2005. Influence of submarine springs and wastewater on nutrient dynamics of Caribbean seagrass meadows. Estuar. Coast. Shelf Sci. 64, 191–199. Chan, L.H., Drummond, D., Edmond, J.M., Grant, B., 1977. On the barium data from the Atlantic GEOSECS expedition. Deep-Sea Res. 24, 613–649. Chow, T.J., Goldberg, E.D., 1960. On the marine geochemistry of barium. Geochim. Cosmochim. Acta 20, 192–198. Church, T.M., Wolgemuth, K., 1972. Marine barite saturation. Earth Planet. Sci. Lett. 15, 35–44. Cole, J.E., Shen, G.T., Fairbanks, R.G., 1993. Recent variability in the southern oscillation: isotopic results from a Tarawa Atoll coral. Science 260, 1790–1793. Corrège, T., Delcroix, T., Récy, J., Beck, W., Cabioch, G., Cornec, F.L., 2000. Evidence for stronger El Niño-Southern Oscillation (ENSO) events in a mid-Holocene massive coral. Paleoceanography 15, 465–470. Crook, E.D., Potts, D., Rebolledo-Vieyra, M., Hernandez, L., Paytan, A., 2011. Calcifying coral abundance near low-pH springs: implications for future ocean acidification. Coral Reefs. http://dx.doi.org/10.1007/s00338-011-0839-y.
1585
de Villiers, S., Graves, M., Elderfield, H., 2002. An intensity ratio calibration method for the accurate determination of Mg/Ca and Sr/Ca of marine carbonates by ICPAES. Geochem. Geophy. Geosy., doi:2001GC000169. de Villiers, S., Shen, G.T., Nelson, B.K., 1994. The Sr/Ca-temperature relationship in coralline aragonite: influence of variability in (Sr/Ca)seawater and skeletal growth parameters. Geochim. Cosmochim. Acta 58, 197–208. Deslarzes, K.J.P., Boothe, P.N., Presley, B.J., Steinmetz, G.L., 1995. Historical incorporation of barium in thr reef building coral Montastrea annularis at the Flower Garden Banks, North-West Gulf of México. Mar. Pollut. Bull. 30, 718– 722. Druffel, E.R.M., 1997. Geochemistry of corals: Proxies of past ocean chemistry, ocean circulation and climate. Proc. Nat. Acad. Sci. USA 94, 8354–8361. Evans, M.N., Cane, M.A., Schrag, D.P., Kaplan, A., Linsley, B.K., Villalba, R., Wellington, G.M., 2001. Support for tropically – driven Pacific decadal variability based on paleoproxy evidence. Geophys. Res. Lett. 28, 3689–3692. Fallon, S.J., McCulloch, M.T., van Woesik, R., Sinclair, D.J., 1999. Corals at their latitudinal limits: laser ablation trace element systematic in Porites from Shirigai Bay, Japan. Earth Planet. Sci. Lett. 172, 221–238. Fleitmann, D., Dunbar, R.B., McCulloch, M., Mundelsee, M., Vuille, M., McClanahan, T.R., Cole, J.E., Eggins, S., 2007. East African erosion recorded in a 300 year old colony from Kenya. Geophys. Res. Lett. 34, L04401. http://dx.doi.org/10.1029/ 2006GL028525. Frappier, A., Sahagian, D., González, L.A., Carpenter, S.J., 2002. El Niño events recorded by stalagmite carbon isotopes. Science 298, 565. Gagan, M.K., Ayliffe, L.K., Beck, J.W., Cole, J.E., Druffel, E.R.M., Dunbar, R.B., Schrag, D.P., 2000. New view of tropical paleoclimate from corals. Quatern. Sci. Rev. 19, 45–64. Glover, R.M., Owen, R.M., 1978. An evaluation of methods used to determine trace element partitioning in coral. Can. J. Spectrosc. 23, 27–30. Granel-Castro, E., Gález-Hita, L., 2002. Deterioro de la calidad del agua subterranean por el desarrollo poblacional: Cancún. Q. Roo. Ingeniería Rev. Acad. 6, 41–53. Guzmán, H.M., Jarvis, K.E., 1996. Vanadium century record from Caribbean reef corals: a tracer of oil pollution in Panama. Ambio 25, 523–526. Hanor, J.S., Chan, L.-H., 1977. Non-conservative behavior of barium during mixing of Mississippi River and Gulf of Mexico waters. Earth Planet. Sci. Lett. 37, 242–250. Hanshaw, B.B., Back, W., 1980. Chemical mass-wasting of the northern Yucatán Peninsula by groundwater dissolution. Geology 8, 222–224. Horowitz, A.J., Elrick, K.A., Smith, J.J., 2001. Annual suspended sediment and trace element fluxes in the Mississipi, Columbia, Colorado and Rio Grande drainage basins. Hydrol. Process. 15, 1169–1207. Jupiter, S., Roff, G., Marion, G., Henderson, M., Schrameyer, V., McCulloch, M.T., Hoegh-Guldberg, O., 2008. Linkages between coral assemblages and coral proxies of terrestrial exposure along a cross-shelf gradient on the southern Great Barrier Reef. Coral Reefs 27, 887–903. Lea, D.W., Boyle, E.A., 1991. Barium in planktonic foraminifera. Geochim. Cosmochim. Acta 55, 3321–3331. Lea, D.W., Shen, G.T., Boyle, E.A., 1989. Coralline barium records temporal variability in equatorial Pacific upwelling. Nature 340, 373–376. Lewis, S.E., Shields, G., Kamber, B.S., Lough, J.M., 2007. A multi-trace element coral record of land-use changes in the Burdekin River catchment, NE Australia. Palaeogeog. Palaeoclimatol. Palaeoecol. 246, 471–487. Linn, L.J., Delaney, M.L., Druffel, R.M., 1990. Trace metals in contemporary and seventeenth-century Galapagos coral: records of seasonal and annual variations. Geochim. Cosmochim. Acta 54, 387–394. Mann, M.E., 2002. The value of multiple proxies. Science 297, 1481–1482. Mann, M.E., 2004. On smoothing potentially non-stationary climate time-series. Geophys. Res. Lett. 31, L07214. http://dx.doi.org/10.1029/2004GL019569. Marshall, J.F., McCulloch, M.T., 2002. An assessment of the Sr/Ca ratio in shallow water hermatypic corals as a proxy for sea surface temperature. Geochim. Cosmochim. Acta 66, 3263–3280. McCulloch, M.T., Fallon, S., Wyndham, T., Hendy, E., Lough, J., Barnes, D., 2003. Coral record of increased sediment flux to the inner Great Barrier Reef since European settlement. Nature 421, 727–730. McCulloch, M.T., Gagan, M.K., Mortimer, G.E., Chivas, A.R., Isdale, P.J., 1994. A high– resolution Sr/Ca and d18O coral record from the Great Barrier Reef, Australia, and the 1982–1983 El Niño. Geochim. Cosmochim. Acta 58, 2747–2754. Merino, M., 1997. Upwelling on the Yucatan Shelf: hydrographic evidence. J. Mar. Syst. 13, 101–121. Min, G.R., Edwards, R.L., Taylor, R.W., Recy, L., Gallup, C.D., Beck, J.W., 1995. Annual cycles of U/Ca in coral skeletons and U/Ca thermometry. Geochim. Cosmochim. Acta 59, 2025–2042. Mitsuguchi, T., Matsumoto, E., Abe, O., Uchida, T., Isdale, P.J., 1996. Mg/Ca thermometry in coral skeletons. Science 274, 961–963. Moore, W.S., 1997. High fluxes of radium and barium from the mouth of the Ganges–Brahmaputra River during low river discharge suggest large groundwater source. Earth Planet. Sci. Lett. 150, 141–150. Moore, W.S., 1999. The subterranean estuary: a reaction zone of ground water and sea water. Mar. Chem. 65, 111–125. Morán, Z.D.J., 1985. Geología de la República Mexicana. Facultad de Ingeniería (UNAM) and Instituto Nacional de Estadística, Geografía e Informatica. Mexico City, Mexico. Perry, E.C., Swift, J., Gamboa, J., Reeve, A., Sanborn, R., Marin, L.E., Villasuso, M., 1989. Geologic and environmental aspects of surface cementation, north coast, Yucatan, Mexico. Geology 17, 818–821.
