Stable isotopes of planktonic foraminifera from tropical Atlantic/Caribbean core-tops: Implications for reconstructing upper ocean stratification

delta O-18 values of nine tropical-subtropical planktonic foraminiferal species with different preferential habitat depths collected from 62 core-top samples along an east-west transect across the tropical Atlantic/Caribbean were used to test the applicability of interspecific delta O-18 gradients for reconstructions of tropical upper ocean stratification. In general, the delta O-18 difference (Delta delta O-18) between intermediate- and shallow-dwelling species decreases, and Delta delta O-18 between deep and intermediate dwellers increases with increasing thermocline depth towards the west. The statistical significance of regional differences in Delta delta O-18 highlights Delta delta O-18 between the intermediate dwellers (in particular Globorotalia scitula and Globorotalia tumida) and the shallow dweller Globigerinoides ruber pink, as well as Delta delta O-18 between the deep dwellers Globorotalia crassaformis or Globorotalia truncatulinoides dextral and intermediate dwellers as most sensitive to changes in tropical Atlantic thermocline depth. Based on the observed regional variations in interspecific Delta delta O-18, we propose a multispecies stratification index "STRA(trop)" (delta O-18(intermediate) - delta O-18(shallow)) / (delta O-18(deep) - delta O-18(shallow)) for the tropical ocean. Statistically significant differences in STRA(trop) values between the E-Atlantic and the Caribbean suggest that this index may be a useful tool to monitor variations in tropical upper ocean stratification in the geological record. (C) 2009 Elsevier B.V. All rights reserved.