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Abstract Submission No. | ABS-2022-03-0369 |
Title of Abstract | Spatial distribution of dissolved Nd concentrations and eNd in equatorial and southern Indian Ocean: Impact of water mass circulation and dust deposition |
Authors | Vineet Goswami*, Sunil K. Singh |
Organisation | Physical Research Laboratory |
Address | Geosciences Division, Physical Research Laboratory Ahmedabad, Gujarat, India Pincode: 380009 Mobile: 9998154205 E-mail: vineetg@prl.res.in |
Country | India |
Presentation | Oral |
Abstract | The surface waters of the western equatorial to southern Indian Ocean (4°N to 65°S, 45°E to 67°E) were analyzed for dissolved Nd abundances and isotopic composition (eNd). These samples were collected during the boreal spring (Feb-Apr 2009). In addition, to investigate the water mass structure of the upper Antarctic Circumpolar Current (ACC), three shallow stations (<1000 m depth) were sampled in high resolution (every 100 m) and investigated for Nd and eNd in the southern Indian Ocean and Indian sector of Southern Ocean (65°S to 35°S, 57.5°E). The dissolved Nd and eNd distribution in the surface waters of the western Indian Ocean exhibit significant spatial variations. The surface water Nd concentrations in the equatorial to southern Indian Ocean vary from 10-20 pmol/kg, however, in the southern Indian Ocean (58°S), the surface waters how a very high Nd concentration (60.1 pmol/kg), hinting at significant Nd input to the southern Indian ocean waters sourced from iceberg-hosted atmospheric dust and sediments [1]. Similar pathway for Fe delivery to the surface polar waters has been suggested earlier [1]. The spatial distribution of Nd isotopic compositions in surface layers of the western Indian Ocean show a significant variation, varying from -18.0 to -7.0. Overall, eNd of the northern (north of 10°S) and southern (south of 45°S) Indian Ocean are radiogenic (eNd > -10) relative to the central Indian Ocean (10°S to 45°S; eNd < -10). The eNd in the surface waters of the equatorial western Indian Ocean (0° to 20°S) is quite low, around -7. We used an inverse modelling approach to quantify the proportion of various water masses in the Indian Ocean surface waters. Our inverse model computations suggest significant influence (~60 80%) of the Indonesian Throughflow Waters (ITW) in the equatorial western Indian Ocean region, supplied from the eastern Indian Ocean [2, 3]. Further, the inverse model calculations show a significant contribution (~18 35%) of the Arabian Sea High Salinity Waters (ASHSW) in the equatorial Indian Ocean, which could be supplied from the Arabian Sea through Somali Current (SC), and South Equatorial Countercurrent (SECC) [3]. Two shallow vertical profiles in the southern Indian Ocean (35°S, 41°S; 57.5°E) show consistent Nd concentrations with depth (average ~ 13 pmol/kg; 11 to 15 pmol/kg). The eNd measured in surface and intermediate waters in the Southern Ocean near Antarctica (65°S; 57.5°E) is around -9, intermediate between Atlantic and Pacific waters. However, a vertical profile of surface and intermediate waters in the Subantarctic zone (35°S; 57.5°E) show a larger spread with eNd varying from -17.4 to -11.9 suggesting substantial mixing of northward progressing Antarctic waters with surface to intermediate Indian Ocean waters. In this work, the water mass circulation in the southern Indian Ocean and Indian sector of the Southern Ocean have been studied using Nd abundances and isotopic composition (eNd). In addition, proportions of various water masses have been quantified using an inverse modelling approach. [1] Raiswell et. al., (2016) Biogeosciences 13, 38873900. [2] Amakawa et. al., (2000) Geochim. Cosmochim. Acta 64, 17151727. [3] Schott and McCreary (2001) Prog. Oceanography 51, 1123. |