International Indian Ocean Expedition Research Articles

Aerosol and atmospheric dynamics over the tropical Indian ocean: A study from the IInd international Indian Ocean expedition

The study addresses the aerosol distribution, boundary layer dynamics and associated shortwave radiative forcing over the Tropical Indian Ocean. The observations were carried out onboard Ocean Research Vessel Sagar Nidhi in December 2015 as a part of the International Indian Ocean Expedition-II (IIOE-II). The dominance of continentally originated aerosols was observed near the coast because of northeasterly winds, while marine aerosols abounded offshore. The uneven distribution of aerosols in the study region was due to varying atmospheric conditions triggered by various convective processes, wherein the convective available potential energy and convective inhibition energy ranged between 0.0274 and 2535.2 J kg−1 and 0 and -387.5 J kg−1, respectively. The atmospheric forcing varied in tandem with aerosol loading. It was evident from the high forcing values (17.98 W m−2) and corresponding heating rate of 0.504 K day−1 observed near the coast. The average heating rate in the far offshore (stations 6–10) region was 0.063 ± 0.017 K day−1, which amounted to an ∼87% decrease from the coastal location.

Microbial dimethylsulfoniopropionate (DMSP) cycling in the ultraoligotrophic eastern Indian Ocean

Dimethylsulfoniopropionate (DMSP) is an important source of dissolved organic matter for the marine food web and its cycling is a key step in ocean-atmosphere fluxes involved in the global sulfur cycle. To date, the abundance and biogeography of the genes encoding bacterial DMSP cycling in the eastern Indian Ocean (EIO) is virtually unknown. Moreover, DMSP measurements from the IO are sparse compared to other major oceans. In May–June 2019, we characterized dissolved DMSP (DMSPd) concentrations and the abundance of representative bacterial DMSP cycling genes along the 110 °E transect line as part of a voyage that contributed to Australia's involvement in the second International Indian Ocean Expedition. During the multidisciplinary voyage, surface water samples were collected from 19 stations spanning temperate to tropical waters of the EIO (39.5 °S to 11.5 °S, 110 °E). Somewhat surprisingly, a trend of greater DMSPd was measured in ultraoligotrophic (<0.02 μmol L−1 of nitrate/nitrite), low latitude waters compared to relatively nutrient-rich high latitudes, which contradicts global DMSPd patterns of high concentrations at high latitudes. Additionally, the average DMSPd concentration in EIO samples (17.2 ± 18.64 nM) was an order of magnitude greater than concentrations previously reported at similar latitudes in the Pacific and Atlantic Oceans, which suggests DMSPd is a readily available food source for microbes in a region that is often considered an ocean desert. The abundances of the bacterial DMSP production gene (dsyB), the DMSP lyase gene (dddP) and phylogenetically diverse DMSP demethylation genes (dmdA subclade A/1, D/all and E/2) were reported for the first time in the EIO region, demonstrating significant shifts in all genes with latitude. The SAR11 dmdA (D/all) gene was the dominant DMSP degradation gene across the transect (3.4 ± 0.94% of bacteria) and was notably positively correlated to DMSPd, demonstrating a tight coupling between the variables across the 30° transect. Our results also showed greater DMSPd and relative abundance of genes encoding both DMSP degradation pathways (dddP, dmdA A/1 and D/all) within a Leeuwin Current meander when compared to adjacent stations outside of the meander, providing evidence that mesoscale perturbations from the Leeuwin Current can greatly influence the EIO sulfur cycle. Overall, our data indicates that reduced sulfur in the form of DMSP is an abundant and readily available food source for some microbial metabolisms within the ultraoligotrophic surface waters of the EIO.

