Substantial open-ocean phytoplankton blooms to the north of South Georgia, South Atlantic, during summer

Whitehouse, M. J.; Priddle, J.; Trathan, P. N.; Brandon, Mark A.

doi:10.3354/meps140187

Cited by 33 publications

(19 citation statements)

References 25 publications

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“…These interpretations are not supported by recent findings, which suggest that the PF is consistently > 250 km to the north of South Georgia (Orsi et al 1995. However, there is some evidence that warm water eddies of PFZ origin may influence the South Georgia region from the west , Whitehouse et al 1996b). …”

Section: South Georgia In the Antarctic Circumpolar Currentmentioning

confidence: 69%

South Georgia, Antarctica: a productive, cold water, pelagic ecosystem

Atkinson¹,

Whitehouse²,

Priddle³

et al. 2001

Mar. Ecol. Prog. Ser.

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257

188

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The South Georgia region is characterised by high biomass and productivity of phytoplankton, zooplankton and vertebrate predators. Important commercial fisheries have been based at the island since the late 1700s, initially exploiting seals and whales, and currently taking krill Euphausia superba and finfish. Despite studies dating from the beginning of the last century, the causes of the high productivity remain unclear. The island lies within the Antarctic Zone of the Antarctic Circumpolar Current, to the south of the Polar Front. The offshore waters to its north and east are affected by a northwards deflection of the Southern Antarctic Circumpolar Current Front, together with waters from the Weddell-Scotia Confluence. Despite a retentive circulation over the shelf, the high productivity of phytoplankton and copepods is widespread, occurring far downstream and possibly extending to the Polar Front. High phytoplankton concentrations (>20 mg chlorophyll a m , equally dominated by krill and copepods. This greatly exceeds typical values for Antarctica, and is high compared to productive northern shelves. Zooplankton, and in particular krill, appear to have a pivotal role in regulating energy flow in this food web, through selective grazing and possibly also through nutrient regeneration. Abundances of krill and copepods are negatively related across a wide range of scales, suggesting direct interaction through competition or predation. Evidence suggests that when phytoplankton stocks are low, energy flow through krill is maintained by their feeding on the large populations of small copepods. Metazoans and higher predators at South Georgia can feed across several trophic levels according to prey abundance, and they regenerate substantial quantities of reduced nitrogen. Therefore we suggest that these groups have a controlling influence on lower trophic levels, both stabilising population sizes and maintaining high rates of energy flow. Hydrography, nutrient concentrations, phytoplankton, copepod, and krill biomasses fluctuate between years. Periodically (once or twice a decade), shortages of krill in summer result in breeding failures among many of their predators. This appears to be a downstream effect from wider scale, Scotia Sea phenomena, although the processes involved are unclear. The elevated biomass and energy flows at South Georgia appear to be caused by locally enhanced growth rates; there is no evidence so far for any physical concentration mechanism. Even for krill, which do not breed there, local growth rates are probably of a similar order to the biomass removed by their main land-based predators in summer. Thus the transfer of energy to higher predators depends on local enhancement of fluxes through the food web as well as the supply of plankton to the island by the Antarctic Circumpolar Current.

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Section: South Georgia In the Antarctic Circumpolar Currentmentioning

confidence: 69%

South Georgia, Antarctica: a productive, cold water, pelagic ecosystem

Atkinson¹,

Whitehouse²,

Priddle³

et al. 2001

Mar. Ecol. Prog. Ser.

Self Cite

257

188

View full text Add to dashboard Cite

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“…High phytoplankton concentrations ð41:0 mg m À3 Þ are found below 60 m in the study area (El-Sayed and Weber, 1982;Bianchi et al, 1992;Tre´guer and Jacques, 1992;Smith et al, 1996;Whitehouse et al, 1996). Deep chlorophyll maxima have been observed mostly in the summer/fall in the Scotia Sea (El-Sayed and Weber, 1982), western Antarctic Peninsula (Bianchi et al, 1992;Tre´guer and Jacques, 1992;Smith et al, 1996) and near South Georgia (Whitehouse et al, 1996); they are not observed during winter/spring (El-Sayed and Weber, 1982;Smith et al, 1996).…”

Section: Deep Chlorophyll Maximummentioning

confidence: 86%

“…Deep chlorophyll maxima have been observed mostly in the summer/fall in the Scotia Sea (El-Sayed and Weber, 1982), western Antarctic Peninsula (Bianchi et al, 1992;Tre´guer and Jacques, 1992;Smith et al, 1996) and near South Georgia (Whitehouse et al, 1996); they are not observed during winter/spring (El-Sayed and Weber, 1982;Smith et al, 1996). Due to limited data this feature was not included in this modeling approach, although it may well be one additional food source available to krill in summer.…”

Section: Deep Chlorophyll Maximummentioning

confidence: 99%

“…Interannual variability of Antarctic krill around South Georgia is well recognized (Harmer, 1931;Kemp and Bennet, 1932;Mackintosh, 1972), with substantially greater catches of krill in colder years (Mackintosh, 1972). Analyses of historical data sets suggest that variability in Antarctic krill abundance within the South Georgia ecosystem may be the manifestation of periodic variations across the Scotia Sea and indeed the whole Southern Ocean (Priddle et al, 1988;Murphy et al, 1995;Fedoulov et al, 1996;Whitehouse et al, 1996;Atkinson et al, 2004). During the last 20 years, krill abundance around South Georgia was much reduced in at least 4 years (Priddle et al, 1988;Brierley et al, 1997), which affected many krill predators.…”

