Thomas M. Marchitto - US grants

Under this award the PIs will calibrate multiple paleoceanographic geochemical proxies in several species of benthic foraminifera. This work should contribute significantly to the understanding and application of benthic foraminiferal geochemical proxies. Since such measurements form the foundation of many paleoclimatic studies, improved calibrations are essential and will be widely employed. Proxies include estimators for temperature and salinity (Mg/Ca, d18O), nutrient content (Cd/Ca, Zn/Ca, d13C), pH (d11B), and possibly carbonate ion concentration (U/Ca, Li/Ca). A series of multicore tops and seawater samples were collected from 38 locations between Florida and Cuba in 2002, expressly for this purpose. This collection represents a unique calibration opportunity for several reasons: (1) abundant benthic foraminifera, high sedimentation rates, and large volumes of collected sediment allow for multiple measurements of near-modern specimens; (2) the sites span large ranges of the targeted parameters (e.g., 15 C, 1.9 psu, 0.24 pH); and (3) seawater collected from a Niskin bottle mounted on the multicorer provides accurate determinations of in-situ water conditions, namely salinity, d18O, elemental concentrations, and carbonate system parameters (accurate temperatures are available from accompanying CTD casts).

The use of paired elemental and stable isotopic measurements to reconstruct past changes in climate and hydrology has been growing rapidly yet for benthic foraminifera there are still many outstanding questions about its reliability. Under this award the PIs will use SIMS and SEM techniques in samples from preserved subsections of OCE205 box cores previously collected along the southern flank of Little Bahamas Bank to determine the source of their high Mg/Ca values. These cores were used to calibrate Mg/Ca temperatures higher than about 12 degrees C but there is evidence that the equations are not reproduced in nearby cores from the Florida Straits. SIMS and ICP-MS will be used to measure the variability between tests of benthic foraminiferal species and to compare live (stained) individuals with recent fossil individuals to determine the extent of early diagenesis in altering the primary Mg/Ca signal. Cleaning experiments will show how chemical treatment may affect the distribution and amount of magnesium in the foraminiferal test. This research will help to determine the soundness of this approach when applied to benthic foraminifera and studies of deep ocean hydrography. The results of this study will be presented in classes and for graduate training at WHOI and CU, undergraduate lectures at CU and Sea Education Association, international conferences and peer reviewed journals.

Glacial-Interglacial Carbon Reorganization and Carbonate Compensation in the Pacific Ocean (PI: T. Marchitto)

Past variations in the dissolution and preservation of seafloor calcium carbonate (CaCO3) offer fundamental insights into the workings of the global carbon cycle and the controls on atmospheric carbon dioxide (CO2) levels. According to the 'CaCO3 compensation' hypothesis, there was a net shift of CO2 from the upper ocean into the deep ocean during the last glacial period, resulting in seafloor dissolution of CaCO3 and an increase in whole-ocean pH that compounded the glacial atmospheric CO2 drop. This project will quantitatively test several aspects of the CaCO3 compensation hypothesis, building upon preliminary foraminiferal trace metal and shell weight work in the deep eastern equatorial Pacific (EEP). The project will be divided into the testing of four main hypotheses: (1) carbonate chemistry in the EEP was tightly coupled to atmospheric CO2 over the last glacial-interglacial cycle, with transient carbonate ion [CO3] minima during CO2 drops and [CO3] maxima during CO2 rises; (2) the magnitudes of the Termination I and II (deglacial) [CO3] spikes were roughly equivalent at ~30 umol/kg; (3) [CO3] rises during glacial terminations were associated with the release of CO2 from the deep ocean into the upper ocean, recorded by the carbon isotopic composition (d13C) of benthic and planktonic foraminifera; and (4) regrowth of forests following deglaciation produced secondary [CO3] spikes after Terminations I and II. This work promises to contribute significantly to the understanding of the ocean's role in atmospheric CO2 cycles. Society may ultimately benefit from such knowledge if the oceans hold any hope for sequestration of anthropogenic CO2; or if future increases in CO2 uptake by the oceans impact deep sea carbonate chemistry, resulting in feedbacks on atmospheric CO2. This project will provide extensive learning and training experiences for a new PhD student, a geology undergraduate student, and a professional research assistant.

