CSIR National Institute of Oceanography, Dona Paula, Goa 403004
CSIR National Institute of Oceanography, Biological Oceanography Division, Dona Panaji, Goa, India Pincode: 403004 Mobile: 8007789245 E-mail: email@example.com
The Arabian Sea is one of the highest productive zones in the global oceans and possesses several highly interesting biogeochemical features including open-ocean upwelling, monsoon reversal of currents, persistent oxygen minimum zone. These features collectively attracted oceanographers from all over the world. This dynamic land-locked basin has been thoroughly investigated in the past under two major multidisciplinary oceanographic observational programs 1) International Indian Ocean Expedition- I (IIOE-I) during 1962-1965, and 2) Joint Global Ocean Flux Study (JGOFS) by the international and Indian scientists. Several biogeochemical peculiarities were noticed during these research expeditions. In the present context of climate change, it has been documented that the entire north Indian Ocean is warming faster than any other ocean basin in the world and the Arabian Sea also showed a steady warming trend which may potentially impact the biogeochemical features. Unfortunately, in the last two decades, any systematic sampling and data analysis have been stopped in the central Arabian Sea due to several logistical problems. Further, among other seasons, the data from the summer monsoon (time of highest biological productivity) is scarce mostly due to rough weather conditions. Hence, the missing data set in the last two decades does not allow us to understand if there is any change that is happening due to warming. To fill this lacuna, a program was initiated under CSIR funding to revisit the India JGOFS track in 2017 to capture the seasonal variability of the key biogeochemical features and compare it with the existing data. We have completed two summer monsoon cruises (2017, 2018) using CSIR-NIOs research vessel RV Sindhu Sadhana (SSD 40 and 55) covering 25 stations in the eastern Arabian Sea (western Indian shelf) and the central Arabian Sea. In addition to water column monitoring, atmospheric dust fall and benthic community analyses were the two major components included in this program. More than 20 parameters including physical, biological, and chemical features were sampled and measured during these cruises. We present the first complete set of basic physicochemical and biological parameters during the summer monsoon from this area. A very strong south-north gradient was noticed in the western Indian shelf water and the central Arabian Sea influenced by upwelling. A strong inter-annual variability was noticed during two consecutive summer monsoon seasons and atmospheric forcing seemed to play the key role in this process. Very high atmospheric deposition was registered in the central Arabian Sea in association with strong summer monsoon winds coming from the Somalia region. Our onboard incubation experiments revealed that dust fall along with increasing CO2 has a strong potential to change phytoplankton community structure. No significant change in the biogeochemical feature was noticed compared to the JGOFS reports.