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.