This award will provide funds to test three hypotheses related to the formation of intermediate and deep water in the Nordic Seas north of Iceland. Specifically, was 1) Denmark Straight Overflow Water (DSOW) formation dampened by freshening of Atlantic Water entering the Nordic Seas through the end of the deglaciation of the Laurentide Ice Sheet, ca. 6,700 cal years ago? 2) Does the middle Holocene interval of greatest DSOW flow correspond to a time of minimal freshwater forcing from north and south and maximal salinity and inflow of the Irminger Current? 3) Was diminished DSOW formation in the late Holocene due to freshwater forcing from the Arctic Ocean by southward advancing Polar Water and sea ice? These hypotheses will be tested via analyses of sediment geochemistry and Mg/Ca, d18O and Cd/Ca of foraminifera assemblages from a suite of North Atlantic deep sea cores, as part of a broader international collaboration including the IPY project WARMPAST. Broader impacts include graduate and undergraduate involvement in the research, a strong international collaborative component and research on a societally-relevant scientific question related to ocean-climate linkages and mechanisms of climate change during the Holocene (last 10,000 years).

This research will test the overarching hypothesis that ventilation of the Southern Ocean caused low-D14C waters to spread northward via Antarctic Intermediate Water (AAIW) in two stages during the last deglaciation. The work follows on recent results from off the southern tip of Baja California that show dramatic drops in intermediate water D14C during each of the two deglacial atmospheric CO2 increases (atmospheric D14C decreases); such observations appear to require the injection of very old waters from a presumed abyssal reservoir.

This work will provide crucial mechanistic evidence tying together established deglacial changes in ocean circulation, atmospheric CO2, and oceanic and atmospheric D14C. Studies are based on bottom- and surface- water D14C reconstructions in a depth transect of sediment cores from the continental margin off southern Baja California and from the southern Chilean Margin. D14C reconstructions are derived from benthic and planktic foraminiferal 14C measurements in sediments with independent climate-stratigraphic age control.

This research adds to the mechanistic understanding of the ocean's role in glacial-interglacial atmospheric CO2 cycles and provides concrete targets for testing of ocean-atmosphere numerical models that are used to project future changes. The project also provides extensive training for a PhD student and a Geological Sciences undergraduate.

Small variations in the Sun's brightness over past centuries may have impacted certain modes of the Earth's ocean-atmosphere circulation, such as the El Niño - Southern Oscillation (ENSO). Some climate model simulations suggest that a persistently brighter sun leads to a colder or more "La Niña-like" state in the tropical Pacific. This response is dubbed the "ocean dynamical thermostat" because the ENSO response tends to counteract the direct warming effect of solar heating. However, paleoclimatic evidence in support of a thermostat response to solar forcing is thus far equivocal and limited to the past 1000 years. Initial results from an ocean sediment core collected off of Baja California appear to support centennial-to-millennial-scale solar forcing of the ENSO system over the past 14,000 years, as well as a slower response related to changes in the Earth's orbit around the Sun. This new study, led by a researcher at the University of Colorado, Boulder, will use additional cores from the same location to further elucidate the response of ENSO to both solar and orbital changes over the past 12,000 years.

This work will test the hypothesis that a major mode of the climate system is more sensitive to solar forcing than is currently simulated by most climate models. If the data generated here support that assertion, they will provide a crucial target for IPCC-class models. This type of data-model intercomparison could ultimately lead to more robust predictions of future climate change, particularly for a system that results in economically and societally important impacts on agriculture, fisheries, and natural disasters. This project will also provide research and training experiences for a PhD student and an undergraduate geology student.

This INSPIRE award is jointly funded by the Information Integration and Informatics Program in the Information and Intelligent Systems Division of the Computer and Information Sciences Directorate, the Marine Geology and Geophysics Program in the Ocean Sciences Division of the Geosciences Directorate, the Arctic Natural Sciences Program in the Arctic Sciences Division and the Antarctic Glaciology Program in the Antarctic Sciences Division in the Office of Polar Programs, and the Office of Cyberinfrastructure.

