Water mass evolution at intermediate depths off somalia for the past 31 kyr based on the benthic foraminiferal chemistry

Abstract

Studying past changes in temperature and salinity of bottom water is of interest because they reflect not only regional expressions, but also global changes in heat flux and circulation patterns at depth. Here we present the results of sediments off Somalia to identify the water mass distribution present at the intermediate depths in the Arabian Sea for the past 31 kyr using paired Mg/Ca and d18O measurements of epi-benthic foraminifer Cibicidoides kullenbergi. First, we calibrate Mg/Ca in C. kullenbergi and Cibicidoides wuellerstorfi with measured in situ bottom water and isotopic temperatures from core-tops along a depth transect off Somalia. We compare the new data with the published calibrations and discuss other potential effects (e.g., carbonate ion). Second, we investigate temperature and salinity changes from the coupled d18O and Mg/Ca records of C. kullenbergi for the past 31 kyr off Somalia at ~1580 m water depth. The results show that the glacial water mass at the intermediate depth was warmer and more saline compared to the present day. We suggest that this water mass is Glacial Arabian Sea Intermediate Water (GASIW) and bathed the slope at intermediate levels offshore Somalia during the last glacial. The GASIW is most likely to be originated in the northern Arabian Sea although a possible influence of glacial Red Sea water can not be excluded