Catlin Arctic Survey: Spring blooms in the Arctic

By Dr. Victoria Hill
It’s exciting to be here in the Catlin Ice Base at the seasonal change from winter to spring. Warmer temperatures make living on the sea ice much more pleasant, and the plankton world is feeling the coming of spring too.
I’m here to help answer why current model predictions have all underestimated the rate at which the sea ice is melting when compared to observations over the past decade.

Dr. Victoria Hill (c) Martin Hartley/WWF
We know that solar energy causes warming in the oceans, but the exact values for solar absorption in the Arctic are undefined. The increased surface temperature of the Arctic Ocean is one of the main drivers for sea ice melt.
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). This material is a strong absorber of sunlight in both the ultraviolet and blue region of the light spectrum.
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.

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.
This 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.  It’s important to be up here during these swift changes, and as Arctic marine life blooms.