Abstract
Abstract. The relative abundance of Globigerinoides bulloides was used to infer Holocene paleo-productivity changes on the Oman margin and at the southern tip of India. Today, the primary productivity at both sites reaches its maximum during the summer season, when monsoon winds result in local Eckman pumping, which brings more nutrients to the surface. On a millennium time-scale, however, the % G. bulloides records indicate an opposite evolution of paleo-productivity at these sites through the Holocene. The Oman Margin productivity was maximal at ~9 ka (boreal summer insolation maximum) and has decreased since then, suggesting a direct response to insolation forcing. On the contrary, the productivity at the southern tip of India was minimum at ~9 ka, and strengthened towards the present. Paleo-reconstructions of wind patterns, marine productivity and foraminifera assemblages were obtained using the IPSL-CM4 climate model coupled to the PISCES marine biogeochemical model and the FORAMCLIM ecophysiological model. These reconstructions are fully coherent with the marine core data. They confirm that the evolution of particulate export production and foraminifera assemblages at our two sites were directly linked with the strength of the upwelling. Model simulations at 9 ka and 6 ka BP show that the relative evolution between the two sites since the early Holocene can be explained by the weakening but also the southward shift of monsoon winds over the Arabian Sea during boreal summer.
Highlights
The northern tropical Indian Ocean and the surrounding lands are the location of a strong monsoon system, which has a profound impact on the socio-economy of one of the most densely populated areas of the world (Saha et al, 1979; Mooley et al, 1981; Mall et al, 2006)
Paleo-reconstructions of wind patterns, marine productivity and foraminifera assemblages were obtained using the IPSL-CM4 climate model coupled to the PISCES marine biogeochemical model and the FORAMCLIM ecophysiological model
Opposite to what we have just observed for the Oman Margin site, the G. bulloides relative abundance at the southern tip of India reaches its lowest level at the beginning of the Holocene (∼9 ka BP; Fig. 4b)
Summary
The northern tropical Indian Ocean and the surrounding lands are the location of a strong monsoon system, which has a profound impact on the socio-economy of one of the most densely populated areas of the world (Saha et al, 1979; Mooley et al, 1981; Mall et al, 2006). In response to the monsoon wind reversal, the flow in the NEC reverses and combines with a weakened Equatorial Counter-Current to form the South-West Monsoon Current This affects the characteristics of the mixed layer depth by stratifying the surface ocean. There is a clear need to conduct data-model comparisons in order to better understand and simulate the relationship between the large-scale variations in the monsoon flow and the characteristics of the water column in different areas of the Indian Ocean. To compare the temporal evolution over the Holocene of monsoon-driven upwellings from the Oman margin and the southern tip of India based on sedimentary records of productivity changes; 2. In the final part of this paper, we will combine data and model over the whole Holocene period to explore the climatic implications of environmental changes recorded at the two sites studied
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