ALBERT

Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution December 1985

Description: Samples from time-series sediment traps deployed in three distinct oceanographic settings (North Pacific, Panama Basin, and Black Sea) provide strong evidence for rapid settling of marine particles by aggregates. Particle water column residence times were determined by measuring the time lag between the interception of a flux event in a shallow trap and the interception of the same event in a deeper trap at the same site. Effective sinking speeds were determined by dividing the vertical offset of the traps (meters) by the interception lag time (days). At station Papa in the North Pacific, all particles settle at 175 m day-1, regardless of their composition, indicating that all types of material may be settling in common packages. Evidence from the other two sites (Panama Basin and Black Sea) shows that particle transport may be vertical, lateral, or a combination of directions, with much of the Black Sea flux signal being dominated by lateral input. In order to ascertain whether marine snow aggregates represent viable transport packages, surveys were conducted of the abundance of these aggregates at several stations in the eastern North Atlantic and Panama Basin using a photographic technique. Marine snow aggregates were found in concentrations ranging from ~1 mm3 liter-1 to more than 500 mm3 liter-1. In open ocean environments, abundances are higher near the surface (production) and decline with depth (decomposition). However, in areas near sources of deep input of resuspended material, concentrations reach mid-water maxima, reflecting lateral transport. A model is proposed to relate the observed aggregate abundances, time series sediment flux and inferred circulation. In this model, depthwise variations in sediment flux and aggregate abundance result from suspension from the sea floor and lateral transport of suspended aggregates which were produced or modified on the sea floor. Temporal changes in sediment flux result from variations in the input of fast-sinking material which falls from the surface, intercepts the suspended aggregates, and transports them to the sea floor. A new combination sediment trap and camera system was built and deployed in the Panama Basin with the intent of measuring the flux of marine snow aggregates. This device consists of a cylindrical tube which is open at the top and sealed at the bottom by a clear plate. Material lying on the bottom plate is illuminated by strobe lights mounted in the wall of the cylinder and photographed by a camera which is positioned below the bottom plate. Flux is determined as the number of aggregates arriving during the time interval between photographic frames (# area-1 time-1). Results show that essentially all material arrives in the form of aggregates with minor contributions of fecal pellets and solitary particles. Sinking speeds (m day-1), calculated by dividing the flux of aggregates (# m-2 day-1) by their abundance (# m-3), indicate that the larger (4-5mm) aggregates are flocculent and sink slowly (~1m day-1) while the smaller aggregates (1-2.5mm) are more compact and sink more quickly (~36m day-1). These large, slow-sinking aggregates may have been re-suspended from the sediment water interface at nearby basin margins.

Description: This research was supported by ONR contract numbers N00014-82-C-0019 and N00014-85-C-0001, NSF grant numbers OCE-83-09024, OCE-84-17106, and DPP-85-01152 and the WHO1 education office.

Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 1986

Description: A study of the remineralization of organic carbon was conducted in the organic-rich sediments of Buzzards Bay, MA. Major processes affecting the carbon chemistry in sediments are reflected by changes in the stable carbon isotope ratios of dissolved inorganic carbon (ΣCO2) in sediment pore water. Six cores were collected seasonally over a period of two years. The following species were measured in the pore waters: ΣCO2, δ13C-ΣCO2, PO4, ΣH2S, Alk, DOC, and Ca. Measurements of pore water collected seasonally show large gradients with depth, which are larger in summer than in winter. The δ13C (PDB) of ΣCO2 varies from 1.3 o/oo in the bottom water to approximately -10 o/oo at 30 cm. During all seasons, there was a trend towards more negative values with depth in the upper 8 cm due to the remineralization of organic matter. There was a trend toward more positive values below 8 cm, most likely due to biological irrigation of sediments with bottom water. Below 16-20 cm, a negative gradient was re-established which indicates a return to remineralization as the main process affecting pore water chemistry. Using the ΣCO2 depth profile, it was estimated that 67-85 gC/m2 are oxidized annually and 5 gC/m2-yr are buried. The amount of carbon oxidized represented remineralization occurring within the sediments. This estimate indicated that approximately 20% of the annual primary productivity reached the sediments. The calculated remineralization rates varied seasonally with the high of 7.5 x 10-9 mol/L-sec observed in August 84 and the low (0.6 x 10-9) in December 83. The calculated remineralization rates were dependent on the amount of irrigation in the sediments; if the irrigation parameter is known to ±20%, then the remineralization rates are known to this certainty also. The amount of irrigation in the sediments was estimated using the results of a seasonal study of 222Rn/22R6a disequilibria at the same study site (Martin, 1985). Estimates of the annual remineralization in the sediments using solid-phase data indicated that the solid-phase profiles were not at steady-state concentrations. The isotopic signature of ΣCO2 was used as an indicator of the processes affecting ΣCO2 in pore water. During every month, the oxidation of organic carbon to CO2 provided over half of the carbon added to the ΣCO2 pool. However, in every month, the δ13C of ΣCO2 added to the pore water in the surface sediments was greater than -15 o/oo, significantly greater than the δ13C of solid-phase organic carbon in the sediments (-20.6 o/oo). The δ13C of ΣCO2 added to the pore water in the sediments deeper than 7 cm was between -20 and -21 o/oo, similar to the organic carbon in the sediments. Possible explanations of the 13C-enrichment observed in the surface sediments were: a) significant dissolution of CaC0, (δ13C = + 1.7 o/oo), b) the addition of significant amounts of carbonate ion from bottom water to pore water, c) an isotopic difference between the carbon oxidized in the sediments and that remaining in the sediments. The effect of CaCO3 dissolution was quantified using measured dissolved Ca profiles and was not large enough to explain the observed isotopic enrichment. An additional source of 13C-enriched carbon was bottom water carbonate ion. In every month studied, there was a net flux of ΣCO2 from pore water to bottom water. The flux of pore water ΣCO2 to bottom water ranged from a minimum of 10 x 10-12 mol/cm2-sec in December 83 to a maximum of 50 x 10-12 mol/cm2-sec in August 84. However, because the pH of bottom water was about 8 while that of the pore water was less than or equal to 7, the relative proportion of the different species of inorganic carbon (H2CO*3, HCO-3, CO2-3 was very different in bottom water and pore water. Thus, while there was a net flux of ΣCO2 from pore water to bottom water, there was a flux of carbonate ion from bottom water to pore water. Because bottom water ΣCO2 was more 13C-enriched than pore water ΣCO2, the transfer of bottom water carbonate ion to pore water was a source of 13C-enriched carbon to the pore water. If the δ13C of CO2 added to the pore water from the oxidation of organic carbon was -20.6 o/oo, then the flux of Co2-3 from bottom water to pore water must have been 10-30% of the total flux of ΣCO2 from pore water to bottom water. This is consistent with the amount calculated from the observed gradient in carbonate ion. Laboratory experiments were conducted to determine whether the δ13C of CO2 produced from the oxidation of organic carbon (δ13C-OCox) was different from the δ13C of organic carbon in the sediments (δ13C-SOC). In the laboratory experiments, mud from the sampling site was incubated at a constant temperature. Three depths were studied (0-3, 10-15, and 20-25 cm). For the first study (IE1), sediment was stirred to homogenize it before packing into centrifuge tubes for incubation. For the second study (IE2), sediment was introduced directly into glass incubation tubes by subcoring. The second procedure greatly reduced disturbance to the sediment. Rates of CO2 production were calculated from the concentrations of ΣCO2 measured over up to 46 days. In both studies, the values of Rc in the deeper intervals were about 10% of the surface values. This was consistent with the field results, although the rates decreased more rapidly in the field. In all cases, the remineralization rates during the beginning of IE1 were much greater than those at the beginning of IE2. The sediment for IE1 was collected in February 84. The measured value of Rc in the surface sediment of the laboratory experiment (24 x 10-9 mol/L-sec) was much greater than the value of Rc observed in the field in another winter month, December 83 (.62 x 10-9). The sediment for IE2 was collected in August 85. The measured values of Rc in the surface sediment (6.6-12 x 10-9 mol/L-sec) were consistent with the field values from August 84 (7.5 x 10-9). The ΣCO2 results indicated that IE2 reproduced field conditions more accurately than IE1 did. The isotopic results from the experiments strongly suggested that δ13C-OCox in the surface sediments (-17.8 o/oo ± 1.9 o/oo) was greater than δ13C-SOC (-20.6 ± 0.2 o/oo). The magnitude of the observed fractionation was small enough that the observed values of δ13C-ΣCO2 in the pore waters could be explained by fractionated oxidation coupled with the diffusion of carbonate ion from bottom water to pore water. The observed fractionation was most likely due to the multiple sources of organic carbon to coastal sediments. A study of the natural levels of radiocarbon In these sediments indicated that the carbon preserved in the sediments is approximately 30% terrestrial while the rest is from phytoplankton.

Description: Financial support was provided by the Education Office of the Massachusetts Institute of Technology/Woods Hole Oceanographic Institution Joint Program In Oceanography, by an Andrew W. Mellon Foundation grant to the Coastal Research Center, WHOI, and by the National Science foundation under grant NSF OCE83-15412.

Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution April 1975

Description: The influence of natural short-term fluctuations in environmental parameters on three components of transient benthic invertebrate community structure: abundance of individuals and species, biomass of individuals, and species diversity, were investigated in this study. The effect of low dissolved-oxygen on transient benthic community structure was studied with samples from Golfo Dulce, an intermittently anoxic basin off the west coast of Costa Rica and the Posa de Cariaco, an anoxoic trench off the north coast of Venezuela. Periodic fluctuations in oxygen concentration were accompanied by a community numerically dominated by a single polychaete species and low species diversity. As the frequency of fluctuations in oxygen concentration decreased, the number of species and individuals in the community increased with a corresponding increase in species diversity. In contrast to fluctuating oxygen conditions which eliminated many species from the community, fluctuating amounts of suspended matter in the bottom water allowed one species to proliferate while maintaining the total species list length. High rates of terrigenious sedimentation occurring naturally off the Spanish Sahara coast produced conditions which apparently hampered the feeding mechanisms of a spionid polychaete. Further offshore, where the diversity should be expected to increase, the spionids were able to flourish. The result was greater numerical abundance and biomass offshore and a lower transient diversity value. Results of simulation of catastophic burial by in situ burial of small isolated portions of Buzzards Bay sediment indicated that sedimentation rates recorded off Spanish Sahara would not eliminate species by burial. However, the small size of the organisms found off Spanish Sahara is probably a result of the constant expenditure of energy for escape. In regions of fluctuating environmental conditions, diversity values are low, principally because of dominance by a single species. Increasingly stable conditions, even though stressful, result in a more even distribution of individuals among the species present and a correspondingly high transient value.

Description: This work was funded by a Woods Hole Oceanographic Institution Predoctoral Fellowship, N.S.F. Grant GA-3655l, and N.S.F. Grant GA-33502.

Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution August 1980

Description: Dissolved free amino acids (DFAA) were measured in interstitial water samples squeezed from sediments collected in a variety of depositional environments. These sediments were further characterized by measurements of total organic carbon, total nitrogen, dissolved organic carbon, total hydrolyzable amino acids, and pore water-dissolved remineralization products. Surface sediments from the oxygen minimum zone of the Peru Upwelling Region, which consisted of a filamentous bacterial mat, were sampled at three locations. DFAA concentrations within the mat ranged from 5 to 220 μM, with the highest concentrations found in the upper 4 cm at two stations on the landward and seaward edges of the zone, and lower concentrations at a station in the middle of the oxygen minimum zone. Within cores, lower concentrations were found at depths below the mat; and below 30 cm depth concentrations were between 0.7 and 3 μM. Two short cores of offshore sediments had concentrations between 14 and 40 μM (1400 m depth) and between 3 and 8 μM (5200 m). Glutamic acid was the predominant amino acid in nearly all surface sediments samples, making up 30 to 70 mole %. In sediments below 15 cm depth, β-aminoglutaric acid was often more abundant than glutamic acid and other amino acids were virtually absent. Glutamic acid, both from several analyses performed during this work and from data available in the literature is a major DFAA of bacterial pools, and bacteria are a likely source for the high concentrations seen in interstitial water samples. DFAA may be extracted from living cells by the squeezing process, or may be excreted by the bacteria under natural conditions. β-Aminoglutaric acid is s non-protein amino acid isomer of glutamic acid which has not been previously reported as a natural product. However, this work has shown it to be a constituent of the free amino acid pools of some bacteria at about 5 mole %. Its much larger relative abundance in sediments could stem from organisms which biosynthesize greater amounts than those analyzed, or from relatively slow biodegradation. Buzzards Bay, Massachusetts surface sediments (17 m water depth) also contained high DFAA concentrations, near; 50 μM, which decreased gradually with depth to about 5 μM at 30 cm. Glutamic acid and β-aminoglutaric acid were the major components, with β-aminoglutaric acid becoming relatively more abundant with depth in core. Repeated sampling of this station was carried out, and both the concentration and composition of DFAA in replicate samples was very similar. Sediments from the Pettaquamscutt River Estuary, Rhode Island (an anoxic basin), had low DFAA concentrations ranging from 2 to 6 μM. Glutamic and β-aminoglutaric acids made up 30 to 50 % of the total. Three cores of Gulf of Maine basin sediments had DFAA concentrations and compositions which were similar to each other and to Buzzards Bay sediments, except that glycine was a major constituent of some of the samples. Its distribution was irregular over the less than 30 cm depth intervals sampled. Glycine is the major DFAA in the pools of many benthic invertebrates. Its presence in these cores is consistent with independent evidence that Gulf of Maine basin sediments are extensively bioturbated. Two cores of carbonate-rich sediments from the continental rise to the east of the Gulf of Maine and from the Bermuda Rise had surface sediment DFAA concentrations of 33 and 0.9 μM, respectively. Despite the large difference in concentration, compositions were very similar, with glycine and glutamic acid the major constituents. The very low concentrations in the Bermuda Rise sediments may be related to very low metabolizable organic carbon concentrations. Two nonprotein amino acids, γ-aminobutyric acid and β-alanine, were major constituents of the total hydrolyzable amino acids in the Bermuda Rise sediments. Biological processes, specifically microbial, appear to be responsible for the major features of DFAA concentration and composition in the sediments studied. The concentrations of DFAA measured could be of significance to the nutrition of benthic organisms via transepidermal uptake or to the formation of humic substances in sediments, if these levels are found outside cells . However, as a sink for DFAA in sediments, the latter two processes are slow relative to microbial uptake.

