Mixing and advection of a cold water cascade over the Wyville Thomson Ridge |
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| Institution: | 1. Scottish Association for Marine Science, Dunstaffnage Marine Laboratory, Oban, Argyll PA37 1QA, UK;2. Fisheries Research Services Aberdeen Laboratory, P.O. Box 101, Victoria Road, Aberdeen AB11 9DB, UK;1. BEV - Federal Office of Metrology and Surveying, Austria;2. BOKU - University of Natural Resources and Life Sciences, Vienna, Austria;3. ENEA - Agenzia Nazionale per le nuove tecnologie l’energia e lo sviluppo economico sostenibile, Italy;4. CEA/LNHB - Commissariat à l’énergie atomique et aux énergies alternatives, France;5. CIEMAT, Spain;6. National Physical Laboratory, United Kingdom;7. SURO - Statni ustav radiacni ochrany v.v.i., Czechia;8. JRC-Geel, European Commission, Belgium;9. Czech Metrological Institute, Czechia;10. NRPA - Norwegian Radiation Protection Authority, Norway;11. GIG - Glowny Instytut Gornictwa, Poland;12. IRSN - Institut de Radioprotection et de Sûreté Nucléaire, France;13. STUK – Sateilyturvakeskus, Finland;14. IST - Instituto Superior Tecnico, Portugal;15. MKEH - Magyar Kereskedelmi Engedelyezesi Hivatal, Hungary;p. IJS - Institut Jozef Stefan, Slovenia;1. Department of Nuclear Chemistry, Czech Technical University in Prague, 115 19 Prague 1, Czech Republic;2. Laboratory of Ion Beam Physics, ETH Zürich, 8093 Zürich, Switzerland;3. Nuclear Physics Insitute, Czech Academy of Sciences (NPI CAS), Husinec - ?e? 250 68, Czech Republic;1. Department of Nuclear Chemistry, Czech Technical University in Prague, 115 19 Praha 1, Czech Republic;2. VERA Laboratory, Institute of Isotopic Research and Nuclear Physics, University of Vienna, Währinger Straße 17, A1090 Vienna, Austria;1. Leibniz-Institut für Analytische Wissenschaften–ISAS–e.V., Dortmund, Germany;2. Department of Cardiology and Cardiovascular Medicine, Tübingen, Germany;3. Department of Physiology, University of Tübingen, Tübingen, Germany;4. Medizinische Fakultät, Ruhr-Universität Bochum, Bochum, Germany;5. College of Physical Sciences, University of Aberdeen, Old Aberdeen, United Kingdom;1. Institut für Radioökologie und Strahlenschutz, Leibniz Universität Hannover, Germany;2. Bundesamt für Seeschifffahrt und Hydrographie (BSH), 20305, Hamburg, Germany;3. Laboratory of Ion Beam Physics, ETH Zürich, 2093, Zürich, Switzerland |
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| Abstract: | The Wyville Thomson Ridge forms part of the barrier to the meridional circulation across which cold Nordic Sea and Arctic water must traverse to reach the Atlantic Ocean. Overflow rates across the ridge are variable (but can be dramatic at times), and may provide a subtle indicator of significant change in the circulation in response to climate change. In spring 2003, a series of CTD sections were conducted during a large overflow event in which Norwegian Sea Deep Water (NSDW) cascaded down the southern side of the ridge into the Rockall Trough at a rate of between 1 and 2 Sv. The NSDW was partially mixed with overlying North Atlantic Water (NAW), and comprised about 1/3rd of the cascading water. The components of NAW and NSDW in the overflow were sufficiently large that there must have been a significant divergence of the inflow through the Faroe-Shetland Channel, and of the outflow through the Faroe Bank Channel.As the plume descended, its temperature near the sea bed warmed by over 3 °C in about a day. Although the slope was quite steep (0.03), the mean speed of the current (typically 0.36 m s?1) was too slow for significant entrainment of NAW to occur (the bulk Richardson number was of order 5). However, very large overturns (up to 50 m) were evident in some CTD profiles, and it is demonstrated from Thorpe scale estimates that the warming of the bottom waters was due to mixing within the plume. It is likely that some of the NSDW had mixed with NAW before it crossed the ridge. The overflow was trapped in a gully, which caused it to descend to great depth (1700 m) at a faster rate, and with less modification due to entrainment, than other overflows in the North Atlantic. The water that flowed into the northern part of the Rockall Trough had a temperature profile that ranged from about 3 to 8 °C. Water with a temperature of >6 °C probably escaped into the Iceland Basin, between the banks that line the north-western part of the Trough. Colder water (< 6 °C) must have travelled down the eastern side of the Rockall Bank, and may have had a volume flux of up to 1.5 Sv. |
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