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

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 5-29 ka, and that the intensity of this source was greatest between 11 and 17 ka, 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 29 ka. 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.