Description: Financial support was provided by the Woods Hole Oceanographic Institution Education Office, the Paul M. Fye Fellowship, ONR Contract N00014-79-C-0071, and NSF Grant No. OCE 79-08665. Travel funds to Peru were provided by NSF Grant No. OCE 77-26180.

Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution February 1997

Description: The goals of this thesis were: (1) to establish methods for the determination of nitrogen and carbon isotope ratios in marine particulate and sedimentary chlorophyll derivatives; (2) to establish chlorophyll δ15N and δl3C as proxies for the nitrogen and carbon isotopic composition of marine phytoplankton; and (3) to use chlorophyll nitrogen isotopic ratios to understand the origin of Late Quaternary Eastern Mediterranean sapropels. Techniques are presented for the determination of chlorin nitrogen and carbon isotopic ratios in marine particles and sediments with a precision greater than 0.15 per mil for both isotopes. The procedure can be performed in about 4 hours for particulate and 8 hours for sediment samples, and relies on multiple chromatographic purifications. About 20 g of a moderately organic-rich sediment are required. A technique is also presented for the determination of chlorin nitrogen and carbon isotopic ratios by isotope-ratio monitoring gas chromatography-mass spectrometry (irmGC-MS) by synthesizing bis-(tert.-butyldimethylsiloxy)Si(IV) chlorin derivatives. However, yields for the 4-step synthesis were only about 5-6% and there was a net isotopic depletion of 1.2 (± 0.3) per mil in the derivative, relative to the starting material. These techniques are then used to show that the nitrogen isotopic difference between chlorophyll and whole cells in six species of marine phytoplankton is 5.16 ± 2.40 per mil. For carbon, the isotopic difference between chlorophyll and whole cells in five species of marine phytoplankton is -0.02 ± 2.12 per mil. A model of the distribution of 15N in phytoplankton is constructed and it is demonstrated that the interspecies variability observed for the nitrogen isotopic difference between chlorophyll and whole cells can be attributed to differences in the partitioning of cellular nitrogen between non-protein biochemicals. In the field, where mixed assemblages of phytoplankton prevail, the isotopic difference beween chlorophyll and whole cells is expected to tend toward the average value of 5.16 per mil. Finally, the average nitrogen isotopic composition of chlorins from six Late Quaternary Eastern Mediterranean sapropels (-5.01 + 0.38 per mil) was found to be very similar to the δ15N of chlorophyll from the modem deep chlorophyll maximum (-6.38 ± 1.80 per mil) in the Eastern Mediterranean. In addition, sapropel photoautotrophic material, calculated from the chlorin δ15N, had the same isotopic composition (0.15 per mil) as both bulk sapropel sediments (-0.08 ± 0.53 per mil) and deep water nitrate (-0.05 per mil). These data suggest (a) that bottom waters were anoxic, (b) that organic matter burial efficiency was enhanced, and (c) that oligotrophic conditions similar to today persisted, in the Eastern Mediterranean during sapropel deposition. These results contradict earlier interpretations of Late Quaternary bulk sedimentary δ15N in the Eastern Mediterranean. The latter concluded that the pattern of high δ15N values in intercalated marl oozes and low values in sapropels was the result of decreased nutrient utilization, and hence, increased primary production, during sapropel events. The low δ15N of deep water nitrate in the Eastern Mediterranean suggests a significant source of new nitrogen from biological N2-fixation. It is suggested that attempts to reconstruct the nitrogen isotopic composition of marine organic matter in the past by measuring the δ15N of whole sediments may be subject to misinterpretation due to the alteration of isotopic ratios during diagenesis. The partial oxidation of marine organic matter can result in significant isotopic enrichment of the preserved residual. The magnitude of this enrichment appears to be large when bottom waters are well-oxygenated, and small when bottom waters are anoxic. Environments where large temporal reqox changes have occurred are expected to be the most problematic for the interpretation of bulk sedimentary δ15N. In these environments, the diagenetic signal can be at least as large as the primary isotopic signal being sought. The Eastern Mediterranean Sea during the Late Quaternary appears to be one such environment.

