Thesis: Ph. D., Joint Program in Chemical Oceanography (Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2015. / Cataloged from PDF version of thesis. / Includes bibliographical references. / Fifty-six million years ago Earth experienced rapid global warming (~6°C) that was caused by the release of large amounts of carbon into the ocean-atmosphere system. This Paleocene-Eocene Thermal Maximum (PETM) is often cited as an analogue of anthropogenic climate change. Many trigger mechanisms for the carbon release at the PETM have been proposed. Common to all scenarios is rapid release of isotopically light carbon (<¹³C/¹²C values) from methane hydrates, terrestrial or marine organic matter, as indicated by a pronounced excursion to light carbon isotope values across the PETM. I test the hypothesis that the PETM warming and isotope excursion were caused by the intrusion of a magmatic sill complex into organic-rich sediments in the North Atlantic. The intrusion of magma into sedimentary rocks will cause heating and metamorphic reactions in a thermal aureole around the intrusion. If these sediments are rich in organic matter, large volumes of isotopically light carbon are rapidly released. I examine geochemical evidence from lead, osmium, and organic carbon to place constraints on the extent the carbon isotope excursion during the PETM may have been caused by contact metamorphism of organic-rich sediments. Potential terrestrial and submarine analogs are examined to determine the behavior of these elements during thermal alteration. Furthermore, geochemical evidence from sediment cores at the PETM provides additional information about what might have caused the carbon isotope excursion. I find that lead is not a suitable proxy for carbon mobilization to the overlying seawater during contact metamorphism. Osmium, however, is mobilized together with carbon. Making reasonable assumptions for the ¹⁸⁷Os/¹⁸⁸Os of the sediments from the North Atlantic Magmatic Province (NAMP), constrained by the ¹⁸⁷Re/¹⁸⁸Os of organic-rich sediments and the depositional age of the sediment, the entire marine osmium isotope anomaly at the PETM could be explained without the need to invoke enhanced continental weathering. Based on estimates of the extent of mobilization of organic carbon relative to osmium, approximately 47% to 60% of the carbon released at the PETM may have been derived from thermal alteration of organic-rich sediments in the NAMP. / by Andrea Rose Dubin. / Ph. D.

Thesis (Ph. D.)--Joint Program in Chemical Oceanography (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2009. / Includes bibliographical references. / The application of elemental and isotopic metal palaeoredox tracers to the geologic past rests on an understanding of modern metal cycles. This study reevaluates the surface-cycling of Mo and Re in near-surface reservoirs. Revised river averages of Mo and Re are 1.8- and 7.9-fold larger than previous estimates. The river concentrations of 8.0 nmol Mo kg-1 and 11.2 pmol Re kg- (pre-anthropogenic), result in shorter seawater response times of 4.4 x 105 yr ([Tau]Mo) and 1.3 x 105 yr ([Tau]Re pre-anthropogenic). These metals, especially Re, are more sensitive to changing source and sink fluxes than previously thought. Evaluation of Mo and Re concentrations in high temperature fluids from the Manus Basin indicate that Re is essentially absent from the hydrothermal end member and Mo is present at concentrations considerably lower than ambient seawater. The sink fluxes represented by hydrothermal circulation are negligible in comparison to the revised river source fluxes. Anthropogenic contributions to the Re flux to seawater are seen in the high concentrations of certain impacted water samples such as those associated with mining sites. It may also be seen in a significant, variable, Re enrichment feature in the Hudson River estuary. This Re enrichment feature is not the result of estuarine mixing or the remobilization of sediment-hosted Re. On the basis of a Re - SO2- correlation we are able to quantify and correct for the anthropogenic Re, which corresponds to ~33% of the modern river average. This study documents the development of an analytical method for stable Re isotopes. / (cont.) Though complicated by analyte requirements and 187Re 1870s decay, Re isotope measurements have a reproducibility of ±0.05%o for analyte concentrations of 20 ng Re mL-1. Total Re isotopic variability to date is 0.9%o. This includes 0.3%0 across five commercially available Re products, and 0.5%0 across a black shale weathering profile. 6187Re variability across the weathering profile was systematic with the most weathered samples showing the most significant [delta]187Re depletions. The Re isotopic weathering profile is well described by both two-component mixing and Rayleigh fractionation. There are currently insufficient data to discriminate between the two models. / by Christian Alexander Miller. / Ph.D.

