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, Department of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2016. / Cataloged from PDF version of thesis. / Includes bibliographical references. / In the spring and summer within the ablation zone of the Greenland Ice Sheet (GrIS), meltwater drains to the ice sheet bed through an evolving network of efficient channelized and inefficient distributed drainage systems. Distributed system drainage is a key component in stabilizing GrIS velocity on interannual time scales and controlling geochemical fluxes. During the spring and summer of 2011 and 2012, I conducted fieldwork at a large outlet glacier in southwest Greenland underlain by metamorphic silicate rocks. Data collected from a continuous 222Rn monitor in the proglacial river were used as a component of a mass balance model. I demonstrated that Jdis, the 222Rn fraction derived from the distributed system, was >90% of the 222Rn flux on average, and therefore, 222Rn can be used as a passive flow tracer of distributed system drainage. Supraglacial meltwater runoff estimated using two independent models was compared with ice velocity measurements across the glacier's catchment. Major spikes of Jdis, occurred after rapid supraglacial meltwater runoff inputs and during the expansion of the subglacial channelized system. While increases in meltwater runoff induced ice acceleration, they also resulted in the formation of efficient subglacial channels and increased drainage from the distributed system, mechanisms known to cause slower late summer to winter velocities. Sr, U, and Ra isotopes and major and trace element chemistry were used to investigate the impact of glacial hydrology on subglacial weathering. Analysis of partial and total digestions of the riverine suspended load (SSL) found that trace carbonates within the silicate watershed largely controlled the 'Sr/'Sr ratio in the dissolved load. Experiments and sampling transects downstream from the GrIS demonstrated that [delta]234U in the dissolved phase decreased with increasing interaction with the SSL. The (2 2 8Ra/2 26Ra) value of the dissolved load was significantly higher than that of the SSL and therefore, was not the result of the source rock material but of extensive mineral surface weathering and the faster ingrowth rate of 228Ra (t1 2=5.75 y) relative to 22 6Ra (t112=1600 y). In summary, extensive, repeated cycles of rapid supraglacial meltwater runoff to subglacial drainage networks leads to increased distributed system drainage and mineral weathering. / by Benjamin Shawn Linhoff. / 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.

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 (pages 169-190). / Terrestrial organic carbon (OC) erosion, remineralization, transport through river networks, and burial in marine sediments is a major pathway of the global carbon cycle. However, our ability to constrain these processes and fluxes is largely limited by (i) analytical capability and (ii) temporal sampling resolution. To address issue (i), here I discuss methodological advancements and data analysis techniques for the Ramped PyrOx serial oxidation isotope method developed at WHOI. Ramped-temperature pyrolysis/oxidation coupled with the stable carbon (¹²C, ¹³C) and radiocarbon (¹⁴C) analysis of evolved CO₂ is a promising tool for understanding and separating complex OC mixtures. To quantitatively investigate distributions of OC source, reservoir age, and chemical structure contained within a single sample, I developed a kinetic model linking RPO-derived activation energy, ¹³C composition, and radiocarbon content. This tool provides a novel method to fundamentally address the unknown relationship between OC remineralization rates and chemical structure in various environmental settings. To address issue (ii), I additionally present results from time-series sample sets collected on two end-member systems: the Congo River (Central Africa) and the LiWu River (Taiwan). For the Congo River, bulk and plant-wax-lipid ¹³C compositions indicate that a majority of particulate OC is consistently derived from downstream, C₃-dominated rainforest ecosystems. Furthermore, bulk radiocarbon content and microbial lipid molecular distributions are strongly correlated with discharge, suggesting that pre-aged, swamp-forest-derived soils are preferentially exported when northern hemisphere discharge is highest. Combined, these results provide insight into the relationship between hydrological processes and fluvial carbon export. Lastly, I examined the processes controlling carbon source and flux in a set of soils and time-series fluvial sediments from the LiWu River catchment located in Taiwan. A comparison between bedrock and soil OC content reveals that soils can contain significantly less carbon than the underlying bedrock, suggesting that this material is remineralized to CO₂ prior to soil formation. Both the presence of bacterial lipids and a shift toward lower activation energy of ¹⁴C-free OC contained in soil saprolite layers indicate that this process is microbially mediated and that microbial respiration of rock-derived OC likely represents a larger geochemical flux than previously thought. The results presented in this thesis therefore provide novel insight into the role of rivers in the global carbon cycle as well as their response to environmental perturbations. / by Jordon Dennis Hemingway / 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. / A 225-year old coral from the south shore of Bermuda (64°W, 320N) provides a record of decadal-to-centennial scale climate variability. The coral was collected live, and sub-annual density bands seen in x-radiographs delineate cold and warm seasons allowing for precise dating. Coral skeletons incorporate strontium (Sr) and calcium (Ca) in relative proportions inversely to the sea surface temperature (SST) in which the skeleton is secreted. [Delta]180 of the coral skeleton changes based on both temperature and the [delta]180 of sea water ([delta]Ow), and 6Ow is proportional to sea surface salinity (SSS). Understanding long-term climate variability requires the reconstruction of key climate parameters, such as sea surface temperature (SST) and salinity, in records extending beyond the relatively short instrumental period. The high accretion rates, longevity, and skeletal growth bands found in coral skeletons make them an ideal resource for well-dated, seasonal climate reconstructions. Growing between 2 and 6 mm/year and reaching more than im in length, slow-growing corals provide multi-century records from one