Description: Abstract:Five hydrographic transects at nominal longitudes 0°E and 30°E, and fourteen expendablebathythermograph (XBT) sections near the former longitude are used to study the baroclinictransport of the Antarctic Circumpolar Current (ACC) between Africa and Antarctica. Thebottom-referenced geostrophic transport between the Subtropical Front and the ACC SouthernBoundary is 147±10 Sv. Estimating the transport from the XBTs using a technique previouslyemployed south of Australia proves delicate because of an irregular bathymetry and watermass variations. It nevertheless confirms ACC transports around 150 Sv. Gathering these andother estimates from the Atlantic sector suggests that, while North Atlantic Deep Water isinjected in the current west of 35°W, a partially compensating loss of Deep CircumpolarWater occurs east of this longitude. Another transport increase from 0°E to 30°E might reflectsouthward transfer across the Subtropical Front south of the Agulhas retroflection.

Description: Satellite-relay data loggers (SRDLs) were deployed on southern elephant seals hauled out at Marion Island as part of the International Polar Year project, Marine Mammal Exploration of the Oceans Pole to Pole (MEOP). We describe the dive behaviour responses of one male elephant seal to changes in oceanographic conditions during two post-moult migrations. The seal concentrated his diving activity in a small area (〈200 square km) in close proximity to the Prince Edward Islands during both migrations. The restricted area utilised by the animal allowed for temporal comparisons in dive behaviour and excluded potential effects associated with changes in geographic position. The SRDLs transmitted a total of 16806 temperature points (1265 temperature profiles). Mean monthly in situ surface temperatures were significantly correlated with remotely sensed (MODIS) SST data for the study area. Surface and subsurface temperatures in the study area remained stable throughout both migrations, but were colder in October 2006 due to an intrusion of a cold, anti-cyclonic feature. Dive depths obtained by the seal were similar between years, though dives were longer during 2007. The differences in dive durations between years were a result of the seal spending more time at depths between 300m and 500m during 2007, when compared to 2006. During the colder period of October 2006, the instrumented seal performed shallower and shorter dives when compared to the rest of the migration period. The seal spent relatively more time near the maximum depths of dives during this period, indicating a likely increase in foraging effort. Our results highlight a link between oceanographic data obtained from seal-borne instrumentation and dive behaviour of elephant seals. This is even more pronounced by deploying tags to the same individual over several consecutive years, which excludes interspecific effects in multiyear comparisons. We furthermore suggest that elephant seals alter their dive behaviour on a fine scale to maximise foraging benefits associated with variations in oceanographic conditions, particularly in proximity to mesoscale features.

Description: The potential effects of ocean warming on top predators are largely unknown, though the impact on the distribution of prey in vertical space may have far reaching impacts on diving predators such as southern elephant seals. We used data from satellite-tracked southern elephant seals from Marion Island (46° 54’S; 37° 45’E) to investigate the relationship between their dive characteristics (dive depths, dive durations and time-at-depth index values) and environmental variables (temperature at depth, depth of Tmax below 100m, frontal zone and bathymetry) as well as other demographic and behavioural variables (migration stage, age-class, track day and vertical diel strategy). While other variables, such as bathymetry and vertical diel strategy influenced dive depth, our results also consistently indicated a significant influence of temperature at depth on dive depths. This relationship was positive for all groups of animals, indicating that seals dived to deeper depths when foraging in warmer waters. Female seals adjusted their dive depths proportionally more than males in warmer water. Dive durations were also influenced by temperature at depth, though to a lesser extent. Results from time-at-depth indices showed that both male and female seals spent less time at targeted dive depths in warmer water, and were presumably less successful foragers when diving in warmer water. Continued warming of the Southern Ocean may result in the distribution of prey for southern elephant seals shifting either poleward and/or to increasing depths. Marion Island elephant seals are expected to adapt their ranging and diving behaviour accordingly, though such changes may result in greater physiological costs associated with foraging.

