Circulation timescales of Atlantic Waters in the Arctic Ocean determined from anthropogenic radionuclides

Abstract. The inflow of Atlantic Waters to the Arctic Ocean is a crucial determinant for the future trajectory of this ocean basin with regard to warming, loss of sea-ice and ocean acidification. Yet many details of the fate and circulation of these waters within the Arctic remain unclear. Here, we use the two long-lived artificial radionuclides 129I and 236U together with two tracer age models to constrain the pathways and circulation times of Atlantic waters in the surface and in the mid-depth Atlantic layer (250–800 m depth). We thereby benefit from the unique time-dependent tagging of Atlantic waters by these two isotopes. In the surface layer, a binary mixing model yields tracer ages of Atlantic Waters between 9–16 years in the Amundsen Basin, 12–17 years in the Fram Strait (East Greenland Current) and up to 20 years in the Canada Basin, reflecting the pathways of Atlantic Waters through the Arctic and their exiting through Fram Strait. In the mid-depth Atlantic layer (250 to 800 m), the transit time distribution (TTD) model yields mean ages in the central Arctic ranging between 15 and 65 years, while the mode ages representing the most probable ages of the TTD range between 2 and 30 years. The estimated mean ages are overall in good agreement with previous studies using artificial radionuclides or ventilation tracers. Although we find the overall flow to be dominated by advection, the shift of the mode age towards a younger age compared to the mean age reflects also the presence of a substantial amount of lateral mixing. For applications interested in how fast signals are transported into the Arctic's interior, the mode age appears to be a suitable measure. The short mode ages obtained in this study suggest that changes in the properties of Atlantic Waters will quickly spread through the Arctic Ocean and can lead to relatively rapid changes throughout the upper water column in future years.

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Circulation timescales of Atlantic Water in the Arctic Ocean determined from anthropogenic radionuclides

Ocean Science ◽

10.5194/os-17-111-2021 ◽

2021 ◽

Vol 17 (1) ◽

pp. 111-129

Author(s):

Anne-Marie Wefing ◽

Núria Casacuberta ◽

Marcus Christl ◽

Nicolas Gruber ◽

John N. Smith

Keyword(s):

Arctic Ocean ◽

Atlantic Water ◽

Ocean Basin ◽

The Arctic ◽

Fram Strait ◽

Anthropogenic Radionuclides ◽

East Greenland Current ◽

The Arctic Ocean ◽

Lateral Mixing ◽

Binary Mixing

Abstract. The inflow of Atlantic Water to the Arctic Ocean is a crucial determinant for the future trajectory of this ocean basin with regard to warming, loss of sea ice, and ocean acidification. Yet many details of the fate and circulation of these waters within the Arctic remain unclear. Here, we use the two long-lived anthropogenic radionuclides 129I and 236U together with two age models to constrain the pathways and circulation times of Atlantic Water in the surface (10–35 m depth) and in the mid-depth Atlantic layer (250–800 m depth). We thereby benefit from the unique time-dependent tagging of Atlantic Water by these two isotopes. In the surface layer, a binary mixing model yields tracer ages of Atlantic Water between 9–16 years in the Amundsen Basin, 12–17 years in the Fram Strait (East Greenland Current), and up to 20 years in the Canada Basin, reflecting the pathways of Atlantic Water through the Arctic and their exiting through the Fram Strait. In the mid-depth Atlantic layer (250–800 m), the transit time distribution (TTD) model yields mean ages in the central Arctic ranging between 15 and 55 years, while the mode ages representing the most probable ages of the TTD range between 3 and 30 years. The estimated mean ages are overall in good agreement with previous studies using artificial radionuclides or ventilation tracers. Although we find the overall flow to be dominated by advection, the shift in the mode age towards a younger age compared to the mean age also reflects the presence of a substantial amount of lateral mixing. For applications interested in how fast signals are transported into the Arctic's interior, the mode age appears to be a suitable measure. The short mode ages obtained in this study suggest that changes in the properties of Atlantic Water will quickly spread through the Arctic Ocean and can lead to relatively rapid changes throughout the upper water column in future years.

