Christopher Charles - US grants

9316691 Charles An impressive network of oxygen and hydrogen isotopic records from ice cores, lake cores, deep sea cores and tree rings can now be compiled for a variety of time periods. These records potentially offer quantitative insight to past changes in climate processes, but their true climatic significance cannot be fully realized without knowledge of the fundamental driving forces for isotopes in precipitation. Simple air parcel models cannot account for the range of processes which control regional isotope distributions, and therefore the coupling of isotope tracers to a general circulation model (GCM) represents a necessary first step towards a more complete understanding of the isotope signals recorded in the geologic record. We propose to investigate these isotopic records by means of the Goddard Institute for Space Studies General Circulation Model (GISS GCM). The major issue we will pursue is how the changes in sourcewater characteristics, air mass trajectories, and air mass mixing-- all factors which must have varied over climate cycles with the major components of the climate system--affect regional isotopic distributions. Over the next two years, we will conduct a number of paleoclimatic simulations to determine the sensitivity of the model moisture source contributions and isotope fields to specific changes in boundary conditions (ice sheets, sea ice, sea surface temperature, etc.) Results of the paleoclimatic simulations will be compared to the observations, which we will compile. This data-model comparison will help identify the components of Northern Hemisphere climate system that are most important in shaping the isotope records. The comparison will also provide a test for the reliability and sensitivity of the GCM's hydrological cycle.

9503931 Charles This collaborative field program in the sub-Antarctic ocean involves researchers from University of Florida, Georgia Tech, Scripps Institution of the University of California at San Diego and Lamont-Doherty Earth Observatory of Columbia University. The objectives of the research cruise planned for early 1996 are to sample sediments deposited within various water masses of the Antarctic ocean for studies of climatic and oceanographic variations over the past few hundred thousand years. The Antarctic region has a major influence on global oceanography, for it is here that many of the intermediate and bottom waters of the world ocean are formed, and thus the heat and chemical budgets of the ocean are dependent in a number of ways on changes in climate and oceanography here. The record of these variations is recorded in microfossils preserved in the sediments, and this group of investigators will sample sediments from all of the major intermediate and deep water masses of the region. Their research will include faunal, chemical and pore water analysis of the sediments recovered to construct chronologies of change in a large number of parameters throughout the last two or three glacial cycles (as far as their piston cores will reach). In addition, the data they collect will be used to define suitable sites for drilling by JOIDES Resolution in 1997 or 1998 at sites which have been highly ranked as part of the Ocean Drilling Program, the international program for scientific ocean drilling of which NSF is a major sponsor. Though presently considered a high drilling priority, these Antarctic sites do not presently have sufficient site survey information to allow precise hole locations, and this project will provide those necessary geophysical and sedimentological data. ***

This award will support the generation of planktic and benthic foraminiferal stable isotope data, and concentration of ice-rafted detritus, at multi-century-scale resolution for sediment cores from the Southern Ocean Spanning the last half million years. The data will be used to determine how millenial-scale variability has evolved during the late Pleistocene and its relation to orbital forcing.

This award will support research on annually-laminated lake sediments (varves) to provide detailed records of past climate from the Great Lakes region of the United States over the past 12,000 years. Such varved sediment records can prove a treasure trove of information critical to addressing issues of drought frequency and abrupt climate change in the region.

By constructing continuous oxygen isotope time series of Holocene climate variability for lead dated sediment records from individual lake sites, the investigators will evaluate climatic controls on oxygen isotope records with existing regional instrumental records of temperature, precipitation amount, and dominant atmospheric circulation patterns. By focusing on high-resolution oxygen isotope analyses across discrete Holocene climatic events, the researchers will establish the characteristic and rate of past natural climate variability.

0216643
Charles
This Major Research Instrumentation award to University of California at San Diego provides funds for acquisition of an isotope ratio mass spectrometer for shared use in studies of climate and global climate change, ocean sciences and anthropology at the Scripps Institution of Oceanography and other UCSD departments. The award is supported by the Division of Ocean Sciences at NSF. UCSD will provide cost-share support from non-federal funds for 33% of total project costs.
***

Funds are provided for a cruise to collect a suite of cores from the Southwest African margin to construct several detailed depth transects to monitor the full dynamic range and stratal geometry of the mid depth water masses. The post-cruise proposed research program will establish the sensitivity of Southern Hemisphere ocean circulation to major instability during the Pleistocene and Holocene by mapping changes in the distribution of radiocarbon in benthic foraminifera over specific abrupt events to deduce the ventilation history of mid-depth water and help delineate northern vs. southern sources.

