Vertical Nutrient Transport

In much of the surface ocean, the vertical transport of nutrients, either through advection (upwelling) or diapycnal turbulent mixing (eddy diffusivity), is the main control on biological productivity. Thus, accurate estimates of nutrient transport rates and temporal/spatial dynamics are critical to our understanding of ecosystem-to-regional scale biological production.

For example, during my dissertation work, I used a mass balance of 7Be to estimate upwelling velocity at a coastal time series station in the Southern California Bight (black symbols below). This approach yielded upwelling velocities that were for the most part consistent with the Bakun Upwelling Index (green bars), a wind-speed based parameterization of upwelling over the entire Bight. However, the 7Be-based approach indicated that upwelling likely began earlier and more dramatically than the Bakun Index predicted (Feb) during the time of year when export efficiency is highest. Without the more-local 7Be signal, we would not have been able to detect the precise timing of upwelling initiation, which likely triggers a community shift significantly affecting carbon export.

fig3_upwelling

Also using a 7Be-based approach in the Eastern Tropical South Pacific (ETSP), my colleagues and I were able to determine that vertical nitrate fluxes through both upwelling and eddy diffusivity balanced organic matter export at 20°S, but overestimates particle flux at 10°S, supporting the notion that the offshore HNLC region is micronutrient limited and horizontal transport of nitrate and dissolved organic nitrogen is likely a significant term in the regional nutrient budget.

Collaborators: Doug Hammond (USC), David Kadko (FIU), Angela Knapp (FSU), Nicholas Nidzieko (UCSB)