25 August - 31 August 2008 (Reykjavik – Bremerhaven)

We continue our transit towards the East Siberian Sea this week. On Monday, we have to interrupt our way towards the research area to evacuate a sick scientist. He is flown to a hospital at Inuvik (Canada). In the meantime, he has arrived in Germany in good physical condition.

The oceanography program during this cruise focuses on obtaining vertical profiles of physical ocean parameters from onboard the ship and to deploy ocean buoys for autonomous observations on drifting ice floes:  Ocean velocity is measured continuously on the ship using an Acoustic Doppler Current Profiler (ADCP).  This instrument sends sound pulses that are reflected throughout the water column, depending on the sound speed, and then measured at the device.

The water velocity is measured making use of the Doppler effect which modifies the sound pulses due to the (moving parts) of the water column relative to the ship. In conjunction with navigation data, the absolute velocity of the water can be calculated. The first vertical water profile of temperature and salinity was obtained in the Baffin Bay using an expendable measurement system. This system, called XCTD (Expendable Conductivity Temperature Depth), can be deployed from the moving ship and infers depth from the falling speed of the measurement probe.  During the fall, temperature and electrical conductivity are measured, which combined allow us to calculate other parameters, such as salinity and sound velocity. These profiles reach down to a maximum of 1100m and have been obtained along the transect from the mouth of the McKenzie river, after leaving the Canadian Exclusive Economic Zone, to the Chukchi Plateau and the Mendeleev Ridge.
 
So far, the transect has shown very low salinity surface waters in the upper 50m due to the recent spin-up of the Beaufort Gyre, collecting more freshwater likely originating from the Arctic rivers, and an increase in sea ice melt.  Below this surface layer in the Canadian Basin, we find indications of Pacific Summer Water and even further down Pacific Winter Water, formed by convection during winter atmospheric cooling and ice formation. The Atlantic Water on our transect is located several hundred meters deep and shows the characteristic temperature maximum.

The upcoming weeks will be used obtaining more XCTD profiles, measuring similar profiles using a more accurate shipboard CTD system while the ship is stationary, and preparing equipment for the ocean buoy deployments on the ice.

On August 29th, we started the seismic reflection profiling. Details and objectives will be reported in later reports. In the meantime, the typical summer Arctic weather is established: temperature around 0°C, fog and snow fall.

Best wishes to the readers at home!

Wilfried Jokat

78°09’N 178°51’E, -1.1°C