Seasonal changes in the isotopic composition of planktonic foraminifera collected in Panama Basin sediment traps

Abstract

Isotopic analyses have been made on five species of planktonic foraminifera collected in two deployments of PARFLUX Mark II time-series sediment traps in the Panama Basin. The automated sampling system on the traps provided 4 one-month samples from 29 July to 16 November 1979 and 6 two-month samples from December 1979 to November 1980. The δ 18O values of Globigerinoides ruber and Globigerinoides sacculifer in this region are primarily affected by a low-salinity surface layer that forms during the early winter. These species each show a 1‰ total range in δ 18O. The δ 18O values of the colder-water species Globorotalia menardii, Neogloboquadrina dutertrei, and Globorotalia theyeri show smaller seasonal changes in δ 18O. The δ 13C values of G. ruber and G. sacculifer exhibit small seasonal changes (0.35 and 0.4‰ respectively) despite large seasonal changes in surface water productivity. The colder-water species exhibit only slightly larger changes in δ 13C (up to 0.55‰) throughout the year. All colder-water species exhibit minimum or near minimum δ 13C values during February and March, which is the period of maximum upwelling and primary productivity. Seasonal variations in the flux of foraminifera in the water column at this location will have only a small effect on the isotopic composition of the sediment assemblage; extreme values of δ 18O and δ 13C do not occur during the periods which are associated with the high flux of foraminiferal tests.