Occurrence of cetaceans and seabirds along the Indian Ocean 110°E meridian from temperate to tropical waters

The first extensive physical and biological observations of the Indian Ocean were made from 1959 to 1965, during a ship-based International Indian Ocean Expedition (IIOE-1). Decades later in 2019, the 110°E meridian was revisited during the second International Indian Ocean Expedition (IIOE-2). The aim of this study, as part of a large number of related studies, was to examine the occurrence of cetaceans and seabirds along the 110°E meridian from temperate to tropical waters (39.5–11.5°S). Cetaceans and seabirds were actively scanned for across a four-week period spanning austral autumn to winter. Acoustic recordings of vocalising cetaceans were made using directional and omnidirectional sonobuoys (n = 87 deployments). In total, seven cetacean sightings (six baleen whale, one toothed whale), 186 seabird sightings and 225 cetacean acoustic detections were recorded. The baleen whale species detected acoustically were assigned to Antarctic blue whales (Balaenoptera musculus intermedia; Z-calls), pygmy blue whales (B. m. brevicauda; south east Indian Ocean 3-component calls, D-calls), fin whales (B. physalus; 20 Hz-pulses), southern right whales (Eubalaena australis; upcalls), Antarctic minke whales (B. bonaerensis; bio-duck calls) and an unknown signal; a “spot call”. The toothed whale species detected acoustically were Kogia sperm whales (Kogia sp.) and delphinids (from whistles).. Pygmy blue whales were detected across Subantarctic to Tropical Surface Waters, and were the most commonly detected cetacean. There was some delineation in other cetaceans: the spot call was detected in Subantarctic and Subtropical Surface Water (south of 23°S); fin whales in Subtropical Surface Water (between 23° and 30.5°S); and Antarctic minke whales in Tropical Surface Water (between 14° and 23°S). Data were not collected on cetaceans during IIOE-1, so data here represent baseline occurrence along 110°E for future studies. A total of 22 seabird species were sighted, including, petrels, albatrosses, tropicbirds, terns, shearwaters, boobies, frigatebirds, gannets, gulls, skuas and prions. Soft-plumaged petrels (Pterodroma mollis) were observed across all water masses and were the most commonly sighted seabird. There was some delineation of seabird species; albatrosses were sighted south of the Subtropical Front (south of 32°S); flesh-footed shearwaters (Ardenna carneipes) in Subantarctic and Subtropical Surface Waters (south of 27°S); and tropicbirds in Tropical Surface Water (north of 20°S). The occurrence of highly mobile species is particularly important to investigate as the waters in the eastern Indian Ocean have been warming faster than in the Pacific and Atlantic Oceans.

Latitudinal variation, and potential ecological indicator species, in the dinoflagellate genus Tripos along 110°E in the south-east Indian Ocean

Variations in oceanic environmental conditions influence phytoplankton community composition, distribution, seasonality and abundance. The dinoflagellate genus Tripos is globally widespread and as a recognised key indicator has the potential for being a marker for climate-based changes in the ocean. As part of the Australian effort for the Second International Indian Ocean Expedition, 20 stations along the 110°E line from 39.5° to 11.5°S were sampled from the RV Investigator in 2019. Oceanic conditions ranged from cold, nutrient-rich Subantarctic waters in the south to warm, oligotrophic tropical waters in the north. The Tripos assemblages along the transect were assessed relative to the changing environmental variables. We found four main Tripos groups at a 50% dissimilarity level where the assemblages were correlated with groups based on the environmental conditions observed during the voyage. A number of potential indicator species were identified for each group, specifically Tripos lineatus which was found to be a strong indicator of cold, nitrate-rich and silicate-poor Subantarctic water and Tripos muelleri var. pulchellus as an indicator of warmer, oligotrophic waters.

Watermass characteristics and circulation near 110°E in the southeast Indian Ocean

We present a description of the large-scale physical oceanography of the southeast Indian Ocean to provide context for this special issue, revisiting 110°E as part of the Second International Indian Ocean Expedition. Full watermass properties and circulation are introduced based on the hydrographic observations, as well as underway systems and satellite sea surface height measurements. The 110°E line provides a window into the global meridional overturning circulation and the shallow overturning of the Indian Ocean. Measurements of change along this line provide valuable insight into the pulse of the climate system. The full depth hydrographic transects of 1963 and 2019 will provide invaluable calibration points for investigation of climate variability using the diverse observations that contribute to the Indian and global ocean observing systems.