ABSTRACT

OCE-0454870


Despite clear evidence for iron limitation in the modern ocean, the sedimentary record of "paleoproductivity" has not provided a link between changes in dust flux and regional/global productivity. A scientist from Scripps Institute of Oceanography will examine the relationship between trace element chemistry and paleoproductivity through analysis of biogenic opal. Results from a pilot study wherein a newly developed technique was used to separate and purify sedimentary opal from detrital contaminants indicated that this mineral phase faithfully records dissolved oceanic concentrations of cosmic ray-produced radionuclides (10Be, 26Al) and trace elements (Fe, Mn, Ti, Zn). Thus, one sedimentary phase within the sediment column could be used to compare directly a proxy for aeolian input of micronutrients (Fe, Ti) with a proxy for production (26Al/Al ratios). As part of this project, the PI will continue to extend the pilot study using sediment cores from the Southern Ocean diatomaceaous ooze belt to provide an integrated assessment of paleoproductivity in this region. In addition, the temporal records of trace elements and cosmic nuclides will be determined in sediments from the equatorial Pacific and the southeastern Atlantic, two contrasting regions of upwelling and productivity. These areas are expected to differ in their response to global climate fluctuations and micronutrient input, thereby providing a comparison/contrast with records obtained from the Southern Ocean. It is anticipated that this study will reveal how the chemistry and biological productivity in the marine environment has changed with climate in the past.

In terms of the broader impacts, this study will document to use of biogenic opal as a recorder of dissolved trace element concentrations and cosmic ray-produced radionuclides, as well as provide the ocean science community with a new techniques for separating biogenic opal from other detritus within a sediment sample. Results from this study will be included in a new climate exhibit dedicated to how scientists use the marine sedimentary record to infer about past climate entitled Nature's Time Capsule opening in the Fall of 2006 at the Scripps Explorers Galley in the Birch Aquarium. Training and support of graduate and undergraduate students has been included in the study.

Chris Charles and Rick Fairbanks

Submerged fossil coral reefs are both a diagnostic measure of past sea level change and an unparalleled archive of tropical climate change. In many regions of the tropics, the submerged reef sequences were deposited throughout the major natural climate experiment of the last deglaciation. However, thus far, successful surveying and sampling of these reefs has only been achieved in a few locations. This award will equip a cruise to the Seychelles for the purpose of surveying and drilling submerged reefs in the western Indian Ocean that were likely deposited over the last 50,000 years. The objectives of the cruise activities are three-fold: (1) To understand the structure, age, and extent of fossil reefs--in essence, the response of the reefs to the known sea level variations of the last ice age cycle (2) To acquire coral samples that captured the state of the surface during times of greatly different forcing. (3) To acquire samples that allow paired radiocarbon and U/Th dating and that therefore might be used to calibrate the radiocarbon time scale. The operations, involving CHIRP seismic profiling and dredging, will be conducted off the eastern flank of the Seychelles Bank. This region features bathymetric (and other anecdotal) evidence for submerged reef terraces. The cruise will serve as an ideal platform for student training and will include two underrepresented minority students. This project is supported by the Marine Geology & Geophysics Program of the Ocean Sciences Division.

One of the most pressing questions in the projection of future climate change is the issue of whether the variability of climate depends on the average state of the climate system. A large part of this question involves the behavior of the El Nino/Southern Oscillation phenomenon: for example, do El Nino events become stronger and more frequent as the climate warms? This project will address this question by developing a record of ENSO and tropical Pacific climate that spans the last 6,000 years - a period characterized by known changes in the seasonality of solar radiation. These reconstructions will test whether the ENSO system was forced by these solar radiation changes and if so, how and when changes occurred. To reconstruct ENSO behavior, the skeletal composition of ~12 fossil corals that were collected on the beaches of several of the Line Islands in the central tropical Pacific (Palmyra, Fanning and Christmas Islands) will be dated using U/Th techniques and analyzed with monthly resolution for their stable isotope and elemental composition. Previous research has shown that the skeletal chemistry of modern corals in this region captures a monthly-resolved record of ENSO with a fidelity that is on par with instrumental observations. Preliminary data suggest that the fossil coral geochemistry has not been altered, it is comparable to modern corals, and the ages of the fossil coral samples are characterized by a continuum of ages less than 6,000 years old. The broader impacts of this research will be invaluable to climate modelers seeking to improve the understanding and prediction of climate variability and the project will support graduate and undergraduate student training. This study also has socio-political impact that is related to the broader issues of climate change and global warming.

