The fluorescence of dissolved organic matter in porewaters of marine sediments

Marine Chemistry, 45 (1994) 31-42 0304-4203/94/$07.00

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© 1994 - Elsevier Science B.V. All rights reserved

The fluorescence of dissolved organic matter in porewaters of marine sediments Robert F. Chen l, Jeffrey L. Bada Scripps Institution of Oceanography, University of California, San Diego, La Jolla, CA 92093-0212, USA (Received August 19, 1992; revision accepted April 15, 1993)

Abstract The fluorescence of porewaters from marine sediment cores from six different areas was measured. In most cases, fluorescence was affected primarily by the diagenesis of organic carbon first through sulfate reduction and subsequently by methane generation. Typically, fluorescence, dissolved organic carbon (DOC), absorbance, alkalinity, and ammonium ion concentrations correlate quite well, increasing in the upper sections of anoxic sediments and co-varying in deeper sections of these cores. The good correlation of DOC with fluorescence in the three cores in which DOC was measured indicates that fluorescence can be used to make a first order estimate of DOC concentration in anoxic porewaters. Data are consistent with a model in which labile organic matter in the sediments is broken down by sulfur reducing bacteria to low molecular weight monomers. These monomers are either remineralized to CO 2 or polymerize to form dissolved, fluorescent, high molecular weight molecules. The few exceptions to this model involve hydrothermally generated hydrocarbons that are formed in situ in the Guaymas Basin or are horizontally advected along the decollement in the Nankai Trench.

1. Introduction

Although the oxidation of organic matter in recent sediments often dominates early diagenetic reactions, consideration of the specific nature and reactivity of the organic matter is often neglected. The chemistry of DOC in sediment porewaters is a key component to understanding the carbon cycle in recent sediments. Interactions between the dissolved and sedimentary organic matter include adsorption, condensation, polymerization, dissolution, and mineralization. DOC is thought to be an intermediate in the remineralization of labile sedimentary organic matter and the conversion of labile DOC to refractory humic substances (Krom and Sholkovitz, 1977; Krom and i Present address: Woods Hole Oceanographic Institution, Fye Laboratory, Woods Hole, MA 02543, USA. SSDI 0304-4203(93)E0012-N

Westrich, 1981), and, therefore, may affect the total amount of carbon buried in the sediment versus that which is remineralized. Porewater DOC may also control the dissolved concentrations of trace metals such as V, Cr, and Mo (Brumsack and Gieskes, 1983). Fluorescent DOC in anoxic porewaters apparently diffuses out of sediments into overlying seawater (Chen and Bada, 1989; Chen et al., 1993) and contributes locally to seawater DOC. Despite the possible significance of porewater DOC, only a few studies have been undertaken. Porewaters have been found to exhibit two patterns of DOC with depth. DOC in oceanic, oxic porewaters appears to be ~ 10 times enriched when compared to overlying waters, but remains constant with depth. In contrast, DOC increases downcore to very high values in anoxic, organic-rich sediments (Starikova, 1970). Nissenbaum et al. (1972) suggest that low

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molecular weight (LMW) molecules such as amino acids and sugars may complex to form humic materials. In the recent sediments of Scottish Fjords (< 80 cm), LMW compounds have been found to remain constant with depth (,-~ 10 mg 1-1) while high molecular weight (HMW) compounds increase gradually in anoxic porewaters (Krom and Sholkovitz, 1977). Krom and Westrich (1981) presented a model to explain these observations in terms of the conversion of labile organic matter to LMW compounds, which in turn either are remineralized or polymerize to form HMW material. Several specific organic compounds have been identified in porewaters. Dissolved free amino acids (DFAA) have been measured at 1.3 to 6.0 mg 1-l in Black Sea oozes (Starikova and Korzhikova, 1972), 0.8 to 5.6 mg 1-1 in Buzzards Bay, Massachusetts (Henrichs and Farrington, 1979), and 0.0 to 0.05 mg 1-1 in deep sea sediments (Ishizuki et al., 1988). In Saanich Inlet porewaters, fatty acids were ~0.04 mg 1-t (Nissenbaum et al., 1972). Martens (1990) found acetate and propionate concentrations of greater than 0.66 mg 1-1 and greater than 14.8 mg 1-1, respectively, in the hydrothermally altered sediments of the Guaymas Basin. Barcelona (1980) found concentrations of 5-50 mg 1-1 for C1 to C5 acids in Santa Barbara Basin sediments. Glucose has been measured at 0.020 to 0.135 mg 1-1 in porewaters from the Georgia Shelf (Tenore et al., 1978). The identifiable compounds compose 10-50% of the DOC in porewaters, the remaining material being called HMW polymer, "GelbstolT', or humic substances. Total DOC concentrations have been measured by various methods to be 5 to 480 mgC 1-1 in a variety of marine sediment porewaters (Lyons et al., 1979; Barcelona, 1980; Michaelis et al., 1982; Henrichs and Farrington, 1987; Bauer et al., 1991). Fluorescence is a bulk property of porewater that is easy to measure and may reveal the behavior of the high molecular weight fraction of the DOC. To date, only two other studies of