The critical first step in the analysis of paleoclimate records like ice or sediment cores is the construction of an age model, which relates the depth in a core to the calendar age of the material at that point. The reasoning involved in age-model construction is complex, subtle, and scientifically demanding because the processes that control the rate of material accumulation over time, and that affect the core between formation and sampling, are unknown. Geoscientists approach this problem by treating the core like a crime scene and asking the question: "What physical and chemical processes could have produced this situation, and what does that say about the timeline?" However, the sheer number of possibilities, coupled with the volume and complexity of the climatology data that is currently available and is continually collected, severely limit the scope of these investigations. The goal of this project is to remove this roadblock. This research will lead to an integrated software tool called CScibox, that uses automated reasoning techniques to help scientists analyze ice and sediment cores. It employs a cyberinfrastructure that provides powerful, intuitive tools on a scientist's desktop while taking full advantage of modern data- and computation-intensive computing and networking infrastructure -- including workflow-based computation, parallel execution, distributed systems, cluster machines and the cloud.

CScibox will not only improve the ability of individual geoscientists analyze single cores; it has the potential to transform the field of paleoclimatology by facilitating rapid, reproducible analysis and synthesis of the information in the diverse collections of raw data available in data archives to foster understanding and improved scientific decision making. This will have broad impacts for society by allowing scientists to develop deeper insights into the roles of various factors in the complex relationships that give rise to geological records of the earth's climate that are used in today's models of environmental change. This project also has a broad educational impact. Students involved in the development and implementation of CScibox will develop skills in interdisciplinary research and will learn how to apply computational methodology in a challenging scientific context that has not yet significantly benefitted from developments in information technology. CScibox is designed to be easy to install and use; see the project web site (http://www.cs.colorado.edu/~lizb/cscience.html) for source code, documentation, and examples of its use. Future steps include extending the work to other paleoclimate data, working with geoscientists to make the user interface as intuitive as possible, and holding demos and workshops at geosciences conferences to educate that community about what the tool can do and how to use it.

The goal of this project is to develop an automated system for identification of foraminifera (single-celled organisms with shells). Currently undergraduate workers are often employed to hand pick several thousands of specimens from ocean sediments for each study. This is tedious and time consuming work. By automating the bulk of the identification process, user expertise can be focused on verification and identification of subtle differences.

A visual identification system will be developed in order to automate the identification of target microorganisms. The visual system will incorporate a controllable LED lighting ring used to capture images by illuminating the specimens from several directions, mimicking an important step in the traditional identification process. These images will be used to create a 3D model of the organism in real-time within a second. Computer vision and pattern recognition techniques will be tuned to acceptable recognition rates set by feedback from an expert in paleoceanography who will also provide labeled samples for training and validation. The initial proof of concept study will focus on identifying six species of planktonic foraminifera, and their morphotypes, that are widely used by paleoceanographers.

Over large parts of the globe including the United States, El Niño-Southern Oscillation (ENSO) is a leading cause of climate variations from one year to the next. Regional impacts can be catastrophic, including drought, wildfires, flooding, mudslides, and fisheries collapse. Furthermore, ENSO has a significant influence on global mean air temperature, and a strong El Niño event contributed to the record warmth experienced during 2015-2016. Despite the clear importance of ENSO to modern climate variability, the computer models used to make climate projections offer no clear consensus on ENSO's future behavior. The various computer models can be improved, with broad benefit to society, by evaluating their ability to simulate past time periods when ENSO behaved differently. However, that approach requires more and better paleo-ENSO observations from geologic archives like ocean sediment cores. This project aims to ground-truth a new method to reconstruct ENSO variability during the geologic past. It relies on the fact that the chemistry of microscopic seashells (foraminifera) reflects the temperature at which the shell formed. By measuring the chemistry of numerous individual shells, researchers will be able to reconstruct the variability of sea surface temperature in regions where temperature is dominated by the ENSO phenomenon. This project will also provide extensive learning and training experiences for a female PhD student and two undergraduates.

