Rebecca Robinson - US grants

Given the hypothesized role for the marine nitrogen cycle in governing carbon cycling, reconstructions of nitrogen biogeochemistry are critical to improve our understanding of global geochemical cycles. Scientists from Harvard University and the University of Rhode Island propose to complete their development of a new analytical method to achieve reliable, high-throughput analyses of nitrogen isotope composition (del15N) values of sedimentary porphyrins. Values of porphyrin-del15N should reflect both the overall state of the nitrogen cycle, and in particular, conditions of nutrient supply and demand in the surface ocean. In addition, the scientists plan to measure the nitrogen isotopic fractionation in prokaryotes and eukaryotes, Last Glacial Maximum-to-Holocene sediments from sites characterized by different nitrogen dynamics, and analyze Mediterranean sapropels and Cretaceous Ocean Anoxic Events. The goal of this research is to help constrain the global importance of denitrification and nitrogen fixation.
As regards broader impacts, results from this research will improve our understanding of water column biogeochemistry which will be critical in predicting the response of the nitrogen cycle to climatic events. One graduate student at Harvard University and one undergraduate student from the University of Rhode Island will be supported and trained.

ABSTRACT

Collaborative Research: N and Si Dynamics in the Glacial Southern Ocean


The Southern Ocean plays a key role in regulating past and present atmospheric CO2 concentrations through primary production (carbon pump) and ventilation of the CO2-rich deep waters. Evaluating the importance of the carbon pump through time is of primary importance to understanding climate change. One hypothesis proposed to explain the observed lower glacial CO2 concentrations is that changes in the supply of Fe and water column stratification influenced biological productivity in the Southern Ocean which altered the nutrient composition of waters flowing from the Southern Ocean to low latitude oceans. Changes in biological production are difficult to assess but two new tools, the Si and N isotopic compositions of diatoms, now allow estimates of nutrient consumption over time. These techniques will be applied to fossil diatom samples from existing sediment cores to evaluate changes in nutrient use in the Southern Ocean during the past 2 glacial events. Combining theses new results with existing proxies, such as biogenic silica fluxes and dust/Fe records, will provide estimates of past nutrient dynamics in the Southern Ocean and test the hypothesis of changes in Southern Ocean and global production through nutrient use. This research will lead to a better understanding of how nutrient dynamics and biogeochemical cycling affects the climate of the Earth. The broader impacts include interaction with local K-12 teachers to help younger students understand past and present climate changes. The project will also support the early careers of two young women scientists who have not had prior NSF funding as well as provide training of both graduate and undergraduate students. The results of this project will be broadly disseminated and data will be posted on web databases such as the National Geophysical Data Center. This project is jointly funded by the Ocean Sciences Marine Geology & Geophysics Program, Polar Programs Antarctic Earth Sciences Program and Emerging Topics in Biogeochemical Cycle.

