Very large pulses of particulate organic matter intermittently sink to the deep waters ofudthe open ocean in the Northeast Atlantic. These pulses, measured by moored sedimentudtraps since 1989, can contribute up to 60% of the organic flux to 3000 m in a particularudyear and are thus a major cause of the variability in carbon sequestration from theudatmosphere in the region. Pulses occur in the late summer and are characterized byudmaterial that is very rich in organic carbon but with low concentrations of theudbiominerals opal and calcite. A number of independent lines of evidence have beenudexamined to determine the causes of these pulses: (1) Data from the ContinuousudPlankton Recorder (CPR) survey show that in this region, radiolarian protozoansudintermittently reach high abundances in the late summer just preceding organic pulsesudto depth. (2) CPR data also show that the interannual variability in radiolarianudabundance since 1997 mirrors very closely the variability of deep ocean organicuddeposition. (3) The settling material collected in the traps displays a strong correlationudbetween fecal pellets produced by radiolaria and the measured organic carbon flux.udThese all suggest that the pulses are mediated by radiolarians, a group of protozoansudfound throughout the world’s oceans and which are widely used by paleontologistsudto determine past climate conditions. Changes in the upper ocean community structureud(between years and on longer timescales) may have profound effects on the abilityudof the oceans to sequester carbon dioxide from the atmosphere.
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