1586
G. Horta-Puga, J.D. Carriquiry / Applied Geochemistry 27 (2012) 1579–1586
Perry, E., Velázquez-Oliman, G., Marin, L.E., 2002. The hydrogeochemistry of the karst aquifer system of the Northern Yucatan Peninsula, Mexico. Int. Geol. Rev. 44, 191–221. Prouty, N.G., Field, M.E., Stock, J.D., Jupiter, S.D., McCulloch, M., 2010. Coral Ba/Ca records of sediment input to the fringing reef of the southshore of Molokai’I, Hawai’I over the last several decades. Mar. Pollut. Bull. 60, 1822–1835. Prouty, N.G., Hughen, K.A., Carrilli, J., 2008. Geochemical signature of land-based activities in Caribbean coral surface samples. Coral Reefs 27, 727–742. Ramos, A.A., Inoue, Y., Ohde, S., 2004. Metal contents in Porites corals: anthropogenic input of river run-off into a coral reef from an urbanized area. Okinawa. Mar. Pollut. Bull. 48, 281–294. Reeve, A.S., Perry, E.C., 1994. Carbonate geochemistry and the concentrations of aqueous Mg2+, Sr2+ and Ca2+: western north coast of Yucatan, Mexico. Chem. Geol. 112, 105–117. Reuer, M.K., Boyle, E.A., Cole, J.E., 2003. A mid-twentieth century reduction in tropical upwelling from coralline trace element proxies. Earth Planet. Sci. Lett. 210, 437–452. Santos, I.R., Eyre, B.D., Huettel, M., 2012. The driving forces of porewater and groundwater flow in permeable coastal sediments: a review. Estuar. Coast Shelf. Sci. 98, 1–15. Schrag, D.P., 1999. Rapid analysis of high-precision Sr/Ca ratios in corals and other marine carbonates. Paleoceanography 14, 97–102. Shaw, T.J., Moore, W.S., Kloepfer, J., Sochaski, M.A., 1998. The flux of barium to the coastal waters of the southeastern USA: the importance of submarine groundwater discharge. Geochim. Cosmochim. Acta 62, 3047–3054. Shen, G.T., Boyle, E.A., 1988. Determination of lead, cadmium and other trace metals in annually-banded corals. Chem. Geol. 67, 47–62. Shen, G.T., Sanford, C.L., 1990. Trace element indicators of climate change in annually-banded corals. In: Glynn, P.W. (Ed.), Global Ecological Consequences of the 1982–83 El Niño. Elsevier, New York, pp. 255–283. Sinclair, D.J., 2005. Non-river flood barium signals in the skeletons of corals from coastal Queensland, Australia. Earth Planet. Sci. Lett. 237, 354–369. Sinclair, D.J., McCulloch, M.T., 2004. Corals record low mobile barium concentrations in the Burdekin River during the 1974 flood: evidence for limited Ba supply to rivers? Palaeogeog. Palaeoclimatol. Palaeoecol. 214, 155–174.
Sinclair, D.J., Kinsley, L.P.J., McCulloch, M.T., 1998. High resolution analysis of trace elements in corals by laser ablation ICP-MS. Geochim. Cosmochim. Acta 62, 1889–1901. Smith, S.V., Buddemeier, R.W., Redalje, R.C., Houck, J.E., 1979. Strontium-calcium thermometry in coral skeletons. Science 204, 404–407. Steinich, B., Marín, L.E., 1997. Determination of flow characteristics in the aquifer of the northwestern Peninsula of Yucatan, Mexico. J. Hydrol. 191, 315–331. Swarenski, P.W., Reich, C.D., Spechler, R.M., Kindinger, J.L., Moore, W.S., 2001. Using multiple geochemical tracers to characterize the hydrogeology of the submarine spring off Crescent Beach, Florida. Chem. Geol. 179, 187–2022. UNAM, CMC, 2008. Universidad Nacional Autónoma de México, Centro de Ciencias de la Atmósfera. Base de datos de precipitación pluvial v0705.