Description: Funding for this work came from an Office of Naval Research Graduate Fellowship, the Woods Hole Oceanographic Institution Ocean Ventures Fund, and a Petroleum Research Grant(# 30124-AC2).

Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution May 1998

Description: Planktonic protozoan grazers have the potential to significantly affect the chemistry of particle-associated trace metals. This is due both to the importance of protists as consumers of bacterial-sized particles, and to the unique low-pH, enzyme-rich microenvironment of the grazer food vacuole. This thesis examines the role of protozoan grazers in the marine geochemistry of strongly hydrolyzed, particle-reactive trace metals, in particular Th and Fe. A series of tracer experiments was carried out in model systems in order to determine the effect of grazer-mediated transformations on the chemical speciation and partitioning of radioisotopes C9Fe, 234Th, 51Cr) associated with prey cells. Results indicate that protozoan grazers are equally able to mobilize intracellular and extracellular trace metals. In some cases, protozoan regeneration of trace metals appears to lead to the formation of metal-organic complexes. Protozoan grazing may generate colloidal material that can scavenge trace metals and, via aggregation, lead to an increase in the metal/organic carbon ratio of aggregated particles. Model system experiments were also conducted in order to determine the effect of grazers on mineral phases, specifically colloidal iron oxide (ferrihydrite). Several independent techniques were employed, including size fractionation ors9Fe-labeled colloids, competitive ligand exchange, and iron-limited diatoms as "probes" for bioavailable Fe. Experimental evidence strongly suggests that protozoan grazing can affect the surface chemistry and increase the dissolution rate of iron oxide phases through phagotrophic ingestion. In further work on protozoan-mediated dissolution of colloidal Fe oxides, a novel tracer technique was developed based on the synthesis of colloidal ferrihydrite impregnated with 133Ba as an inert tracer. This technique was shown to be a sensitive, quantitative indicator for the extent of ferrihydrite dissolution/alteration by a variety of mechanisms, including photochemical reduction and ligand-mediated dissolution. In field experiments using this technique, grazing by naturally occuring protistan assemblages was shown to significantly enhance the dissolution rate of colloidal ferrihydrite over that in non-grazing controls. Laboratory and field results indicate that, when integrated temporally over the entire euphotic zone, protozoan grazing may equal or exceed photoreduction as a pathway for the dissolution of iron oxides.

Description: This work was financially supported by a Department of Defense ONR-NDSEG Graduate Fellowship, Office ofNaval Research AASERT Award (N00014-94-1-0711), and the National Science Foundation EGB Program (OCE-9523910).

Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution January 1993

Description: Although the association between soft-sediment invertebrates and a specific sediment type has been documented for many habitats, most studies have been correlative and have failed to convincingly demonstrate any single mechanism to explain this association. Sediment type has generally been characterized by grain size, however, many other potential causal factors correlate with grain size, including organic content, microbial content, stability, food supply, and larval supply. One hypothesis for animal-sediment associations is that settling larvae are transported as passive particles and are sorted into different sedimentary habitats much like sediment grains. To test the hypothesis that near-bed hydrodynamics may modify larval settlement, field and flume experiments were conducted where larval settlement was compared between microdepositional environments (small depressions) and non-trapping environments (flush treatments). Depressions have been observed to trap passive particles, and these experiments were therefore designed to test whether settling larvae would be trapped in depressions like passive particles. Flume flow simulations were carried out with the polychaete Capitella sp. I and the bivalve Mulinia latera/is. Experiments with flush and depression sediment treatments were conducted in the absence of the potentially confounding effects of suspended sediment and organic matter and therefore offered a highly controlled, explicit test of passive hydrodynamic deposition of larvae in depressions. Although larvae of both species were generally able to actively select a high-organic sediment over a low-organic alternative with a comparable grain size, elevated densities of both species were observed in depressions for a given sediment treatment. Thus, both species appeared to be vulnerable to hydrodynamic trapping. M. latera/is larvae, however, often made a "poor choice" by settling in high numbers in depressions containing the low-organic sediment while Capitella sp. I larvae were generally able to "escape" from depressions if the sediment was unsuitable. In field experiments carried out at Station R in Buzzards Bay, Massachusetts, significantly higher densities of Mediomastus ambiseta juveniles, spionid polychaete juveniles, bivalves, gastropod larvae, and nemerteans were observed in depressions compared with flush treatments over 5 relatively short experimental periods (3 or 4 days each) during the summer of 1990. Of the abundant taxa, only Capitella spp. was not significantly more abundant in depressions compared with flush treatments, although numbers tended to be higher in depressions. Experiments were conducted over a short time period to minimize potential biological interactions between taxa and reduce the likelihood that organic material would accumulate in depressions and provide a cue for settling larvae. Thus, higher numbers in depressions suggest that larvae were passively entrained. These flume and field experiments suggest that near-bed hydrodynamics may modify settlement at some scales, and that both active and passive processes may operate in determining larval distributions in shallow-water, muddy habitats. In deep-sea ecosystems, the role of near-bed hydrodynamics is also of interest because of the potential role that larval settlement in organic patches may play in maintaining the immense species diversity characteristic of many deep-sea ecosystems. To try to understand the role of organic patches in deep-sea communities, several investigators have used colonization trays containing sediments that have been treated in different ways. These experiments have been criticized in the past because the sediment surface in the trays was elevated above the bottom and may therefore have interfered with natural boundary layer flow. Flume simulations of flow over these colonization trays revealed serious flow artifacts generated by the trays, and that flow across the sediment surface of the trays was characterized by turbulent eddies, accelerated velocities and boundary layer thickening. These sorts of flow characteristics would not be expected over natural sediments, and an alternative colonization tray was designed to eliminate these artifacts. To test the hypothesis that different types of food patches would result in different types of larval response, and determine how near-bed hydrodynamics may influence larval settlement, flush colonization trays filled with prefrozen sediment were deployed in tandem with artificial depressions south of St. Croix, U.S.V.I at 900 m depth. Colonization trays and artificial depressions were either unenriched or enriched with Thalassiosira sp. and Sargassum sp. two types of algae chosen to mimic natural food patches on the sea floor. Unexpectedly high densities of organisms colonized trays after only 23 days. The Thalassiosira trays were colonized by high densities of a relatively low diversity, opportunistic fauna, Sargassum trays were colonized by lower densities of a higher diversity fauna, and unenriched trays were colonized by very low numbers of a very diverse fauna. All tray faunas were markedly different in composition from the natural, ambient fauna. These fmdings suggest that different patch types did, indeed, result in a specialized faunal response to each of the "patch" types. Depressions on the sea floor provide a natural mechanism for food patch formation because passive particles such as detritus and algae tend to be entrained in the depressions. To determine whether dominant colonizers would be entrained in depressions like passive particles or could differentiate between depression "patch" types in a flow environment that might be expected to make active selection more difficult, artificial depressions were unenriched or enriched with Sargassum sp. or Thalassiosira sp. Total densities of organisms and densities of the most abundant species were substantially lower in artificial depressions than in trays. Densities in Thalassiosira depressions were lower than in Sargassum depressions and densities in unenriched depressions were extremely low, suggesting that dominant colonizers were not passively entrained in depressions and that colonization was specialized and highly active for these taxa. A different fauna was also observed in natural depressions compared with flush sediments, suggesting that natural depressions do contribute to species coexistence. Long-term tray deployments designed to test whether different faunas would be present in "patches" of different ages indicated that time may also play an important part in a deep-sea patch mosaic.

Description: This was funded by NSF and ONR, NOAA, NSERC (Canada), WHOI Ocean Ventures Fund and the WHOI Ditty Bag Fund.

Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 1993

Description: In a shallow water ocean environment, the range-dependent variation of the geoacoustic properties of the seabed is one of the crucial factors affecting sound propagation. Since the local modes of propagation depend on the spatial changes in the bottom sediments, the local eigenvalues of these modes are useful as tools for examining the range dependence of the sediment properties. In order to extract the local eigenvalues from measurements of the pressure field in a laterally inhomogeneous waveguide, the zero-order asymptotic Hankel transform with a short sliding window is utilized. The local peak positions in the output spectra differ from the local eigenvalues due to both the range variation of the local modes and the interference of adjacent modes. The departure due to the former factor is evaluated analytically by using the stationary phase method. In order to reduce the error induced by the latter factor, mode filtering is utilized by incorporating data from a fixed vertical array of receivers. The use of the above zero-order Hankel transform in a three-dimensionally varying waveguide results in an underestimate of the local eigenvalues due to the effect of horizontal refraction. Thus a general asymptotic Hankel transform with a 2-D sliding window is used to correct for the underestimated amount. By expanding the latter transform with respect to the azimuthal angle, it can also be shown that the first term in the Taylor series corresponds to the former transform; the rest of the terms account for the value difference between the underestimated and actual local eigenvalues. In order to obtain the spatial variation of the sediment properties from the rangedependent variation of the extracted local eigenvalues, the analytical relationship between these two variations is derived by using a perturbation method in a horizontally varying, multi-layered bottom model. Upon use of the n2-linear profile in each layer, the relationship can be obtained in closed form. As a result, the range variation of the local eigenvalues may be separated into terms that depend on each geoacoustic parameter. Based on this relation, an inversion method for determining the range-dependent geoacoustic parameters is developed. The methods developed in this thesis are applied to simulated pressure field data as well as experimental field data. It is shown that the evolution with range of the local modes as well as the range-dependent geoacoustic properties can be successfully estimated.

Description: Financial support for my research was provided by the WHOI Education Department and the Office of Naval Research.

Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution May 1993

Description: The goal of this thesis was to develop and apply an integrated chemical and microbial approach to study the effects of chemical structure on the rates and patterns of carbohydrate degradation by anaerobic marine bacteria. Polysaccharides produced by five species of marine plankton, Dunaliella tertiolecta, Emiliania huxleyi, Stephanopixis palmeri, a Phaeocystis sp., and Synechococcus WH7335, were surveyed using one- and two-dimensional nuclear magnetic resonance spectroscopy (NMR). Two carbohydrates from Synechococcus WH7335 were characterized in detail. Synechococcus produced an α(1,4) glucose polysaccharide with α(1,6) branches, which probably functions as an energy reserve. The nominal molecular weight of the polysaccharide was ~5000 daltons. Large quantities of a glycerolpolysaccharide, which was tentatively identified as a teichoic acid similar in structure to teichoic acids found in cell walls of gram-positive bacteria, were also produced by Synechococcus WH7335. This is the first report of teichoic acids in cyanobacteria. Enrichment of bacteria from anoxic marine sediments on specific carbohydrates yielded reproducible model systems with which to study the degradation of chemically well-defined substrates. Headspace gases (C02, H2, CH4, H2S) were monitored by gas chromatography, and carbohydrate substrates and intermediates were separated and quantified via gel-permeation chromatography and high-pressure liquid chromatography. The transfer of carbon from substrates through to end products was followed quantitatively. Nuclear magnetic resonance spectroscopy was used to check for selective structural alterations (such as preferential cleavage of specific linkage types or positions) of the substrates. A series of enrichment experiments showed that mixed cultures of marine bacteria distinguish even between small, very closely-related substrates which do not require extracellular hydrolysis prior to uptake. A galactose-β(1,3)-arabinose dimer was degraded at half the rate of seven other similar disaccharides and three larger oligosaccharides. A further series of degradation experiments with polysaccharides (pullulan, laminarin) showed that they are degraded by bacteria at virtually the same rate as structurally related substrates in the molecular weight range of 300-600 daltons. Degradation of the branched glucan and the teichoic acid-type polysaccharide from Synechococcus WH7335 was also very rapid. The time-course of bacterial hydrolysis of pullulan was examined with gel permeation chromatography and NMR to provide the first molecular-level evidence in marine systems of the bacterial extracellular transformation of high molecular weight organic matter to lower molecular weight organic matter. NMR spectra provided evidence that the pullulan was hydrolyzed by pullulanase, an endo-acting extracellular enzyme which preferentially hydrolyzes α(1,6) linkages. This is the first experimental evidence of pullulanase activity among marine mesophilic bacteria. The culture results suggest that enzymatic hydrolysis of macromolecular carbohydrates to transportable pieces is not the slow step in bacterial degradation of at least some types of polysaccharides. The results from the oligosaccharide experiments suggest that certain heteropolysaccharides may not be degraded as quickly. Chemical structure can be more important than molecular weight in determining degradation rates of carbohydrates. Varying rates of organic polymer degradation in anoxic sediments may be largely determined by the sensitivity of bacterial enzymatic and transport systems to structural features.

Description: Funding for this work was provided by a graduate fellowship from the Office of Naval Research, and grants from the WHOI Ocean Ventures Fund and the Department of Energy's Ocean Margins Program (DE-FG02-92ER61428).

