Journal cover Journal topic
Climate of the Past An interactive open-access journal of the European Geosciences Union
doi:10.5194/cp-2016-88
© Author(s) 2016. This work is distributed
under the Creative Commons Attribution 3.0 License.
Research article
13 Sep 2016
Review status
This discussion paper is under review for the journal Climate of the Past (CP).
From Monsoon to marine productivity in the Arabian Sea: insights from glacial and interglacial climates
Priscilla Le Mézo1, Luc Beaufort2, Laurent Bopp1, Pascale Braconnot1, and Masa Kageyama1 1LSCE/IPSL, UMR 8112 - CEA/CNRS/UVSQ, Centre CEA-Saclay, Orme des Merisiers, 91191 Gif-sur-Yvette, France
2CEREGE, UMR 7330, CNRS-IRD-Aix Marseille Université, Av. Louis Philibert, BP80, 13545 Aix en Provence, France
Abstract. The Indian monsoon is known to boost biological productivity in the Arabian Sea. This paradigm has been extensively used to reconstruct past monsoon variability from paleo-proxies indicative of changes in surface productivity. Here, we test this paradigm by simulating changes in marine primary productivity for 8 contrasted climates from the last glacial-interglacial cycle. We show that there is no straightforward correlation between boreal summer productivity of the western and central Arabian Sea and summer monsoon strength across the different simulated climates. Locally, productivity is fueled by nutrient supply driven by Ekman dynamics depending on both wind stress and wind stress curl. In our simulations, a stronger monsoon with intensified wind stress on the Arabian Sea can lead to either increased or reduced productivity depending on the exact ocean surface on which increased wind stress and a positive wind stress curl are acting. The effects of winds onto the ocean are modulated by the Indian summer monsoon intensity and pattern (e.g. position of the low-level jet over the Arabian Sea), which in turn are driven by the orbital parameters and the ice sheet cover. The orbital parameters are indeed shown to impact wind stress intensity in the Arabian Sea through large scale changes in the meridional gradient of upper tropospheric temperature. But both the orbital parameters and the ice sheets affects the pattern of wind stress curl through the position of the sea level depression barycentre over the monsoon region (20° W–150° W, 30° S–60° N). The combined changes in monsoon intensity and pattern lead to higher glacial productivity during the summer season, in agreement with some paleo-productivity reconstructions.

Citation: Le Mézo, P., Beaufort, L., Bopp, L., Braconnot, P., and Kageyama, M.: From Monsoon to marine productivity in the Arabian Sea: insights from glacial and interglacial climates, Clim. Past Discuss., doi:10.5194/cp-2016-88, in review, 2016.
Priscilla Le Mézo et al.
Priscilla Le Mézo et al.
Priscilla Le Mézo et al.

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Short summary
The paper focuses on the relationship between the Arabian Sea biological productivity and the Indian summer monsoon in climates of the last 72 kyr. A General Circulation Model coupled to a biogeochemistry model simulates the changes in productivity and monsoon intensity and pattern. The paradigm stating that a stronger summer monsoon enhances productivity is not always verified in our simulations. This work highlights the importance of considering the monsoon pattern in addition to its intensity.
The paper focuses on the relationship between the Arabian Sea biological productivity and the...
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