Bulk and diatom-bound nitrogen isotope ratios, opal, TOC, and TN from ODP Hole 178-1098B

Intense seasonal productivity and carbon drawdown on the West Antarctic Peninsula (WAP) is driven by upwelling of nutrient-rich Circumpolar Deep Water (CDW) and subsequent stratification. CDW influence on the WAP is thought to have varied dramatically during the mid-Holocene, 5-7 ka. Here, we use diatom-bound nitrogen isotopes (δ15NDB), a nutrient utilization proxy, from ODP Site 1098 in Palmer Deep to study variations in the presence of CDW on sub-millennial timescales in the mid-Holocene. CDW intrusion is synchronous with atmospheric warming over Antarctica, suggesting that stronger and/or more southerly Southern Hemisphere westerlies enhanced CDW intrusion onto the WAP shelf. Our results also suggest that bulk sedimentary nitrogen isotopes (δ15Nbulk) do not track the same processes as δ15NDB at this site and that this cannot be explained by changes in diatom assemblages.