scholarly journals Summer microplankton community structure across the Scotia Sea: implications for biological carbon export

2010 ◽  
Vol 7 (1) ◽  
pp. 343-356 ◽  
Author(s):  
R. E. Korb ◽  
M. J. Whitehouse ◽  
M. Gordon ◽  
P. Ward ◽  
A. J. Poulton
Keyword(s):  
Austral Summer ◽  
Open Water ◽  
Carbon Export ◽  
Scotia Sea ◽  
South Georgia ◽  
Group A ◽  
Circumpolar Current ◽  
Physical Features ◽  
Previous Summer ◽  
Mixed Community

Abstract. During the austral summer of 2008, we carried out a high resolution survey of the microplankton communities along a south to north transect covering a range of environments across the Scotia Sea, Southern Ocean; high and low productivity, sea-ice to open water conditions, and over a number of oceanographic fronts and bathymetric features. Cluster analysis revealed five distinct communities that were geographically constrained by physical features of bathymetry and fronts. From south to north the communities were: (1) the South Orkney group, a mixed community of naked dinoflagellates and heavily silicified diatoms, (2) southern Scotia Sea, a mixed community of cyptophytes and naked dinoflagellates, (3) central Scotia Sea, dominated by naked dinoflagellates, (4) southwest of the island of South Georgia, lightly silicified diatoms and naked dinoflagellates (5) northwest of South Georgia, dominated by diatoms. Data from a previous summer cruise (2003) to the Scotia Sea followed a similar pattern of community distribution. MODIS images, Chlorophyll a and macronutrient deficits revealed dense phytoplankton blooms occurred around the island of South Georgia, were absent near the ice edge and in the central Scotia Sea and were moderate in the southern Scotia Sea. Using these environmental factors, together with community composition, we propose that south of the Southern Antarctic Circumpolar Current Front, biogenic silica is preferentially exported and north of the front, in the vicinity of South Georgia, carbon is exported to depth.

scholarly journals Summer microplankton community structure across the Scotia Sea: implications for biological carbon export

2009 ◽  
Vol 6 (5) ◽  
pp. 9781-9815
Author(s):  
R. E. Korb ◽  
M. J. Whitehouse ◽  
M. Gordon ◽  
P. Ward ◽  
A. J. Poulton
Keyword(s):  
Austral Summer ◽  
Open Water ◽  
Carbon Export ◽  
Scotia Sea ◽  
South Georgia ◽  
Group A ◽  
Circumpolar Current ◽  
Physical Features ◽  
Previous Summer ◽  
Mixed Community

Abstract. During the austral summer of 2008, we carried out a high resolution survey of the microplankton communities along a south to north transect covering a range of environments across the Scotia Sea, Southern Ocean; high and low productivity, sea-ice to open water conditions, and over a number of oceanographic fronts and bathymetric features. Cluster analysis revealed five distinct communities that were geographically constrained by physical features of bathymetry and fronts. From south to north the communities were: (1) The South Orkney group, a mixed community of naked dinoflagellates and heavily silicified diatoms, (2) Southern Scotia Sea, a mixed community of cyptophytes and naked dinoflagellates, (3) Central Scotia Sea, dominated by naked dinoflagellates, (4) southwest of the island of South Georgia, lightly silicified diatoms and naked dinoflagellates (5) northwest of South Georgia, dominated by diatoms. Data from a previous summer cruise (2003) to the Scotia Sea followed a similar pattern of community distribution. MODIS images, chlorophyll-a and macronutrient deficits revealed dense phytoplankton blooms occurred around the island of South Georgia, were absent near the ice edge and in the central Scotia Sea and were moderate in the southern Scotia Sea. Using these environmental factors, together with community composition, we propose that south of the Southern Antarctic Circumpolar Current Front, biogenic silica is preferentially exported and north of the front, in the vicinity of South Georgia, carbon is exported to depth.

scholarly journals Krill transport in the Scotia Sea and environs

1998 ◽  
Vol 10 (4) ◽  
pp. 406-415 ◽  
Author(s):  
Eileen E. Hofmann ◽  
John M. Klinck ◽  
Ricardo A. Locarnini ◽  
Bettina Fach ◽  
Eugene Murphy
Keyword(s):  
Flow Field ◽  
Antarctic Peninsula ◽  
Antarctic Circumpolar Current ◽  
Large Scale ◽  
Scotia Sea ◽  
South Georgia ◽  
Composite Flow ◽  
Large Scale Flow ◽  
Circumpolar Current ◽  
The Antarctic