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Coral Ba/Ca molar ratios as a proxy of precipitation in the northern Yucatan Peninsula, Mexico Guillermo Horta-Puga a,1, José D. Carriquiry a,⇑ a
Instituto de Investigaciones Oceanológicas, Universidad Autónoma de Baja California, Apdo. Postal #453, Ensenada, Baja California 22800, Mexico
a r t i c l e
i n f o
Article history: Received 4 October 2011 Accepted 14 May 2012 Available online 22 May 2012 Editorial handling by R. Fuge
a b s t r a c t The Yucatan Peninsula consists of a karstic terrain that allows the aquifer to directly recharge from rainfall. Due to the various dissolution/precipitation reactions occurring during groundwater flow, the groundwater discharge in the coastal zone becomes a source of trace elements including Ba. The aim of this study was to use the coralline Ba/Ca record as a proxy of precipitation under the consideration that rainfall rates vary at inter-annual time scales. Annual Ba/Ca ratios, both the total content (Ba/CaTC) and the Ca-substitutive fraction (Ba/CaCaF), were quantified in a 52-a old coral colony of Montastraea annularis from the Punta Nizuc Reef, Mexican Caribbean. Average Ba/CaTC (5.90 ± 0.56 lmol/mol) was 20% higher than Ba/CaCaF (4.85 ± 0.33 lmol/mol) indicating that Ba is also incorporated in other fractions. Correlation between annual precipitation and Ba/CaTC time-series is significant (r = 0.77, p < 0.05), allowing the use of the Ba/CaTC ratio as a proxy of precipitation, and hence, enabling the reconstruction of precipitation patterns through time. Likewise, the Ba/CaCaF ratio can be used for the reconstruction of dissolved Ba in coastal seawater. Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction The geochemical record contained in annually banded hermatypic corals has been extensively used as a reliable tool for the reconstruction of recent climate variability at weekly, seasonal, inter-annual, decadal, and even secular time-scales; and has been especially important in tropical areas where there are no available instrumental meteorological/oceanographical data (Druffel, 1997; Gagan et al., 2000; Evans et al., 2001; Mann, 2002). Sea surface temperature (SST) from tropical reef areas has been reconstructed using the coralline ratios of: Sr/Ca (Smith et al., 1979; Beck et al., 1992; de Villiers et al., 1994; McCulloch et al., 1994; Corrège et al., 2000; Marshall and McCulloch, 2002), Mg/Ca (Mitsuguchi et al., 1996; Sinclair et al., 1998; Fallon et al., 1999; Wei et al., 2000), U/Ca (Min et al., 1995), and Ba/Ca (Allison and Finch, 2007). The O stable isotopic record (d18O) has also been used for the reconstruction of SST, salinity and the hydrological regime (precipitation and evaporation) (Cole et al., 1993; Carriquiry et al., 1994; McCulloch et al., 1994; Gagan et al., 2000). As previously suggested by Shen and Sanford (1990), the variability of the coralline Ba/Ca molar ratio from corals growing near coastal areas has been successfully used to infer: salinity and sediment load changes associated with river runoff and soil erosion; volume
⇑ Corresponding author. Tel.: +52 646 1744601; fax: +52 646 1745303. E-mail address: [email protected] (J.D. Carriquiry). Present address: UBIPRO, FES Iztacala, Universidad Nacional Autónoma de México, Av. de los Barrios 1, Los Reyes Iztacala, Tlalnepantla, México 54090, Mexico. 1
0883-2927/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.apgeochem.2012.05.008
of fluvial discharge; and even to calculate the concentration of Ba in river water (dissolved + desorbed from particulate phases) using the effective river’s end-member concentration (Alibert et al., 2003; McCulloch et al., 2003; Sinclair and McCulloch, 2004; Ramos et al., 2004; Sinclair, 2005; Fleitmann et al., 2007; Lewis et al., 2007; Jupiter et al., 2008; Carrilli et al., 2010; Carriquiry and Horta-Puga, 2010; Prouty et al., 2010). Because the volume of freshwater flow from mainland to coastal areas is highly dependent on rainfall, and the levels of coastal Ba increase with increases in river outflow, the coralline Ba/Ca geochemical record could be used as a tracer of precipitation. The northeastern part of the Yucatan Peninsula (NYP) is a relatively flat, low-lying platform consisting of Cretaceous-Tertiary carbonate rocks, predominantly limestone that has evolved into a highly permeable and complex karstic system; hence, surface flow and streams are absent (Ward, 1985; Morán, 1985). Rainwater infiltrates through the porous limestone framework forming groundwater aquifers that flow into the coastal zone and discharge as submarine springs (Back and Hanshaw, 1970; Back et al., 1986; Perry et al., 1989, 2002; Crook et al., 2011). By reacting with atmospheric CO2, rainwater becomes slightly acidified enhancing the dissolution of limestone (Hanshaw and Back, 1980; Back et al., 1986; Beach, 1998), and during the process different minerals (mainly carbonates and sulfates) and trace elements released from the dissociation of these minerals reach the coastal ocean, both in solution or adsorbed to particles (Reeve and Perry, 1994; Carruthers et al., 2005; Young et al., 2008). Also, as freshwater approaches the continental margin, the mixing with seawater generates a highly reactive geochemical zone that enhances dissolution of the carbonate rock
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(Back et al., 1986; Perry et al., 2002) and the desorption of Ba from sedimentary particles, as occurs in an estuarine environment (Hanor and Chan, 1977; Horowitz et al., 2001); in fact, the zone where these reactions take place has been called a ‘subterranean estuary’ (Moore, 1999). Despite that Ba minerals like BaSO4 and BaCO3 are not very water-soluble (Chow and Goldberg, 1960; Church and Wolgemuth, 1972), it has been reported that the contribution of groundwater to the Ba-pool in some coastal areas is very important, accounting for up to 3.5 times the Ba delivered via river flow (Moore, 1997; Shaw et al., 1998). In Florida, consisting of carbonate rock that has developed into a karstic terrain like the NYP, groundwater collected in submarine springs contain up to 4.5 times more Ba than ambient seawater (Swarenski et al., 2001). Therefore, it is hypothesize that as coastal seawater becomes enriched with trace elements, including Ba, especially during high rainfall years, corals should record those events as geochemical records in their growth bands. The Mesoamerican Barrier Reef System (MBRS) is the largest coral reef system in the Caribbean Sea. It lies at the eastern margin of the Yucatan Peninsula, extending from the northeastern tip of the peninsula to the south, as far as Islas de la Bahía, in Honduras. It is a unique reef ecosystem due to its length, reef types, and diverse assemblage of corals and reef-related species. The Punta Nizuc Reef (PNR), which is part of the MBRS, is located 13 km to the south of Cancun, one of the most important resort destinations in the Caribbean, and near the entrance channel that communicates with the Nichupte coastal lagoon. Because of its location in the NYP, the PNR does not receive surface runoff (Granel-Castro and Gález-Hita, 2002; Carruthers et al., 2005). Hence, most terrigenous materials arrive at the coastal zone via groundwater discharge. It is hypothesizee that hermatypic corals growing in the PNR may record annual rainfall variability of the adjacent land, as variations of the Ba/Ca molar ratio in the annual density bands of the skeleton, in a similar way as occurs in areas influenced by river discharge (Alibert et al., 2003; McCulloch et al., 2003; Sinclair and McCulloch, 2004; Carriquiry and Horta-Puga, 2010). Hence, an annual time-scale sampling resolution is enough for reconstructing the environmental molar ratios (Metal/Ca) from the coral growth bands (Shen and Boyle, 1988; Lea et al., 1989; Linn et al., 1990; Reuer et al., 2003). It has been shown that some trace elements, like Cd, Cu, Pb and Ba, that are divalent cations with a ionic radius similar to that of Ca, may enter the CaCO3 molecule ‘‘camouflaging’’ for Ca in the skeleton of hermatypic corals, and the proportion of the substitution varies concomitantly with the element concentration in the dissolved phase in the water column (Shen and Sanford, 1990). However, since the isolation of the Ca-substitutive fraction requires a thorough and timeconsuming cleaning protocol of large samples, usually >0.5 g, as an alternative but simultaneous protocol, the quantification of the total Ba content in addition to the Ca-substitutive molar ratios, on an annual basis, was considered in order to assess its reliability for reconstructing annual precipitation rates.
Fig. 1. Punta Nizuc Reef, Mexican Caribbean.
2. Materials and methods 2.1. Study area and coral collection A living and healthy colony of the hermatypic scleractinian coral Montastraea annularis was collected in August 1998 on the outer slope of the PNR (21°010 3300 N, 86°460 3100 W), near the Nizuc channel that connects with the Nichupte Lagoon. The site is located south of the city of Cancun, in the Mexican Caribbean (Figs. 1 and 2). 2.2. Sample treatment The coral colony was cut into a slab and X-rayed at a local commercial X-ray medical facility (Picker X-ray unit G850S: 31–35 kV,
Fig. 2. Northeastern Yucatan Peninsula. The quadrat centered at 21°N, 87°W depicts the area where precipitation data were obtain.