This award will support the participation of ~40 students and young scientists in the 10th International Conference on Paleoceanography (ICP), which will be held in late summer 2010 at the Scripps Institute of Oceanography in LaJolla, CA. The ICP meeting is held once every three years, and is the largest and longest-standing meeting dedicated to the field of Paleoceanography. This will be the first time a US institution has hosted the conference in over 20 years. The ICP meeting offers an important means for intellectual and social networking, particularly for students and young scientists. Participant support will be based on applicants? statements of purpose and will target under-represented groups. This award will also support a professional development forum at the meeting, and advertising of the meeting in relevant trade journals.

The dynamical response of the tropical thermocline to continued greenhouse gas forcing represented one of the primary feedbacks influencing the future evolution of ocean warming, and understanding of past variability of this response based on paleo records is crucial for accurate simulation of future changes by global ocean/atmosphere models. The impact of the Indonesian Throughflow on the western Indian Ocean thermocline is rarely considered explicitly in climate models, despite the fact that it represents a substantial transfer of heat and energy. This project is aimed at analyzing trends in stable isotopes, trace elements, and radiocarbon in multiple coeval sclerosponge specimens to arrive at a robust, biennially resolved reconstruction of western tropical Indian Ocean thermocline change across the 20th century. The comparison of the radiocarbon trends with stable isotopic/trace element trends will help determine the extent to which the characteristics or strength of the Indonesian Throughflow (ITF) were responsible for the inferred thermocline changes. The research will generate valuable baseline data for assessing present and future impacts of anthropogenic environmental change on deep reef fauna. The award supports a graduate student's dissertation research, as well as outreach efforts in collaboration with the Birch Aquarium at Scripps.

The PI requests MRI funding to acquire a gas source mass spectrometer and carbonate preparation device for applications in the geosciences. This instrument will be used to support projects in mantle geochemistry, paleoceanography and paleoclimatology, and physical anthropology. Current demand for this instrument requires the ability to measure up to 10,000 samples per year, primarily in the form of foraminifera, coral powder, enamel and phenocryst CO2. The proposed instrument is designed to replace the aging instrumentation without catastrophic loss of productivity, while also enabling the measurement of small mass samples that are currently being "outsourced" to other laboratories.

Broader Impacts: The instrument will be placed in a newly reorganized SIO Center for Isotope Geochemistry - part of a larger network of core analytical facilities. Intensive "hands on" training of graduate students and advanced undergraduates is an essential goal of the center. The instrumentation would also support classroom instruction on graduate and undergraduate levels, and it would serve as a natural means for strengthening existing programs aimed at increasing diversity in science. The "STARS" program - Summer Training Academy for Research in the Sciences. Funded by NSF and administered through UCSD, this program each year looks to place undergraduates from underrepresented groups into laboratory environments. The proposed instrument would provide an ideal platform for participants in this program.

There is considerable evidence that the deep ocean plays some role in governing the evolution of Pleistocene ice ages and interglacial periods. Yet after several decades of research, there is still debate over the degree to which sedimentary tracers can distinguish differences in deep ocean circulation between ice age oceans and the modern ocean. This collaborative project will investigate past ocean circulation changes by generating multi-proxy records for several common paleoceanographic tracers (including benthic d18O and d13C, radiocarbon, Cd/Ca, Zn/Ca and B/Ca) for eight time slices over the last glacial-interglacial cycle using cores along a depth transect from the Namibian margin and Cape Basin. These time slices would represent the step in evolution from interglacial state through a full glacial cycle. The research will focus around a series of questions concerning water mass evolution in the Atlantic Ocean, the connection between circulation and carbon cycling, differences between conservative and non-conservative proxies, and the possibility for major boundary condition changes distinct from ocean mixing effects.

Broader impacts:
This project will provide a detailed picture of the mixing between the two principal deep water masses of the world's ocean across a full ice cycle, which will be of widespread use to oceanographers and climate scientists. Funding will support two Ph.D. students and provide significant experience in proxy data collection and interpretation. The project will also serve as a platform for a summer REU fellow and provide support for several undergraduate students to learn research and laboratory techniques. Additionally, funding will help develop a lesson on deep earth circulation through the Deep Earth Academy at Texas A&M University.

The dynamics of the tropical Indian Ocean represent a major wildcard in the projections of many large-scale aspects of the climate system. In principle, the strength of the South Asian monsoon, the inter-ocean linkages of interannual-centennial variability throughout the tropics, and the expression of greenhouse gas induced warming of the upper ocean must all be influenced by, or mediated through the tropical thermocline. Despite its importance, there are a number of first order questions about the dynamics and variability in this system that remain unanswered.

