Effects of changing sea ice on phytoplankton bloom strength and composition at the Rothera Time Series

• Main Authors: Venables, Hugh, Meredith, Michael, Clarke, Andrew, Rozema, Patrick
• Format: Conference Object
• Language: English
• Published: 2016
• Subjects: Antarctic; Antarctic Peninsula; Rothera; Rothera Research Station; Ryder; Ryder Bay; The Antarctic; Antarc*; Sea ice
• Online Access: https://hdl.handle.net/11370/677cdcfd-a405-4157-b8d4-270407772b4b; https://research.rug.nl/en/publications/677cdcfd-a405-4157-b8d4-270407772b4b; https://www.liverpool.ac.uk/media/livacuk/challenger2016/documents/All_Abstracts.pdf

The Rothera Time Series has collected year-round physical, biological and biogeochemical data from Ryder Bay since 1998. The sample site is 500m deep, close to Rothera Research Station on the west Antarctic Peninsula, just inside the Antarctic Circle. Over the course of the time series there has been considerable variation in winter sea ice cover, in part mirroring the long term decline in sea ice observed along the western peninsula. In low ice years there are strong physical changes, with deep mixing in winter leading to heat loss to the atmosphere and reduced castration the following summer. The lower stratification preconditions the water column to increased mixing during the phytoplankton bloom period and leads to a significant reduction in chlorophyll concentrations. Light levels however are often favorable as ice melt ensures the mixed layer is normally very shallow. In the two most heavily affected years phytoplankton concentrations were persistently low (relative to the time series record) and there was a notable shit in community composition, from diatoms dominating to a mix with cryptophytes and haptophytes. In other low ice years, chlorophyll concentration exceed 15mg m3 but only for short periods, rather than the prolonged blooms seen in high ice years, again indicating more unstable conditions. The reduced stratification in summer also results in significantly higher heat uptake in the upper 70m, showing that there is indeed enhanced summer mixing and also providing a positive feedback towards reduced ice cover. Work is ongoing to expand the sampling further offshore using ocean gliders.