Philip 'Flip' Froelich

Research

Ge/Si-Opal and the "Missing Sink"
Investigations of Germanium Geochemistry and Paleoredox

Over the last several years we demonstrated that Ge/Si-opal records from Pleistocene piston and drill cores monitor paleoceanographic variations in whole ocean Ge/Si-seawater. These records are coherent with the marine isotope record of global ice volume. We attributed these Ge/Si variations to glacial-to-interglacial changes in continental weathering intensity and climate-driven changes in the delivery of Ge/Si to the sea. This view has been updated with recent developments, which include

(1) Establishment of a robust hydride-generation single-ion-monitoring ICP-MS method for the determination of Ge in small mass solid phase and pore water samples; and

(2) Discovery from sediment pore water and solid phase extraction profiles that inorganic-Ge undergoes a diagenetic reaction in the suboxic zone that may represent a non-opal "missing Ge-sink" needed to balance the opal, fluvial and hydrothermal Ge/Si cycle in the ocean.

We propose here a two-year program to accomplish two major goals:

(1) Document the diagenetic behavior of Ge and related redox elements in marine sediments from pore water and solid phase extracts of cores recovered in 1996 during TTN-057 (South Atlantic-Antarctic), ODP-177 in 1997-98 (South Atlantic-Antarctic) and the Palmer JGOFS Benthic Processes leg (AESOPS) in 1998 (South Pacific-Antarctic). Our goal is to quantify the sedimentary Ge balance (the "missing sink" in the global Ge-cycle) and to evaluate the extent to which changes in ocean redox (bottom water oxygen and vertical carbon fluxes) might be responsible for oceanic Ge/Si variations.

(2) Test the working hypothesis that Ge/Si is not fractionated during biouptake by analyzing intrinsic opal for Ge/Si-opal in Antarctic JGOFS traps, surface and last-glacial maximum sediments across the South Pacific-Antarctic Ocean. In conjunction with this work, we will also test whether Antarctic opal carries measurable Al and Fe to test Dymondâs equatorial Pacific model for inverting sediment Al/Ti ratios to opal paleo-rain and opal-Fe to dust fluxes. This work is a natural extension of our long-term effort to develop paleochemical tracers in intrinsic opal, and will be performed in collaboration with JGOFS investigators measuring Al/Ti in Antarctic traps and whole sediments. You can read more about this in a recent Southern Ocean Odyssey article (PDF Version).

These data, in conjunction with hydrographic Ge/Si profiles from the major oceans and OGCM models of the Ge/Si cycle, will permit us to better interpret the marine sediment Ge/Si-opal and opal accumulation rate records for a deeper understanding of the interactions among climate change, ocean chemistry and paleoproductivity.

U.S. JGOFS Southern Ocean Process Study
RVIB N.B. Palmer Cruises

Click on image for full sized map.