2023 / The photobleaching of chromophoric dissolved organic matter (CDOM) is considered an important loss process for CDOM absorption in sunlit natural waters, where it can regulate the biota’s exposure to sunlight, surface solar heating, and dissolved organic matter (DOC) dynamics. Understanding the global significance of CDOM photobleaching is essential for assessing its impact on the light field of the surface ocean, related biogeochemical processes, and climate dynamics. Despite its importance, this sink remains poorly quantified, primarily due to the difficulty of: 1. determining photobleaching apparent quantum yields (AQY) that capture the dual spectral dependency of this process and are applicable to polychromatic sunlight; 2. constraining the variability of AQY across the land-ocean aquatic continuum under diverse environmental conditions. This dissertation seeks to quantify the global role of photobleaching as a sink of CDOM.Chapter 1 presents a simple method to determine CDOM photobleaching AQY matrix (AQY-M) for natural water samples that does not require any a-priori assumptions about the spectral dependency of photobleaching. It combines controlled irradiation experiments, a partial-least-square regression (PLSR) and an optimization procedure to produce AQY matrices that are spectrally coherent and optimized for modeling accurate photobleaching rates in natural waters. Water temperature and the solar-exposure history of CDOM had a major influence on the magnitude and spectral characteristics of the AQY-M. These factors should be considered when determining the AQY-M of samples, and provide constraints when modeling photobleaching rates in natural waters. Chapter 2 builds a model to constrain the natural variability of CDOM photobleaching AQY-M in natural waters. This model was developed using AQY-Ms determined for a set of water samples (n=27) collected from surface waters along the land-ocean aquatic continuum (range of salinity: 0-35.79 PSU). The analysis investigated the dependencies of the measured AQY-M on CDOM composition, water temperature, and exposure duration. The results demonstrated a strong relationship between the magnitude and spectral characteristics of the AQY-M and the CDOM composition and solar exposure duration. Terrigenous CDOM exhibited a higher overall magnitude of AQY-M compared to oceanic CDOM. Additionally, water temperature was found to influence the extent of photobleaching. The model used principle components (PCs) to re-present the spectral characteristics in the AQY-M, and used a series of linear regressions to describe PCs’ dependencies on these variables. The AQY-M prediction model perform well in the independent cross-validation with training samples (n=27) and in the validation with extra samples (n=12), showing promise for global applicability in estimating photobleaching AQY-M. Chapter 3 expands the investigation to a global scale, aiming to develop a comprehensive understanding of CDOM photobleaching significant, seasonal dynamics and sensitivities to climate change in the surface ocean. The chapter combines remote sensing and modeling approaches to create a global climatology of CDOM photobleaching rates. The chapter explores the seasonal variability (high in the summer and low in the winter) of photobleaching rates, calculates the annual global sink (~1.5% to 6.5%) of CDOM due to photobleaching, and examines the sensitivity (increase ~2% to 6% due to sea surface temperature increase in this century) of this process to climate change-induced variations in ocean physical properties. The annual CDOM photobleaching turnover rate in the mixed layer (~1 to 6 times) varied seasonally and, with the highest rates observed near the equator (~25 times at 350 nm) in the open ocean. Overall, this dissertation contributes to the field of CDOM photobleaching research by providing insights into the quantification of photobleaching rates, the natural variability of AQY-M in natural waters, and the global dynamics of CDOM photobleaching in the surface ocean. The methodologies and findings presented in these chapters enhance our understanding of CDOM photobleaching processes, their dependencies, and their implications for aquatic ecosystems and climate dynamics. / 2026-02-06T00:00:00Z