Copepods and mixotrophic Rhizaria dominate zooplankton abundances in the oligotrophic Indian Ocean

The large, tropical oligotrophic gyres of the world's oceans are understood to be relatively unproductive, with low phytoplankton and zooplankton biomass, and inefficient food webs, although data are scarce. Here we investigate changes in the zooplankton assemblage along a 15 °C temperature gradient from 20 stations on the 110°E transect as part of the second International Indian Ocean Expedition. To ensure that we reflect most of the zooplankton biodiversity, we used a 100 μm mesh net to capture the small copepod and microzooplankton components that are important and often overlooked in tropical systems. Further, to obtain a synoptic view, we towed the Continuous Plankton Recorder between stations across 30° of latitude. We found that copepod assemblages clustered into four groups, with the most distinct being at the highest latitudes south of the sub-tropical Front. As the ocean temperature increased from south to north along the transect, zooplankton abundance and diversity also increased. The dominant copepod species changed accordingly and were predominantly those with the ability and/or preference to selectively feed on microzooplankton. Although copepods were the most abundant taxon, the proportion of microzooplankton, particularly, mixotrophic Rhizaria, was consistently high. Thus, our study found a highly mixotrophic system supporting secondary production in the oligotrophic Indian Ocean.

Microbial community biomass, production and grazing along 110°E in the eastern Indian Ocean

We investigated plankton biomass structure, production and grazing rates from temperate to tropical waters (39.5–11.5°S) along the historic 110°E transect in the eastern Indian Ocean (IO) during May–June 2019. The timing captures the seasonal transition from moderate productivity in the subtropical sector to seasonally high primary production in tropical waters as described in IIOE (International Indian Ocean Expedition) studies of the 1960s. Carbon-based estimates of phytoplankton production and microzooplankton grazing were determined from depth profiles of dilution incubations analyzed by flow cytometry and pigments; mesozooplankton biomass and grazing were determined from net sampling and gut fluorescence for the integrated euphotic zone. Phytoplankton biomass varied from 860 to 1740 mg C m−2, averaging 1187 mg C m−2 with no latitudinal trend. Mixed-layer C:Chla ranged from 20 to 40 in the nitrogen-rich subtropical front to 100–180 in tropical waters. Prochlorococcus increased from 141 to 915 mg C m−2 between 39.5°S and 20°S and averaged 700 mg C m−2 at lower latitudes. Synechococcus and photosynthetic eukaryotes contributed least to biomass (3.6 and 30.5%, respectively) at mid-transect locations (15.5–27.5°S). Dinoflagellates and diatoms were typically rare (28 and 6 mg C m−2, respectively). Among heterotrophs, bacteria averaged 476 mg C m−2, with a subtropical front maximum but no latitudinal trend; ciliates averaged 112 mg C m−2, and mesozooplankton increased significantly south-to-north (131–488 mg C m−2). Phytoplankton production and grazing averaged 466 and 461 mg C m−2 d−1, respectively, based on the sums for flow-cytometry measured populations, and 618 and 604 mg C m−2 d−1, respectively, based on Chla-determined rates. Our results highlight key relationships that link stocks and process rates across oceanographic provinces of the eastern IO. Production and grazing increased 6–8 fold from south to north. Prochlorococcus dominated productivity, and microzooplankton accounted for 85–89% of grazing. Production and grazing were strongly coupled and balanced on average. Over the transect, increasing growth conditions (light and temperature) mainly manifested as more rapid biomass turnover and mesozooplankton biomass accumulation.

