(Table 1) Characteristics of air temperature, sea surface temperature, sea surface salinity, nutrients, and total particulate matter for Admiralty Bay and Potter Cove, King George Island, Antarctica

Since the early 1990s, phytoplankton has been studied and monitored in Potter Cove (PC) and Admiralty Bay (AB), King George/25 de Mayo Island (KGI), South Shetlands. Phytoplankton biomass is typically low compared to other Antarctic shelf environments, with average spring - summer values below 1 mg chlorophyll a (Chl a)/m**3. The physical conditions in the area (reduced irradiance induced by particles originated from the land, intense winds) limit the coastal productivity at KGI, as a result of shallow Sverdrup's critical depths (Zc) and large turbulent mixing depths (Zt). In January 2010 a large phytoplankton bloom with a maximum of around 20 mg Chl a/m**3, and monthly averages of 4 (PC) and 6 (AB) mg Chl a/m**3, was observed in the area, making it by far the largest recorded bloom over the last 20 yr. Dominant phytoplankton species were the typical bloom-forming diatoms that are usually found in the western Antarctic Peninsula area. Anomalously cold air temperature and dominant winds from the eastern sector seem to explain adequate light : mixing environment. Local physical conditions were analyzed by means of the relationship between Zc and Zt, and conditions were found adequate for allowing phytoplankton development. However, a multiyear analysis indicates that these conditions may be necessary but not sufficient to guarantee phytoplankton accumulation. The relation between maximum Chl a values and air temperature suggests that bottom-up control would render such large blooms even less frequent in KGI under the warmer climate expected in the area during the second half of the present century.

Composition of particulate matter in the neutrally buoyant plumes of the TAG and Broken Spur Hydrothermal Fields

This publication considers data on aquatic anomalies (hydrothermal plumes) in the areas of 26° and 29°N of the Mid-Atlantic Ridge (MAR). Mass of hydrothermal iron supply and intensity of iron sedimentation onto the bottom were estimated by means of sediment traps. It was found that the plume of the TAG hydrothermal vent 6 km**3 in volume contained about 67 tons of particulate Fe; the plume of the Broken Spur field (up to 8.24 km**3 in volume) contained 23.5 tons of particulate Fe or less because of its lower concentration. Data on sediment matter fluxes showed that 0.3-0.5% of hydrothermal iron was precipitated immediately from the neutrally buoyant plume onto the bottom; the bulk of iron was dissipated into environment. From dimensions of the plumes, flow dynamics, iron concentrations in the plumes, and amounts of iron supplied by hydrothermal vents, it was found that resident time of the plumes considered was from 5 to 10 days.