Abundance of microplankton in the eastern Mediterranean Sea in March and April 2008 during SES_GR1

The dataset is based on samples taken from 12 stations in Southern Aegean Sea, Northern Aegean Sea, Ionian Sea and Libyan Sea during March-April 2008. 12 Niskin bottles (8lt) made by PVC with rubber coated o rings and stainless steel ss springs. Seawater samples (150 ml) were collected from selected depths of the water column (2, 20, 50, 75, 100 m) for the identification and enumeration of phytoplankton cells (>=5 µm). The samples were fixed with Lugol solution and concentrated to 25 ml by sedimentation. Phytoplankton species abundance was determined with an inverted light microscope (OLYMPUS IX70) according to the Utermohl method (Utermohl, 1958).

Measurements of ocean microstructure, physical oceanography and current in the Weddell Sea, Antarctica, during the RRS Ernest Shackleton cruises ES033 and ES060

Turbulence profile measurements made on the upper continental slope and shelf of the southeastern Weddell Sea reveal striking contrasts in dissipation and mixing rates between the two sites. The mean profiles of dissipation rates from the upper slope are 1-2 orders of magnitude greater than the profiles collected over the shelf in the entire water column. The difference increases toward the bottom where the dissipation rate of turbulent kinetic energy and the vertical eddy diffusivity on the slope exceed 10?7 W kg?1 and 10?2 m2 s?1, respectively. Elevated levels of turbulence on the slope are concentrated within a 100 m thick bottom layer, which is absent on the shelf. The upper slope is characterized by near-critical slopes and is in close proximity to the critical latitude for semidiurnal internal tides. Our observations suggest that the upper continental slope of the southern Weddell Sea is a generation site of semidiurnal internal tide, which is trapped along the slope along the critical latitude, and dissipates its energy in a inline image m thick layer near the bottom and within inline image km across the slope.

Silicate and opal in the Ross Sea

Thirty-five box cores were collected from the continental shelf in the Ross Sea during cruises in January and February, 1983. Pb-210 and Pu-239, 240 geochronologies coupled with biogenic-silica measurements were used to calculate accumulation rates of biogenic silica. Sediment in the southern Ross Sea accumulates at rates ranging from <=0.6 to 2.7 mm/y, with the highest values occurring in the southwestern Ross Sea. Biogenic-silica content in surface sediments ranges from 2% (by weight) in Sulzberger Bay and the eastern Ross Sea to 41% in the southwestern Ross Sea. Biogenic-silica accumulation in the southwestern Ross Sea averages 2.7 * 10**-2 g/cm**2/y and is comparable to accumulation rates in high-productivity, upwelling environments from low-latitude continental margins (e.g., Gulf of California, coast of Peru). The total rate of biogenic-silica accumulation in the southern Ross Sea is approximately 0.2 * 10**14 g/y, with most of the accumulation occurring in basins (500-1000 m water depth). If biogenic-silica accumulation in the southern Ross Sea continental shelf is typical of other basins on the Antarctic continental shelf, as much as 1.2 * 10**14 g/y of silica could be accumulating in these deposits. Biogenic-silica accumulation on the Antarctic continental shelf may account for as much as a fourth of the dissolved silica supplied to the world ocean by rivers and hydrothermal vents.

