Last night we began to head north away from the polar waters at the ice edge and back towards the Polar Front and sub-polar waters. We are currently about mid-way between the South Orkney Islands and South Georgia in the Scotia Sea. The flat calm, penguins, seals and icebergs have gone, replaced by the more typical uneven water, petrels and albatrosses that we experienced whilst crossing Drake Passage. This is an important part of the cruise since we are passing across significant gradients of carbonate chemistry that occur between polar and sub-polar regions.
Much of my work on this cruise is to obtain phytoplankton samples for genetic analysis. We are particularly interested in how different types of phytoplankton will respond in the long term to changes in ocean chemistry that are associated with ever increasing levels of carbon dioxide in the atmosphere and ocean surface water. One way of trying to discover this is to try to assess the ways in which different types of phytoplankton respond to experimentally imposed changes. To do this we take freshly isolated phytoplankton cells from the cruise and culture them back in the laboratory at home for more detailed experimental analysis. In parallel we are building a record of genetic variability by taking many samples for DNA analysis. We also extract RNA from our samples which, when analysed, can give an indication of the genes that are switched on or off in particular phytoplankton groups. This kind of molecular genetic analysis can also tell us how much natural variation there is in a single species – and it is that level of variation that can determine how fit a population is to survive changes. In this respect our main interests are in the calcifying coccolithophores, particularly the globally distributed species Emiliania huxleyi.
While the main focus of my research interests is in the calcifying coccolithophores, the samples that we have obtained in the cold polar waters have been dominated by diatoms and dinoflagellates.
The picture shows a few examples of live diatoms and other phytoplankton in fresh samples from polar waters. A: A single cell of a chain-forming species of Chaetoceros; B: Left image shows a very large diatom (Rhizosolenia spp.) with a smaller unidentified diatom (top), and two dinoflagellates. The image of chlorophyll fluorescence shows that these cells are all photosynthetic, apart from the dinoflagellate at the bottom left which has no chlorophyll (heterotrophic). C: Another very large diatom (Coscinodiscus spp.) with a very small unidentified diatom (bottom right); D: A population of small diatoms. Interestingly, different sampling stations give different proportions of very large and very small diatoms; E: A silicoflagellate (Dichtyocha speculum). Middle picture: A minke whale. Note the pictures are not all at the same scale!
Taking pictures of phytoplankton while we are sampling gives a feeling of reassurance that there is actually something alive in this freezing cold water. Microscopy at sea, however does come with some problems. Firstly, a moving, vibrating ship is not an ideal platform for looking at creatures a few microns in size. However, modern fast, sensitive cameras have made this far less of a problem than it used to be. Secondly, staring down a microscope on a lurching rolling ship can seriously affect your digestion. Fortunately we all have our sea legs at this stage of the cruise. Thirdly, there is a real danger of becoming too immersed in the amazing diversity of these ocean drifters at the expense of the more “routine” , but no less essential, filtering and washing jobs.
As we travel north we expect the waters to become more enriched in coccolithophores. The sampling on the cruise represents only the beginning of the work. There will be much analysis to be done back in the lab, extending well into the next year or two before we begin to get answers to some of the questions that we are asking.