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200 mA, 0.05 s). The position of annual density bands (low + high) were determined using the X-ray images in order to reconstruct the chronology or age model of the coral colony by assigning calendar years to each band couplet when counting backwards from the band-couplet/year of collection (Fig.3). As the interest was in determining the correlation between rainfall and the Ba/Ca coral record at an inter-annual scale, two replicate samples (1 g blocks) were obtained with a rotary tool equipped with a diamond-cutting wheel from each annual skeletal band. Samples were crushed in an agate mortar, sieved to retain the 280–700 lm fraction, and thoroughly cleaned in 0.2 M HNO3 with ultrasonic agitation to remove contamination associated with the cutting and crushing processes. The two replicates were later processed for separate Ba/Ca molar ratio analysis (i.e., the total content and the Ca-substitutive fractions). For the determination of the total content of Ba, samples were only cleaned several times with a 5 mM HNO3 solution with ultrasonic agitation (Guzmán and Jarvis, 1996). However, for the extraction of the Casubstituting fraction, Shen and Boyle (1988) developed an intense cleaning protocol consisting of a series of oxidation, reduction and weak acid treatments, in order to eliminate trace elements, including Ba, associated with the interchangeable, organic, and authigenic fractions. Thus, the only trace elements that remained in samples were those that substituted for Ca in the coral skeletal carbonate (Shen and Boyle, 1988; Linn et al., 1990). In summary, for the extraction of the Ca-substituting fraction: (1) samples were cleaned with a 1:1 oxidant solution mixture of 30% H2O2: and 0.2 M NaOH, to oxidize the organic matter; (2) samples were cleaned with a reducting solution (1:6:3) of hydrazine (H2NNH2), 2 M NH4OH, and 0.3 M citric acid in 7 M NH4OH, to eliminate oxide coatings, and finally, (3) samples were rinsed several times with a 5 mM HNO3 solution under ultrasonic agitation to remove any persistent metal contamination on the sample surfaces. Once samples were treated following both separate protocols, 200 mg from each thoroughly cleaned annual sample were digested in 2 mL of 2.5 M HNO3. For measuring the annual Ba/Ca molar ratios, an aliquot of 10 lL was obtained from each resulting digested solution and diluted to a final volume of 5 mL with 2% HNO3; hence, the final solution had a Ca concentration of 76 lg/L ([CaCO3]coral 0.2 mg/mL), which is adequate to avoid interferences during instrumental analysis (de Villiers et al., 2002). 2.3. Instrumental analysis The Ba/Ca molar ratios were determined using an ICP-OES (Thermo Jarrell Ash, IRIS/APÒ) with a charge injection solid-state detector, coupled to an ultrasonic nebulizer (CETAC U-5000AT+Ò). All instrumental parameters were adjusted for the highest sensitivity and stability. The instrument was calibrated by the intensity ratio method (de Villiers et al., 1994; Villaescusa-Celaya and Carriquiry, 2004) using the spectral lines with the best stability (i.e., Ba 455.4 and Ca 373.6 nm), and with standard solutions prepared with a known Ba/Ca molar ratio of 2.5–9.0 lmol/mol. To improve the accuracy of the Ba/Ca measurements a standard solution was measured every five samples and a correction factor was calculated for each sample bracketed between measured standard solutions in order to eliminate the effects of instrumental drift, similar to the method proposed by Schrag (1999). Routine instrument precision during the analysis was 4.0%.
Fig. 3. X-radiograph (positive image) of the M. annularis colony from the Punta Nizuc Reef showing annual density bands.
3. Results
2.4. Precipitation data
3.1. Growth rates of M. annularis
Annual precipitation data for the period 1950–1998 was calculated from a 0.5° 0.5° (lat long) cell centered at 21°N, 87°W (UNAM, CMC, 2008), in the adjacent mainland area near the collection site (Fig. 2).
The growth record of the M. annularis colony from the PNR spans 52 a, encompassing the period from 1946 to 1997 (Fig. 3). Average annual growth rate (linear extension) was 9.2 ± 1.1 mm/ a. This growth rate is higher than the 8.2 mm/a reported for this
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species in Puerto Morelos (Carricart-Ganivet, 2004), 25 km south of PNR (see Fig. 1), suggesting that the coral colony was growing healthily.
Raw Ba/Ca time-series of both fractions (Ba/CaCaF and Ba/CaTC) in M. annularis from the PNR are shown in Fig. 4. Annual molar ratios in the Ba/CaCaF ranged from 4.26 lmol/mol (in 1956) to 5.59 lmol/mol (in 1983), with an annual average of 4.85 ± 0.33 lmol/mol. The Ba/ CaTC values ranged from 4.66 lmol/mol (in 1975) to 7.52 lmol/mol (in 1959), with an annual average of 5.90 ± 0.56 lmol/mol. It is interesting to note that the Ba/CaTC average is 20% higher than that for the Ba/CaCaF, this being a statistically significant difference (paired T-test, p < 000.1). The average proportion of non-lattice bound Ba in M. annularis is 0.17 ± 0.09. Correlation between both time-series is low (r = 0.31, p = 0.0213), suggesting that different processes could be influencing coral Ba concentrations in the different geochemical fractions. 3.3. Coral Ba/Ca and precipitation The relationship between raw coral annual Ba/Ca in M. annularis and annual precipitation rates in the land adjacent to the PNR was low for the Ba/CaCaF (r = 0.28, p = 0.044), but for the Ba/CaTC was higher and statistically significant (r = 0.70, p < 0.0001). The correlation between variables did not increase when applying a time lag of 1 or 2 years, hence no lag-time correction was applied while developing a predictive model. Considering that this study was aimed at reconstructing annual precipitation rates using the coral Ba/Ca record as a proxy, in order to filter high-frequency variability, the Ba/CaTC and precipitation time-series were smoothed using a five-a running average following the standard procedure in climate time-series analysis, particularly for developing predictive models (von Storch and Zwiers, 1999; Mann, 2004). The correlation of the filtered time-series increased to r = 0.77, p < 0.0001 (Fig. 5). The predictive model (equation, Fig. 7) obtained from the linear regression analysis of the filtered time-series data relating annual Ba/CaTC versus precipitation (R2 = 0.59, p < 0.001) is presented in Fig. 8.
Precipitation (mm/year)
3.2. Coralline Ba/Ca molar ratios
7.0
1500 1400
6.5
1300 1200
6.0
1100 1000
5.5
900
Ba /Ca ( µm ol/m ol)
1582
5.0
800 700 600 1950
1955
1960
1965
1970
1975
Years
1980
1985
1990
1995
4.5 2000
Fig. 5. Ba/CaTC molar ratio in the annual bands of M. annularis from PNR (gray line), and annual precipitation rates for a 0.5° 0.5° (lat. long.) cell, centered at 21°N, 87°W (black line). Both time-series were filtered using a 5-a running average.
than those measured in areas directly influenced by river discharge with a high input of terrigenous sedimentary particles, such as the Flower Garden Banks in the Northwestern Gulf of Mexico (Deslarzes et al., 1995) and Montastrea faveolata from the Veracruz Reef System in the Southern Gulf of Mexico (Carriquiry and HortaPuga, 2010), both sites averaging 7.8 lmol/mol. However, the mean Ba/Ca molar ratios from the PNR are slightly above the coral records from other species and geographical areas characterized by carbonate sedimentary environments, like in Pavona clavus from Galapagos (Lea et al., 1989), Porites spp. from the Great Barrier Reef (Alibert et al., 2003; McCulloch et al., 2003; Sinclair and McCulloch, 2004; Jupiter et al., 2008), M. annularis from the Venezuelan Caribbean (Reuer et al., 2003), and M. faveolata from the Southern MBRS (Prouty et al., 2008; Carrilli et al., 2010), which suggests the existence of an additional source of Ba in the NYP area. Merino (1997) has shown that, on a seasonal basis, waters from a depth of 220–250 m upwell in the NYP margin during spring and summer; therefore, it cannot be ruled out that some of the Ba in surface waters, released from remineralization processes in the water column, could be transported from deep water by upwellings in the NYP margin. This also contributes to explain the higher coral Ba/Ca molar ratios observed in the PNR area.