colony. Additionally, unlike the fast growing (10-20 mm/year) species Porites, slow-growing species are generally found in both tropical and sub-tropical locations greatly expanding the geographical location of these records. A high resolution record (HRR, ~11 samples per year) was drilled for the entire length of the coral record (218 years). Samples were split and Sr/Ca, [delta]180, and [delta]13C were measured for each sample. Sr/Ca was used to reconstruct winter time and mean-annual SST. Oxygen isotopic measurements were used to determine directional salinity changes, in conjunction with Sr/Ca based SST reconstructions. / (cont.) Winter-time and mean annual SSTs show SSTs -1.5 'C colder during the end of the Little Ice Age (LIA) relative to today. Simultaneously, SSS is fresher during that time. Sr/Ca based climate reconstructions from coral skeletons have been met with some skepticism because some reconstructions show temperature changes back in time that are 2-4 times greater than the reconstructions of other marine proxies. In this study, we show that when using bulk-sampled, slow-growing corals, two steps are critical to producing accurate reconstructions: 1) incorporating growth rate into multi-variant regressions with SST and Sr/Ca and 2) using multiple colonies that grew at the same time with varying average growth rates and Sr/Ca. Application of these novel methods over the period of the instrumental record from Hydrostation S (monthly since 1954, 32°10'N, 64°30'W) reduces the root mean square of the residuals between the reconstructed SST and the instrumental SST by as much as 1.52'C to 0.460C for three coral colonies. Winter-time SSTs at Bermuda are correlated to phases of the North Atlantic Oscillation (NAO), a meridional oscillation in atmospheric mass. Much uncertainty remains about the relationship between the NAO and the ocean, and one critical outstanding question is whether anthropogenic changes are perturbing the system. Using winter Sr/Ca as a proxy for temperature, we show strong coherence to the NAO at multi-decadal and inter-annual frequencies. These coral records show significant changes in variance in the NAO during the late 20th century compared to the cooler LIA, but limited changes in the mean phase (positive or negative) of the NAO, implying that climate change may be pushing the NAO to extremes but not to a new mean position. / by Nathalie Fairbank Goodkin. / 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), 2014. / Cataloged from PDF version of thesis. / Includes bibliographical references. / Marine particles include all living and non-living solid components of seawater, representing an extremely dynamic and chemically diverse mixture of phases. The distributions of these phases are poorly constrained and undersampled in the oceans, despite interactions between living organisms and non-living minerals having central roles within many globally relevant biogeochemical processes. Through a combination of method development, basin-scale particulate collection and analyses, modeling, and field experiments, this thesis examines both the distributions of marine particulate trace metals and the underlying processes-inputs, scavenging, vertical and horizontal transport, and biotic uptake-in which marine particles participate. I first present the results of an intercalibration exercise among several US laboratories that analyzed filtered particles on shared polyethersulfone filters. We use inter-lab and intra-lab total elemental recoveries of these particles to determine our state of our intercalibration (</= 21% one-sigma inter-lab uncertainty for most elements; 9% intra-lab) and to identify means of future improvement. We also present a new chemical method for complete dissolution of polyethersulfone filters and compare it to other total particle digestion procedures. I then present the marine particulate distributions of the lithogenic elements Al, Fe, and Ti in the North Atlantic GEOTRACES section. Inputs of lithogenic particles from African dust sources, hydrothermal systems, benthic nepheloid layers and laterally-sourced margin influences are observed and discussed. Lithogenic particle residence times, size-fractionation patterns, Ti-mineral speciation, and relationships to biological aggregation processes are calculated and described. A one-dimensional, size-fractionated, multi-box model that describes lithogenic particle distributions is also proposed and its parameter sensitivities and potential implications are discussed. The thesis concludes with the presentation of results from a series of bottle incubations in naturally iron-limited waters using isotopically labeled Fe-minerals. We demonstrate both biotic and abiotic solubilization of the minerals ferrihydrite and fayalite via transfer of isotopic label into suspended particles. These results are the first of their kind to demonstrate that minerals can be a source of bioavailable iron to euphotic communities and that spatial and ecological variations in mineral Fe-bioavailability may exist. / by Daniel Chester Ohnemus. / 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), 2015. / Cataloged from PDF version of thesis. / Includes bibliographical references. / Tracing the evolution of Earth's redox history is one of the great challenges of geobiology and geochemistry. The accumulation of photosynthetically derived oxygen transformed the redox state of Earth's surface environments, setting the stage for the subsequent evolution of complex life. However, the timing of the advent of oxygenic photosynthesis relative to the Great Oxidation Event (GOE; -2.4 Ga) is poorly constrained. After the deep ocean became oxygenated in the early Phanerozoic, hydrogen sulfide, which is toxic to most aerobes, may have transiently accumulated in the marine photic zone (i.e. photic zone euxinia; PZE) during mass extinctions and oceanic anoxic events. Here, the molecular fossil evidence for oxygenic photosynthesis and eukaryotes is reevaluated, where the results imply that currently existing lipid biomarkers are contaminants. Next, the stratigraphic distribution of green and purple sulfur bacteria biomarkers through geologic time is evaluated to test whether these compounds reflect a water column sulfide signal, which is implicit in their utility as PZE paleoredox proxies. Results from a modern case study underscore the need to consider allochthonous and microbial mat sources and the role of basin restriction as alternative explanations for these biomarkers in the geologic record, in addition to an autochthonous planktonic source. / by Katherine L. French. / Ph. D.