R.F. Chen, J.L. Bada/Marine Chemistry 45 (1994) 31-42

the fluorescence of porewaters have been undertaken: one examining sedimentary humic and fulvic acids as fluorescent materials (Hayase and Tsubota, 1985), and one evaluating the importance of colloidal organic matter to total DOC (Lyutsarev et al., 1984). The first fluorescence depth profiles are presented here and in Chen and Bada (1989). The laser-based detection system which we have developed (Chen and Bada, 1990) is ideal for studying the small porewater samples generally available. In anoxic porewaters, DOC correlates well with both alkalinity and absorbance (Krom and Sholkovitz, 1977; Krom and Westrich, 1981), and fluorescence correlates well with alkalinity (Chen and Bada, 1989) and DOC (Chen et al., 1993). In this paper, the relationship between fluorescence, DOC, absorbance, and alkalinity is explored, and the implications for early diagenesis of organic carbon are discussed.

2. Materials and methods

Porewater samples from Santa Barbara Basin and Ocean Drilling Program (ODP) 808A were filtered (0.45 #m) and frozen in amber glass vials until analysis. All other samples were filtered and stored at room temperature in translucent polycarbonate vials or sealed polyethylene tubing. Fluorescence (Aex= 325 nm, )~em = 450 nm) was measured with a laser-induced fluorescence (LIF) system described in detail elsewhere (Chen and Bada, 1990). Briefly, the LIF system is comprised of the 325 nm excitation radiation of a HeCd laser focused into a fiber optic (100/~m) that is inserted directly into a fused silica capillary (200 #m ID) flow-through cell, and the resulting emission radiation is collected at right angles and measured with a photomultiplier tube. Uncorrected emission spectra were analyzed with a Farrand MK2 spectrofluorometer when sufficient sample (> 1.5 ml) was available. A 2.8 #g 1-1 quinine sulfate standard solution was set to 45 flu (Chen and Bada, 1992).

R.F. Chen, J.L. Bada/Marine Chemistry 45 (1994) 31-42

A stable, suitable standard was not found for LIF, but LIF is shown to give a linear response over 4 orders of magnitude (Chen and Bada, 1990). Although the LIF system has a higher tolerance for internal quenching than a conventional fluorometer due to its small cell volume (Chen and Bada, 1990), the very high fluorescence intensities of some porewaters made dilution necessary. Therefore, samples were diluted by a factor of 10 with Milli-Q water. DOC was measured with the high temperature catalytic oxidation (HTCO) method (Sugimura and Suzuki, 1988; Druffel et al., 1989; Suzuki et al., 1992) in Dr. Y. Suzuki's laboratory (Tsukuba, Japan). A five point calibration of glucose in HPLC grade water determined the system response, and total blank values (system blank+water blank) were ~ 100 #M. While this blank is quite high, it is generally on the same order as the precision (2-5%) and was not accounted for in the DOC values reported. Storage of these porewater samples may affect the fluorescence measurement. Even though pH affects seawater fluorescence, with fluorescence increasing 10-15% from pH 3 to pH 8 (Laane, 1982), acidified samples from Santa Barbara Basin yield similar profiles to non-acidified, frozen samples from a different cruise. The most fluorescent samples from Ocean Drilling Program (ODP) 808 were 10-15% less fluorescent when stored in translucent vials at room temperature than when stored in amber vials and frozen. This is most likely due to photochemical bleaching of the fluorophores which are bleached (probably photodegraded) rapidly when exposed to sunlight. Also, freezing the organic-rich porewaters may cause aggregation of DOC, and these aggregates may remain upon thawing. Nevertheless, storage variations were small and general trends were clear. With these precautionary notes in mind, we suggest future sampling as follows: filter and store porewaters in amber glass vials at 4°C until analysis.

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3. Areas of study The Santa Barbara Basin is one of several marine basins in the Southern California Borderlands. A sill depth of ~ 410 m and high productivities in surface waters lead to very low oxygen levels (< 9 #M) in bottom waters and organic-rich, anoxic, varved sediments (Hulsemann and Emery, 1961; Reimers et al., 1990). Samples were taken with box cores and a Kasten core as described by Chen and Bada (1989) to a depth of ,~ 2 m. Samples from ODP Leg 131, Site 808 were sampled according to ODP protocols. One major feature of this drill site in the Nankai Trough, off southern Japan, is the apparent influence of fluid flow along the decollement ~945-965 m below the surface (mbsf) as a result of compaction and shortening at the toe of the accretionary prism. The rapidly deposited upper section (0-200 mbsf) is characterized by large increases in alkalinity and ammonium ion concentration as a result of sulfate reduction (sulfate is depleted below ~ 8 mbsf) and methane production below this (You et al., 1993). Sites 496 and 499 in the Middle America Trench, off Guatemala, are dominated by organic matter decomposition (Harrison et al., 1982). Site 496 shows rapid increases in alkalinity in the upper 100 m. Organic carbon is high, and sulfate reduction is essentially complete in the upper 10 mbsf. Site 499, at the bottom of the trench, is much more complex consisting of alternating trench-fill turbidites and hemipelagic muds that lead to large reversals in alkalinity and other properties with depth. DSDP site 525 on the Walvis Ridge is an open ocean sediment (sedimentation rate < 10m/my) (Gieskes et al., 1984) and does not show large increases in alkalinity and ammonium ion or decreases in sulfate. These are the only "sub-oxic" porewaters examined in this study. High productivities and terrigenous sediment sources lead to high sedimentation rates and organic-rich sediments at Deep Sea Drilling

