Intermediate water formation plays a critical role in the redistribution of heat and freshwater, making it an important driver of climate change. Various water masses can be identified by their chemical characteristics. This study investigates the utility of lead isotopic ratios incorporated into marine barite to address changes in intermediate water circulation over glacial/interglacial time scales in the Equatorial Pacific.
Lead and its isotopes are introduced into the ocean primarily through the weathering of continental rock. These rocks may have distinct isotopic signatures, depending on the age of the eroded material. Lead has a short residence time in the ocean. As a result of these characteristics different water masses have distinct lead isotope signatures that depend on the source regions of the water mass and climate related weathering and erosion processes.
Marine barite is known to precipitate at mid water depths directly from seawater in micro-environments containing decaying organic mater. It has been shown to record seawater chemistry for a variety of trace elements. Marine barite does not exchange with seawater or porewater after formation and thus constitutes a nice archive of ocean chemistry.
Lead isotope ratios in marine barite from core top sediments are distinct from those of deep-water ferromanganese nodules and are more similar to the leachable fraction of aerosol dust. This is consistent with the formation of barite at intermediate water depth.
Records from two cores in the Equatorial Pacific, TTN013- PC72 and TTN013-PC83,collected at 0° and 2°N 140°W respectively, show similar trends over the past 450 kyr and show a correlation to the seawater oxygen isotope record (SPECMAP, Imbrie et al., 1984) suggesting climatically related changes in lead isotopes of intermediate water at these sites. Such changes may indicate either changes in the relative contribution of northern vs. southern sources of water or changes in the source or flux of dust deposition to the Eqatorial Pacific. Comparison with other proxies of dust deposition and circulation changes will help resolve the specific mechanisms for the observed changes.
The Monterey Canyon defines the bathymetry of the Monterey Bay and is comparable to the Grand Canyon in depth, but its age and origin are unknown. Ph.D. Candidate Tracey Conrad will use hydrogenetic ferromanganese (Fe-Mn) crusts to help constrain the time at which incision of the Monterey Canyon stopped by tracing the changes in local seawater lead and neodymium isotope composition. Fe-Mn crusts form from seawater on elevated topographical surfaces such as seamounts and record the chemistry of paleo seawater in which they grew.
Lead and neodymium isotopes in Fe-Mn crusts from Davidson and Taney Seamounts that formed over the past five to fifteen million years will be investigated to identify terrestrial inputs into the California margin such as lead carried by large river inputs or weathering of Sierra Nevada igneous provinces are recorded in Fe-Mn crusts and can be identified. Transport of terrestrial material by rivers will be the main input mechanism considered in this coastal setting. Lead and neodymium isotope ratios from central Pacific Fe-Mn crusts D11-1 and CD29-2 and existing water column isotope profiles will be used for comparison to help differentiate between terrestrial sources and open-ocean isotope fluxes in the Pacific Intermediate water from which the Fe-Mn crusts used in this study formed.
Paleoclimatic records from the Yucatan Peninsula of Mexico can provide insight into the patterns and driving mechanisms of drought cycles in the Caribbean region and other sub-tropical areas of the world. They also reveal evidence for the interaction of climate change and human activity in determining the rise and fall of prehistoric civilizations in this region. We are developing a multi-proxy record of past hydrology and paleoenvironmental change at the Celestun Lagoon estuary, in the northwestern Yucatan, based on isotopic and ecological indicators. The goal is to clarify the magnitude and spatial extent of climate-induced drought inferred from previous proxy records, and to provide insight into the responses of estuarine systems to climatic change.
Freshwater input to Celestun is dominated by groundwater with a strontium isotope signature (87Sr/86Sr), distinct from that of seawater, that correlates to salinity and leaves a record in microfossils in the surface sediments. Preliminary down-core variations in 87Sr/86Sr suggest that salinity in the lagoon has changed markedly over the late Holocene. Measurements of carbon and nitrogen isotopes and elemental abundances in sedimentary organic matter provide information about organic matter sources and carbon cycling and storage in this ecosystem during different climate regimes, while pollen and microfossil assemblages provide a perspective on paleoecological changes in the estuary. This project has involved researchers from U. C. Santa Cruz, Cornell University, LacCore at the University of Minnesota, and Centro de Investigacion y Estudios Avanzados in Merida, Mexico.
The Interuniversities Institute of Israel is also aiding this project with uranium dating (U-Th) of carbonate sediment cores to constrain age models for these periods of drought and foraminifera culture studies. The isotope signals of forams elucidate physical processes of the hydrologic cycle but may also imprint biologic fractionation signals on the ambient isotope ratio values. Understanding the growth behavior of these forams facilitates interpretation of the data they yield.
We are using barite accumulation rates to construct paleoproductivity in different ocean areas and different time intervals.
1, Increased efficiency of globally ocean carbon sequestration during PETM plays a key role on the climate recovery
A perturbation of the carbon cycle and biosphere, linked to globally increased temperatures about 55.9 Ma ago, characterized the Paleocene–Eocene Thermal Maximum (PETM). Its effect on global oceanic productivity is controversial. In this project we investigated that general globally increased export productivity during PETM based on barite accumulation rates, possibly play a key role on the atmosphere CO2 sequestration to remit the green house effecting. Higher seawater temperatures at that time increased bacterial activity and organic matter regeneration to generate dissolved inorganic and organic carbon. Considering the proportion of refractory dissolved organic carbon (RDOC) inherited from the carbon export, our estimated export productivity is consisted with the amount of carbon redistribution expected for the recovery from the Paleocene–Eocene Thermal Maximum.
