High Arabian Sea productivity conditions during MIS 13 – odd monsoon event or intensified overturning circulation at the end of the Mid-Pleistocene transition?

Abstract

Abstract. 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 throughout the Northern Hemisphere. Here, we present a multi-proxy study of a sediment core taken from the Murray Ridge at an intermediate water depth in the northern Arabian Sea that covers the last 750 000 years. Our results indicate that primary productivity conditions were anomalously high during MIS 13 in the Arabian Sea and led to extreme carbonate dissolution and glauconitization in the deep-sea sediments. These observations could be explained by increased wind driven upwelling of nutrient-rich deep waters and, hence, by the occurrence of an exceptionally strong summer monsoon event during MIS 13, as it was suggested in earlier studies. However, ice core records from Antarctica demonstrate that atmospheric methane concentrations, which are linked to the extent of tropical wetlands, were relatively low during this period. This constitutes a strong argument against an extremely enhanced global monsoon circulation during MIS 13 which, moreover, is in contrast with results of transient climate modelling experiments. As an alternative solution for the aberrant conditions in the Arabian Sea record, we propose that the high primary productivity was probably related to the onset of an intensive meridional overturning circulation in the Atlantic Ocean at the end of the Mid-Pleistocene transition. This may have led to an increased supply of nutrient-rich deep waters into the Indian Ocean euphotic zone, thereby triggering the observed productivity maximum.

Past dynamics of the Australian monsoon: precession, phase and links to the global monsoon concept

“…Because most of these latter records come from the Arabian Sea where the summer monsoon is well expressed, this late phase is usually accepted as the "monsoon phase", and the records that display an early phase are considered as independent tropical climatic phenomena. Our findings, that all these records are responding to the same phenomenon, thereby explaining their synchronicity, are in agreement with Ruddiman, 2006;Reichart et al, 1998;Ziegler et al 2010b;Braconnot et al, 2008;Wang et al, 2005Zheng et al, 2008. It seems, therefore, that the "Global Monsoon" concept, which has been discussed for modern climates (Wang and Ding, 2008;Trenberth et al, 2000) is also valid for the paleo-variability of the tropical climates.…”

Precession phasing offset between Indian summer monsoon and Arabian Sea productivity linked to changes in Atlantic overturning circulation

“…All this suggests that the North Atlantic cold events not only weakened the summer monsoon, the primary driver of upwelling in the Arabian Sea, but also reduced the AMOC which reduced nutrient supply to the Arabian Sea surface hence reducing export production there. In this light, the extreme high productivity conditions in the Arabian Sea during marine isotope stage 13 has also been explained by a similar combination of oceanic (AMOC) and atmospheric (Monsoon) processes rather than atmospheric forcing alone [ Ziegler et al , 2010b].…”

A multi-proxy analysis of Late Quaternary ocean and climate variability for the Maldives, Inner Sea

“…Evaluations of deep-sea sediment archives from the Arabian Sea deliver not only comprehensive information on the pacing and intensity of the Indian summer monsoon on orbital timescales Prell, 1990, 2003;Clemens et al, 1991Clemens et al, , 1996Ziegler et al, 2010;Caley et al, 2011a), but also show variance within orbital bands to more rapid climate shifts on suborbital timescales (Schulz et al, 1998;Altabet et al, 2002;Pichevin et al, 2007;Böning and Bard, 2009;Caley et al, 2013;Deplazes et al, 2013). Records from the equatorial Indian Ocean provide a more diverse and partly contradictory picture since this region is not only influenced by the summer and winter monsoons but also by the strength of Indian Ocean Equatorial Westerlies (IEW), which are stronger during the intermonsoon seasons in spring and fall and are inversely related to the Indian Ocean Dipole (Hastenrath et al, 1993;Beaufort et al, 2001).…”