The combined influence of Pacific decadal oscillation and Atlantic multidecadal oscillation on central Mexico since the early 1600s

Earth and Planetary Science Letters 464 (2017) 1–9

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Earth and Planetary Science Letters www.elsevier.com/locate/epsl

The combined influence of Pacific decadal oscillation and Atlantic multidecadal oscillation on central Mexico since the early 1600s Jungjae Park a,∗ , Roger Byrne b , Harald Böhnel c a b c

Department of Geography and Institute for Korean Regional Studies, Seoul National University, Sillim-dong, Gwanak-gu, Seoul, 151-742, Republic of Korea Department of Geography, University of California at Berkeley, CA 94720, USA Centro de Geociencias, Universidad National Autónoma de México, Querétaro 76230, Mexico

a r t i c l e

i n f o

Article history: Received 26 July 2016 Received in revised form 26 January 2017 Accepted 7 February 2017 Available online xxxx Editor: H. Stoll Keywords: Pacific Decadal Oscillation (PDO) Atlantic Multidecadal Oscillation (AMO) central Mexico ITCZ droughts climate variability

a b s t r a c t Periodic droughts have been one of the most serious environmental issues in central Mexico since the earliest times. The impacts of future droughts are likely to become even more severe as the current global warming trend increases potential evaporation and moisture deficits. A full understanding of the mechanism underlying climate variability is imperative to narrow the uncertainty about future droughts and predict water availability. The climatic complexity generated by the combined influence of both Atlantic and Pacific forcings, however, causes considerable difficulty in interpreting central Mexican climate records. Also, the lack of high-resolution information regarding the climate in the recent past makes it difficult to clearly understand current drought mechanisms. Our new high-resolution δ 18 O record from Hoya Rincon de Parangueo in central Mexico provides useful information on climate variations since the early 1600s. According to our results, the central Mexican climate has been predominantly controlled by the combined influence of the 20-year Pacific Decadal Oscillation (PDO) and the 70-year Atlantic Multidecadal Oscillation (AMO). However, the AMO probably lost much of its influence in central Mexico in the early 20th century and the PDO has mostly driven climate change since. Marked dryness was mostly associated with co-occurrence of highly positive PDO and negative AMO between ∼1600 and 1900. © 2017 Elsevier B.V. All rights reserved.

1. Introduction Central Mexico has been one of the most populous regions in the world for a long time. However, its dense population often undermined ecological resilience and increased the vulnerability of societies to climate shifts (e.g. De Tapia, 2012). In particular, periodic drought conditions have been serious threats faced by poor people in the region, who consistently suffered from environmental degradation and consequent subsistence deficit (Liverman, 1990; Enfield and O’Hara, 1999). Today’s situation is not much different from the past. Drought is still one of the main environmental problems in central Mexico (Ortega-Gaucin and Velasco, 2013; Aguilar-Barajas et al., 2016). There is an urgent need for a better approach to this issue since central Mexican states, including Guanajuato, Mexico, and Puebla, only have about 12% of the water in the nation despite containing ∼60% of the total population (Enge and Whiteford, 1989; Liverman, 1992). Urban development and intensive agriculture have substantially lowered the ground-

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Corresponding author. Fax: +82 62 530 2689. E-mail address: [email protected] (J. Park).

http://dx.doi.org/10.1016/j.epsl.2017.02.013 0012-821X/© 2017 Elsevier B.V. All rights reserved.

water table, exacerbating the outcomes of drought (Barker et al., 2000). Current global warming is also believed to increase potential evaporation and thus decrease moisture availability in central Mexico (Seager et al., 2009). A full understanding of the mechanisms underlying climate variability seems to be imperative to reduce the uncertainty of future droughts and better predict water availability (e.g. Dai, 2011). However, the climatic complexity generated by the combined influence of both Atlantic and Pacific forcings causes considerable difficulty in interpreting central Mexican climate records. Most of all, the lack of high-resolution information regarding climate change in the recent past does not allow us to clearly understand current drought mechanisms. Short and incomplete rainfall observations also contribute to the difficulty. Several tree ring records from central Mexico have contributed to developing an understanding of climate dynamics (Therrell et al., 2006; Stahle et al., 2011, 2012). Climate variation in central Mexico appears to be mainly driven by the Pacific Decadal Oscillation (PDO)/El Nino Southern Oscillation (ENSO) and Atlantic Multidecadal Oscillation (AMO)/North Atlantic Oscillation (NAO) (Stahle et al., 2012). In addition, the Pacific forcing over central Mexico has been suggested to be more dominant during the late

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Fig. 1. The location of the study site and paleoclimate proxy records discussed in this study. (1) and (2) Southern and Baja California (MacDonald and Case, 2005; Biondi et al., 2001), (3) La Hoya Rincon de Parangueo, this study, (4) Dos Anas cave system in Northwestern Cuba (Fensterer et al., 2012), and (5) Cariaco Basin, Venezuela (Black et al., 1999). This map was modified from UNAVCO map tool (UNAVCO Inc., jules.unavco.org).

