Thesis (Ph. D.)--Joint Program in Oceanography (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2012. / Cataloged from PDF version of thesis. / Includes bibliographical references. / Trace metal cycling is one of many processes that influence ocean ecosystem dynamics. Cobalt, iron, and manganese are redox active trace metal micro-nutrients with oceanic distributions that are influenced by both biological and abiotic sources and sinks. Their open ocean concentrations range from picomolar to nanomolar, and their bioavailabilities can impact primary production. Understanding the biogeochemical cycling of these hybrid-type metals with an emphasis on cobalt was the focus of this thesis. This was accomplished by determining the dissolved distributions of these metals in oceanic regions that were characterized by different dominant biogeochemistries. A large subsurface plume of dissolved cobalt, iron, and manganese was found in the Eastern South Atlantic. The cause of this plume is a combination of reductive dissolution in coastal sediments, wind-driven upwelling, advection, biological uptake, and remineralization. Additional processes that are discussed as sources of metals to the regions studied during this thesis include isopycnal uplift within cold-core eddies (Hawaii), ice melt (McMurdo Sound, Antarctica), riverine input (Arctic Ocean), and winter mixing (McMurdo Sound). The biological influence on surface ocean distributions of cobalt was apparent by the observation of linear relationships between cobalt and phosphate in mid to low latitudes. The cobalt:phosphate ratios derived from these correlations changed over orders of magnitude, revealing dynamic variability in the utilization, demand, and sources of this micronutrient. Speciation studies suggest that there may be two classes of cobalt binding ligands, and that organic complexation plays an important role in preventing scavenging of cobalt in the ocean. These datasets provided a basis for comparing the biogeochemical cycles of cobalt, iron, and manganese in three oceanic regimes (Hawaii, South Atlantic, McMurdo Sound). The relative rates of scavenging for these metals show environmental variability: in the South Atlantic, cobalt, iron, and manganese were scavenged at very different rates, but in the Ross Sea, mixing and circulation over the shallow sea was fast, scavenging played a minor role, and the cycles of all three metals were coupled. Studying the distributions of these metals in biogeochemically distinct regions is a step toward a better understanding of their oceanic cycles. / by Abigail Emery Noble. / Ph.D.

Thesis (Ph.D.)--Joint Program in Oceanography (Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, and the Woods Hole Oceanographic Institution), 2001. / Includes bibliographical references. / by Paulo Salles. / Ph.D.

Thesis: S.M., Joint Program in 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 (pages 139-148). / 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 5180 (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. / by Daniel Edward Amrhein. / S.M.

Thesis: Ph. D., Joint Program in Oceanography/Applied Ocean Science and Engineering (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. / At the land-ocean interface, terrestrial groundwater interacts with seawater to form a subterranean estuary, which can play host to dynamic biogeochemical cycling of nutrients, trace metals and radionuclides. This chemically altered groundwater enters the ocean through submarine groundwater discharge (SGD), a process that is driven by a number of physical processes acting on aquifers and the coastal ocean. In this thesis, seasonal variability in chemical cycling and associated loading to the coastal ocean was observed in a monthly time series within the Waquoit Bay (MA, USA) subterranean estuary. The position of the aquifer mixing zone moved seaward with an increase in hydraulic gradient, resulting in low salinity conditions and reduced mixing, while a decrease in gradient led to landward movement, high salinity groundwater and enhanced mixing. At this location, seasonal variability in sea level, not groundwater level, was the dominant variable driving the hydraulic gradient and therefore SGD. Fluxes of sediment bound cations to the ocean increased coincidently with sea level rise due to desorption. There was enhanced nitrogen attenuation during winter, potentially due to longer groundwater residence times, with greater nutrient delivery to coastal waters during the spring and summer bloom. Interannual climate fluctuations that control sea level and precipitation may ultimately control the timing and magnitude of chemical and water flux via SGD. In addition to temporal variability, aquifer lithology influences chemical export. This thesis also demonstrates that SGD from karst subterranean estuaries may play a role in local and global element budgets. The potential for the chemical signature of SGD to be recorded in the coral record was tested through a combination of coral culture experiments and field and modeling studies in the Yucatan Peninsula. Coral barium was well correlated with precipitation for a twelve-year record, with coral geochemistry reflecting the passage of a hurricane in 2002. While additional complexities in deciphering coral records remain, this proxy offers the potential to extend SGD records into the past. / by Meagan Joan Eagle Gonneea. / Ph. D.

