South Georgia and ancient algal blooms ... by Rowan Dejardin

South Georgia is a strikingly beautiful, uninhabited island in the Southern Ocean, west of Patagonia and hundreds of miles from any major landmasses. Remote it may be but its ancient algal blooms and sediments potentially hold the key to understanding relationships between the carbon cycle and climate change in the past and, therefore, the future. Rowan Dejardin has just started his PhD within the Centre for Environmental Geochemistry (University of Nottingham and the BGS) and tells us more about his search for South Georgian algal blooms...

South Georgia is located in the path of powerful ocean currents that wrap around the island, transporting iron from the South Georgia shelf and plankton and krill larvae from the Antarctic Peninsula, causing intense algal blooms northeast of the island. The algal blooms account for a significant transfer of atmospheric carbon to the oceans interior and the currents may have been a major source of CO2 during the last deglaciation.

South Georgia

The position and strength of the currents that wrap around South Georgia are known to vary greatly from year to year but these changes have not been looked in terms of longer timescale climatic changes, such as those through the Holocene. Based on records from elsewhere in the Southern Ocean, it appears that these currents were located closer to Antarctic during the early-mid Holocene. This change could have reduced the amount of iron, a key controlling factor in the algal blooms, reaching northeast South Georgia, potentially resulting in less productive and/or more easterly blooms.

Me collecting samples from BAS for the pilot
study, with supervisors Vicky and George

To investigate whether the front was closer to the pole in the South Georgia region of the Southern Ocean during the early-mid Holocene my project will produce micropalaeontological and geochemical records of past ocean conditions, from cores along the northern coast of South Georgia. These records will be produced using a wide range of proxies, including microfossils and stable isotopes, in order to ensure the reconstruction and interpretation of past ocean conditions is robust.

In spite of only starting my PhD at the end of September, I have already been able to collect a small number of samples from the British Antarctic Survey (BAS) in Cambridge (where I also met all my supervisors), for a pilot study on a core (GC666!) close to Royal Bay. Since then I have been busily preparing these samples for isotopic and micropalaeontological analysis; excitingly, in addition to being packed full of diatoms (microscopic algae with a shell made of silica), the samples appear to contain plenty of excellently preserved benthic and planktonic foraminifera (microscopic organisms with a calcite shell, living on the seafloor or in the water column), promising many happy hours searching through ocean floor mud to find them!

Map showing the location of South Georgia and
  the Antarctic currents that wrap around the island (inset)

The PhD is supervised by Prof Melanie Leng and Dr Sev Kender (University of Nottingham/BGS), Dr George Swann (University of Nottingham), Dr Vicky Peck and Dr Claire Allen (BAS), and Dr Alastair Graham (University of Exeter).

Rowan Dejardin

lgxrld@nottingham.ac.uk
@rowandejardin