Marine sediment record of natural environmental variability and recent warming

Eugene Domack, Geology Department, Hamilton College, Clinton, NY
E-mail: edomack@hamilton.edu

Amy Leventer, Geology Department, Colgate University, Hamilton, NY
E-mail: aleventer@mail.colgate.edu

Over the past twenty years, hundreds of sediment cores have been retrieved from the Antarctic Peninsula continental shelf. With sediment accumulation rates that range from 0.01 mm/year to 100 mm/year, and Ocean Drilling Program Cores that reach 100 meters in length, a resolution of climate variability on the scale of years to decades to centuries is possible. In addition to a high-resolution data set from the Palmer Deep, based on ODP Site 1098, we have recovered many other high quality marine sediment cores from as far south as Lallemand Fjord to the northern tip of the Peninsula and eastward into the Weddell Sea. Collectively, these cores, with chronologies well constrained by AMS radiocarbon dating, provide the basis for a detailed reconstruction of the past 10,000 years, with a current emphasis on the mid to late Holocene. Our proxy data help us constrain changes in primary productivity and ice distribution over time; however, links to global-scale atmospheric and oceanic circulation changes need more attention. For example, in the more polar setting of Lallemand Fjord, both terrigneous and biogenic input are relatively low, with sedimentation rates ranging from ~0.6-0.8 mm / year. In these lower resolution records, changes in primary productivity, most likely driven by changes in sea ice extent, are recorded by downcore variability in the organic carbon content (% TOC) of the sediments. These data document more productive oceanographic conditions through the mid-Holocene, lasting until about 2500 Calendar years BP (cal yr BP), followed by a less productive neoglacial interval. Both the Medieval Warm Period (MWP, ~1100 - 700 cal yr BP) and the Little Ice Age (LIA, ~700-150 cal yr BP) are recorded as well, with higher and lower %TOC characterizing these events, respectively. Farther north, in the more subpolar-polar waters of the Palmer Deep, higher sedimentation rate cores with subsequently higher resolution, illustrate a clear transition from the MWP to the LIA, with a more open water diatom assemblage of the MWP being replaced by species associated with greater sea ice, during the LIA. Data from Andvord Bay, at an almost equivalent latitude but located in a more restricted physiographic setting , show a strong and distinct response to recent warming. Within the past 100 years, a shift toward the warmer water morphology of a common Antarctic diatom is observed, suggesting a marked increase in surface water temperatures, in accord with air temperature records for the region. Finally, sediment cores from Brialmont Cove, a site with high terrigenous input and an average sedimentation rate of ~5cm/yr demonstrate increased sand deposition. This observation can be attributed to increased meltwater input due to warmer summer temperatures over the last 40 years.