Thesis (S.M.)--Joint Program in Chemical Oceanography (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences and the Woods Hole Oceanographic Institution), 2001. / Includes bibliographical references (leaves 65-72). / A comparison of monthly biogeochemical measurements made from 1993 to 1995, combined with hydrography and satellite altimetry, was used to observe the impacts of nine eddy events on primary productivity and particle flux in the Sargasso Sea. Measurements of primary production, thorium-234 flux, nitrate+nitrite, and photosynthetic pigments made at the US JGOFS Bermuda Atlantic Time-series Study (BATS) site were used. During the three years of this study, four out of six high thorium- 234 flux events over 1000 dpm/m 2/d occurred during the passage of an eddy. Primary production nearly as high as the spring bloom maximum was observed in two modewater eddies (May 1993 and July 1995). The 1994 spring bloom at BATS was suppressed by the passage of an anticyclone. Distinct phytoplankton community shifts were observed in mode-water eddies, which had an increased percentage diatoms and dinoflagelletes, and in cyclones, which had an increased percentage cyanobacteria (excluding Prochlorococcus). The difference in the observations of mode-water eddies and cyclones may result from the age of the eddy, which was very important to the biological response. In general, eddies that were one to two months old elicited a large biological response; eddies that were three months old may show a biological response and were accompanied by high thorium flux measurements; eddies that were four months old or older did not show a biological response or high thorium flux. Our conceptual model depicting the importance of temporal changes during eddy upwelling and decay fit the observations well in all 7 upwelling eddies. Additional information is needed to determine the importance of deeper mixed layers and winter mixing to the magnitude of the eddy impacts. Also, sampling generally captured only the beginning, end, and /or edge of an eddy due to the monthly to semi-monthly frequency of the measurements made at BATS. Lagrangian studies, higher resolution time-series, and/or more spatial coverage is needed to provide additional information for improved C and N budgets in the Sargasso Sea and to complete our understanding of the temporal changes that occur in an eddy. / by Erin N. Sweeney. / S.M.

Thesis (Ph. D.)--Joint Program in Chemical Oceanography (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2011. / Cataloged from PDF version of thesis. / Includes bibliographical references. / A combination of uptake field studies on natural phytoplankton assemblages and laboratory proteomic and physiological experiments on cyanobacterial isolates were conducted investigating the interactions of cadmium (Cd), zinc (Zn), and phosphorus (P) in marine Synechococcus. Enriched stable isotope field uptake studies of ¹¹⁰CD in the Costa Rica Upwelling dome, a Synechococcus feature, showed that uptake of Cd occurs in waters shallower than 40 m, correlates positively with chlorophyll a concentrations and is roughly equivalent to the calculated upwelling flux of cadmium inside the dome. In laboratory experiments, Synechococcus WH5701 cells exposed to low picomolar quantities of free Cd under Zn deficiency show similar growth rates to no added Cd treatments during exponential growth phase, but show differences in relative abundances of many proteins involved in carbon and sulfur metabolism suggesting a great metabolic impact. During stationary phase, chronic Cd exposure in this coastal isolate causes an increase in relative chlorophyll a fluorescence and faster mortality rates. The interactions of acute Cd exposure at low picomolar levels with Zn and phosphate (PO4³-) were investigated in Synechococcus WH8102, an open ocean isolate. The presence of Zn appears vital to the response of the organism to different PO4 ³- cocentrations. Comparisons with literature transcriptome analyses of PO4 ³- stress show similar increases in relative abundance of PO4 ³- stress response proteins including a PO4 ³- binding protein and a Zn-requiring alkaline phosphatase. A bacterial metallothionein, a Zn-associated protein, appears to be correlated with proteins present under low PO4 conditions. Together, these experiments suggest that the interactions of Cd and Zn can affect Synechococcus and play a role in the acquisition of PO4 ³-. / by Alysia Danielle Cox. / Ph.D.

