Impact of nutrient injection from an ageostrophic submesoscale front on phytoplankton community composition.

Chantal Mears 1, Christina Schallenberg2, Peter Strutton1, Tamara Schlosser1, Moninya Roughan3, Marina do Valle Chagas Azaneu3, Albertina Dias2, Giselle Firme4
1Institute for Marine and Antarctic Studies, University of Tasmania, Hobart, Tasmania, Australia
2CSIRO Oceans and Atmosphere, Hobart, Tasmania, Australia
3School of Biological Earth and Environmental Sciences, University of New South Wales Sydney, NSW, Australia
4School of Life Sciences, University of Technology Sydney, NSW, Australia

Nutrient limitation governs primary productivity across much of the open ocean. Along large scale frontal features, the redistribution of nitrogen and coinciding biological response are well understood, but less is known about the impacts of smaller scale, submesoscale (1-10km) features. In this work, repeated observational transects show an active submesoscale front in shutdown. During the active phase, strong evidence of frontogenesis was observed, where subsurface nutrients and oxygen were advected vertically into the mixed layer. This nutrient injection provoked both a spike in surface chlorophyll, resulting in an order of magnitude greater than the background measured by satellite, and a distinct shift in the phytoplankton community composition away from the oligotrophic background community. As the front shut down, fluorescence reduced, but the shift in the phytoplankton community composition remained, suggesting that the impact of submesoscale features on localized biogeochemistry can outlast the ageostrophic life span of the front. This study provides novel insight into the duration of ageostrophic tendencies in a submesoscale frontal system and their lasting impact on the local biogeochemistry and the phytoplankton community composition.