Holocene since AMO signals shown in these data are relatively weak. The AMO influence on central Mexico, however, should also be substantial given its intermediate position between two oceans. It is indeed generally agreed that the Atlantic forcing plays a major role in regulating summer rainfall over central Mexico (Méndez and Magaña, 2010). The difficulty in detecting the AMO may have to do with the PDO/ENSO influence, which complicates the pattern of AMO-related climate shifts (Mo et al., 2009; Hu and Feng, 2012). Also, regional/local SST variability might not be represented well by the AMO index since the latter is defined as annual mean SST anomalies averaged over the entire North Atlantic basin. Detecting the AMO and PDO separately in central Mexican climate data would be important for a clear understanding of past drought that apparently have predictive potential. Also, the drought hypothesis for past societal events could be more objectively tested once these two major drivers are better understood. Temporal correlation between climate variation and social upheavals has been vigorously attempted in central Mexico (Therrell et al., 2006; Stahle et al., 2011; Lachniet et al., 2012; Bhattacharya et al., 2015) but their causal links still seem rather weak for wide acceptance (e.g. Cowgill, 2015). In this paper, we provide a new high-resolution δ 18 O record from Hoya Rincon de Parangueo, a maar lake in the Valle de Santiago area of Guanajuato, Mexico. This study aims to 1) reconstruct climate change since 1610 in central Mexico, 2) find past temporal patterns of dryness/wetness, and 3) separately detect the influence of the Pacific and Atlantic forcings from our records. 2. Study area La Hoya Rincon de Parangueo, hereafter referred to as Rincon, is a maar crater located near Valle de Santiago in southern Guanajuato, Mexico (Figs. 1–2). Its age has not been determined, but Hoya San Nicolas and Hoya Alberca, two other maars located ca. 4 km to the south and south-east of Rincon (Fig. 2), have respectively produced Potassium/Argon ages of 1.2 Ma and 0.37 Ma (Murphy, 1986). As recently as the 1980s, there was a 30 m + deep lake at Rincon. Lowering of the regional water table due to ground water extraction for irrigation, however, has since caused the lake to desiccate (Alcocer et al., 2000; Escolero-Fuentes and Alcocer-Durand, 2004).

The Valle de Santiago area is one of several lowland areas in this section of the Rio Lerma watershed. Collectively they are known as the Bajío. The Bajío has been one of Mexico’s most important agricultural areas since the second half of the 16th century, and thus, the vegetation of the area has been heavily disturbed by human activities. At present, most of the Valle de Santiago area is agricultural, especially the alluvial plain that borders the Rio Lerma. On the volcanic uplands, the vegetation is subtropical deciduous woodland and scrub, and most of it is disturbed by woodcutting and browsing of domesticated animals. The more inaccessible Rincon crater contains a floristically rich remnant of subtropical woodland (Aguilera Gómez, 1991). The present climate of the area is temperate with a strongly seasonal pattern of rainfall. Mean monthly temperatures range from 14.7 ◦ C in January to 22.8 ◦ C in May (Servicio Meteorológico Nacional). Eighty percent of the precipitation falls between April and November as the Bermuda high shifts northward and tropical easterlies move on to the Mexican plateau (Mosiño Alemán and García, 1974). During the winter and spring months, the area is under the influence of high pressure and monthly rainfall totals are minimal. Instrumental data indicate that PDO and AMO are important drivers of the central Mexican climate during the summer season (Sutton and Hodson, 2005; Pavia et al., 2006; Méndez and Magaña, 2010). Warm ENSO/PDO and cold AMO (Atlantic SSTs) are suggested to cause persistent drought in central Mexico while cold ENSO/PDO and warm AMO cause relatively wet conditions (Seager et al., 2009; Méndez and Magaña, 2010). 3. Materials and methods In 2004 we recovered a 4 m-long sediment core (UC2004) from Rincon (20◦ 23 N/101◦ 15 W) with a 5 cm diameter Livingstone corer equipped with butyrate liners (Park et al., 2010). In this study, undisturbed upper sediments between depths of 85 and 155 cm were used to investigate recent climate variability. According to local informants, the marl reef that surrounds the lake was fractured during the Mexico City earthquake of September 19, 1985. We assumed therefore that the slump deposit extending from the surface to 84 cm was deposited during that event (Fig. 3). Lead 210 dating and tephrochronology have since confirmed this assumption.

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Fig. 2. Map of the study area (a) and the coring location (b). The cross-section of the Rincon de Parangueo crater along the transect AB (refer to the upper crater map (b) for the location) (c).

Fig. 4. High-resolution Rincon δ 18 O records between ∼1610–1954.

Fig. 3. The age–depth profile and digital and x-ray photos of Rincon sediment.

Apart from a non-laminated section below the slump deposit, 85 cm to 103 cm, the sediments are either well laminated or indistinctly laminated (Fig. 3). The laminations are alternately light and dark in color and each couplet is about 1 mm thick. The light laminations consist mainly of authigenic carbonate and the dark laminations, of organic material and clay. The former are assumed to have been precipitated during the dry season (winter and spring) when the lake water was saturated with calcium carbonate due to evaporation and photosynthesis, and the latter to have been deposited in the rainy season (summer and fall). The microstratigraphy and tephrochronology of the upper part is discussed in more detail in a companion paper by Kienel et al. (2009).