R.F. Chen, J.L. Bada/Marine Chemistry 45 (1994) 31-42

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Project (DSDP) sites 478 and 479 from Leg 64 in the Guaymas Basin, Gulf of California. Site 478 is located in the central basin (water depth 1500 m) while site 479 is on the slope (water depth ~ 747 m). Sulfate is depleted below 100 mbsf at site 478 and is essentially depleted below 10 mbsf at site 479 (Gieskes et al., 1982). Splits of 3 samples from site 479, sealed in clear glass ampoules, were analyzed for DOC by Michaelis et al. (1982) and by us (this study) using the HTCO method (Sugimura and Suzuki, 1988) and the resulting DOC values were in good agreement. This suggests that the storage of samples did not affect them significantly, and that the Erba Science TCM 400/P total carbon monitor, which operates on the principle of high temperature wet oxidation, used in that study agrees well with the HTCO method for porewaters. Guaymas Basin surface sediment porewaters were sampled with push cores near a hydrothermal outflow in 1985. Cores 1617, 1629, and 1630 are strongly influenced by this high temperature diffusive flow and contain hydrothermally generated hydrocarbons that overwhelm normal organic diagenetic patterns (Gieskes et al., 1988). (flu)

Fluorescence

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4. Results and discussion

The fluorescence of porewaters from the six areas described above are presented in Fig. 1 and tabulated in Appendix 1. The samples come from remarkably different sedimentary environments, and while many factors may control individual measurements, several trends appear clear regardless of the sample diversity: (1) Rapid increases in anoxic porewaters with depth primarily due to organic carbon diagenesis and subsequent decreases in fluorescence below this region, possibly due to adsorption or precipitation (e.g. Fig. la, the Gulf of California [O, D], and the Middle America Trench [A, /k]; Fig. lb, the Nankai Trough [B]; and Fig lc, the Santa Barbara Basin [O]). (2) Constant, relatively low intensities in suboxic, organic-poor sediments (e.g. Fig. la, the Walvis Ridge [(~]). (3) Localized increases in fluorescence in areas associated with inputs of hydrothermally generated hydrocarbons (e.g. Fig lb, the Nankai Trough [11] near 965 m; Fig lc, the Guaymas Basin [x, +, Eli). In anoxic porewaters, fluorescence, absorbance, alkalinity, and DOC have similar profiles (Appendix 1). The data presented here are consistent with a

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Fig. 1. Porewater fluorescence profiles in (a) the Gulf of California, Sites 478 (O) and Site 479 (IS]);the Middle America Trench, Sites 496 (A) and 499 (A); and the Walvis Ridge (()); (b) the Nankai Trough (11); and (c) the surface sediments of Santa Barbara Basin (Q) and Guaymas Basin, cores 1617 (x), 1629 (+), and 1630 (El). Please note changes in depth and fluorescence scales, especially in (c) where data are shown for the upper 0.5 m of sediment.

R.F. Chen, J.L. Bada/Marine Chemistry 45 (1994) 31-42

model developed by Krom and Westrich (1981) to explain various aspects of the reactions and processes associated with DOC in anoxic porewaters (Fig. 2). According to this model, low molecular weight (LMW) organics are common intermediates during remineralization and humification. As labile organic matter in the sediment is broken down first in the sulfate reducing zone and then in the zone of methane production, LMW monomers are released into the interstitial waters. These non-fluorescent, LMW monomers are then either remineralized to CO2, producing increases in alkalinity and ammonium ion, or polymerize to produce fluorescent HMW compounds. Ultimately, the dissolved HMW compounds may undergo adsorption or precipitation and rejoin the refractory sedimentary organics that are buried in the sediments. As evidence for this model, fluorescence and DOC were found to co-vary in the three anoxic cores in which HTCO-DOC was measured (Chen et al., 1993; Appendix 1), suggesting that the majority of the DOC produced is fluorescent HMW material. The correlation of DOC with fluorescence in porewaters from three diverse locations has important implications. The diagenetic or physical processes controlling porewater DOC can be observed by measuring fluorescence. In the Santa Barbara Basin, fluorescence was observed to increase below the sill depth and then rise sharply in the sediment poreLabile Organic Matter in the Sediment

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sediment Fig. 2. Model of organic diagenesis in anoxic sediments, after Krom and Westrich (1981).

