Solar insolation driven periodicities in southwest monsoon and its impact on NE Arabian Sea paleoceanography

In the northeastern (NE) Arabian Sea, the fluctuation in terrestrial and freshwater runoff directly depends on southwest monsoon (SWM) precipitation as well as the meltwater flux provided by Indus River. Therefore, analysis of multi-proxy spectral signatures was carried out to trace the high-resolution SWM periodicities and their influence on the productivity, regional sea level fluctuations and depositional processes in the NE Arabian Sea. The time series data of stable isotopes of oxygen (δ¹⁸O_G.ruber), carbon (δ¹³C_G.ruber and δ¹³C_org) and nitrogen (δ¹⁵N), Total Organic Carbon (TOC), planktic-benthic foraminiferal ratio (P/B ratio) and >63 μm coarse fraction (CF) were used from two coastal sedimentary cores located offshore Saurashtra, NE Arabian Sea (Core SK-240/485 having 88 m water depth; Core GC/SK-240/496 having 174 m water depth). The REDFIT based spectral analysis recorded significant periodicities (>90% significance) in δ¹⁸O time series centered at ~1609, ~667, ~525, ~296, ~290 and ~256 years. Further, the significant periodicities recorded in carbon isotopes time series (δ¹³C_G.ruber and δ¹³C_org) centered at ~681, ~512, ~471, ~452, ~438, ~360, ~292, ~275, ~269, ~245 and ~209 years. The significant periodicities in TOC include ~471 and ~322 years whereas δ¹⁵N time series recorded significant periodicity centered at ~360 years. The significant periodicities in P/B ratio time series centered at ~512, ~388, ~304, ~250, ~235, ~217, ~152, ~139 and ~135 years while CF recorded ~268, ~216, ~209, ~198, ~188, ~173 and ~140 years significant periodicities. The observed periodicities in the multi-proxy record consist of similar cycles (within the radiocarbon dating error) which also match with previously reported solar insolation influenced SWM and other global and regional cycles. Further, the stationarity of the data has been verified using wavelet analysis and shows similar periodicities as observed in REDFIT analysis. Thereafter, the depositional behaviour was studied using correlation analysis of the common periods of δ¹⁸O time series of both the cores. The result suggests that the depositional behaviour was different for both the core sites during the early Holocene and became similar during the middle Holocene. The correlation analysis of Total Solar Index (TSI) with δ¹⁸O time series reveals a significant correlation with the core SK-240/485 whereas an insignificant correlation with the core GC/SK-240/496. These observations suggest that the solar insolation has been a leading factor responsible for the SWM trends during the Holocene which may have further influenced the productivity, regional sea level fluctuations and depositional conditions in the NE Arabian Sea. However, these trends are better preserved in shallow marine sediments as compared to the deeper marine sediments.