These varved deposits appear to have been preserved when livestock wastes caused lake eutrophication and oxygen deficits during colonial times. Enhanced photosynthetic rates relative to CO2 influx in lake water is strongly indicated by marked increase in δ 13 C values (not shown here). The 80 cm to 130 cm section of the core was dated by lead 210 counting (Table 1). Samples at 80 and 84 cm produced very low activity levels and thereby helped define the base of the slump. A laminated section from 80 cm to 84 cm containing 3 varves was initially thought to be a pre-slump deposit but the low activities indicate that it is actually part of the slump. Age estimates for the samples at 87 through 109 cm were obtained using the constant rate of supply model. The estimates agree well with the tephra dates discussed below and also confirm that the slump deposit dates to the Mexico City earthquake of 1985 (Kienel et al., 2009). The activity levels in the 113, 119 and 129 cm samples were too low to assign reliable age estimates. In addition, tephrochronology and varve counting were used to date the core section between 103 cm and 155 cm. The Rincon tephras are poorly preserved, probably due to the alkalinity of the lake water, and precise mineralogical characterization has therefore not been possible. Fortunately, the same tephras are present in good condition in a core recovered from Hoya la Alberca just

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Table 1 Pb-210 dates for the Rincon 2004 core. Sample number

Depth (cm)

Weight of sample counted (g)

Po-210 total activity (DPM/g)

Po-210 unsupported activity (DPM/g)

Age at bottom of extrapolated section in years (CRS model estimate)

293-1 293-2 293-3 293-4 293-5 293-6 293-7 293-8 293-9 293-10

79–80 83–84 86–87 89–90 96–97 102–103 108–109 112–113 118–119 128–129

0.526 0.521 0.521 0.540 0.658 0.540 0.657 0.558 0.535 0.543

0.17 0.70 2.26 1.75 0.77 1.43 2.10 0.92 0.29 0.20

−0.02

slump slump 3.7 12.1 17.6 31.8 70.8

a

0.51 2.07 1.56 0.58 1.24 1.91 0.73 0.10 0.01

CRS sediment accumulation rate (g/cm2 /yr)a

Pb-210 age (year AD)

0.2947 0.3251 0.7058 0.2442 0.0731

1982.1 1973.7 1968.2 1954.0 1915.0

Sediment accumulation rate and age estimates were obtained using the constant rate of supply (CRS) model (Appleby and Oldfield, 1978).

Fig. 5. Detrended δ 18 O values of Rincon sediments (b) in comparison with CRU precipitation data for 20◦ 00 N/101◦ 15 W (Hulme et al., 1998) (a) and Rincon (MXRP3) titanium records (Kienel et al., 2009) (c). A five-year smoothing was applied to CRU data and titanium records (thick curves). Dry conditions are indicated by yellowish bars. They show a fair correlation, thus raising the reliability of Rincon δ 18 O records. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

4.5 km to the southeast of Rincon (Fig. 2). The mineralogy of the Alberca tephras, equivalent to the tephras at 104 cm and 111 cm in the 2004 Rincon core, indicates that the tephras are attributable to eruptions of the Paricutín volcano in 1943/1944 and the Fuego de Colíma in 1913, respectively (Kienel et al., 2009). Furthermore, the fact that there are 30 alternating light-dark laminae between the two tephras demonstrates that the laminae couplets are true varves. The tephra at 130 cm in the 2004 Rincon core has not been characterized mineralogically but a varve count of the section 112 cm to 130 cm indicates that it dates to ca. 1770, which coincides with the eruption of El Jorullo in the state of Michoacan (Newton et al., 2005). Independent varve counts by three people indicate that the time period represented is ∼1610 to 1954 CE. For most of this section, the varves are well defined and can easily be counted on x-radiographs and digital images. The average thickness for each varve couplet is 1.3 mm. Thus, the age–depth model for the UC 2004 core was developed with 3 tephras linked to historic eruptions, lead 210 age estimates on 5 samples, and varve chronology (Fig. 3).

Bulk sediment samples containing thin laminations of authigenic calcite were taken at 0.2–0.3 cm intervals to measure oxygen isotope ratios (δ 18 O). All samples were oven dried at 40 ◦ C for 48 h and were homogenized with a mortar and pestle. Ten to 100 micrograms of calcite were analyzed in a GV IsoPrime mass spectrometer with Dual-Inlet and MultiCarb systems. Several replicates of two international standards, NBS18 and NBS19, and one lab standard, HKC-I, were measured along with the samples for each run. The overall external analytical precision is ±0.07h (internal precision: ±0.007h). A continuous wavelet transform was carried out using the MatLab wavelet package (available at http://noc.ac.uk/using-science/ crosswavelet-wavelet-coherence) to investigate the time–frequency character of Rincon δ 18 O data and other proxy records, which had been modified to evenly-spaced time series (Grinsted et al., 2004). The results of wavelet transform were thereafter compared to identify common periodicities between proxy data. The 95% confidence intervals for the correlation coefficients were calculated by Pearson

