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 mid-Holocene 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.
Highlights
The Indian summer monsoon (ISM) is the dominant driver for intraseasonal changes of wind directions and precipitation patterns in one of the world’s most densely populated regions in southern Asia
Significant reconstructions of summer sea surface temperatures (SSTs) from planktic foraminiferal (PF) assemblages and Mg / Ca SST from G. bulloides are colder than present summer temperatures, indicating vigorous monsoonal winds and upwelling intensity during the early to midHolocene
ISM conditions were generally strongest around 8 ka BP and gradually decreased towards 5.8 ka BP
Summary
The Indian summer monsoon (ISM) is the dominant driver for intraseasonal changes of wind directions and precipitation patterns in one of the world’s most densely populated regions in southern Asia. For the agricultural development and economic prosperity of the region, it is vital to assess the variability in the monsoon system on societally relevant decadal to centennial timescales. This might help to better understand how potential driving forces might be controlling ISM variability and how it might develop under future climate scenarios. L. Berger, 1978) and monsoon circulations (Kutzbach and Street-Perrott, 1985) This period was marked by a steep decline in solar insolation changes, whilst climatic conditions were largely unaffected by human-induced greenhouse gas emissions.
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