2, Export productivity evaluation in the EEP during Plio-Pleistocene
The Mid-Pliocene is the most recent interval in the Earth's history to have experienced warming of the magnitude predicted for the second half of the twenty-first century and is, therefore, a possible analogue for future climate conditions, while the Eastern Equatorial Pacifica (EEP) is particularly important for understanding the links between climate and ocean productivity because a large fraction of global export production is associated with this upwelling region, in this project we compare our reconstructed productivity in EEP with sea water temperature and global ice volume records in the same area, results suggest that in the EEP mechanisms that affect nutrient supply and/or ecosystem parameters and in turn carbon export on orbital time scales differ from those operating on longer time scales. These differences should be accounted for in climate models to ensure better climate change predictions.
3, Indo-Pacific Warm Pool (IPWP) productivity change during the Pliocene climate transition
Unlike the EEP upwelling area, few studies were carried concern West Pacific Warm Pool and the Indian high temperature area due to the deep thermocline and low productivity currently. The importance in research about Pliocene in emphasized as above in EEP project, however, the earth climate went through a continually gradually cooling during the Mid-Pliocene followed by the initiation of North Hemisphere glaciation. The closure of Indonesia seaway through tectonic events during 3-4Ma is thought to play a major role for this grand climate change by switching source of Indonesia throughflow (ITF), leading to the change of global circulation and the heat transportation. For those oceans across ITF, western Equatorial Pacific and eastern India Ocean, still control the significant climate phenomena, ENSO and monsoon, in the modern time. Researches revealed that the surface temperature (SST) didn’t have significant change during the Pliocene climate change in both western Equatorial Pacific and eastern Indian Ocean, while dramatic variations of subsurface temperature in the eastern India Ocean were recorded. Reasons for this transition are still controversial, but the ocean export productivity, via which the CO2 were taken up and sequestrated into the deep ocean, potentially acted as a predominance function to reduce the green house gas, hence decrease the global temperature. In this project we are reconstructing the productivity across ITF combine with other temperature data, further assess the effect/feedback of productivity in this area on climate change during the Pliocene climate transition. Gradient change of productivity across ITF will also be analyzed by using spectral analyze and multivariate process to reveal circulation and thermocline change.
Temperature rise, ocean acidification and expanding hypoxic zones in the ocean are the most prominent environmental parameters predicted to impact marine ecosystem health on a global scale. In particular, recent research has shown that pH, temperature and oxygen concentration are the main causes for current ocean biology decline. Presently, no one knows if these three drivers varied simultaneously in the past, how these parameters impacted species diversity or population change, and/or quantified climate impacts on these coupled parameters due to the difficulty of measuring these parameters concurrently in sedimentary archives.
To address this challenge, this project we will measure pH, temperature, and O2 concentration simultaneously by measuring elemental and isotopic data (B/Ca, Mg/Ca, U/Ca, δ18O) on single benthic foraminifera and aggregates of foraminifera. The comparison of the different data sets (single foram and bulk foram) will reduce data uncertainty due to digenesis in foraminifera shells, and help understand seasonal fluctuations. We will focus two time intervals: (1) last 200 years and (2) the Younger Dryas (11000-12500 ypb), both periods of rapidly changing climate which are expected to have affected pH, O2, T at the CA margin.
Ultimately, the datasets will be used to determine if recent changes in oceanic pH, T, and O2 have accelerated due to anthropogenic influences on climate, how the rates of change compare to pre-anthropogenic times, and how these current trends may impact historic and future local/regional biota and industries tied to plankton, fish and mollusks systems.
This research takes advantage of the unique opportunity provided by IODP Expedition 339, which took water, mudline and core samples in the Gibraltar Gateway. We will analyze the extant coccolith assemblages, and reconstruct the paleoceanographic changes in the last glacial-interglacial cycle based on changes in species abundance and geochemical and isotopic signatures recorded in coccoliths. We will utilize the water and the mudline samples from all the Expedition 339 sites and down core late Quaternary samples from Site U1390. The high sedimentation rates and good preservation of coccoliths in these sediments allows for high resolution records. Comparison between living assemblages and the fossil assemblage changes is the key to interpret temporal changes of coccolith distribution and abundance in the geological past and their relation to climatic changes.
Specifically, we will combine biological, micropaleontological and biogeochemical approaches to reconstruct the paleocirculation in the Gulf of Cadiz, from the LGM toward the Holocene. The coccolithophore records and specific morphotype-based proxies will be used to reconstruct nutrient availability and SST. The key component of this research is to analyze water and mudline samples from the core site area in order to better interpret the environmental signals from the coccolith fossil record. As is the case for all paleoceanographic proxies, continued calibration studies are required to further improve our understanding of coccolithophore based proxy systems and increase confidence in their application (Stoll and Ziveri, 2004).
Page last updated October 5, 2015