April 20, 2011 | 3
There have been many media headlines recently concerning the melting of the sea ice in the Arctic Ocean, often focused on the opening of the North West Passage and further commercial opportunities in this region. Current predictions are that there will be no summer time sea ice coverage by 2050. This increased flux of fresh water from the melting of the sea ice could contribute to the slowing of the thermohaline circulation, as I mentioned in my previous blog post.
What’s melting the sea ice?
What interests me is that current model predictions have all underestimated the rate at which the sea ice is melting when compared to our observations over the past decade. There must be another factor that we are not taking into account and that is what I am researching this year at the Catlin Arctic Survey Ice Base.
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. You can see vividly just how much light the Arctic Ocean absorbs if you compare the oil black waters of a lead (pronounced ‘leed’, the gap between two ice packs as they draw apart) and the brilliant white of the surrounding snow and ice.
What is arctic tea?
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 Colored 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.
CDOM is important in the process of solar absorption as it absorbs visible light from the more energetic UV, blue and green end of the spectrum.
How much CDOM is there?
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. 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 coloring caused by photosynthetic pigments. This was from the bottom of the ice core, in the five centimeters 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.
How are the seasons changing?
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 touch 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.
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.
I do think that CDOM is a missing part of the puzzle in understanding and predicting sea ice melt in the Arctic Ocean. Getting this kind of data at this time of year is so difficult and this opportunity so rare, that I am more than happy to sleep in an unheated tent at -35C, not shower for 6 weeks, and work long hours in the biting cold.
I have my small questions to answer, my data to gather and my samples to process. The answers I find should help us better understand this important part of the world.
Photo credits: The Catlin Arctic Survey, Copyright Martin Harley.
Editor’s Note: The Catlin Arctic Survey is a unique collaboration among polar explorers and scientists to gather data on the impacts of climate and environmental change in the Arctic.
This 10-week international scientific expedition will travel to the farthest reaches of the Arctic to research the impact of melting ice caps on the world’s oceans and weather systems. In recent years, the surface area of Arctic ice has declined to levels that were not expected until 2070. The Catlin Arctic team will seek to understand how climate and environmental changes affect ocean currents, which have a major impact on weather patterns throughout North America. Scientists are predicting that climate-related changes in the way that ocean currents circulate could result in a dramatic increase in the frequency and intensity of storms and cause extensive flooding, coastal erosion and damage to crops, homes and cities across the U.S. and around the world. The scientific team will be based at a unique research station located on sea ice in the Canadian Arctic shelf.
Simultaneously, a team of polar explorers will undertake two separate Arctic missions: the first across the Prince Gustav Adolf Sea, and the second from the North Geographic Pole toward Greenland.
Victoria Hill is research professor of ocean, earth and atmospheric sciences at Old Dominion University, Norfolk, Va.