Season :    2015

Voyage :     8

Cruise Name :     Indian Southern Ocean Expedition (ISOE)

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

Ship Name :     ORV-Sagar Nidhi

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

Name of Deputy Chief Scientist / Leader :     Dr. Rajani Kanta Mishra

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:  To understand the hydrodynamics, current structure and volume transport, and food web dynamics between PF and coastal Antarctica.  To understand source of freshwater, water mass characteristics with special reference to Antarctic Bottom Water [AABW] and computation of meridional transport.  Impact of near-shore processes on nutrient distribution and cycling with special emphasis on Si.  Distribution of TCO2, Carbon dioxide fluxes and its links to biology and hydrodynamics within STF, PF and coastal waters.  Distribution, source and molecular fractionation of organic carbon: TOC, DOC, POC, TEP, Carbohydrate and protein distribution.  Microbial carbon uptake, respiration and demand: a. Glucose uptake b. Oxygen respiration c. Biomass  Cross validation of 14C (radioactive) and 13C (stable)-based primary productivity (PP) estimates so as to standardize the latter method in the study area.  To identify the environmental controls on variability in PP and phytoplankton physiology by FRRF-based study, and to develop a fluorescence-based method for estimating daily PP.  Role of new productivity in carbon sequestration. Investigate the role of preferential nutrient-uptake on PP.  To characterize the underwater light fields through measurements of inherent optical properties (IOP) and apparent optical properties (AOP) of the study area.  Collection of sediment core at coastal area of Antarctica for diatom and dinoflagellates cyst analysis.

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

From	Depart	To	Arrive
Chennai, India	03/01/2015	Port Louis, Mauritius	23/02/2015

The 8th Indian Expedition to the SO (ISOE) was the 5th successive expedition of ORV-Sagar Nidhi to this remote oceanic ecosystem. The voyage started at 0600 hrs on 9th January 2015 from Chennai and culminated at 1830 hrs on 23rd February 2015 at Port Louis, Mauritius. The vessel followed a diagonal path from Chennai to 56.26ºS (southern most point during this expedition). After reaching 56.26ºS the voyage followed a zigzag path so as to sample the frontal regions (Figure 1). In total 33 surface sampling stations and 9 multidisciplinary sampling stations were covered during this expedition. At all the multidisciplinary stations sampling was started at around 0600 hrs (IST). 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) Multiple plankton net sampling for mesozooplankton (iv) WP net haul for collecting surface mesozooplankton (v) FRRF operation for measuring phytoplankton physiology and instantaneous productivity (vi) Hyperspectral radiometer operation to measure inherent optical properties of the water column, (vii) On-deck incubation for (a) primary productivity studies by 14C, 13C and DO-based methods, (b) nitrification experiment, (c) zooplankton grazing experiment, (viii) VEL net operation to collect fish eggs and larvae, (ix) Observations of atmospheric parameters, black carbon, CO2 concentration, halogen oxides, ozone concentration, concentration of plastic in surface waters etc., (x) Radiosonde launching for studying vertical structure of the atmosphere, (xi) Argo buoy deployment for profiling the water column for a considerable period of time, (xii) Survey of marine mammals to identify them and study their behavior. Water samples were preserved (as such or filtered onto filter papers) for physicochemical, biological, bio-optical, microbiological and isotopic analyses in the shore laboratory at the concerned participant’s institute. Table 1: Overview of onboard operations of different instruments during SOE-8. Sl. No Instruments/Operations No. of times operated Remarks 1 CTD Carousel 31 2 Multiple Plankton Sampler 09 3 Vertical Egg and Larval (VEL) Net 08 4 Fast Repetition Rate Fluorometer (FRRF) 08 5 Micro profiler 08 6 Hyperspectral Radiometer 08 7 Bongo Net 01 Bongo Net lost on 05-02-2015 while collecting samples from 0m depth. 8 WP-equivalent Net 08 WP-equivalent Net lost on 11-02-2015 while collecting samples from 0m depth. However, sampling was continued by using spare WP net available onboard. 9 XCTD 47 10 XBT 13 11 Weather Balloon (Radiosonde) Launching 40 12 ARGO Floats 10