DESCRIPTION (provided by applicant): The adult central nervous system (CNS) has a very limited intrinsic ability to regenerate after injury. Traumatic brain injuries or neurodegenerative diseases cause neuronal cell leads to long-lasting functional impairments. The profound effect observed from these injuries results from a series of events that occurs immediately following injury and persists for several weeks. These events take place not only at the intrinsic level via intracellular signaling pathways but at the extrinsic level as well. Recent evidence indicates that in order to promote significant regeneration in the damaged CNS, a combinatorial approach addressing both the intrinsic and extrinsic barriers to regeneration is necessary. Our goal is to understand how modification of the post-injury microenvironment will affect nerve regeneration. Specifically, our hypothesis is that transplantation of neural progenitor cells (NPCs) into the retina combined with administration of an epidermal growth factor receptor (EGFR) inhibitor via an engineered construct will enhance nerve regeneration in an optic nerve axotomy model. This hypothesis is based on two observations: (1) NPCs can differentiate into neurons and incorporate into existing neural networks, and (2) administration of EGFR inhibitors to damaged optic nerve and spinal cord result in regeneration of injured neurons. We will use an optic nerve crush injury model to determine the effectiveness of our treatment. At the site of injury, we will implant a polymer construct allowing controlled delivery of the EGFR inhibitor, followed by injection of NPCs into the vitreous of the eye. Our specific aims are to: (1) develop and characterize a drug delivery system for the controlled release of the EGFR inhibitor, (2) develop and characterize a construct for in vivo delivery of the inhibitor at the injury site, and (3) assess the effects of a combinatorial treatment approach on nerve regeneration in vivo in an optic nerve injury model. Combinatorial treatments provide a promising new option for therapy in CNS repair. We believe this approach in conjunction with cell transplantation therapy will provide important information regarding nerve regeneration in the mature >CNS. Accomplishing the specific aims outlined will provide an understanding of nerve regeneration and the glial scar microenvironment in vivo. Relevance: The central nervous system has very limited repair capabilities. This limitation is due to neuronal cell death and a post-injury cellular environment that is not favorable to regrowth of nerves. A combinatorial treatment of transplantation of neural progenitor cells and administration of an epidermal growth factor inhibitor can address both of these factors simultaneously, thus providing a new avenue for therapy.

An amino acid-based isotopic method for studying the dynamics of ancient ecosystems

PI: David E. Fastovsky; Co-PIs: Rebecca S. Robinson; Steven L. D¡¦Hondt

The idea behind this proposal is to develop a method by which we can measure the nitrogen isotopic composition of amino acids from fossil bones and teeth. It has been shown that the amount of 15N/14N (which we measure as ?Ô15N) increases each trophic step in a food chain. This means in effect that the 15N/14N ratio is lowest among primary producers (in the terrestrial realm, this generally means plants), and increases in those organisms that eat the primary producers, and increases even further in those animals that eat the animals that eat the primary producers. So the ?Ô15N signature is actually a way to measure at which levels long-extinct organisms functioned in long-extinct ecosystems.
The mechanics of the development of this technique, which is in fact the point of this proposal, is fraught with problems. Most significant among these are contamination and volume. The contamination problem is the same one that plagues all studies of ancient molecules: there is a very real possibility that the ?Ô15N numbers that we obtain could come from younger organisms ¡V possibly even those living today ¡V and if so their ?Ô15N signatures would obviously be wrong. To avoid this possibility, we would like to obtain our nitrogen from known molecules. We have chosen to use an amino acid signature profile for each tooth, which would tell us that we are at least looking at ancient, preserved molecules. This takes us to the volume problem, because if we are looking at the ?Ô15N signature for just a particular series of identifiable amino acids, then we are obviously required to deal with much smaller samples than if we were looking at the bulk, or total, ?Ô15N signature of a particular tooth or bone. Moreover, during the degradation that takes place as molecules age, certain amino acids are preferentially maintained while others are lost. By targeting of specific amino acids (preferably more than one) and tracing their ?Ô15N signatures through a food web, we will provide a much more reliable picture of dietary relationships than traditional bulk-organic methods allow.
The fractionation of nitrogen isotopes as a record of trophic position has been repeatedly demonstrated for both marine and terrestrial ecosystems. With the development of the technique this proposal supports, we anticipate having a precise isotopic tool that identifies (and avoids) problems due to alteration or contamination of fossil material. For this reason, the technique has broad applications for studying ancient ecosystems.

Recent work has demonstrated the importance of nutrient supply in driving export productivity events in the eastern equatorial Pacific and stimulating denitrification downstream. However, this view is limited to the last 30,000 years. On orbital timescales, variations likely relate to changes in overturning rate in the high latitude Southern Ocean. On million-year timescales, it is hypothesized that the shoaling of the ventilated thermocline, due to global cooling, strengthened the connection between high and low latitude biogeochemistry.