Thesis: Ph. D., Joint Program in Oceanography/Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Department of Civil and Environmental Engineering; and the Woods Hole Oceanographic Institution), 2013. / Pages 181 and 182 blank. Cataloged from PDF version of thesis. / Includes bibliographical references. / Steroidal estrogens are potent endocrine disrupting chemicals that are naturally excreted by vertebrates (e.g., humans and fish) and can enter natural waters through the discharge of treated and raw sewage. Because estrogens are detrimental to aquatic organisms at picomolar concentrations, many studies have measured so-called "free" estrogen concentrations in wastewater effluents, rivers, and lakes. Yet, to our knowledge, no studies have characterized the broader range of estrogens that includes free, conjugated, and halogenated forms. Conjugated estrogens are important because they can be easily converted to potent free forms by bacteria in wastewater treatment plants and receiving waters. And halogenated estrogens, produced during wastewater disinfection, are only slightly less potent than free estrogens but much more likely to bioaccumulate. We have developed a tandem mass spectrometry method that is capable of simultaneously quantifying free, conjugated, and halogenated estrogens at picomolar levels in wastewater effluent and coastal seawater. The method was validated using treated effluent from the greater Boston metropolitan area, where we found that halogenated estrogens represented over 50 % of the total estrogen discharge flux. A kinetic model of estrogen halogenation was used to predict the distribution of free and halogenated forms in wastewater effluent and suggested that chlorinated estrogens may be formed en route to the wastewater treatment plant. In the receiving waters of Massachusetts Bay, we detected a range of conjugated, free, and halogenated forms at concentrations that were well-predicted by dilution near the sewage outfall. Farther downstream, we found significantly higher estrone concentrations which points to large inputs of estrogens from sources other than sewage. Finally, we have used compound-specific measurements of 13C and 14C in commercial and pharmaceutical estrogen preparations to evaluate the potential for using carbon isotopes to distinguish between synthetic and endogenous steroids in wastewater and other environmental matrices. Our results show that synthetic estrogens and progestogens exhibit significantly depleted [delta]13 C values (~30 0/00) compared to endogenous steroids (-16 0/00 to -26 0/00). This isotopic difference should make it possible to apportion synthetic and endogenous hormone sources in complex environments. / by David R. Griffith. / Ph. D.

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), 2017. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 185-213). / In this thesis, I use coastal measurements of dissolved O₂ and inert gases to provide insight into the chemical, biological, and physical processes that impact the oceanic cycles of carbon and dissolved gases. Dissolved O₂ concentration and triple isotopic composition trace net and gross biological productivity. The saturation states of inert gases trace physical processes, such as air-water gas exchange, temperature change, and mixing, that affect all gases. First, I developed a field-deployable system that measures Ne, Ar, Kr, and Xe gas ratios in water. It has precision and accuracy of 1 % or better, enables near-continuous measurements, and has much lower cost compared to existing laboratory-based methods. The system will increase the scientific community's access to use dissolved noble gases as environmental tracers. Second, I measured O₂ and five noble gases during a cruise in Monterey Bay, California. I developed a vertical model and found that accurately parameterizing bubble-mediated gas exchange was necessary to accurately simulate the He and Ne measurements. I present the first comparison of multiple gas tracer, incubation, and sediment trap-based productivity estimates in the coastal ocean. Net community production estimated from ¹⁵NO₃⁻ uptake and 02 /Ar gave equivalent results at steady state. Underway O₂/Ar measurements revealed submesoscale variability that was not apparent from daily incubations. Third, I quantified productivity by O₂ mass balance and air-water gas exchange by dual tracer (³He/SF₆ ) release during ice melt in the Bras d'Or Lakes, a Canadian estuary. The gas transfer velocity at >90 % ice cover was 6 % of the rate for nearly ice-free conditions. Rates of volumetric gross primary production were similar when the estuary was completely ice-covered and ice-free, and the ecosystem was on average net autotrophic during ice melt and net heterotrophic following ice melt. I present a method for incorporating the isotopic composition of H₂O into the O₂ isotope-based productivity calculations, which increases the estimated gross primary production in this study by 46-97 %. In summary, I describe a new noble gas analysis system and apply O₂ and inert gas observations in new ways to study chemical, biological, and physical processes in coastal waters. / by Cara Charlotte Marie Manning. / Ph. D.

Thesis (Ph. D.)--Joint Program in Oceanography/Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2013. / Cataloged from PDF version of thesis. / Includes bibliographical references. / Predicting the response of net community calcification (NCC) to ocean acidification OA and declining aragonite saturation state [Omega]a requires a thorough understanding of controls on NCC. The diurnal control of light and net community production (NCP) on NCC confounds the underlying control of [Omega]a on NCC and must be averaged out in order to predict the general response of NCC to OA. I did this by generating a general NCC-[Omega]a correlation based on data from 15 field and mesocosm studies around the globe. The general relationship agrees well with results from mesocosm experiments. This general relationship implies that NCC will transition from net calcification to net dissolution at a [Omega]a of 1.0 ± 0.6 and predicts that NCC will decline by 50% from 1880 to 2100, for a reef of any percent calcifier cover and short reef water residence time. NCC will also decline if percent calcifier cover declines, as evidenced by estimates of NCC in two Caribbean reefs having declined by an estimated 50-90% since 1880. The general NCC-([Omega]a relationship determined here, along with changes in percent calcifier cover, will be useful in predicting changes in NCC in response to OA and for refining models of reef water [Omega]a. / by Whitney Nicole Bernstein. / Ph.D.

