ALBERT

Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Oceanographic Engineering at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution February 2019.

Description: Marine microbes are key drivers of biogeochemical transformations within the world’s oceans. Although seawater appears uniform at scales that humans often interact with and sample, the world that marine microbes inhabit can be highly heterogeneous, with numerous biological and physical processes giving rise to resource hotspots where nutrient concentrations exceed background levels by orders of magnitude. While the impact of this microscale heterogeneity has been investigated in the laboratory with microbial isolates and theoretical models, microbial ecologists have lacked adequate tools to interrogate microscale processes directly in the natural environment. Within this thesis I introduce three new technologies that enable interrogation of microbial processes at the microscale in natural marine communities. The IFCB-Sorter acquires images and sorts individual phytoplankton cells, directly from seawater, allowing studies exploring connections between the diversity of forms present in the plankton and genetic variability at the single-cell level. The In Situ Chemotaxis Assay (ISCA) is a field-going microfluidic device designed to probe the distribution and role of motility behavior among microbes in aquatic environments. By creating microscale hotspots that simulate naturally occurring ones, the ISCA makes it possible to examine the role of microbial chemotaxis in resource acquisition, phytoplankton-bacteria interactions, and host-symbiont systems. Finally, the Millifluidic In Situ Enrichment (MISE) is an instrument that enables the study of rapid shifts in gene expression that permit microbial communities to exploit chemical hotspots in the ocean. The MISE subjects natural microbial communities to a chemical amendment and preserves their RNA in a minute-scale time series. Leveraging an array of milliliter-volume wells, the MISE allows comparison of community gene expression in response to a chemical stimulus to that of a control, enabling elucidation of the strategies employed by marine microbes to survive and thrive in fluctuating environments. Together, this suite of instruments enables culture-independent examination of microbial life at the microscale and will empower microbial ecologists to develop a more holistic understanding of how interactions at the scale of individual microbes impact processes in marine ecosystems at a global scale.

Description: I’d like to thank the Gordon and Betty Moore Foundation, the National Science Foundation, and NSERC for funding portions of my research.

Description: I’d like to thank the Gordon and Betty Moore Foundation, the National Science Foundation, and NSERC for funding portions of my research.

Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Oceanography/Applied Ocean Science and Engineering at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution June 2019.

Description: Over the past several decades, the West Antarctic Peninsula (WAP) has undergone physical and ecological changes at a rapid pace, with warming surface ocean and a sharp decrease in the duration of the sea ice season. The impact of these changes in the ocean chemistry and ecosystem are not fully understood and have been investigated by the Palmer-LTER since 1991. Given the data acquisition constraints imposed by weather conditions in this region, an ocean circulation, sea ice and biogeochemistry model was implemented to help fill the gaps in the dataset. The results with the present best case from the suite of sensitivity experiments indicate that the model is able to represent the seasonal and interannual variations observed in the circulation, water mass distribution and sea ice observed in the WAP, and has identified gaps in the observations that could guide improvement of the simulation of the regional biogeochemistry. Comparison of model results with data from the Palmer-LTER project suggests that the large spatial and temporal variability observed in the phytoplankton bloom in the WAP is influenced by variability in the glacial sources of dissolved iron. Seasonal progression of the phytoplankton bloom is well represented in the model, and values of vertically integrated net primary production (NPP) are largely consistent with observations. Although a bias towards lower surface dissolved inorganic carbon (DIC) and alkalinity was identified in the model results, interannual variability was similar to the observed in the Palmer-LTER cruise data.

Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 2018

Description: Many chemical constituents are removed from the ocean by attachment to settling particles, a process referred to as “scavenging.” Radioisotopes of thorium, a highly particle-reactive element, have been used extensively to study scavenging in the ocean. However, this process is complicated by the highly variable chemical composition and concentration of particles in oceanic waters. This thesis focuses on understanding the cycling of thorium as affected by particle concentration and particle composition in the North Atlantic. This objective is addressed using (i) the distributions 228,230,234Th, their radioactive parents, particle composition, and bulk particle concentration, as measured or estimated along the GEOTRACES North Atlantic Transect (GA03) and (ii) a model for the reversible exchange of thorium with particles. Model parameters are either estimated by inversion (chapter 2-4), or prescribed in order to simulate 230Th in a circulation model (chapter 5). The major findings of this thesis follow. In chapters 2 and 3, I find that the rate parameters of the reversible exchange model show systematic variations along GA03. In particular, 𝑘1, the apparent first-order rate "constant" of Th adsorption onto particles, generally presents maxima in the mesopelagic zone and minima below. A positive correlation between 𝑘1 and bulk particle concentration is found, consistent with the notion that the specific rate at which a metal in solution attaches to particles increases with the number of surface sites available for adsorption. In chapter 4, I show that Mn (oxyhydr)oxides and biogenic particles most strongly influence 𝑘1 west of the Mauritanian upwelling, but that biogenic particles dominate 𝑘1 in this region. In chapter 5, I find that dissolved 230Th data are best represented by a model that assumes enhanced values of 𝑘1 near the seafloor. Collectively, my findings suggest that spatial variations in Th radioisotope activities observed in the North Atlantic reflect at least partly variations in the rate at which Th is removed from the water column.

Description: This work was supported by the US National Science Foundation. Two US NSF grants have supported the research in this thesis (OCE-1232578 and OCE-155644).

Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution February 2017

Description: Although over a dozen elements are needed to support phytoplankton growth, only a few are considered to be growth-limiting. As the central atom in vitamin B12, cobalt is crucial for metabolism, but its status as a limiting nutrient is uncertain. This thesis investigates the geochemical controls on oceanic cobalt scarcity and their biological consequences. Analysis of over 1000 samples collected in the Tropical Pacific Ocean reveals a dissolved cobalt distribution that is strongly coupled to dissolved oxygen, with peak concentrations where oxygen is lowest. Large cobalt plumes within anoxic waters are maintained by three processes: 1) a cobalt supply from organic matter remineralization, 2) an amplified sedimentary source from oxygen-depleted coastlines, and 3) low-oxygen inhibition of manganese oxidation, which scavenges cobalt from the water column. Rates of scavenging are calculated from a global synthesis of recent GEOTRACES data and agree with cobalt accumulation rates in pelagic sediments. Because both sources and sinks are tied to the extent of oxygen minimum zones, oceanic cobalt inventories are likely dynamic on the span of decades. Despite extremely low cobalt in the South Pacific gyre, the cyanobacterium Prochlorococcus thrives. Minimum cobalt and iron requirements of a Prochlorococcus strain isolated from the Equatorial Pacific are quantified. Cobalt quotas are related to demand for ribonucleotide reductase and methionine synthase enzymes, which catalyze critical steps in DNA and protein biosynthesis, respectively. Compared to other cyanobacteria, a streamlined metal physiology makes Prochlorococcus susceptible to competitive inhibition of cobalt uptake by low levels of zinc. Although phytoplankton in the Equatorial Pacific are subject to chronic iron-limitation, widespread cobalt scarcity and vulnerability to zinc inhibition observed in culture imply that wild Prochlorococcus are not far from a cobalt-limitation threshold.

Description: I am lucky to have benefitted from major financial support of the Saito Lab by the National Science Foundation and the Gordon and Betty Moore Foundation. Specifically, National Science Foundation grants for the Center for Microbial Oceanography Research and Education (CMORE, DBI-0424599), GEOTRACES Pacific and Artic projects (OCE-1233261 and OCE- 1540254), and OCE-1220484 funded my thesis work. National Science Foundation grants OCE- 1031271 and OCE-1337780 and Gordon and Betty Moore Foundation grants 3782 and 3934 to the Saito lab also provided instrumentation and funded field expeditions that enabled this work.

Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution June 2017

Description: Thecosome pteropods are planktonic mollusks that form aragonite shells and that may experience increased dissolution and other adverse effects due to ocean acidification. This thesis focuses on assessing the possible biological effects of ocean acidification on the shells and locomotion of pteropods and examining the response of a local pteropod population to environmental change over time. I analyzed shell condition after exposing pteropods to elevated CO2 as well as in natural populations to investigate the sensitivity of the shells of different species to aragonite saturation state (ΩA). The pteropods (Limacina retroversa) from laboratory experiments showed the clearest pattern of shell dissolution in response to decreased ΩA, while wild populations either had non-significant regional trends in shell condition (Clio pyramidata) or variability in shell condition that did not match expectations due to regional variability in ΩA (Limacina helicina). At locations with intermediate ΩA (1.5-2.5) the variability seen in L. helicina shell condition might be affected by food availability more than ΩA. I examined sinking and swimming behaviors in the laboratory in order to investigate a possible fitness effect of ocean acidification on pteropods. The sinking rates of L. retroversa from elevated CO2 treatments were slower in conjunction with worsened shell condition. These changes could increase their vulnerability to predators in the wild. Swimming ability was mostly unchanged by elevated CO2 after experiments that were up to three weeks in duration. I used a long-term dataset of pteropods in the Gulf of Maine to directly test whether there has been a population effect of environmental change over the past several decades. I did not observe a population decline between 1977 and 2015, and L. retroversa abundance in the fall actually increased over the time series. Analysis of the habitat use of L. retroversa revealed seasonal associations with temperature, salinity, and bottom depths. The combination of laboratory experiments and field surveys helped to address gaps in knowledge about pteropod ecology and improve our understanding of the effects of ocean acidification on pteropods.

Description: Funding for this research was provided by a National Science Foundation grant to Lawson, Lavery, Wang, and Wiebe (OCE-1041068), a National Science Foundation grant to Lawson, Maas, and Tarrant (OCE-1316040), a WHOI Coastal Ocean Institute Student Research Proposal Award to Bergan (COI-27040178), the Pickman Foundation, the Tom Haas Fund at the New Hampshire Charitable Foundation, and the WHOI Academic Programs Office.

Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and Woods Hole Oceanographic Institution September 2017

Description: Population connectivity is a fundamental process that governs the spatial and temporal dynamics of marine ecosystems. For many marine species, population connectivity is driven by dispersal during a planktonic larval phase. The ability to obtain accurate, affordable, and meaningful estimates of larval dispersal patterns is therefore a key aspect of understanding marine ecosystems. Although field observations provide insight into dispersal processes, they do not provide a comprehensive assessment. Individual-based models (IBMs) that couple ocean circulation and particle-tracking models provide a unique ability to examine larval dispersal patterns with high spatial and temporal resolution. Obtaining accurate results with IBMs requires simulating a sufficient number of particles, and the sequential Bayesian procedure presented in chapter 2 identifies when the number of particles is adequate to address predefined research objectives. In addition, this method optimizes the particle release locations to minimize the requisite number of particles. Even after applying this method, the computational expense of IBM studies is still large. The model in chapter 3 seeks to increase the affordability of IBM studies by transferring some of the calculations to graphics processing units. Chapter 4 describes three algorithms that assist in interpreting IBM output by identifying coherent geographic clusters from population connectivity data. The first two algorithms have existed for nearly a decade and recently been applied separately to marine ecology, and we provide a direct comparison of the results from each. Additionally, we develop and present a new algorithm that simultaneously considers multiple species. Finally, in chapter 5, we apply these tools and a trait-based modeling framework to assess which species traits are most likely to impact dispersal success and patterns in the Gulf of Maine. We conclude that the traits influencing spawning distributions and habitat requirements for settlement are most likely to influence dispersal.

Description: Financial support was provided by the Department of Defense (DoD) through the National Defense Science & Engineering Graduate Fellowship (NDSEG) Program, Woods Hole Oceanographic Institution (WHOI) via the Ocean Ventures Fund (OVF), and the National Science Foundation through grant numbers OCE-1459133, 0928442, and 1031256.

Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution June 2017

Description: This thesis documents the origin, distribution, and fate of methane and several of its isotopic forms on Earth. Using observational, experimental, and theoretical approaches, I illustrate how the relative abundances of 12CH4, 13CH4, 12CH3D, and 13CH3D record the formation, transport, and breakdown of methane in selected settings. Chapter 2 reports precise determinations of 13CH3D, a “clumped” isotopologue of methane, in samples collected from various settings representing many of the major sources and reservoirs of methane on Earth. The results show that the information encoded by the abundance of 13CH3D enables differentiation of methane generated by microbial, thermogenic, and abiogenic processes. A strong correlation between clumped- and hydrogen-isotope signatures in microbial methane is identified and quantitatively linked to the availability of H2 and the reversibility of microbially-mediated methanogenesis in the environment. Determination of 13CH3D in combination with hydrogen-isotope ratios of methane and water provides a sensitive indicator of the extent of C–H bond equilibration, enables fingerprinting of methane-generating mechanisms, and in some cases, supplies direct constraints for locating the waters from which migrated gases were sourced. Chapter 3 applies this concept to constrain the origin of methane in hydrothermal fluids from sediment-poor vent fields hosted in mafic and ultramafic rocks on slow- and ultraslow-spreading mid-ocean ridges. The data support a hypogene model whereby methane forms abiotically within plutonic rocks of the oceanic crust at temperatures above ca. 300 C during respeciation of magmatic volatiles, and is subsequently extracted during active, convective hydrothermal circulation. Chapter 4 presents the results of culture experiments in which methane is oxidized in the presence of O2 by the bacterium Methylococcus capsulatus strain Bath. The results show that the clumped isotopologue abundances of partially-oxidized methane can be predicted from knowledge of 13C/12C and D/H isotope fractionation factors alone.

Description: The research activities documented in this thesis were made possible by grants to my advisor from the U.S. National Science Foundation (NSF award EAR-1250394), the National Aeronautics and Space Administration (NASA) Astrobiology Institute (NAI, University of Colorado, Boulder, CAN 7 under Cooperative Agreement NNA15BB02A), the Department of Energy (DOE, Small Business Innovation Research program, contract DE-SC0004575), the Alfred P. Sloan Foundation via the Deep Carbon Observatory, and a Shell Graduate Fellowship through the MIT Energy Initiative. I completed the bulk of the work in this thesis while being supported by a National Defense Science and Engineering Graduate (NDSEG) Fellowship awarded through the Office of Naval Research of the U.S. Department of Defense. The StanleyW.Watson Fellowship Fund provided support during my first summer term at WHOI.The Charles M. Vest Presidential Fellowship at MIT supported me in the first year of my Ph.D. studies. I received additional support that year through NSF award EAR-1159318 (to S. Ono and T. Bosak) and theWalter & Adel Hohenstein Graduate Fellowship of Phi Kappa Phi. The MIT Earth Resources Laboratory and PAOC Houghton Fund funded my attendance at several conferences.

Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution February 2017

Description: Salt marshes are physically, chemically, and biologically dynamic environments found globally at temperate latitudes. Tidal creeks and marshtop ponds may expand at the expense of productive grass-covered marsh platform. It is therefore important to understand the present magnitude and drivers of production and respiration in these submerged environments in order to evaluate the future role of salt marshes as a carbon sink. This thesis describes new methods to apply the triple oxygen isotope tracer of photosynthetic production in a salt marsh. Additionally, noble gases are applied to constrain air-water exchange processes which affect metabolism tracers. These stable, natural abundance tracers complement traditional techniques for measuring metabolism. In particular, they highlight the potential importance of daytime oxygen sinks besides aerobic respiration, such as rising bubbles. In tidal creeks, increasing nutrients may increase both production and respiration, without any apparent change in the net metabolism. In ponds, daytime production and respiration are also tightly coupled, but there is high background respiration regardless of changes in daytime production. Both tidal creeks and ponds have higher respiration rates and lower production rates than the marsh platform, suggesting that expansion of these submerged environments could limit the ability of salt marshes to sequester carbon.

Description: Financial support for my doctoral research was provided by the United States Department of Defense through the National Defense Science and Engineering Graduate Fellowship Program, the National Science Foundation under grant OCE-1233678, and the Woods Hole Oceanographic Institution (WHOI) under grants from the WHOI Coastal Ocean Institute, Ocean and Climate Change Institute, and Ocean Life Institute. WHOI Academic Programs Office also provided funding support for research, through the Ocean Ventures Fund, and for my stipend, as graduate research assistantships including an assistantship from the United States Geological Survey administered by WHOI.

