The interaction between waters from the Arctic Ocean and the Nordic Seas north of Fram Strait and along the East Greenland Current: results from the Arctic Ocean-02 Oden expedition

Abstract

In spring 2002, the Swedish icebreaker Oden conducted an extensive oceanographic survey of the East Greenland Current from north of Fram Strait to south of Denmark Strait as a part of the Arctic Ocean 2002 programme to study the Nordic Seas, while RV Knorr of Woods Hole worked in the ice-free parts. The Oden survey concentrated on water mass formation in ice covered water and the interactions between the water of the Arctic Ocean and the Nordic Seas. The CTD observations made on Oden are presented by following the Oden cruise track. They describe all major, and many of the more subtle, mixing processes occurring in the Arctic Mediterranean Sea. In Storfjorden, ice formation and brine rejection had created the highest bottom salinities observed in the last 20 years. The Atlantic Water (AW) entering the Arctic Ocean close to Svalbard was cooled and freshened down to 600 m implying that dense, brine enriched shelf water from the northern Svalbard shelf had convected into the Atlantic core. The upper part of the Atlantic Water was cooled by heat loss to the atmosphere and to ice melt. About 30% of the heat went to ice melt leading to a less saline upper layer that eventually forms the embryo of the Arctic Ocean halocline water. North of the Yermak Plateau Atlantic Water as well as Arctic Intermediate Water (AIW) and Nordic Seas Deep Water (NDW) were seen to enter the Arctic Ocean. North of 81°N the Arctic Ocean water masses dominated west of 0°E, while recirculating waters from the south were observed first at 79°N. The properties of the intermediate and deep waters exiting the Arctic Ocean in the East Greenland Current changed considerably from Fram Strait to the Greenland Sea indicating interactions with recirculating waters. The salinity of the Polar Surface Water (PSW) increased from Fram Strait to Denmark Strait but the thickness of the low salinity upper layer also increased and the freshwater content appeared to be conserved. The Denmark Strait overflow plume was stratified and several of the different water masses present at the sill in Denmark Strait at the Oden crossing could contribute to the overflow. Arctic Atlantic Water (AAW) and Recirculating Atlantic Water (RAW) as well as Polar Intermediate Water (PIW) would supply the less dense part, while the ultimate origin of densest component of the overflow, found at the Iceland side of the trench, still is an open question. The low salinity lid found on top of the overflow plume in the Irminger Sea suggests that entrainment of ambient water into the overflow plume was small.