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waters (Chen and Bada, 1989), and diffusion of fluorescent organic matter was suggested to explain these observations. Similar to fluorescence, DOC values in the water column increase slightly near the bottom and rise sharply in the porewaters (Chen et al., 1993). Diffusion of DOC into the overlying water column is likely, and this process is more easily observed by fluorescence measurements than by DOC measurements. However, the significance of this process seems to be minor when considering the global cycle of fluorescent DOC (Chen et al., 1993). Fluorescence also reveals something about the chemical nature of DOC. Non-fluorescent DOC (presumably LMW monomers) probably composed of simple amino acids, carbohydrates and lipid material, remains constant ~ 1 mM as suggested by the x-intercept of a plot of DOC vs. fluorescence (Chen et al., 1993, fig. 2). Therefore, the vast majority of anoxic porewater DOC is likely composed of compounds containing fluorophores: polyconjugated double bonds or most likely unsaturated ring structures. Fluorescence increases apparently accompany DOC increases at a rate of ~ 4 flu/#M DOC (Chen et al., 1993). The fluorescent HMW compounds may increase to greater than 10 mM, or greater than 90% of the total DOC. The process for fluorescent DOC production in porewaters is common to cores from extremely diverse locations, namely the Santa Barbara Basin, the Nankai Trough, and the Guaymas Basin. Further evidence for the Krom and Westrich (1981) model was presented by Michaelis et al. (1982) who observed that DOC is generally negatively correlated with total amino acid and total carbohydrates percentages, major components of the low molecular weight fraction. They showed that oxic depositional environments yield low DOC and a high relative percentage of amino acids and sugars while anoxic environments yield high DOC and relatively low percentages of amino acids and sugars. The same observations are made here with fluorescence. In sub-oxic cores, DOC and fluorescence are

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R.F. Chen, J.L. Bada/Marine Chemistry 45 (1994) 31-42

low and the relative percentage of non-fluorescent organic carbon is fairly high while in anoxic cores, fluorescence and D O C are high and sugars and amino acids may have polymerized to yield a low percentage of non-fluorescent organic carbon. Variations in oxygen levels of depositional environments may explain variations in DOC, fluorescence, absorbance, and alkalinity relationships; however, general trends are reasonably consistent with the model of Krom and Westrich (1981). Further, Michaelis et al. (1982) observed that porewater D O C values are nearly independent of sedimentary carbon content supporting the model in that an equilibrium between the sedimentary organic carbon and the porewater D O C is not apparent, but rather production of fluorescent macromolecular material appears to be kinetically controlled. It should be noted that there is apparently a slight increase in the ratio of fluorescence to DOC with increasing depth (Appendix 1). This is consistent with humic substances losing electron withdrawing functional groups and becoming more condensed, with a greater fluorescence Emission

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quantum yield. Parallel observations are that the emission maximum (excitation A = 325 nm) decreases with depth and the fluorescence to absorbance ratio (flu/abs) increases with depth (Fig. 3a,b). As the AA between excitation and emission A's decreases, fluorescence increases relative to both DOC and absorbance. However, the change in fluorescence/DOC ratio is small over several hundreds of meters of sediment at site 808, so fluorescence gives a good first order approximation of DOC. Alkalinity also correlates quite well with fluorescence in the Nankai Trough, the Santa Barbara Basin, the Guaymas Basin, and the Middle America Trench (Fig. 4). This observation is also consistent with Krom and Westrich's (1981) model as fluorescence represents the H M W organics, the humification pathway, whereas alkalinity represents the remineralization pathway. The two properties correlate because of the common intermediate, the L M W monomers, which are produced when labile sedimentary organic matter is initially broken down by bacteria. However, unlike the

(nm)

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Fig. 3. (a) Fluorescenceemission maximum vs. depth and (b) fluorescence/absorbanceratio with depth in the Nankai Trough (11). Absorbancewas measured at 325 nm. Also added are data from the Gulf of California, Sites478 (C)) and Site 479 (VI),and the Middle America Trench, Sites 496 (A) for comparison.

