The Southern Ocean (SO) is a very challenging region compared to other oceans for accomplishing any scientific investigation due to its harsh climate, inaccessibility and remoteness. A drastic heat and mass transport occurs across Antarctic Circumpolar Current (ACC). Hence understanding this current system plays a major role in climatic variability studies. The Indian Ocean sector of SO is a region that remains under-investigated, where sparse data impede our knowledge to understand the role of SO in the climatic variabilities. Availability of long term sea truth data from this area is thus imperative in understanding the various processes affecting the climate so as to evolve suitable mitigating measures. Therefore, large-scale, detailed, multi-ship, synoptic and time series sea truth observations of this region deserve highest priority.
The Indian research on Southern Ocean is conducted by the National Centre for Antarctica and Ocean Research (NCAOR), an Earth Science System Organization (ESSO) under the Ministry of Earth Sciences (MoES), Government of India. It is a multi-disciplinary, multi- institutional program which commenced in 2004 and encompasses all the major areas of research, including air-sea-ice interaction, hydrodynamics, biogeochemistry and palaeo-environmental studies (Figure 1) with a main objective to understand “Role and response of Southern Ocean in the global and regional climatic variabilities”.
Since the inception of the SO program, eight multi-disciplinary and multi-institutional expeditions to the Indian Ocean sector of the Southern Ocean have been implemented. The expeditions have been carried out only during austral summer (December-February) as the sailing and sampling conditions are relatively better. Basic and advanced research studies are undertaken under this program to understand the dynamics of the formation & distribution of water masses, currents, investigate the relationship between oceanic & atmospheric circulation systems and the physical basis for biological productivity and assessment of the distribution, and carbon sequestration.
Some significant findings have been achieved from the previous expeditions include- i) identifying the zones of sink (52°S) and ventilation (45°S) of CO2 ii) Southward meandering of ACC attributed to bottom topography iii) The fast degree of warming and freshening of the Antarctic Bottom Water (AABW) due to glacier melting iv) North-south movement of water masses due to the influence of cyclonic and anticyclonic eddies v) Dominance of non sea salt aerosols in the SO vi) Enhanced productivity in the shallow subtropical region, and vii) the influence of melt water on productivity in the coastal and open ocean. Based on these findings nearly 60 papers were published in peer-reviewed national and international journals. Special issues in Current Science and Deep Sea Research II have been published in November 2010 and August 2015, respectively
Although subtle changes are observed in the air-sea fluxes, hydrography and biological responses to hydrodynamics, the data is not enough to predict the behaviour of the region in a rapidly changing climate scenario and it’s influence on tropical climate variability. The future research in these waters will therefore largely focus on these issues and include acquiring continuous data that involve long-term continuous observations using remotely operated platforms including moorings, floats, gliders etc.
The Indian Southern Ocean Expedition 2016-17 will be launched in December 2016 from Port Louis, Mauritius onboard MV Agulhas to have a comprehensive study in the Antarctic Zone (AZ) with special reference to the coastal waters of the India’s third Antarctic station Bharati (69°S 76°E). The forthcoming expedition will include a meridional transect and zonal transects within the AZ (Figure 2). The samplings during this expedition will include sediment core samples from coastal waters of Antarctica, water column and atmospheric parameters from the entire study region with the focal scientific themes viz. atmospheric sciences, water column dynamics, biogeochemistry, food-web dynamics and paleoclimatic studies etc.
As a part of the forthcoming expedition, NCAOR proposes to establish subsurface mooring system in the Sub-tropical frontal waters (40°S 57°30’E). The proposed mooring includes sediment traps to capture sinking particles as a measure of carbon flux in to the deeper layers, Acoustic Doppler Current Profiler [ADCP] and Recording Current meters for current measurements, CTDs for hydrography and sensors for turbidity and oxygen. The deployment of the mooring equipments is aimed i) to estimate the sedimentation rate of particles, carbon flux and composition of settling particles ii) to understand the oceanographic conditions that regulate/control the carbon flux in the sub-tropical front.
Figure 1. Map showing transects of and equipment operated during Indian expeditions to Southern Ocean. CTD: Conductivity-Temperature-Depth; FRRF: Fast Repetition Rate Fluorometer.
Figure 2. Map showing the cruise transect of the Indian Southern Ocean Expedition 2016-17. The yellow circle indicates the location (40°S, 57.5°E) for the mooring to be deployed during this expedition.