Cornelius W. Sullivan

Distributions of phytoplankton blooms in the southern ocean.

A regional pigment retrieval algorithm for the Nimbus-7 Coastal Zone Color Scanner (CZCS) has been tested for the Southern Ocean. The pigment concentrations estimated with this algorithm agree to within 5 percent with in situ values and are more than twice as high as those previously reported. The CZCS data also revealed an asymmetric distribution of enhanced pigments in the waters surrounding Antarctica; in contrast, most surface geophysical properties are symmetrically distributed. The asymmetry is coherent with circumpolar current patterns and the availability of silicic acid in surface waters. Intense blooms (>1 milligram of pigment per cubic meter) that occur downcurrent from continental masses result from dissolved trace elements such as iron derived from shelf sediments and glacial melt.

Ecology of sea ice biota - 2. Global significance

SummaryThe sea ice does not only determine the ecology of ice biota, but it also influences the pelagic systems under the ice cover and at ice edges. In this paper, new estimates of Arctic and Antarctic production of biogenic carbon are derived, and differences as well as similarities between the two oceans are examined. In ice-covered seas, high algal concentrations (blooms) occur in association with several types of conditions. Blooms often lead to high sedimentation of intact cells and faecal pellets. In addition to ice-related blooms, there is progressive accumulation of organic matter in Arctic multi-year ice, whose fate may potentially be similar to that of blooms. A fraction of the carbon fixed by microalgae that grow in sea ice or in relation to it is exported out of the production zone. This includes particulate material sinking out of the euphotic zone, and also material passed on to the food web. Pathways through which ice algal production does reach various components of the pelagic and benthic food webs, and through them such top predators as marine mammals and birds, are discussed. Concerning global climate change and biogeochemical fluxes of carbon, not all export pathways from the euphotic zone result in the sequestration of carbon for periods of hundreds of years or more. This is because various processes, that take place in both the ice and the water column, contribute to mineralize organic carbon into CO2 before it becomes sequestered. Processes that favour the production and accumulation of biogenic carbon as well as its export to deep waters and sequestration are discussed, together with those that influence mineralization in the upper ice-covered ocean.

Coastal zone color scanner pigment concentrations in the southern ocean and relationships to geophysical surface features

The spatial and seasonal distributions of phytoplankton pigment concentration over the entire southern ocean have been studied for the first time using the coastal zone color scanner historical data set (from October 1978 through June 1986). Enhanced pigment concentrations are observed between 35°S and 55°S throughout the year, with such enhanced regions being more confined to the south in the austral summer and extending further north in the winter. North and south of the polar front, phytoplankton blooms (>1 mg/m3) are not uniformly distributed around the circumpolar region. Instead, blooms appear to be located in regions of ice retreat (or high melt areas) such as the Scotia Sea and the Ross Sea, in relatively shallow areas (e.g., the Patagonian and the New Zealand shelves), in some regions of Ekman upwelling like the Tasman Sea, and near areas of high eddy kinetic energy such as the Agulhas retroflection. Among all features examined by regression analysis, bathymetry appears to be the one most consistently correlated with pigments (correlation coefficient being about −0.3 for the entire region). The cause of negative correlation with bathymetry is unknown but is consistent with the observed abundance of iron in shallow areas in the Antarctic region. It is also consistent with resuspension of phytoplankton cells by wind-induced mixing, especially in shallow waters. On the other hand, in the deep ocean (especially at latitudes 30%) in average pigment concentration over the entire region during different seasons indicates possible influence of time dependent parameters.

Ecology of sea ice biota

SummaryPolar regions are covered by extensive sea ice that is inhabited by a variety of plants and animals. The environments where the organisms live vary depending on the structure and age of the ice. Many terms have been used to describe the habitats and the organisms. We here characterize the habitats and communities and suggest some standard terms for them. We also suggest routine sampling methods and reporting units for measurements of biological and chemical variables.

Ecology of sea ice biota - 1. Habitat, terminology, and methodology

SummaryPolar regions are covered by extensive sea ice that is inhabited by a variety of plants and animals. The environments where the organisms live vary depending on the structure and age of the ice. Many terms have been used to describe the habitats and the organisms. We here characterize the habitats and communities and suggest some standard terms for them. We also suggest routine sampling methods and reporting units for measurements of biological and chemical variables.

Physical controls on the development and characteristics of Antarctic sea ice biological communities— a review and synthesis

Abstract Ice structures found in Antarctic sea ice and related morphological processes are summarized, including: frazil ice growth; the flooded snow layer; pressure ridge induced flooding; thermally driven brine drainage; and platelet-ice formation. The associated colonization, physiological adaptation, and growth of sea ice biota within these structures, to the levels presently identifiable, are also reviewed. A strong interaction exists between the physical processes that form, evolve and deteriorate sea ice, and the biological communities located within sea ice. Variability of ice structure and associated biological communities over small spatial scales necessitated analysis of the biological component in combination with physical and chemical properties of the sea ice. The ice microstructure provides indications of the growth and evolution of the ice properties and initially defines how ice biota colonize the ice. The light, temperature, space and nutrient fields within which ice biota subsequently adapt and grow, are the other key determinants of the biology. While the ice microstructure shapes the localized biological response, relatively large regions of pack ice have characteristic microstructures. Regional patterns of biomass and biological productivity within the Antarctic sea ice zone may therefore be predictable as a result of these physical-biological associations. Examples from the drifting pack ice and fast ice zones of the Weddell and Ross Seas are given.

