Unique oceanographic observations - "Jotun Arctic" on survey to East Greenland fjord

During the last three years the Nansen Center has collected unique oceanographic measurements in order to quantify the subsurface fjord melting of the Greenland Ice Sheet. New data were collected in the Sermilik Fjord (SF) and adjacent East Greenland shelf in August 2010 (see map). It was proposed that a submarine melting of a glacier’ ice fronts in Greenland as well as in Antarctica is an important mechanism driving recent curving front’s retreat and glaciers acceleration. The expeditions by the Nansen Center in 2008 and 2009 confirmed that Atlantic Water (AW) from Irminger Sea with temperature reached more than 4.5°C fill all deep parts of the ~80 km long Sermilik Fjord.

The AW being the main conduit between the World Ocean and the Greenland Ice Sheet (GrIS) transfers climatic signals to the grounded glacier terminuses or floating tongues from source areas. Therefore monitoring of the AW properties and pathways is essential for understanding of the glaciers and GrIS response to climate change, which was the main target of the expeditions.

Exceptionally hard ice conditions in the fjord prevented penetration into the inner parts of the SF where three tide-water glaciers (including highly productive Helheim glacier) terminate into fjord water. Nevertheless, 152 oceanographic stations were completed measuring temperature and salinity profiles down to 650 meter. Series of sections across East Greenland Coastal Current and in the SF were repeated for the third year to achieve short-term and inter-annual variability in properties of the water masses.

In addition to previous years measurements following highlights was made during August 2010:

1. For the first time in history the Johan Petersen fjord (PF) was surveyed from the mouth to the head where several tongues of glacier ice from GrIS stream enter into the fjord water along very steep slope. Measurements confirm that the AW propagates up to end of the PF occupying near surface layer. The morphology of the Petersen fjord are similar to that of the Helheim Fjord, however no measurements could be done in the latter due to the heavy ice conditions..
2. The AW properties were traced from 66oN (the northernmost reached station) along more than 80km long section over deepest part of the SF and through the deep canyon linking the fjord mouth with the East Greenland shelf.
3. Water samples were collected (Niskin Water Sampler 1.2L) for oxygen isotopes (160 stations), alkalinity (20) and salinity (24) with emphasizes to measure the vertical water mass structure. Four chemistry stations were completed with sampling at 10 depth levels.
4. Currents speed and direction were measured using three current meters (SD6000 at 1, 50 and 450m) installed on drifted buoys with GPS tracking for 30 hours. At the same time CTD profiles were completed with one hour time interval to resolve tidal influence on currents and the vertical structure of the water column.
5. Four icebergs were tracked by the sailboat with concurrent CTD profiling for comparison water properties and simultaneous tracking of the icebergs in consecutive satellite radar images (SAR) for studies of the influence melting of iceberg on surrounding water.
6. One GPS with high and two GPS with low temporal resolution were installed on two icebergs to measure their trajectories of movement. GPS with low resolution transmit the icebergs position every six hours (see http://fotspor.org/gps-position/)
7. Continuous meteorological records (air temperature, humidity, wind direction and speed, air pressure) with 5 minutes interval were obtained from installed weather station on board “Jotun Arctic”.
8. Continuous recording of the water depth and surface water salinity (conductivity) and temperature were obtained using onboard equipment.

The data obtained will require further processing and integration. However, some early observations shows that the ice conditions in the Sermilik Fjord are much more difficult in 2010. Nevertheless, comparison of the temperature profiles repeated at the same locations along the entrance of the Sermilik Fjord indicates in general that the water temperatures are much warmer in 2010 compared to 2009 for all main layers – upper layer, Polar Water layer and Atlantic Water layer. Temperature increase in the AW layer exceeds 1-1.5°C for stations revisited in 2010. However, the temperature profiles from 2008 were even higher than in 2010. Of the three years 2010 seem to be intermittent wrt. the water temperatures.

From comparison of iceberg tracking and repeated vertical profiles measurements during one survey it is possible to conclude that offshore wind and generated currents exert a major forcing mechanism on circulation and vertical water properties within the SF. During an event of strong gale along the Greenland shelf, the icebergs where forced northward into the fjord with twice the speed compared to the southward drift out of the fjord.

The unique record of three years of oceanographic measurements confirm that the ice and oceanographic conditions in the Sermilik Fjord are highly variable even on short-term scales and very depended from external forcing. Further monitoring, analysis and numerical ocean and iceberg drift modeling will be done in order to improve the understanding the fjord-shelf interaction processes along the coast of East Greenland.

Learn more about the "Jotun Arctic" cruise to the East Greenland fjords in August 2010 at:

http://fotspor.org/