Krill along the 110°E meridian: Oceanographic influences on assemblages in the eastern Indian Ocean

In pelagic ecosystems in all oceans, euphausiids (krill) are important components of the zooplankton. In May–June 2019, euphausiids were investigated from temperate to tropical waters along the 110°E meridian, originally surveyed in 1962–1963 during the first International Indian Ocean Expedition (IIOE). A total of 28 species of tropical, subtropical and temperate euphausiids were identified from day and night vertical hauls using an Indian Ocean Standard Net (IOSN) through the upper 200 m of the water column between 11.5°S and 39.5°S. Abundances of larvae, juveniles and adults were generally higher in warmer tropical waters, as were the number of species, albeit the highest abundance recorded (4240 inds·1000 m−3), comprising of Thysanoessa gregaria, occurred in the cooler waters south of the Subtropical Front. Species from the genera Stylocheiron and Euphausia dominated along most of the transect line. The different water masses together with the influence of ocean currents appeared to affect the euphausiid assemblages with, for example, the occurrence of the Pacific Ocean species, Euphausia pacifica/nana, likely reaching the study region via the Indonesian Throughflow, and the occurrence of the typically neritic Pseudeuphausia latifrons, likely a result of the westward propagation of Leeuwin Current eddies. Redundancy analysis showed that the properties of water masses had a stronger influence on euphausiid assemblage variability than food availability (chlorophyll a), which was relatively low across most of the transect. In comparison to the first IIOE, which used the same IOSN collection method, a similar number of species was identified from the more temporally extensive sampling period in 1962–1963, though the occurrences of rare species were different. At comparable latitudes during May–June in 1963 and 2019, total euphausiid abundances and proportions of life stages were similar. This rare opportunity to repeat an open ocean transect provides an updated baseline on euphausiid species occurrence, distribution and assemblages in the eastern Indian Ocean.

Vertical distribution patterns of early stages of mesopelagic fishes along 110 °E, south-east Indian Ocean

This study examines vertical distribution of the early stages of mesopelagic fishes in the south-eastern Indian Ocean and oceanographic factors that may affect it. This investigation along the 110 °E transect formed part of the second International Indian Ocean Expedition (IIOE-2). Depth-stratified samples to 500 m depth of early stages of mesopelagic fishes were obtained by means a multinet EZ-1 m2. This net captured larvae and transforming stages, but juveniles and adults were also caught, particularly at night. Diel vertical patterns of the different species and stages were analysed relative to the oceanographic conditions encountered at the 20 stations along the transect. This paper provides the ranges of vertical occurrence and weighted mean depth for larvae (135 taxa), and post-metamorphic stages (75 taxa) of fishes caught during the survey. Despite the varying vertical profiles of oceanographic parameters encountered, there were consistent patterns within species and families along the transect, with broader vertical distribution of larvae at the southern stations, where the upper mixed layer was deeper. During both day and night, larval stages of all the species were concentrated in the epipelagic zone, with some differences in terms of weighted mean depth (WMD) between taxa, but with no significant differences in vertical location between day and night. Transforming and juvenile-adult stages, however, presented a wider vertical distribution range than larval stages, and showed important differences among families and species. For example, Myctophidae and Phosichthyidae species presented the highest concentrations in the upper 50–100 m at night, and a much deeper distribution during the day, thereby indicating night vertical migration behaviour of transforming and juvenile-adult stages. By contrast, during these stages the Gonostomatidae Cyclothone spp. and the Sternoptychidae Argyropelecus spp. occurred deeper than the epipelagic layer during both day and night. Although these vertical patterns concur with results from other oceans, the WMD along 110 °E was slightly deeper than that observed in other areas, such as the eastern Atlantic, possibly related to water transparency in this oligotrophic part of the world's oceans.

The WIO Regional Benthic Imagery Workshop: Lessons from past IIOE-2 expeditions

Originating from the Second International Indian Ocean Expedition (IIOE-2), the main goal of the Western Indian Ocean (WIO) Regional Benthic Imagery Workshop, was to provide information and training on the use of various underwater imagery platforms in benthic research. To date, attempts made to explore the bottom of the ocean range from simple diving bells to more advanced camera systems, and the rapidly expanding field of underwater image-based research has supported marine exploration in many forms, from biodiversity surveys, spatial analyses and temporal studies, to monitoring schemes. Alongside the increasing use of underwater camera systems worldwide, there is an evident need to improve training and access to these techniques for students and researchers from institutes within the WIO. The week-long virtual event was conducted between 30 August and 3 September 2021 with 266 participants. Sessions consisted of lessons, practical demonstrations and interactive discussions which covered the steps required to conduct underwater imagery surveys, taking participants through elements of sampling design, data acquisition and processing, considerations for statistical analysis and, effective managment of data. The session recordings from the workshop are available online as a teaching aid which has the potential to reach marine researchers both regionally and globally. It is crucial that we build on this momentum by continuing to develop and strengthen the network established through this initiative for standardised benthic-image-based research within the WIO.

