Productivity of the Antarctic waters—A reappraisal

The region between Elephant Island and the South Orkney Islands (53.5" S, 46.5" W) was occupied by Winter Weddell Sea water and a t h c k layer of summer and surface modified Weddell Water. High correlations between nutrients (nitrate, total inorganic carbon, silicate) and oxygen with salinity were found in the upper 150 m near the ice-edge. Nutrient depletion was calculated and correlated with the melting ice processes. When 1 m of ice melts, the average amount of total carbonate and nutrients removed is equivalent to a production of 33 g C m-' yr-'. Increases of oxygen were detected with high rates of nutrient and carbon depletion. However, significant oxygen losses in the melting water body were estimated from the conservative 'NO' parameter. The amount of nutrients removed during pack-ice melting was about 3 times higher than that taken up in the water column. Analyses of particulate material in the ice samples showed similar C:N ratios to those estimated by the decrease of nutrients in the water column.

Section: Phytoplankton Biomass and Nutrient Deficitmentioning

confidence: 99%

mentioning

confidence: 99%

Nutrient depletion and particulate matter near the iceedge in the Weddell Sea

Pérez¹,

Figueiras²,

Rı́os³

1994

“…The release of the more significant urine (or metabolic) nitrogen depends on the grazer population density, grazer metabolic rates and the residence time of the grazers in the euphotic zone. El-Sayed (1984) has described the profound effect that grazing by krill can have on the phytoplankton standing crop. Significant ammonia release can result from such intense grazing.…”

Section: Latitude Latitudementioning

confidence: 99%

Nitrate and silicic acid in the world ocean: patterns and processes

Kamykowski¹,

Zentara²

1985

Two world ocean data sets, GEOSECS and NODC, were analyzed for patterns in the nitrate versus silicic acid regression relation. Significant regional nitrate or silicic acid excesses (i.e. amount of one of these plant nutrients remaining in the water after the other is no longer measurable) tend to occur in some areas of upwelling, shallow sills, deep convection or high rainfall/river outflow. The Southern Ocean is unique in the intensity and complexity of projected (regression intercepts on the nitrate [y] or silicic acid [X] axis) excesses. These global nutrient depletion patterns pertain to regional comparisons of phytoplankton succession and thus to the overall character of plankton community structure. Intercept patterns in different areas are affected by the processes that determine absolute nutrient concentrations at the beginning, and their relative decline during, the growth season. The region south of the southern Polar Front is unlque because winter nutrient concentrations are unusually high around Antarctica due to water mass characteristics and because nutrients generally remain unusually abundant over the growth season partly in response to the cycle of incident solar radiation. The patterns in the regression intercepts in this region largely result from variations in the regression slopes which respond to different weightings of the chemical and biological pathways that determine nitrate and silicic acid concentrations in the upper water column. The nitrate and silicic acid profiles in the Southern Ocean contain information on the temporal average of primary production and of nitrogen recycling up to the tlme of sample collection within the growth season. The interpretation of this information depends on the detail to which the processes that determine the water column concentrations of nitrate and silicic acid are known.

“…Antarctic waters have the highest nutrient (N and P) concentrations and, therefore, potential biological production in the surface waters of the ocean, but the realised production is at least an order of magnitude below this potential (El-Sayed 1984). Hypotheses to account for this paradox span the full spectrum of possible limiting factors, including limitation by resources (nutrients and iron, light) and consumer pressure (e.g.…”

Section: Introductionmentioning

confidence: 99%

Experimental induction of a large phytoplankton bloom in Antarctic coastal waters

Agustı́¹,

Duarte²

2000

The experimental enclosure of an Antarctic planktonic community in a large (35 m 3 ) mesocosm moored in Johnson's Dock (62°39.576' S, 60°22.408' W, Livingston Island, Bransfield Sector, Antarctica) was followed by a large phytoplankton bloom. This bloom, dominated by the large diatom Thalassiosira antarctica, reached a biomass 1000-fold greater than in the ambient waters. The net growth rate of T. antarctica averaged 0.53 ± 0.17 d -1 , with maximum net growth rates close to 1.0 d -1 , exceeding the predicted maximal population growth rates by 60 to 200%. The gross primary production in the mesocosm (49 mmol C m -3 d -1 ) was about 30 times greater than the concurrent gross production in the ambient waters, while sedimentation losses removed only between 2.1 to 13% of the biomass d -1 and cell mortality was negligible. The bloom development led to a decline of dissolved inorganic nutrient concentrations to values several times lower than those in the ambient waters, indicating that the ambient nutrients were both available and sufficient to allow the development of the massive algal bloom observed. Light-limitation of the phytoplankton community was likely the factor responsible for the low biomass and production in ambient waters relative to the mesocosm, as indicated by: (1) limited water transparency of about 1 m, which increased up to 6 m as a result of the sedimentation of the glacial flour in the mesocosm; (2) dense pigment packaging (14.7 ± 3 pg chl a µm -3 ) inside the phytoplankton cells of the community in the ambient waters compared to much lower values (4.2 ± 0.8 pg chl a µm -3 ) in the mesocosm community; (3) a specific light absorption of the phytoplankton community in the ambient waters 10 times higher (average specific PAR absorption ± SE = 0.018 ± 0.0038 m -1 mg chl a -1 ) than in the mesocosm community (0.0087 ± 0.002 m -2 mg -1 chl a); and (4)