One of the most tell-tale signs of climate change is the retreat of Arctic sea ice. The decline has been especially rapid in the most recent couple of decades, and long gone are the times when thick sea ice covered most of the Arctic Ocean even in summer. This thick old sea ice has now been largely replaced with thinner and younger sea ice.
The recent rapid decline has not been well reproduced in climate models in part because most of our fundamental understanding of Arctic sea ice stems from observations done in an era with thick old ice. We believe that the dynamics of the younger and thinner sea ice now covering the Arctic Ocean is different and requires new understanding of key processes that drive sea ice change, for this to be better reproduced by climate models.
The well-known Norwegian polar explorer and scientist, Fridtjof Nansen, drifted across the Arctic Ocean in his custom-made ship the “Fram” in 1893-1896 and revolutionized our knowledge of the north polar region. Tellingly, a similar drift conducted during the International Polar Year in 2006/7/8, took roughly half as long, as ice drift speed has increased.
In the spirit of Nansen our research group designed a scientific campaign, the Norwegian young sea ICE cruise (N-ICE2015), in drifting sea ice in the Arctic Ocean, between Svalbard and the North Pole, in order to observe the functioning of a thinner sea ice pack.
For this we used the ice-strengthened research vessel “Lance” as our base, conducting scientific observations from the nearby ice floes while drifting with the ice.
N-ICE2015 took place in the winter and spring of 2015, and we battled fierce winter storms, rapid ice drift, break-up of ice floes and the occasional curious polar bear that wanted to sniff our equipment.
All this, while working on sea ice only three to five feet thick, that has become the norm in this region.
Many of the results of our research campaign are now published in a joint special issue of JGR: Oceans, JGR: Atmospheres and JGR: Biogeosciences. Together, this collection provides a comprehensive examination of how the now thinner sea ice responds to forcing from atmosphere (winds, precipitation and air temperatures), and how this in turn affects the ice pack (growth, drift and deformation), affects the mixing in the ocean below and eventually influences the marine ecosystem. In a coupled system all these processes are interlinked and affect each other, creating complex feedbacks.
Multiple papers in the special issue show significant effects from short-lived but fierce storms. These frequently pass through this region. Storms bring high wind speeds, warm air and moisture to a place that is otherwise cold, dry and stable. Although short-lived (only a couple of days) storms create such intense dynamics that, for example, the air sea exchange of carbon dioxide on seasonal time scales is governed by multiple short-lived storms. Storms accumulate a deep snow pack that insulates the ice from the cold atmosphere and the ice grows thinner. The thinner ice pack is also weaker and more easily responds to wind forcing, affecting ice drift, which in turn can transfer more energy to the ocean below and allow the mixing of heat in the ocean to melt the underside of the sea ice, even in midst of winter. At most intense these processes are during or directly after storms.
These fundamental processes typically occur on very short time scales but, more importantly, also act on very small scales (order of meters rather than kilometers), much smaller than at what typical climate models can resolve processes. These need to be carefully represented in models to make realistic predictions of Arctic sea ice in the future. Results from this experiment can serve as a guide for what to focus on in the next generation of models.
—Mats A. Granskog, Norwegian Polar Institute; email: [email protected]