R.F. Chen, J.L. Bada/Marine Chemistry 45 (1994) 31-42 80000

t= 60000

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Fig. 4. Fluorescence vs. alkalinity in the Santa Barbara Basin (O), the Nankai Trough (m), the Guaymas Basin (O), and the Middle America Trench (A). Lines of best fit are drawn in for comparison.

correlation between fluorescence and DOC, the ratio of fluorescence to alkalinity is not constant from one location to another. Alkalinity is also affected by calcite dissolution and precipitation. A detailed study of fluorescence and alkalinity due solely to organic matter remineralization (Alkrem) may reveal that the fluorescence/ Alkrem ratio is a measure of the fraction of organic matter condensing to form humic substances and therefore, the amount of carbon ultimately buried. The sub-oxic sediments at Site 525 on the Walvis Ridge show little variation with depth in alkalinity, ammonium ion (Gieskes et al., 1984), and fluorescence (Fig. la). Complete oxidation of sedimentary organic matter to CO2 is dominant, not allowing polymerization of LMW compounds. If the sub-oxic porewater DOC value is about 10× that of seawater or about 1 mM (Starikova, 1970), and the fluorescence is measured as 800 flu or about 40x seawater, then there is a 4 × enrichment in fluorescence to DOC ratio in oxic porewaters relative to seawater. This implies that porewater DOC is significantly more aromatic than seawater

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DOC. The fluorescence to DOC ratio is much lower in sub-oxic cores (,-~ 0.8 flu/#M) than in anoxic cores (,-,4-5 flu/#M) where H M W compounds are being formed. This indicates that about five times as much fluorescent organic matter is being produced and sequestered in anoxic sediments compared to sub-oxic sedimentary environments or that the DOC in anoxic cores is much more fluorescent. Fluorescence and absorbance have been shown to correlate in natural waters where the humic substances, "GelbstolT', dominate (Ferrari and Tassan, 1991). In addition, absorbance and DOC correlate quite well in porewaters (Krom and Sholkovitz, 1977). Thus, it is not surprising that fluorescence and absorbance correlate in the porewaters investigated in this study (Fig. 5) (You et al., 1993). Diversions in the fluorescence-absorbance relationship reveal that processes other than remineralization and humification are taking place. The 6 m and 221 m samples from the Middle America Trench 80000

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Fig. 5. Fluorescence vs. absorbance in the Nankai Trough (m), Gulf of California, Sites 478 (O) and Site 479 (D), and the Middle America Trench, site 496 (A). Note the high fluorescence/absorbance ratio near the decollement in the Nankai Trough. Excluding the top (6 m) and bottom points (221 m) at site 496 and the Nankai Trough decollement sample which appear to have quite anomalous characteristics, the correlation coefficient r 2 = 0.904.

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seem to be anomalous, and further study of the organics in this region is required to evaluate these deviations from the general trend. In the Nankai Trough, the sharp increase in flu/abs ratio at about 1000 m indicates the presence of some highly fluorescent organic matter without the accompanying increases in absorbance. For purely logistical reasons, fluorescence and absorbance were both measured on only the one sample closest to the decollement. Interpolated absorbance values for samples near the decollement on which fluorescence was measured show the influence of the decollement (high fluorescence to absorbance ratios) much more clearly (You et al., 1993). Preliminary results involving the composition of the organic matter (You et al., 1993) suggest that a different type of organic matter, possibly associated with hydrothermal processes has been advected horizontally along the decollement along with the elements, Br, B, and Mn. A well-documented case for hydrothermally generated hydrocarbons is in the surface sediments of Guaymas Basin (Gieskes et al., 1988). Here, polyaromatic hydrocarbons (PAH) are most likely responsible for fluorescence in porewaters, not humic substances. PAH are known to be more fluorescent per carbon than humics (Guilbault, 1973) and therefore, the DOC/fluorescence and flu/abs ratios should be different in Guaymas Basin surface sediments than in "normal" sediments. Further, diffusion of these hydrothermally produced hydrocarbons dominates their profiles, and alkalinity, DOC, and absorbance relationships are likely to be quite different. In each case, a subsurface fluorescence maximum at about 2 or 10 cm depth shows rapid changes in fluorescence with depth (Fig. lc). The measured blue-shifted emission spectrum of a few of these porewaters in comparison with the Santa Barbara Basin porewaters is consistent with PAH fluorescence rather than humic fluorescence. The compositional differences are further supported by high performance liquid chromatography (HPLC) chromatograms that show longer retention times for Guaymas Basin

R.F. Chen, J.L. Bada/Marine Chemistry 45 (1994) 31-42

surface porewaters than for Santa Barbara Basin porewaters (Chen, 1992, unpubl, data). Unfortunately, DOC was not measured on the Guaymas Basin porewaters in order to evaluate the fluorescence to DOC ratios of this site.

5. Summary and conclusions Fluorescence and DOC data from porewaters from six different areas are consistent with Krom and Westrich's (1981) model in which labile organic matter is broken down to low molecular weight monomers, and these monomers are remineralized or polymerize to form fluorescent high molecular weight organic compounds. Correlations of fluorescence and DOC allow first order estimations of DOC with fluorescence. Correlations of alkalinity with fluorescence also allow some understanding of the fate of organic carbon in the sediment. With the ease of making fluorometric measurements on small sample volumes and the rapidly advancing technologies allowing in situ fluorometric measurements, fluorescence may vastly increase the understanding of DOC cycling in marine sediments.

