Blog & News
Insights into our latest mission to the Arctic.
The Arctic Spring Bloom
April 20, 2011
Posted by: Dr Victoria Hill (Ice Base Scientist)
It’s exciting to be here at the change from winter to spring. For the past few days, the temperature at the Ice Base has been much warmer at -25C. It’s made living on the sea ice much more pleasant, and the plankton world is feeling the coming of spring too.
Within the ocean there are a number of different substances that absorb the sunlight, we can break these down into particles (algae, sediment, detritus) and dissolved materials. I am looking at a substance called Coloured Dissolved Organic Material (CDOM). When you make a cup of tea – you put dead organic material (tea leaves) in hot water. The hot water breaks down the cell walls and releases the CDOM into the water. This material is a strong absorber of sunlight in both the ultraviolet and blue region of the light spectrum.
The same happens in the oceans. Plant material in the ocean is broken down by cell death, microbial action and grazing by zooplankton, producing CDOM. This CDOM can come from marine plants, such as algae, or can come from the surrounding land, where rivers carry out the CDOM from the plants on the tundra or forests. In terms of solar absorption in the ocean, during the first stage of ice break up there is little to no phytoplankton in the water and so CDOM is the biggest factor in light absorption at the start.
I am looking at two types of sample to examine the solar absorption in the water column – samples from the ocean taken through our ice hole and samples from ice cores which are then melted. Already this year I have seen visible changes in the amount of algae in the sea ice. A few nights ago, I was crushing a filter from an ice core sample, and saw clearly a green colouring caused by photosynthetic pigments. This was from the bottom of the ice core, in the five centimetres nearest the ocean and its nutrients. Just yesterday, I found chlorophyll in the whole bottom 20 cms of the ice core, this indicates that the ice algae are really starting to increase production and my colleagues have found similar increases in zooplankton numbers which feed on the ice and water column algae.
I have the latest samples in my lab tent ready to process them to see how much CDOM there is. Judging by the amount of chlorophyll, I would imagine that there will be quite a lot. It has been exciting to go from zero CDOM in the ice when I arrived and see this steadily increasing as the algae start to grow and multiply.
The speed of change in the high Arctic is astounding. Just three weeks ago we had clear periods of night, of darkness. Now the days trickle into one another. I haven’t seen darkness since late March. The sun sets past midnight. Day does not follow night, instead day trips through twilight and then back again. Two days ago we had 2 hours 49 minutes, where the sun was below the horizon, even then it’s still light here no need for a head torch when getting into bed. Tonight that will only be 1 hour 4 minutes. It shows just how important it is to be up here during these swift and important changes. In temperate climes, in Washington or London, there is space for the gentle turning of seasons. Not so here.