Latitudinal variation in diversity and abundance of mesopelagic fishes associated with change in oceanographic variables along 110°E, south-east Indian Ocean

As part of the second International Indian Ocean Expedition, an oceanic transect from 39.5°S to 11.5°S along 110°E in the south-eastern Indian Ocean enabled concurrent oceanographic measurements and sampling of early stages of mesopelagic fishes within the upper 500 m of the water column. Notable oceanographic features along the generally oligotrophic transect included an increase in surface water temperature from 12 to 28 °C from south to north and low salinities at both ends of the transect. High salinity Subtropical Surface Water was evident over the central part of the transect and low dissolved oxygen occurred at depth at the northern end where tropical waters were influenced by the Indonesian Throughflow. Throughout the study region larval fish stages were generally concentrated in the epipelagic zone. Species richness, abundance and diversity of fishes (n = 166 species) increased towards the tropical waters. The families Myctophidae (lanternfishes; 60 species), Phosichthyidae (lightfishes; 2 species) and Gonostomatidae (bristlemouths; 5 species) were numerically dominant. Clustering of integrated abundance data (0–500 m depth) revealed four major fish assemblages along the transect. When linked to oceanographic variables, multivariate multiple regression indicated that surface temperature, surface salinity and dissolved oxygen at 400 m depth provided the best fitting model explaining fish distribution patterns. Where possible, comparisons have been made with early data collected along this 110° E line in the 1960s during the first International Indian Ocean Expedition.

Was this career shaped by people or by chance?

Abstract This paper discusses the people and events that influenced my career and the lessons I learnt along the way. In this essay I attempt to pass these lessons on to others. Born and growing up in Cape Town, from my earliest recollections at the age of four I have wanted to be associated with fish and the sea. My first mentor was the Professor of Zoology at the University of Cape Town, who gave me the opportunity to go to sea on the University research ship, and later to join the International Indian Ocean Expedition where I met others who influenced me. Then a postdoctoral fellowship in Nova Scotia led me to meet Ken Mann, a SCOR working group, and a series of wonderful colleagues and friends. The contribution of each of these to my development is discussed, along with the lessons learned. The friends I have made on my journey in marine science and my academic family of former students have enriched my life enormously and if I had my life again, I would have it no other way.

The International Indian Ocean Expedition and the Pursuit of Science in the Developing World

Between 2015 and 2020, UNESCO and oceanographers who study the Indian Ocean sponsored an international expedition to pursue current research topics about the region. Known as the Second International Indian Ocean Expedition, the project recapitulated an effort that had begun 56 years earlier. The International Indian Ocean Expedition (IIEO) ran from 1959 to 1965 and was the first major oceanographic expedition to focus on a developing world region. With 22 participating countries, the IIEO pursued large‐scale, collaborative science as state formation began after the collapse of European empires. The wave of decolonizations in Africa and Asia after the Second World War was more than just the refusal of alien rule followed by the formation of new nation‐states [1]. It was a moment when the citizens of newly independent countries, including India, the most active developing‐world participant in the IIOE, sought to recalibrate international hierarchies. As African and Asian politicians and thinkers shaped international institutions to their benefit, including the United Nations, of which UNESCO was a part, developing world scientists also expanded their say in the pursuit of science [2]. Oceanography was a young field, often practiced minimally in wealthy countries, but pursued vigorously by India in the years after independence. This effort occurred in the context of a Cold War pursued by the primary funders of the IIOE, the US and USSR, that eventually undercut international cooperation in science but did not squelch Indian institution‐building in oceanography. The IIOE, then, offers a window into the historical geography of science in the postwar period and into the under‐recognized agency of scientists outside the West in creating regional science infrastructure.

