Articles | Volume 19, issue 4
https://doi.org/10.5194/os-19-1225-2023
© Author(s) 2023. This work is distributed under
the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/os-19-1225-2023
© Author(s) 2023. This work is distributed under
the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Research article
| 
16 Aug 2023
Research article |
| 16 Aug 2023
| 16 Aug 2023
The Iceland–Faroe warm-water flow towards the Arctic estimated from satellite altimetry and in situ observations
Bogi Hansen
CORRESPONDING AUTHOR
Environmental Department, Faroe Marine Research Institute, Tórshavn, Faroe Islands
Karin M. H. Larsen
Environmental Department, Faroe Marine Research Institute, Tórshavn, Faroe Islands
Hjálmar Hátún
Environmental Department, Faroe Marine Research Institute, Tórshavn, Faroe Islands
Steffen M. Olsen
Danish Meteorological Institute, Copenhagen, Denmark
Andrea M. U. Gierisch
Danish Meteorological Institute, Copenhagen, Denmark
Svein Østerhus
NORCE Norwegian Research Centre, Bjerknes Centre for Climate
Research, Bergen, Norway
Sólveig R. Ólafsdóttir
Environmental Division, Marine and Freshwater Research Institute, Hafnarfjörður,
Iceland
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Compared to other freshwater sources, runoff from Iceland is small and usually flows into the Nordic Seas. Under certain wind conditions, it can, however, flow into the Iceland Basin and this occurred after 2014, when this region had already freshened from other causes. This explains why the surface freshening in this area became so extreme. The local and shallow character of this runoff allows it to have a disproportionate effect on vertical mixing, winter convection, and biological production.
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Two decades of observations of the Arctic Mediterranean (AM) exchanges show that the exchanges have been stable in terms of volume transport during a period when many other components of the global climate system have changed. The total AM import is found to be 9.1 Sv and has a seasonal variation in amplitude close to 1 Sv, and maximum import in October. Roughly one-third of the imported water leaves the AM as surface outflow.
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Preprint withdrawn
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Compared to other freshwater sources, runoff from Iceland is small and usually flows into the Nordic Seas. Under certain wind conditions, it can, however, flow into the Iceland Basin and this occurred after 2014, when this region had already freshened from other causes. This explains why the surface freshening in this area became so extreme. The local and shallow character of this runoff allows it to have a disproportionate effect on vertical mixing, winter convection, and biological production.
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Short summary
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The Faroe Bank Channel is one of the main passages for the flow of cold dense water from the Arctic into the depths of the world ocean where it feeds the deep branch of the AMOC. Based on in situ measurements, we show that the volume transport of this flow has been stable from 1995 to 2015. The water has warmed, but salinity increase has maintained its high density. Thus, this branch of the AMOC did not weaken during the last 2 decades, but increased its heat transport into the deep ocean.
Adrienne J. Sutton, Christopher L. Sabine, Richard A. Feely, Wei-Jun Cai, Meghan F. Cronin, Michael J. McPhaden, Julio M. Morell, Jan A. Newton, Jae-Hoon Noh, Sólveig R. Ólafsdóttir, Joseph E. Salisbury, Uwe Send, Douglas C. Vandemark, and Robert A. Weller
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Ocean carbonate observations from surface buoys reveal that marine life is currently exposed to conditions outside preindustrial bounds at 12 study locations around the world. Seasonal conditions in the California Current Ecosystem and Gulf of Maine also exceed thresholds that may impact shellfish larvae. High-resolution observations place long-term change in the context of large natural variability: a necessary step to understand ocean acidification impacts under real-world conditions.
S. M. Olsen, B. Hansen, S. Østerhus, D. Quadfasel, and H. Valdimarsson
Ocean Sci., 12, 545–560, https://doi.org/10.5194/os-12-545-2016, https://doi.org/10.5194/os-12-545-2016, 2016
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About half of the warm Atlantic water that enters the Norwegian Sea flows between Iceland and the Faroes. Here it crosses the Iceland-Faroe Ridge and dynamically interacts with the cold, dense and deep return flow across the ridge. This flow is not resolved in climate models and the lack of interaction prevents realistic heat anomaly propagation towards the Arctic.
E. Darelius, I. Fer, T. Rasmussen, C. Guo, and K. M. H. Larsen
Ocean Sci., 11, 855–871, https://doi.org/10.5194/os-11-855-2015, https://doi.org/10.5194/os-11-855-2015, 2015
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Quasi-regular eddies are known to be generated in the outflow of dense water through the Faroe Bank Channel. One year long mooring records from the plume region show that (1) the energy associated with the eddies varies by a factor of 10 throughout the year and (2) the frequency of the eddies shifts between 3 and 6 days and is related to the strength of the outflow. Similar variability is shown by a high-resolution regional model and the observations agree with theory on baroclinic instability.