This study, led by a researcher from the University of Rhode Island, seeks to understand how variations in nutrient supply, export productivity, oxygen demand, and water column denitification relate to large scale changes in ocean circulation on long timescales. Longer records are essential in order to evaluate the significance of high latitude nutrient supply in driving low latitude biogeochemical shifts, and will provide insight into both the cyclic changes occurring on orbital timescales and longer timescale shifts. The study focuses on two key questions: 1) What is the role of nutrient supply from high latitudes in driving documented episodes of high productivity in the eastern equatorial Pacific?, and 2) What is the role of enhanced export and oxygen demand in modulating water column denitrification in the eastern tropical Pacific? The study builds on available downcore data and add nitrogen isotope and export productivity records from the Southern Ocean and tropical Pacific across the last 3 million years. Records from a series of sites across the tropical Pacific will result in a stacked record of denitrification changes and an estimate of nutrient supply changes in the eastern equatorial Pacific. The Southern Ocean records will be used to estimate preformed nutrient concentrations at the origin of mode waters. The new records will be incorporated into a larger international collaboration that aims to develop a coherent picture of how climate-driven circulation changes in the Plio- Pleistocene impact the global cycling of nitrogen and carbon. This project also represents a first step toward developing a complete Cenozoic history of nutrient cycling and export productivity in the eastern equatorial Pacific.

Broader impacts include education and training of a graduate student, public outreach activities, and international collaboration with a French scientist.

Increasing atmospheric CO2 is recognized as one of the world's most pressing environmental challenges. Many details of this challenge require further scientific understanding, including the feedbacks between ocean circulation, atmospheric CO2 and climate. It is generally accepted that CO2 transfer between the ocean and atmosphere has driven the co-variation of CO2 and climate over the past 800,000 years. However, there is no consensus on what drives these transfers principally because there is a lack of data to test proposed mechanisms. The proposed project is directly aimed at understanding the relationship between ocean circulation and climate, particularly atmospheric CO2, during the Last Glacial Maximum (LGM, ~18,000 years ago). The improved understanding of the relationship between ocean circulation and climate is societally important because future changes in the circulation are likely to have large effects, such as changes in the climate of northwest Europe, the position of the Intertropical Convergence Zone (ITCZ) and the uptake of anthropogenic CO2 into the ocean. Scientific understanding of the controls of ocean response to climate change will inform the societal response to anthropogenic CO2. Additionally, this project will support full participation and leadership development of a female Ph.D. student in science.

More specifically, the work focuses on laboratory analysis of sedimentary pore fluids collected during a recent research expedition in the North Atlantic, and interpretation of the data. This analytical and interpretative work is aimed at addressing the following hypotheses:
- During the Last Glacial Maximum (LGM), deep-ocean density stratification in the North Atlantic was dominated by salinity variation rather than temperature variation.
- During the LGM, North Atlantic deep water was a mixture of water originating in the North Atlantic and water originating in the Southern Ocean.
- The present relationship between d18O and water density existed during the LGM, enabling use of benthic carbonate d18O to infer density.
- The relative balance of the key nitrate (NO3-) removal processes was similar to that of today, as was the average NO3- concentration in deep water.
- Deep water in the LGM North Atlantic was dominated by low preformed nutrient water.
- A significant fraction of atmospheric pCO2 reduction during the LGM was due to the low pre- formed nutrients in the Atlantic.

The analytical work includes, high precision determination of chloride concentrations by titration, the development of a new density based method of paleo-salinity determination and the isotopic analysis (O and N isotopes) of nitrate. This data will be used to constrain inverse diffusion models to infer bottom water properties of the LGM western North Atlantic.