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Fig. 6. Comparison among paleoclimate reconstructions. Tree ring-based PDO reconstructions of MacDonald and Case (2005) (a) and Biondi et al. (2001) (b), Rincon sediment δ 18 O, this study (c), PDSI from grids 169 and 170 (Cook et al., 2004) (d), Cuban speleothem δ 18 O (Fensterer et al., 2012) (e), and the abundance of planktonic foraminifera from the Cariaco Basin (Black et al., 1999) (f). For the location of each site, refer to Fig. 1. Yellowish bars in the diagram (d) indicate dry conditions. Rincon, Cuban, and Cariaco Basin records were detrended using a 100-year filter. Also, a ten-year smoothing was applied to all the proxies (thick curves). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

T3 (Ólafsdóttir and Mudelsee, 2014), which is designed for estimating the correlation between unevenly spaced autocorrelated data. 4. Results and discussion 4.1. Late Holocene lake-sediment δ 18 O record from central Mexico In central Mexico, high-resolution paleoclimate proxy records showing multiannual to multidecadal-scale climate variation have been so far produced mostly via dendroclimatic studies (see Stahle et al., 2016). Tree ring data are generally believed to be the most reliable high-resolution proxy data for the detection of short-term climate change. However, it is always necessary to have various types of proxy data because even tree ring data are not free of the inherent limitations caused by non-climate factors. Most of all, the total number of existing proxy records in central Mexico are too small to come to any reliable conclusion about regional climate shift or to provide practical implications on droughts.

Our new high-resolution δ 18 O record from central Mexico shows wetness/dryness variations during the last approximately 340 years (Fig. 4). Relatively high δ 18 O ratios with a large range of values (1–7h) indicate that Rincon sediments were deposited under closed-lake conditions. Carbonate δ 18 O in closed-basin lake sediments generally reflect variations in the ratio of evaporation to precipitation (E/P), as a high E/P ratio preferentially enriches heavier oxygen (18 O) in lake water (Leng and Marshall, 2004). The Rincon δ 18 O record was detrended with a 100-year filter to retain low-frequency variations possibly related to PDO or AMO and was then evaluated for whether it is a reliable proxy for droughts in central Mexico. We compared it with CRU precipitation data for 20◦ 00 N/101◦ 15 W (Hulme et al., 1998) and Rincon (MXRP3) titanium records that had been previously reported by Kienel et al. (2009) (Fig. 5). An increase in δ 18 O values generally coincides with a decrease in total annual precipitation and with low titanium count rates in the early 1850s and 1890s and late 1910s, 1930s, and 1940s.

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−0.18) was observed between 20-year smoothed PDSI and 10-year smoothed Rincon δ 18 O records. Correlations with PDO reconstruc-

Fig. 7. Continuous transform wavelet power spectrums for each proxy record in Fig. 6. The black contour lines delineate the 5% significance level against the AR(1) red noise signal and the shaded area below the black cone is the region in which edge effects become important. Dashed black and white lines indicate the 20-year PDO cycle and 70-year AMO cycle, respectively.

4.2. Combined influence of PDO and AMO on central Mexico To understand the mechanism behind climate shifts in central Mexico, our record was compared with other proxies such as the Palmer Drought Severity Index (PDSI) from central Mexico (Cook et al., 2004), tree ring-based PDO indices from Southern California (Biondi et al., 2001; MacDonald and Case, 2005), a speleothem δ 18 O record from Cuba (Fensterer et al., 2012), and planktonic foraminiferal abundance from Cariaco Basin (Black et al., 1999) (for site locations, see Fig. 1). We also detrended Cuban and Cariaco Basin records with a 100-year filter to facilitate the comparison (Fig. 6). The comparison diagram demonstrates that Rincon records are relatively well correlated with central Mexican PDSI, enhancing their reliability as a paleoclimate proxy. The latter was obtained by averaging PDSI reconstructions from grids 169 (22◦ 30 N/100◦ 00 W) and 170 (20◦ 00 N/100◦ 00 W) in Cook et al. (2004)’s study. A correlation coefficient of −0.31 with 95% confidence interval (−0.44;

