Glacial-interglacial productivity contrasts along the eastern Arabian Sea: Dominance of convective mixing over upwelling

Abstract

a b s t r a c tThe western continental margin of India is one of the highly productive regions in the global ocean. Primary productivity is induced by upwelling and convective mixing during the southwest and northeast monsoons respectively. Realizing the importance of high primary productivity, a sediment core was collected below the current oxygen minimum zone (OMZ) from the southwestern continental margin of India. This was dated by AMS radiocarbon and as many as 60 paleoclimate/paceoceanographic proxies, such as particle size, biogenic components, major, trace and rare earth elements (REEs) which were measured for the first time to determine sources of sediment, biogeochemical processes operating in the water column and their variations since the last glacial cycle. R-mode factor analysis of comprehensive data indicates that the dominant regulator of paleoproductivity is the southwest monsoon wind induced upwelling. Other paleoproductivity related factors identified are the marine biogenic component and biogenic detritus (as an exported component from the water column added to the bottom sediment). All paleoproductivity components increased significantly during the marine isotope stage-1 (MIS-1) compared to those accumulated from MIS-4 to MIS-2. The second group of factors identified are the terrigenous sediments with heavy minerals like zircon and ilmenite. The terrigenous sediment, in particular, increased during MIS-2 when the sea-level was lower; however, the heavy mineral component fluctuated over time implying pulsed inputs of sediment. The diagenetic fraction and reducing component are the third group of factors identified which varied with time with increased accumulation during the MIS transitions.The primary productivity along the southwestern continental margin of India seems to have been controlled principally by the upwelling during the southwest monsoon season that was weaker from MIS-4 to MIS-2, as relative to that during the MIS-1. In contrast, increased glacial productivity noticed in sediments deposited below the current oxygen minimum zone (OMZ) along the north of the study area that can be linked to entrainment of nutrients through the intensified convective mixing of surface water during the northeast monsoon. The sequestration of greenhouse gases by the western continental margin of India was higher during glacial than interglacial cycles.Ó 2015, China University of Geosciences (Beijing) and Peking University. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/ licenses/by-nc-nd/4.0/).

Detrital Sr–Nd isotopes, sediment provenances and depositional processes in the Laxmi Basin of the Arabian Sea during the last 800 ka

“…At Site U1456 in the Laxmi Basin, the pelagic sedimentation is more closely related to the increase of palaeoproductivity than to the decrease of terrigenous particles. In general, palaeoproductivity in the Arabian Sea increased during the interglacial periods when the SW monsoon was intensified (Thamban et al 2001;Pattan et al 2003;Banakar et al 2005;Avinash et al 2015;Naik et al 2017). During pelagic sedimentation, detrital particles characterized by low 87 Sr/ 86 Sr ratios and high εNd values might be more strongly influenced by the Tapi River (Fig.…”

Enhanced CO2 Degassing From the Tropical Indian Ocean During Cold Climatic Events of the Last Glacial Cycle

“…The upper 100 cm of core was subsampled at ∼1 cm intervals, and the remaining core was subsampled at an interval of ∼2 cm. The chronology of upper part of the core was established based on six AMS radiocarbon ( 14 C) dates (Avinash et al., 2015). The chronology of lower part of the core was established based on tuning of oxygen isotope (δ 18 O) record of the planktic foraminifera, G. rube r with the global benthic stack LR04 (Lisiecki & Raymo, 2005).…”

Biotic Response of Plankton Communities to Middle to Late Miocene Monsoon Wind and Nutrient Flux Changes in the Oman Margin Upwelling Zone

“…In the Arabian Sea -one of the most productive marine regions today (Lee et al, 1998;Honjo et al, 1999;Munz et al, 2017;Rixen et al, 2019b) -significant variability in productivity has been identified in glacial-interglacial timescales. For example, higher productivity in the Late Pleistocene is associated with interglacial periods (Schubert et al, 1998;Pourmand et al, 2007;Avinash et al, 2015;Naik et al, 2017). Conversely, these climatically driven changes in primary productivity affect the volume of the oxygen minimum zone (OMZ) and the intensity of denitrification in the region (Gaye et al, 2018).…”