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Acta Geologica Sinica(English Edition) 2012年第5期86卷 1265-1275页

作者： Saraswat RAJEEV nigam rajiv Mackensen ANDREAS Weldeab SYEE Micropaleontology Laboratory National Institute of OceanographyGoaIndia Alfred Wegner Institute for Polar and Marine Research BremerhavenGermany Department of Earth Science University of CaliforniaSanta BarbaraUSA

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.

关键词： oxygen isotope Mg/Ca Globigerinoides ruber salinity insolation Indian Ocean

Deterioration of Early Holocene coral reef due to sea level rise along west coast of India:Benthic foraminiferal testimony

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Geoscience Frontiers 2012年第5期3卷 697-705页

作者： Abhijit Mazumder rajiv nigam Pravin J.Henriques Birbal Sahni Institute of Palaeobotany 53 University RoadLucknow 226 007India National Institute of Oceanography Dona PaulaGoa 403 004India Department St.Xavier's CollegeMahapalika MargMumbai 400 001India

A total of 103 surface sediment samples collected from the water depth range of 15-3300 m along Vijaydurg-Karwar stretch of central west coast of India were analyzed for foraminiferal content. Relict benthic foraminiferal assemblage was noted within 50--135 m water depth. The relict benthic foraminiferal assemblage that includes Amphistegina, Operculina and Alveolinella in sediment samples within the water depth of 85-- 135 m indicates presence of coral reef at this depth during Early Holocene. The presence of barnacle fouling on Relict foraminifera at 60--90 m confirms the paleo-shoreline. The shallow depth zone is characterized by presence of agglutinated relict foraminifera. The agglutinated forms indicate freshwater influx, which eventually increased the sea level and subsequently deteriorated the paleo-coral reef.

关键词： Relict benthicforaminifera Early Holocene coral reefPaleo-shoreline West coast of India Sea level rise

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

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Acta Geologica Sinica(English Edition) 2019年第1期93卷 175-182页

作者： KURTARKAR R.Sujata SARASWAT Rajeev KAITHWAR Amrata nigam rajiv Micropaleontology Laboratory Geological Oceanography Division National Institute of Oceanography

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.

关键词： Cymbaloporetta plana culture experiment temperature food reproduction

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

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Acta Geologica Sinica(English Edition) 2017年第6期91卷 2268-2282页

作者： Rajeev SARASWAT Manumalenki MANASA Thejasino SUOKHRIE Mohammad Syed SAALIM rajiv nigam Micropaleontology Laboratory CSIR-National Institute of Oceanography

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.

关键词： Asterorotalia trispinosa ecology paleomonsoon riverine influx Bay of Bengal

Modeling tropical river runoff: A time dependent approach

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Research in Cold and Arid Regions 2014年第3期6卷 247-256页

作者： Rashmi nigam Sudhir nigam Sushil K. Mittal Dept. of Mathematics University Institute of Technology Rajiv Gandhi Technical UniversityBhopal India Dept. of Civil Engineering Lakshmi Narain College of Technology & ScienceBhopal India Dept. of Civil Engineering Maulana Azad National Institute of TechnologyBhopal India

Forecasting of rainfall and subsequent river runoff is important for many operational problems and applications related to hydrology. Modeling river runoff often requires rigorous mathematical analysis of vast historical data to arrive at reasonable conclusions. In this paper we have applied the stochastic method to characterize and predict river runoffofthe perennial Kulfo River in southem Ethiopia. The time series analysis based auto regressive integrated moving average （ARIMA） approach is applied to mean monthly runoff data with 10 and 20 years spans. The varying length of the input runoff data is shown to influence the forecasting efficiency of the stochastic process. Preprocessing of the runoff time series data indicated that the data do not follow a seasonal pattern. Our forecasts were made using parsimonious non seasonal ARIMA models and the results were compared to actual 10-year and 20-year mean monthly runoff data of the Kulfo River. Our results indicate that river runoff forecasts based upon the 10-year data are more accurate and efficient than the model based on the 20-year time series.

关键词： flood warning stochastic process ARIMA evaluation univariate, performance error