Stable Isotopes as Tracers for Freshwater Fluxes into the North Atlantic

Abstract

The Arctic acts as both an indicator and a facilitator of global climate change. Many studies have identified the manifold changes in the Arctic hydrological system resulting from global warming. These changes have affected the freshwater balance of the northern North Atlantic and therefore pose a problem to deep water formation in this region, further impacting the global climate. This thesis uses the quasi-conservative properties of oxygen and hydrogen isotopes in watermasses to identify and quantify the freshwater sources to the ocean currents exiting the Arctic into the northern North Atlantic.

Comparison of historical oxygen isotope data from the East Greenland Current system with data presented here indicates that its freshwater isotope signature has not been temporally constant. Specifically, in 2005, there was a shift to a value ? 10 h heavier than the long-term mean, indicating a large increase in sea ice meltwater admixture that coincides with a large, short-term peak in the Fram Strait sea ice export. Therefore, interannual variations in the sea ice export are transported to the watermasses downstream.

Oxygen isotope data from the West Greenland Current confirm that the freshwater signal in the East Greenland Current system is transferred around the tip of Greenland. However, there is an apparent decrease in the freshwater concentration in the West Greenland Current relative to the east. This potentially corroborates the previously reported retroflection of part of the East Greenland Current into the North Atlantic subpolar gyre. The primary freshwater sources to the Labrador Current are identified as Arctic surface waters exported via the Canadian Archipelago, Hudson Strait and the West Greenland Current. There is also considerable sea ice formation and melt influence on the Labrador Shelf.

The world surface ocean oxygen and hydrogen isotope mixing relationship is observed to be regionally and seasonally robust, with the exception of areas with a high meteoric water influence. The use of hydrogen isotopes as a tracer for Greenland glacial meltwater in the East Greenland Current system is investigated and the preliminary results are positive although further work is necessary to establish the value of this tracer.

This thesis highlights the importance of stable isotope studies for identifying and quantifying the freshwater in the currents exiting the Arctic, allowing the key pathways of Arctic freshwater into regions of deep water formation in the North Atlantic to be identified and monitored. These pathways are: the East Greenland Current into the Nordic Seas and the North Atlantic subpolar gyre; the West Greenland Current into Labrador Sea; and the Labrador Current into the general North Atlantic circulation.

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