Articles | Volume 13, issue 5
Research article
19 May 2017
Research article |  | 19 May 2017

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

Philipp M. Munz, Stephan Steinke, Anna Böll, Andreas Lückge, Jeroen Groeneveld, Michal Kucera, and Hartmut Schulz

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.

Short summary
We present the results of several independent proxies of summer SST and upwelling SST from the Oman margin indicative of monsoon strength during the early Holocene. In combination with indices of carbonate preservation and bottom water redox conditions, we demonstrate that a persistent solar influence was modulating summer monsoon intensity. Furthermore, bottom water conditions are linked to atmospheric forcing, rather than changes of intermediate water masses.