New record of Lissoporcellana demani Dong &amp; Li, 2014 (Decapoda, Anomura, Galatheoidea, Porcellanidae) from southeast Africa

Abstract The porcellanid crab Lissoporcellana demani Dong &amp; Li, 2014 is reported for the first time from southeast Africa, based on material collected from trawls off Mozambique during the International Indian Ocean Expedition in 1963-1964. Lissoporcellana demani has been known only from the western Pacific, and the present specimens greatly extend the previously known distribution range of this species to the western Indian Ocean. Illustrations of a specimen are provided. Morphological variations of L. demani and characters distinguishing it from closely related congeneric species are discussed.

Mesozooplankton biomass and temperature-enhanced grazing along a 110°E transect in the eastern Indian Ocean

Low-latitude waters of the Indian Ocean are warming faster than other major oceans. Most models predict a zooplankton decline due to lower productivity, enhanced metabolism and phytoplankton size shifts that reduce trophic transfer efficiency. In May-June 2019, we investigated mesozooplankton biomass and grazing along the historic 110°E transect line from the International Indian Ocean Expedition (IIOE) of the 1960s. Twenty sampling stations from 39.5 to 11.5°S spanned latitudinal variability from temperate to tropical waters and a pronounced 14°C gradient in mean euphotic zone temperature. Although mesozooplankton size structure was similar along the transect, with smaller (&lt;2 mm) size classes dominant, total biomass increased 3-fold (400 to 1500 mg dry weight m-2) from high to low latitude. More dramatically, gut-fluorescence estimates of grazing (total ingestion or % euphotic zone chl a consumed d-1) were 14- and 20-fold higher, respectively, in the low-latitude warmer waters. Biomass-normalized grazing rates varied more than 6-fold over the transect, showing a strong temperature relationship (r2 = 0.85) that exceeded the temperature effects on gut turnover and metabolic rates. Herbivory contributed more to satisfying zooplankton energetic requirements in low-chl a tropical waters than chl a-rich waters at higher latitude. Our unexpected results are inconsistent with trophic amplification of warming effects on phytoplankton to zooplankton, but might be explained by enhanced coupling efficiency via mixotrophy. Additional implications for selective herbivory and top-down grazing control underscore the need for rigorous field studies to understand relationships and validate assumptions about climate change effects on the food webs of tropical oceans.

Observation of the deep Indonesian throughflow using helium isotopes

Helium isotopes in the ocean are very useful tracers of hydrothermal input and deep-sea circulation. Unlike labile trace elements, noble gases are inert and do not react with other substances in the water column. Previous studies in the Indian Ocean showed that helium isotopes in the region were discharged mainly from the central Indian midocean ridge, convergent boundaries, and the Pacific Ocean via currents that flow through the Indonesian archipelago. These Indonesian waters then exit out as the Indonesian Throughflow (ITF) into the Indian Ocean through shallow sills. The ITF plays a significant role in global climate, because it serves as the main pathway of thermocline waters between the Pacific Ocean and Indian Ocean. We present new helium isotope data from International Indian Ocean Expedition (IIOE-2) at the east Indian Ocean in December 2018. Helium isotopes were measured using a Noble Gas Mass Spectrometer at the Atmosphere and Ocean Research Institute, The University of Tokyo. We compare our data with those from previous expeditions and discuss the source and distribution of helium isotopes near Java. Waters with high excess 3He from the ITF were observed at 1000 m. Application of two-components mixing model enabled us to estimate ITF fraction in the observed area and to clarify the ITF flow in the deep layer. Moreover, flow rate of the deep ITF from Savu sill to Indian Ocean was estimated to be ~ 0.8–1.6 Sv. Based on stations near the Java coast, there could be a deep current or hydrothermal source at 3000 m that advects water enriched in 3He southwards along the Java Island.