Thesis (Ph. D.)--Joint Program in Oceanography (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and, the Woods Hole Oceanographic Institution), 2004. / Includes bibliographical references. / The most ubiquitous source of polycyclic aromatic hydrocarbons (PAHs) to the environment is incomplete combustion. This study generated a high-resolution historical record of pyrogenic PAH emissions since pre-industrial times from anoxic aquatic sediments, allowing for detailed comparison with energy consumption data. We show that an increase in PAH concentrations over the last decade may be due to a rise in emissions from diesel-powered vehicles. Compound-specific radiocarbon measurements demonstrated unequivocally that the proportion of PAHs derived from fossil fuel combustion has increased substantially during the 20th century. [delta]¹³C and [delta]¹⁴C measurements were also used to constrain the relative importance of combustion versus in situ production as sources of perylene. In addition, a comparison of the down-core concentration and isotopic profiles of black carbon (BC) generated by a combination of chemical and/or thermal oxidation methods highlighted the limitations of these methods when applied to sedimentary matrices. Finally, parallel lead and cesium isotopic records revealed two new potential stratigraphic markers in North American sedimentary records. ²⁰⁶Pb/²⁰⁷Pb profiles show a distinct peak in the mid-19th century, while a ¹³⁷Cs peak was found to coincide with the 1986 Chernobyl accident. / by Anna Lúcia Cessel de Lima. / Ph.D.

Thesis (Ph. D.)--Joint Program in Marine Geology and Geophysics (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2009. / Includes bibliographical references. / To explore the ability of melting mafic lithologies to produce alkaline ocean-island basalts (OIB), an experimental study was carried out measuring clinopyroxene (Cpx)melt and garnet (Gt)-melt partition coefficients during silica-poor garnet pyroxenite melting for a suite of trace elements, including U and Th, at 2.5GPa and 1420-1450°C. Partition coefficients range from 0.0083+0.0006 to 0.020+0.002 for Th and 0.0094+0.0006 to 0.024+0.002 for U in Cpx, and are 0.0032+0.0004 for Th and 0.013+0.002 for U in Gt. Forward-melting calculations using these experimental results to model time-dependent uranium-series isotopes do not support the presence of a fixed quantity of garnet pyroxenite in the source of OIB. To use U-series isotopes to further constrain mantle heterogeneity and the timing and nature of melting and melt transport processes, U-Th-Pa-Ra disequilibria, radiogenic isotopes, and trace-element compositions were measured for the slow-spreading Arctic mid-ocean ridges (MOR). A focused case study of 33 young (<10ka) MOR basalts (MORB) from the shallow endmember of the global ridge system, the Kolbeinsey Ridge (67°05'-70°26'N) found that unaltered Kolbeinsey MORB have universally high (230Th/238U) (1.165-1.296) and relatively uniform (230Th/232Th) (1.196-1.324), ENd (8.4310.49), 87Sr/86Sr (0.70274-0.70301), EHf(16.59-19.56), and Pb isotopes (e.g. 208Pb/206Pb 2.043-2.095). This suggests a homogeneous mantle source and a long peridotite melting column produces the thick Kolbeinsey crust. Trace element ratios suggest a young, depleted mantle source. Data from the slow- to ultraslow Mohns and Knipovich Ridges north of Kolbeinsey form a sloped array, and (230Th/232Th) correlates systematically with radiogenic isotopic variations. / (cont.) These data are readily reproduced by models for heterogeneous mantle melting. MORB from 85oE on the global ultraslow-spreading endmember Gakkel Ridge are homogeneously depleted with low (230Th/238U) and high (226Ra/230Th) that lie along a global negative correlation. Arctic data support a global mantle temperature control on mean (230Th/238U). / by Lynne J. Elkins. / 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. / 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 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 105-114). / The circulation of air in the stratosphere is important for the distribution of radiatively-important trace gases, such as ozone and water vapor, and other chemical species, including ozone-depleting chlorofluorocarbons. Age of air in the stratosphere is an idealized tracer with unique mathematical properties, which we exploit to derive a theory for the relationship of tracer observations to the stratospheric circulation. We show that the meridional age gradient is a measure of the global diabatic circulation, the total overturning strength through an isentropic surface, and test this time-dependent theory in a simple atmospheric general circulation model. We apply the theory to satellite data of sulfur hexafluoride (SF6 and nitrous oxide to derive the first observationally-based estimates of the global meridional overturning circulation strength at all levels in the stratosphere. These two independent global satellite data products agree to within 5% on the strength of the diabatic circulation in the lower stratosphere. We compare to re-analyses and find broad agreement in the lower stratosphere and disagreement (~ 100%) in the upper stratosphere. To understand the relationship between the diabatic circulation and other metrics of the circulation, we calculate it in a state-of-the-science atmospheric model and in three different reanalysis data products. The variability of the global diabatic circulation is very similar to one typical circulation metric, and it is correlated with total column ozone in the tropics and in Southern hemisphere mid latitudes in both a model and in reanalysis-data comparisons. Furthermore, we develop a metric for the mean adiabatic mixing, showing that it is related to the meridional age difference and the vertical gradient of age. We calculate this metric for a range of simple model runs to determine its utility as a measure of mixing. We find very little mixing of air into the tropics in the mid-stratosphere, and the vertical structure of mixing in the lower stratosphere and upper stratosphere varies among model runs and between hemispheres. A picture of global average stratospheric circulation could thus be obtained using age of air data, given reliable long-term records. / by Marianna Katherine Linz. / Ph. D.

