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 important to the study of the causes and implications of changes in paleoproductivity during the Last Glacial Maximum (LGM). We studied seven EEP coretops representing a gradient of increasing primary productivity from west to east. Comparison of the coretop data indicates calcification depth and temperature for each planktonic foraminiferal species may change depending on the vertical position of hydrographic features such as the degree of stratification of the water column, as well as associated biological parameters such as the depths of the photic zone and the chlorophyll maximum. Because these biological parameters are related to primary productivity, calcification depth and temperature patterns for each species are somewhat different for high and low productivity regions in the EEP. We use the relationship between modern surface hydrography and coretop planktonic foraminiferal abundances and isotopic composition to interpret upwelling and productivity changes in the EEP over the last 20,000 years. While data indicate higher primary 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.