9508072 Froelich Recent advance in our understanding of minor biological fractionation of Ge/Si by oceanic diatoms suggest that (Ge/Si) opal variations measured in late Pleistocene piston cores and Cenozoic drill cores are recording whole ocean (Ge/Si) seawater variations driven by rapid and large glacial to interglacial changes in continental weathering intensity and river fluxes to the sea. If so, then it is clearly important to produce high resolution records of (Ge/Si) opal in cores with well-established 18 O and 14 C stratigraphies across transitions to establish the shape and timing of the oceanic Ge/Si response relative to other climate and weathering indicators. In addition, in order to resolve whole ocean changes in the face of small biological fractionation effects, it is necessary to carefully evaluate and remove the effects of Ge/Si fractionation in local records. With the development of a rapid and highly- sensitive HG-ICP-MS Ge-method, these problems can be addressed and unraveling the causes and timing and ocean chemical variations can begin. As a result, this is aimed at accomplishing two major goals: (1) Produce high resolutions late Pleistocene (Ge/Si) opal records in cores that contain abundant diatoms and forams in collaboration with others' measurements of the appropriate paleogeochemical tracer in the same cores (e.g. 87Sr/86Sr); and (2) Provide tests to refine the effects of Ge/Si biological fractionation with diatom cultures, hydrographic and core top transects, and runs of the Hamburg ocean Ge/Si model. In addition, opal paleoproductivity work in the Antarctic (expanding into the North and South Pacific Oceans), and other ancillary programs will be continued.
