Decadal resolution record of Oman upwelling indicates solar forcing of the Indian summer monsoon (9–6 ka)

Abstract

Abstract. The Indian summer monsoon (ISM) is an important conveyor in the ocean-atmosphere coupled system on a trans-regional scale. Here we present a study of a sediment core from the northern Oman margin, revealing early to midHolocene ISM conditions on a near-20-year resolution. We assess multiple independent proxies indicative of sea surface temperatures (SSTs) during the upwelling season together with bottom-water conditions. We use geochemical parameters, transfer functions of planktic foraminiferal assemblages and Mg / Ca palaeothermometry, and find evidence corroborating previous studies showing that upwelling intensity varies significantly in coherence with solar sunspot cycles. The dominant ∼ 80-90-year Gleissberg cycle apparently also affected bottom-water oxygen conditions. Although the interval from 8.4 to 5.8 ka BP is relatively short, the gradually decreasing trend in summer monsoon conditions was interrupted by short events of intensified ISM conditions. Results from both independent SST proxies are linked to phases of weaker oxygen minimum zone (OMZ) conditions and enhanced carbonate preservation. This indicates that atmospheric forcing was intimately linked to bottom-water properties and state of the OMZ on decadal timescales.

Monsoons, Upwelling, and the Deoxygenation of the Northwestern Indian Ocean in Response to Middle to Late Miocene Global Climatic Shifts

“…Both the initial drop in sea surface temperature and increased seasonal amplitude (Zhuang et al, ), as well as the initiation of Mn depletion (Figures d and e), can be directly linked to the intensification of the prevailing wind system controlling the SAM and thus Oman Margin upwelling (Betzler et al, ). At the same time upwelled water likely began to progressively incorporate more Antarctic Intermediate Waters that today are a major component of the waters upwelling in the Arabian Sea (e.g., Munz et al, ). These changes likely led to an increase in nutrient availability across much of the Indian Ocean as evidenced by the initiation of significant biogenic silica accumulation (Keller & Barron, ; Figure ).…”

“…Today the oxygen minimum zone (OMZ) in the Arabian Sea is one of the world's most oxygen deficient marine regions that today extends at intermediate water depths between~100 and 1,000 m (Munz et al, 2017). The OMZ results from the intense seasonal/monsoonal upwelling along the Oman Margin (Banse et al, 2014;Lewis & Luther, 2000;Morrison et al, 1999;Stramma et al, 2008;Ward et al, 2009).…”

“…The upwelling cells are forced by prevailing alongshore winds along the Somali Coast, the Somali/Findlater Jets (e.g., Findlater, 1969;Schott et al, 2009; Figure 1). Upwelling along the Oman Margin and its effect on surface water cooling and productivity are also considered a good proxy for past South Asian Monsoon (SAM) variability in the region (Kroon et al, 1991;Munz et al, 2017;Murtugudde et al, 2007).…”

Glacial–interglacial changes and Holocene variations in Arabian Sea denitrification

“…S4). Calibration and reservoir age correction were done in the same way as for SL163 (Munz et al, 2017). Both cores have a conspicuous sedimentation hiatus around 5700 years BP.…”

“…The age model for SL163 was published by Munz et al (2017) and is based on 15 accelerator mass spectrometry (AMS) 14 C datings. In this study the upper 50 cm were taken from multicore MC681.…”