Climate of the Past Discussions www.clim-past-discuss.net 1814-9340 1814-9359 5 4 2009 10.5194/cpd-5-1989-2009 http://www.clim-past-discuss.net/5/1989/2009/ http://www.clim-past-discuss.net/5/1989/2009/cpd-5-1989-2009.html http://www.clim-past-discuss.net/5/1989/2009/cpd-5-1989-2009.pdf 1989 2018 2009-07-27 Anomalously high Arabian Sea productivity conditions during MIS 13 M. Ziegler ziegler@geo.uu.nl L. J. Lourens E. Tuenter G.-J. Reichart Department of Earth Sciences, Utrecht University, Utrecht, The Netherlands Institute for Marine and Atmospheric research Utrecht (IMAU), Utrecht University, Utrecht, The Netherlands Marine isotope stage (MIS) 13 (~500 000 years ago) has been recognized as atypical in many paleoclimate records and, in particular, it has been connected to an exceptionally strong summer monsoon in East Asia. Here we present a multi-proxy study of a sediment core taken from the Murray Ridge at intermediate water depth in the northern Arabian Sea that covers the last 750 000 years. Our results indicate that upwelling driven primary productivity conditions were anomalously high during MIS 13 and led to extreme carbonate dissolution and glauconitization. We argue that an extreme summer monsoon circulation was probably not responsible for these aberrant conditions, because such an event does not show up in the Antarctic methane record and transient modeling results. As an alternative, we propose that high productivity was related to the onset of an intensive meridional overturning circulation in the Atlantic Ocean at the end of the Mid-Pleistocene transition. This led to an increased supply of nutrient-rich deep waters into the Indian Ocean euphotic zone, thereby triggering the observed productivity maximum. 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