Interactions between ice shelves and phytoplankton blooms in the Amundsen Sea, and their relevance to the Southern Ocean

• Main Author: Twelves, Andrew G.
• Other Authors: Goldberg, Daniel, Gourmelen, Noel, Henley, Sian, Thomas, Alex
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: The University of Edinburgh 2022
• Subjects: Phytoplankton; Antarctica; Polynya; Ice shelf; Biogeochemistry; Southern Ocean; Amundsen Sea; Antarctic; The Antarctic; Antarc*; Ice Shelf; Ice Shelves; Sea ice
• Online Access: https://hdl.handle.net/1842/39292; https://doi.org/10.7488/era/2543

The coastal Southern Ocean is both highly sensitive to climate change and disproportionately important as a regulator of global carbon and nutrient fluxes. In particular, the polynyas which occur at many locations along the coastline host annual phytoplankton blooms which act as sinks of nutrients and carbon, whilst fueling the growth of higher trophic levels. Spring phytoplankton blooms in the Amundsen Sea are amongst the most intensely productive in the Southern Ocean and occur near some of the fastest melting ice shelves around Antarctica. In recent years both observations and modelling have been used to investigate the possible role of ice shelf melting in fuelling phytoplankton growth, with ice shelves implicated as sources of the dissolved iron whose scarcity would otherwise severely limit primary production. However there remains debate in the literature as to the importance of this iron limitation in comparison to light limitation, and as to the precise mechanism by which ice shelf melting enhances local iron concentrations. Meanwhile, expanded observations and advances in data assimilation have revealed pronounced zonal variation in both physical and biogeochemical aspects of oceanography near the Antarctic margin. In this thesis, idealised and realistic models of the Amundsen Sea are combined to examine the role that ice shelves play in driving Net Primary Production (NPP) in ice-free polynyas on Antarctic continental shelves, and how this role is affected by climate-driven processes. Addtionally, the impact of phytoplankton blooms themselves on the physical components of the Antarctic margin – particularly ice shelf melting and sea ice cover – are investigated. The modelling is undertaken using the MIT General Circulation Model (MITgcm) to represent ocean physics and the Biology Light Iron Nutrients and Gases (BLING) to represent biogeochemistry. This is the same combination used for the Biological Southern Ocean State Estimate (BSOSE), here modified and repurposed to study coastal processes with an ...