- Dona Paula, Goa, India.
- +91-0832- 2450327
- iiosc2020[at]nio[dot]org
| Abstract Submission No. | ABS-2022-05-0069 |
| Title of Abstract | Dissolved aluminium cycling in the Indian Ocean: Implications to lithogenic matter transport, and regional circulation and scavenging |
| Authors | Naman Deep Singh*, Sunil Kumar Singh, Venkatesh Chinni |
| Organisation | CSIR-National Institute of Oceanography |
| Address | PMN Building, CSIR-National Institute of Oceanography Dona Paula, Goa, India Pincode: 403004 Mobile: 9106747210 E-mail: namandsk@gmail.com |
| Country | India |
| Presentation | Oral |
| Abstract | Distribution of dissolved aluminium (dAl) in ocean water column acts as a proxy of lithogenic matter input to the ocean basin. However, varying nature of internal cycling of dAl in different oceanic basins, in terms of water mass mixing, variations in dAl removal rates and fractional solubility of Al from the lithogenic sediment supply, etc., could also influence the distribution of dAl. Therefore, a comprehensive understanding of dAl cycling is a prerequisite for using the dAl distribution as a tracer of continental material input to the ocean basins. We measured dAl concentrations in 52 vertical water column profiles, sampled along three separate GEOTRACES-India transects (GI-01, GI-05 and GI-06) to understand the biogeochemical cycling of dAl in the northern (i.e. the Bay of Bengal (BoB), the Andaman Sea and the Arabian Sea), equa-torial and subtropical gyre region of the Indian Ocean. Al released from the large input of lithogenic sediments from the Ganga-Brahmaputra (G-B) river system, Indian peninsular rivers and sediment resuspension from the continental shelf and slope, predominantly controls the dAl distribution throughout the vertical water column in the BoB. Using the observed surface dAl concentrations and the estimates of the lithogenic sediment flux in the upper water column of the BoB, the frac-tional solubility of Al from the lithogenic sediments in the surface waters of the BoB is calculated to be in the range of 1.1-4.7 %. Surface dAl distribution in the Arabian Sea demonstrates an east-west gradient, i.e., elevated dAl (12.7-20.9 nM) close to the Indian coastal region and low dAl (1.5-3.3 nM) along the western boundary of the Arabian Sea. Given that the Arabian Sea is marked by significant spatio-temporal changes in surface dAl levels, an attempt is made to simulate the sea-sonal variability in surface dAl concentrations in the western Arabian Sea region using a simple one-dimensional, non-steady-state model to understand the control of seasonal changes in dust de-position input and scavenging removal fluxes on the surface dAl distribution. Such a model could be utilized as a first-order tool to estimate the seasonal variations in dust deposition flux using the surface dAl variations, and vice-versa, in highly meteorologically dynamic basins such as the Ara-bian Sea. Under the influence of the Northeast Monsoon Current, advective mixing between the dAl-rich surface waters of the southern BoB and relatively, dAl-depleted surface waters of the southern Arabian Sea dAl controls the surface dAl distribution in the equatorial Indian Ocean. Advection of dAl enriched Arabian Sea High Salinity Water and Persian Gulf Water results in ele-vated dAl levels in the upper thermocline water depths of the northern and central Arabian Sea. In the subtropical gyre region, deposition of the Australian dust and advection of the Indonesian Throughflow Water set the dAl distribution pattern in the upper water column (<500 m). Using a 1-D scavenging-advection-diffusion model, the scavenging removal time of dAl in the deep waters of the equatorial Indian Ocean is estimated to be in the range of 92-141 years. Near uniform dAl ob-served in the deeper waters (>1000 m) at the southern Andaman Sea results due to rapid renewal of and vertical mixing in the deeper waters relative to scavenging removal of dAl. Sediment resuspen-sion near the Central Indian Ridge probably enrich the dAl in the ambient deep water depths (2000⿿3500 m) and this signal dampens as the deep waters progress north-westward in the Central Indian Ocean Basin. The bottom water (>3500 m) advects across the Ninety East Ridge from the Western Australian Basin to bring the dAl-rich waters to the northern end of the Central Indian Ocean Basin. |