Thesis (Ph. D.)--Joint Program in Chemical Oceanography (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2007. / Includes bibliographical references. / Zinc (Zn) stable isotopes can record information about important oceanographic processes. This thesis presents data on Zn isotopes in anthropogenic materials, hydrothermal fluids and minerals, cultured marine phytoplankton, natural plankton, and seawater. By measuring Zn isotopes in a diverse array of marine samples, we hope to understand how Zn isotopes are fractionated in the oceans and how Zn isotopes may be used as tracers of marine biogeochemical processes. Common forms of anthropogenic Zn had [delta]66Zn from +0.08 %o to +0.32 %o, a range similar to Zn ores and terrigenous materials. Larger variations were discovered in hydrothermal fluids and minerals, with hydrothermal fluids ranging in 666Zn from 0.02 %o to +0.93 %o, and chimney minerals ranging from -0.09 %o to +1.17 %o. Lower-temperature vent systems had higher [delta]666Zn values, suggesting that precipitation of isotopically light Zn sulfides drives much of the Zn isotope fractionation in hydrothermal systems. In cultured diatoms, a relationship was discovered between Zn transport by either high-affinity or low-affinity uptake pathways, and the magnitude of Zn isotope fractionation. We established isotope effects of [delta]66Zn = -0.2 %o for high-affinity uptake and [delta]66Zn = -0.8 %o for low-affinity uptake. This work is the first to describe the molecular basis for biological fractionation of transition metals. Biological fractionation of Zn isotopes under natural conditions was investigated by measuring Zn isotopes in plankton collected in the Peru Upwelling Region and around the world. / (cont.) Seawater dissolved Zn isotopes also reflect the chemical and biological cycling of Zn. The [delta]66Zn of deep seawater in the North Pacific and North Atlantic is about 0.5%0, and the dissolved [delta]66Zn gets lighter in the upper water column. This is unexpected based our observations of a biological preference for uptake of light Zn isotopes, and suggests that Zn transport to deep waters may occur by Zn adsorption to sinking particles rather than as primary biological Zn. The thesis, by presenting data on several important aspects of Zn isotope cycling in the oceans, lays the groundwork for further use of Zn isotopes as a marine biogeochemical tracer. / by Seth Greeley John. / Ph.D.

Thesis (Ph. D.)--Joint Program in Chemical Oceanography (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2006. / Includes bibliographical references. / This thesis explores the potential of zinc, cobalt, and phosphorus to influence primary production in the subarctic North Pacific, the Bering Sea, and the North Atlantic Ocean. In the North Pacific and Bering Sea, total zinc concentrations were measured along a near-surface transect and in selected deep profiles. Zinc speciation was also measured with a novel anodic stripping voltammetry method, and the results were consistent with previous studies using different methods. The potential for zinc to impact primary production in the North Pacific was demonstrated in a shipboard incubation and by comparing two phytoplankton pigment markers to total zinc and free zinc ion concentrations. In the North Atlantic, total dissolved zinc and cobalt concentrations were measured and compared to concentrations of dissolved inorganic phosphorus and chlorophyll. In some areas of the North Atlantic the concentrations of zinc and cobalt were decoupled.The relationship between cobalt and inorganic phosphorus suggests that cobalt drawdown may be related to a high alkaline phosphatase related demand at low phosphorus concentrations. This trend compliments a shipboard incubation where alkaline phosphatase activities increased after cobalt addition. The presence of measurable alkaline phosphatase activity indicated that the phytoplankton community in the Sargasso Sea was experiencing phosphorus stress. Shipboard incubations generally confirmed this with inorganic phosphorus additions resulting in chlorophyll increases at 4 out of 5 stations. Further, the addition of dissolved organic phosphorus, as either a phosphate monoester or a phosphonate compound, resulted in a chlorophyll increase in 3 out of 3 incubations. This suggests that dissolved organic phosphorus may be an important phosphorus source for phytoplankton in low phosphorus environments and that the ability to use phosphonates may be more widespread than previously recognized. Overall, this thesis adds to our understanding of how the nutrients phosphorus, zinc, and cobalt may influence primary production. / by Rachel J. Wisniewski. / Ph.D.

