Dana to investigate the East Greenland Current

In September 1860 Colonel Schaffner of the British Navy collected surface water samples in the Denmark Strait (between Greenland and Iceland) for Professor Georg Forchhammer,the Director of the Polytechnic Institution at Copenhagen (modern day the Technical University of Denmark).

Forchhammer had devised a series of chemical analyses to determine the salt content of seawater, referred to as salinity. With these measurements and samples from other ocean explorers he then began to speculate on regional ocean circulation patterns, among them those around Greenland. Later the practical application of salinity to modern oceanography was greatly advanced by Professor Martin Knudsen of DTU Aqua in the early 1900’s, providing tools to map ocean circulation patterns.

Today scientists are still studying the sea around Greenland trying to decipher the composition and origins of the currents and their global climate significance.

In September, the Danish research vessel Dana, run by the Technical University of Denmark, will return to the waters off East Greenland, and with the insight and tools developed by these early Danish marine science pioneers, the scientists on board will investigate the sources and mixing of water masses within this globally important region.

Dana's investigations will take place in the waters of the East Greenland Current along the east coast of Greenland.
 

The cruise is jointly funded by the Danish Center for Marine Research and the Danish Strategic Research Council, as part of the research project “North Atlantic-Arctic Ocean coupling in a changing climate (NAACOS)” led by Professor André Visser of DTU.

Linking the Arctic to the Northern Atlantic

The Danish investigations will take place in the waters of the East Greenland Current, which brings colder and less salty waters from the Arctic Ocean to the northern North Atlantic, and can potentially influence global ocean circulation and hereby also our climate.

“The waters in the Nordic Seas, between Greenland, Iceland and Norway, play a pivotal role in controlling global climate. Here the warm saline surface waters arriving as the tail end of the Gulf Stream are cooled to form very dense water, which sinks to the bottom of the ocean and starts a global journey at great depth before eventually returning to the region at the surface via the Gulf Stream. This is referred to as Meridional Overturning Circulation (MOC),” explains cruise leader and DTU Aqua Associate Professor, Colin Stedmon.

When the deepwater forms and sinks it takes with it dissolved carbon dioxide from the atmosphere and essentially stores it in the dark ocean until the waters reappear as a surface current 100’s of years later and the carbon dioxide is again exchanged with the atmosphere. The speed of this circulation and the volume of water involved influences the levels of carbon dioxide in the atmosphere and herein our climate.

“The supply of freshwater to East Greenland from the Arctic Ocean and Greenland ice melt is increasing. Any subsequent increase in the transport of these relatively fresher waters to the Nordic Seas will potentially weaken deepwater formation and the MOC as a whole, so it is important to understand circulation in this region,” Stedmon says.

The 20 scientists on the cruise include chemical and biological oceanographers from research institutions in Denmark and Greenland, and include collaborations with scientists in The United States of America and Norway.

In addition to charactering water masses the team will also be studying the influence that organisms such as bacteria, phytoplankton and zooplankton have on the transport of carbon to the ocean’s deep water layers.

As far north as the ice permits

During the intense two week scientific cruise, Dana will be sampling along three transects to provide a comprehensive suite of physical, chemical and biological oceanographic measurements across the East Greenland shelf and extending into the Greenland Sea.

These sampling locations are selected to ensure that the cruise results can be used directly to supplement climate monitoring already being carried out at existing Greenlandic research sites in fjords and on land. Additionally Norwegian scientists are collaborating and sampling at the same time, further north in the Fram Strait between Greenland and Spitsbergen.

Dana will be samling in three areas in East Greenland during the two week cruise.

The first sampling area is the Denmark Strait between Iceland and Denmark. The second transect starts further north at Scoresby Sound (Ittoqqortoormiut) and sails offshore. The final transect is off Young Sound (Daneborg) at approximately 74 ° N, and supplements the intensive sampling already taking place within the Greenland Ecosystem Monitoring Program around Zackenberg.

In September sea ice conditions for working in the region are at their best; a so called ice minimum. After a long summer much of the sea ice that can extend far down the Greeenlandic coast, has melted and the ice edge has retreated North to about 75° N.

Hope to find sources of the East Greenland Current

In order to trace and quantify the origins of the waters of the southbound cold East Greenland Current, Colin Stedmon and his fellow researchers will combine existing techniques based on inorganic nutrient concentrations, alkalinity, salinity and oxygen isotopes with a promising new technique to trace dissolved organic matter – using optical fingerprinting. The ultimate goal is to tease apart the relative contributions of Atlantic water, Arctic river water, Pacific water and Greenland ice melt.

Colin Stedmon, DTU Aqua:
“There is a concern to what extent increased freshwater from the Arctic will influence deep convection in the Nordic Seas and consequently the Meridional Overturning Circulation. Small changes in the freshwater escaping the East Greenland Current can potentially greatly influence convection and deep water production. The data we collect will help us evaluate the origins of the freshwater in the current and can be used to form, validate and improve the circulation and ecological models for this important region.”

In the footsteps of Forchhammer

The fingerprinting technique, although new, builds on the work of pioneers like Forchammer.

“Forchammer carried out some of the earliest work on investigating the origins of waters in currents based on the measurement of the major components of seawater. With modern techniques we can now measure even more of the salts and compounds present in seawater and use these to further differentiate between different waters, for instance freshwater from Siberian rivers compared to melt water from sea ice or Greenland),” says Colin Stedmon.

150 years ago, with the limited number of samples from the region and the unfortunate location of Schaffners sampling points too far from the Greenland coast, Forchammer concluded that the East Greenland Current was not a polar current, but a returning branch of the Gulf Stream due to its high salinity. However, had his samples originated from closer to the coast, he would have found the true East Greenland Current with polar waters of low salinity and temperatures below zero.

“Today we understand the pivotal role that the waters east of Greenland play in the global circulation of water and climate. The samples collected and methods developed on the upcoming Dana cruise will hopefully help to connect the dots even further, so that scientists can improve and refine their calculation on how the ocean willrespond to and influence a changing climate” concludes the cruise leader.

Further information:

Cruise leader Colin Stedmon, DTU Aqua

cost@aqua.dtu.dk

+45 29418314

http://www.staff.dtu.dk/cost

During cruise from September 2nd-16th 2012:
Professor Andre Visser, DTU Aqua (head of the NAACOS project)

awv@aqua.dtu.dk
+45 35883425
http://www.aqua.dtu.dk/English/About/Employees.aspx?lg=showcommon&id=39695&type=person