Poster Presentation Australian Marine Sciences Association Annual Meeting 2023

Phytoplankton Dynamics at the IMOS SOTS Site: First Observations of a Multi-species Dinoflagellate Bloom in the Sub-Antarctic Zone (SAZ). (#409)

Ruth Eriksen 1 2 3 , Jacob Larsen 4 , Diana Davies 1 3 , Cathryn Wynn-Edwards 1 3 , Christina Schallenberg 1 2 , Pete Jansen 1 , Tom Trull 1 , Elizabeth Shadwick 1 3
  1. CSIRO Environment, Battery Point, Tasmania, Australia
  2. Institute of Marine and Antarctic Studies, University of Tasmania, Hobart, Tasmania, Australia
  3. Australian Antarctic Program Partnership, Hobart, Tasmania, Australia
  4. University of Copenhagen, Copenhagen, Denmark

The Southern Ocean Time Series (SOTS) site is the longest running biogeochemical time-series in the Southern Ocean, and is representative of a broad longitudinal swath of the High Nutrient Low Chlorophyll properties of the Sub-Antarctic Zone (SAZ; Shadwick et al., 2015). High temporal-resolution observations in this region are critical to resolve ecosystem processes affecting carbon cycling, ocean productivity and marine responses to climate change.

Measuring seasonal cycles of phytoplankton community composition and influential environmental variables in the SAZ is difficult to achieve with ship-based observations in this remote region. To address this gap, the SOTS program uses an autonomous water sampler in the surface mixed-layer, which returns high-frequency sensor data and discrete water samples preserved in situ for analysis once the package is retrieved (Eriksen et al, 2018).

Near-weekly surface samples of phytoplankton community composition, coupled with sensor and nutrient measurements during the SOFS8 deployment (2019-2020) revealed an unusual multi-species bloom of the mixotrophic dinoflagellate genus Prorocentrum. The dinoflagellate bloom followed a pulse of the large diatom Corethron pennatum, and is the first time that such a bloom event has been recorded at the SOTS site.  Analysis of the 2021-2022 samples suggest a similar, but less prominent transition also occurred.

  1. Eriksen R, Trull TW, Davies D, Jansen P, Davidson AT, Westwood K, van den Enden R (2018) Seasonal succession of phytoplankton community structure from autonomous sampling at the Australian Southern Ocean Time Series (SOTS) observatory. Mar Ecol Prog Ser 589:13-31. https://doi.org/10.3354/meps12420
  2. Shadwick EH, Trull TW, Tilbrook B, Sutton AJ, Sabine CL, Schulz E (2015) Seasonality of biological and physical controls on surface ocean CO2 from hourly observations at the Southern Ocean Time Series site south of Australia. Global Biogeochem Cycles 29: 223−238