Particulate export and lateral advection in the Antarctic Polar Front (Southern Pacific Ocean): One-year mooring deployment

An instrumented mooring line with sediment traps, current meters and recorders of temperature and conductivity was deployed just south of the Antarctic Polar Front (63° 26′ S, 178° 03′E; water depth 4400m) from January 9th 1999 to January 10th 2000. Sediment traps at 900 and 3700m had a single large cup to collect particulate material throughout the 1-year study whereas time-series sediment traps were used to characterize the temporal variability at 1300 and 2400m. Samples were characterized via several parameters including total mass flux, elemental composition (organic carbon, total nitrogen, biogenic silica, and calcium carbonate), concentration of metals (aluminum, iron, barium, and manganese), ²¹⁰ Pb activity, and foraminifera identification. High vertical fluxes of biogenic particles were observed in both summer 1999 and 2000 as a result of seasonal algal blooms associated with sea ice retreat and water column stratification. During autumn and winter, several high energy events occurred and resulted in advecting resuspended biogenic particles from flat-topped summits of the Pacific Antarctic Ridge. Whereas the distance between seabed and uppermost sediment traps was sufficient to avoid lateral advection processes, resuspension was significant in the lowermost sediment traps accounting for ~60 and ~90% of the material caught at 2400 and 3700m, respectively. Although resuspended material showed an elemental composition relatively similar to vertical summer fluxes, samples collected during high energy events contained benthic foraminifera and exhibited significantly higher ²¹⁰ Pb activity indicating a longer residence time in the water column. In addition, during quiescent periods characterized by low mass fluxes, the content of lithogenic particles increased at the expense of phytodetritus indicating the influence of material advected through the benthic nepheloid layer. Organic matter content was particularly high during these periods and showed statistically significant linear correlations with metals suggesting adsorption of organic coatings onto the mineral surface of lithogenic particles.