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Annual variability of the long-lived anthropogenic radionuclides 129I and 236U in the Fram Strait and their use as water mass composition tracers

10.5194/egusphere-egu21-8662 ◽

2021 ◽

Author(s):

Anne-Marie Wefing ◽

Núria Casacuberta ◽

Marcus Christl ◽

Michael Karcher ◽

Paul A. Dodd

Keyword(s):

Arctic Ocean ◽

Water Mass ◽

Atlantic Water ◽

The Arctic ◽

Mass Composition ◽

Fram Strait ◽

Anthropogenic Radionuclides ◽

Mixing Processes ◽

East Greenland Current ◽

The Arctic Ocean

Anthropogenic chemical tracers are powerful tools to study pathways, water mass provenance and mixing processes in the ocean. Releases of the long-lived anthropogenic radionuclides 129I and 236U from European nuclear reprocessing plants label Atlantic Water entering the Arctic Ocean with a distinct signal that can be used to track pathways and timescales of Atlantic Water circulation in the Arctic Ocean and Fram Strait. Apart from their application as transient tracers, the difference in anthropogenic radionuclide concentrations between Atlantic- and Pacific-origin water provides an instrument to distinguish the interface between both water masses. In contrast to classically used water mass tracers such as nitrate-phosphate (N:P) ratios, the two radionuclides are considered to behave conservatively in seawater and are not affected by biogeochemical processes occurring in particular in the broad shelf regions of the Arctic Ocean.Here we present a time-series of 129I and 236U data across the Fram Strait, collected in 2016 (as part of the GEOTRACES program) and in 2018 and 2019 (by the Norwegian Polar Institute). While the overall spatial distribution of both radionuclides was similar among the three sampling years, significant differences were observed in the upper water column of the EGC, especially between 2016 and 2018. This study is the first attempt to investigate the potential of 129I and 236U as water mass composition tracers in the East Greenland Current (EGC). We discuss how the 129I - 236U tracer pair can be applied to estimate fractions of Atlantic and Pacific Water, especially considering their time-dependent input into the Arctic Ocean.

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Does the East Greenland Current exist in the northern Fram Strait?

Ocean Science ◽

10.5194/os-14-1147-2018 ◽

2018 ◽

Vol 14 (5) ◽

pp. 1147-1165 ◽

Cited By ~ 6

Author(s):

Maren Elisabeth Richter ◽

Wilken-Jon von Appen ◽

Claudia Wekerle

Keyword(s):

Arctic Ocean ◽

Atlantic Water ◽

Shelf Break ◽

The Arctic ◽

Current Loop ◽

Fram Strait ◽

Boundary Current ◽

East Greenland ◽

East Greenland Current ◽

The Arctic Ocean

Abstract. Warm Atlantic Water (AW) flows around the Nordic Seas in a cyclonic boundary current loop. Some AW enters the Arctic Ocean where it is transformed to Arctic Atlantic Water (AAW) before exiting through the Fram Strait. There the AAW is joined by recirculating AW. Here we present the first summer synoptic study targeted at resolving this confluence in the Fram Strait which forms the East Greenland Current (EGC). Absolute geostrophic velocities and hydrography from observations in 2016, including four sections crossing the east Greenland shelf break, are compared to output from an eddy-resolving configuration of the sea ice–ocean model FESOM. Far offshore (120 km at 80.8∘ N) AW warmer than 2 ∘C is found in the northern Fram Strait. The Arctic Ocean outflow there is broad and barotropic, but gets narrower and more baroclinic toward the south as recirculating AW increases the cross-shelf-break density gradient. This barotropic to baroclinic transition appears to form the well-known EGC boundary current flowing along the shelf break farther south where it has been previously described. In this realization, between 80.2 and 76.5∘ N, the southward transport along the east Greenland shelf break increases from roughly 1 Sv to about 4 Sv and the proportion of AW to AAW also increases fourfold from 19±8 % to 80±3 %. Consequently, in the southern Fram Strait, AW can propagate into the Norske Trough on the east Greenland shelf and reach the large marine-terminating glaciers there. High instantaneous variability observed in both the synoptic data and the model output is attributed to eddies, the representation of which is crucial as they mediate the westward transport of AW in the recirculation and thus structure the confluence forming the EGC.

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Does the East Greenland Current exist in northern Fram Strait?