4. Discussion 4.1. Ba/Ca molar ratios in corals from non-terrigenous sedimentary environments The average Ba/Ca ratios observed in M. annularis (Ba/ CaTC = 5.90 lmol/mol, Ba/CaCaF = 4.85 lmol/mol) of PNR are lower
8.0
Ba/Ca (µ µmol/mol)
7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 1945 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000
Years
Fig. 4. Ba/Ca molar ratio in the annual bands of M. annularis from PNR. Ba/CaTC = dark line. Ba/CaCaF = gray line.
4.2. Ba incorporation into the aragonite lattice in M. annularis from the PNR Although Carriquiry and Horta-Puga (2010) reported that almost all Ba contained in the skeleton of M. faveolata from the Southern Gulf of Mexico is incorporated as a Ca-substituting element in the aragonite structure, the present study with M. annularis from the Mexican Caribbean shows that the Ba/CaTC average is 20% higher than the Ba/CaCaF. This indicates that at least in M. annularis from the Mexican Caribbean, an important proportion of Ba is incorporated not as a Ca-substitutive element in the aragonite lattice, but in different geochemical fractions occluded in the skeleton, like particulate, organic and/or authigenic phases that also contain trace elements, as has been widely documented for scleractinian corals (Amiel et al., 1973; Glover and Owen, 1978; Shen and Boyle, 1988; Allison, 1996; Sinclair and McCulloch, 2004). To date the geochemical/biochemical processes involved in the incorporation of Ba into the coral skeleton are not well known. Hence, the process of partition among the different geochemical fractions that differentiates M. annularis from M. faveolata, as well as the sources of Ba for each of the geochemical fractions in the coral skeleton, are also not known. Nonetheless, the geochemical record of annually-banded corals has been shown
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Fig. 6. Annual precipitation rates (dark line), and the relative proportion of lattice-bound Ba (1 Ba/CaCaF/Ba/CaTC) in annual bands of the coral M. annularis from the PNR (gray line).
4.3. Relationship between precipitation and coral Ba/Ca
Ba/Ca ( µ mol/mol)
7.0 6.5 6.0 5.5 Ba/Ca = 0.001(P) + 4.010 R = 0.59 p< 0.001
5.0 4.5
700
800
900
1000
1100
1200
Precipitation (mm/year)
1300
1400
1500
Fig. 7. Regression analysis between the filtered time-series of the Ba/CaTC molar ratio in the annual bands of M. annularis from the PNR and the annual average precipitation. Correlation coefficient between time-series is r = 0.77, p < 0.0001.
Precipitation (mm/year)
2000 1750 1500 1250 1000 750 500 1945 1950 1955 1960 1965 1970 1975
1980 1985 1990 1995 2000
Years Fig. 8. Comparative annual precipitation rates in the NYP. Reported raw precipitation data (black line), and reconstructed using the M. annularis Ba/CaTC record (raw data) from the PNR (gray line).
to reliably record past environmental conditions (McCulloch et al., 2003; Fleitmann et al., 2007; Carriquiry and Horta-Puga, 2010; Prouty et al., 2010), and in this study the use the Ba/Ca record from the PNR is proposed as a proxy for reconstructing historical precipitation, and the dissolved Ba concentrations in the seawater, of the NYP area.
In order to assess the effect of groundwater outflows from karstic terrains into reef areas, which should be influenced by inter-annual variations in rainfall, the annual Ba/Ca coralline record was plotted versus the annual precipitation in the PNR continental adjacent area. Fig. 5 shows that the filtered time-series of Ba/CaTC closely follows the inter-annual variation in rainfall. The correlation is statistically significant (r = 0.77, p < 0.001), supporting the hypothesis that as Ba is transported by groundwater flow into the coastal environment it gets incorporated into the Ba/CaTC of the coral skeletons. It is important to observe that the time-series showed a high correlation with no time lag, a fact that could be explained by the high permeability (j > 1 m2) of the karst in the continental area near the Nichupte Lagoon (Granel-Castro and Gález-Hita, 2002; Crook et al., 2011), which permits groundwater to outflow to the coastal zone almost immediately after precipitation, due to higher hydraulic pressures that are generated in the aquifer (Santos et al., 2012). However, as there are no data on the aquifer’s extent and the average Ba concentration in the limestone of the NYP, it becomes very difficult to assess the residence times and the contribution of the dissolution products of limestone to the coastal seawater pool of Ba. The same analysis was also applied to the Ba/CaCaF timeseries and the correlation was lower (r = 0.28, p < 0.05), which suggest that the coralline Ba-signal in the Ca-substitutive geochemical fraction is not responding entirely to precipitation. Furthermore, the correlation between the proportion of annual non-latticebound Ba relative to the total Ba content (1 Ba/CaCaF/Ba/CaTC) versus precipitation is positive (Fig. 6) with a moderate correlation (r = 0.48, p < 0.001). It is worth noting that during dry years with low precipitation rates (<1000 mm/a), the proportion of nonlattice-bound Ba decreased, on average, down to 10% of the total content in the annual band; but during the years of higher precipitation (>1000 mm/) this proportion increased to >20%. This suggests that, as annual precipitation rates increase, the proportion of Ba that is incorporated into the coral skeleton other than the Ca-substitutive fraction also increases, and vice versa. Therefore, it appears that in the years/periods with low precipitation rates, groundwater does not carry sufficient dissolved/suspended terrigenous materials; hence, the background levels of dissolved-Ba in seawater nearby the collection site comprise the main source of Ba for Ca-substitution. But, when groundwater flow (and/or precipitation) exceeds some threshold, it enhances the delivery of higher amounts