Description: Submitted in partial fulfillment of the requirements for the degree of Master of Science at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution March 1997

Description: Isotopic analyses have been made on four species of foraminifera collected with a PARFLUX Mark VI sediment trap in the Arabian Sea during the 1986 and 1987 monsoons. Two of the species are non-spinose thermocline dwellers (Neogloboquadrina dutertrei, Globorotalia menardii) and two are spinose surface dwellers (Globigerinoides sacculifer, Globigerina bulloides). Individual tests were measured for shape, and analyzed for carbon and oxygen isotopes to document how each species responded to phases of the upwelling system, and to determine the utility of these planktonic foraminifera as upwelling indicators. The oxygen isotopic composition of the two thermocline dwellers remained fairly constant during the seasonal monsoon cycle, showing little to no effect from upwelling whereas the surface dwellers exhibited a wider range of δ18O values. The δ13C signal shows a similar pattern, with the thermocline dwellers showing less variation than the surface dwellers. Results are compared to the empirical model of Kroon and Ganssen (1989) that describes a faunal succession of planktonic foraminiferal species based on isotopic composition and timing of optimum growth conditions. The succession of species based on fluxes was inconclusive and although three of the species showed the same isotopic patterns as described in the model, G. bulloides was not enriched in δ13C, as predicted. The covariance of δ13C and δ180 in this particular species suggests that G. bulloides is isotopically unreliable for reconstruction of monsoon-induced upwelling in the Arabian Sea.

Description: This research was made possible through funding from two sources, the Office of Naval Research (grant #N00014-93-1-0709) and the National Science Foundation (grant #OCE-9311396).

Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Woods Hole Oceanographic Institution and the Massachusetts Institute of Technology June 1995

Description: In marine ecology, the variability of the physical environment is often considered a main determinant of biological pattern. A common approach to identifying key environmental forcings is to match scales of variability: fluctuations of a biological variable at a particular frequency are attributed to forcing by the physical environment at a similar frequency. In nonlinear systems, however, different scales of variability interact and forcing at one frequency can produce variability at a different frequency. The general theme of this dissertation regards the interplay of scales in nonlinear ecological systems, with an emphasis on the mismatch of scales between biological variables and environmental forcings in the plankton. The approach is theoretical: I use simple models to identify conditions leading to such a mismatch. The models are motivated by planktonic systems and focus on one ubiquitous nonlinear ecological interaction, that between a consumer and a resource. This work is organized in three main parts as follows. In the first part, I consider the interaction between a phytoplankton population and a limiting nutrient resource. Most models for this interaction consider all cells as equal and group them under a single variable, the total biomass or cell density. They do not take into account any population heterogeneity resulting from the life histories of individual cells. However, single cells do have life histories: each cell progresses through a determinate sequence of events preceding cell division and the population is distributed in stages of the cell cycle. I incorporate this distribution (i.e. population structure) , as well as observations on resource control of cell cycle progression, into chemostat models for the phytoplankton-nutrient interaction. Simulation results demonstrate that the· population structure can generate oscillatory dynamics under a constant nutrient supply, and that such oscillations are important to population dynamics under a variable nutrient supply. Specifically, for a periodic resource supply, the population displays an aperiodic response with frequencies different from that of the forcing. I then show that a chemostat model without population structure (the Droop equations) does not exhibit this transfer of variability: a periodic nutrient supply produces a periodic population response of exactly the same frequency. In the second part, I consider a predator and a prey that interact and diffuse along an environmental gradient. The model is a reaction-diffusion equation, a type of model used in biological oceanography for planktonic interactions in turbulent flows. I demonstrate that weak diffusion along a spatial gradient may drive an otherwise periodic system into complex temporal dynamics that include chaotic behavior. I provide evidence for a quasiperiodic route to chaos as the diffusion rate decreases. Then, I focus on the spatial properties of the gradient and their consequences for the spatia-temporal dynamics of the system. In particular, I ask: how do the spatial patterns of the populations compare to the underlying environmental gradient in the different dynamic regimes (periodicity, quasiperiodicity, and chaos)? I show that the spatial patterns of predator and prey can differ strongly from the environmental gradient. In the route to chaos, as diffusion becomes weaker, this difference is magnified and the populations display smaller spatial scales. In the work summarized so far, nonlinearity leads to variability in biological variables at scales not present in the environmental forcings. In the third part of this work, I consider another consequence of the transfer of variability in nonlinear systems: the lack of a dominant scale. Patterns that lack a dominant scale but exhibit scale similarity are known as fractals. The characterization of numerical quantities that vary intermittently has motivated a generalization of fractals known as multifractals. Here, I give a first application of multifractals to biological oceanography. I analyze an acoustic data set on zooplankton biomass to describe the distribution in time of the total variability in the data. This distribution is highly intermittent: extreme localized contributions account for a large proportion of total variability. I show that multifractals provide a good characterization of such variability.