Collaborative Proposal: A field and laboratory examination of the diatom N and Si isotope proxies: Implications for assessing the Southern Ocean biological pump

The rise in atmospheric carbon dioxide concentrations and associated climate changes make understanding the role of the ocean in large scale carbon cycle a priority. Geologic samples allow exploration of potential mechanisms for carbon dioxide drawdown during glacial periods through the use of geochemical proxies. Nitrogen and silicon isotope signatures from fossil diatoms (microscopic plants) are used to investigate changes in the physical supply and biological demand for nutrients (like nitrogen and silicon and carbon) in the Southern Ocean. The project will evaluate the use the nitrogen and silicon isotope proxies through a series of laboratory experiments and Southern Ocean field sampling. The results will provide quantification of real relationships between nitrogen and silicon isotopes and nutrient usage in the Southern Ocean and allow exploration of the role of other factors, including biological diversity, ice cover, and mixing, in altering the chemical signatures recorded by diatoms. Seafloor sediment samples will be used to evaluate how well the signal created in the water column is recorded by fossil diatoms buried in the seafloor. Improving the nutrient isotope proxies will allow for a more quantitative understanding of the role of polar biology in regulating natural variation in atmospheric carbon dioxide. The project will also result in the training of a graduate student and development of outreach materials targeting a broad popular audience.

This project seeks to test the fidelity of the diatom nitrogen and silicon isotope proxies, two commonly used paleoceanographic tools for investigating the role of the Southern Ocean biological pump in regulating atmospheric CO2 concentrations on glacial-interglacial timescales. Existing ground-truthing data, including culture experiments, surface sediment data and downcore reconstructions, all suggest that nutrient utilization is the primary driver of isotopic variation in the Southern Ocean. However, strong contribution of interspecific variation is implied by recent culture results. Moreover, field and laboratory studies present some contradictory results in terms of the relative importance of interspecific variation and of inferred post-depositional alteration of the nutrient isotope signals. Here, a first order test of the N and Si diatom nutrient isotope paleo-proxies, involving water column dissolved and particulate sampling and laboratory culturing of field-isolates, is proposed. Southern Ocean water, biomass, live diatoms and fossil diatom sampling will be conducted to investigate species and assemblage related variability in diatom nitrogen and silicon isotopes and their relationship to surface nutrient fields and early diagenesis. Access to fresh materials produced in an analogous environmental context to the sediments of primary interest is critical for making robust paleoceanographic reconstructions. Field sampling will occur along 175°W, transecting the Antarctic Circumpolar Current from the subtropics to the marginal ice edge. Collection of water, sinking/suspended particles and multi-core samples from 13 stations and 3 shipboard incubation experiments will be used to test four proposed hypotheses that together evaluate the significance of existing culture results and seek to allow the best use of diatom nutrient isotope proxies in evaluating the biological pump.

This project seeks to reconstruct changes in the position of the Subtropical Front (STF) in the Agulhas region of the Southern Ocean south of Africa over the last 1.5 million years. Ocean currents play a significant role in the distribution of heat and salt in the global ocean. Ultimately, changes in these currents influence marine nutrient distribution, ocean uptake of atmospheric CO2, and global climate. South of Africa, the Agulhas Current moves warm, salty water from the southern Indian Ocean into the South Atlantic Ocean. However, during intervals of near-global cooling, it is thought that the amount of this warm water escaping around Africa decreases or is even stopped, cutoff by a northward migration of the STF. Because a northward shift of the STF has the potential to both expand the surface area of the Southern Ocean and limit water exchange between the Indian and Atlantic Oceans, the region south of Africa is an important climate target to advance our understanding of how the physical movements of the STF may impact regional and global climate. Migrations of the STF are relatively poorly resolved for the past 1.5 million years, in part due to a prior lack of sediment cores in the critical region of front migration. This research combines multiple proxy records of ocean changes at a location sensitive to STF position to study how STF movement may have influenced ocean circulation and CO2 uptake. The project will support two female PIs (one early career) as well as two graduate students and several undergraduates. Broader public outreach is planned in the context of K-12 classroom and web-based materials.

