Alkenones as tracers of surface ocean temperature and biological pump processes on the Northwest Atlantic margin

We have examined alkenone distributions, specifically the temperature proxy U37K′, in sinking particulate organic matter (POM) intercepted at three depths by time-series sediment traps deployed between 2004 and 2007 on the Northwest Atlantic margin. The goal was to assess physical and biogeochemical processes acting upon alkenones during passage through the water column. U37K′ did not exhibit any systematic trend with increasing depth despite several-fold attenuation in alkenone flux. Because of the extensive reduction in C37 alkenone flux in the water column and more efficient alkenone degradation during the period of high alkenone flux, the temperature bias toward that of more productive seasons was reduced with increasing trap depth. The temporal variation of U37K′ and alkenone-derived temperature compared best with the satellite-derived SST at an upstream region approximately 160 km east of the mooring site with a time lag of about 30 days, suggesting this region as the dominant source of alkenone-bearing POM. The alkenone-derived temperature of core-top sediments (15 °C) at the study site was lower than the flux-weighted average alkenone-derived temperature of sinking POM at 50 m above the seafloor. This discrepancy may reflect additional supply of resuspended sediment carrying alkenones produced in cooler waters to the northeast, and transported in bottom nepheloid layers.