Long time-series of export fluxes in the western Ross Sea (Antarctica)

The export of particulate organic carbon (POC) from the sea surface is an essential part of thebiological pump. Export fluxes are the result of what is produced in surface water and how muchis consumed during particle sinking in the water column. In the Ross Sea, fluxes of POC and totalmass are well correlated implying that particle fluxes are dominated by biogenic debris.Here, we report new and reference data of vertical particle fluxes to below the productive layerobtained on decadal time scales (1990-2017) by automatic sediment traps tethered to moorings inthe western Ross Sea (Antarctica). Compilation of all data available in the Ross Sea (23 sites, >1000samples) shows that annual POC fluxes to below 200 m average 4.4±3.3 g C m-2 y-1. Particle fluxesare relatively low when primary production is high (spring-summer) followed by enhancedsedimentation in late summer-fall. The high degree of decoupling between production andsedimentation is unusual compared to records of Antarctic Peninsula and may represent lowgrazing rates. Furthermore, data exhibit a large interannual variability and a decreasing trend overtime, with a clear shift after 2000. Do the reduced export fluxes depend on lower biologicalproduction, enhanced OM consumption, or other processes (e.g., lateral transfer of biogenicparticles outside the study area)?Satellite observations allow us to reconstruct the seasonal and interannual change of chlorophyllbiomass, and sea ice extent and duration. Water temperature recorded at mid-depth is used tomonitor the different intrusion over time of CDW, the main driver of temporal variability of Fesupply for the Ross Sea. Time series of particle fluxes, chlorophyll, sea ice cover and mid-depthtemperature will be compared in order to test if the recent reduction of downward particle fluxesdepend on primary production changes.