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

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 CO 2 . The 230 Th normalized opal fluxes and 231 Pa/ 230 Th 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 231 Pa/ 230 Th 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 CO 2 levels during the late glacial. However, the data do support results from previous studies that invoke increased El Niño–like conditions during this time.