Thesis (Ph. D.)--Joint Program in Chemical Oceanography (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), February 2001. / Includes bibliographical references. / Processes that enable marine phytoplankton to acquire trace metals are fundamental to our understanding of primary productivity and global carbon cycling. This thesis explored the biogeochemistry of cobalt using analytical chemistry and physiological experiments with the dominant phytoplankton species, Prochlorococcus. A high sensitivity method for Co speciation was developed using hanging mercury drop cathodic stripping voltammetry. Dissolved Co at the Bermuda Atlantic Time Series station (BATS) in the Sargasso Sea was bound by strong organic complexes with a conditional stability constant of logK=16.3+0.9. A depth profile of Co at BATS revealed a nutrient-like profile. Biweekly time series measurements of total cobalt near Bermuda from the MITESS sampler were 0-47pM throughout 1999, and averaged 20±1 OpM in 1999. A transect of total cobalt from BATS to American coastal waters ranged from 19- 133pM and correlated negatively with salinity (r2=0.93), suggestive of coastal waters as an input source. Prochlorococcus strains MED4-Ax and SS120 showed an absolute requirement for Co, despite replete Zn. 57Co uptake rates and growth rates were enhanced by additions of filtered low Co cultures, suggesting that a ligand is present that facilitates Co uptake. Bottle incubations from a Synechococcus bloom in the Pacific showed production of 425pM strong cobalt ligand. These and other lines of evidence support the hypothesis that a cobalt ligand, or cobalophore, is involved in cobalt uptake. Co-limited Prochlorococcus cultures exhibited an increase in the fraction of cells in G2 relative to other cell cycle stages during exponential growth, and the durations of this stage increased with decreasing cobalt concentrations. This effect was not observed with Fe, N, or P-limited cultures, suggestive of a specific biochemical function of cobalt that would interfere with the late stages of the cell cycle. The ligand Teta was explored as a means to induce cobalt limitation. The CoTeta complex was not bioavailable to the Sargasso Sea microbial assemblage in short-term experiments. Bottle incubations with Teta did not induce cobalt limitation of Prochlorococcus. These results are consistent with the lower conditional stability constant for CoTeta (logK= 11.2+0.1) relative to natural cobalt ligands in seawater, and with culture studies that suggest uptake of cobalt via strong organic ligands. / by Mak A. Saito. / Ph.D.

Thesis: Ph. D., Joint Program in Chemical Oceanography (Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2017. / Cataloged from PDF version of thesis. / Includes bibliographical references. / Particulate organic carbon (POC) in the ocean and mobilized by rivers on land transfers -0. 1% of global primary productivity to the deep ocean sediments. This small fraction regulates the long-term carbon cycle by removing carbon dioxide from the atmosphere for centuries to millennia. This thesis investigates mechanisms of POC transfer to the deep ocean by analyzing particles collected in transit through two globally significant carbon reservoirs: the Southern Ocean and the Amazon River Basin. These endeavors test the hypothesis that organic matter composition controls the recycling and transfer efficiency of POC to the deep ocean, and illustrate new applications for ramped pyrolysis/oxidation (RPO), a growing method of POC characterization by thermal stability. By coupling RPO to stable and radiocarbon isotope analyses of riverine POC, I quantify three thermally distinct soil organic carbon pools mobilized by the Amazon River, and evaluate the degradability and fate of these different pools during transport to the coastal Atlantic Ocean. More directly, RPO analyses of marine samples suggest that POC transfer in the water column is in fact selective. Observations of consistent biomolecular changes that accompany transport of phytoplankton-derived organic matter to depth across the Southern Ocean support the argument for preferential degradation of specific POC pools in the water column. Combining discussions of POC recycling and transfer across both marine and terrestrial systems offer new perspectives of thermal stability as a proxy for diagenetic stability and POC degradation state. The challenges of interpreting RPO data in these two environments set the stage for applying the technique to more controlled experiments that trace POC from source to long-term sink. / by Sarah Zhou Rosengard. / Ph. D.

