Harrow and Hillingdon Geological Society

Previous Meetings

Arctic Ocean research

 Renske Gelderloos

The speaker is a physical oceanographer who is a post-doctoral research associate in the Department of Earth Sciences at the University of Oxford. She opened by showing the common view of the Arctic Ocean but commented that there is a lot more to the Arctic than ice and polar bears!

The Arctic Ocean is almost completely surrounded by land with a deep central basin and wide shelf margins extending from the surrounding land masses of the Canadian archipelago, Alaska, Russia, Norway and Greenland. It is connected to the Pacific Ocean by the narrow gap of the Bering Strait and to the Atlantic west of Greenland via Baffin Bay and the Davis Strait and between Greenland and Norway by the Greenland Sea and the Barents Sea.

Ocean circulation

The circulation of the Arctic Ocean is not fully understood but it is known that warm saline water from the Atlantic enters through the Greenland Sea and after circulation leaves via the same route and, to a much lesser extent, via the west of Greenland. Less saline water enters from the Pacific through the Bering Strait and fresh water enters from rivers in northern Russia and Canada. This fresher water leaves via the Greenland Sea and down the west side of Greenland. The only deep connection is to the Atlantic through the Greenland Sea.

The North Atlantic current enters and circulates in a number of gyres and the fresh water circulates on top of the warm water in the Beaufort Gyre and the Trans-Polar current.

Land ice versus sea ice

There is an important distinction between land ice and sea ice. Land ice is mainly in Greenland with some on the northern Canadian islands and it is permanent and several hundreds to over a thousand metres thick. Sea ice is only a couple of metres thick and grows every year.

The melting of the Greenland ice sheet in 1992 – 2010 compared to 1961 – 1990 showed an increase of 17 – 49% depending on the locality. The melt water goes into the Arctic and Atlantic Oceans. This was illustrated by the water channels on the Petermann Glacier, one of only 4 major outlet glaciers that have a grounding line below sea level (the others are the Humboldt, 79 North and Jakobshavn Isbrea). Ocean water also melts these glaciers from beneath floating ice shelves. Warm water from the Atlantic remains below the cold fresher water (at a temperature of about 0.2 ^oC, which may not seem very warm but it is compared to the fresher water). This constant melting from above and below results in the calving of icebergs and the speaker cited news items on the breaking off the Petermann Glacier of an iceberg twice the size of Manhattan.

Sea ice changes throughout the year, extending much farther in March at the end of the winter than in September at summer’s end. Some areas of open water remain as polynia, which are very important for marine ecosystems and which are probably the most biologically productive areas in the northern hemisphere. Maximum sea ice distribution at end-September 2013 was well within the 1981 – 2010 median line and showed a decline of 4Mkm ² (out of 8Mkm²) for 1979 – 2013. In contrast, winter ice extent in March 2014 was almost identical to the 1981 – 2010 median and showed a decline of only 1.5Mkm² (out of 16km²) for 1979 – 2014.

The speaker illustrated the use of a moored sonar instrument to measure sea-ice thickness and showed the recovered instrument had been damaged by an iceberg from the Petermann Glacier. She also showed the problems of damage to land-based instruments with cables at an inland weather station chewed through, probably by arctic foxes or hares and the bending of a metal plate, almost certainly by a polar bear.

Thermo-haline circulation

Warm water flows north in the Atlantic into the Arctic Ocean, where it cools, sinks and flows southwards as a cold density current. One of the key factors is the densification of the water, by becoming colder. We do not know if it is changing. This circulation is responsible for the relatively mild climate of Western Europe compared to the Labrador coast of North America. If the thermo-haline circulation were to stop, climate models show that the whole of the northern hemisphere would cool by 4 – 6^oC. There is some observational evidence for freshening of the high-latitude North Atlantic in recent decades.

Working in the Arctic Ocean

The speaker illustrated some of the work, in which she has been involved in the Nares Strait between Greenland and Ellesmere Island, Canada. Summer temperatures are generally in the range of 0 – 5^oC but the weather can vary considerably.

She showed the instrument, which is lowered into the sea for conductivity (from which salinity can be derived), temperature and depth measurements(CTD). Stations are every 5km across the strait and water samples are collected at chosen depth levels and a continuous CTD profile is available in real-time.

The National Science Foundation International Polar Year project – Canadian archipelago through-flow study 2003 – 2012 was illustrated. A sonar mooring array was deployed in the Cape Jefferson area of the Nares Strait in 2007 – 2009, with 4 instruments per mooring to measure flow velocity and conductivity and temperature, with samples every 15 minutes. The instrument was designed for sliding under the ice. Salinity and density cross-sections were similar with salinity ranging from 31psu in the surface waters to 34 – 35psu in deeper waters. Mean depth-averaged flow for 2003 – 2006 was southward along the western edge and the middle of the strait but northwards on the eastern margin.

Summary

The speaker summarised her experience of Arctic Ocean research as showing that:

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