Poster Australian Marine Sciences Association 2022

Effect of Light on the Distribution of Copper, Macronutrient Stocks and Fv/Fm in the East Australian Current: A Mesocosm Experiment (#531)

Prayna Maharaj 1 , Michael Ellwood 1
  1. Research School of Earth Sciences, The Australian National University, 142 Mills Road, Acton, ACT, Australia

Phytoplankton productivity is controlled by the availability of essential nutrients. A 8-day shipboard incubation experiment was conducted at a high productivity site in the East Australian Current (EAC) to investigate the role of light on the biogeochemical cycling of Cu and essential macronutrients.  The seawater used for the incubation experiment was pumped via a trace metal clean surface tow-fish system, and was characterized by an average surface dissolved δ65Cu of   ̴  0.5 ‰. Unfiltered seawater was incubated in four 210 L bags under four light conditions. The distribution of Cu, nitrate, phosphate and silicate varied in all the treatments. This is influenced by processes such as biological uptake and scavenging. Fv/Fm value decreased over the course of the experiment which was accompanied by a parallel decline in the rate of biomass accumulation. The reduction in Fv/Fm is greater in the high light treatment when compared to low light treatment which could be due to photo-damage of the PSII reaction centre proteins, increased nutrient stress or a shift in the dominant phytoplankton groups. Overall, this study provides novel insights about the the important influences of photochemical processes on the cycling of Cu and macronutrients in the natural waters of the EAC.