Interests I, along with scientists from Scripps Institution of Oceanography and Texas A&M, collected water samples and a suite of sediment cores, ranging in water depth from 500 to 3200 meters, aboard the R/V Melville in the spring of 2003. These cores were taken to build continuous depth transects that sample all the principal watermasses involved in the thermohaline circulation of the Atlantic. I have analyzed these cores for stable isotopes as well as radiocarbon (mixed benthic species and monospecific planktonic foraminifera). The results will be used to determine how the ventilation age of various water masses changed in the mid-depth ocean in order to ascertain changes in northern vs. southern dominance over the abrupt events of the late Pleistocene. Thesis Title: Collaborators: --------------------------------------------------------------------------------------- Abstract submitted to the ICP-8 (International Conference on Paleoceanography) in the Fall of 2004 Southern Hemisphere influences on the stability of the global overturning circulation (Click Here for Poster): The stability of the ocean’s global thermohaline circulation ranks among the most prominent sources of uncertainty for projecting future climate change. Available observations from the deep-sea sedimentary record of the late Pleistocene provide many examples of dramatic and abrupt changes in conditions, and a variety of evidence shows that the ocean was somehow involved in these global climate changes. However, there currently is no consensus on the origin of this apparent thermohaline instability. Thus far, the overwhelming majority of effort has been devoted to documenting and understanding the relationship between ventilation of the deep North Atlantic and the salt balance of the surface North Atlantic Ocean. By contrast, it has recently been suggested that Southern Hemisphere processes may actually be more important for governing the stability of the global thermohaline circulation. Of course, resolution of the actual mechanisms that promoted an unstable thermohaline circulation during the Pleistocene is prerequisite for assessing whether past “catastrophies” are at all relevant for present and future climate. Basic theoretical considerations suggest that to understand why the global thermohaline circulation may have become unstable in the past – and, indirectly whether the system is close to a threshold of stability today – it is necessary to document the dynamics of the mid-depth ocean. In particular, it is essential to resolve changes in the density contrast between water sinking from opposite hemispheres. Here we present the first results of a field experiment to address this very issue. In early 2003, we conducted a sediment coring cruise on the R/V Melville and collected a detailed depth transect of cores off Namibia. This is a region where, within a limited area, the seafloor intersects all the principal watermasses involved in the thermohaline circulation of the Atlanticincluding those of northern and southern hemisphere origin.
The cores range in water depth from 500 to 3200 meters and are spaced at 100 meter intervals, allowing the possibility for a detailed history of the intermediate water masses (Antarctic Intermediate Water and Labrador Sea Water) throughout the last deglaciation.
Initial results suggest that the cores are characterized by sediment rates in excess of 5 cm/kyr, and they can be correlated stratigraphically with each other on the basis of physical properties and isotopic profiles. Radiocarbon offers the potential for resolving water mass origin and for understanding ventilation rates, while the oxygen isotopic composition of foraminifera may be taken as a proxy for density. We will present detailed benthic foraminiferal profiles of physical tracers and radiocarbon analyses across several discrete time horizons. These profiles will define the primary deglacial changes in water density, temperature, and ventilation age of the mid depth Atlantic Ocean. We will also discuss various tests of the fidelity of benthic-planktonic C-14 age difference method as a proxy for ventilation ages. I will also provide a link to her CV here.... (soon to be).
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