Description: The Education Office partially supported this work through the Ocean Ventures Fund. The Office of Naval Research and the National Science Foundation generously supported this work through the following grants to Hal Caswell: ONR-URIP Grant N00014-92-J-1527 and NSF Grant OCE-8900231.

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

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

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

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

Description: The Maestrichtian biogeography of calcareous nannoplankton is investigated in order to characterize paleoenvironmental conditions in the marine photic zone during the latest Cretaceous. Different theories explaining the biospheric turnover at the Cretaceous/Paleocene (KIP) boundary have alternatively suggested or denied substantial environmental perturbations during the last ~500 ky of the Cretaceous. The purpose of this study is to determine whether evidence from calcareous nannoplankton supports a gradual (or stepwise) decline of the photic zone environment presaging the K/P boundary. In order to achieve this goal a detailed quantitative study of the biogeography of calcareous nannoplankton was carried out in three time slices from early and late Maestrichtian. Well preserved material was investigated from five sections: Ocean Drilling Program Site 690 in the Atlantic sector of the Southern Ocean represents the Maestrichtian high southern nannoplankton province. Indian Ocean Sites 217 and 761, South Atlantic Site 528 and the land based, epicontinental section from Millers Ferry, Alabama, represent the Maestrichtian mid-/low latitudinal bioprovince. Quantitative counts were performed on settling slides under the light microscope. Occasionally scanning electron microscopy was employed to resolve taxonomic uncertainties. A pronounced turnover from early to late Maestrichtian occurred in the nannoplankton in high southern latitudes. Numerous taxa (Biscutum boletum, B. coronum, B. dissimilis, B. magnum, Misceomarginatus spp., Monomarginatus spp., Neocrepidolithus watkinsii, Nephrolithus corystus, Octocyclus magnus, Phanulithus obscurus, Psyktosphaera firthii, and Reinhardtites spp.) that are restricted to (or most abundant in) high southern latitudes became extinct in the latest early and earliest late Maestrichtian (between ~72.4 and 70.4 Ma), resulting in a loss of about one third of the early Maestrichtian nannoplankton (corresponding to ~20-25% of the assemblage). It is argued that the extinctions are not a consequence of temperature changes alone. Instead they may be a consequence of increased surface water fertility (and only secondarily due to a temperature decrease). In addition to the extinctions, about another third of all taxa present (Biscutum constans, B. notaculum, Biscutum sp. 1, Chiastozygus garrisonii, C. amphipons, Discorhabdus ignotus, Rhombolithion rhombicum, Scapholithus fossilis, Staurolithites laffittei, Watznaueria barnesae , Zygodiscus compactus, and Z. diplogrammus) disappeared from high southern latitudes during the same time interval (~72.4 and 70.4 Ma) but persisted until the end of the Maestrichtian in lower latitudes. These geographic restrictions are interpreted as a consequence of global cooling. No comparable changes were recorded in mid- and low latitudes in the early Maestrichtian, but this may represent an artifact of sampling. While previous speculations on the paleoenvironmental preferences of some nannofossil taxa have been confirmed, several commonly accepted interpretations of the biogeographic significance of other taxa are contradicted. Micula staurophora seems to be a warm water indicator and abundance peaks of this species cannot be attributed exclusively to diagenetic effects. The biogeographic evolution of the high latitude taxon Ahmuellerella octoradiata does not correlate with temperature trends suggested from stable isotope studies implying that this taxon is not a cold water indicator. Abundance changes of other high latitude taxa (e.g. Nephrolithus frequens, Cribrosphaerella? daniae, Kamptnerius magnificus, and Gartnera&o spp.) correlate roughly with temperature changes, but seem to respond only beyond a certain threshold. No gradual or stepwise extinctions were observed during the last 500 ky of the Maestrichtian. Environmental perturbations as indicated by stable isotope studies (e.g. warming pulse, circulation changes) led to abundance fluctuations of a few taxa, but did not result in any extinctions. This supports previous observations that the extinctions of the calcareous nannoplankton at the K/P boundary were not presaged during the Maestrichtian.