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), 2019 / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 193-220). / Southern Ocean net community productivity plays an out sized role in regulating global biogeochemical cycling and climate dynamics. The structure of spatial-temporal variability in phytoplankton ecosystem dynamics is largely governed by physical processes but a variety of competing pathways complicate our understanding of how exactly they drive net population growth. Here, I leverage two coupled, 3-dimensional, global, numerical simulations in conjunction with remote sensing data and past observations, to improve our mechanistic understanding of how physical processes drive biology in the Southern Ocean. In Chapter 2, I show how different mechanistic pathways can control population dynamics from the bottom-up (via light, nutrients), as well as the top-down (via grazing pressure). In Chapters 3 and 4, I employ a higher resolution, eddy resolving, integration to explicitly track and examine closed eddy structures and address how they modify biomass at the mesoscale. / Chapter 3 considers how simulated eddies drive bottom-up controls on phytoplankton growth and finds that division rates are, on average, amplified in anticyclones and suppressed in cyclones. Anomalous division rates are predominately fueled by an anomalous vertical iron flux driven by eddy-induced Ekman Pumping. Chapter 4 goes on to describe how anomalous division rates combine with anomalous loss rates to drive anomalous net population growth. Biological rate-based mechanisms are then compared to the potential for anomalies to evolve strictly via physical transport (i.e. dilution, stirring, advection). All together, I identify and describe dramatic regional and seasonal variability in when, where, and how different mechanisms drive phytoplankton growth throughout the Southern Ocean. Better understanding this variability has broad implications to our understanding of how oceanic biogeochemisty will respond to, and likely feedback into, a changing climate. / Specifically, the uncertainty associated with this variability should temper recent proposals to artificially stimulate net primary production and the biological pump via iron fertilization. In Chapter 5 I argue that Southern Ocean Iron Fertilization fails to meet the basic tenets required for adoption into any regulatory market based framework. / by Tyler W. Rohr. / Ph. D. / 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)

Massive amounts of 13 C-depleted carbon rapidly entered the ocean more than once during the early Paleogene, providing a geological framework for understanding future perturbations in carbon cycling, including ocean acidification. To assess the number of events and their impact on deep-sea carbonate accumulation, I have studied carbonate ooze units of the upper Paleocene-lower Eocene, which were deposited on a subsiding flank of the East Pacific Rise (ODP Site 1215). From this record several proxies were used to ascertain changes in carbonate dissolution: carbonate content, foraminiferal test fragmentation, and planktic/benthic foraminiferal ratio. Based on these analyses, 1 observe that carbonate preservation generally increased from the late Paleocene (56 Ma) through the early Eocene (51.5 Ma), after which it became poor to negligible. This trend was punctuated by four short-term intervals characterized by carbonate dissolution and pronounced negative d 18 O and d 13 C excursions. It is inferred that these were anomalously warm periods (hyperthermals) caused by massive and relative fast 13 C-depleted carbon injections. These correspond to the PETM (∼55.5 Ma), H1/ETM-2 (∼53.7 Ma), I1 (∼53.2 Ma), and K/X (∼52.5 Ma) events. I also calculated carbonate, planktic, and benthic foraminiferal mass accumulation rates for the Site 1215. These were used to comprehensively examine the history of carbonate accumulation in the equatorial Pacific Ocean throughout the early Paleogene. I deduce that in the long-term (>10 5 yr) the lysocline and calcite compensation depth (CCD) generally deepened between 55.4 and 51.5 Ma; but rapidly (≤10 5 yr) shoaled and subsequently overcompensated during and after the four intervals of massive carbon injection. Planktic foraminiferal assemblages found in the record of Site 1215 follow a predicted pattern for selective dissolution. Species of Acarinina are preferentially preserved over Morozovella, which are preferentially preserved over Subbotina, Igorina and Globanomalina. A tiny and previously overlooked species, Praetenuitella antica n.sp, is formally described in this manuscript. This species is also resistant to dissolution. The findings of this study provide firm constraints to model the short and long-term carbon cycle dynamics during the early Paleogene

