EPOC aims to generate a new concept of the AMOC, its function in the Earth system and how it impacts weather and climate. The Artic forms an important part of that picture as it forms the northernmost extension of the AMOC, but the Arctic is where climate change is occurring faster than anywhere else on the planet - nearly four times as fast. Hence, increases in the ocean heat transported to the Arctic can add to that warming, and vice versa - changes in sea-ice cover and freshwater input can modify the AMOC. Here we present some highlights from EPOC’s important work on changes in the Arctic Ocean.
The Arctic is currently one of the fastest changing environments on Earth. In light of ongoing climate change it is essential to quantify Arctic-Subarctic ocean exchanges over time as changes therein can impact ocean circulation and sea ice conditions both in the Arctic and in the Subarctic.
A pan-Arctic inverse model is being developed for 2004 – 2022 based on all available ocean temperature, salinity, sea ice and velocity data provided by the mooring arrays and hydrographic sections in Fram Strait, Barents Sea Opening, Bering Strait and Davis Strait (Fig. 1).
The inverse solution will provide net Arctic freshwater, heat fluxes and volume transports through these four Arctic Gateways, as well as estimates of Arctic overturning, which continues the work carried out by Tsubouchi et al. (2023). The preliminary transports are already quite well balanced and results will be improved through the inverse model (Fig. 2) The aim is to develop a system so that annual updates can easily be made once new data are collected from the moored observatories, helping to track changes in the Arctic Ocean.
Reference: Tsubouchi et al. (2023) DOI: 10.1175/JPO-D-23-0056.1
The Norwegian Atlantic Current (NwAC) forms part of the Atlantic Meridional Overturning Circulation (AMOC), transporting ocean heat poleward through the Nordic Seas. Its variability exerts a critical influence on high-latitude climate, water mass transformation in the Nordic Seas, and Arctic Ocean inflows.
A 30-year (1993-2022) hydrographic dataset is obtained from four repeat sections across the NwAC spanning from southern Norway to Svalbard (Fig. 3). Temperature and salinity data together with surface geostrophic currents from satellite altimetry provide absolute geostrophic velocities, allowing to analyse the NwAC’s properties, its progression through this domain, and changes therein.
Water properties and transports show substantial variability on seasonal to multi-annual timescales, with significant trends in temperature:
At present, the potential drivers of this reduced cooling are being investigated, thereby improving our understanding of the evolving role of the NwAC in regulating oceanic heat transport toward the Arctic.
Fram Strait is the main gateway between the Arctic Ocean and the North Atlantic, where warm, saline Atlantic Water (AW) flows northward via the West Spitsbergen Current (WSC) as part of the AMOC’s upper limb. The WSC constitutes the main source (~80%) of oceanic heat and salt entering the Arctic Ocean and variations in the AW inflow strongly influence both Arctic Ocean and sea ice conditions.
An array of moorings has been monitoring the year-round inflow of AW in the WSC, providing hydrographic and current data from 1997 – 2024 (Fig. 4). An unequivocal multi-decadal warming trend in the AW that enters the Arctic Ocean was identified, as AW temperatures increased at a rate of 0.20°C/decade, amounting to a total warming of 0.54°C over the 27-year record. When combined with historical hydrographic data, the warming trend persists over 56 years, demonstrating robust, multi-decadal AW warming. A number of multi-annual warm and cold anomalies were identified in the WSC which propagate northward into the Arctic Ocean. Therefore, the expected continued rise in AW temperatures and associated heat transport will have profound and lasting impacts on the future state of the Arctic Ocean.
Tracking model experiments show how Arctic waters can spread quickly to the North Atlantic, Newfoundland, east coast of USA and Europe. These can impact climate, marine ecosystems and fisheries, and transport terrestrial matter and contaminants from the Arctic to the North Atlantic rim.
Arctic waters entrained in the transpolar drift in the Arctic appear near Greenland after 2-3 years and flow into the North Atlantic. Overall, it takes about 6 years for Arctic waters to reach Newfoundland, and about 12 years to arrive at the West European Shelf. The waters form the West European Shelf flow pathways to the Arctic through the Barents Sea, arriving at the original release site in the Laptev Sea after another 12 years, thus completing the “Great Arctic – Atlantic Loop” within 24 years (Fig. 5). The loop provides insight into how the Arctic and North Atlantic oceans are connected by currents and demonstrates that Arctic waters can impact the West European Shelf and vice versa on the timescales as short as 12 years. A radioactive technetium (Tc) signal from Sellafield and Hague was obseved and tracked in the Western Barents Sea about 5 years after Tc release (Kershaw et al., 1997) and found near the East Greenland after 17 years and near the Iceland after 25 years (Lin et al, 2022).
References:
Kershaw et al. (2004) DOI: 10.1016/j.jmarsys.2003.08.003
Lin et al. (2022) DOI: 10.1016/j.chemgeo.2022.121007
