The vertical flux of biogenic and lithogenic material in the Ross Sea: Moored sediment trap observations 1996-1998

As part of the USJGOFS-AESOPS program, we deployed an array of moored sediment traps and determined the composition and vertical flux of particulate matter through the water column of the continental shelf environment of the Ross Sea. We deployed two moorings, with two traps each. One mooring was located in the southcentral Ross Sea along the line of AESOPS process studies; the other mooring was located in the northcentral Ross Sea. The flux in the southern Ross Sea was generally double that in the north; and there was a significant increase in flux into the deep traps indicating horizontal transport and possible focusing of particulate matter. The particles are primarily biogenic although lithogenic contributions can increase to over 30% of the flux in the near-bottom trap nearer to the ice shelf. The fluxes collected by the traps were generally low but within the range of previous observations. Several unique observations stand out from these data: (1) The export of organic matter to 200 m during the spring and summer was extremely low, consistent with observations that the ongoing phytoplankton bloom was being stored or recycled in the upper-water column; (2) A major pulse of biogenic silica export occurred in the fall, just as ice was reforming. The correlation of this event with lithogenous particles, excess Fe, and with the early breakout of katabatic winds suggests that this event might be related to Fe fertilization of diatom production and export; (3) The largest flux of organic matter during 1996-1997 was carried by the pteropod Limacina helicina and was observed at both moorings under the ice in the late fall, just after the diatom pulse. Although it is difficult to estimate the proportion of these organisms that were swimmers contaminating the flux, we believe that a significant fraction settled into the traps and may represent the die-out of this herbivore population after the suspended POM concentration had dropped to very low levels. Fluxes to the upper traps were much lower than estimates of export flux made by other methods during synoptic ship studies. These differences are discussed and the fluxes are compared with preliminary data from the ROAVERRS trap program, which was simultaneously deployed in the Ross Sea. (C) 2000 Elsevier Science Ltd. All rights reserved.