10.5194/os-2018-54 ◽

2018 ◽

Author(s):

Maren Elisabeth Richter ◽

Wilken-Jon von Appen ◽

Claudia Wekerle

Keyword(s):

Arctic Ocean ◽

Atlantic Water ◽

Ocean Model ◽

The Arctic ◽

Current Loop ◽

Fram Strait ◽

Boundary Current ◽

East Greenland ◽

East Greenland Current ◽

The Arctic Ocean

Abstract. Warm Atlantic Water (AW) flows around the Nordic Seas in a cyclonic boundary current loop. Some AW enters the Arctic Ocean where it is transformed to Arctic Atlantic Water (AAW) before exiting through Fram Strait. There the AAW is joined by recirculating AW. Here we present the first summer synoptic study targeted at resolving this confluence in Fram Strait which forms the East Greenland Current (EGC). Absolute geostrophic velocities and hydrography from observations in 2016, including four sections crossing the east Greenland shelfbreak, are compared to output from an eddy-resolving configuration of the sea–ice ocean model FESOM. Far offshore (120 km at 80.8° N) AW warmer than 2 °C is found in northern Fram Strait. The Arctic Ocean outflow there is broad and barotropic, but gets narrower and more baroclinic toward the south as recirculating AW increases the cross-shelfbreak density gradient. This barotropic to baroclinic transition appears to form the well-known EGC boundary current flowing along the shelfbreak further south where it has been previously described. In this realization, between 80.2° N and 76.5° N, the southward transport along the east Greenland shelfbreak increases from roughly 1 Sv to about 4 Sv and the warm water composition, defined as the fraction of AW of the sum of AW and AAW (AW/(AW + AAW)), changes from 19 ± 8 % to 80 ± 3 %. Consequently, in southern Fram Strait, AW can propagate into Norske Trough on the east Greenland shelf and reach the large marine terminating glaciers there. High instantaneous variability observed in both the synoptic data and the model output is attributed to eddies, the representation of which is crucial as they mediate the westward transport of AW in the recirculation and thus structure the confluence forming the EGC.

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The long-lived anthropogenic radionuclides I-129 and U-236 as tracers of water mass provenance, circulation timescales and mixing in the Arctic Ocean and Fram Strait

10.5194/egusphere-egu2020-8697 ◽

2020 ◽

Author(s):

Anne-Marie Wefing ◽

Núria Casacuberta ◽

Marcus Christl ◽

John N. Smith ◽

Paul A. Dodd ◽

...

Keyword(s):

Arctic Ocean ◽

Ocean Circulation ◽

Water Mass ◽

Atlantic Water ◽

The Arctic ◽

Fram Strait ◽

Anthropogenic Radionuclides ◽

Chemical Tracers ◽

Pacific Waters ◽

The Arctic Ocean

Anthropogenic chemical tracers are powerful tools to study ocean circulation timescales, water mass provenance and mixing regimes. In the Arctic Ocean, the releases of artificial radionuclides from European nuclear reprocessing plants (RPs) act as valuable transient tracers as they label the inflowing Atlantic Waters with a distinct anthropogenic signal. In recent years, the combination of the two long-lived radionuclides 129I and 236U has emerged as a new tracer pair and several studies have shown their potential to track pathways and timescales of Atlantic Water circulation in the Arctic Ocean and Fram Strait.The circulation times of Atlantic-origin waters in the Arctic Ocean that were inferred using this tracer pair (in combination with the naturally occurring 238U) agree to those obtained by means of other transient tracers. Moreover, the combination of 129I and 236U promises to be a useful marker of water mass mixing regimes both in the surface waters and the subsurface Atlantic layer. In particular, the interface between Atlantic and Pacific Waters in the polar surface layer of the Arctic Ocean can be easily identified as these two water masses are labelled by very different 129I/236U and 236U/238U atom ratios.Here we present a compilation of 129I and 236U in a quasi-synoptic pan-arctic section including the Fram Strait and we show how this data can be used to gain information about circulation patterns. We discuss timescales and transport characteristics of Atlantic Water flow, the position and variability of the front between Atlantic and Pacific Waters and the temporal variability of Pacific Waters in the Fram Strait.

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The interaction between waters from the Arctic Ocean and the Nordic Seas north of Fram Strait and along the East Greenland Current: results from the Arctic Ocean-02 Oden expedition

Journal of Marine Systems ◽

10.1016/j.jmarsys.2004.06.008 ◽

2005 ◽

Vol 55 (1-2) ◽

pp. 1-30 ◽

Cited By ~ 173

Author(s):

Bert Rudels ◽

Göran Björk ◽

Johan Nilsson ◽

Peter Winsor ◽

Iréne Lake ◽

...

