How will Benthic Foraminifera Respond to Warming and Changes in Productivity ?: A Laboratory Culture Study on Cymbaloporetta plana

Anthropogenic activities are likely to cause global warming. Global warming will affect marine productivityand thus food availability for marine organisms. Both the seawater temperature and food availability affect benthicforaminifera, the most abundant marine calcareous microorganisms. Therefore, a laboratory culture experiment wasconducted on Cymbaloporetta plana to understand the coupled effect of temperature(25°C, 27°C, 30°C) and food(102±5,203±9, 305±14, 407±18, 508±23 diatom cells). At all temperatures, growth increased with increase in food. The specimenssubjected to 27°C temperature attained the maximum growth and those subjected to 25°C were the smallest. All specimensfed with 508±23 cells reproduced, 0 irrespective of temperature. Of all the specimens without food, 40% at 27°C and 20% at25°C reproduced, whereas specimens subjected to 30°C did not reproduce. The 100% rate of reproduction at 27°C suggeststhat it is the optimum temperature for growth and reproduction. All the specimens at 30°C and without additional food,died, whereas at 25°C and 27°C, the mortality rate was 80% and 60%, respectively. The limited growth and reproductionwith decreasing food clearly indicates that food availability also controls the growth and reproduction of shallow waterbenthic foraminifer C. plana. Therefore, warming coupled with decreasing productivity is likely to severely affect thegrowth and abundance of shallow water benthic foraminifera.

Linkage between Seasonal Insolation Gradient in the Tropical Northern Hemisphere and the Sea Surface Salinity of the Equatorial Indian Ocean during the Last Glacial Period

Paired stable oxygen isotope and Mg/Ca analyses in calcite tests of the mixed-layer-dwelling planktic foraminifer Globigerinoides ruber has been used to reconstruct equatorial Indian Oceanδ18O of seawater （δ 18Osw ） over the last ~137 thousand years. On the basis of ice-volume-correctedδ18Osw （δ18Osw-ivc ）, relative changes in sea surface salinity （SSS） have been estimated. The SSS estimates suggest three episodes of higher SSS （131-113 thousand years before present （kyr BP）, 62-58 kyr BP, and 30-24 kyr BP） within the last glacial period as compared with the present. SSS comparison between interglacial episodes reveals that the surface seawater over the core site was significantly saltier during the penultimate interglacial than the Holocene. We suggest that the evolution of a seasonal insolation gradient between the Indian monsoon areas and the equator over the investigated time interval was instrumental in shaping the strength of the Indian winter and summer monsoons that left their imprints on the equatorial Indian Ocean SSS via freshwater input and wind-induced mixing. The study shows that the insolation difference between northern latitudes and the equator during winter affects monsoon strength in the Indian region, especially during cold intervals.

Does Glacial-Interglacial Transition Affect Sediment Accumulation in Monsoon-Dominated Regions?

The spatio-temporal changes in sedimentation rate along the continental margin of the monsoon-dominated eastern Arabian Sea during the last 24 kyr have been estimated from a compilation of 58 radiocarbon dated cores, in order to understand the effect of glacial-interglacial variation on sedimentation. The sedimentation rate has been computed for four-time slices, viz. the last glacial maximum, glacial-interglacial transition, early Holocene and late Holocene. We report that the average sedimentation rate in the slope to the abyssal region of the entire eastern Arabian Sea, although higher during the Holocene as compared with that during the last glacial maximum and glacial-interglacial transition, does not significantly vary during all four-time intervals. The sedimentation rate during any particular time interval, however, varies from core to core, thus indicating zonal changes. We report four zones of relatively high sedimentation rate, viz. the northeastern Arabian Sea, the region off the Gulf of Khambhat, the region off Goa and Mangalore, and off the southern tip of India. We suggest that a complex interaction of land-ocean-atmospheric processes controlled sedimentation rate in the eastern Arabian Sea during the last 24 kyr in such a way that the average sedimentation rate does not vary significantly, even during highly contrasting climatic conditions.

Abundance and Ecology of Endemic Asterorotalia trispinosa from the Western Bay of Bengal: Implications for its Application as a Paleomonsoon Proxy

A total of 97 surface sediment samples were collected from the continental shelf and slope of the western Bay of Bengal to assess the potential application of Asterorotalia trispinosa as a paleomonsoon proxy. The relative abundance of living as well as total （living and dead） A. trispinosa ranges from being absent to a maximum of-31%. The highest abundance ofA. trispinosa is close to the outfall region of the Ganga-Brahmaputra Rivers and decreases away from the river mouths. Contrary to that, A. trispinosa is rare in front of both the Cauvery and Pennar river outfall regions, in the central part of the western Bay of Bengal. The living A. trispinosa abundance is the lowest in between two major river systems, viz. Ganga-Brahmaputra-Mahanadi and Krishna-Godavari. The relative abundance of both the total and living A. trispinosa is strongly positively correlated with ambient seawater temperature, and negatively correlated with %Corg and salinity. Based on the spatial distribution, we conclude that A. trispinosa is stenohaline in nature, rather than euryhaline, and further that the increased relative abundance of A. trispinosa indicates warmer and only marginally hyposaline environment. Even though the ecological preference of A. trispinosa suggests it as a potential paleomonsoon proxy, the restricted distribution implies limited application.