THE JOURNEY

Diatoms and westerly winds
50 Degrees South Trust, Campbell Island Bicentennary Expedition - tarns
50 Degrees South Trust, Campbell Island Bicentennary Expedition - tarns
50 Degrees South Trust, Campbell Island Bicentennary Expedition - tarns
50 Degrees South Trust, Campbell Island Bicentennary Expedition - tarns
50 Degrees South Trust, Campbell Island Bicentennary Expedition - tarns

Diatoms and westerly winds

By Krystyna Saunders:

As part of the CIBE expedition, I spent seven weeks on Campbell Island sampling 45 lakes, tarns and ponds all over the island. At each site we collected water and sediment samples. Back in the lab at the University of Bern, Switzerland, I analysed the diatoms in the sediment and related to them to the water chemistry we measured.

Diatoms are unicellular algae and have a siliceous skeleton. They are found in almost all aquatic environments including fresh and marine waters and soils. They are highly sensitive to their environment and even small changes in water chemistry can lead to large changes in the species found.

Over time layers of sediment accumulate on top of each other, with each layer representing a different period of time. By identifying the diatoms in these layers and using our understanding of their ecology, we can reconstruct what the environment and climate were like when they were at the sediment surface.

We are interested in Campbell Island because not only has there never been a comprehensive survey of diatoms in its water bodies, meaning there is a large gap in our understanding of sub-Antarctic diatom flora, their sensitivity to their environment means we can use them to reconstruct past climates, in particular the strength of the Southern Hemisphere westerly winds. This is important because the westerly winds play a role in the circulation of the Southern Ocean and the climate of the mid-latitudes of the Southern Hemisphere including Tasmania, southern New Zealand and southern South America. Sub-Antarctic islands lie within the core belt of the westerly winds: between the ‘furious fifties’ and ‘screaming sixties’. This means they are ideally located to reconstruct past westerly wind behaviour.

This study was the first comprehensive survey of diatoms in water bodies on Campbell Island, and led to some exciting new results that were recently published in the Journal of Quaternary Science.

Importantly, we found that similar to other sub-Antarctic islands the conductivity measured in Campbell Island’s water bodies is due to sea spray from the strong westerlies. This means that conductivity decreases with distance from the west coast. Most of the diatom species we identified have been found elsewhere in the sub-Antarctic and the differences between water bodies is mostly due to conductivity changes. By working out the relationship between different species and conductivity, we used this information to develop a diatom model for reconstructing conductivity. This is a significant step towards reconstructing how the westerly winds behaved in the past because it means we can apply our model to diatoms identified in a sediment core from the western edge of Campbell Island, which we are currently working on.

If anyone is interested in finding out more, please contact me at: krystyna.saunders@ansto.gov.au