Determination of δ¹⁸O of Seawater in the Deep Ocean during the Last Glacial Maximum

We present a method for determining the δ 18 O of seawater in the deep ocean during the last glacial maximum from the measured δ 18 O values of deep sea pore fluids. Using data from Deep Sea Drilling Project (DSDP) site 576 in the Western Pacific, this method yields a glacial to interglacial change in δ 18 O sw of 1.0±0.25‰. This value for Δδ 18 O sw is the first direct measurement of deep ocean δ 18 O for the last glacial maximum and avoids the problems of spatial and temporal variability of the δ 18 O of surface water implicit in previous determinations. More precise, higher‐resolution pore fluid measurements are required to improve this determination.