Hydrographic patterns in McMurdo Sound, Antarctica and their relationship to local benthic communities

Abstract

Summary. Measurements of hydrographic parameters (temperature, salinity, nitrate, nitrite, phosphate, chlorophyll a, phaeophytin, and oxygen) in McMurdo Sound, Antarctica during spring, 1984, before the regional phytoplankton bloom, and summer, 1984, after the peak of the bloom, indicate the several processes contribute to changes in the vertical and horizontal structure of the water column. Regional variation in the source of water masses within the Sound, ice cover patterns, and meltwater from the Ross Ice Shelf and nearby continental glaciers result in east-west and north-south gradients in the thermohaline, nutrient, and productivity characteristics of the Sound. These patterns are also related to the extremely variable structure and productivity of shallow water benthic macrofaunal communities in McMurdo Sound. Hydrographic patterns during Spring (November) were indicative of conditions at the end of winter prior to the spring phytoplankton bloom. The water column was nearly isothermal with temperatures near or below the surface freezing point of seawater with only a slight salinity increase with depth. Salinity was lower in the west Sound than in the east, probably in response to glacial meltwater input from the Ross Ice Shelf and/or terrestrial sources. Nutrient levels were high and nearly homogeneous throughout the Sound. Chlorophyll a was low (< 1.0 ~tg/1) throughout most of the Sound, but was lowest in the western sound, as expected from the circulation pattern (Barry and Dayton 1988). Oxygen was uniformly low during spring. The summer hydrographic distributions, estimated from samples collected during the decline of the regional plankton bloom, were dramatically different than in during spring. Both the salinity and temperature were vertically stratified at all sites, particularly in the west Sound. Temperatures near the surface were well above the freezing point and occasionally near or above 0 °C. Near surface salinity in the western Sound was nearly fresh (0.4 ppt) at some locations in the southwestern Sound. Chlorophyll a was high throughout the Sound relative to spring concentrations, and nutrient levels (NO3, PO4) were strongly depressed near the surface, due mainly to phytoplankton uptake rather than by dilution. Primary productivity estimates based on the summer nitrate and phosphate deficits over 90 days were 1.96-2.02 and 0.39-1.02 gCm-2d -1 for the east and west sound, respectively. Nutrient ratios indicated that glacial meltwater from the Ross Ice Shelf and/or nearby terrestrial sources may be an important component of the summer meltwater input to the western Sound. Enhanced water column stability due to this input may prolong the maintenance of high water column stability as this water mass flows northward and result in particularly high productivity in northern McMurdo Sound.

Structural characteristics of congelation and platelet ice and their role in the development of antarctic land-fast sea ice

“…and Wadhams, 1989). In the austral winters of 1984, Barry (1988 and Crocker and Wadhams ( 1989) respectively reported that, prior to basal melting, the locations of the thickest platelet-ice accumulations corresponded to the areas of maximum surface supercooling reported by Lewis and Perkin (1985). The pattern of occurrence and quantity of platelet ice in our…”

Association of bacteria with Phaeocystis sp. In McMurdo Sound, Antarctica

“…Our sampling sites were located about 10 to 25 km west of Ross Island. The current at our sampling sites consistently came from the north; thus we were likely sampling water recently advected into the region from the southwestern Ross Sea (Barry 1988). Although we will discuss our findings in terms of a seasonal trend it is important to note that we did not follow the same water mass throughout the study.…”

“…By 10 January macrocolony abundance and cell size were both greatly decreased as the alga apparently entered a different part of its life cycle. It is not clear what environmental factor causes the change in morphology and presumably growth rate, since concentrations of major nutrients remain high and temperature fluctuations in McMurdo Sound are small during this period (Littlepage 1965, Barry 1988.…”

Trophic Structure of Coastal Antarctic Food Webs Associated With Changes in Sea Ice and Food Supply

“…While sea ice algal productivity in McMurdo Sound may be high (Palmisano and Sullivan 1983), its contribution through detrital fallout to benthic systems is poorly understood (Dayton 1990). During summer Phaeocystis blooms, the eastern sound receives plankton-rich waters, which flow southward from the Ross Sea, while the western sound is subject to relatively plankton-poor waters that flow northward after circulating under the Ross Ice Shelf (Barry andDayton 1988, Grebmeier and. The locations we sampled encapsulated the variability in the strong east-west and north-south gradients in different potential food sources and productivity in the high latitude waters of the southwestern Ross Sea coast.…”