Sea Ice Microbial Communities in AntarcticaThese communities may provide an important food resource in deep-water pelagic systems

ccounts of early naturalists first suggested the richness of Antarctic waters. Along with observations of abundant stocks of great whales, seals, and seabirds came reports of sea ice floes stained and discolored by algae. Although sea ice microbial communities (SIMCOs) have been observed and studied for several decades, fundamental questions about their role remain. Do these communities represent a significant food source for benthic or pelagic food webs in ice-covered oceans? If so, what factors contribute to their productivity? Studies of SIMCOs in the landfast ice at McMurdo Sound and in the pack ice region of the Weddell Sea are part of an ongoing effort to understand the role and importance of sea ice communities in the Antarctic marine ecosystem and the physical and chemical attributes of their habitat.

Particulate matter and nutrient distributions in the ice-edge zone of the Weddell Sea: relationship to hydrography during late summer

Previous estimates of the marginal ice zones quantitative contribution to biogeochemical cycles and annual productivity in the Southern Ocean may be conservative because of assumptions that phytoplankton blooms are associated only with actively retreating ice edges. Observations during March 1986, near an almost stationary ice edge in the northwestern Weddell Sea, revealed very low geostrophic currents, no appreciable horizontal gradients in temperature or salinity and no significant net melting or freezing in the ice-edge region. Vertical stratification within the upper 50 m was evident throughout the study area, and resulted primarily from prior melting of pack ice. In contrast with previous observations in marginal ice zones, the distribution of phytoplankton biomass showed little correlation with the meltwater field; here, significant horizontal biomass gradients occurred in an area where vertical stability was almost uniform laterally and both elevated biomass and diminished nutrient levels extended well below the pycnocline. Absolute levels of chlorophyll were modest (generally 10, 1.5 and 3.5 μmol l−1, respectively) were similar to those found previously during a spring phytoplankton bloom at the Weddell-Scotia Sea ice edge. The mean mole ratio of biogenic silica to organic carbon within the particle assemblage was 0.44, which is very high for surface seawater and about three times higher than that typically found in pure diatom cultures. Therefore, despite relatively low chlorophyll levels, the ice edge remained a localized maximum in biogenic particulate matter at least through March and this material was unusually rich in silica. Combined, these physical and biological data show that elevated phytoplankton biomass in the ice-edge zone can persist well past the time when net melting stops and the ice edge becomes stationary.

Sea ice microbial communities (SIMCO)

SummarySea ice microbial communities (SIMCO) grow luxuriantly within several microhabitats of sea ice, indicating that the microorganisms comprising these communities are well adapted to the physicochemical gradients which characterize sea ice. We used SIMCO obtained from the bottom of congelation ice in McMurdo Sound, Antarctica, to test the hypothesis that low temperature limits microbial productivity in polar oceans and also to investigate the effect of salinity on rates of autotrophic and heterotrophic metablism. Substantial rates of carbon fixation, incorporation of thymidine, and uptake of glutamate occurred at the in situ temperatures of-1.9°C, with maximum rates at temperatures considerably warmer but below 15°C. Microalgae and bacteria of SIMCO are thus indicated to be psychrophiles. The relative rates of autotrophic and heterotrophic microbial growth (based on rates of fixation of 14CO2 by microalgae and incorporation of 3H-thymidine by bacteria, respectively) were similar and overlapped from 4° and 7°C. These data suggest that a recent hypothesis proposing the uncoupling of primary production and bacterial production in cold water, due to differential growth of phytoplankton and bacterioplankton at low temperatures, is refuted with respect to SIMCO. Maximum rates of carbon fixation by autotrophs of SIMCO occurred at salinities which characterized the ice from which the SIMCO were collected. In contrast, heterotrophs of SIMCO exhibited a more stenohaline response to variable salinity, with maximum incorporation of thymidine and uridine from 20‰ to 30‰. Adaptations by autotrophs and heterotrophs of SIMCO that permit substantial metabolism and growth at very low temperatures and variable salinities are significant when considering production and trophodynamics in polar oceans. Actively growing microorganisms in these unique communities contribute to overall production in polar oceans, provide carbon for food webs associated with sea ice, and upon release from melting ice may contribute to microbial blooms in marginal ice edge zones, which in turn support cryopelagic food webs.

Autumn Bloom of Antarctic Pack-Ice Algae

An autumn bloom of sea-ice algae was observed from February to June of 1992 within the upper 0.4 meter of multiyear ice in the Western Weddell Sea, Antarctica. The bloom was reliant on the freezing of porous areas within the ice that initiated a vertical exchange of nutrient-depleted brine with nutrient-rich seawater. This replenishment of nutrients to the algal community allowed the net production of 1760 milligrams of carbon and 200 milligrams of nitrogen per square meter of ice. The location of this autumn bloom is unlike that of spring blooms previously observed in both polar regions.