tions are also particularly apparent after 1750. PDO is a strong periodic pattern of oceanic SST variations in the mid-latitude Pacific basin. During its positive phase, the eastern Pacific Ocean warms, reducing the thermal gradient to the continental interior and hence, monsoonal precipitation in central Mexico. The Atlantic influence on central Mexico is indicated by general similarities between Rincon records and AMO proxies from the Cariaco Basin and Cuba. Cariaco Basin foraminiferal records reflect the movement of ITCZ in the North Atlantic. The more northerly position of ITCZ weakens Easterlies over the Cariaco Basin and reduces upwelling and planktonic foraminiferal abundance as a result (Black et al., 1999). Since northward movement of ITCZ usually causes increased rainfall over central Mexico and Cuba as well as the Cariaco Basin, the low abundance of Cariaco foraminifera is indicative of wetter conditions in these areas. The ITCZ movement seems to be substantially attributable to North Atlantic SST shifts (expressed as the AMO index) that may be controlled by thermohaline circulation changes. AMO and ITCZ movement is therefore believed to be generally coupled (Dong and Sutton, 2002; Knight et al., 2006). To clarify the PDO and AMO influence in central Mexico, continuous wavelet transforms were performed on Rincon δ 18 O records and all other proxy data discussed in this paper. Wavelet results from Rincon records reflect the influence from both the PDO and AMO with 20- and 70-year cycles, respectively (Fig. 7). The 20-year PDO periodicity, well demonstrated by tree ring records from southern California, is robustly observed in instrumental data for the 20th century (Mantua and Hare, 2002). It is difficult to verify the 70-year AMO periodicity with Atlantic SST observations that only span the past ∼150 years. This cycle has been however strongly suggested as the main AMO mode by many reconstructions from both tree ring sites (Delworth and Mann, 2000; Gray et al., 2004) and oceanic sites (Kilbourne et al., 2008; Saenger et al., 2009; Knudsen et al., 2011). Our results also similarly indicate that the forcing with a 70-year periodicity has influenced central Mexico since at least the early 17th century. A similar 50 to 75-year variation is, however, also identified in PDO observations (Minobe, 1997; Mantua and Hare, 2002), which makes it difficult to separate between the two different oceanic influences on central Mexico based on periodicity. In PDO reconstructions, however, unlike instrumental data, the ∼70-year cycle is not clearly identified (Biondi et al., 2001, D’Arrigo et al., 2001; D’Arrigo and Wilson, 2006; MacDonald and Case, 2005; Shen et al., 2006). This is particularly obvious in Biondi et al.’s data showing only intradecadal to bidecadal cycles (Fig. 7b). Our wavelet results thus imply that the central Mexican climate has been mainly controlled by the 20-year PDO cycle and the 70-year AMO cycle since ∼AD 1600 (Figs. 7c and 7d). Méndez and Magaña’s (2010) 20th-century meteorological records verify that dry periods in central Mexico coincided with the combination of the warm PDO phase and cool AMO phase. They suggest that convection over central Mexico is weakened during the positive phase of PDO as Caribbean low-level jet strengthens and easterly wave activity declines. However, it is still unclear how negative AMO phases influence central Mexico. This relationship between droughts and +PDO/−AMO is also identified in tree ring data from central Mexico (Stahle et al., 2012). The combined influence of Pacific and Atlantic SSTs on Mesoamerican climates has been thus already emphasized in previous paleoclimate studies (Stahle et al., 2012; Jones et al., 2015). However, their reconstructions were not robustly correlated with North Atlantic SSTs, even though the latter is believed to play a major role in producing multidecadal climate variability in Mesoamerica. Thus, they tended to say that the Atlantic forcing might not

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Fig. 8. The PDO and AMO influence on climate in central Mexico. Tree ring-based PDO reconstruction by Biondi et al. (2001) (a) and its 20-year filter with central frequency = 0.05 and bandwidth = 0.02 (b), Rincon sediment δ 18 O and the composite curve created by combining the PDO and AMO filter (c), and AMO-related Cuban speleothem δ 18 O (e) and its 70-year filter with a central frequency = 0.014 and a bandwidth = 0.02 (d).

have been as important as the Pacific forcing for Mesoamerican climates. However, our results suggest Pacific and Atlantic multidecadal modulations have both been significant at least until ∼AD 1900. In this study, the influences of the Atlantic and Pacific oceans on central Mexico can be both verified through an investigation into dominant periodicities in paleoclimate proxy data. These PDO and AMO influences are more clearly demonstrated in the comparison between Rincon data and a composite curve comprising a PDO reconstruction (Biondi et al., 2001) and AMOrelated Cuban δ 18 O (Fensterer et al., 2012) (Fig. 8). We applied the former with ∼20-year bandpass filter and the latter with ∼70-year filter then combined the outputs to see to what extent the central Mexican climate was influenced by the PDO and AMO. A robust visual correlation between Rincon data and the combined curve since 1750 in particular strongly suggests that the 20-year PDO cycle and the 70-year AMO cycle have been principal climate drivers in central Mexico. In addition, climate in central Mexico has also been significantly influenced by ENSO events (Mendoza et al., 2005; Seager et al., 2009; Stahle et al., 2012). However, the temporal resolution of the Rincon δ 18 O record is not sufficient to state with confidence how interannual SST variability in the tropical Pacific modulates PDO and AMO influence on the climate in central Mexico. Rincon δ 18 O records indicate a coincidence of AMO and PDOinduced aridity resulted in more persistent and severe droughts in the past. For example, dryness in the 1620s, 1650s, 1700s,

1730s, 1780s, 1850s, and 1930s was presumably associated with a co-occurrence of highly positive PDO and negative AMO. Most of them were also identified in historical documents (Mendoza et al., 2005). However, according to Atlantic SST observations (Enfield et al., 2001), the late 1930s were characterized by a positive AMO phase. Such uncertainty of the AMO influence is also reflected in opposing trends between Cariaco Basin and Cuban records since 1910 (Figs. 6e and 6f), and this issue is discussed in more detail in the following section. 4.3. Implications for future drought assessment If these PDO and AMO cycles still control the climate of central Mexico in the present, it would be possible to roughly predict the occurrence of future droughts. However, the aforementioned ambiguity of the AMO influence needs to be clarified first and instrumental data provide necessary information in this respect. Rincon records exhibit four periods of marked wetness every 70 years in general; for example, periods centered around 1690, 1760, 1840, and 1905. According to rainfall observations (KNMI) and the CRU precipitation data of Hulme et al. (1998), another period of marked wetness occurred at ∼1975, about 70 years after the last one indicated in Rincon records (Fig. 9). Thus, the 70-year oscillation may have remained an important driver of climate change even after the temporal pattern of AMO was altered.

