Atlantic Water inflow north of Svalbard; new insights from recent years

Transcription

1 Atlantic Water inflow north of Svalbard; new insights from recent years Arild Sundfjord, Norwegian Polar Institute, Tromsø Partners: Norwegian Polar Institute, Institute of Marine Research, Universty of Tromsø, UNIS, Institute of Oceanology PAS, Woods Hole Oceanographic Institution, Akvaplan-niva, MET, SINTEF

2 Atlantic Water inflow north of Svalbard; new insights from recent years Overview High-resolution ocean and sea ice modeling Long-term observations Process studies Summary of main findings Role of AW inflow locally; sea ice cover, nutrients & organisms Role of local modification processes on downstream areas

3 Numerical model of ocean circulation and sea ice cover. Arctic Ocean on 4 x 4 km horizontal resolution, Svalbard area 800 x 800 m. West Spitsbergen Current splits up at NW Svalbard; recirculation, Yermak Plateau Branch, Svalbard Branch. Largest inflow to the Arctic Ocean follows upper part of continental slope. Seasonality; larger inflow in autumn and early winter, with higher temperature! Eddies transport large volumes away from the core current branches. colors: temperature at 100 m depth gray shading: sea ice cover Hattermann, T., et al., Eddy-driven recirculation of Atlantic Water in Fram strait. GRL, DOI: /2016GL068323

4 the A-TWAIN project Long-term variability and trends in the Atlantic Water inflow region Map of cruise area and mooring line location north of Svalbard in September Mooring positions (vertical lines) and temperature (color) during the 2012 A-TWAIN cruise.

5 the A-TWAIN project Long-term variability and trends in the Atlantic Water inflow region Seasonality in: Sea ice cover Current along the slope Temperature Nitrate Chlorophyll-a fluorescence Randelhoff, A., Sundfjord, A., Reigstad, M Seasonal variability and fluxes of nitrate in the surface waters over the Arctic shelf slope. GRL, DOI: /2015GL063655

6 the A-TWAIN project Long-term variability and trends in the Atlantic Water inflow region Heat loss and vertical heat flux along the slope Daily averaged temperature at 50 m depth at 20 and 31 E moorings. Difference of weekly means with a 2 week lag to account for the passage of the 145 km distance between moorings. Average vertical heat flux of ~25 Wm -2, periodically exceeding 50 Wm -2. Renner, A.H.H. et al. Oceanic influence on the sea ice cover over the Atlantic Water boundary current in the Arctic Ocean northeast of Svalbard. Manuscript in prep for JGR-Oceans, 2017

7 the A-TWAIN project Long-term variability and trends in the Atlantic Water inflow region Eddy generation and propagation Temperature: boundary current AND eddy Current: boundary current AND rotation of eddy Våge, K., et al The Atlantic Water boundary current in the Nansen Basin: Transport and mechanisms of lateral exchange, JGR-Oceans, DOI: /2016JC

8 N-ICE2015; RV Lance drifting with the sea ice Jan-Jun 2015 Meyer, A. et al. Winter to summer oceanographic observations in the Arctic Ocean north of Svalbard. Manuscript accepted for publication in JGR-Oceans.

9 Flow pattern; new observartions of Yermak Branch Meyer, A. et al. Winter to summer oceanographic observations in the Arctic Ocean north of Svalbard. Manuscript accepted for publication in JGR-Oceans.

10 Heat fluxes Storms significantly enhance vertical heat flux, both in winter and summer Increased mixing over steep topography Largest heat flux over shallow AW maximum ice melt rate of 25 cm/day! Meyer, A. et al. Mixing rates and vertical heat fluxes north of Svalbard from Arctic winter to spring. Manuscript in revision for JGR-Oceans.

11 Nitrate, stratification and mixing New, simultaneous measurements of hydrography, nitrate concentration and small-scale turbulence Randelhoff, A. et al, Vertical fluxes of nitrate in the seasonal nitracline of the Atlantic sector of the Arctic Ocean, JGR-Oceans, doi: /2016jc011779

12 Winter nitrate distribution Nitrate, stratification and mixing Typical profiles from spring and late summer, with and without sea ice Spring nitrate distribution Randelhoff, A. et al, Vertical fluxes of nitrate in the seasonal nitracline of the Atlantic sector of the Arctic Ocean, JGR-Oceans, doi: /2016jc011779

13 Atlantic Water inflow north of Svalbard; new insights from recent years Summary of key findings The Svalbard Branch is persistent all year, but with pronounced seasonality. The warm water is very near the surface even as far east as 30 E. The AW current is strong over the steep slope north of Svalbard. Vertical mixing and heat flux is large, and it appears to be an area where eddies are generated. The Yermak Branch is more seasonal and loses a lot of its heat, at least in the upper part of the water column, in the viscinity of Yermak Plateau.

14 Atlantic Water inflow north of Svalbard; new insights from recent years Summary of key local effects of the AW inflow north of Svalbard The sea ice cover has reduced significantly in recent years, with larger open water area and longer ice-free periods. This trend is primarily caused by ocean heat rather than atmospheric conditions. [e.g. Onarheim et al and ongoing A- TWAIN analysis] The inflow of AW with high nutrient content, combined with strong vertical mixing and reduced sea ice cover, implies that there is a potential for increasing local primary production. [Randelhoff et al, GRL (2015), Randelhoff et al. JGR-Oceans (2016)] Higher temperature of the inflow means that the presence of boreal species, both phytoplankton, zooplankton, and higher trophic levels, can increase.

15 Thanks to Vladimir Pavlov, NPI Randi Ingvaldsen, IMR Marit Reigstad, U. Tromsø Agnieszka Beszynska-Møller, IOPAS Bob Pickart, WHOI Angelika Renner, IMR Tore Hattermann, Akvaplan-niva Jon Albretsen, IMR Mats Granskog, NPI Achim Randelhoff, NPI/UiT Markus Janout, AWI Amelie Meyer, NPI and many more! Photo from