Physical drivers of biogeochemical variability in the Polar Front Meander

• Published in: Journal of Geophysical Research: Oceans
• Main Authors: Yang, X, Strutton, PG, Cyriac, A, Phillips, HE, Pittman, NA, Rodriguez Vives, C
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley-Blackwell Publishing Inc. 2022
• Subjects: biogeochemical variability; polar front; climate; Southern Ocean
• Online Access: https://eprints.utas.edu.au/46773/; https://eprints.utas.edu.au/46773/1/150660%20-%20Physical%20drivers%20of%20biogeochemical%20variability%20in%20the%20Polar%20Front.pdf

The Southern Ocean plays a vital role in global ocean circulation, and the Polar Front (PF) isone of its most important physical features. The PF meander south of Tasmania, around 153°E, 55°S, is a verydynamic region which spawns mesoscale eddies, and influences local biogeochemistry and sea-air interaction.By using voyage and ancillary data, we investigated the unusually strong spring bloom in the vicinity of the PFmeander in 2018. We infer that the upwelling of deep water at the front and in eddies, brings macronutrientsand dissolved iron (dFe) to the surface. Chlorophyll concentration peaked at over 0.6 mg m −3, which isanomalously high for this area. With reduced iron limitation, the physiological characteristics of phytoplanktonin the northern, downstream part of the study area also changed. The photochemical efficiency was improvedand released this area from its usual high-nutrient low-chlorophyll (HNLC) status. This was mainly indicatedby the increase in the dawn Fv/Fm maximum (indictor of photochemical efficiency) from 0.2 to over 0.5.With the biomass increase and healthier community status, we observed consumption of surface dissolvedinorganic carbon and increased particulate organic carbon production to about 40 μmol L −1, forming a weaklocal carbon sink. Through the investigation of multiple years, a weak positive correlation between mixed layerdepth shoaling and phytoplankton growth was found, but there was significant interannual variability in thisrelationship, likely caused by variable eddy conditions and dFe delivery.