The investigators will generate an integrated reconstruction of upper ocean dynamics along the Subtropical Front over the last 1.5 million years from sediments in a new International Ocean Discovery Program core (Site U1475) recovered from the southern Indian Ocean at a location well suited to monitor STF position. They will use multiple sediment proxies to generate an integrated reconstruction of upper ocean dynamics along the STF using reconstructions of water temperature, export production, and nutrient utilization. North-south migrations of the STF have been hypothesized to control movement of water through the Indo-Atlantic Gateway, an exchange that has important implications for the air-sea balance of CO2 and the strength of the meridional overturning circulation of the Atlantic. The resulting data will be used to document the location of the STF with respect to the core site and the nutrient status of the subantarctic region of the Southern Ocean during episodes of expansion. Specifically, the investigators will produce new high-resolution records of water temperature (using Uk37, TEX86, and foraminiferal census counts using a Modern Analog Technique), export production (using total organic carbon, biogenic silica, and total alkenone (C37tot) content), and nutrient dynamics (using foraminiferal-bound organic matter d15N) for the last 1.5 million years to constrain the history of the STF and its response to climate change. Emphasis will be placed on the Mid Pleistocene Transition (MPT), the time interval between 1.25 and 0.7 million years ago when the dominant periodicity of climate cycles changed from 41 kiloyears to 100 kiloyears in the absence of substantial change in orbital forcing. Reconstructing the location of the STF across the MPT is key to understanding the role that STF migration may have played in altering the Southern Ocean biological pump (with consequent changes in atmospheric CO2).

This award will provide funds to acquire a bench-top scanning electron microscope (SEM) system and upgrade an aging laser ablation (LA) system that is paired with an existing inductively-coupled plasma mass spectrometer, both of which enable analysis and imaging of microscopic geological samples, including microfossils, volcanic fragments, and natural and synthetic glasses, rocks, and minerals. The two requested instruments, which may work in tandem or independently in the laboratory, will vastly enhance and complement the established research capabilities at the University of Rhode Island. Each of the principal investigators has a robust research program that will see immediate benefit to NSF research projects within the Geosciences. These instruments will contribute to the professional development of numerous undergraduate and graduate students, support the growing research program of an early-career scientist, and enable a broader platform of collaboration among Earth scientists across many disciplines among Rhode Island institutions.

Upgrade of the LA system maintains and improves functionality of an established and productive laboratory, whereas acquisition of a compact SEM system adds new imaging capabilities in addition to enhancing and informing the use of the LA system. Measurements and images enabled by these instruments positively impact the PIs' endeavors to address key hypotheses across a range of Earth science fields, including (1) the role of volatiles and trace elements in plate tectonic cycles, (2) fragmentation processes during explosive and effusive submarine volcanism, (3) the mechanisms by which Earth's interior produces a diversity of magma compositions, and (4) the roles of preservation, taxonomy, and inherent chemical heterogeneity in microfossil records of past climate conditions.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

The Earth?s flow of energy ? from animals, to plants, to microbes ? is dictated by electron transfers, namely, moving electrons from one molecule or element to another to gain energy. Photosynthesis is perhaps the most familiar such reaction, where the electrons from carbon dioxide and water are used to make oxygen and sugar. However, before the appearance of oxygen-generating metabolisms, early life metabolism was governed by different electron transfer reactions ? most of these involving metals because of their ability to readily donate and accept electrons. As a result of this early evolution, metals still play a central role in microbial life, as essential elements in enzymes. One such important metal is manganese (Mn), which is particularly good at donating and accepting electrons given that it can be in three different forms in the ocean. One form of Mn is a solid Mn-oxide, which is very reactive and almost as strong an oxidant as oxygen itself. This form of Mn is completely generated by bacteria, but we still know little about how bacteria do this, or why! One good place to understand these Mn reactions is in areas where oxygen is not present, because there, Mn reactions may dominate. The Gulf of Mexico is a region where oxygen concentrations have been decreasing steadily due to over-enrichment of nutrients from anthropogenic sources. This system is ideal for examining Mn reactions under low oxygen conditions, so in this project, how Mn reacts under different levels of oxygen will be determined. Scientists from the University of Rhode Island and Texas A&M University will also specifically target the bacteria that make these solid Mn oxides, to try and understand the mechanism of formation. Finally, the scientists will try to measure where the Mn is coming from and where it is going, to get a better idea of how Mn may undergo a complete reaction cycle. Understanding how metals cycle in the ocean is central to understanding life on Earth, as the inventory of metals has been subject to shifts in chemistry, like changing oxygen conditions, over the Earth?s history. A science communications student, an artist at sea, and a videographer will be incorporated into cruise activities to link the science with public outreach. This project will support three graduate students, undergraduate students, and two early career researchers. This project will focus on recruitment of underrepresented minorities to provide an introduction to STEM research and field work.