Five profiles of the silver concentration in the subArctic Northeast Pacific Ocean yield a broad correlation between the Ag content and dissolved Si. However, silver is depleted at intermediate depths where the 02 content is low, implying removal from oxygen-deplete waters. An eighteen-month series of measurements of dissolved and particulate Ag from Saanich Inlet, BC indicate that Ag concentrations in near-surface waters are influenced by processes occurring outside the inlet. Dissolved silver was not detected in sulphide-bearing deep waters in the fjord. Ag in sediment-trap particles was associated with both biogenic and mineral phases. The Ag/biogenic Si ratio of the particles is related to the concentration of dissolved Ag in the surface waters suggesting a direct link between availability of the metal and its sequestration by diatoms.

While ocean acidification (OA) is predicted to inhibit calcification in marine macroalgae, species whose photosynthesis is limited by current dissolved inorganic carbon (DIC) levels may benefit. Furthermore, variations in macroalgal morphology will likely give rise to a range of OA tolerance in calcifying macroalgae. One genus of calcifying macroalgae that has shown varying species’ tolerance to OA is Halimeda, a major carbonate sediment producer on tropical reefs. Species within this genus occupy a range of habitats within tropical environments (reefs and lagoons), illustrating their ability to adapt to diverse environmental conditions (e.g. carbonate chemistry, irradiance). To date it is not clear if morphological and photophysiological diversity in Halimeda will translate to different tolerances to OA conditions (elevated pCO2 and lower pH). / Includes bibliography. / Dissertation (Ph.D.)--Florida Atlantic University, 2016. / FAU Electronic Theses and Dissertations Collection

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.

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), 2013. / Cataloged from PDF version of thesis. / Includes bibliographical references. / Iron is a redox active trace metal micronutrient essential for primary production and nitrogen acquisition in the open ocean. Dissolved iron (dFe) has extremely low concentrations in marine waters that can drive phytoplankton to Fe limitation, effectively linking the Fe and carbon cycles. Understanding the marine biogeochemical cycling and composition of dFe was the focus of this thesis, with an emphasis on the role of the size partitioning of dFe (<0.2 jm) into soluble (sFe<0.02 jm) and colloidal (0.02ptm<cFe<0.2 m) size fractions. This was accomplished through the measurement of the dFe distribution and size partitioning along basin-scale transects experiencing a range of biogeochemical influences. dFe provenance was investigated in the tropical North Atlantic and South Pacific Oceans. In the North Atlantic, elevated dFe (>I nmol/kg) concentrations coincident with the oxygen minimum zone were determined to be caused by remineralization of a high Fe:C organic material (vertical flux), instead of a laterally advected low oxygen-high dFe plume from the African margin. In the South Pacific Ocean, dFe maxima near 2000m were determined by comparison with dissolved manganese and 3He to be caused by hydrothermal venting. The location of these stations hundreds to thousands of kilometers from the nearest vents confirms the "leaky vent" hypothesis that enough dFe escapes precipitation at the vent site to contribute significantly to abyssal dFe inventories. The size partitioning of dFe was also investigated in order to trace the role of dFe composition on its cycling. First, the two most commonly utilized methods of sFe filtration were compared: cross flow filtration (CFF) and Anopore filtration. Both were found to be robust sFe collection methods, and sFe filtrate through CFF (10 kDa) was found to be only 74±21% of the sFe through Anopore (0.02pjm) filters at 28 locations, a function of both pore size differences and the natural variability in distribution of 1 OkDa- 0.02 [m colloids. In the North Atlantic, a colloidal-dominated partitioning was observed in the surface ocean underlying the North African dust plume, in and downstream of the TAG hydrothermal system, and along the western Atlantic margin. However, cFe was depleted or absent at the deep chlorophyll maximum. A summary model of dFe size partitioning in the North Atlantic open ocean is presented in conclusion, hypothesizing that a constant dFe exchange between soluble and colloidal pools modulates the constant partitioning of nearly 50% dFe into the colloidal phase throughout the subsurface North Atlantic Ocean, while sFe and cFe cycle independently in the upper ocean. / by Jessica Nicole Fitzsimmons. / Ph.D.