Award: OCE-0963026

We collected large (>51um) and small (<51um) marine particles from the whole water column (surface to 5500m depth) from 22 stations across the North Atlantic ocean as part of the US GEOTRACES North Atlantic Zonal Transect project. This was a collaborative project between several dozen scientists, each an expert at measuring and interpreting the concentrations of trace elements and isotopes (TEIs), with the goal of understanding how these TEIs are cycled in the ocean. Particles in the ocean are a key mediator of the cycling of TEIs. For example, mineral dust blowing from the Sahara desert over the North Atlantic is deposited into the ocean as micron-sized particles. These particles partially dissolve, supplying essential micronutrients such as iron that help fuel biological production. In all oceans including the North Atlantic, the even more dominant source of particles is from the biological production of phytoplankton in the surface ocean, which produces particulate organic matter, as well as shells made of calcium carbonate or silica. Phytoplankton are also in the micron to tens of micron size range, a size that is small enough that they generally donÆt sink on their own. But when phytoplankton die, the relatively small phytoplankton particles are actively (through being eaten and excreted) or passively (through sticking) packaged into large aggregates, generally >51um, which then sink out of the surface ocean. In the process of aggregation, other small particles such as dust are swept into the process, and are also removed. This sinking of large particles is termed the biologial pump, and is one mechanism by which the ocean sucks carbon dioxide from the atmosphere. As large particles sink, they tend to break up as they are decomposed into small particles again, which can be a source or sink of dissolved TEIs deeper in the water column. Our data elucidate this process of particle dynamics, providing a key piece to the puzzle of cycling of TEIs in the ocean. This is the first ever full ocean depth section of size-fractionated particle composition. This alone would make this project significant, but the even greater impact is in the synergies that have emerged from having dozens of scientists work collaboratively to solve the mysteries of the cycling of key elements in the ocean. This project has provided many training opportunities for developing the next generation of scientists, as well as for diversifying our scientific workforce. It is a main part of Daniel OhnemusÆ PhD thesis dissertation. It has also provided training opportunities for two female undergraduate students, both of whom were from Historically Black Colleges. Last Modified: 06/28/2013 Submitted by: Phoebe J Lam