Benthic foraminifera in the Tasman Sea, Emerald Basin and Challenger Plateau

Im Rahmen des TASQWA-Projektes (Quarternary Variability of Water Masses in the Southern Tasman Sea and the Southern Ocean) wurde eine erstmalige quantitative und taxonomische Bestandsaufnahme der rezenten, benthischen Tiefseeforaminiferen der Korngrößenfraktion > 250 µm in 27 Sedimentoberflächenproben aus dem austral-antarktischen Gebiet durchgeführt. Es konnten 137 Arten bestimmt werden, wobei aber keine Art dominante Anteile in den Proben erreichte. Über benthische Tiefseeforaminiferen im untersuchten Gebiet existiert kaum Literatur. Es gibt zwar aus dem 19. Jhrd. sehr gut dokumentierte Foraminiferen in diesem Bereich, diese decken aber längst nicht alle gefundenen Exemplare ab. Erst um die Jahrtausendwende beschäftigten sich Autoren wieder intensiver mit den australischen und neuseeländischen, benthischen Foraminiferen. Aber auch sie drangen nicht bis in die Tiefsee vor, sondern blieben vorwiegend im Schelfbereich. Aufgrund dieser spärlichen Literatur ist jede einzelne Art ausführlich mit Synonymieliste und Abbildung dokumentiert worden. Die PAST-Analyse generierte mit den 137 Arten und den 27 Stationen sechs Faunenvergesellschaftungen, die überwiegend bathymetrisch zoniert sind. Ab 562 m beginnt am Campbell Plateau in der Hochproduktionszone die Bulimina-Vergesellschaftung. Diese Vergesellschaftung zeichnet sich durch die höchste Individuenzahl aus. Ab 959 m findet sich die Rhizammina-Vergesellschaftung, die im Untersuchungsgebiet am weitesten verbreitet ist. Die weniger oft anzutreffende Cibicides-Vergesellschaftung läßt sich ab 1660 m Tiefe finden. Nur in einer einzigen Probe an der Tasmanschwelle in 2146 m Tiefe, tritt die Reophax-Vergesellschaftung auf, in der die Textulariina überwiegen. Die weniger oft anzutreffende Ehrenbergina-Vergesellschaftung läßt sich ab 1841 m finden. In dieser Vergesellschaftung, in der die Artenanzahl fast an das Niveau der Hochproduktionszone heranreicht, halten sich Rotaliina und Textulariina die Waage. Im Emerald Becken ab 3909 m Tiefe beginnt die Jaculella- Vergesellschaftung. Diese liegt in einem echten Hungergebiet und besteht hauptsächlich aus Textulariina. Im gesamten Untersuchungsgebiet lassen sich durch die Probenauswertung vier unterschiedliche Lebensräume (Challenger Plateau, Campbell Plateau, Emerald Becken und Tasmanschwelle) ausmachen. Da jedoch nur zwei Sedimentoberflächenproben am Challenger Plateau genommen wurden, konnte dieser Bereich nur eingeschränkt mit den anderen drei Bereichen verglichen werden. Die Foraminiferengemeinschaften des Challenger Plateaus und der Tasmanschwelle können jedoch im oberen Bereich der Wassersäule auch nur eingeschränkt miteinander verglichen werden, da man an der Tasmanschwelle Sedimentoberflächenproben erst ab 1634 m genommen hat und am Campbell Plateau Proben ab 562 m vorhanden sind. Die oberen Bereiche (ab 562 m bis ca. 1300 m) des Campbell Plateaus sind Hochproduktionsbereiche, die die höchsten Individuenzahlen pro 10 cm**3 Sediment und die höchste Artenvielfalt aufweisen. Am Südwesthang des Campbell Plateaus läßt sich eine Abfolge der verschiedenen Foraminiferenvergesellschaftungen bis hinunter in das Emerald Becken nachweisen. An der Tasmanschwelle selbst läßt sich keine ausgeprägte Hochproduktionszone erkennen. Generell gibt es hier weniger Arten und weniger Individuen pro 10 cm**3 Sediment als am Cambell Plateau. Das Emerald Becken, als tiefster Bereich des Untersuchungsgebietes und als echtes Hungergebiet, nimmt eine Sonderrolle ein.

Sedimentology of surface samples from the Weddell Sea, Antarctica

Mineralogical and granulometric properties of glacial-marine surface sediments of the Weddell Sea and adjoining areas were studied in order to decipher spatial variations of provenance and transport paths of terrigenous detritus from Antarctic sources. The silt fraction shows marked spatial differences in quartz contents. In the sand fractions heavy-mineral assemblages display low mineralogical maturity and are dominated by garnet, green hornblende, and various types of clinopyroxene. Cluster analysis yields distinct heavy-mineral assemblages, which can be attributed to specific source rocks of the Antarctic hinterland. The configuration of modern mineralogical provinces in the near-shore regions reflects the geological variety of the adjacent hinterland. In the distal parts of the study area, sand-sized heavy minerals are good tracers of ice-rafting. Granulometric characteristics and the distribution of heavy-mineral provinces reflect maxima of relative and absolute accumulation of ice-rafted detritus in accordance with major iceberg drift tracks in the course of the Weddell Gyre. Fine-grained and coarse-grained sediment fractions may have different origins. In the central Weddell Sea, coarse ice-rafted detritus basically derives from East Antarctic sources, while the fine-fraction is discharged from weak permanent bottom currents and/or episodic turbidity currents and shows affinities to southern Weddell Sea sources. Winnowing of quartz-rich sediments through intense bottom water formation in the southern Weddell Sea provides muddy suspensions enriched in quartz. The influence of quartz-rich suspensions moving within the Weddell Gyre contour current can be traced as far as the continental slope in the northwestern Weddell Sea. In general, the focusing of mud by currents significantly exceeds the relative and absolute contribution of ice-rafted detritus beyond the shelves of the study area.

Bellingshausen Sea bathymetric compilation

The southern Bellingshausen Sea (SBS) is a rapidly-changing part of West Antarctica, where oceanic and atmospheric warming has led to the recent basal melting and break-up of the Wilkins ice shelf, the dynamic thinning of fringing glaciers, and sea-ice reduction. Accurate sea-floor morphology is vital for understanding the continued effects of each process upon changes within Antarctica's ice sheets. Here we present a new bathymetric grid for the SBS compiled from shipborne echo-sounder, spot-sounding and sub-ice measurements. The 1-km grid is the most detailed compilation for the SBS to-date, revealing large cross-shelf troughs, shallow banks, and deep inner-shelf basins that continue inland of coastal ice shelves. The troughs now serve as pathways which allow warm deep water to access the ice fronts in the SBS. Our dataset highlights areas still lacking bathymetric constraint, as well as regions for further investigation, including the likely routes of palaeo-ice streams. The new compilation is a major improvement upon previous grids and will be a key dataset for incorporating into simulations of ocean circulation, ice-sheet change and history. It will also serve forecasts of ice stability and future sea-level contributions from ice loss in West Antarctica, required for the next IPCC assessment report in 2013.