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  • 1
    Publication Date: 2023-02-08
    Description: Knowledge of bio-physicochemical variables is essential to better understand the functioning of tropical marine ecosystems, which are rich in biodiversity and provide nutrition and livelihoods to billions of people in the developing countries. This study analysed the spatial and temporal variability of phytoplankton and zooplankton with chlorophyll, primary productivity, temperature, salinity, oxygen and nutrients in the Bay of Bengal (BoB), collecting data from the World Ocean, and COPEPOD and Aqua MODIS records. The results indicated a strong gradient in bio-physicochemical conditions of the BoB, from the coast to the open sea. Specifically, the spatial variability in chlorophyll was negatively correlated (R2 = 0.59) with temperature and zooplankton, while a positive correlation (R2 = 0.70) was noted between chlorophyll and silicate, nitrate, phosphate, dissolved oxygen and salinity. All the variables exhibited a strong vertical gradient at depths up to 500 m. Temperature, nutrients, zooplankton and to a lesser extent salinity and rainfall had an influence on the annual abundance of phytoplankton. Over the long term, a significant positive trend in temperature and a significant negative trend in primary productivity were observed in the BoB. The findings of this study will be useful to draw insights on the state of fisheries habitats and the overall environmental conditions of the BoB in response to future climate changes.
    Type: Article , PeerReviewed
    Format: text
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  • 2
    Publication Date: 2018-03-02
    Description: Antarctic Intermediate Water (AAIW) formation constitutes an important mechanism for the export of macronutrients out of the Southern Ocean that fuels primary production in low latitudes. We used quality-controlled gridded data from five hydrographic cruises between 1990 and 2014 to examine decadal variability in nutrients and dissolved inorganic carbon (DIC) in the AAIW (neutral density range 27 〈 γ n 〈  27.4) along the Prime Meridian. Significant positive trends were found in DIC (0.70 ± 0.4 μmol kg− 1 year− 1) and nitrate (0.08 ± 0.06 μ mol kg− 1 year− 1) along with decreasing trends in temperature (− 0.015 ± 0.01∘C year− 1) and salinity (− 0.003 ± 0.002 year− 1) in the AAIW. Accompanying this is an increase in apparent oxygen utilization (AOU, 0.16 ± 0.07 μ mol kg− 1 year− 1). We estimated that 75% of the DIC change has an anthropogenic origin. The remainder of the trends support a scenario of a strengthening of the upper-ocean overturning circulation in the Atlantic sector of the Southern Ocean in response to the positive trend in the Southern Annular Mode. A decrease in net primary productivity (more nutrients unutilized) in the source waters of the AAIW could have contributed as well but cannot fully explain all observed changes.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
    Format: application/pdf
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  • 3
    Publication Date: 2015-11-23
    Description: The positive trend in the Southern Annular Mode (SAM) perturbs circulation and biology in the Southern Ocean (SO). We aim to provide observational evidence of the SAM effect on SO circulation for 1990-2012 using Argo data. Preliminary results indicate immediate but seasonally different changes in Mixed Layer Depth (MLD) and Sea Surface Temperature in response to SAM. A marked effect of the summer SAM signal on the Southern Ocean SST is visible. We observe a positive trend in yearly mean MLD since 2000 (ΔMLD about 5 m/13 years) and an elevated inter-annual variability in MLD anomalies since 2005, especially in mode water formation regions. Further investigation revealed that SAM and winds can only partly explain MLD changes. In contrast, the changes in MLD anomalies are strongly correlated with observed salinity changes. The impact of MLD changes onto chlorophyll concentrations as a proxy for biological productivity will be presented.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , notRev
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  • 4
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    In:  EPIC3European Geosciences Union General Assembly 2016, Vienna, 2016-04-17-2016-04-22
    Publication Date: 2016-05-12
    Description: An up-to date 16-year time series of satellite chlorophyll from the ocean color climate change initiative (OC-CCI), was used together with its drivers (MLD and winds) to assess and explain recent trends in chlorophyll in the Southern Ocean. The evaluation of trends using linear regression analysis reveals a regionally varying chlorophyll increase. MLD deepens in a circumpolar band in the Subantarctic front regions and extends further to southeast- wards in the Pacific sector. The regions of chlorophyll increase are located to the north of that, in the subtropical zone. These regions of MLD deepening have over the last two decades experienced intensification in zonal wind and a positive trend in northwards Ekman transport. We propose that increased northward Ekman transport of nutrient-rich (iron, silicate and nitrate) upwelled water is the main physical process that drives the change we observe in chlorophyll north to these regions. These findings suggest that Southern Ocean biology is changing in response to recent change in circulation in that region, partly induced by the positive trend in the Southern Annular Mode (SAM) index.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , notRev
    Format: application/pdf
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  • 5
    Publication Date: 2019-01-30
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , notRev
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  • 6
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    In:  EPIC3SOOS-WCRP-ESA Workshop on Southern Ocean Surface Fluxes, Frascati, Italy, 2015-09-21-2015-09-23
    Publication Date: 2015-11-24
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , notRev
    Format: application/pdf
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