Description: I gratefully acknowledge receiving a Graduate Research Assistantship from the Woods Hole Oceanographic Institution during most of my tenure in the Joint Program. Additional funding from the following sources is also appreciated: a travel grant from the Austrian-American Educational Commission (Fulbright Commission); a Grant-in-Aid from the American Association of Petroleum Geologists (1990); a grant from the Ocean Ventures Fund at W.H.O.I. (1991); a Research Grant-in-Assistance from the Paleontological Society/Margaret C. Wray Trust (1991 ); a Grant-in-Aid of Research from the Sigma Xi Society (1992).

Description: Submitted in partial fulfillment of the requirements for the degree of Master of Science at the Massachusetts Institute of Technology and Woods Hole Oceanographic Institution February 1994

Description: Planktonic foraminiferal flux was collected at four sediment trap locations spanning a 34° latitude range in the North Atlantic during 1988-1990. Satellite-derived sea surface temperature (SST) and CTD data were integrated with time-corrected flux data to determine the effects of seasonal hydrographic changes on foraminiferal production and species succession in surface waters. The thermal structure of the upper water column controls foraminiferal production by regulating levels of phytoplankton production and by directly influencing the preferred temperature habitats of individual species in the community. Sediment traps deployed at the two southern sites (34°N and 48°N) were part of the U.S. Joint Global Ocean Flux Study (JGOFS) and were located in regions influenced by upwelling events induced by mesoscale eddy activity. The timing of maximum foraminiferal production at each trap location coincides with the northward progression of the spring bloom in the North Atlantic. The magnitude of total flux during bloom periods varies considerably with location and is positively correlated with the amount of primary productivity in surface waters. Foraminiferal production is highest at JGOFS 48 and probably results from the greater influence of mesoscale variability in this region on local hydrographic conditions. The upwelling associated with cyclonic cold-core eddies appears to be an effective mechanism for increasing local foraminiferal production in the North Atlantic by enhancing food availability. The preferred production of individual species during upwelling periods may depend on the vertical distribution of chlorophyll in the water column. Seasonal variation in SST is also an important factor controlling the relative abundance of species with preferred thermal habitats. A distinct seasonal species succession occurs at both JGOFS sites but is absent at higher latitudes due to decreases in both faunal diversity and seasonal temperature variations with increasing latitude in the North Atlantic. Foraminiferal :flux data, expressed in terms of relative abundance, is the best direct method of comparing species distributions of living populations with fossil assemblages in the sedimentary record. Preferred temperature ranges for G. ruber, G. bulloides, and N. pachyderma are estimated in this study. The tolerance limits for these species and other ecological inferences derived from these flux data may prove useful for paleoceanographic reconstruction in deep-sea cores. Future studies will be necessary, however, to establish the consistency of these results among different ocean basins.

Description: This research was funded by National Science Foundation Grant No. ATM-9115619.

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

Description: The width of the main lobe of the acoustic backscatter directivity pattern of decapod shrimp (Palaemonetes vulgaris) is examined versus acoustic frequency. Using the distorted wave Born approximation (DWBA) and the geometry of a prolate spheroid, an analytic formula for the backscatter cross section as a function of orientation angle is derived. A directivity pattern is determined from the analytic formula and the width of the main lobe (beam width) is computed. The relationship between beamwidth and acoustic frequency is presented in plots of beamwidth versus ka and L/λ. The model is adapted to experimental limitations of animal motion, discrete sampling and observed side lobe levels. The backscatter directivity patterns of live decapod shrimp, determined experimentally at frequencies between 72 and 525kHz, are presented. A non-monotonic relationship between beamwidth and frequency is illustrated in this study. This relationship is in contrast to the monotonic relationship exhibited when sound scatters off of an impenetrable flat plate. Reasonable agreement is found between the theoretically predicted beamwidths and most experimental data, where the beamwidth was more-or-less oscillatory about a mean value of 19°. The structure can at least be partly explained by scattering theory.