Phytoplankton

We are here to study Antarctic phytoplankton. Phytoplankton are microscopic little plants (OK, officially they are protists) that grow in the water everywhere. They are the basis of all life in the oceans, so kinda important. They need light for photosynthesis and nutrients for growth. In the Antarctic waters iron is often the limiting nutrient for phytoplankton growth. Iron is very insoluble in water and there are few sources of iron in Antarctica. Even though phytoplankton only need a little bit of iron, there is still often not enough available for optimal growth. One of our research questions is to determine if the phytoplankton are limited by the availability of iron or light and how different phytoplankton species respond to different availability of these two factors.

We are now sampling Antarctic waters in the spring, earlier in the season than I have ever been here. During the winter, there is no light, so phytoplankton cannot grow. When the spring begins the days get longer very rapidly and the light availability increases, so phytoplankton can start to grow. We always thought that around this time light availability controls the phytoplankton growth.  We reasoned that there is still plenty iron available for the phytoplankton, as they have not had the time to take it up yet. However, we now measure very low concentrations of iron in the water, so we may have to rethink that. It may be that the phytoplankton are constantly starved for iron, throughout the whole growing season. Another factor is that large areas are still covered by sea ice that prevents a lot of light from penetrating the water, so here the phytoplankton are still in the dark. Moreover, phytoplankton also grow in the ice. They are then called “ice algae” and they grow at the bottom of the ice, where there is a bit of light available. We have no idea how much iron is available to these algae, but we’re trying to measure it (the methods to measure iron in sea ice are not well developed, so we’re giving it a try).  Some ice algae are different species from the ones we find in the water column, and some are the same. We are now finding a lot of a species that we normally find in the water column in the ice, which is very cool. It raises all kinds of questions on how a unicellular species goes from growing in the ice to growing in the water column and vice versa.

One of the coolest pieces of equipment on the ship takes pictures through microscope lenses of all the phytoplankton in samples that we take from the ice and the water column. So we get a lot of very pretty pictures and a good sense of what is growing in the ice and in the waters below it. 

Eucampia

Phaeocystis

Chaetoceros

Diatom

Radiolarian