Acknowledgements We would like to thank Joris Gieskes and Chen-Feng You for making DSDP and ODP samples available for study and for absorbance data, Clare Reimers for the ship time and alkalinity data in the Santa Barbara Basin, NSF's Summer Institute in Japan Program and Dr. Yoshimi Suzuki for making the DOC measurements possible, and the Deep Sea Drilling Program and the Ocean Drilling Program for samples. This research was funded by ONR grant No. N00014-89-J-JB./JB.

References Barcelona, M.J., 1980. Dissolved organic carbon and volatile fatty acids in marine sediment pore waters. Geochim. Cosmochim. Acta, 44: 1977-1984.

R.F. Chen, J.L. Bada/Marine Chemistry 45 (1994) 31-42 Bauer, J.E., Haddad, R.I. and Marais, D.J.D., 1991. Method for determining stable isotope ratios of dissolved organic carbon in interstitial and other natural marine waters. Mar. Chem., 33: 335-351. Brumsack, H.J. and Gieskes, J.M., 1983. Interstitial water trace-metal chemistry of laminated sediments from the Gulf of California, Mexico. Mar. Chem., 14: 89-106. Chen, R.F. and Bada, J.L., 1989. Seawater and porewater fluorescence in the Santa Barbara Basin. Geophys. Res. Lett., 16: 687-690. Chen, R.F. and Bada, J.L., 1990. A laser-based fluorometry system for investigations of seawater and porewater fluorescence. Mar. Chem., 31: 219-230. Chen, R.F. and Bada, J.L., 1992. The fluorescence of dissolved organic matter in seawater. Mar. Chem., 37: 191-221. Chen, R.F., Bada, J.L. and Suzuki, Y., 1993. The relationship between fluorescence and dissolved organic carbon (DOC) in porewaters of anoxic marine sediments: Implications for estimating benthic DOC fluxes. Geochim. Cosmochim. Acta 57: 2149-2153. Druffel, E.R.M., Williams, P.M. and Suzuki, Y., 1989. Concentrations and radiocarbon signatures of dissolved organic matter in the Pacific Ocean. Geophys. Res. Lett., 16: 991-994. Ferrari, G.M. and Tassan, S., 1991. On the accuracy of determining light absorption by "yellow substance" through measurements of induced fluorescence. Limnol. Oceanogr., 36: 777-786. Gieskes, J.M., Elderfield, H., Lawrence, J.R.., Johnson, J., Meyers, B. and Campbell, A., 1982. Geochemistry of interstitial waters and sediments, Leg 64, Gulf of California. In: J. Blakeslee, L.W. Platt and L.N. Stout (Editors), Init. Rep. Deep Sea Drill. Proj. US Gov. Print. Off., Washington, DC, pp. 675-694. Gieskes, J.M., Johnston, K. and Boehm, M., 1984. Interstitial water studies, Leg 74. In: T.C. Moores Jr. et al. (Editors), Init. Rep. Deep Sea Drill. Proj. US Gov. Print. Off., Washington, DC, pp. 701-711. Gieskes, J.M., Simoneit, B.R.T., Brown, T., Shaw, T., Wang, Y.C. and Manganheim, A., 1988. Hydrothermal fluids and petroleum in surface sediments of Guaymas Basin, Gulf of California: a case study. Can. Mineral., 26:589 602. Guilbault, G.G., 1973. Practical Fluorescence: Theory, Methods, and Techniques. Dekker, New York, NY, 664 pp. Harrison, W.E., Hesse, R. and Gieskes, J.M., 1982. Relationship between sedimentary facies and interstitial water chemistry of slope, trench, and Cocos Plate sites from the Middle America Trench transect, active margin off Guatemala, Deep Sea Drilling Project Leg 64. In: J. Auboin et al. (Editors), Init. Rep. Deep Sea Drill. Proj. US Gov. Print. Off., Washington, DC, pp. 603-613. Hayase, K. and Tsubota, H., 1985. Sedimentary humic acid