Historical observations of the large-scale flow and frontal structure of the Antarctic Circumpolar Current in the Scotia Sea region were combined with the wind-induced surface Ekman transport to produce a composite flow field. This was used with a Lagrangian model to investigate transport of Antarctic krill. Particle displacements from known krill spawning areas that result from surface Ekman drift, a composite large-scale flow, and the combination of the two were calculated. Surface Ekman drift alone only transports particles a few kilometres over the 150-day krill larval development time. The large-scale composite flow moves particles several hundreds of kilometres over the same time, suggesting this is the primary transport mechanism. An important contribution of the surface Ekman drift on particles released along the continental shelf break west of the Antarctic Peninsula is moving them north-northeast into the high-speed core of the southern Antarctic Circumpolar Current Front, which then transports the particles to South Georgia in about 140–160 days. Similar particle displacement calculations using surface flow fields obtained from the Fine Resolution Antarctic Model do not show overall transport from the Antarctic Peninsula to South Georgia due to the inaccurate position of the southern Antarctic Circumpolar Current Front in the simulated circulation fields. The particle transit times obtained with the composite large-scale flow field are consistent with regional abundances of larval krill developmental stages collected in the Scotia Sea. These results strongly suggest that krill populations west of the Antarctic Peninsula provide the source for the krill populations found around South Georgia.

scholarly journals The Osservatorio Geofisico Sperimentale marine magnetic surveys in the Antarctic Seas

1999 ◽  
Vol 42 (2) ◽  
Author(s):  
E. Lodolo ◽  
F. Coren ◽  
C. Zanolla
Keyword(s):  
Tectonic Evolution ◽  
Ross Sea ◽  
Austral Summer ◽  
Geological Structure ◽  
Seismic Profiles ◽  
Scotia Sea ◽  
Geophysical Surveys ◽  
Scientific Results ◽  
The Antarctic ◽  
Derived Data

About 40 000 km of marine magnetic and gradiometric data have been collected during eight geophysical surveys conducted since the Austral summer 1987/1988 in the circum-antarctic seas, by the research vessel OGS-Explora. For the most surveyed areas (Ross Sea, Southwestern Pacific Ocean, and Southern Scotia Sea), the analysis of the acquired data have contributed to clarify important aspects of their geological structure and tectonic evolution. The main scientific results, obtained combining other available geophysical data (multichannel seismic profiles and satellite-derived data), will be briefly illustrated.

scholarly journals Bacterioplankton composition in the Scotia Sea, Antarctica, during the austral summer of 2003

2006 ◽  
Vol 45 ◽  
pp. 229-235 ◽  
Author(s):  
JN Topping ◽  
JL Heywood ◽  
P Ward ◽  
MV Zubkov
Keyword(s):  
Austral Summer ◽  
Scotia Sea

scholarly journals Albedo of the ice covered Weddell and Bellingshausen Seas

2012 ◽  
Vol 6 (2) ◽  
pp. 479-491 ◽  
Author(s):  
A. I. Weiss ◽  
J. C. King ◽  
T. A. Lachlan-Cope ◽  
R. S. Ladkin
Keyword(s):  
Sea Ice ◽  
Surface Albedo ◽  
Austral Summer ◽  
Open Water ◽  
Weddell Sea ◽  
First Year ◽  
Pack Ice ◽  
Bellingshausen Sea ◽  
The Mean ◽  
The Antarctic

Abstract. This study investigates the surface albedo of the sea ice areas adjacent to the Antarctic Peninsula during the austral summer. Aircraft measurements of the surface albedo, which were conducted in the sea ice areas of the Weddell and Bellingshausen Seas show significant differences between these two regions. The averaged surface albedo varied between 0.13 and 0.81. The ice cover of the Bellingshausen Sea consisted mainly of first year ice and the sea surface showed an averaged sea ice albedo of αi = 0.64 ± 0.2 (± standard deviation). The mean sea ice albedo of the pack ice area in the western Weddell Sea was αi = 0.75 ± 0.05. In the southern Weddell Sea, where new, young sea ice prevailed, a mean albedo value of αi = 0.38 ± 0.08 was observed. Relatively warm open water and thin, newly formed ice had the lowest albedo values, whereas relatively cold and snow covered pack ice had the highest albedo values. All sea ice areas consisted of a mixture of a large range of different sea ice types. An investigation of commonly used parameterizations of albedo as a function of surface temperature in the Weddell and Bellingshausen Sea ice areas showed that the albedo parameterizations do not work well for areas with new, young ice.