At present, scientists from the University of Rhode Island and Texas A&M University have developed the chemical techniques to deconvolute manganese redox cycling in marine environments but have yet to thoroughly apply these new methods in diverse environmental systems or to couple manganese speciation and cycling with that of other elements. Here, the scientists propose to fully speciate manganese in the Gulf of Mexico, evaluating the formation, prevalence, and bioavailability of Mn(III)-L compounds and the role of microbes in facilitating Mn(III)-L and Mn oxide formation. In particular, the scientists seek to examine the stability of Mn(III)-L complexes across seasonal, salinity and oxygen gradients and to characterize both terrestrial and biotic Mn(III)-binding ligands. We hypothesize that Mn cycling, particularly in seasonally anoxic and suboxic zones, is intricately but enigmatically linked to the cycling of other redox sensitive species, including nitrogen and organic carbon compounds. This study will study these dynamics in the Gulf of Mexico, which has gradients in (1) productivity on a seasonal cycle, (2) salinity and terrestrial input via its tributaries and (3) a dynamic and seasonal oxygen regime. All of these gradients profoundly impact the redox chemistry of Mn and other elements and thus must be taken into account to create an accurate framework for understanding coupled redox cycling. In conducting this research, not only will we broadly elucidate the marine manganese cycling, we will also highlight previously cryptic chemical dynamics that drive the formation and dissipation of oxygen minimum zones in fragile coastal ecosystems.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

Samples of seafloor rocks, cores, corals, hydrothermal vent fluids and chimney deposits, sediments, other materials are valuable scientific resources that are collected at great expense on scientific oceanographic expeditions. Some samples come from shallow, near-shore environments of unusual and ephemeral character and others come from mid-ocean ridges, seamounts, the abyssal plain, the roots of volcanic islands, and continental shelves. Many samples come from inaccessible places miles below the surface of the ocean and are retrieved from the seafloor by specialized robotic vehicles, human occupied submersibles, coring devices, and/or rock dredges. To preserve these valuable samples and make them available to other scientists for studies not envisioned by the original collectors, the Marine Geology and Geophysics Program of the Division of Ocean Sciences of the National Science Foundation funds four professionally run repositories that house samples collected by seagoing scientists. This award funds the curation, storage, and distribution of marine seafloor samples by the University of Rhode Island's Marine Geological Sample Laboratory. Samples are distributed upon request to scientists and educators wishing to better understand the ocean basins, the distribution of its resources, and how the Earth works.
Over the past 3 years, this repository has distributed almost 800 samples of seafloor material to US and international scientists to advance our knowledge of the seafloor, ocean crust, mantle, seafloor volcanism, and the history of ocean chemistry and Earth's climate. Samples from the repositories have been used to pioneer new analytical techniques and provide important insights into the seafloor, the continental margins, and sub-oceanic magmatic processes. Broader impacts of the work include training of graduate students in curation and the techniques used to collect samples, graduate level course involvement, and public outreach via tours for primary and secondary school groups, local community organizations, and other interested parties. This award also provides support for an essential piece of marine geology infrastructure and provides support to an institution in a state that does not receive a significant amount of Federal funding (i.e., an EPSCoR state).

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.