Articles | Volume 13, issue 5
Clim. Past, 13, 491–509, 2017
Clim. Past, 13, 491–509, 2017

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. Munz1,2, Stephan Steinke3, Anna Böll4, Andreas Lückge5, Jeroen Groeneveld6, Michal Kucera6, and Hartmut Schulz2 Philipp M. Munz et al.
  • 1Senckenberg Centre for Human Evolution and Palaeoenvironment (HEP) at the University of Tübingen, Hölderlinstr. 12, 72074 Tübingen, Germany
  • 2Department of Geosciences, University of Tübingen, Hölderlinstr. 12, 72074 Tübingen, Germany
  • 3Department of Geological Oceanography, Xiamen University, Xiping Building, Xiang'an South Road, Xiamen 361102, China
  • 4Institute of Geology, University of Hamburg, Bundesstr. 55, 20146 Hamburg, Germany
  • 5Bundesanstalt für Geowissenschaften und Rohstoffe (BGR), Stilleweg 2, 30655 Hannover, Germany
  • 6MARUM – Center for Marine Environmental Sciences, Germany, Leobener Str., 28359 Bremen, Germany

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.