The secret life of Antarctic Phytoplankton

It's hard work digging through the Antarctic ice but Rob is ready. Picture: Rob Johnson

 

A 65-day expedition to the sea ice zone of the Antarctic as part of the Sea-Ice Physics & Ecosystem Experiment (SIPEX-II) Expedition yielded some exciting and potentially breakthrough findings on under ice microbial life below 60 degrees south. The voyage left Hobart on 14 September to study the links between Antarctic sea ice and Southern Ocean Ecosystems, one of the core missions of the Australian Antarctic Division (AAD) and the Antarctic Climate and Ecosystems Cooperative Research Centre (ACE CRC).

As a PhD student at the University of Tasmania's Institute for Marine and Antarctic Studies (IMAS) studying under Dr Peter Strutton, the key focus of my work is the use and assimilation of a long term, (more than 10 years and continuing) biological and oceanographic dataset from the Southern Ocean and Antarctica. As part of my studies I was the fortunate recipient of the opportunity to participate in the SIPEX-II mission. My role on SIPEX-II was to investigate the primary productivity, photosynthesis, and health of phytoplankton living in the water column under the Antarctic sea ice.

Phytoplankton are small microscopic plants responsible for almost half the photosynthesis and primary production on our planet. Through photosynthesis these tiny organisms produce oxygen and soak up carbon in world's oceans. Literally, the oxygen in every second breath we take comes from phytoplankton and thus is vitally important to our everyday lives and the health of our atmosphere.

My work on this voyage was to use a relatively new and exciting piece of technology known as a Fast Repetition Rate Fluorometer (FRRF) affectionately dubbed "Furf" by the ship’s crew. When phytoplankton photosynthesise, they absorb the sunlight passing through the ocean; they can't absorb all the light that hits them and the excess light is re-emitted as fluorescence. Using the FRRF we can measure this re-emitted light and determine how healthy the phytoplankton are based on how efficiently they use the light that's available to them.

The frame for lowering equipment through the ice. Picture: Robert Johnson.

 

At each ice station on the voyage I lowered the FRRF through a hole in the sea ice. As it descended from the bright light at the surface to the darkness of the deep ocean the FRRF flashed known quantities of light at the phytoplankton drifting past its sensor. This allowed us to look at the vertical distribution of phytoplankton and record how their photosynthesis and health varies under the sea ice. The next step of my work is to feed this information into mathematical models and equations in order to calculate the phytoplankton's ability to produce oxygen and to fix carbon under the relative darkness of the sea ice.

I'll also attempt to compare the FRRF method with the more traditional, and time-consuming, method of primary production measurements using radioactive carbon isotopes (the 14C method). Unlike the 14C method, which takes hours or even days to get one result, the FRRF can take several measurements every second and it is able to estimate primary production in near real time. By combining these new bio-optical methods with traditional oceanographic techniques, such as a Conductivity Temperature and Depth (CTD) rosette, we have been able to build up a comprehensive picture of what the microbial community does under the ice throughout the harsh Antarctic winter and how it is able to recover and flourish in the Spring/Summer.

I will spend the next six months back in the lab analysing the more than 600 chemical and biological samples we collected alongside the FRRF. If all goes well we will be able to shed some light on the secret life of Antarctic phytoplankton and validate the new FRRF methodology at the same time.

You can see a wonderful selection of Robert's photos at his Picasa site.

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