Season :    2017

Voyage :     9

Cruise Name :     Indian Southern Ocean Expedition (ISOE)

Voyage Classification :     Multidisciplinary Expedition to the Indian sector of Southern Ocean

Ship Name :     MV SA-Agulhas

Name of Chief Scientist / Leader :     Dr. Sarat Chandra Tripathy, NCPOR

Name of Deputy Chief Scientist / Leader :     Dr. Anoop Sharad Mahajan, IITM

The broad objectives envisaged for this expedition is to study the “role and response of the SO to the regional and global climate variability”. Towards achieving this objective, the following specific/focal themes have been identified to be achieved:  Understand the hydrodynamics, current structure and volume transport between PF and Prydz Bay region of coastal Antarctica.  Understand source of freshwater, water mass characteristics with special reference to AABW and computation of meridional transport.  Understand the spatial and temporal variability of diapycnal mixing in the Indian sector of SO.  Impact of near-shore processes on nutrient distribution and cycling with special emphasis on Si.  Distribution of TCO2, CO2 fluxes and its links to biology and hydrodynamics within STF, PF and coastal waters.  Distribution, source and molecular fractionation of organic matter: TOC, DOC, POC, TEP, Carbohydrate and protein distribution including isotopic studies of Particulate Organic Matter (POM).  Microbial carbon uptake, respiration and demand: (a) Glucose uptake, (b) Oxygen respiration and (c) Biomass.  Estimate phytoplankton biomass (fluorometry) and primary productivity (13C-based) in the study area.  Measure the light absorption capacity of phytoplankton and detritus and to quantify the the concentration of suspended sediments in the study area.  Study phytoplankton community structure using different techniques (microscopy, HPLC and flowcytometry).  Understand the micro and mesozooplankton community structure and diversity with reference to the biogeochemical properties.  Observation of atmospheric trace gases (halogens), black carbon contents and aerosols.  Observation of isotopic composition of O2 and H in air and water.  Estimation of iodides in the sweater and its implications on photochemistry.

The Expedition was very successful and all the planned research activities were accomplished.

From	Depart	To	Arrive
Port Louis, Mauritius	06/01/2017	Port Louis, Mauritius	28/02/2017

The 9th ISOE was the first expedition onboard MV SA-Agulhas to this remote and dynamic oceanic ecosystem. The voyage started at 11:35 hrs [local time] on 06th January 2017 from Port Louis, Mauritius ended at 08:00 hrs on 28th February 2017 at Port Louis, Mauritius. Along 57o 30'E, the vessel followed a straight path southward from Port Louis to reach 40oS (Figure 1). After surveying the bathymetry a suitable place was identified for deployment of subsurface sediment-trap mooring at 40o 11'S and 58o 30'E followed by multidisciplinary observations. Thereafter, the vessel followed a diagonal path to reach off Kerguelen Island at 47oS and 67oE. after two multidisciplinary stations outside the EEZ of the Kerguelen Island the vessel headed towards Prydz Bay (68oS and 72oE). After reaching Prydz Bay, timeseries measurements were carried out followed by other planned stations. In total more than 30 surface sampling stations, 1 time series, and 17 multidisciplinary sampling stations were conducted during this expedition. At most of the multidisciplinary stations, sampling was started at around 06:00 hrs (local time) to nullify the difference in time of sampling between stations. The major operations/observations carried out during the expedition were (i) profiling and water sampling of upper 1000 m water column using CTD carousel, (ii) micro-profiler operations for turbulence studies (iii) firing of XCTDs to delineate the vertical temperature profile of the water column with high resolution, (iv) profiling of lowering ADCP, (v) multiple plankton net sampling for mesozooplankton (vi) bongo net haul for collecting surface mesozooplankton (vii) on-deck incubation for (a) PP studies by 13C methods, (b) nitrification experiment, (viii) observations of atmospheric trace gasses by MAX-DOAS and ozone monitor (ix) black carbon, Aerosols and AOD measurements, (x) radiosonde launching for studying vertical structure of the atmosphere and (xi) argo buoy deployment for profiling the water column for a considerable period of time. By following standard methods (please see respective sections for details), water samples were preserved (as such or filtered onto filter papers) at appropriate temperature for physicochemical, biological, microbiological, bio-optical and isotopic analyses in the shore laboratory at the concerned participant’s institutes.

