Presenter: Veronica Tamsitt (University of South Florida)

Description:
Recent observations indicate that open-ocean phytoplankton blooms in iron-limited regions of the Southern Ocean are fueled by upwelling of hydrothermally-sourced iron from the deep ocean. However, the pathways and timescales of this upwelling, and the relative contributions of different Southern Ocean hydrothermal vent sources to this iron supply, are not well known. In this work we use a virtual particle tracking experiment in an eddying ocean-sea ice model to characterize the interior upwelling pathways of iron from known hydrothermal vents throughout the Southern Ocean, and investigate the impact of the three-dimensional ocean circulation on the extent, location, and timescales of this upwelling. We find that the extent of upwelling (or downwelling) of hydrothermal iron in the Southern Ocean is strongly dependent on the location of vents within the three-dimensional overturning circulation, not only on vent depth. As a result, iron sourced from vents located in the upwelling limb of the overturning can upwell in timescales of years to decades, while fluid from vents located in the downwelling limb of the overturning travels northward into the abyssal ocean. The eventual outcropping location of upwelled hydrothermal iron into the seasonal pycnocline depends both on the locations of upwelling hydrothermal sources and large spatial variations in the depth of the maximum winter mixed layer depth. Hydrothermal iron from shallow vents and/or rapid upwelling pathways emerges in the upper ocean on timescales of 0-3 years in key hotspots, and less than a decade in broader regions of the Southern Ocean. Finally, we relate these results to observational evidence of hydrothermal iron upwelling from tracer measurements, and compare with observed Southern Ocean primary productivity.