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Fig. 9. The comparison between 5-year smoothed summer rainfall data (June–September) of the study area, Rincon δ 18 O, and annual PDO observations (a) and 10-year smoothed PDO (b). Yellowish bars in the diagram (a) indicate PDO-induced dry conditions while the blue area in the diagram (b) does a wet phase attributable to the ∼70 year cycle forcing. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

It is however difficult to speculate about underlying processes behind the maintenance of the 70-year cycle at this point. The influence of the lower-frequency PDO (∼60 year cycle) may possibly have been enhanced for some reason to weaken the AMO modulation of the central Mexican climate since the early 20th century. This hypothesis is supported by considerable similarity between rainfall and smoothed PDO observations (Fig. 9). Tree ring data also reflect the predominant PDO control of the climate during the 20th century (Stahle et al., 2012). Central Mexico probably became less influenced by the ITCZ migration and instead became more influenced by PDO-related monsoonal activities. By contrast, Rincon δ 18 O records clearly show a bidecadal cycle temporally coherent with both PDO observations and reconstructions. A link between Rincon δ 18 O data and rainfall observations in the early to mid 20th century suggests that the entire observed precipitation data would identify continuous bidecadal PDO influence (Fig. 9a). Relatively dry periods (1935–1940, 1955–1960, 1977–1982, and 1995–2000) indicated in rainfall observations, may therefore have been attributable to the warm PDO phase. This reasoning would lead us to speculate that another warm PDO phase and a consequent drought may occur after 2015. However, some caution may be needed in interpreting the results since climate in central Mexico is also modulated by ENSO events, as mentioned

earlier. This phase might not be so severe anyway as wet conditions are expected in lower-frequency PDO cycles (Fig. 9b). In addition, the drought mechanism in this study could be used to assess possible links between past droughts and social unrest in central Mexico. Acknowledgement This work was supported by the National Research Foundation of Korea (NRF-2015R1D1A1A01056638). Financial support for this study was also partially funded by the University of California Institute for Mexico and the United States (UC MEXUS), a Stahl grant from Archaeological Research Facility in University of California at Berkeley, and an Esther Larsen grant from the Department of Earth and Planetary Science in UC Berkeley. We thank the editor and three anonymous reviewers for their useful comments and suggestions for improving the manuscript. References Aguilar-Barajas, I., Sisto, N.P., Magaña-Rueda, V., Ramírez, A.I., Mahlknecht, J., 2016. Drought policy in Mexico: a long, slow march toward an integrated and preventive management model. Water Policy 18, 107–121.