More specifically, the work proposed here will develop a new proxy for sea surface temperature variability, "wet chemistry" Mg/Ca ratios in individual planktic foraminifera, for probing ENSO variance during the past. Preliminary measurements and Monte Carlo simulations show that individual foraminifera from well-preserved sediments are reliable recorders of calcification temperature. Past changes in ENSO variance should therefore leave imprints on the distributions of individuals' Mg/Ca at carefully chosen core sites. In the tropical Pacific however, seafloor dissolution of CaCO3 and low sedimentation rates present dual challenges to this method, so it will be important to ground-truth the approach using late Holocene sediments. This work will use single-specimen Mg/Ca in two species of planktic foraminifera to test two main hypotheses: (1) The observed lowering of planktic foraminiferal Mg/Ca in partially dissolved samples is caused by a percentage Mg loss from each shell, and not by a molar amount lost, nor by breakup and loss of higher-Mg individuals formed in warmer waters; (2) Regardless of the exact nature of the dissolution artifact, information about temperature variability (including ENSO) is retained in single-specimen Mg/Ca distributions from tropical Pacific core top sediments above the lysocline. Hypothesis 1 will be tested using four core tops from a depth transect on Ontong Java Plateau in the western tropical Pacific, and Hypothesis 2 will be tested using 10 additional core tops spanning a range of annual and interannual temperature variability regimes across the tropical Pacific.

Changes in the amount of sea ice and low salinity surface water (together called freshwater) that flow from the Arctic Ocean to the North Atlantic have global ocean circulation and climate impacts. The research involves analysis of the timing and consequences of the opening of the western route for Arctic freshwater flux after the retreat of glacier ice at the end of the last glaciation. The Arctic freshwater flows through the western route to the Labrador Sea, which is a critical area of deep ocean convection. Diverse analyses of sediment cores from northern Baffin Bay and computer modeling will be used to document and explore the large changes in sea-ice cover, Arctic freshwater flux, ocean circulation, marine productivity, and ocean acidification over the last 11,000 years that are associated with opening of the western freshwater route. An important component of the research is to study the history of the North Water Polynya (NOW), an oasis of high productivity and low sea-ice cover that forms where the Arctic freshwater enters northern Baffin Bay. The productivity of the NOW owes to the high nutrient content of the Arctic freshwater and to the blockage of Arctic sea-ice floes by the constricted channels forming the gateway. The NOW is a hotspot of biological productivity that has attracted humans to the area for millennia and sustains Arctic communities today. Both the history of freshwater flux via the western freshwater route and the history of the NOW are very poorly known, yet the behavior of this system is poised to change in response to continuing reductions in Arctic sea-ice cover. The understanding of how the opening of the western route of Arctic freshwater and the initiation of the NOW have changed through time will provide context to understand how these systems will affect the Arctic systems and global climate in future.

The project uses existing sediment cores from the NOW polynya, and areas upstream of and downstream from it using both novel (nutrient tracers from Inductively Coupled Plasma Mass Spectrometry and algal biomarkers) and traditional (quantitative X-ray mineralogy, foraminiferal assemblages, stable C and O isotopes) proxies, climate modeling with the Community Earth System Model (CESM) and Glacial Isostatic Adjustment modeling and chronology development (radiocarbon and paleomagnetic secular variation) to test three hypotheses: Hypothesis 1: The opening of the western freshwater route of the Arctic-Atlantic throughflow changed the freshwater outflow to the North Atlantic with consequences for the Atlantic Meridional Overturning Circulation (AMOC). Hypothesis 2: Significant shallowing of the CAA channels by glacial isostatic uplift has changed the composition of the Arctic outflow with consequences for carbonate preservation and the AMOC. Hypothesis 3: The NOW formed in the middle to late Holocene as a consequence of increased Arctic sea-ice. The project is an international effort involving Canadian and EU cooperation and foreign graduate student interaction with CU faculty and scientists. It will provide support and mentoring for a female post-doc who will receive training in novel biogeochemical laboratory techniques. A PhD student will work on the CESM modeling. Several undergraduate students will receive training and participate in the research.

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.