Evaporation-precipitation changes in the eastern Arabian Sea for the last 68 ka: Implications on monsoon variability

Abstract

[1] Variations in sea surface temperature (SST), d18 O of sea water (d 18 Ow), and salinity were reconstructed for the past 68 ka using a sediment core (AAS9/21) from the eastern Arabian Sea (EAS) in order to understand the changes in evaporation and precipitation associated with the monsoon system. The Mg/Ca-derived SST record varies by ∼4°C; it shows that marine isotope stage (MIS) 4 was warmer than MIS 3, that the Last Glacial Maximum was 4°C cooler than the present, and that there was a 2°C increase within the Holocene. MIS 4 records higher d18 Ow and salinity values than MIS 2, suggesting variable flow of low-salinity Bay of Bengal flow into the EAS during glacial periods. The transition from MIS 4 to MIS 3 was marked with a conspicuous shift from higher to lower d18 Ow values, which reflects a decrease in the evaporationprecipitation budget in the EAS, perhaps due to the strengthening of southwest monsoon. Monsoon reconstructions based on d18 Ow reveal that monsoon-driven precipitation was higher during MIS 3 and MIS 1 and was lower during MIS 2 and MIS 4. This is consistent with earlier monsoon reconstructions based on upwelling indices from the western Arabian Sea. However, the amplitude of monsoon fluctuations derived through upwelling indices and d 18 Ow varies significantly, which may indicate spatial variability of monsoon rainfall.

Holocene aridification of India

“…Similar to other tropical regions, Holocene sea surface temperature (SST) fluctuations in the northern Indian Ocean were small (up to 2.5°C) after $8,000 years BP (see Anand et al [2008] and Govil and Naidu [2010] for eastern Arabian Sea, Rashid et al [2007] for the Andaman Sea, and Govil and Naidu [2011] for the western Bay of Bengal) accounting for a maximum of 0.56‰ change in d…”

“…C 4 vegetation is favored by aridity, high temperature, and low atmospheric CO 2 conditions over C 3 plants. Given the minimal variability in annual sea surface temperature in the northern Indian Ocean region [Govil and Naidu, 2010;Anand et al, 2008;Rashid et al, 2007;Govil and Naidu, 2011] and increasing CO 2 over the Holocene, our leaf wax d 13 C record reflects the integrated rainfall variations or aridity in the Godavari river catchment where natural vegetation cover is a mixture of savanna, tropical grassland, and tropical forest [Asouti and Fuller, 2008]. Modeled bulk organic carbon d…”

Glacial–interglacial changes and Holocene variations in Arabian Sea denitrification

“…All original data and all calculations are presented as Tables S1 and S2 in the Supplement. In our compilation, temperature reconstructions from the eastern and southeastern Arabian Sea are based on Mg / Ca ratios of planktonic foraminifera (see methods in, e.g., Govil and Naidu, 2010;Mahesh and Banakar, 2014;Saraswat et al, 2013;Tiwari et al, 2015) except core MD90963, which has alkenone temperatures . All other records are alkenone temperatures calculated with the core top calibration of Sonzogni et al (1997b).…”

High-Resolution Monsoon Records Since Last Glacial Maximum: A Comparison of Marine and Terrestrial Paleoarchives from South Asia

“…This reduces the sea surface salinity (SSS) that is reflected in the oxygen isotopic composition (δ 18 O) of planktic foraminifera. Such reconstructions have indicated increasing strength of SWM precipitation during the Holocene [21,22,27]. Similarly, Agnihotri et al [28] have found increasing productivity during the Holocene based on denitrification intensity (δ 15 N), which is relatable to SWM strength.…”