Description: Submitted in partial fulfillment of the requirements for the degree of Master of Science at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution May 1996

Description: This thesis details two years of research conducted with the guidance and support of three advisors: Dr. J. K. Whelan, Dr. J. S. Seewald and Dr. T. I. Eglinton. Each of the three chapters represents a different, self-contained research project. All of the projects are related to the organic geochemistry of marine sediments, however, this is a fairly encompassing area of study. Chapters 1 and 2 stem from the same experimental study -the use of hydrous-pyrolysis to investigate mechanisms leading to the production of petroleum-related products during kerogen maturation. Chapter 3, on the other hand, utilizes a recently developed technique of isolating and AMS-14C dating individual compounds from complex sedimentary organic mixtures. The samples used in each investigation came from all over the world. The first two chapters utilize ancient marine sediment samples obtained from an outcrop in California (Chpts. 1 and 2) and from a well in Alabama (Chpt. 2). In contrast, recent marine sediment samples were obtained from the Arabian and Black Seas for the third chapter. Several preparative and analytical methods are common to all three studies. Nevertheless, each employ techniques totally unique from one another and from previous investigations. In Chapter 1, for example, X-ray absorption spectroscopy (XANES) is used to determine the speciation of organic sulfur present in kerogen, bitumen, and bulk sediment samples. While Chapter 3 represents the first study in which the 14C ages of individual, known hydrocarbon biomarkers are determined after isolation by Preparative Capillary Gas Chromatography (PCGC). The insights gained by these investigations are discussed in detail in the following chapters. The common thread between the three chapters is that the source of organic matter, the rate at which it is delivered to marine sediments and the depositional environment, all set the stage for kerogen formation and eventual petroleum generation.

Description: Submitted in partial fulfillment of the requirements for the degree of Master of Science at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution February 2014

Description: Observations suggest that during the last deglaciation (roughly 20,000-10,000 years ago) the Earth warmed substantially, global sea level rose approximately 100 meters in response to melting ice sheets and glaciers, and atmospheric concentrations of carbon dioxide increased. This interval may provide an analog for the evolution of future climate. The ocean plays a key role in the modern climate system by storing and transporting heat, salt, and nutrients, but its role during the last deglaciation remains uncertain. Prominent signals of the last deglaciation in the ocean are a gradual warming and a decrease of the seawater oxygen isotope ratio 18O (a signature of melting land ice sheets). These changes do not occur uniformly in the ocean, but propagate like plumes of dye over hundreds and thousands of years, the aggregate results of turbulent advective and diffusive processes. Information about changing temperatures and oxygen isotopes is stored in the shells of benthic organisms recovered in ocean sediment cores. This thesis develops and applies an inverse framework for understanding deglacial oxygen isotope records derived from sediment cores in terms of the Green functions of ocean tracer transport and ocean mixed layer boundary conditions. Singular value decomposition is used to find a solution for global mixed layer tracer concentration histories that is constrained by eight last-deglacial sediment core records and a model of the modern ocean tracer transport. The solution reflects the resolving power of the data, which is highest at model surface locations associated with large rates of volume flux into the deep ocean. The limited data resolution is quantified and rationalized through analyses of simple models. The destruction of information contained in tracers is a generic feature of advective-diffusive systems. Quantifying limitations of tracer records is important for making and understanding inferences about the long-term evolution of the ocean.

Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 2000

Description: Phosphorus, an essential nutrient, is removed from the oceans only through burial with marine sediments. Organic phosphorus (Porg) constitutes an important fraction (ca. 25%) of total-P in marine sediments. However, given the inherent lability of primary Porg biochemicals, it is a puzzle that any Porg is preserved in marine sediments. The goal of this thesis was to address this apparent paradox by linking bulk and molecular-level Porg information. A newly-developed sequential extraction method, which isolates sedimentary Porg reservoirs based on solubility, was used in concert with 31P nuclear magnetic resonance spectroscopy (31P-NMR) to quantify Porg functional group concentrations. The coupled extraction/31P-NMR method was applied to three sediment cores from the Santa Barbara Basin, and the first-ever high-resolution depth profiles of molecular-level Porg distribution during diagenesis were generated. These depth profiles were used to consider regulation of Porg distribution by biomass abundance, chemical structure, and physical protection mechanisms. Biomass cannot account for more than a few percent of sedimentary Porg. No evidence for direct structural control on remineralization of Porg was found. Instead, sorptive protection appears to be an important mechanism for Porg preservation, and structure may act as a secondary control due to preferential sorption of specific Porg compound classes.

Description: My first three years in the Joint Program were funded by a fellowship from the Office of Naval Research. The WHOI education office provided funding for the balance of my graduate studies.