The Arabian Sea possesses an intense oxygen minimum zone because of high primary productivity. These important biogeochemical aspects of the Arabian Sea have led us to investigate air−sea exchanges over the region. The measurements of the isoprene mixing ratio in marine air and biological parameters in seawater were conducted during the inter-monsoon period of April−May 2017. The year 2017 was the second warmest year since 1880 for the global ocean with positive sea surface temperature (SST) anomalies over the Arabian Sea during the campaign. The overall variation of isoprene follows the distribution of chlorophyll-a (Chl-a) with lower (0.38 ± 0.14 ppbv) and higher (0.75 ± 0.17 ppbv) values over central and northern regions, respectively. The diurnal pattern of isoprene covaries with solar flux, equivalent potential temperature, and wind speed as the daytime mixing ratio was ∼55% higher than its night-time value. Major enhancements (>0.6 ppbv) were associated with the blooms of Trichodesmium and Thalassiosira in oligotrophic conditions. High abundance of diatoms and cyanobacteria, intense solar flux, and high SST favored the production of isoprene from microbial sources. The estimated emission fluxes of isoprene were in the range of 1.5 × 10 7 to 1.2 × 10 8 molecules cm −2 s −1 . Levels of isoprene in marine air and its emission fluxes were higher than the values reported for most of the other highly productive oceans. This study highlights implications of the "Arabian Sea Paradox" on regional atmospheric chemistry.
31The present study details the effects of basin-scale hydrographic characteristics of the Red Sea 32 on the macroecology of Chaetognatha, a major plankton component in the pelagic realm. The 33 hydrographic attributes and circulation of the Red Sea as a result of its limited connection with 34 the northern Indian Ocean make it a unique ecohydrographic region in the world ocean. Here, we 35 aimed to identify the prime determinants governing the community structure and vertical 36 distribution of the Cheatognatha in this ecologically significant world ocean basin. The intrusion 37 of Gulf of Aden Water influenced the Chaetognatha community composition in the south, 38 whereas the overturning circulation altered their vertical distribution in the north. The existence 39 of hypoxic waters (<100 µmol kg -1 ) at mid-depth also influenced their vertical distribution. The 40 detailed evaluation of the responses of the different life stages of Chaetognatha revealed an 41 increased susceptibility of adult individuals to hypoxic waters compared to immature stages.
42Higher oxygen demands of the adults for the egg and sperm production might have prevented 43 them from inhabiting the oxygen deficient mid-depth zones. The carbon and nitrogen content of 44 the Copepoda and Chaetognatha communities and the quantification of the predation impact of 45 Chaetognatha on Copepoda based on the feeding rate helped in corroborating the significant 46 trophic link between these two prey-predator taxa. The observed influences of physical and 47 chemical attributes on the distribution of Chaetognatha can be used as a model example for the 48 role of the hydrography on the zooplankton community of the Red Sea. 49 Zooplankton 51 52 53 54The phylum Chaetognatha embraces a major component of pelagic plankton in the global oceans 55 and their marginal seas (Nair 1978; Bohata and Koppelmann, 2013; Terazaki 2013; Kürten et al. 56 2014). As carnivores, chaetognaths are known to consume ~1 to 12 prey day -1 ranging from 57 oligotrophic to productive environments (Kimmerer 1984; Kehayias 2003) and therefore play a 58 pivotal role in the trophodynamics of marine ecosystems. Their sensitivity to the physical and 59 chemical environment leading to their association with specific water masses makes them 60 suitable bioindicators of ecohydrographic provinces (Nagai et al. 2006; Buchanan and Beckley 61 2016) and for regions with increased primary productivity and the underlying physical processes 62 (e.g. eddies, fronts, and upwelling) (Kusum et al. 2014; Lima 2014; Nair et al. 2015). 63 The Red Sea, geographically positioned between the Asian and African continents and 64 characterized by an area of 4.51 × 10 5 km 2 and a length of ~2000 km is a semi-enclosed inlet of 65 the Indian Ocean (Sofianos and Johns 2002). The high evaporation rates (>2 m yr -1 ), low 66 precipitation (0.05 -0.15 m yr -1 ) and negligible river discharges makes the Red Sea one of the 67 saltiest ocean basins with a salinity range of 36 to 41 (Miller 1964; Grasshoff...
The study addressed the impact of the El Niño 2015-2016 on the ecosystem functioning and the subsequent effects on the distribution and community structure of zooplankton in the Kavaratti reef, a prominent coral atoll in the tropical Indian Ocean. The elevated ocean temperature (SST) associated with El Niño resulted in a mass bleaching event affecting > 60% of the live corals of the Kavaratti atoll. The concomitant changes observed in the nutrient concentration, coral health, and phytoplankton of the reef environment during the course of the El Niño led to discernible variations in the zooplankton community with markedly higher abundance and heterogeneity in distribution during the peak period of El Niño compared to its waning phase. A notable shift was also evident in the community structure of Copepoda, the dominant zooplankton taxon, with a predominance of calanoids and poecilostomatoids in the peak period and by harpacticoid copepods in the waning phase of the El Niño. The harpacticoid, Macrosetella gracilis, dominated in the waning phase because of their unique adaptability in the utilization of Trichodesmium erythraeum, both as nutritional and physical substrates in the nutrient-depleted environment of the reef ecosystem.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.