Near Ice Oceanographic Observations of the Breiðamerkurjökull Glacier Melt Plume in Jökulsárlón Lagoon, Iceland

Abstract:

The Breiðamerkurjökull glacier flows down from the Vatnajökull ice cap and it has a marine terminus in a lagoon connected to the North Atlantic Ocean. The lagoon waters have characteristics determined by the Atlantic water, subglacial run-off and the local melting of ice calved from the glacier. The lagoon is not a fjordic environment, but many similar physical processes are operating. We conducted four hydrographic sections within the lagoon to determine the effects of the ocean on the glacier. Three of the sections across the lagoon allow us to determine the pathway of Atlantic water towards the glacial ice. One hydrographic section of 16 stations along the Breiðamerkurjökull glacier face was always within 3 to 30m from the ice face. This very near ice section showed both the warmest and coldest water sampled in the lagoon. The coldest water was close to the maximum depth of our measurements and was formed through contact with the ice. A heat and salt conservation model has enabled the relative contributions of the inflowing Atlantic derived saline water, the sub glacial fresh water run-off and the melt from the ice face to be determined. Overall the dominant freshwater contribution to the lagoon in the upper 20 m is from the sub-glacial freshwater. Beneath 20 m the dominant factor is modified North Atlantic water. The contribution from melting ice is observed below 10 m, and below 40 m depth this is in layers. Individual CTD measurements show that within the layers of higher ice melt there are strong peaks of increased melt, and so there is a 3 dimensional structure to the melt. The highest resolution data we obtained show that the water at these depths is in places statically unstable.