Seawater Exchange and Freshwater Input to the Eocene Arctic Ocean from Nd-Sr Isotope Proxies in Fossil Fish Debris
Abstract
The neodymium isotopic composition of Eocene Arctic Intermediate Water (AIW) has been determined by proxy compositions measured in early to middle Eocene ichthyoliths from Lomonosov Ridge (IODP Arctic Coring Expedition 302). ɛNd compositions are distinctly more radiogenic than modern AIW, suggesting several possible sources of Nd to the Eocene Arctic Ocean. Periodic marine inputs from Tethys, the Pacific, and North Atlantic (or Norwegian-Greenland Sea) all likely contributed to the Eocene AIW Nd signature at Lomonosov Ridge between 55 and 45 Ma, in contrast to the prevailing view that exchange was highly restricted. The Eocene Sr isotopic record at Lomonosov Ridge is, in contrast to the Nd record, consistent with fresh to brackish surface water conditions persisting for ca. 10 million years at this location. These data suggest strong decoupling in the sources of Nd and Sr in fish debris, consistent with a salinity-stratified (and strontium- stratified) water column above Lomonosov Ridge. 87Sr/86Sr values of ichthyoliths are more radiogenic than Eocene seawater and probably record the overall balance of river Sr flux to the surface Eocene Arctic Ocean. These data support previous conclusions that fresh water inputs via direct precipitation and rivers combined with unprecedented warmth to support a dynamic, largely ice-free Arctic hydrologic cycle during the early and middle Eocene.
- Publication:
-
AGU Spring Meeting Abstracts
- Pub Date:
- May 2009
- Bibcode:
- 2009AGUSMPP73A..04G
- Keywords:
-
- 1040 Radiogenic isotope geochemistry;
- 1050 Marine geochemistry (4835;
- 4845;
- 4850);
- 4900 PALEOCEANOGRAPHY (0473;
- 3344);
- 4924 Geochemical tracers;
- 4948 Paleocene/Eocene thermal maximum