ALBERT

Description: Considerable interannual differences were observed in river water and sea-ice meltwater inventory values derived from d18O and salinity data in the Eurasian Basin along the continental margin of the Laptev Sea in the summers of 1993 and 1995, and in the summers of 2005 and 2006 during Nansen and Amundsen Basins Observational system (NABOS) expeditions. The annually different pattern in river and sea-ice meltwater inventories remain closely linked for all of the years studied, which indicates that source regions and transport mechanisms for both river water and sea-ice formation are largely similar over the relatively shallow Laptev Sea Shelf. A simple Ekman trajectory model for surface Lagrangian particles based solely on wind forcing can explain the main features observed between years with significantly different wind patterns and vorticities, and can also explain differences in river water distributions observed for years with a generally similar offshore wind setting. An index based on this simplified trajectory model is rather similar to the vorticity index, but reflects the hydrology on the shelf better for distinctive years. This index is not correlated with the Arctic Oscillation, but rather with a local mode of oscillation, which controls the outflow and distribution of the Eurasian Basin major freshwater source on an annual timescale. Keywords: Arctic Ocean halocline; atmospheric forcing; Laptev Sea; stable isotopes; water masses. (Published: 1 January 2011) Citation: Polar Research 2011, 30 : 5858 - DOI: 10.3402/polar.v30i0.5858

Description: Considerable interannual differences were observed in river water and sea-ice meltwater inventory values derived from d18O and salinity data in the Eurasian Basin along the continental margin of the Laptev Sea in the summers of 1993 and 1995, and in the summers of 2005 and 2006 during Nansen and Amundsen Basins Observational system (NABOS) expeditions. The annually different pattern in river and sea-ice meltwater inventories remain closely linked for all of the years studied, which indicates that source regions and transport mechanisms for both river water and sea-ice formation are largely similar over the relatively shallow Laptev Sea Shelf. A simple Ekman trajectory model for surface Lagrangian particles based solely on wind forcing can explain the main features observed between years with significantly different wind patterns and vorticities, and can also explain differences in river water distributions observed for years with a generally similar offshore wind setting. An index based on this simplified trajectory model is rather similar to the vorticity index, but reflects the hydrology on the shelf better for distinctive years. This index is not correlated with the Arctic Oscillation, but rather with a local mode of oscillation, which controls the outflow and distribution of the Eurasian Basin major freshwater source on an annual timescale.

Description: Reliable estimates of bottom-water oxygen contents are crucial to understanding the formation of past oxygen-depleted environments. Here, we investigate the relationship between pore density in calcareous benthic foraminiferal tests and environmental factors like bottom-water oxygen and nitrate concentration, water depth, and temperature in living (Rose Bengal stained) specimens of the shallow-infaunal species Bolivina pacifica, and the two deep-infaunal species Fursenkoina mexicana, and Chilostomella oolina. Used samples span an oxygen-gradient (0.10 to 4.62 ml L−1) across oxygen minimum zones (OMZ) off Namibia and Pakistan. Bolivina pacifica and F. mexicana display an inverse correlation between pore density and in-situ bottom-water oxygen content (BW-O2), indicating a morphological response of the foraminifers to decreasing oxygenation. Supporting previous results, we suggest that both species may increase their pore numbers to improve the ability of oxygen uptake in low-oxygen environments. Comparison of the calculated pore densities for B. pacifica and F. mexicana with bottom-water nitrate concentration (BW-NO3−) and temperatures, however, illustrates that these factors might also influence the pore density. Our results for the deep-infaunal species C. oolina show no significant relationship between pore density and BW-O2. This suggests that C. oolina, rather than increasing its pore density, has another life-strategy to survive sustained low-oxic conditions, possibly nitrate respiration. The non-correlation between pore densities and BW-NO3−, however, suggests that pores are not involved in the denitrification process. According to our data we suggest that the pore density of some benthic foraminiferal species is controlled by BW-O2. This relation is, however, species-specific. Overall, our data suggest that this morphological response could provide the basis for an independent proxy for BW-O2 in future studies.

Description: The population structure, particularly growth, age, mortality and somatic production of the olivid snail Olivancillaria deshayesiana were investigated. Annual formation of internal shell growth marks was confirmed by the record of stable oxygen isotopes in the shell, which reflects seasonal patterns of water temperature. A von Bertalanffy growth model fitted to 81 size-at- age data pairs, indicating that O. deshayesiana may attain 31 mm SL in about 10 years. The estimated total mortality Z and natural mortality M were 0.651 y-1 and 0.361 y-1, respectively. Fishing mortality F was 0.290 y-1, and the exploitation rate E was 0.445, indicating that this population was not overexploited at the time of the study. However, this situation may well change in the future, since the important prawn and shrimp fisheries (in intensity and scale) in the Mar del Plata area (38°20’S, 57°37’W) may indirectly affect the exploitation status of the studied population