Multi-proxy reconstruction of surface water pCO₂ in the northern Arabian Sea since 29ka

We report here the results of a multi-proxy study to reconstruct surface water pCO₂ concentrations in the northern Arabian Sea. Our results show that δ¹¹B and Mg/Ca measurements of the planktonic foraminifer Globigerinoides sacculifer yield consistent pCO₂ values with those reconstructed from the δ¹³C of alkenones when used in conjunction with foraminifera δ¹³C and Cd/Ca values. They reveal that this area of the oceans has been a constant source of CO₂ to the atmosphere during the interval 5-29ka, and that the intensity of this source was greatest between 11 and 17ka, when atmospheric CO₂ levels were rising rapidly. We interpret our data as reflecting variation in the strength of the Asian Summer Monsoon (ASM), thus indicating that the strength of the ASM varied in phase with summer insolation over the Tibetan plateau between 5 and 29ka. In contrast to a previous study (Clemens and Prell, 2003), we observe no significant lag between the rise in insolation and the response of the ASM. Rather, our data support a recent study by Rohling et al. (2009) that northern hemisphere climatic forcing factors play a greater role in controlling the intensity of the ASM during times of intense monsoon activity, and that the southern hemisphere forcing is more important during times of weak monsoons.