39 and fulvic acid as fluorescent organic materials. Geochim. Cosmochim. Acta, 49: 159-163. Henrichs, S.M. and Farrington, J.W., 1979. Amino acids in interstitial waters of marine sediments. Nature, 279: 319-322. Henrichs, S.M. and Farrington, J.W., 1987. Early diagenesis of amino acids and organic matter in two coastal marine sediments. Geochim. Cosmochim. Acta, 51: 1-15. Hulsemann, J. and Emery, K.O., 1961. Stratification in recent sediments of Santa Barbara Basin as controlled by organisms and water character. J. Geol., 69: 279-290. Ishizuki, T., Nozaki, Y. and Shimooka, K., 1988. Amino acids in the interstitial waters of ESOPE long cores from two North Atlantic abyssal plains. Geochem. J., 22: 1-8. Krom, M.D. and Sholkovitz, E.R., 1977. Nature and reactions of dissolved organic matter in the interstitial waters of marine sediments. Geochim. Cosmochim. Acta, 41: 1565-1573. Krom, M.D. and Westrich, J.T., 1981. Dissolved organic matter in the pore waters of recent marine sediments; a review. Coll. Int. CNRS, 293: Biogeochimie de la matiere organique a l'interface eau-sediment marin, pp. 103-111. Laane, R.W.P.M., 1982. Influence of pH on the fluorescence of dissolved organic matter. Mar. Chem., 11: 395-401. Lyons, W.B., Gaudette, H.E. and Hewitt, A.D., 1979. Dissolved organic matter in pore water of carbonate sediments from Bermuda. Geochim. Cosmochim. Acta, 43: 433-437. Lyutsarev, S.V., Gorshkova, O.N. and Chubarov, V.V., 1984. Study of dissolved colloidal organic matter in marine and interstitial water by laser fluorimetry. Oceanology, 24: 71-75. Martens, C.S., 1990. Generation of short chain organic acid anions in hydrothermally altered sediments of the Guaymas Basin, Gulf of California. Appl. Geochem., 5:71 76. Michaelis, W., Mycke, B., Vogt, J., Schuetze, G. and Degens, E.T., 1982. Organic geochemistry of interstitial waters, Sites 474 and 479, Leg 64. In: J. Blakeslee, L.W. Platt and L.N. Stout (Editors) Init. Rep. Deep Sea Drill. Proj., 64. US Gov. Print. Off., Washington, DC, pp. 933-937. Nissenbaum, A., Baedecker, M.J. and Kaplan, I.R., 1972. Studies on dissolved organic matter from interstitial water of a reducing marine fjord. In: H.R.V. Gaertner and H. Wehner (Editors), Advances in Organic Geochemistry, 1971. Pergamon, Oxford, pp. 427-440. Reimers, C.E., Lange, C.B., Tabak, M. and Bernhard, J.M., 1990. Seasonal spillover and varve formation in the Santa Barbara Basin, California. Limnol. Oceanogr., 35:1577 1585. Starikova, N.D., 1970. Vertical distribution patterns of dissolved organic carbon in surface waters. Oceanology, 10: 796-807. Starikova, N.D. and Korzhikova, L.I., 1972. Amino acid

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40 contents and compositions in water, suspended matter, sediments, and ooze solutions from the Black Sea. Geochem. Int., 9: 142-150. Sugimura, Y. and Suzuki, Y., 1988. A high-temperature catalytic oxidation method for the determination of non-volatile dissolved organic carbon in seawater by direct injection of a liquid sample. Mar. Chem., 24: 105-131. Suzuki, Y., Tanoue, E. and Ito, H., 1992. A high-temperature catalytic oxidation method for the determination of dissolved organic carbon in seawater: analysis and improvement. Deep-Sea Res., 39: 185-198.

Tenore, K.R., Chamberlain, C.F., Dunstan, W.M., Hanson, R.B., Sherr, B. and Tietjen, J.H., 1978. Possible effects of Gulf Stream intrusions and coastal run off on the benthos of the continental shelf of the Georgia Bight. In: M. Wiley (Editor), Estuarine Interactions. Academic Press, New York, NY, pp. 577-598. You, C.F., Gieskes, J.M., Chen, R.F., Spivack, A. and Gamo, T., 1993. I, Br, B, M n and dissolved organic carbon in interstitial waters of organic carbon rich marine sediments: observations in the Nankai accretionary prism. In: ODP Proc., Sci. Results, 131: 165-173.

Appendix 1 Sample

(ODP 808A)

(ODP 808B)

(ODP 808C)

Nankai Trough

1-3 1-4 2-3 3-3 4-1 5-6 7-4 8-1 9-3 10-3 13-2 5-1 7-1 11-2 24-2 4-1 10-2 12-1 13-2 14-3 15-1 15-4 16-2 17-4 18-3 19-2 20-4 21-1 22-3 32-3 34-2 35-4 36-2 42-3 43-5 46-2 48-3 57-2 71-2 72-3 73-5 77-4

Depth (m)

Flu (flu)

3.0 6.0 9.3 18.8 26.8 43.6 59.7 64.7 72.8 80.8 109.0 151.0 170.0 209.7 328.0 328.6 388.1 406.0 417.2 428.6 435.1 439.5 445.9 458.6 466.8 474.8 487.6 492.6 505.4 601.6 619.4 632.1 638.7 697.8 709.3 734.4 755.6 841.0 976.0 986.0 999.5 1034.6

16020 47630 59500 54870 52300 50270 48230 46240 48760 44410 40180 21640 24210 19160 21940 14880 22510 21090 23590 22560 21760 21210 19210 19060 18640 20460 20030 17410 18610 11260 10790 10710 10360 14540 19160 10890 13760 21240 33660 29590 26690 23930

DOC (#M) 7478.9 8383.6 10031.4 12952.3 9116.5 9136.6 8980.1 7639.1

9209.8

Alk (mM)

