What Happened in the Jane Basin, NE Antarctic Peninsula, ODP Site 697, 3.34 my ago?
Abstract
We examine sediments from 2.0-3.8 Ma from ODP Site 697 in the Jane Basin, NE of the Antarctic Peninsula. This is a dynamic area, where surface and deep water exit the Weddell Sea, making it an ideal location to monitor bottom water and ice rafted detritus (IRD).
There is a distinct boundary at around 3.34 Ma just before MIS M2. Between 3.8 and 3.34 Ma, the weight percent of the fraction > 63 microns (IRD)), varies from 24.2% to 3.4% and averages 7.8%. Between 3.34 and 2.0 Ma the IRD varies between 5.8% and 0% and averages 1.0%. 40Ar/39Ar provenance ages on the 150-500 micron fraction from sediment deposited 3.8 to 3.0 Ma are grouped into three age categories, Grenvillian (G), Pan-African (PA) and Mesozoic+Cenozoic (MC). Between 3.8 and 3.34 Ma, provenance ages are older, 37.5% G, 56.3% PA and 6.3% MC. Between 3.34 and 3.0 Ma, the provenance age distribution is 6.3% G, 81.3% PA and 12.5% MC. The provenance ages suggest that the farthest traveled ice bergs, may have originate from the Rhone-Filchner Ice Shelf, about 2000 km from Site 697. The < 63 micron fraction is dominated by clay-size particles, primarily illite. Bottom currents, as measured by the sortable silt mean (SSm) were slightly more vigorous and variable before 3.34 Ma than after. A cross plot of the wt.% coarse fraction and SSm shows no correlation, so the coarser SSm is not caused by the fine-fraction component of glacial sediment. We interpret this data to indicate that prior to M2 sedimentation and circulation in the Jane Basin allowed abundant iceberg transport and melting, and more vigorous Antarctic Bottom Water (AABW) production. Coastal polynyas, which allow cold water to flow downslope and enable the passage of sediment transporting icebergs, maybe have contributed to this environment. Beginning with M2, and the resulting 40 to 60 m sea level drop and continuing through the remainder of the Pliocene, including the mid-Piacenzian Warm Period, bottom water flow was consistently weaker and wt.% IRD is low. IRD wt. % remains low through the early Pleistocene. The lack of distinction between wt.% IRD in the mid-Pliocene warm period and the subsequent cooling suggests that the western Weddell Sea and into the Jane Basin did not warm after M2. Coring into other small sub-Antarctic Basins during IODP Expedition 382, will provide additional insight into the climatic evolution of this region.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFMPP23E1548O
- Keywords:
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- 3036 Ocean drilling;
- MARINE GEOLOGY AND GEOPHYSICSDE: 4914 Continental climate records;
- PALEOCEANOGRAPHYDE: 4926 Glacial;
- PALEOCEANOGRAPHYDE: 4954 Sea surface temperature;
- PALEOCEANOGRAPHY