Changes in phytoplankton concentration now drive increased Arctic Ocean primary production

Science ◽  
2020 ◽  
Vol 369 (6500) ◽  
pp. 198-202 ◽  
Author(s):  
K. M. Lewis ◽  
G. L. van Dijken ◽  
K. R. Arrigo
Keyword(s):  
Sea Ice ◽  
Primary Production ◽  
Arctic Ocean ◽  
Open Water ◽  
Water Area ◽  
The Arctic ◽  
Carbon Export ◽  
Phytoplankton Primary Production ◽  
Open Water Area ◽  
The Arctic Ocean

Historically, sea ice loss in the Arctic Ocean has promoted increased phytoplankton primary production because of the greater open water area and a longer growing season. However, debate remains about whether primary production will continue to rise should sea ice decline further. Using an ocean color algorithm parameterized for the Arctic Ocean, we show that primary production increased by 57% between 1998 and 2018. Surprisingly, whereas increases were due to widespread sea ice loss during the first decade, the subsequent rise in primary production was driven primarily by increased phytoplankton biomass, which was likely sustained by an influx of new nutrients. This suggests a future Arctic Ocean that can support higher trophic-level production and additional carbon export.

Changes in seabird species abundance near South Georgia during a period of rapid change in sea surface temperature

1992 ◽  
Vol 4 (1) ◽  
pp. 15-22 ◽  
Author(s):  
G.L. Hunt ◽  
J. Priddle ◽  
M.J. Whitehouse ◽  
R.R. Veit ◽  
R.B. Heywood
Keyword(s):  
Surface Temperature ◽  
Sea Surface Temperature ◽  
Rapid Change ◽  
Species Abundance ◽  
Sea Surface ◽  
Resident Species ◽  
Seabird Species ◽  
Scotia Sea ◽  
South Georgia ◽  
Time Observation

During a three month research cruise near the island of South Georgia, sea surface temperature (SST) increased from c. 2°C to over 4°C. Satellite derived SST show that this corresponded to a rapid southward and eastward shift of isotherms in the northern Scotia Sea, which could have resulted from changes in the wind field. At the same time, observation from the ship of seabirds close to the island indicated changes in the abundance of some non-resident species, whereas resident breeders from South Georgia, such as black-browed albatrosses (Diomedea melanophris) and prions (Pachyptila spp.) which were foraging locally, were present at consistent density in both halves of the survey. Blue petrels (Halobaena caerulea) left the area after breeding, so were associated only with the low water temperatures during the first part of the cruise. In contrast, great shearwaters (Puffinus gravis) and soft-plumaged petrels (Pterodroma mollis) migrated into the area later in the survey. These birds were almost certainly non-breeders which were feeding in the warmer water which had moved towards the island.

scholarly journals Coccolithophore populations and their contribution to carbonate export during an annual cycle in the Australian sector of the Antarctic zone

2018 ◽  
Vol 15 (6) ◽  
pp. 1843-1862 ◽  
Author(s):  
Andrés S. Rigual Hernández ◽  
José A. Flores ◽  
Francisco J. Sierro ◽  
Miguel A. Fuertes ◽  
Lluïsa Cros ◽  
...  
Keyword(s):  
Southern Ocean ◽  
Ocean Acidification ◽  
Deep Ocean ◽  
Sediment Traps ◽  
Global Ocean ◽  
Field Observations ◽  
Scotia Sea ◽  
Allochthonous Species ◽  
Circumpolar Current ◽  
The Antarctic

Abstract. The Southern Ocean is experiencing rapid and relentless change in its physical and biogeochemical properties. The rate of warming of the Antarctic Circumpolar Current exceeds that of the global ocean, and the enhanced uptake of carbon dioxide is causing basin-wide ocean acidification. Observational data suggest that these changes are influencing the distribution and composition of pelagic plankton communities. Long-term and annual field observations on key environmental variables and organisms are a critical basis for predicting changes in Southern Ocean ecosystems. These observations are particularly needed, since high-latitude systems have been projected to experience the most severe impacts of ocean acidification and invasions of allochthonous species. Coccolithophores are the most prolific calcium-carbonate-producing phytoplankton group playing an important role in Southern Ocean biogeochemical cycles. Satellite imagery has revealed elevated particulate inorganic carbon concentrations near the major circumpolar fronts of the Southern Ocean that can be attributed to the coccolithophore Emiliania huxleyi. Recent studies have suggested changes during the last decades in the distribution and abundance of Southern Ocean coccolithophores. However, due to limited field observations, the distribution, diversity and state of coccolithophore populations in the Southern Ocean remain poorly characterised. We report here on seasonal variations in the abundance and composition of coccolithophore assemblages collected by two moored sediment traps deployed at the Antarctic zone south of Australia (2000 and 3700 m of depth) for 1 year in 2001–2002. Additionally, seasonal changes in coccolith weights of E. huxleyi populations were estimated using circularly polarised micrographs analysed with C-Calcita software. Our findings indicate that (1) coccolithophore sinking assemblages were nearly monospecific for E. huxleyi morphotype B/C in the Antarctic zone waters in 2001–2002; (2) coccoliths captured by the traps experienced weight and length reduction during summer (December–February); (3) the estimated annual coccolith weight of E. huxleyi at both sediment traps (2.11 ± 0.96 and 2.13 ± 0.91 pg at 2000 and 3700 m) was consistent with previous studies for morphotype B/C in other Southern Ocean settings (Scotia Sea and Patagonian shelf); and (4) coccolithophores accounted for approximately 2–5 % of the annual deep-ocean CaCO3 flux. Our results are the first annual record of coccolithophore abundance, composition and degree of calcification in the Antarctic zone. They provide a baseline against which to monitor coccolithophore responses to changes in the environmental conditions expected for this region in coming decades.

