Vertical fluxes of coccolithophores and foraminifera and their contributions to CaCO3 flux off the coast of Ensenada, Mexico

Abstract

Coccoliths and foraminifera fluxes and their contributions to CaCO₃ were estimated by analyzing the material collected by a sediment trap installed in the area adjacent to Ensenada, Baja California (Mexico). Coccoliths were identified and counted from images obtained with a Zeiss-Supra 55VP scanning electron microscope. Foraminifera were identified and analyzed with a Leica EZ4 stereoscope. Total CaCO₃ was determined by coulometry. A total of 33 species of coccoliths were recorded; the most abundant species were Emiliania huxleyi type A, Gephyrocapsa oceanica (Equatorial), E. huxleyi type B, and G. oceanica (Larger), contributing 74% of total coccolith flux. The maximum flux of coccoliths was 1,539 × 106 m^–2·d^–1 in sample A-8, the minimum zero in sample A-10, and the average 1,028 × 106 m^–2·d^–1. Coccolith contribution to CaCO₃ content ranged from 0.14 mg·m^–2·d^–1 in sample A-12 to 25.00 mg·m^–2·d^–1 in sample A-1, with an average of 5.60 mg·m^–2·d^–1. Helicosphaera carteri made the highest contribution with 10.00 mg·m^–2·d^–1 in sample A-1, and the rest of the species contributed <7.00 mg·m^–2·d^–1. Six genera of planktonic foraminifera were identified: Globigerina, Neogloboquadrina, Globorotalia, Pulleniatina, Globigerinoides, and Orbulina. The maximum flux of foraminifera was recorded in summer (513 m^–2·d^–1) and the minimum in spring (9 m^–2·d^–1). Benthic foraminifera were found to make an important contribution, even greater than the contribution from planktonic foraminifera, reflecting horizontal resuspension and/or transport processes. CaCO₃ contributions by coccoliths and foraminifera were <1% of total CaCO₃, and the rest was contributed by fragments of the other calcareous groups.