A MID TO LATE HOLOCENE ULTRA HIGH-RESOLUTION FORAMINIFERAL BIOFACIES RECORD FROM IODP EXPEDITION 318: WILKES LAND, ADELIE TROUGH, ANTARCTICA

An ultra high-resolution foraminiferal biofacies study was conducted using samples from the Integrated Ocean Drilling Program (IODP) Expedition 318: Wilkes Land, Site U1357, which is located in the Adélie Trough, Antarctica. The Adélie Trough is a glacially scoured, ~1000 meters deep basin, located on the continental shelf off of Wilkes Land. In collaboration with Stanford University, a total of 1,800 samples were taken from the 186-meter long core from Hole U1357A at 10 cm intervals for foraminiferal analysis. For this study, 800 samples were taken from the upper half of the core (<90 meters below sea floor, mbsf), which was dated from ~6.4 kyr to present. These samples were washed to remove the clay and silt size particles and then were examined using stereo binocular microscopes to pick and identify both planktonic and benthic foraminifers. Thus far, over 300 samples have been examined for foraminiferal biofacies and stable isotope analysis from the foraminiferal tests to investigate paleoceanographic and paleoclimatic changes in the Adélie trough in the middle to late Holocene.

Preliminary results show generally low foraminiferal abundances and diversity throughout the study interval. Over 30 species of benthic foraminifers have so far been identified, with Neogloboquadrina pachyderma sinstral representing over 98% of the planktonic foraminifers observed. Planktonic foraminiferal abundances are generally higher below 49.2 mbsf (3.7 kyr). The agglutinated Trochammina spp. species are generally the dominant taxa throughout the samples examined. Cibicides spp. abundances are higher between 27 to 60 mbsf (2.7 to 4.7 kyr) and again above 10 mbsf (<1,000 kyr). Epistominella spp. are more abundant between 47.8 and 75.7 mbsf (3.6 and 5.5 kyr). Globocassidulina and Quinquelculina spp. are also more abundant below 70 mbsf (~5.2 kyr).

The higher abundances of calcareous benthic forms are interpreted to represent higher oxygen levels and less corrosive waters for the bottom waters. This suggests better ventilated bottom waters may have been occurring during the Mid Holocene warming. The high dominance of agglutinated forms in the upper part of the section suggests that bottom waters during the Neoglacial (3.5 kyr- present) were more corrosive and contained lower oxygen content.