National Institute Of Oceanography Dona Paula, Goa, India Pincode: 403004 Mobile: 9764009443 E-mail: email@example.com
The Arabian Sea is surrounded by various arid and semi-arid regions, receives a substantial amount of mineral dust particularly during SW monsoon  (June-September) which provides various macro and micronutrients to the surface water which can modulate surface ocean biogeochemistry . In this study, wet deposition (WD) samples have been collected at a coastal location in the North-Eastern Arabian Sea (NEAS) during the Southwest Monsoon (SWM) period of 2013, 2014, 2015, and 2019 at Goa (15.4̿ N, 73.8̿ E). These WD samples have been used to characterize and identify sources of mineral dust using mineralogical, elemental as well as isotopic (Sr and Nd) signatures. The samples collected during SWM have been classified as Beginning of Monsoon (BM, June samples), Mid Monsoon (MM, July- August samples), and End of Monsoon (EM, September samples).
Palygorskite, Smectite, Kaolinite (K), Illite (I), and Chlorite (C) are the major clay minerals identified, and their ratios and abundance were used to assess changes in the source contribution of WD dust . It is observed that at the BM (of 2013, 2014, and 2015), palygorskite (average = 40%) content is very high, which subsequently found to decrease in MM, including 2019 samples (20-25 %) and almost negligible (0-10%) in EM samples. However, smectite is found to be highest during MM (30-35%) except for a few samples collected during the SW monsoon period of August 2019. Smectite is found to be inversely proportional to palygorskite. An increase in the I/K ratio from BM to MM with the highest at the EM is observed during the SW monsoon period of 2013, 2014, 2015, and 2019. This increase, possibly, indicates a change in dust sources from the Arabian Peninsula to SW Asia . An increase in the K/C ratio at BM, which decreases gradually at MM and reaches the minimum at the EM during the SW monsoon period of 2013, 2014, 2015, and 2019 is observed. The lower value of K/C indicates its source from SWA  while the higher values indicate its source from the Arabian Peninsula. This considerable variation in the relative percentage of clay minerals suggests significant temporal variability in dust sources impacting during the SW monsoon.
The 87Sr/86Sr ratios and εNd values of silicate fraction of wet deposited particulates (2013, 2014, 2015, and 2019) range from 0.7091 to 0.7194 and -0.6 to -9.1 respectively. The 87Sr/86Sr ratios at the BM are relatively less radiogenic than the MM samples and more radiogenic at the EM. The εNd values show the opposite trend to that of the 87Sr/86Sr ratios throughout the monsoon, with more radiogenic εNd in the MM, and less radiogenic at the EM. The large variation in isotopic ratios (87Sr/86Sr and εNd) indicates different sources of dust reaching the NEAS during the SW monsoon period. The variation in isotopic ratios during BM, MM, and EM period shows the abundance of dust sources such as the Arabian Peninsula, NE Africa, and SW Asia particularly during SW monsoon .
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