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of particulate material, to the coastal zone which are added to the background levels of Ba in the PNR area, therefore, imprinting its signal in the coral geochemical record through its incorporation into the skeleton, mainly in the non-lattice-bound fraction, as is empirically evidenced by the results obtained here. A similar situation has been reported for the coral Porites spp., which is influenced by the fluvial plume of the Burdekin River in the Great Barrier Reef (Alibert et al., 2003; Sinclair, 2005). Likewise, it has been observed in Porites lobata from Hawaii, wherein episodic releases of higher amounts of Ba-bearing sediments from a nearby mangrove forest, are the source/cause of higher coral Ba/Ca molar ratios (Prouty et al., 2010). Hence, it may not be necessary to isolate the Ca-substituting geochemical fraction, since the Ba/CaTC is the geochemical signal in the coral skeletons that responds to precipitation, and concomitantly to groundwater supply of Ba to the fringing reefs of the NYP. Fig. 7 shows the regression analysis between the filtered Ba/ CaTC and precipitation time-series data, which suggests that the variability in the coral Ba/Ca ratios could be explained by rainfall (R2 = 0.59, p < 0.05). Fluid-rock interaction rates in coastal karstic aquifers seem to be controlled by rainfall rates in which the dissolution products are transported into reef waters to ultimately become encoded in the coral skeletal records. This reveals that the coralline Ba/CaTC record of the hermatypic coral M. annularis can be reliably used as a proxy of precipitation in the NYP. The probable explanations for not finding a higher correlation may be: (1) the annual precipitation data were obtained from a very large quadrant (2830 km2) that may not be entirely representative of the local rainfall rates around the PNR, wherein there are no available long-term records, and the actual extent of the karstic aquifer that flushes freshwater into the coastal zone is unknown (GranelCastro and Gález-Hita, 2002); (2) the variability of the groundwater outflow volume into any specific coastal area due to the karstic nature of the terrain (Hanshaw and Back, 1980; Steinich and Marín, 1997), and although several submarine springs have been located in the adjacent Nichupte Lagoon, none of them has been studied, hindering the ability to calculate the freshwater discharge volume and rates (Granel-Castro and Gález-Hita, 2002); (3) quantitatively undetermined diagenetic and/or dolomitization rates that release or capture unknown quantities of trace elements in the groundwater mixing zone (Ward and Halley, 1984; Moore, 1999); (4) unquantified amounts of dissolved and/or particulate materials carried by groundwater to the coastal area released by the varying hydrogeochemical conditions that yield differential dissolution rates of carbonate soils and rocks (Back et al., 1979, 1986); and (5) the unknown contribution of upwelling waters in the NYP area (Merino, 1997). Equivalent processes have been identified in karstic caves in which, from initial fluid-rock interactions and the transport of the dissolution products, yield the formation of speleothems containing highly reliable geochemical records of environmental and/or climatic change (e.g., Wang et al., 2001; Frappier et al., 2002). 4.4. Reconstructed precipitation in the NYP As coralline Ba/CaTC correlates well with precipitation (Fig. 5), this relationship was used for reconstructing the historical annual precipitation rates in the NYP. The calibration line, obtained from the linear regression analysis of the parameters (Fig. 8), is:
Precipitationðmm=aÞ ¼ 347:3½Ba=CaTC ðlmol=molÞ 939:2 Observed and reconstructed precipitation rate times-series for the 1946–1997 period are shown in Fig. 7. As expected both time series show the same pattern through time with some departures due to the uncertain role or weight of each of the factors considered in the previous section. Considering these uncertainties, this
45 44 43 42
Ba (nmol/kg)
1584
41 40 39 38 37 36 35 34 33 1945
1950 1955 1960 1965
1970 1975
1980 1985
1990 1995
2000
Years Fig. 9. Reconstructed dissolved Ba concentration in seawater in the NYP coastal zone.
equation is the first attempt to use the coralline Ba/Ca record as a proxy for reconstructing precipitation rates in coastal areas not influenced by significant fluvial discharge, at least in the study area. 4.5. Reconstructed seawater Ba concentrations Considering that: (1) the CaF in corals is responding directly to the concentration of Ba in the dissolved phase in seawater (Shen and Boyle, 1988; Shen and Sanford, 1990), (2) that the empirical distribution coefficient reported for Ba/Ca molar ratios in Montastraea and other coral species is Ba/Cacoral/Ba/Caseawater 1.3 (Lea et al., 1989; Reuer et al., 2003), and (3) that the concentration of Ca in seawater is conservative: [Ca]seawater = 0.412 g/kg (Bruland, 1983), the significance of the Ba/CaCaF in the annual bands of coral as a proxy for the dissolved concentration of Ba in seawater in PNR was investigated. Assuming that salinity is constant (35 PSU), then, the concentration of dissolved Ba in seawater varied from 33.7 nmol/kg in 1957, to 44.3 nmol/kg in 1984, with an average concentration of 38.4 ± 2.7 nmol/kg (Fig. 9). These values are slightly higher than the average concentration of Ba of 34 nmol/kg in oceanic surface waters in the Atlantic (Chan et al., 1977; Lea and Boyle, 1991), but agree well with those expected for coastal surface seawater influenced by groundwater discharge (Swarenski et al., 2001). Hence, the Ca-substituting geochemical fraction of Ba in the coral skeleton (i.e., the Ba/CaCaF ratio) from the PNR seems to coherently record the inter-annual variability of Ba concentration in the coastal zone of the NYP. 5. Conclusions Varying rainfall rates at inter-annual to decadal timescales on the coastal karstic terrain of the NYP is directly related to the groundwater recharge variability of the aquifer of this area. Concomitantly, the changes occurring during groundwater recharge promote fluid-rock interactions, such as carbonate dissolution. The products of dissolution, such as trace elements, are delivered into reef waters via submarine springs to ultimately become incorporated in the coral skeletal records. This study provides evidence that the coralline Ba/CaTC record of the hermatypic coral M. annularis can be reliably used as a long term proxy for precipitation in the NYP. The analytical protocol followed here reveals that it is not necessary to isolate the Ca-substituting fraction, in order to use it as a proxy for rainfall. However, when following a more exhaustive cleaning protocol to isolate the Ca-substituting levels
