Mooring observations in the Chukchi Sea off the coast of Utqiaġvik (formerly known as Barrow) locating in the northernmost Alaska were conducted in the period from early to mid-August 2017. Such observations have been carried out since 2009 under a cooperation between Hokkaido University and University of Alaska Fairbanks with the support from local science institutions.
The ocean off the northern Alaskan coast is covered by sea ice in winter, and coastal polynyas are formed there. A coastal polynya is a large open water or thin ice area in a thicker pack ice region, which is created due to offshore-ward sea-ice transport by winds. In a coastal polynya, the ocean surface is well cooled by cold atmosphere directly because of the lack of thick ice which acts as a lid on the ocean, resulting in high ice production. Because sea ice rejects saline water to the ocean when it freezes from seawater, the dense water which can contribute to heat and material transport in deep ocean is formed in polynyas. In addition, some recent studies suggest that sea ice incorporates materials originating from the ocean-bottom sediment in shallow regions within polynyas. As these materials can be transported with sea-ice drift and finally released into the ocean when ice melts, a coastal polynya likely drive the material cycle in the polar ocean. However, our understanding of such processes in polynyas is not enough, because in-situ observations have been limited due to logistical challenges in sea-ice areas. Moreover, sea ice in the Chukchi Sea in summer is rapidly retreating in recent years. We have conducted long-term oceanographic and sea ice observations by moorings in such a region.
For the observations off Utqiaġvik, mooring deployments and recoveries were carried out by from a small boat. In 2017, two moorings were recovered and three moorings were deployed. During observational periods, seawater temperature, salinity, ocean currents and turbidity were measured. In addition, sea-ice thickness was measured by an acoustic instrument with high temporal resolution. Thus, we have obtained such oceanographic and sea-ice data over eight years. This year, we sampled the ocean-bottom sediment from the boat. Analyzing these data, we can reveal following things: what water masses exist around the mooring sites and where these water masses come from, how fast sea ice grows, and how thick the maximum ice thickness can be. Moreover, the comparison of these mooring data with satellite data such as the sea-ice concentration make us understand how sea-ice and oceanographic conditions affect each other and evaluate the possible future change in the Arctic.
Masato Ito (JSPS／Hokkaido University)