Description: Ocean circulation and bioproductivity in the Weddell Gyre: geochemical findingsW. GEIBERT1, C. HANFLAND1, J.SCHWARZ1, R.USBECK1,2, A.WEBB3, AND I.ANSORGE31Alfred Wegener Institute for Polar and Marine Research, Am Handelshafen 12, 27570 Bremerhaven, Germany; wgeibert@awi-bremerhaven.de2FIELAX, Company for Scientific Data Management, Bremerhaven, Germany3University of Cape Town, Dept. of Oceanography, Cape Town, South AfricaAtypical distribution of tracersThe Weddell Gyre is one of the key areas for ocean circulation, and consequently for global climate. Here, deep waters reach the surface, and new production of bottom water brings surface signals at depth. This unusual situation is mirrored in the distribution of naturally occuring radionuclides like Radium isotopes or 227Ac in the water column. Not only tracers for ocean circulation show anomalies here. Tracers of particle flux also indicate atypical processes, reaching from the sea surface to the sediment.Atypical productivityResults of an expedition to the Eastern Weddell Gyre (Polarstern Expedition ANT XX/2) now have given a more comprehensive view of the whole Weddell Gyre. Together with measurements of nutrient distribution and other parameters, they reveal that the Weddell Gyre may not only be important in terms of ocean circulation, but it may also represent a site of suprisingly high bioproductivity. Pronounced differences between the Western part of the Gyre and its Eastern part were observed.Here, we present a comprehensive set of radiotracer data from the Weddell Gyre, together with oxygen and nutrient distribution data. Additionally, data of chlorophyll-a illustrate the vertical distribution of phytoplankton, explaining why satellite measurements lead to an underestimation of productivity in the Weddell Gyre. First results for sediment accumulation rates in the Eastern Weddell Gyre will also be presented.

Description: The Eastern Weddell Gyre an overlooked high productivity regionThe Weddell Gyre (WG) is generally known as a region of low bioproductivity. This view has hitherto been supported by relatively low chlorophyll concentrations as detected by satellites, high nutrient concentrations at the sea surface, and very low sedimentation rates in the underlying sediments. However, recent results from inverse modeling suggest a completely different situation for the Eastern part of the Weddell Gyre, from about 10° E to 35° E. The high productivity proposed by the model in the Eastern Weddell Gyre (EWG) is mainly a consequence of a substantial nutrient depletion at the surface, and a corresponding oxygen consumption in deeper layers, as known from the very few data available for that region. Satellite data do not show elevated chlorophyll concentrations in the EWG compared to neighbouring regions.In order to contribute new data from this poorly know region, and to help understanding the contrasting satellite and model data, Polarstern expedition ANT XX/2 into the EWG was carried out in the season 2002/03. A synoptical investigation (Synpart project) of productivity-related ocean properties was performed by the Alfred Wegener Institute together with scientists from the University Cape Town during the cruise. The measurements include fluorimetric detection of chlorophyll in the water column, determination of nutrient and oxygen concentrations, 234Th as a tracer for particle concentration and export, tracers for shallow and deep water circulation (228Ra, 227Ac). In addition, samples from the sediment surface were taken to allow for the determination of particle fluxes into the sediments by means of 230Th. This dataset gives insights into particle flux from the very surface of the ocean to the deep-sea floor. Additionally, data of pCO2 and a comprehensive oceanographic dataset are available from the expedition.The results clearly confirm the strong nutrient depletion in the surface waters of the EWG, in our case observed at 23°E, from about 62°30Ž S to 57°30Ž S. High concentrations of particulate 234Th are found there, in some cases in combination with a depletion of 234Th, which means export of particles from the sea surface. The fluorimetric determination of chlorophyll-a revealed that deep chlorophyll maxima were responsible for the contrasting satellite and model data. In some cases, high nutrient depletion together with deep chlorophyll was found where hardly any chlorophyll was visible at the sea surface by satellite. Compared to other parts of the Weddell Gyre, high opal concentrations in surface sediments of the EWG suggest that at least a fraction part of this productivity reaches the sea-floor (see presentation by Seeberg-Elverfeldt, this meeting). As the feature of deep chlorophyll maxima was not only found in the Eastern Weddell Gyre, but observed throughout the Weddell Gyre, there are implications for the interpretation of satellite images from the entire region. The productivity of the Weddell Gyre, especially of its Eastern part, must be considered to be currently substantially underestimated.