The 9th Indian Southern Ocean Expedition [ISOE, 2016-17] commenced at 11:35 hrs [local time] on 06th January 2017 from Port Louis, Mauritius. For the 1st time the ISOE was carried out onboard a South African research vessel MV SA-Agulhas. The expedition team consisted of 18 scientists, representing 5 different research institutions/universities of India and 1 participants from the University of York, UK. Besides, 2 engineers from NORINCO Pvt. Ltd., Chennai, 1 medical doctor, 4 seamen and 66 personnel comprising of the captain, ice-pilot, officers, crew members and cadets/trainee were part of the expedition team. The voyage was aimed to go up to 68oS [Prydz Bay] in order to conduct interdisciplinary scientific observations in the under sampled coastal Antarctic zone, and the cruise plan was implemented effectively. For the 1st time, deployment of a sub-surface sediment trap mooring was successfully carried out in the Sub-tropical Frontal region [40o 11'S and 58o 30'E] of the Indian sector of Southern Ocean (SO) by Indian/ESSO-NCAOR initiatives. The deployed mooring shall be retrieved after one year during the next ISOE. During the expedition more than 30 surface water sampling stations, 17 interdisciplinary observation stations and 1 time series station [for 72h @6h interval] were carried out (Figure 1) to understand the hydrodynamics and biogeochemistry of Indian sector of SO. Apart from this, continuous measurements of atmospheric black carbon, trace gases etc. were conducted. After completing the 54 days voyage, the vessel SA Agulhas port called at Port Louis (Mauritius) on 28th February 2017, where all the scientific team disembarked and the vessel headed for Cape Town. High resolution measurements in the water column was carried out starting from the mooring station, and subsequently two more interdisciplinary stations were conducted out side the EEZ of the Kerguelen Island to investigate the effect of Island on the adjacent waters. Then the vessel straightaway headed towards Prydz Bay, Antarctica. Upon reaching 68o 00'E and 72o 00'E, interdisciplinary measurements were started followed by time series measurements at 68o 00'E and 74o 00'E. Phytoplankton bloom like conditions were observed in Prydz Bay, which propelled us to go further south and conduct 1 interdisciplinary station at 69o 25'E and 76o 00'E, which is pretty close to the Indian Research Station (Bharati) in Antarctica. Considering the observed high productive signatures and interesting thermohaline characteristics of Prydz Bay, it would be prudent to study this Bay extensively during forthcoming expeditions. Due to presence of pack ice we could not proceed east of 77o 00'E. High resolution measurements were carried out along 66 o 00'S following 1000 m contour line along the continental selves till we reached 66o 00'S and 57o 30'E. Due to persistent severe weather conditions we had to skip some of the coastal stations. On the return track selected stations were chosen along the 57 30oE for operation of deep CTD casts (>4000 m) to study the bottom water freshening and meridional transport of water mass. One station representative of the Polar Front (PF) 1 and 2, Sub-Antarctic Front (SAF) and Sub-tropical Front (STF) were chosen for sampling to understand the various biogeochemical processes and hydrodynamics of the study area. In addition, extensive observations on atmospheric parameters were also performed to establish link between climatic variability and biogeochemical cycling. The frontal regions were chosen for sampling because of the sharp gradients in their physicochemical characteristics; and to carry out a comparative study among fronts, which would help us to understand the food-web dynamics and biogeochemistry with respect to diverse oceanographic conditions. During the expedition, surface samples were collected at more than 30 stations without stopping the vessel. At multidisciplinary stations water samples were collected up to 1000 m using Niskin samplers attached to a CTD carousel. Besides, operation of Microprofiler (turbulence measurement), Multiple plankton sampler (vertical mesozooplankton collection), Bongo net (surface mesozooplankton collection), XCTD (vertical temperature and salinity measurement), and Radiosonde launching (weather balloon) was carried out at multidisciplinary stations (Table 1). In addition, Lowering ADCP (current velocity and direction) measurements were introduced for the first time. Different experimental studies were also conducted such as estimation of phytoplankton primary productivity by 13C methods, ocean acidification experiment. Water samples were collected to study the ecology, diversity and phylogeny of marine bacteria, to study the phytoplankton pigments, taxonomy, nutrients, zooplankton taxonomy and biomass, suspended sediments, iodides in water and phytoplankton absorption parameters. Atmospheric studies (AWS), observations of halogens oxides, nitrogen oxide, oxidised volatile organic compounds (MAX-DOAS), surface ozone observations, atmospheric black carbon was carried out all along the cruise track continuously. Besides the above activities, the ESSO-National Center for Antarctic and Ocean Research (NCAOR) participants also volunteered to deploy 11 ARGO floats provided by ESSO-INCOIS, Hyderabad. The SO is known for its severe weather conditions and high sea state. During this expedition, in deteriorating sea conditions, we had to abandon the operations and move on quite a few times. However, meticulous planning, sincere effort and perseverance made this expedition a very successful one. The samples/data collected from this remote location during this austral summer would certainly result in generating high quality datasets that could be used to publish some exciting papers and explain the biogeochemistry and hydrodynamics of the study area further, which would enhance our understanding of the role/response of SO in global climatic variations.

Please refer Voyage Report

5.1. Physical Oceanographic Processes 5.2. Biogeochemistry, Food-web Dynamics and Microbial Oceanography 5.2.1. Biogeochemistry of CO2 system, Oxygen and Nutrients in SO 5.2.2. Chemistry of Particulate Organic Matter 5.2.3. Microbiology and Carbon Biogeochemistry 5.2.4. Phytoplankton Biomass, Productivity, Absorption and TSM 5.2.5. Zooplankton Biomass and Diversity 5.3. Study on Boron, Silicon and Neodymium Isotopes of SO to understand Carbon and Silica Cycling and Ocean Circulation 5.4. Spatio-temporal Variability of Aerosol and Associated Radiative Forcing – In Response to Local Meteorological Variability and Effects of Long Range Transport Over Indian Sector of SO 5.5. Studies of δ13C and δ18O of Atmospheric CO2 to Understand the Temporal Variation in the CO2 Sinking 5.6. Isotopic Characterization of the Hydrological Cycle over the SO 5.7. Oceanic Volatiles and their Impact on Atmospheric Halogens and Cloud-forming Aerosols in the SO 5.8. Synoptic Observations of the Trace Metal-Nutrient Distributions and Interactions in the Surface Waters of SO aerosols in the Southern Ocean 5.9. Impacts of Iodine Volatilisation from the Sea Surface