THE ROSS SEA

We present budgets of carbon and nitrogen for the Ross Sea, Antarctica. The novelty of this study consists in estimating both vertical water-column to sedimentary fluxes as well as horizontal exchanges due to water mass lateral transport between the continental shelf and the open ocean. To this end, we relied upon a large data set combining results from ten Italian oceanographic cruises as well as from literature data, in order to have the largest possible data set. The results presented here have largely benefited from consulting several US-JGOFS studies (AESOPS, 1996-98 cruises) and from international collaborations, the ROAVERRS project (1996-98). The quantities thus calculated can be referred to a budget of an average productive season lasting from November to February. The deep layer, the most relevant for the continental shelf pump, releases carbon to the deep ocean as dissolved inorganic carbon (937 Gmol), dissolved organic carbon (13 Gmol) and particulate organic carbon (7 Gmol). As to particulate organic nitrogen, less than 1 Gmol is released to the deep ocean, but the nitrogen balance becomes strongly positive considering the 19 Gmol imported from the open ocean. Our estimates indicate that during an average austral summer, the amount of matter recycled through biological and sedimentary processes within the Ross Sea is almost one order of magnitude higher than the amount exchanged with the open ocean. Within the upper layer 3486 and 523 Gmol of carbon and nitrogen, respectively, are incorporated into biomass, of which about 50 % are later exported to the deep layer. Since the burial is negligible (less than 0.5 %), considering the upper and deep layer together, we estimate that about 3155 Gmol of carbon and 473 Gmol of nitrogen are channelled to the higher trophic levels and to the dissolved organic pools. Thus, grazing becomes the most important way of export of the Ross Sea.