Description: Chlorophyll and other indicators of productivity in the Eastern Weddell Gyre between 0°E and 23°E - Preliminary Results of Polarstern Expedition ANT XX/2, Synpart projectWalter Geibert (1), Regina Usbeck (1), (2), Jill Schwarz (1), Claudia Hanfland (1), Adrian Webb (3) and Isabelle Ansorge (3)(1) Alfred Wegener Institute for Polar and Marine Research, Bremerhaven, Germany(2) Now Fa. Fielax, Company for Scientific Data Management, Bremerhaven, Germany(3) University of Cape Town, Dept. of Oceanography, Cape Town, South AfricaAuthor to whom correspondence should be addressed: wgeibert@awi-bremerhaven.deThe Weddell Gyre, extending from the Antarctic Peninsula to about 35°E, is one of the most dynamic regions with respect to the vertical exchange of heat, salt, and nutrients. Deep upwelling supplies large amounts of nutrients to the surface, which results in a large potential productivity, but the region south of the Polar Front is commonly described as a HNLC (High Nutrient, Low Chlorophyll) region, which is partly supported by satellite derived surface chlorophyll values and sediment accumulation rate data. Although the western part of the Weddell Gyre, the Weddell Sea, is relatively well described, there is a lack of data from the Eastern Weddell Gyre. Data from nearby areas as well as results from inverse modelling (Usbeck et al. 2002) point to unexpectedly high export of biogenic silica from the surface waters to intermediate depths. The Synpart project (Synoptical investigation of particle flux in the Eastern Weddell Gyre) was initiated in order to get a comprehensive impression of particle flux in this region. Therefore, the Synpart project comprises SeaWiFS satellite data of chlorophyll a, the measurement of vertical chlorophyll profiles, nutrient and oxygen data, and determination of Thorium export from the surface layer. In the near future, accumulation rates on sediment surface samples taken during ANT XX/2 will be determined via 230Th. Here we present preliminary results of the expedition that give an impression on one of the poorest known regions of the Southern Ocean.

Description: Ocean circulation and bioproductivity in the Weddell Gyre: geochemical findingsW. GEIBERT1, C. HANFLAND1, J.SCHWARZ1, R.USBECK1,2, A.WEBB3, AND I.ANSORGE31Alfred Wegener Institute for Polar and Marine Research, Am Handelshafen 12, 27570 Bremerhaven, Germany; wgeibert@awi-bremerhaven.de2FIELAX, Company for Scientific Data Management, Bremerhaven, Germany3University of Cape Town, Dept. of Oceanography, Cape Town, South AfricaAtypical distribution of tracersThe Weddell Gyre is one of the key areas for ocean circulation, and consequently for global climate. Here, deep waters reach the surface, and new production of bottom water brings surface signals at depth. This unusual situation is mirrored in the distribution of naturally occuring radionuclides like Radium isotopes or 227Ac in the water column. Not only tracers for ocean circulation show anomalies here. Tracers of particle flux also indicate atypical processes, reaching from the sea surface to the sediment.Atypical productivityResults of an expedition to the Eastern Weddell Gyre (Polarstern Expedition ANT XX/2) now have given a more comprehensive view of the whole Weddell Gyre. Together with measurements of nutrient distribution and other parameters, they reveal that the Weddell Gyre may not only be important in terms of ocean circulation, but it may also represent a site of suprisingly high bioproductivity. Pronounced differences between the Western part of the Gyre and its Eastern part were observed.Here, we present a comprehensive set of radiotracer data from the Weddell Gyre, together with oxygen and nutrient distribution data. Additionally, data of chlorophyll-a illustrate the vertical distribution of phytoplankton, explaining why satellite measurements lead to an underestimation of productivity in the Weddell Gyre. First results for sediment accumulation rates in the Eastern Weddell Gyre will also be presented.

Description: Based on body size dimorphism, southern elephant seals from Marion Island were expected to display significant differences betweensexes in depth use while at sea. We instrumented 53 adult and sub-adult animals of both sexes with satellite-relay data loggers(SMRU) between 2004 and 2008. These devices transmitted basic dive data, as well as location and temperature data while theinstrumented animals were at sea. Using a simple calculation, we determined time spent by individual animals in various depthcategories during a total of 182 882 dives. Animals of both sexes targeted depths between 300m and 600m more than other depthcategories, and substantial overlap between sexes was recorded for time spent in depths between 500m and 600m. Male elephantseals however targeted and spent significantly more time in depths between 600m and 1250m (p 〈 0.05). Female elephant sealstargeted and spent significantly more time in depths between 200m and 500m (p 〈 0.05). No significant differences were recorded fordepth use between adult and sub-adult males. The overlap in mid-water depth use by both sexes suggests that the limited segregationobserved in depth use by southern elephant seals from Marion Island is likely driven by different physiological capabilities, and notforage selection or predator avoidance.