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The vertical flux of particulate matter from the surface of the Ross Sea, Antarctica, has been suggested as being large, with substantial seasonal and spatial variations. We conducted a study in which vertical flux was quantified using sediment traps deployed at 200 m and compared to estimates calculated from one-dimensional budgets of nutrients (nitrogen and silicon). Estimates of flux were collected at two locations in the southern Ross Sea from late December to early February during four years: 2001–2002, 2003–2004, 2004–2005, and 2005–2006. Phytoplankton biomass and vertical flux varied substantially seasonally and spatially between the two sites, and among years. The greatest flux was observed in 2001–2002, with a short-term maximum organic carbon flux of 3.13 mmol m−2 d−1, and the summer mean organic carbon flux equal to 0.93 mmol m−2 d−1. In contrast, the mean carbon flux at the same site in 2003–2004 was over an order of magnitude less, averaging 0.19 mmol m−2 d−1, despite the fact that productivity in that year was substantially greater. In 2005–206 the contribution of fecal pellets to flux was smallest among all years, and the pellet contribution ranged from

The vertical distribution and temporal changes in aggregate abundance and sizes were measured in the Ross Sea, Antarctica, during two field seasons, one in austral spring 1994 and one in early summer, 1995/96. Aggregate abundance, size and potential sinking rates were determined by photographic techniques. Measurements ofwater column parameters, including particulate organic carbon concentrations, were assessed simultaneously, as was the flux oforganic matter with floating sediment traps. The numbers ofaggregates (and to a lesser extent their size) increased with time, although there was substantial spatial variability in these variables at any point in time. Some aggregates appeared to sink extremely rapidly, and for these, our photographic measurements were able to estimate only a minimum sinking rate, which equaled 288 m d � 1 . Estimates ofaggregate organic carbon flux were compared to those determined by floating sediment traps. From these results, aggregate fluxes appear to have dominated the vertical export oforganic matter f the euphotic zone. The genesis and flux ofaggregates in the Ross Sea are the critical processes controlling the export of biogenic material from the surface layer. r 2003 Elsevier Science Ltd. All rights reserved.

To test the hypothesis that phytoplankton assemblages dominated by different taxa have distinct biogeochemical characteristics and cycles, the temporal and spatial variations in phytoplankton biomass and composition were studied within the Ross Sea polynya, where diatoms and the haptophyte Phaeocystis antarctica are thought to have spatially distinct distributions. Two cruises were completed, with the first conducted in spring, 1994, and the second in late spring–early summer, 1995/1996. Ice concentrations decreased substantially from spring to summer. Mixed layer depths for the region decreased markedly in early spring and were relatively invariant thereafter; the strength of the stratification varied both in time and space. Mixed layers were greater in spring in assemblages dominated by diatoms (as determined by HPLC pigment concentrations) than those dominated by Phaeocystis antarctica, whereas in summer no difference was observed. Nutrient concentrations were initially high and near winter values, but decreased throughout November and December. Nitrate : phosphate removal ratios varied widely, with ratios exceeding 20 in spring but decreasing below 14 in summer. N : P removal ratios at stations dominated by diatoms were less than the Redfield ratio in both spring and summer, and at those stations dominated by P. antarctica the N : P removal ratio was ca. 19 in both seasons. Chlorophyll and particulate matter concentrations increased as nutrients decreased. Spatial and temporal variations of phytoplankton pigments occurred, with 19′-hexanoylfucoxanthin, a pigment of P. antarctica, exceeding 3.9 μg l−1 during spring in the south-central polynya, and fucoxanthin, an accessory pigment of diatoms, found in concentrations >1 μg l−1 in the western Ross Sea. The distributions were not mutually exclusive, and concentrations of both pigments were greatest in spring. The early growth of P. antarctica appears to be related to earlier stratification and disappearance of ice from the south-central Ross Sea. Ratios of FUCO/CHL were relatively invariant, but substantial changes in the HEX/CHL and POC/CHL ratios were observed through time. A one-dimensional nitrogen budget for the spring–early summer period suggests that much of the surface production was partitioned into particles, most (53%) of which remained in the upper 200 m. The rest was partitioned into dissolved organic matter (14%), remineralized as ammonium (19%), or sank from the surface layer as particles (13%). The region may serve as a useful analog to other polar systems, and an understanding of the processes controlling assemblage composition, production, and biomass accumulation may provide insights into biogeochemical cycles of other Antarctic environments.

Abstnct-Zn situ settling speeds of marine snow aggregates were determined with the Marine Aggregate Settling Collector and Observation Tower (MASCOT) in the central Black Sea and in the northern Gulf of Mexico. The Black Sea data showed a wide distribution in size and settling speeds of marine snow aggregates (0.5-55 mm diameter and 1.3-280 m/d) with an average settling speed of 11.7 m/d over all size classes. However, these settling speeds might have been inlhtenced by the addition of salt (0.9% above the background seawater) plus formalin to the water in one side of the acrylic chamber of the MASCOT. Data from the Gulf of Mexico had a smaller range in terms of size and speed (0.5-3.5 mm diameter and IO-89 m/d). The average settling speed over all size classes was approximately three times higher (33.8 m/d) than for aggregates measured in the Black Sea. Stokes’ Law predicts that settling speeds are determined by both density and volume of an aggregate. For both study sites no statistically significant correlation of settling speed with the equivalent spherical diameter (ESD) of the aggregates was found. It was therefore concluded that variations in density controlled the aggregate settling speeds measured in these two study areas. 0 1997 Elsevier Science Ltd