Reconstructions of upwelling, productivity, and photic zone depth in the eastern equatorial Pacific Ocean using planktonic foraminiferal stable isotopes and abundances

In the hydrographically complex eastern equatorial Pacific Ocean (EEP), the distinction between changes in productivity and changes in upwelling is im portant to the study of the causes and implications of changes in paleoprod uctivity during the Last Glacial Maximum (LGM). We studied seven EEP coreto ps representing a gradient of increasing primary productivity from west to east. Comparison of the coretop data indicates calcification depth and temp erature for each planktonic foraminiferal species may change depending on t he vertical position of hydrographic features such as the degree of stratif ication of the water column, as well as associated biological parameters su ch as the depths of the photic zone and the chlorophyll maximum. Because th ese biological parameters are related to primary productivity, calcificatio n depth and temperature patterns for each species are somewhat different fo r high and low productivity regions in the EEP. We use the relationship bet ween modern surface hydrography and coretop planktonic foraminiferal abunda nces and isotopic composition to interpret upwelling and productivity chang es in the EEP over the last 20,000 years. While data indicate higher primar y productivity and lower SSTs, they do not indicate that there was greater upwelling at the location of our site during the LGM relative to present.