A bottom-up view of the biological pump: Modeling source funnels above ocean sediment traps

The sinking of particles that make up the biological pump is not vertical but nearly horizontal. This means that the locations where the particles are formed may be distant from their collection in a sediment trap. This has led to the development of the concept of the statistical funnel to describe the spatial-temporal sampling characteristics of a sediment trap. Statistical funnels can be used to quantify the source region in the upper ocean where collected particles were created (source funnels) or the location of the collected particles during that deployment (collection funnels). Here, we characterize statistical funnels for neutrally buoyant, surface-tethered and deep-ocean moored trap deployments conducted just north of Hawaii in the Pacific Ocean. Three-dimensional realizations of the synoptic velocity field, created using satellite altimeter and shipboard acoustic Doppler current profiler data, are used to advect sinking particles back to their source for sinking velocities of 50-200 m per day. Estimated source- and collection-funnel characteristics for the 5-day collections made by neutrally buoyant and surface-tethered traps are similar with typical scales of several km to several 10s of km. Deep-moored traps have daily source-funnel locations that can be many 100s of km distant from the trap and have long-term containment radii that range from 140 to 340 km depending upon sinking rate. We assess the importance of particle source regions using satellite estimates of chlorophyll concentration as a surrogate for the spatial distribution of particle export. Our analysis points to the need to diagnose water-parcel trajectories and particle sinking rates in the interpretation of sinking-particle fluxes from moored or freely drifting sediment traps, especially for regions where there are significant horizontal gradients in the export flux. But whence come the little siliceous and calcareous shells... [brought up] from the depth of over miles? Did they live in the surface waters immediately above? Or is their habitat in some remote part of the sea, whence, at their death, the currents were set forth as pallbearers, with the command to deposit the dead corpses where the plummet found them? (Maury, 1858). (c) 2007 Elsevier Ltd. All rights reserved.