Thesis (Ph. D.)--Joint Program in Biological Oceanography (Massachusetts Institute of Technology, Dept. of Biology; and the Woods Hole Oceanographic Institution), 2008. / Includes bibliographical references. / In this dissertation, I explored metapopulation dynamics and population connectivity, with a focus on the softshell clam, Mya arenaria. I first worked towards developing a method for using elemental signatures retained in the larval shell as a tag of natal habitat. I designed and implemented an experiment to determine whether existing methods commonly used for fishes would be applicable to bivalves. I found that the instrumentation and setup I used were not able to isolate and measure the first larval shell of M. arenaria. In concert with developing this method for bivalves, I reared larval M. arenaria in the laboratory under controlled conditions to understand the environmental and biological factors that may influence elemental signatures in shell. My results show that growth rate and age have significant effects on juvenile shell composition, and that temperature and salinity affect larval and juvenile shell composition in variable ways depending on the element evaluated. I also examined the regional patterns of diversity over the current distribution of M. arenaria using the mitochondrial gene, cytochrome oxidase I (COI). I found minimal variability across all populations sampled, suggesting a recent population expansion in the Northwest Atlantic. Finally, I employed theoretical approaches to understand patch dynamics in a two-patch metapopulation when one patch is of high quality and the other low quality. I developed a matrix metapopulation model and compared growth rate elasticity to patch parameters under variable migration scenarios. I then expanded the model to include stochastic disturbance. I found that in many cases, the spatial distribution of individuals within the metapopulation affects whether growth rate is most elastic to parameters in the good or bad patch. / by Carly A. Strasser. / Ph.D.

Thesis (Ph.D.)--Joint Program in Oceanography (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2010. / This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. / Cataloged from student submitted PDF version of thesis. / Includes bibliographical references. / Anthropogenic activity is rapidly changing the global climate through the emission of carbon dioxide. Ocean carbon and sulfur cycles have the potential to impact global climate directly and through feedback loops. Numerical modeling, field and laboratory studies are used to improve our mechanistic understanding of the impact of natural variability on carbon and sulfur cycling. Variability in ocean physics, specifically changes in vertical mixing, is shown to significantly impact both cycles. The impact of interannual variability on the detection and attribution of anthropogenic carbon (Canthro) and the storage of Canthro in the Atlantic Ocean is analyzed using a three-dimensional global ocean model. Several regions are identified where empirical methods used to estimating Canthro are not able to correct for natural variability in the ocean carbon system. This variability is also shown to bias estimates of long term trends made from hydrographic observations. In addition, the storage of Canthro in North Atlantic mode waters is shown to be strongly influenced by water mass transformation during wintertime mixing events. The primary mechanisms responsible for seasonal variability in dimethylsulfoniopropionate (DMSP) degradation and dimethylsulfide (DMS) production in the oligotrophic North Atlantic are investigated using potential enzyme activity and gene expression and abundance data. Vertical mixing and UV radiative stress appear to be the dominant mechanisms behind seasonal variability in DMS production in the Sargasso Sea. This thesis demonstrates the importance of and dynamics of bacterial communities responsible for DMSP degradation and DMS production in oligotrophic surface waters. These findings suggest that modifications to current numerical models of the upper ocean sulfur cycle may be needed. Specifically, current static parameterizations of bacterial DMSP cycling should be replaced with a dynamic bacterial component including DMSP degradation and DMS production. / by Naomi Marcil Levine. / Ph.D.