Keyword(s):

Arctic Ocean ◽

The Arctic ◽

Fram Strait ◽

Nordic Seas ◽

East Greenland ◽

East Greenland Current ◽

The Arctic Ocean

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Seasonal patterns in Arctic planktonic metabolism (Fram Strait – Svalbard region)

Biogeosciences ◽

10.5194/bg-10-1451-2013 ◽

2013 ◽

Vol 10 (3) ◽

pp. 1451-1469 ◽

Cited By ~ 24

Author(s):

R. Vaquer-Sunyer ◽

C. M. Duarte ◽

J. Holding ◽

A. Regaudie-de-Gioux ◽

L. S. García-Corral ◽

...

Keyword(s):

Arctic Ocean ◽

Early Spring ◽

The Arctic ◽

Fram Strait ◽

Metabolic Rates ◽

Net Community Production ◽

Western Sector ◽

The Arctic Ocean ◽

European Arctic ◽

Community Production

Abstract. The metabolism of the Arctic Ocean is marked by extremely pronounced seasonality and spatial heterogeneity associated with light conditions, ice cover, water masses and nutrient availability. Here we report the marine planktonic metabolic rates (net community production, gross primary production and community respiration) along three different seasons of the year, for a total of eight cruises along the western sector of the European Arctic (Fram Strait – Svalbard region) in the Arctic Ocean margin: one at the end of 2006 (fall/winter), two in 2007 (early spring and summer), two in 2008 (early spring and summer), one in 2009 (late spring–early summer), one in 2010 (spring) and one in 2011 (spring). The results show that the metabolism of the western sector of the European Arctic varies throughout the year, depending mostly on the stage of bloom and water temperature. Here we report metabolic rates for the different periods, including the spring bloom, summer and the dark period, increasing considerably the empirical basis of metabolic rates in the Arctic Ocean, and especially in the European Arctic corridor. Additionally, a rough annual metabolic estimate for this area of the Arctic Ocean was calculated, resulting in a net community production of 108 g C m−2 yr−1.

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Danian Mollusks from the Prince Creek Formation, Northern Alaska, and Implications for Arctic Ocean Paleogeography

Journal of Paleontology ◽

10.1017/s0022336000062259 ◽

1993 ◽

Vol 67 (S35) ◽

pp. 1-35 ◽

Cited By ~ 8

Author(s):

Louie Marincovich

Keyword(s):

Arctic Ocean ◽

World Ocean ◽

Ocean Basin ◽

The Arctic ◽

The North ◽

The World ◽

The Arctic Ocean ◽

Molluscan Fauna ◽

Endemic Genera ◽

Northern Alaska

The marine molluscan fauna of the Prince Creek Formation near Ocean Point, northern Alaska, is of Danian age. It is the only diverse and abundant Danian molluscan fauna known from the Arctic Ocean realm, and is the first evidence for an indigenous Paleocene shallow-water biota within a discrete Arctic Ocean Basin faunal province.A high percentage of endemic species, and two endemic genera, emphasize the degree to which the Arctic Ocean was geographically isolated from the world ocean during the earliest Tertiary. Many of the well-preserved Ocean Point mollusks, however, also occur in Danian faunas of the North American Western Interior, the Canadian Arctic Islands, Svalbard, and northwestern Europe, and are the basis for relating this Arctic Ocean fauna to that of the Danian world ocean.The Arctic Ocean was a Danian refugium for some genera that became extinct elsewhere during the Jurassic and Cretaceous. At the same time, this nearly landlocked ocean fostered the evolution of new taxa that later in the Paleogene migrated into the world ocean by way of the northeastern Atlantic. The first Cenozoic occurrences are reported for the bivalves Integricardium (Integricardium), Oxytoma (Hypoxytoma), Placunopsis, Tancredia (Tancredia), and Tellinimera, and the oldest Cenozoic records given for the bivalves Gari (Garum), Neilo, and Yoldia (Cnesterium). Among the 25 species in the molluscan fauna are four new gastropod species, Amauropsis fetteri, Ellipsoscapha sohli, Mathilda (Fimbriatella) amundseni, and Polinices (Euspira) repenningi, two new bivalve genera, Arcticlam and Mytilon, and 15 new bivalve species, Arcticlam nanseni, Corbula (Caryocorbula) betsyae, Crenella kannoi, Cyrtodaria katieae, Gari (Garum) brouwersae, Integricardium (Integricardium) keenae, Mytilon theresae, Neilo gryci, Nucula (Nucula) micheleae, Nuculana (Jupiteria) moriyai, Oxytoma (Hypoxytoma) hargrovei, Placunopsis rothi, Tancredia (Tancredia) slavichi, Tellinimera kauffmani, and Yoldia (Cnesterium) gladenkovi.

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