Section: Introductionmentioning

confidence: 99%

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Transport of Antarctic krill (Euphausia superba) across the Scotia Sea. Part II: Krill growth and survival

Fach

Hofmann

Murphy

2006

Deep Sea Research Part I: Oceanographic Research Papers

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A time-dependent, size-structured, physiologically based krill growth model was used in conjunction with a circulation model to test the hypothesis that Antarctic krill (Euphausia superba) populations at South Georgia are sustained by import of individuals from upstream regions. Surface phytoplankton concentrations along the simulated drifter trajectories were extracted from historical Coastal Zone Color Scanner (CZCS) measurements and sea ice biota concentrations were calculated from sea ice concentration and extent extracted along drifter trajectories from Special Sensor Microwave/ Imager measurements. As additional food sources, a time series of heterotrophic food was constructed from historical data, and time series of detritus concentrations were calculated using phytoplankton concentrations extracted from CZCS measurements together with measured particulate organic carbon to chlorophyll a ratios. These food resources along specified drifter trajectories were then input to the krill growth model to determine the size and viability of krill during transport from the source region to South Georgia. The krill growth model simulations showed that no single food source can support continuous growth of krill during the 58-306 days needed for transport to South Georgia. However, under the current assumptions results indicate that combinations of food sources during the transport time enhanced krill survival, with heterotrophic food and detritus being particularly important during periods of low phytoplankton concentrations. The growth model simulations also showed that larval and juvenile krill originating along the western Antarctic Peninsula can grow to 1þ (14-36 mm) and 2þ (26-45 mm) age and size classes observed at South Georgia during the time needed for transport to this region. Krill originating in the Weddell Sea need 20 months for transport, which allows retention in a potentially high food environment, provided by sea ice, for almost 1 year. Krill then complete transport to South Georgia in the following year and larval and juvenile krill grow to 2þ (26-45 mm) and 3þ (35-60 mm) age and size classes during transport. The results of this study show that the successful transport of krill to South Georgia depends on a multitude of factors, such as the location of the spawning area and timing of spawning, food concentrations during transport, predation, and variations in the location of the Southern Antarctic Circumpolar Current Front (SACCF) and in sea ice extent. r

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“…The waters south of the SACCF, influenced by the Weddell -Scotia Confluence, are rich in nutrients, especially silicate; hence, eddies from the SACCF could be an important mechanism for the enhancement of local productivity (Whitehouse et al, 1996). The cold core eddy that was formed in OCCAM rejoined the SACCF after 1 month; data from the Southern Ocean Argo program (a global array of temperature/salinity profiling floats; Roemmich and Owens, 2000) should help to describe the characteristics and fate of these eddies in the ocean.…”

Section: Discussionmentioning

confidence: 99%

Variability of the southern Antarctic Circumpolar Current front north of South Georgia

Thorpe

Heywood

Brandon

et al. 2002

Journal of Marine Systems

114

108

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South Georgia ( f 54jS, 37jW) is an island in the eastern Scotia Sea, South Atlantic that lies in the path of the Antarctic Circumpolar Current (ACC). The southern ACC front (SACCF), one of three major fronts associated with the ACC, wraps anticyclonically around South Georgia and then retroflects north of the island. This paper investigates temporal variability in the position of the SACCF north of South Georgia that is likely to have an effect on the South Georgia ecosystem by contributing to the variability in local krill abundance.A meridional hydrographic section that crossed the SACCF three times demonstrates that the SACCF is associated with a geopotential anomaly of 4.5 J kg À 1 in the eastern Scotia Sea. A high resolution (1/4j Â 1/4j) map of historical geopotential anomaly shows the mean position of the SACCF retroflection north of South Georgia to be at 36jW, 400 km further east than in previous work. It also reveals temporal variability associated with the SACCF in the South Georgia region. A near-surface drifter provides evidence for variability in the western extent of the SACCF north of South Georgia and for the presence of eddies in the region. Output from a 3-year (1993 -1995) high frequency wind forced run of the eddy-permitting Ocean Circulation and Climate Advanced Modelling project (OCCAM) model, used to investigate the frontal variability, shows two periods of anomalous westward extent of the SACCF north of South Georgia and associated eddy-shedding. The SACCF variability affects the near-surface transport of passive drifters into the region with implications for the South Georgia ecosystem. D

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Substantial open-ocean phytoplankton blooms to the north of South Georgia, South Atlantic, during summer

Cited by 33 publications

References 25 publications

South Georgia, Antarctica: a productive, cold water, pelagic ecosystem

South Georgia, Antarctica: a productive, cold water, pelagic ecosystem

Transport of Antarctic krill (Euphausia superba) across the Scotia Sea. Part II: Krill growth and survival

Variability of the southern Antarctic Circumpolar Current front north of South Georgia

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