Evaluating the effects of regional climate trends along the West Antarctic Peninsula shelf based on the seabed distribution of naturally occurring radioisotopic tracers

Measurements of Th-230, C-14, Pb-210 and Th-234 activities were made on sediment cores collected along a N-S transect exhibiting a gradient in annual sea-ice duration off the West Antarctic Peninsula. The resultant data were used to evaluate the effects of regional warming on particle flux reaching the seabed on timescales from millennial to seasonal. Shelf samples were collected at five stations, over three cruises, between February 2008 and March 2009, as part of the FOODBANCS2 Project. Sea-ice conditions (the number of days ice-free prior to core collection) were evaluated at the five stations to understand the relationship between ice abundance and particle/radionuclide flux. Based on the millennial tracer C-14, rates of sediment accumulation along the peninsula decrease southward, consistent with the observed sea-ice gradient. Th-230 data provide additional evidence on millennial timescales that sediment focusing (i.e., lateral transport) occurs to a greater extent in the northern reaches of the study area compared to the southernmost stations. The distribution of steady-state, Pb-210 flux to the seabed (representing centurial trends) displays a similar trend to C-14, showing higher radionuclide/particle flux in the northern study area (where sea-ice duration is diminished) and lower flux southward as sea-ice duration increases. Additionally, Pb-210 data suggest that lateral transport plays an important role in the sediment distributions of this radiotracer on hundred-year timescales, which is explainable by the relatively short circulation times of peninsular waters relative to Pb-210's half-life. On seasonal and annual time scales, the distribution of steady-state Th-234 flux to the seabed shows an increase in radionuclide flux at the southernmost stations. This increase in radionuclide flux on seasonal and annual time scales is consistent with the warming trend along the peninsula and the reduction in sea-ice duration over the past decade. A significant statistical relationship, however, could not be established between annual sea-ice free days and Th-234-derived particle flux to the seabed. The fluxes/distributions of long-lived particle-reactive tracers (C-14, Th-230, and Pb-210) on the West Antarctic Peninsula shelf appear to be controlled primarily by the long-term pattern of increasing annual sea-ice duration in the southward direction, whereas the fluxes of the short-lived tracer (Th-234) are consistent with the more recent decreases in sea-ice duration (associated with climate change) that have occurred over the past decade, primarily in the southern West Antarctic Peninsula stations.