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of Ba incorporated in the coral skeleton (the Ba/CaCaF ratio) an adequate reconstruction of dissolved Ba concentrations in coastal seawater can be achieved. Hence, the Ba/CaCaF ratio can be used as a proxy for dissolved Ba in seawater in the NYP. However, the exact mechanisms explaining the cause-effect relationship between seawater (dissolved or particulate) and coral Ba concentrations, in any or all geochemical fractions, are still not known. This is a research issue that should be properly addressed in the future, in order to fully understand the processes involved in the geochemistry of the skeleton of M. annularis. Acknowledgements We thank Julio Villaescusa and Pedro Castro (UABC, IIO) for their collaboration in all stages of laboratory work. Also thanks for the comments and suggestions of two anonymous reviewers, which notably improved this manuscript. This study was financed in part by a grant from the National Science and Technology Council of Mexico to J.D. Carriquiry (CONACYT: 46814). References Alibert, C., Kinsley, L., Fallon, S.J., McCulloch, M.T., Berkelmans, R., McAllister, F., 2003. Source of trace element variability in Great Barrier Reef corals affected by the Burdekin flood plums. Geochim. Cosmochim. Acta 67, 231–246. Allison, N., 1996. Geochemical anomalies in coral skeletons and their possible implications for palaeoenvironmental analyses. Mar. Chem. 55, 367–379. Allison, N., Finch, A.A., 2007. High temporal resolution Mg/Ca and Ba/Ca records in modern Porites lobata corals. Geochem. Geophys. Geosys. 8, Q05001. http:// dx.doi.org/10.1029/2006GC001477. Amiel, A.J., Friedman, G.M., Miller, D.S., 1973. Distribution and nature of incorporation of trace elements in modern aragonitic corals. Sedimentology 20, 47–64. Back, W., Hanshaw, W., 1970. Comparison of chemical hydrogeology of the carbonate peninsulas of Florida and Yucatan. J. Hydrol. 10, 330–368. Back, W., Hanshaw, B., Herman, J.S., van Driel, J.N., 1986. Differential dissolution of a Pleistocene reef in the ground-water mixing zone of coastal Yucatan, Mexico. Geology 14, 137–140. Back, W., Hanshaw, B., Pyle, T.E., Plummer, L.N., Wedie, A.E., 1979. Geochemical significance of groundwater discharge and carbonate dissolution to the formation of Caleta Xel-Ha, Quintana Roo, Mexico. Water Resour. Res. 15, 1521–1535. Beach, T., 1998. Soil constraints on Northwest Yucatan, Mexico: Pedoarchaeology and Maya subsistence at Chunchucmil. Geoarchaeology 13, 759–791. Beck, J.W., Edwards, R.L., Ito, E., Taylor, F.W., Recy, J., Rougerie, F., Joannot, P., Henin, C., 1992. Seasurface temperature from coral skeletal strontium/calcium ratios. Science 257, 644–647. Bruland, K., 1983. Trace elements in seawater. In: Riley, J.P., Chester, R. (Eds.), Chemical Oceanography, vol. 8. Academic Press, London, pp. 147–220. Carricart-Ganivet, J.P., 2004. Sea surface temperature and the growth of the West Atlantic reef-building coral Montastraea annularis. J. Exp. Mar. Biol. Ecol. 302, 249–260. Carrilli, J.E., Prouty, N.G., Hughen, K.A., Norris, R.D., 2010. Century-scale records of land-based activities recorde in Mesoamerican coral cores. Mar. Pollut. Bull. 58, 1835–1842. Carriquiry, J.D., Horta-Puga, G., 2010. The Ba/Ca record of corals from the Southern Gulf of Mexico: contributions from land-use changes, fluvial discharge and oildrilling muds. Mar. Pollut. Bull. 60, 1625–1630. Carriquiry, J.D., Risk, M.J., Schwarcz, H.P., 1994. Stable isotope geochemistry of corals from Costa Rica as proxy indicator of the El Niño/Southern Oscillation (ENSO). Geochim. Cosmochim. Acta 58, 335–351. Carruthers, T.J.B., van Tussenbroek, B.I., Dennison, W.C., 2005. Influence of submarine springs and wastewater on nutrient dynamics of Caribbean seagrass meadows. Estuar. Coast. Shelf Sci. 64, 191–199. Chan, L.H., Drummond, D., Edmond, J.M., Grant, B., 1977. On the barium data from the Atlantic GEOSECS expedition. Deep-Sea Res. 24, 613–649. Chow, T.J., Goldberg, E.D., 1960. On the marine geochemistry of barium. Geochim. Cosmochim. Acta 20, 192–198. Church, T.M., Wolgemuth, K., 1972. Marine barite saturation. Earth Planet. Sci. Lett. 15, 35–44. Cole, J.E., Shen, G.T., Fairbanks, R.G., 1993. Recent variability in the southern oscillation: isotopic results from a Tarawa Atoll coral. Science 260, 1790–1793. Corrège, T., Delcroix, T., Récy, J., Beck, W., Cabioch, G., Cornec, F.L., 2000. Evidence for stronger El Niño-Southern Oscillation (ENSO) events in a mid-Holocene massive coral. Paleoceanography 15, 465–470. Crook, E.D., Potts, D., Rebolledo-Vieyra, M., Hernandez, L., Paytan, A., 2011. Calcifying coral abundance near low-pH springs: implications for future ocean acidification. Coral Reefs. http://dx.doi.org/10.1007/s00338-011-0839-y.
1585
de Villiers, S., Graves, M., Elderfield, H., 2002. An intensity ratio calibration method for the accurate determination of Mg/Ca and Sr/Ca of marine carbonates by ICPAES. Geochem. Geophy. Geosy., doi:2001GC000169. de Villiers, S., Shen, G.T., Nelson, B.K., 1994. The Sr/Ca-temperature relationship in coralline aragonite: influence of variability in (Sr/Ca)seawater and skeletal growth parameters. Geochim. Cosmochim. Acta 58, 197–208. Deslarzes, K.J.P., Boothe, P.N., Presley, B.J., Steinmetz, G.L., 1995. Historical incorporation of barium in thr reef building coral Montastrea annularis at the Flower Garden Banks, North-West Gulf of México. Mar. Pollut. Bull. 30, 718– 722. Druffel, E.R.M., 1997. Geochemistry of corals: Proxies of past ocean chemistry, ocean circulation and climate. Proc. Nat. Acad. Sci. USA 94, 8354–8361. Evans, M.N., Cane, M.A., Schrag, D.P., Kaplan, A., Linsley, B.K., Villalba, R., Wellington, G.M., 2001. Support for tropically – driven Pacific decadal variability based on paleoproxy evidence. Geophys. Res. Lett. 28, 3689–3692. Fallon, S.J., McCulloch, M.T., van Woesik, R., Sinclair, D.J., 1999. Corals at their latitudinal limits: laser ablation trace element systematic in Porites from Shirigai Bay, Japan. Earth Planet. Sci. Lett. 172, 221–238. Fleitmann, D., Dunbar, R.B., McCulloch, M., Mundelsee, M., Vuille, M., McClanahan, T.R., Cole, J.E., Eggins, S., 2007. East African erosion recorded in a 300 year old colony from Kenya. Geophys. Res. Lett. 34, L04401. http://dx.doi.org/10.1029/ 2006GL028525. Frappier, A., Sahagian, D., González, L.A., Carpenter, S.J., 2002. El Niño events recorded by stalagmite carbon isotopes. Science 298, 565. Gagan, M.K., Ayliffe, L.K., Beck, J.W., Cole, J.E., Druffel, E.R.M., Dunbar, R.B., Schrag, D.P., 2000. New view of tropical paleoclimate from corals. Quatern. Sci. Rev. 19, 45–64. Glover, R.M., Owen, R.M., 1978. An evaluation of methods used to determine trace element partitioning in coral. Can. J. Spectrosc. 23, 27–30. Granel-Castro, E., Gález-Hita, L., 2002. Deterioro de la calidad del agua subterranean por el desarrollo poblacional: Cancún. Q. Roo. Ingeniería Rev. Acad. 6, 41–53. Guzmán, H.M., Jarvis, K.E., 1996. Vanadium century record from Caribbean reef corals: a tracer of oil pollution in Panama. Ambio 25, 523–526. Hanor, J.S., Chan, L.