Thesis (M.S.)--Joint Program in Chemical Oceanography (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 1988. / Includes bibliographical references (leaves 82-85). / The sulfur content of planktonic and benthic foraminifera was measured in specimens recovered from deep-sea sediment cores and individuals grown in culture. A new method for measuring sulfur in foraminiferal calcium carbonate was developed, employing a high-resolution inductively coupled plasma-mass spectrometer. The sulfur measurements, expressed as sulfur-to-calcium (S/Ca) ratios in the foraminiferal shells, ranged from 0.26 to 6.0 mmol/mol. Most analyses fell in the range of 0.7 to 2.5 mmol/mol. Culturing experiments were conducted in the planktonic foraminifer G. sacculifer to test the hypothesis that S/Ca ratios in the foraminifer are inversely proportional to the carbonate ion concentration in the seawater in which they grow, and hence proportional to the pH of the seawater. The slope of the relationship between cultured G. sacculifer S/Ca and the pH of the seawater medium was -1.92 mmol mol-1/pH unit with a least squares linear correlation coefficient, r2=0.927. The S/Ca ratios of planktonic and benthic foraminifera from Holocene and last glacial period sediments were measured in an effort to use the established relationship of S/Ca and pH to calculate the ocean pH gradient between Holocene and glacial time. The results indicate the pH of global ocean deepwater was 0.10 to 0.15 pH units higher during glacial time than today. Smaller pH gradients were seen for some cores which may have been caused by circulation-induced water mass changes. Surface ocean changes in pH over the Holocene-glacial interval seem to vary from region to region, with up to an 0.2 pH unit increase at the Sierra Leone Rise in glacial time. Benthic foraminifera from coretops in the thermocline of the Little Bahama Bank were analyzed for S/Ca to examine the effects of hydrographic variables on S/Ca. The relationship of S/Ca to pH and [CO3=] has a positive slope, at odds with the expected negative slope from the previous results. The S/Ca results do correlate well with salinity, suggesting that salinity or other hydrographic parameters may also influence foraminiferal S/Ca ratios. / by Jeffrey Nicholas Berry. / M.S.

Thesis (Ph. D.)--Joint Program in Chemical Oceanography (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2009. / Includes bibliographical references. / Systematic differences in trace element compositions (rare earth element (REE), heavy metal, metalloid concentrations) of seafloor vent fluids and related deposits from hydrothermal systems in the Manus back-arc basin (Eastern Manus Basin, EMB and Manus Spreading Center, MSC) are used to investigate processes that affect their formation. Processes responsible for observed differences in fluids and deposits from distinct geologic settings include (a) fluid-rock interaction (with temperature, pressure and crustal composition as variables), (b) magmatic acid volatile input and, (c) local seawater entrainment and mixing with hydrothermal fluids, coupled with sulfide precipitation and metal remobilization. REE distributions in vent fluids in the Manus Basin exhibit a wide range of chondrite-normalized patterns that contrast with the relatively uniform distributions observed in mid-ocean ridge vent fluids. This heterogeneity is attributed to marked differences in fluid pH and fluoride and sulfate concentrations that significantly affect REE solubility. The data indicate that REEs can be used as indicators of the styles of magmatic acid volatile input in back-arc hydrothermal systems. Anhydrite in deposits record the same range of REE patterns, suggesting that REE distributions preserved in anhydrite can be used as indicators of past magmatic acid volatile input. Vent fluid heavy metal and metalloid concentrations also exhibit considerable differences. High metal concentrations in EMB versus MSC vent fluids reflect low pH, largely from input of magmatic acid volatiles (indicated by fluoride concentrations greater than seawater). In EMB, metal concentrations are locally affected by dissolution of previously deposited sulfide owing to low pH conditions affected by magmatic acid volatile input or seawater entrainment and mixing with hydrothermal fluid that leads to sulfide precipitation and secondary acidity generation. / (cont.) Massive sulfide deposits in the Manus Basin exhibit a wide range of mineral compositions and heavy metal enrichments. The formation of Zn-rich (sphalerite/wurtzite) deposits in the MSC and of Cu-Fe and Cu-As-rich (chalcopyrite, tennantite) deposits in the EMB reflects differences in the conditions of sulfide precipitation (temperature, pH) and in metal concentrations. The data suggest that heavy metal and metalloid distributions in massive sulfide deposits can be used as indicators of the conditions of vent deposit formation. / by Paul R. Craddock. / Ph.D.