J. Park et al. / Earth and Planetary Science Letters 464 (2017) 1–9

Aguilera Gómez, L.I., 1991. Estudio Floristico y Sinecologico de la Vegetacíon en el crater “Hoya de Rincón de Parangueo”, Valle de Santiago, Gto. Unpublished Masters thesis, Colegio de Postgraduados, Montecillo, Mexico. Alcocer, J., Escobar, E., Lugo, A., 2000. Water use (and abuse) and its effects on the crater-lakes of Valle de Santiago, Mexico. Lakes & Reserv.: Res. & Manag. 5, 145–149. Appleby, P., Oldfield, F., 1978. The calculation of lead-210 dates assuming a constant rate of supply of unsupported 210 Pb to the sediment. Catena 5, 1–8. Barker, R., Scott, C.A., De Fraiture, C., Amarasinghe, U., 2000. Global water shortages and the challenge facing Mexico. Int. J. Water Resour. Dev. 16, 525–542. Bhattacharya, T., Byrne, R., Böhnel, H., Wogau, K., Kienel, U., Ingram, B.L., Zimmerman, S., 2015. Cultural implications of late Holocene climate change in the Cuenca Oriental, Mexico. Proc. Natl. Acad. Sci. USA 112, 1693–1698. Biondi, F., Gershunov, A., Cayan, D.R., 2001. North Pacific decadal climate variability since 1661. J. Climate 14, 5–10. Black, D.E., Peterson, L.C., Overpeck, J.T., Kaplan, A., Evans, M.N., Kashgarian, M., 1999. Eight centuries of North Atlantic Ocean atmosphere variability. Science 286, 1709–1713. Cook, E.R., Woodhouse, C.A., Eakin, C.M., Meko, D.M., Stahle, D.W., 2004. Long-term aridity changes in the western United States. Science 306, 1015–1018. Cowgill, G.L., 2015. Ancient Teotihuacan: Early Urbanism in Central Mexico. Cambridge University Press, New York. D’Arrigo, R., Villalba, R., Wiles, G., 2001. Tree-ring estimates of Pacific decadal climate variability. Clim. Dyn. 18, 219–224. D’Arrigo, R., Wilson, R., 2006. On the Asian expression of the PDO. Int. J. Climatol. 26, 1607–1617. Dai, A., 2011. Drought under global warming: a review. Wiley Interdiscip. Rev.: Clim. Change 2, 45–65. De Tapia, E.M., 2012. Silent hazards, invisible risks: prehispanic erosion in the Teotihuacan Valley, Central Mexico. In: Cooper, J., Sheets, P. (Eds.), Surviving Sudden Environmental Change. University Press of Colorado, Boulder, pp. 143–166. Delworth, T.L., Mann, M.E., 2000. Observed and simulated multidecadal variability in the Northern Hemisphere. Clim. Dyn. 16, 661–676. Dong, B.W., Sutton, R., 2002. Adjustment of the coupled ocean–atmosphere system to a sudden change in the thermohaline circulation. Geophys. Res. Lett. 29, 1728. Enfield, D.B., Mestas-Nuñez, A.M., Trimble, P.J., 2001. The Atlantic multidecadal oscillation and its relation to rainfall and river flows in the continental US. Geophys. Res. Lett. 28, 2077–2080. Enfield, G.H., O’Hara, S.L., 1999. Degradation, drought, and dissent: an environmental history of colonial Michoacán, west central Mexico. Ann. Assoc. Am. Geogr. 89, 402–419. Enge, K.I., Whiteford, S., 1989. The Keepers of Water and Earth: Mexican Rural Social Organization and Irrigation. University of Texas Press. Escolero-Fuentes, O.A., Alcocer-Durand, J., 2004. Desecación de los lagos cráter del Valle de Santiago, Guanajuato. In: Jiménez, B., Marín, L., Morán, D., Escolero, O., Alcocer, J. (Eds.), El agua en México vista desde la Academia: México, D.F., México. Academia Mexicana de Ciencias, pp. 99–116. Fensterer, C., Scholz, D., Hoffmann, D., Spötl, C., Pajón, J.M., Mangini, A., 2012. Cuban stalagmite suggests relationship between Caribbean precipitation and the Atlantic Multidecadal Oscillation during the past 1.3 ka. Holocene 22, 1405–1412. Gray, S.T., Graumlich, L.J., Betancourt, J.L., Pederson, G.T., 2004. A tree-ring based reconstruction of the Atlantic Multidecadal Oscillation since 1567 AD. Geophys. Res. Lett. 31, L12205. Grinsted, A., Moore, J.C., Jevrejeva, S., 2004. Application of the cross wavelet transform and wavelet coherence to geophysical time series. Nonlinear Process. Geophys. 11, 561–566. Hu, Q., Feng, S., 2012. AMO-and ENSO-driven summertime circulation and precipitation variations in North America. J. Climate 25, 6477–6495. Hulme, M., Osborn, T.J., Johns, T.C., 1998. Precipitation sensitivity to global warming: comparison of observations with HadCM2 simulations. Geophys. Res. Lett. 25, 3379–3382. Jones, M.D., Metcalfe, S.E., Davies, S.J., Noren, A., 2015. Late Holocene climate reorganisation and the North American Monsoon. Quat. Sci. Rev. 124, 290–295. KNMI Climate Explorer (n.d.). Accessed 28 January 2016 from https://climexp. knmi.nl/getstations.cgi. Kienel, U., Bowen, S.W., Byrne, R., Park, J., Böhnel, H., Dulski, P., Luhr, J.F., Siebert, L., Haug, G.H., Negendank, J.F., 2009. First lacustrine varve chronologies from Mexico: impact of droughts, ENSO and human activity since AD 1840 as recorded in maar sediments from Valle de Santiago. J. Paleolimnol. 42, 587–609. Kilbourne, K., Quinn, T., Webb, R., Guilderson, T., Nyberg, J., Winter, A., 2008. Paleoclimate proxy perspective on Caribbean climate since the year 1751: evidence of cooler temperatures and multidecadal variability. Paleoceanography 23, PA3220. Knight, J.R., Folland, C.K., Scaife, A.A., 2006. Climate impacts of the Atlantic multidecadal oscillation. Geophys. Res. Lett. 33, L17706.

