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- Title
Long-lived radionuclides (129I and 236U) as water mass tracers in the North Atlantic and Fram Strait.
- Authors
Wefing, Anne-Marie; Castrillejo, Maxi; Casacuberta, Núria; Christl, Marcus; Vockenhuber, Christof; van der Loeff, Michiel Rutgers; Lherminier, Pascale
- Abstract
Water mass transport and transformation processes in the North Atlantic Ocean play a crucialrole in the Atlantic meridional overturning circulation (AMOC). In this context, circulationprocesses leading to the transport of substances or properties such as heat or greenhousegases from the sea surface to the ocean interior (e.g. by dense-water formation) are of specialinterest. These processes are known to be closely linked to water mass transport in theNordic Seas and to the water exchange between the North Atlantic and the ArcticOcean through Fram Strait. In order to understand the natural variability of the watercirculation and how it will respond to anthropogenic climate forcing, chemical tracers aresuitable tools to complement hydrographic measurements and models. Amongst them,the long-lived artificial radionuclides 129I (T1∕2 ≈ 15.7 Myr) and 236U (T1∕2 ≈23.4 Myr) have been introduced into the marine environment as part of the globalatmospheric deposition of nuclear weapon test fallout (mainly 236U) and as a timelyvarying, point-like release from two nuclear fuel reprocessing plants in westernEurope (mainly 129I). Due to the quite recent introduction of these tracers (sincethe 1950s), the upper water column in the North Atlantic and the Arctic Oceancontains relatively high amounts of 129I and 236U that evolve in time due to thevarying historical releases from reprocessing plants. Thus, the combination of bothradionuclides provides a tool to investigate water mass transport pathways and to estimatetime scales of circulation. Here we combine 129I and 236U results from the FramStrait (2016 and preliminary results from 2018) and the OVIDE section (2014 and2018) to study the water circulation between the Arctic Ocean, the Nordic Seasand the subpolar North Atlantic. We find high concentrations of 129I and 236U aswell as high 129I/236U ratios in the surface waters outflowing the Arctic Ocean(concentrations about twice as high as in the inflowing Atlantic waters in the WestSpitzbergen Current) which are being transported southwards along the coast ofGreenland by the East Greenland Current (EGC). These high concentrations arefurther observed in the deep overflow waters in the Labrador and Irminger Seasdue the influence of waters entering through the Greenland-Iceland passage. Thepresence of 129I has notably increased in time in both the Fram Strait and most ofthe OVIDE section, showing the potential of this tracer for future oceanographicstudies. Finally, the combination of these results with earlier observations allows tounderstand transport pathways and transit times of Atlantic Waters into the NorthAtlantic Ocean. We find both a short loop through the Nordic Seas (8-10 yrs transittime) and a longer loop through the Arctic Eurasian Basin (16-18 yrs transit time).
- Subjects
GREENLAND; ICELAND; WATER masses; REACTOR fuel reprocessing; NUCLEAR weapons testing; MERIDIONAL overturning circulation; STRAITS; RADIOISOTOPES; NUCLEAR medicine
- Publication
Geophysical Research Abstracts, 2019, Vol 21, p1
- ISSN
1029-7006
- Publication type
Article