IMPACTS OF STORMS ON RECENT PLANKTIC FORAMINIFERAL TEST PRODUCTION AND CACO3 FLUX IN THE NORTH-ATLANTIC AT 47-DEGREES-N, 20-DEGREES-W (JGOFS)

Planktic foraminiferal assemblages are well known to vary in accordanc e with seasonal fluctuations in ocean properties, periodic reproductio n cycles, and variations between water masses. Here we report that sto rms also can significantly influence foraminiferal assemblages. During the RV Meteor cruise 21 to the Northeast Atlantic Ocean (BIOTRANS are a), from March to May 1992, planktic foraminifera were sampled using a multiple opening-closing net. While sampling, two storms with wind fo rces up to 12 Beaufort caused intensified surface layer mixing with sh ifts in the depth of the upper ocean mixed-layer from 20-40 m to 170-2 40 m. Subsequently, planktic foraminiferal growth rates increased, res ulting in an elevated quantity of small (100-150 mu m) tests (Phase 1) . When the wind strength increased a second time, the mixed-layer deep ened to a depth below the former position of the pycnocline, and again the abundance of small tests increased (Phase 2). During Phase 2, the weight of calcite in specimens of the productive zone reached its max imum. In the export zone, an associated increase in empty tests occurr ed with a lag time depending on the test sinking velocity. In the uppe r export zone, down to 700 m water depth, CaCO3 flux increased from 9. 3 to 49.8 mg CaCO3 m(-2) d(-1) after the first storm and from 8.9 to 1 9.9 mg CaCO3 m(-2) d(-1) after the second storm. In the 700 to 2500 m depth interval, the flux increased from 5.1 mg CaCO3 m(-2) d(-1) to ab out 9.2 mg CaCO3 m(-2) d(-1). Thus, the standing stock of living foram inifera and export of empty tests from the productive zone increased a fter the storms, leading to pulses of CaCO3 exported from the surface to deep water.