Paleoclimate Science Highlights

In order to understand the biogeochemistry of the polar regions as well as to study the impacts of climate change on marine organisms during recent and past periods Diatom group participated in several expeditions, which include the 1st-4th Indian Scientific expeditions to Southern Ocean, 31st Indian Scientific expedition to Antarctica and Arctic Expedition 2008 and 2012. During these expeditions biogeochemistry data has been collected from Southern Ocean, Antarctic coastal region, Antarctic lakes and Kongsfjorden (Arctic ocean). Apart from Diatoms, the group has also worked on other organisms like Foraminifera, Coccolithophores, Silicoflagellates, Pteropods, and Sea urchins. The quality of the research undertaken by this group is highlighted in the form of several peer-reviewed research publications in national/ international journals. The major findings of the study include:

  • Coccolithophores were studied  inorder to understand the ecology of coccolithophores in the Indian sector of the Southern Ocean, along the 45° E meridian south of Madagascar to Antarctica, during austral summer of 2004 (January–March). Nutrient concentrations increased from the STF to the PF. Silicate concentrations were negatively correlated to both the abundance and diversity of coccolithophore populations. In contrast, high nitrate concentrations corresponds with a high abundance of monospecific assemblages of Emiliania huxleyi at high latitudes. Poleward of the SAF, two morphotypes of E. huxleyi dominate (Type B/C and D) (Mohan et al 2008).
  •  Air-sea carbon dioxide fluxes in Enderby basin of Indian Sector of Southern Ocean were calculated for austral summer 2009 and 2010. Fluxes of 2009 revealed that the Enderby Basin acts as a weak source of CO2 (1.7mmol/m2/d) during March 2009, whereas during February 2010 it acts as a strong source of CO2 (13.9 mmol/m2/d) to the atmosphere. (Shetye et al 2010).
  • Diatoms from the surface waters of the Southern Ocean were studied during the austral summer of 2004. This study investigated the distributional pattern of different diatom species and their relationship with changing sea-surface temperature (SST), salinity and nutrient availability. Among the diatom species identified, Fragilariopsis kerguelensis (O’Meara Hust.) is dominant, contributing more than 90% of the total recorded from 41°S latitude polewards. There is a total absence of diatoms from 25°S to 40°S. The measurement details of dominant species F. kerguelensis from Subtropical Front to Polar Front Zone indicated an increased size relationship with decreasing SST and increasing nutrient concentration (Mohan et al 2011).
  • Diatoms from Surface Sediments of Enderby Basin of Indian Sector of Southern Ocean were investigated for the abundance and distribution of seven key indicator diatom species viz. Sea ice related species Fragilariopsis rhombica, F. separanda, F. curta, F. ritscheri, Thalassiosira tumida and Actinocyclus actinochilus and Open Ocean species F. kerguelensis on the basis of modern physico-chemical parameters. The increasing abundance of F. kerguelensis consecutively suggests the effect of Antarctic bottom water in the study area which is further substantiated by the presence and increasing abundance of F. ritscheri. (Mohan et al 2011).
  • Diatom morphometry was studied to understand the past climatic changes in Southern ocean. Smaller size diatoms are thought to be well adapted to climatically warm conditions (Mohan et al 2011).
  • We tried to investigate the impact of climate change on lateral advection of Transformed Atlantic water in Kongsfjorden. Nonionellina labradorica was the predominant species in the outer fjord, whereas Elphidium excavatum and Cassidulina reniforme were dominant in the inner fjord. Total organic carbon and the test size of Nonionellina labradorica within the fjord showed a decreasing trend towards the inner fjord. Based on the distribution and abundance of Nonionellina labradorica as well as temperature profiles, we suggest that there was little or no major change in the lateral advection of TAW within the fjord in the immediate past. (Shetye et al 2011)
  • Calcification and Variability of Coccolithophorid Emiliana huxleyi was studied in the Southern Indian Ocean during Austral Summer of 2010. Three morphotypes of E. huxleyi i.e.  type A, B/C and D were identified and quantified in the sampled region. The north-south trend of decreased calcification of E. huxleyi in Southern Ocean reflects the role of temperature as well as salinity as major factors for controlling the biogeographical distribution of coccolithophores. The E. huxleyi also observed tough survival in weakly stratified colder waters. During study period the presence of E. huxleyi is reported first time to southern extent below 65°S. (Patil et al 2012)
  • Paleoceanography of the Indian sector of the Southern Ocean was constructed based upon Silicoflagellate assemblage in a sub Antarctic zone sediment core. Distephanus speculum and Dictyocha fibula were the dominating species. Warming as a result of rise in temperature is indicated by the increase of Dictyocha sp. and decrease in Distephanus sp. from the LGM towards the Holocene. The peaks in Silicoflagellate abundance coincided with the peaks of upwelling indicator diatom species Thalassionema nitzschioides and Chaetoceros resting spores, indicating that Silicoflagellate could be used as an indicator for changes in paleo-upwelling intensity. (Shetye et al 2012).
  • Sea surface pCO2 in the Indian Sector of the Southern Ocean has been studied during Austral summer of 2009. This study attempted to understand pCO2 and its relationship with nutrients and biological production in the Indian sector of the Southern Ocean. A significant finding of this study is that although the Southern Ocean is a known sink of carbon dioxide, the vicinity of the Crozet Island, where oceanic fronts are known to merge, suggests to act as a source of atmospheric CO2. It is attributed that “The island mass effect” could also be a factor that generates elevated CO2 in the vicinity of the study area. In the last one decade, we estimate that the oceanic pCO2 increased at a rate 0.77 µatm /year in the region south of the Polar front (Shetye et al 2012).
  • We observed an Iceberg and CO2-driven shift in Phytoplankton dominance in Southern Ocean. Corethron Criophillum was the dominant diatom species encountered in the extreme low temperature and salinity stations. Iceberg samples collected from the Antarctic coastal region indicated 73% Fe. Diatom abundance was limited in high pCO2 and wind speed conditions. Blue green algae (Spirulina and Nostoc) transported by icebergs to the coastal waters, also seem to be inhibiting the abundance and perhaps the growth of diatoms. Iceberg iron could soften impact of climate change but could lead to massive biotic crisis in future (Shetye et al 2012).
  • We studied the phytoplankton community structure in the Indian sector during late austral summer (February, 2009) We used the phytoplankton and microheterotrophs abundance, as also the associated physico-chemical parameters to explain the low phytoplankton abundance in the study region. This study highlights the highly productive polar front nevertheless becomes a region of low phytoplankton abundance, due to community shifts towards pico-phytoplankton (<10 μm) during late austral summer (Patil et al 2013).