The 2014-15 expedition was the 8th expedition to the Indian sector of Southern Ocean, which embarked at 0600 hrs on 09th January 2015 from Chennai. This is the 5th successive time that the Southern Ocean expedition was carried out onboard ORV-Sagar Nidhi. The expedition team consisted of 16 scientists, representing 8 different research institutions and universities of India, 4 engineers from NORINCO Pvt. Ltd., Chennai, 27 staff comprising of captain, officers and crew members. Originally the voyage was aimed to go up to 66ºS in order to carry out multidisciplinary observations in the under sampled coastal Antarctic zone. However, due to inclement weather conditions and limited ship endurance, the ship could only reach 57.5ºS. During the expedition 33 surface sampling stations and 9 multidisciplinary stations were carried out (Figure 1). After completing 45 days voyage, there was port call at Port Louis (Mauritius) on 23rd February 2015 where all the scientists disembarked. High resolution measurements in the water column was carried out in the Polar Front (PF) 1 and 2, Sub Antarctic Front (SAF) and Agulhas Return Front (ARF) 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 33 stations without stopping the vessel. At multidisciplinary stations water samples were collected up to 1000 m using Niskin samplers attached to a CTD carousel. Operation of Microprofiler (turbulence measurement), Multiple plankton net (vertical mesozooplankton collection), Hyperspectral radiometer (optical properties measurement), FRRF (phytoplankton physiology and productivity), VEL net (fish egg and larvae collection), WP net (surface mesozooplankton collection), XCTD and XBT (vertical temperature and salinity measurement), and Radiosonde launching (weather balloon) was carried out at multidisciplinary stations (Table 1). Different experimental studies were also conducted such as estimation of phytoplankton primary productivity by 14C, 13C and DO-based methods, nitrification experiment, zooplankton grazing experiment. Continuous observation (only day time) from the wheel house was carried out to record and identify the marine mammals as and when they surfaced. Water samples were collected to study the ecology, diversity and phylogeny of marine actinobacteria, to study the phytoplankton pigments, taxonomy, nutrients, zooplankton taxonomy and biomass, and bio-optical parameters. Atmospheric studies (AWS), observations of halogens oxides, nitrogen oxide, oxidised volatile organic compounds (MAX-DOAS), surface ozone observations was carried out all along the cruise track. Rain water sampling and surface seawater filtration were conducted to measure isotopic ratios and estimation of plastics in the seawater, respectively. Continuous underway observations were made for echo sounder and thermosalinograph. Besides the above activities, the NCAOR participants also volunteered to deploy ARGO floats provided by INCOIS, Hyderabad. At SAF, 120 liters of water samples from 1000 m was collected, which would be used to prepare nutrient stock solution at ICMAM, Chennai. The Southern Ocean 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 many times. However, meticulous planning, sincere effort and perseverance enabled us to garner handful of samples from this remote location during this austral summer. The measurements taken would certainly result in generating high quality datasets that could be used to explaining the biogeochemistry and hydrodynamics of the study area in more details, which would further help us in understanding the role/response of Southern Ocean in global climatic variations.

Please refer Voyage Report

5.2. Biogeochemistry and Food-web Dynamics 5.2.1. Carbon-di-oxide, Dissolved Gasses and Macro Nutrients 5.2.2. Nitrification Experiment 5.2.3. Measurements of Dissolved Organic Nitrogen and δ18O-NO3-δ15N Compounds 5.2.4. Phytoplankton Taxonomy and Physiological Studies 5.2.5. Phytoplankton Productivity and Radiometric Measurements 5.2.6. Zooplankton Biomass, Diversity and Grazing 5.2.7. Micro and Mesozooplankton Biomass and Diversity 5.3. Ecology, Diversity and Molecular Phylogeny of Marine Actinobacteria from SAF and PF 5.4. Survey of Marine Mammals 5.5. Bio-optical Studies 5.6. Carbon Flux over the Southern Ocean 5.7. Aerosols, Black Carbon and Atmospheric Measurements 5.8. Oceanic volatiles and their impact on atmospheric halogens and cloud-forming aerosols in the Southern Ocean