B. Hansen, K. M. H. Larsen, H. Hátún, R. Kristiansen, E. Mortensen, and S. Østerhus
Ocean Sci., 11, 743–757, https://doi.org/10.5194/os-11-743-2015, https://doi.org/10.5194/os-11-743-2015, 2015
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The Faroe Current is the main ocean current transporting warm Atlantic water into the Arctic region and an important transporter of heat towards the Arctic. This study documents observed transport variations over two decades, from 1993 to 2013. It shows that the volume transport of Atlantic water in this current increased by 9% over the period, whereas the heat transport increased by 18%. This increase will have contributed to the observed warming and sea ice decline in the Arctic.
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E. Jeansson, R. G. J. Bellerby, I. Skjelvan, H. Frigstad, S. R. Ólafsdóttir, and J. Olafsson
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Long-term mean monthly fluxes of carbon and nutrients to the surface layer of the Iceland Sea are presented. From these fluxes we estimate primary production based on newly added nitrate (i.e. new production) and net community production (NCP). The annual new production in the Iceland Sea is estimated to 0.45±0.09mol N/m2/yr, and the net annual NCP to 7.3±1.0mol C/m2/yr. The typical C:N ratio during biological uptake is 9.0, challenging the Redfield C:N as the conversion factor in the area.
V. Racapé, N. Metzl, C. Pierre, G. Reverdin, P. D. Quay, and S. R. Olafsdottir
Biogeosciences, 11, 1683–1692, https://doi.org/10.5194/bg-11-1683-2014, https://doi.org/10.5194/bg-11-1683-2014, 2014
B. Berx, B. Hansen, S. Østerhus, K. M. Larsen, T. Sherwin, and K. Jochumsen
Ocean Sci., 9, 639–654, https://doi.org/10.5194/os-9-639-2013, https://doi.org/10.5194/os-9-639-2013, 2013
M. Eby, A. J. Weaver, K. Alexander, K. Zickfeld, A. Abe-Ouchi, A. A. Cimatoribus, E. Crespin, S. S. Drijfhout, N. R. Edwards, A. V. Eliseev, G. Feulner, T. Fichefet, C. E. Forest, H. Goosse, P. B. Holden, F. Joos, M. Kawamiya, D. Kicklighter, H. Kienert, K. Matsumoto, I. I. Mokhov, E. Monier, S. M. Olsen, J. O. P. Pedersen, M. Perrette, G. Philippon-Berthier, A. Ridgwell, A. Schlosser, T. Schneider von Deimling, G. Shaffer, R. S. Smith, R. Spahni, A. P. Sokolov, M. Steinacher, K. Tachiiri, K. Tokos, M. Yoshimori, N. Zeng, and F. Zhao
Clim. Past, 9, 1111–1140, https://doi.org/10.5194/cp-9-1111-2013, https://doi.org/10.5194/cp-9-1111-2013, 2013
Related subject area
Approach: In situ Observations | Properties and processes: Overturning circulation, gyres and water masses
Continued warming of deep waters in the Fram Strait
Observed change and the extent of coherence in the Gulf Stream system
Anomalous North Pacific subtropical mode water volume and density decrease in a recent stable Kuroshio Extension period from Argo observations
New insights into the eastern subpolar North Atlantic meridional overturning circulation from OVIDE
The Southern Ocean deep mixing band emerges from a competition between winter buoyancy loss and upper stratification strength
Comparing observed and modelled components of the Atlantic Meridional Overturning Circulation at 26° N
Water properties and bottom water patterns in hadal trench environments
Long-term eddy modulation affects the meridional asymmetry of the halocline in the Beaufort Gyre
Technical note: Determining Arctic Ocean halocline and cold halostad depths based on vertical stability
Salar Karam, Céline Heuzé, Mario Hoppmann, and Laura de Steur
Ocean Sci., 20, 917–930, https://doi.org/10.5194/os-20-917-2024, https://doi.org/10.5194/os-20-917-2024, 2024
Short summary
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A long-term mooring array in the Fram Strait allows for an evaluation of decadal trends in temperature in this major oceanic gateway into the Arctic. Since the 1980s, the deep waters of the Greenland Sea and the Eurasian Basin of the Arctic have warmed rapidly at a rate of 0.11°C and 0.05°C per decade, respectively, at a depth of 2500 m. We show that the temperatures of the two basins converged around 2017 and that the deep waters of the Greenland Sea are now a heat source for the Arctic Ocean.
Helene Asbjørnsen, Tor Eldevik, Johanne Skrefsrud, Helen L. Johnson, and Alejandra Sanchez-Franks
Ocean Sci., 20, 799–816, https://doi.org/10.5194/os-20-799-2024, https://doi.org/10.5194/os-20-799-2024, 2024
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The Gulf Stream system is essential for northward ocean heat transport. Here, we use observations along the path of the extended Gulf Stream system and an observationally constrained ocean model to investigate variability in the Gulf Stream system since the 1990s. We find regional differences in the variability between the subtropical, subpolar, and Nordic Seas regions, which warrants caution in using observational records at a single latitude to infer large-scale circulation change.