9

Knudsen, M.F., Seidenkrantz, M.-S., Jacobsen, B.H., Kuijpers, A., 2011. Tracking the Atlantic Multidecadal Oscillation through the last 8,000 years. Nat. Commun. 2, 178. Lachniet, M.S., Bernal, J.P., Asmerom, Y., Polyak, V., Piperno, D., 2012. A 2400 yr Mesoamerican rainfall reconstruction links climate and cultural change. Geology 40, 259–262. Leng, M.J., Marshall, J.D., 2004. Palaeoclimate interpretation of stable isotope data from lake sediment archives. Quat. Sci. Rev. 23, 811–831. Liverman, D.M., 1990. Drought impacts in Mexico: climate, agriculture, technology, and land tenure in Sonora and Puebla. Ann. Assoc. Am. Geogr. 80, 49–72. Liverman, D.M., 1992. Global warming and Mexican agriculture: some preliminary results. In: Reilly, J.M., Anderson, M. (Eds.), Economic Issues in Global Climate Change: Agriculture, Forests and Natural Resources. Westview, Boulder, pp. 332–352. MacDonald, G.M., Case, R.A., 2005. Variations in the Pacific Decadal Oscillation over the past millennium. Geophys. Res. Lett. 32, L08703. Mantua, N.J., Hare, S.R., 2002. The Pacific decadal oscillation. J. Oceanogr. 58, 35–44. Mendoza, B., Jáuregui, E., Diaz-Sandoval, R., García-Acosta, V., Velasco, V., Cordero, G., 2005. Historical droughts in central Mexico and their relation with El Niño. J. Appl. Meteorol. 44, 709–716. Minobe, S., 1997. A 50–70 year climatic oscillation over the North Pacific and North America. Geophys. Res. Lett. 24, 683–686. Mo, K.C., Schemm, J.-K.E., Yoo, S.-H., 2009. Influence of ENSO and the Atlantic multidecadal oscillation on drought over the United States. J. Climate 22, 5962–5982. Mosiño Alemán, P.A., García, E., 1974. The climate of Mexico. In: Bryson, R.A., Hare, F.H. (Eds.), Climate of North America, World Survey of Climatology. Elsevier, Amsterdam, pp. 345–390. Murphy, G.P., 1986. The Chronology, Pyroclastic Stratigraphy, and Petrology of the Valle de Santiago Maar Field, Central Mexico. M.A. Thesis, University of California, Berkeley. Méndez, M., Magaña, V., 2010. Regional aspects of prolonged meteorological droughts over Mexico and Central America. J. Climate 23, 1175–1188. Newton, A.J., Metcalfe, S.E., Davies, S.J., Cook, G., Barker, P.A., Telford, R.J., 2005. Late quaternary and Holocene volcanic record preserved in lakes of Michoacán, central Mexico. Quat. Sci. Rev. 24, 91–104. Ólafsdóttir, K., Mudelsee, M., 2014. More accurate, calibrated bootstrap confidence intervals for estimating the correlation between two time series. Math. Geosci. 46, 411–427. Ortega-Gaucin, D., Velasco, I., 2013. Aspectos socioeconómicos y ambientales de las sequías en México. Aqua-lac 5, 78–90. Park, J., Byrne, R., Böhnel, H., Garza, R.M., Conserva, M., 2010. Holocene climate change and human impact, central Mexico: a record based on maar lake pollen and sediment chemistry. Quat. Sci. Rev. 29, 618–632. Pavia, E.G., Graef, F., Reyes, J., 2006. PDO–ENSO effects in the climate of Mexico. J. Climate 19, 6433–6438. Saenger, C., Cohen, A.L., Oppo, D.W., Halley, R.B., Carilli, J.E., 2009. Surface– temperature trends and variability in the low-latitude North Atlantic since 1552. Nat. Geosci. 2, 492–495. Seager, R., Ting, M., Davis, M., Cane, M., Naik, N., Nakamura, J., Li, C., Cook, E., Stahle, D.W., 2009. Mexican drought: an observational modeling and tree ring study of variability and climate change. Atmósfera 22, 1–31. Servicio Meteorológico Nacional (n.d.). Accessed 30 November 2016 from http:// smn.cna.gob.mx/es/informacion-climatologica-ver-estado?estado=gto. Shen, C., Wang, W.C., Gong, W., Hao, Z., 2006. A Pacific Decadal Oscillation record since 1470 AD reconstructed from proxy data of summer rainfall over eastern China. Geophys. Res. Lett. 33, L03702. Stahle, D., Burnette, D., Diaz, J.V., Heim Jr, R., Fye, F., Paredes, J.C., Soto, R.A., Cleaveland, M., 2012. Pacific and Atlantic influences on Mesoamerican climate over the past millennium. Clim. Dyn. 39, 1431–1446. Stahle, D.W., Cook, E.R., Burnette, D.J., Villanueva, J., Cerano, J., Burns, J.N., Griffin, D., Cook, B.I., Acuña, R., Torbenson, M.C., 2016. The Mexican Drought Atlas: treering reconstructions of the soil moisture balance during the late pre-Hispanic, colonial, and modern eras. Quat. Sci. Rev. 149, 34–60. Stahle, D.W., Diaz, J.V., Burnette, D.J., Paredes, J., Heim, R., Fye, F.K., Acuna Soto, R., Therrell, M.D., Cleaveland, M.K., Stahle, D.K., 2011. Major Mesoamerican droughts of the past millennium. Geophys. Res. Lett. 38, L05703. Sutton, R.T., Hodson, D.L., 2005. Atlantic Ocean forcing of North American and European summer climate. Science 309, 115–118. Therrell, M.D., Stahle, D.W., Diaz, J.V., Oviedo, E.H.C., Cleaveland, M.K., 2006. Treering reconstructed maize yield in central Mexico: 1474–2001. Clim. Change 74, 493–504.