Absorbance

24.06 39.92 47.72 46.55 44.96 48.74 55.14 54.67 53.88 51.72 40.63 24.97 23.49 17.60 14.52 13.48

0.342 0.647 0.839 0.799 0.731 0.666 0.639 0.641 0.642 0.599

16.42 16.88 16.63 15.81

0.274 0.281 0.293 0.244

14.85 11.72 13.14

0.225 0.218 0.211

13.27

0.188

5.39 5.61 5.02 5.50 7.50 9.00 12.00 14.20 17.80 21.45 21.40 21.25 21.23

0.391 0.317 0.239 0.184 0.171

0.083

0.088

R.F. Chen, J.L. Bada/Marine Chemistry 45 (1994) 31-42

41

Sample

Depth (m)

Flu (flu)

78-2 86-2 (DSDP 478) 1-3 2-4 3-4 4-5 6-4 Gulf of Canfornia 7-5 8-4 9-3 11-4 13-3 17-3 19-5 28-3 (DSDP 479) 1-1 3-1 5-1 (DSDP 496) 1-4 3-4 5-6 7-1 9-3 Middle America Trench 11-3 15-4 19-4 21-8 24-4 27-6 30-5 (DSDP 499)

1042.0 1110.8 3.0 10.0 19.5 31.0 48.0 60.0 68.0 76.0 97.0 114.0 150.0 164.0 248.0 2.0 14.0 34.0 6.0 23.0 45.0 56.5 78.5 96.0 137.0 175.5 200.0 221.7 254.0 281.0 8.5 15.0 35.6 45.0 80.0 99.0 118.0 148.0 168.5 198.5 224.0 9 62 102 168 209 284 0.025 0.058 0.088 0.128 0.168 0.208 0.243 0.278 0.313

17040 5060 1201 2544 3083 3571

(DSDP 525) Walfis Ridge

Santa Barbara Basin (Box Core72)

3837 5444 8428 11373 12368 19413 18659 10067 26899 22313 36450 54700 58030 60800 65070 61420 45430 33960 27580 12260 7800 6110 14965 11429 6022 5372 30413 33420 22201 14559 5917 2169 1323 768 876 835 803 884 766 827 1007 1009 1395 1670 1942 1856 2241 2625

DOC (#M)

Alk (mM)

Absorbance

21.23 2939.0 2959.5 2164.5 3549.5 2759.5 4136.0 6036.5 5589.0 4665.5 5119.5 6485.5 6468.5 4242.0 6982.0 6940.0

1147.0 1014.6 1326.9 1329.1

1654.3

11.15 13.54 17.33 20.70 20.70 23.90 31.00 43.80 51.70 56.60 61.50 60.60 9.60 46.00 81.10 76.50 68.50 120.80 120.40 115.70 107.80 112.40 78.20 63.00 51.50 25.70 20.80 17.10 100.90 89.00 19.00 10.40 37.20 77.50 88.20 49.60 25.70 6.24 2.00 2.71 2.37 2.17 2.01 2.09 2.09 4.83 5.97 6.87 7.74 8.87 9.46 10.36 11.10 11.74

0.027 0.086 0.102 0.101 0.125 0.115 0.264 0.207 0.309 0.293

0.460 0.420 0.158 0.705 0.825 0.735 0.885 0.750 0.660 0.480 0.390 0.450

R.F. Chen, J.L. Bada/Marine Chemistry 45 (1994) 31-42

42

Appendix 1 (continued) Sample

Kasten C o r e 8 0

Guaymas 1617

Guaymas 1629

Guaymas1630

Depth (m) 0.348 0.378 0.423 0.458 0.498 0.538 0.578 0.000 0.500 0.560 0.630 0.680 0.750 0.800 0.860 0.920 0.980 1.030 1.090 1.170 1.270 1.370 1.470 1.570 1.650 1.750 1.850 1.950 0.010 0.030 0.050 0.070 0.110 0.000 0.004 0.011 0.023 0.038 0.053 0.068 0.086 0.098 0.113 0.128 0.000 0.008 0.023 0.038 0.053 0.068 0.083 0.098 0.113 0.153 0.173

Flu (flu) 2844 3186 3325 3232 3769 3939 3982 30 3297 3662 3952 4294 4706 4931 5719 5185 6250 8162 7537 7131 8631 9194 9850 7147 10735 7881 12350 12225 9415 10000 6383 4521 2053 346 5085 7798 7447 5851 6277 5745 4468 3830 4255 4362 207 553 908 894 2053 2362 2426 5617 2234 1521 936

D O C (#M)

1787.0

2249.1

1692.6 2034.0

2314.2

2818.4

2814.6 3106.5

4139.2

Alk (mM) 12.43 13.01 14.01 14.90 15.91 16.92 17.94 18.00 18.60 20.20 22.00 23.30 25.50 27.00 28.20 29.00 30.40 31.81 32.85 33.40

Absorbance