Jing Sheng, Cong Liu, Yanzhen Gu, Peiliang Li, Fangguo Zhai, and Ning Zhou
Ocean Sci., 20, 817–834, https://doi.org/10.5194/os-20-817-2024, https://doi.org/10.5194/os-20-817-2024, 2024
Short summary
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The homogeneous water column, named mode water, retains atmosphere conditions and biogeochemical elements from the deep winter mixed layer and became weaker and warmer in the North Pacific subtropical ocean in 2018–2021 even though the Kuroshio Extension was stable. Locally anomalous east wind transporting warm water to the north and enhanced near-surface stratification hinder the deepening of the winter mixed layer. This study has broad implications for climate change and biogeochemical cycles.
Herlé Mercier, Damien Desbruyères, Pascale Lherminier, Antón Velo, Lidia Carracedo, Marcos Fontela, and Fiz F. Pérez
Ocean Sci., 20, 779–797, https://doi.org/10.5194/os-20-779-2024, https://doi.org/10.5194/os-20-779-2024, 2024
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We study the Atlantic Meridional Overturning Circulation (AMOC) measured between Greenland and Portugal between 1993–2021. We identify changes in AMOC limb volume and velocity as two major drivers of AMOC variability at subpolar latitudes. Volume variations dominate on the seasonal timescale, while velocity variations are more important on the decadal timescale. This decomposition proves useful for understanding the origin of the differences between AMOC time series from different analyses.
Romain Caneill, Fabien Roquet, and Jonas Nycander
Ocean Sci., 20, 601–619, https://doi.org/10.5194/os-20-601-2024, https://doi.org/10.5194/os-20-601-2024, 2024
Short summary
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In winter, heat loss increases density at the surface of the Southern Ocean. This increase in density creates a mixed layer deeper than 250 m only in a narrow deep mixing band (DMB) located around 50° S. North of the DMB, the stratification is too strong to be eroded, so mixed layers are shallower. The density of cold water is almost not impacted by temperature changes. Thus, heat loss does not significantly increase the density south of the DMB, so no deep mixed layers are produced.
Harry Bryden, Jordi Beunk, Sybren Drijfhout, Wilco Hazeleger, and Jennifer Mecking
Ocean Sci., 20, 589–599, https://doi.org/10.5194/os-20-589-2024, https://doi.org/10.5194/os-20-589-2024, 2024
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There is widespread interest in whether the Gulf Stream will decline under global warming. We analyse 19 coupled climate model projections of the AMOC over the 21st century. The model consensus is that the AMOC will decline by about 40 % due to reductions in northward Gulf Stream transport and southward deep western boundary current transport. Whilst the wind-driven Gulf Stream decreases by 4 Sv, most of the decrease in the Gulf Stream is due to a reduction of 7 Sv in its thermohaline component.
Jessica Kolbusz, Jan Zika, Charitha Pattiaratchi, and Alan Jamieson
Ocean Sci., 20, 123–140, https://doi.org/10.5194/os-20-123-2024, https://doi.org/10.5194/os-20-123-2024, 2024
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We collected observations of the ocean environment at depths over 6000 m in the Southern Ocean, Indian Ocean, and western Pacific using sensor-equipped landers. We found that trench locations impact the water characteristics over these depths. Moving northward, they generally warmed but differed due to their position along bottom water circulation paths. These insights stress the importance of further research in understanding the environment of these deep regions and their importance.
Jinling Lu, Ling Du, and Shuhao Tao
Ocean Sci., 19, 1773–1789, https://doi.org/10.5194/os-19-1773-2023, https://doi.org/10.5194/os-19-1773-2023, 2023
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With the recent developments in observations and reanalysis data in the Beaufort Gyre, we investigate an improved understanding of eddy activity and asymmetrical halocline variability in the upper ocean. The halocline structures on the southern and northern sides of the central gyre have tended to be identical since 2014. The results suggest that enhanced eddy modulation through eddy fluxes influences oceanic stratification, resulting in reduced meridional asymmetry of the halocline.
Enrico P. Metzner and Marc Salzmann
Ocean Sci., 19, 1453–1464, https://doi.org/10.5194/os-19-1453-2023, https://doi.org/10.5194/os-19-1453-2023, 2023
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The Arctic Ocean cold halocline separates the cold surface mixed layer from the underlying warm Atlantic Water, and thus provides a precondition for sea ice formation. Here, we introduce a new method for detecting the halocline base and compare it to two existing methods. We show that the largest differences between the methods are found in the regions that are most prone to a halocline retreat in a warming climate, and we discuss the advantages and disadvantages of the three methods.
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Short summary
Based on in situ observations combined with sea level anomaly (SLA) data from satellite altimetry, volume as well as heat (relative to 0 °C) transport of the Iceland–Faroe warm-water inflow towards the Arctic (IF inflow) increased from 1993 to 2021. The reprocessed SLA data released in December 2021 represent observed variations accurately. The IF inflow crosses the Iceland–Faroe Ridge in two branches, with retroflection in between. The associated coupling to overflow reduces predictability.
Based on in situ observations combined with sea level anomaly (SLA) data from satellite...
