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Original Research ARTICLE Provisionally accepted The full-text will be published soon. Notify me

Front. Mar. Sci. | doi: 10.3389/fmars.2019.00595

Multi-year observations of fluorescence and backscatter at the Southern Ocean Time Series (SOTS) shed light on two distinct seasonal bio-optical regimes

  • 1Antarctic Climate and Ecosystems Cooperative Research Centre, Australia
  • 2Commonwealth Scientific and Industrial Research Organisation Oceans and Atmospheres Hobart, Australia

This work presents insights from 6 years of chlorophyll-a fluorescence and backscatter (700 nm) data at the Southern Ocean Time Series (SOTS) moorings, located in the Subantarctic Zone southwest of Tasmania. Using local calibrations from available voyage data, the fluorescence and backscatter records were related to chlorophyll-a (Chl) and particulate organic carbon (POC), allowing us to estimate and interpret carbon:Chl ratios. Surprisingly, observed carbon:Chl ratios were higher in winter than in summer, indicating that photo-acclimation of phytoplankton to decreased light levels in the deep winter mixed layer is not the main signal. Instead, the data suggest a seasonal succession of two trophodynamic regimes at SOTS: a phytoplankton-dominated community in summer, while in winter the proportion of “non-phytoplankton” POC increases. The two regimes can also be differentiated in an optical index based on fluorescence and backscatter, indicating two distinct bio-optical populations. Seasonal iron limitation and deep winter mixing in the SAZ, reaching as deep as 600m, likely play key roles in setting the stage for the observed ecological succession of the two trophodynamic regimes.

Keywords: Chlorophyll Fluorescence, Backscatering, subAntarctic area, Particulate organic carbon (POC), Optical index, Southern Ocean (SO), time series, mooring

Received: 18 Apr 2019; Accepted: 05 Sep 2019.

Copyright: © 2019 Schallenberg, Harley, Jansen, Davies and Trull. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence: Dr. Christina Schallenberg, Antarctic Climate and Ecosystems Cooperative Research Centre, Hobart, Australia, christina.schallenberg@utas.edu.au