-H., 1977. Non-conservative behavior of barium during mixing of Mississippi River and Gulf of Mexico waters. Earth Planet. Sci. Lett. 37, 242–250. Hanshaw, B.B., Back, W., 1980. Chemical mass-wasting of the northern Yucatán Peninsula by groundwater dissolution. Geology 8, 222–224. Horowitz, A.J., Elrick, K.A., Smith, J.J., 2001. Annual suspended sediment and trace element fluxes in the Mississipi, Columbia, Colorado and Rio Grande drainage basins. Hydrol. Process. 15, 1169–1207. Jupiter, S., Roff, G., Marion, G., Henderson, M., Schrameyer, V., McCulloch, M.T., Hoegh-Guldberg, O., 2008. Linkages between coral assemblages and coral proxies of terrestrial exposure along a cross-shelf gradient on the southern Great Barrier Reef. Coral Reefs 27, 887–903. Lea, D.W., Boyle, E.A., 1991. Barium in planktonic foraminifera. Geochim. Cosmochim. Acta 55, 3321–3331. Lea, D.W., Shen, G.T., Boyle, E.A., 1989. Coralline barium records temporal variability in equatorial Pacific upwelling. Nature 340, 373–376. Lewis, S.E., Shields, G., Kamber, B.S., Lough, J.M., 2007. A multi-trace element coral record of land-use changes in the Burdekin River catchment, NE Australia. Palaeogeog. Palaeoclimatol. Palaeoecol. 246, 471–487. Linn, L.J., Delaney, M.L., Druffel, R.M., 1990. Trace metals in contemporary and seventeenth-century Galapagos coral: records of seasonal and annual variations. Geochim. Cosmochim. Acta 54, 387–394. Mann, M.E., 2002. The value of multiple proxies. Science 297, 1481–1482. Mann, M.E., 2004. On smoothing potentially non-stationary climate time-series. Geophys. Res. Lett. 31, L07214. http://dx.doi.org/10.1029/2004GL019569. Marshall, J.F., McCulloch, M.T., 2002. An assessment of the Sr/Ca ratio in shallow water hermatypic corals as a proxy for sea surface temperature. Geochim. Cosmochim. Acta 66, 3263–3280. McCulloch, M.T., Fallon, S., Wyndham, T., Hendy, E., Lough, J., Barnes, D., 2003. Coral record of increased sediment flux to the inner Great Barrier Reef since European settlement. Nature 421, 727–730. McCulloch, M.T., Gagan, M.K., Mortimer, G.E., Chivas, A.R., Isdale, P.J., 1994. A high– resolution Sr/Ca and d18O coral record from the Great Barrier Reef, Australia, and the 1982–1983 El Niño. Geochim. Cosmochim. Acta 58, 2747–2754. Merino, M., 1997. Upwelling on the Yucatan Shelf: hydrographic evidence. J. Mar. Syst. 13, 101–121. Min, G.R., Edwards, R.L., Taylor, R.W., Recy, L., Gallup, C.D., Beck, J.W., 1995. Annual cycles of U/Ca in coral skeletons and U/Ca thermometry. Geochim. Cosmochim. Acta 59, 2025–2042. Mitsuguchi, T., Matsumoto, E., Abe, O., Uchida, T., Isdale, P.J., 1996. Mg/Ca thermometry in coral skeletons. Science 274, 961–963. Moore, W.S., 1997. High fluxes of radium and barium from the mouth of the Ganges–Brahmaputra River during low river discharge suggest large groundwater source. Earth Planet. Sci. Lett. 150, 141–150. Moore, W.S., 1999. The subterranean estuary: a reaction zone of ground water and sea water. Mar. Chem. 65, 111–125. Morán, Z.D.J., 1985. Geología de la República Mexicana. Facultad de Ingeniería (UNAM) and Instituto Nacional de Estadística, Geografía e Informatica. Mexico City, Mexico. Perry, E.C., Swift, J., Gamboa, J., Reeve, A., Sanborn, R., Marin, L.E., Villasuso, M., 1989. Geologic and environmental aspects of surface cementation, north coast, Yucatan, Mexico. Geology 17, 818–821.
1586
G. Horta-Puga, J.D. Carriquiry / Applied Geochemistry 27 (2012) 1579–1586
Perry, E., Velázquez-Oliman, G., Marin, L.E., 2002. The hydrogeochemistry of the karst aquifer system of the Northern Yucatan Peninsula, Mexico. Int. Geol. Rev. 44, 191–221. Prouty, N.G., Field, M.E., Stock, J.D., Jupiter, S.D., McCulloch, M., 2010. Coral Ba/Ca records of sediment input to the fringing reef of the southshore of Molokai’I, Hawai’I over the last several decades. Mar. Pollut. Bull. 60, 1822–1835. Prouty, N.G., Hughen, K.A., Carrilli, J., 2008. Geochemical signature of land-based activities in Caribbean coral surface samples. Coral Reefs 27, 727–742. Ramos, A.A., Inoue, Y., Ohde, S., 2004. Metal contents in Porites corals: anthropogenic input of river run-off into a coral reef from an urbanized area. Okinawa. Mar. Pollut. Bull. 48, 281–294. Reeve, A.S., Perry, E.C., 1994. Carbonate geochemistry and the concentrations of aqueous Mg2+, Sr2+ and Ca2+: western north coast of Yucatan, Mexico. Chem. Geol. 112, 105–117. Reuer, M.K., Boyle, E.A., Cole, J.E., 2003. A mid-twentieth century reduction in tropical upwelling from coralline trace element proxies. Earth Planet. Sci. Lett. 210, 437–452. Santos, I.R., Eyre, B.D., Huettel, M., 2012. The driving forces of porewater and groundwater flow in permeable coastal sediments: a review. Estuar. Coast Shelf. Sci. 98, 1–15. Schrag, D.P., 1999. Rapid analysis of high-precision Sr/Ca ratios in corals and other marine carbonates. Paleoceanography 14, 97–102. Shaw, T.J., Moore, W.S., Kloepfer, J., Sochaski, M.A., 1998. The flux of barium to the coastal waters of the southeastern USA: the importance of submarine groundwater discharge. Geochim. Cosmochim. Acta 62, 3047–3054. Shen, G.T., Boyle, E.A., 1988. Determination of lead, cadmium and other trace metals in annually-banded corals. Chem. Geol. 67, 47–62. Shen, G.T., Sanford, C.L., 1990. Trace element indicators of climate change in annually-banded corals. In: Glynn, P.W. (Ed.), Global Ecological Consequences of the 1982–83 El Niño. Elsevier, New York, pp. 255–283. Sinclair, D.J., 2005. Non-river flood barium signals in the skeletons of corals from coastal Queensland, Australia. Earth Planet. Sci. Lett. 237, 354–369. Sinclair, D.J., McCulloch, M.T., 2004. Corals record low mobile barium concentrations in the Burdekin River during the 1974 flood: evidence for limited Ba supply to rivers? Palaeogeog. Palaeoclimatol. Palaeoecol. 214, 155–174.
Sinclair, D.J., Kinsley, L.P.J., McCulloch, M.T., 1998. High resolution analysis of trace elements in corals by laser ablation ICP-MS. Geochim. Cosmochim. Acta 62, 1889–1901. Smith, S.V., Buddemeier, R.W., Redalje, R.C., Houck, J.E., 1979. Strontium-calcium thermometry in coral skeletons. Science 204, 404–407. Steinich, B., Marín, L.E., 1997. Determination of flow characteristics in the aquifer of the northwestern Peninsula of Yucatan, Mexico. J. Hydrol. 191, 315–331. Swarenski, P.W., Reich, C.D., Spechler, R.M., Kindinger, J.L., Moore, W.S., 2001. Using multiple geochemical tracers to characterize the hydrogeology of the submarine spring off Crescent Beach, Florida. Chem. Geol. 179, 187–2022. UNAM, CMC, 2008. Universidad Nacional Autónoma de México, Centro de Ciencias de la Atmósfera. Base de datos de precipitación pluvial v0705.