ALBERT

Description: In the mainframe of the REP14-MED sea trial in June 2014, the hydrography and circulation west of Sardinia, observed by means of gliders, shipborne CTD instruments, towed devices, and vessel-mounted ADCPs, are presented and compared with previous knowledge. So far, the circulation is not well known in this area, and the hydrography is subject to long-term changes. Potential temperature, salinity, and potential density ranges, as well as core values of the observed water masses were determined. Modified Atlantic Water (MAW), with potential density anomalies below 28.72 kg m−3, showed a salinity minimum of 37.93 at 50 dbar. Levantine Intermediate Water (LIW), with a salinity maximum of about 38.70 at 400 dbar, was observed within a range of 28.72 〈 σΘ [kg m−3] 〈 29.10. MAW and LIW showed slightly higher salinities than previous investigations. During the trial, LIW covered the whole area from the Sardinian shelf to 7°15' E. Only north of 40° N was it tied to the continental slope. Within the MAW, a cold and saline anticyclonic eddy was observed in the southern trial area. The strongest variability in temperature and salinity appeared around this eddy, and in the southwestern part of the domain, where unusually low saline surface water entered the area towards the end of the experiment. An anticyclonic eddy of Winter Intermediate Water was recorded moving northward at 0.014 m s−1. Geostrophic currents and water mass transports calculated across zonal and meridional transects showed a good agreement with vessel-mounted ADCP measurements. Within the MAW, northward currents were observed over the shelf and offshore, while a southward transport of about 1.5 Sv occurred over the slope. A net northward transport of 0.38 Sv across the southern transect decreased to zero in the north. Within the LIW, northward transport of 0.6 Sv across the southern transects were mainly observed offshore, and decreased to 0.3 Sv in the north where they were primarily located over the slope. This presentation of the REP14-MED observations helps to further understand the long-term evolution of hydrography and circulation in the Western Mediterranean, where considerable changes occurred after the Eastern Mediterranean Transient and the Western Mediterranean Transition.

Description: The observational part of the REP14-MED experiment was conducted in June 2014 in the Sardo-Balearic Basin west of Sardinia (western Mediterranean Sea). Two research vessels collected high-resolution oceanographic data by means of hydrographic casts, towed systems, and underway measurements. In addition, a vast amount of data was provided by a fleet of 11 ocean gliders, time series were available from moored instruments, and information on Lagrangian flow patterns was obtained from surface drifters and one profiling float. The spatial resolution of the observations encompasses a spectrum over 4 orders of magnitude from ?(101 m) to ?(105 m), and the time series from the moored instruments cover a spectral range of 5 orders from ?(101 s) to ?(106 s). The objective of this article is to provide an overview of the huge data set which has been utilised by various studies, focusing on (i) water masses and circulation, (ii) operational forecasting, (iii) data assimilation, (iv) variability of the ocean, and (v) new payloads for gliders.

Description: In the frame of the REP14-MED sea trial in June 2014, the hydrography and circulation west of Sardinia, observed by means of gliders, shipborne CTD (conductivity, temperature, depth) instruments, towed devices, and vessel-mounted ADCPs (acoustic doppler current profilers), are presented and compared with previous knowledge. So far, the circulation is not well-known in this area, and the hydrography is subject to long-term changes. Potential temperature, salinity, and potential density ranges as well as core values of the observed water masses were determined. Modified Atlantic Water (MAW), with potential density anomalies below 28.72 kg m−3, showed a salinity minimum of 37.93 at 50 dbar. Levantine Intermediate Water (LIW), with a salinity maximum of about 38.70 at 400 dbar, was observed within a range of 28.72

Description: Monthly averaged satellite imagery of chlorophyll a in the south-western sector of the Atlantic Ocean shows intense and recurrent blooms around the Antarctic Peninsula, the Island of South Georgia and the South Sandwich Islands. Analysis of a 10 year long time series of SeaWiFS ocean color images allows studying seasonal trends and inter-annual variability. Although specific areas show a regular pattern of low or high productivity, certain years appear to be strikingly productive or well below the climatological average. Circulation patterns, continental shelves as well as Antarctic Circumpolar Front are shown to be the major factors controlling extension of highly productive patches

