Nd-Sr radiogenic isotope analysis of well-preserved, early-middle Eocene ichthyoliths (fossil fish debris) at Lomonosov Ridge (IODP Arctic Coring Expedition 302) confirms that connections between the Arctic Basin and surrounding oceans were extremely limited from 55 to 45 Ma. Epsilon Neodymium of pre-cleaned ichthyoliths varies from -5.7 to -7.8, suggesting significant REE inputs from Arctic rivers draining the Siberian platform. Seawater exchange with neighboring oceans (e.g., North Pacific, Tethyan, North Atlantic) is not necessary to explain Nd isotope and REE data, although some exchange is permissible from these data. Strontium isotope ratios of pre-cleaned ichthyoliths ( (super 87) Sr/ (super 86) Sr = 0.7079 to 0.7087) are consistently more radiogenic than Eocene seawater, indicating brackish or fresh water environments at the surface of the Arctic Ocean between 55 and 45 Ma. Reduced organic-rich coatings on ichthyoliths (and bulk detritus) are more radiogenic ( (super 87) Sr/ (super 86) Sr>0.7090) than pre-cleaned ichthyoliths, indicating different Sr sources for the organic component. (super 87) Sr/ (super 86) Sr variations may record changes in river inputs of Sr to the Eocene Arctic Basin, or possibly a shifting halocline, consistent with a dynamic Arctic hydrologic cycle superimposed on eustatic-tectonic controls of seawater exchange with the world ocean. Sr mixing calculations are permissible of salinities in the 5 to 20 per mil range, lower than estimates based on O isotopes from Eocene fish bone carbonate (16 to 26 per mil). Low salinity waters during the nearly equal 55 Ma PETM do not correspond to large excursions in (super 87) Sr/ (super 86) Sr ratios, nor is there a shift in (super 87) Sr/ (super 86) Sr during the nearly equal 48.5 Ma Azolla salinity minimum. (super 87) Sr/ (super 86) Sr and Nd isotope data reinforce evidence for low salinity surface waters of dominantly Asian continental provenance within the photic zone over much of the early-middle Eocene at this site, stabilizing a poorly ventilated, anoxic water column that saw only intermittent exchange with the world ocean before the first appearance of sea ice at approximately 46 Ma.

West: -180.0000 East: 180.0000 North: 90.0000 South: 70.0000

West: NaN East: NaN North: NaN South: NaN

Expedition: 302

Provider: SEDIS Publication Catalogue

Data set link: http://sedis.iodp.org/pub-catalogue/index.php?id=2009-027653 (c.f. for more detailed metadata)

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