scholarly journals Accuracy and inter-analyst agreement of visually estimated sea ice concentrations in Canadian Ice Service ice charts using single-polarization RADARSAT-2

2020 ◽  
Vol 14 (4) ◽  
pp. 1289-1310
Author(s):  
Angela Cheng ◽  
Barbara Casati ◽  
Adrienne Tivy ◽  
Tom Zagon ◽  
Jean-François Lemieux ◽  
...  
Keyword(s):  
Image Segmentation ◽  
Sea Ice ◽  
Open Water ◽  
Automated Segmentation ◽  
Exact Match ◽  
High Agreement ◽  
Low Concentrations ◽  
Ice Concentration ◽  
Group A ◽  
Single Polarization

Abstract. This study compares the accuracy of visually estimated ice concentrations by eight analysts at the Canadian Ice Service with three standards: (i) ice concentrations calculated from automated image segmentation, (ii) ice concentrations calculated from automated image segmentation that were validated by the analysts, and (iii) the modal ice concentration estimate by the group. A total of 76 predefined areas in 67 RADARSAT-2 images are used in this study. Analysts overestimate ice concentrations when compared to all three standards, most notably for low ice concentrations (1/10–3/10). The spread of ice concentration estimates is highest for middle concentrations (5/10, 6/10) and smallest for the 9/10 ice concentration. The overestimation in low concentrations and high variability in middle concentrations introduce uncertainty into the ice concentration distribution in ice charts. The uncertainty may have downstream implications for numerical modelling and sea ice climatology. Inter-analyst agreement is also measured to determine which classifier's ice concentration estimates (analyst or automated image segmentation) disagreed the most. It was found that one of the eight analysts disagreed the most, followed second by the automated segmentation algorithm. This suggests high agreement in ice concentration estimates between analysts at the Canadian Ice Service. The high agreement, but consistent overestimation, results in an overall accuracy of ice concentration estimates in polygons to be 39 %, 95 % CI [34 %, 43 %], for an exact match in the ice concentration estimate with calculated ice concentration from segmentation and, 84 %, 95 % CI [80 %, 87 %], for the ±1 ice concentration category. Only images with high contrast between ice and open water and well-defined floes are used: true accuracy is expected to be lower than what is found in this study.

scholarly journals Distribution and recurrence of phytoplankton blooms around South Georgia, Southern Ocean

2013 ◽  
Vol 10 (1) ◽  
pp. 217-231 ◽  
Author(s):  
I. Borrione ◽  
R. Schlitzer
Keyword(s):  
Southern Ocean ◽  
Austral Summer ◽  
Wide Field ◽  
Phytoplankton Blooms ◽  
Chl A ◽  
South Georgia ◽  
The North ◽  
Wide Field Of View ◽  
Georgia Basin ◽  
Second Peak

Abstract. South Georgia phytoplankton blooms are amongst the largest of the Southern Ocean and are associated with a rich ecosystem and strong atmospheric carbon drawdown. Both aspects depend on the intensity of blooms, but also on their regularity. Here we use data from 12 yr of SeaWiFS (Sea-viewing Wide Field-of-view Sensor) ocean colour imagery and calculate the frequency of bloom occurrence (FBO) to re-examine spatial and temporal bloom distributions. We find that upstream of the island and outside the borders of the Georgia Basin, blooms occurred in less than 4 out of the 12 yr (FBO < 4). In contrast, FBO was mostly greater than 8 downstream of the island, i.e., to the north and northwest, and in places equal to 12, indicating that blooms occurred every year. The typical bloom area, defined as the region where blooms occurred in at least 8 out of the 12 yr, covers the entire Georgia Basin and the northern shelf of the island. The time series of surface chlorophyll a (Chl a) concentrations averaged over the typical bloom area shows that phytoplankton blooms occurred in every year between September 1997 and September 2010, and that Chl a values followed a clear seasonal cycle, with concentration peaks around December followed in many years by a second peak during late austral summer or early autumn, suggesting a bi-modal bloom pattern. The bloom regularity we describe here is in contrast with results of Park et al. (2010) who used a significantly different study area including regions that almost never exhibit bloom conditions.

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