Diatom productivity in the equatorial Pacific Ocean from the last glacial period to the present: A test of the silicic acid leakage hypothesis

[ 1] The silicic acid leakage hypothesis (SALH) suggests that during glacial periods, unused silicic acid escaped the Southern Ocean into the equatorial oceans, causing an ecological shift favoring diatoms relative to coccolithophorids and a drawdown of CO2. The Th-230 normalized opal fluxes and Pa-231/Th-230 ratios were measured in eleven equatorial Pacific cores to reconstruct diatom productivity over the past 30 kyr and to test the SALH. Holocene spatial patterns of opal flux are strongly correlated with Pa-231/Th-230 ratios and with satellite estimates of primary productivity. Down-core opal flux records do not support the SALH but show Holocene opal burial to exceed that of the late glacial period by 35%, or 2.8 Gt opal/kyr, across the equatorial Pacific. This suggests that the SALH may not account for lower atmospheric CO2 levels during the late glacial. However, the data do support results from previous studies that invoke increased El Nino-like conditions during this time.