Description: Data coverage in the Southern Ocean is a limiting factor for a full understanding of physical and biological processes: still little is known about their seasonality as well as their regional distribution. In these conditions remote sensing becomes a key tool, as high resolution is possible both in space and time.Focus of this study is the Scotia Sea, included between the Drake Passage and the South Sandwich Islands, the North and South Scotia Ridge. Satellite based measurements of chlorophyll-a show an enhanced biological productivity in the vicinity of the island ecosystems, which is then redistributed by complex circulation patterns. As for other High Nutrient Low Chlorophyll regions, the iron deficiency hypothesis is a well accepted explanation for these confined and intense spring and summer phytoplankton blooms. Several studies suggest that melting of sea-ice, ocean circulation patterns, grazing and the presence of confined land (the so called island mass effect), can regulate their occurrence and extent, although the relative importance of these factors is difficult to ascertain. Here, we address interannual and spatial variability of phytoplankton blooms in the Scotia Sea region; a combination of different datasets is used to describe and study their dynamics. Aqua-MODIS measurements of surface chlorophyll-a concentration and sea surface temperature (SST) were obtained from the NASA Goddard Distributed Active Archive Center. Analysis of regional monthly averaged data allows to track the history of each bloom, as well as to locate its starting point and extension.Fronts and water masses can be contoured by following horizontal temperature gradients. Available Argo float CTD profiles will also contribute with values for the mixed layer depth. Results show a significant inter-annual variability of the bloom starting point, intensity and extent, especially around the South Sandwich and South Georgia islands. However, the complexity of interactions between the phytoplankton communities and the surrounding environment, responsible for bottom-up and top-down control (i.e. micro-nutrient enrichment and grazing) implies the need for more dedicated surveys and high resolution coupled physical-biogeochemical models; the latter would provide further information regarding nutrient fluxes and physical processes, especially during the undersampled winter season.

Description: Abstract Monthly averaged satellite imagery of chlorophyll a in the south-western sector of the Atlantic Ocean shows intense and recurrent blooms around the Antarctic Peninsula, the Island of South Georgia and the South Sandwich Islands. Analysis of a 10 year long time series of SeaWiFS ocean color images allows studying seasonal trends and inter-annual variability. Although specific areas show a regular pattern of low or high productivity, certain years appear to be strikingly productive or well below the climatological average. Circulation patterns, continental shelves as well as Antarctic Circumpolar Front are shown to be the major factors controlling extension of highly productive patches.

Description: The islands of the Southern Ocean, the largest of the High Nutrient Low Chlorophyll (HNLC) regions, have an important role in favouring phytoplankton growth and bloom development. Concentrations of iron, which has been demonstrated to be an important limiting micronutrient, play a major role in regulating the intensity and location of these blooms; however, sea-ice melting, ocean circulation patterns and the “island mass effect” may as well help explain such striking events for a HNLC region. This study will focus on the Southwest sector of the Atlantic Ocean, specifically on the Scotia Sea; this region [52°W – 30°W; 48°S – 56°S] is included between the North and South Scotia Ridge, and between the Drake Passage and the South Sandwich Islands. The main coastal ecosystems are those of the South Georgia, South Orkney and the South Sandwich islands; also the Antarctic Peninsula is included in the domain. The natural dynamics of phytoplankton blooms in the Scotia Sea have been investigated by analysing SeaWiFS, 9km resolution monthly composites of chlorophyll-a concentrations. The retrieved 12-year satellite time series (1997-2009) shows a clear seasonal trend in chlorophyll concentrations, which start increasing in August. Maximum concentrations (〉 3 mg/m^3) are detected between December and January after which bloom regions start shrinking in size, and chlorophyll-a concentrations return to the winter background concentrations. In this presentation we will also show how circulation patterns, bathymetry, continental shelves as well as the Antarctic Circumpolar Fronts are the major factors controlling the extension and location of these highly productive patches. The complexity of interactions between phytoplankton communities and the surrounding environment implies the need for more dedicated surveys and high resolution coupled physical-biogeochemical models; the latter would provide further information regarding nutrient fluxes and physical processes, especially during the under-sampled winter season, and in the deeper layers not captured by satellite images.

Description: Amidst high-nutrient low-chlorophyll waters of the south-western Atlantic sector of the Southern Ocean, an intense phytoplankton bloom is observed annually north of South Georgia (37°W, 55°S). South Georgia blooms have a vital role in the ecosystem surrounding the island, and have been linked to one of the strongest seasonal atmospheric-carbon uptake in the open Southern Ocean. Which environmental conditions drive such remarkable productivity are still under debate, and were investigated in the current study using a multidisciplinary approach. Satellite-derived observations of surface chlorophyll a concentrations and circulation patterns were used to study the annual and inter-annual variability of phytoplankton blooms in the region. Our analysis reveals a time series of very regular blooms, controlled in space by circulation and regulated in time by surface silicate concentrations, temperature and light. The role of the fundamental, yet limiting, micronutrient iron was investigated with the coupled hydrodynamic-biogeochemical model ROMS_AGRIF-PISCES. Model results, validated against available observations, suggest a continuous supply of dissolved iron from the island's shallow shelves that is redistributed in the region by local circulation. Conversely, aeolian sources of iron have a negligible role in the main bloom area, but appear to be more important outside the influence of the South Georgia island mass effect.