Sir Anthony Seymour Laughton. 29 April 1927—27 September 2019

Anthony (Tony) Laughton was an oceanographer who promoted the science of oceanograpy in Britain. Focusing on the shape of the seafloor, his work included underwater photography, ocean drilling, long-range side-scan sonar and scientific charting of the ocean floor. Following undergraduate studies at King's College, Cambridge, he joined Maurice Hill (FRS 1962) at the Cambridge Department of Geodesy and Geophysics, beginning a career in marine geophysics. Following his PhD, he spent a year at Lamont Geological Observatory, USA, where he met many leading US workers, and became interested in deep-seafloor photography and bathymetric mapping. Returning to the UK, he joined the National Institute of Oceanography (Institute of Oceanographic Sciences from 1973) at Wormley, Surrey, and became director in 1978. He developed the first UK seafloor camera, was an enthusiastic supporter and user of the revolutionary Precision Echo Sounder and later of the GLORIA long-range side-scan sonar. He played a significant part in the International Indian Ocean Expedition, subsequently developing a new understanding of the Gulf of Aden. A consummate committee man, he had a vital role in reviving the General Bathymetric Chart of the Oceans and promoted UK involvement in the international Deep-Sea Drilling Project. He was an accomplished amateur musician (playing French horn), small-boat sailor and handyman.

Understanding Iodine Chemistry Over the Northern and Equatorial Indian Ocean

AbstractObservations of halogen oxides, ozone, meteorological parameters, and physical and biogeochemical water column measurements were made in the Indian Ocean and its marine boundary layer as a part of the Second International Indian Ocean Expedition (IIOE‐2). The expedition took place on board the oceanographic research vessel Sagar Nidhi during 4–22 December 2015 from Goa, India, to Port Louis, Mauritius. Observations of mixed layer depth, averaged temperature, salinity, and nitrate concentrations were used to calculate predicted iodide concentrations in the seawater. The inorganic iodine ocean‐atmosphere flux (hypoiodous acid [HOI] and molecular iodine [I2]) was computed using the predicted iodide concentrations, measured atmospheric ozone, and wind speed. Iodine oxide (IO) mixing ratios peaked at 0.47 ± 0.29 pptv (parts per trillion by volume) in the remote open ocean environment. The estimated iodide concentrations and HOI and I2 fluxes peaked at 200/500 nM, 410/680 nmol·m−2·day−1, and 20/80 nmol·m−2·day−1, respectively, depending on the parameterization used. The calculated fluxes for HOI and I2 were higher closer to the Indian subcontinent; however, atmospheric IO was only observed above the detection limit in the remote open ocean environment. We use NO2 observations to show that titration of IO by NO2 is the main reason for this result. These observations show that inorganic iodine fluxes and atmospheric IO show similar trends in the Indian Ocean marine boundary layer, but the impact of inorganic iodine emissions on iodine chemistry is buffered in elevated NOx environments, even though the estimated oceanic iodine fluxes are higher.

About the methane flux into the atmosphere in the South-China sea

The new results of gasgeochemical studies in the integrated expedition of the Russian Academy of Sciences on R/V “Akademik Boris Petrov” (Cruise 42) along the regional profile (3180 km) in the South China Sea (Bien Dong) from January 10-16, 2017 are presented. The expedition conducted in the frame of the Second International Indian Ocean Expedition (IIOE-2). For the first time, five zones of increased methane fluxes were detected. Zones with maximum values of methane fluxes correlate well with the location of hydrocarbon deposits and tectonic faults.

Methane Flux into the Atmosphere in the South China Sea

The regional gas geochemical profile was first performed in the South China Sea in the north–south direction in January 2017 (42nd cruise of the R/V Akademik Boris Petrov). Five zones with methane emission into the atmosphere with a maximum of 30 mole km–2 day–1, were revealed above the oil- and gas-bearing structures in the southern part of the sea, in the Nam Con Son Basin. Methane emission into the atmosphere is generally related to ascending migration of methane from hydrocarbon deposits along fault zones. The expedition was set up by the Council for the Earth’s Hydrosphere of the Federal Agency for Scientific Organization as part of the international project “The 2nd International Indian Ocean Expedition (IIOE-2).”