The Arctic Ocean - Ventilation Timescales, Anthropogenic Carbon and Variability in a Changing Environment
Hydrogeology, Hydrology, Limnology, Urban Water Management, Water Chemistry, Integrated Water Resources Management
Optics, Quantum Optics and Physics of Atoms, Molecules and Plasmas
Final Report Abstract
The Arctic Ocean (AO) is currently undergoing rapid climatic change. Our project applied a multitude of tracers to study its ventilation. As part of the SAS21 ODEN cruise, six complete depth profiles of stable noble gases and the age dating tracers 39Ar, 14C, SF6, and CFC-12 were taken in the central AO. Furthermore, samples were collected for the analysis of halogenated compounds (“Medusa tracers”) as well as the anthropogenic radionuclides 129I and 236U. CFC-12 and SF6 are ventilation tracers in the upper waters, whereas 129I and 236U provide a measure for the horizontal circulation in these layers. 39Ar and 14C are best suited to derive water ages of the deeper layers. Stable noble gases reveal gas saturation anomalies related to surface processes such as rapid cooling or ice formation. In combination, the tracers reveal unprecedented information on the dynamics of the central AO: Very young waters affected by ice formation in the Polar Mixed Layer are followed by the Atlantic Layer, where ages of at most a few decades increase horizontally along the known circulation pathways. Below about 1000 m depth, the ages increase strongly with depth, reaching comparatively constant values in the deep waters below 2000 m. The deep water in the Makarov Basin is substantially older than in the Eurasian Basin, despite evidence for a water exchange via intra-basin processes over the Lomonosov Ridge. A comparison of the new tracer results with published data enables the study of changes of the ventilation regime. The relatively large available data base for CFCs and SF6 documents a multi-decadal variation of the ventilation strength in the intermediate layer (250 – 1500 m) of the Eurasian AO over the past 30 years, with a strengthening between 1991 and 2005 followed by a weakening up to 2021. For 39Ar, which was for the first time analysed by Atom Trap Trace Analysis (ATTA) in the AO in this project, there is only a sparse set of previous results to compare with. Within the experimental uncertainties no clear trends over the past 30 years can be detected, confirmed by constant radiocarbon levels in the deep waters. The full potential of the tracer data is unlocked by modeling, where the data constrain dynamic ocean processes. E.g., noble gases were able to constrain rapid cooling in the source area of Atlantic Layer Water and other processes inducing saturation anomalies of transient gas tracers. The wide range of dating tracers enables the resolution of the full spectrum of the age or transit time distributions (TTDs). The novel Medusa tracers and the anthropogenic radioisotopes 129I and 236U clearly show the value of multiple transient tracers to constrain TTDs. Ultimately, these TTDs provide the basis for the calculation of the anthropogenic carbon uptake of the Arctic Ocean.
Publications
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Sampling and purification methods for dating by Atom Trap Trace Analysis in various environments. Goldschmidt2021 abstracts. European Association of Geochemistry.
Arck, Yannis; Wachs, David; Schmidt, Maximilian; Ringena, Lisa; Robertz, Julian; Oberthaler, Markus & Aeschbach, Werner
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Argon Trap Trace Analysis: Applications on age determination in ocean science and stratified lakes. In: DPG Spring Meeting. Erlangen, 2022. DPG, Q 18.2.
Arck, Y., Robertz, J., Schmidt, M., Wachs, D., Meienburg, F., Aeschbach, W. & Oberthaler, M.
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Circulation times and new data on I-129 and U-236 across the Arctic Ocean. In: Arctic-Subarctic Ocean Fluxes Meeting 2022.
Wefing, A.-M., Payne, A., Casacuberta, N., Christl, M. & Smith, J. N.
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Anthropogenic Carbon in the Arctic Ocean: Perspectives From Different Transient Tracers. Journal of Geophysical Research: Oceans, 129(1).
Raimondi, Lorenza; Wefing, Anne‐Marie & Casacuberta, Núria
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Investigating ventilation and saturation dynamics in the Arctic Ocean using noble gas tracer techniques. EGU 2023.
Arck, Y., Wachs, D., Robertz, J., Aeschbach, W. & Oberthaler, M.
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New ventilation and gas saturation constraints for the Arctic Ocean from dissolved gas tracer data. Goldschmidt2023 abstracts. European Association of Geochemistry.
Arck, Yannis; Gerke, Lennart; Brinkman, Jakob; Engelhardt, Edith; Friedrich, Ronny; Freundt, Florian; Robertz, Julian; Scott, Stanley; Wachs, David; Negele, Sophie; Oberthaler, Markus; Tanhua, Toste; Aeschbach, Werner & Frank, Norbert
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Temporal Variability of Ventilation in the Eurasian Arctic Ocean, ASSW 2023.
Gerke, L. & Tanhua, T.
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Temporal variability of ventilation in the Eurasian Arctic Ocean, Nansen Legacy Symposium 2023.
Gerke, L., Tanhua, T. & Arck, Y.
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Update on Argon Trap Trace Analysis – value of 39Ar measurements in various environmental systems. IAEA, Isotope Hydrology, Vienna, 2023.
Meienburg, F., Robertz, J., Wachs, D., Arck, Y., Kundy, L., Schmidt, M., Rädle, V., Mandaric, N., Oberthaler, M. & Aeschbach, W.
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Using noble gases to constrain Arctic water ages and formation conditions. DINGUE 2023.
Scott, S., Arck, Y., Engelhardt, E., Gerke, L., Freundt, F., Negele, S., Tanhua, T. & Aeschbach, W.
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Analyzing 39Ar depth profiles in the Arctic Ocean with the new ArTTA measuring technique. DPG 2024.
Kindermann, C., Arck, Y., Wachs, D., Robertz, J., Oberthaler, M. & Aeschbach, W.
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Constraining physical gas exchange processes and transient tracer saturations in the Arctic Ocean using noble gases. OSM 2024.
Scott, S., Arck, Y., Engelhardt, E., Gerke, L., Freundt, F., Hubner, C., Negele, S., Tanhua, T. & Aeschbach, W.
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Estimating ventilation timescales by transit time distribution models using dating tracers 39Ar, 14C and CFC-12/SF6 in the Arctic Ocean. OSM 2024.
Arck, Y., Gerke, L., Brinkmann, J., Kindermann, C., Negele, S., Robertz, J., Scott, S., Wachs, D., Frank, N., Oberthaler, M., Tanhua, T. & Aeschbach, W.
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Temporal Variability of Ventilation in the Eurasian Arctic Ocean. Journal of Geophysical Research: Oceans, 129(7).
Gerke, Lennart; Arck, Yannis & Tanhua, Toste
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Temporal variability of ventilation in the Eurasian Arctic Ocean. OSM 2024.
Gerke, L., Tanhua, T., Arck, Y. & Aeschbach, W.