The primary objective of this work is to collect and analyze sediment cores from an under-sampled region with the eventual goal of resolving the mid- to upper tropical Indian Ocean dynamics over ice age cycles. The project takes advantage of a student training expedition that will focus primarily on geophysical mapping of the Sunda Arc, but also allow ample time for surveying and gravity coring of nearby areas. Follow-on work will include laboratory-based analysis of the those sediment cores to establish
stratigraphic context and to test the potential of new methods (e.g., individual foraminiferal analysis) for addressing the overall objectives of the project.

The primary broader impact of this project lies in the exceptional opportunity for heuristic student training in oceanographic sample and data collection. Students will experience the sediment coring process from start to finish--from the strategic design of the cruise plan, through the shipboard execution of gravity coring, and ultimately to the scientific applications. The outcomes of the coring and surveys will also provide the basis for larger basin-wide initiatives to study long-timescale tropical climate change.

The decreased vitality of coral reef ecosystems is often cited as one of the most prominent costs associated with the progressive oceanic uptake of fossil fuel carbon dioxide and the consequent ocean acidification. Yet, despite the prominent concerns, it is presently unknown whether and how regional oceanographically-induced pH variability is actually manifested at the site of coral calcification. This uncertainty requires comprehensive monitoring of diverse reef systems. As a complementary approach to in situ monitoring installations, a research team from the Scripps Institution of Oceanography will make use of the known changes in Pacific ocean/atmosphere variability of the late 20th century as a retrospective monitoring system. In effect, the system of measurements from this targeted network of coral samples will provide a direct comparison to hindcast expectations of the pH variability forced by oceanographic change. These results of this project will allow a direct assessment of the extent to which massive corals in various oceanographic settings were actually sensitive to historical changes in regional pH. The project will serve as the doctoral research of a student who broadens participation of severely underrepresented groups. The project will also be used as a platform for public outreach through SIO Birch Aquarium exhibits.

The research team will measure coral skeletal chemistry in existing coral cores from locations that represent very different geographic poles of historical Pacific basin-wide changes. Specifically, they will apply the boron isotopic proxy for pH, in conjunction with a suite of other skeletal tracers that might be sensitive to perturbations in seawater carbon chemistry, to generate seasonally-resolved records of environmental changes. Two of the study sites, Palmyra and Moorea, feature on going, multi-year in situ pH sensor installations. Accordingly, the research team will collect and analyze the most recent coral growth at these locations, which will provide the best available means for field calibration of the skeletal proxies. In general, the assessment of the scale of pH variability manifested at the site of calcification--and, especially, its relationship with oceanographic perturbations--is essential for establishing the proper perspective for projections of future anthropogenic effects on reef carbon chemistry.

The Southern Ocean holds disproportionate influence in setting atmospheric CO2 variability and carbon storage in the deep ocean because it is a region featuring both upwelling and deep-water formation. Consequently, considerable effort has been devoted to understanding the Southern Ocean conditions and processes that ultimately led to lower atmospheric CO2 during the last ice age. Radiocarbon is in principle the most diagnostic tracer for ocean/atmosphere carbon cycling over this time period. However, the existing body of radiocarbon data for the Southern Ocean is still limited temporally and spatially, while also suffering from some essential uncertainties that preclude firm conclusions about carbon cycling during the last ice age. This project involves a coordinated program of radiocarbon measurements in three distinct archives of Southern Ocean oceanographic change that span the last 30,000 years. These archives, including both marine sediment sequences and deep-sea coral samples, are located so as to capture the surface, intermediate and deep-water carbon cycle response to climate forcing. The objective of this program is to extend existing radiocarbon measurements while also directly resolving some of the principal uncertainties that currently limit the application of existing radiocarbon observations. The program will serve as a natural platform for engagement of underrepresented students to STEM disciplines and will include undergraduate and masters-level students recruited from local community colleges and state universities.

More specifically, the project includes i.) planktonic-benthic foraminiferal radiocarbon age measurements in a newly acquired sediment sequence off Mozambique (IODP Site U1477) that features exceptionally high resolution; the bottom water at this location is recently ventilated water subducted just south of the Subtropical Convergence, and, therefore, the benthic foraminiferal radiocarbon variability monitors that of the sub-Antarctic surface ocean; ii.) U-series/radiocarbon age pairs in a set of deep-sea coral samples collected from intermediate water depths off Tasmania; the radiocarbon variability expressed in this series of samples is intended as a direct comparison to that of the Mozambique foraminiferal sequence; iii.) extension of existing (but not yet definitive) planktonic-benthic foraminiferal age depth pairs in abyssal South Atlantic sedimentary sequences; the benthic foraminiferal radiocarbon variability at these sites should reflect the deep branch of the Meridional Overturning Circulation (MOC). The intention is to provide new observations that, both on their own and by unlocking the potential of existing measurements, will serve as direct tests of models of the relationship between climate forcing and carbon cycling.

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.