Edge of the Arctic Shelf

The Race is On
"Look at this, isn't it beautiful?" Bob Pickart was grinning and holding a piece of paper. On it was a vaguely round red blob, right in the middle of the page. "There's our eddy." I was looking at a plot of the thickness of the eddy we have been chasing for the past several days. Our XCTD survey captured it beautifully. Through snow squalls and biting winds, the CTD watchstanders and Marine Science Technicians worked all night to sample one final section right through the middle of this swirling mass of shelf water. We hope to capture all the information that we can about this oceanographic feature before we have to head south. As Bob was showing me the plot, we were finishing the last VPR and multi-net cast of the section.

During much of the past few weeks, intermittent snow showers have dusted the ship. Very little snow has accumulated--just enough for a short snowball fight. I asked Jessie Cherry, a graduate student writing her doctoral dissertation on Arctic snow, to describe what is known on the topic.

Jessie: "We have a very poor estimate of how much snow falls in the Arctic. Even on land, where there are gauges, snow is very difficult to measure. A snow gauge is kind of like a bucket on top of a 2-meter tall pole. Some gauges are heated and the snow inside is melted and measured automatically. Others are emptied by a person every day or week. The problem is that much of the snow blows horizontally, just like we have been seeing here at sea. So the snow never falls into the gauge. Another problem is the presence of the gauge actually causes some turbulence in the atmosphere around it. This turbulence from the gauge acts as a little gust of wind that blows snow away from the bucket part of the gauge. Some gauges are believed to underestimate the snowfall by as much as 100%."

How much snow falls over the Arctic Ocean?
Jessie: "Scientists have absolutely no idea how much snow falls over the open ocean up here. As you can tell from our Daily Dispatches, the air temperature is right around the freezing point. Only when we were on the ice did it get colder. So even when it snows here, some of the snow will sublimate (turn into water vapor) before it hits the water. In the central Arctic Ocean there were some historic gauges on the ice, deployed by Russian scientists, but by the time air masses reach the central Arctic, there is very little moisture left, so snow amounts are very small and for that reason are even more difficult to measure."

Where does the snow go when it melts?
Jessie: "Snow that falls on land as far south as 45°N melts and flows into rivers that discharge into the Arctic Ocean. Some of the snowmelt evaporates, but the presence of permafrost (permanently frozen soil) means that the soil can’t absorb very much water, so it flows into streams and rivers. This becomes a major source of freshwater for the entire Arctic Ocean. We can see this freshwater in many of our CTD measurements."

Now that our eddy chasing is complete, we are speeding south as fast as we can. We have a new sense of urgency to retrieve our last mooring in the Chukchi Sea central channel. The latest forecast calls for the winds to increase to gale force (35 knots and higher) by tomorrow morning. If the seas become rough, it may become too dangerous to launch the small boat to hook the mooring. Since we need to start heading for Nome by Wednesday afternoon, time is definitely running out. Stay tuned for tomorrow's dispatch to see if Mother Nature interferes with our mooring retrieval plans...