| 1. |
- Roquet, Fabien, 1982, et al.
(författare)
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Unique thermal expansion properties of water key to the formation of sea ice on Earth
- 2022
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Ingår i: Science Advances. - : American Association for the Advancement of Science (AAAS). - 2375-2548. ; 8:46
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Tidskriftsartikel (refereegranskat)abstract
- The formation of sea ice in polar regions is possible because a salinity gradient or halocline keeps the water col-umn stable despite intense cooling. Here, we demonstrate that a unique water property is central to the mainte-nance of the polar halocline, namely, that the thermal expansion coefficient (TEC) of seawater increases by one order of magnitude between polar and tropical regions. Using a fully coupled climate model, it is shown that, even with excess precipitations, sea ice would not form at all if the near-freezing temperature TEC was not well below its ocean average value. The leading order dependence of the TEC on temperature is essential to the coex-istence of the mid/low-latitude thermally stratified and the high-latitude sea ice-covered oceans that character-ize our planet. A key implication is that nonlinearities of water properties have a first-order impact on the global climate of Earth and possibly exoplanets.
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| 2. |
- Bosi, Sofia, et al.
(författare)
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The Role of Stokes Drift in the Dispersal of North Atlantic Surface Marine Debris
- 2021
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Ingår i: Frontiers in Marine Science. - : Frontiers Media SA. - 2296-7745. ; 8
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Tidskriftsartikel (refereegranskat)abstract
- Understanding the physical mechanisms behind the transport and accumulation of floating objects in the ocean is crucial to efficiently tackle the issue of marine pollution. The main sinks of marine plastic are the coast and the bottom sediment. This study focuses on the former, investigating the timescales of dispersal from the ocean surface and onto coastal accumulation areas through a process called "beaching. " Previous studies found that the Stokes drift can reach the same magnitude as the Eulerian current speed and that it has a long-term effect on the trajectories of floating objects. Two particle tracking models (PTMs) are carried out and then compared, one with and one without Stokes drift, named PTM-SD and PTM-REF, respectively. Eulerian velocity and Stokes drift data from global reanalysis datasets are used for particle advection. Particles in the PTM-SD model are found to beach at a yearly rate that is double the rate observed in PTM-REF. The main coastal attractors are consistent with the direction of large-scale atmospheric circulation (Westerlies and Trade Winds). After 12 years (at the end of the run), the amount of beached particles is 20% larger in PTM-SD than in PTM-REF. Long-term predictions carried out with the aid of adjacency matrices found that after 100 years all particles have beached in PTM-SD, while 8% of the all seeded particles are still floating in PTM-REF. The results confirm the need to accurately represent the Stokes drift in particle models attempting to predict the behaviour of marine debris, in order to avoid overestimation of its residence time in the ocean and effectively guide policies toward prevention and removal.
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| 3. |
- Brisson-Curadeau, E., et al.
(författare)
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Investigating two consecutive catastrophic breeding seasons in a large king penguin colony
- 2023
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Ingår i: Scientific Reports. - 2045-2322. ; 13:1
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Tidskriftsartikel (refereegranskat)abstract
- Large-scale breeding failures, such as offspring die-offs, can disproportionately impact wildlife populations that are characterized by a few large colonies. However, breeding monitoring-and thus investigations of such die-offs-is especially challenging in species with long reproductive cycles. We investigate two unresolved dramatic breeding failures that occurred in consecutive years (2009 and 2010) in a large king penguin Aptenodytes patagonicus colony, a long-lived species with a breeding cycle lasting over a year. Here we found that a single period, winter 2009, was likely responsible for the occurrence of breeding anomalies during both breeding seasons, suggesting that adults experienced poor foraging conditions at sea at that time. Following that unfavorable winter, the 2009 breeding cohort-who were entering the late stage of chick-rearing-immediately experienced high chick mortality. Meanwhile, the 2010 breeding cohort greatly delayed their arrival and egg laying, which would have otherwise started not long after the winter. The 2010 breeding season continued to display anomalies during the incubation and chick-rearing period, such as high abandonment rate, long foraging trips and eventually the death of all chicks in winter 2010. These anomalies could have resulted from either a domino-effect caused by the delayed laying, the continuation of poor foraging conditions, or both. This study provides an example of a large-scale catastrophic breeding failure and highlights the importance of the winter period on phenology and reproduction success for wildlife that breed in few large colonies.
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| 4. |
- Caneill, Romain, 1994, et al.
(författare)
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The Polar Transition from Alpha to Beta Regions Set by a Surface Buoyancy Flux Inversion
- 2022
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Ingår i: Journal of Physical Oceanography. - : American Meteorological Society. - 0022-3670 .- 1520-0485. ; 52, s. 1887-1902
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Tidskriftsartikel (refereegranskat)abstract
- The stratification is primarily controlled by temperature in subtropical regions (alpha ocean) and by salinity in subpolar regions (beta ocean). Between these two regions lies a transition zone, often characterized by deep mixed layers in winter and responsible for the ventilation of intermediate or deep layers. While of primary interest, no consensus on what controls its position exists yet. Among the potential candidates, we find the wind distribution, air–sea fluxes, or the nonlinear cabbeling effect. Using an ocean general circulation model in an idealized basin configuration, a sensitivity analysis is performed testing different equations of state. More precisely, the thermal expansion coefficient (TEC) temperature dependence is explored, changing the impact of heat fluxes on buoyancy fluxes in a series of experiments. The polar transition zone is found to be located at the position where the sign of the surface buoyancy flux reverses to become positive, in the subpolar region, while wind or cabbeling are likely of secondary importance. This inversion becomes possible because the TEC is reducing at low temperature, enhancing in return the relative impact of freshwater fluxes on the buoyancy forcing at high latitudes. When the TEC is made artificially larger at low temperature, the freshwater flux required to produce a positive buoyancy flux increases and the polar transition moves poleward. These experimets demonstrate the important role of competing heat and freshwater fluxes in setting the position of the transition zone. This competition is primarily influenced by the spatial variations of the TEC linked to meridional variations of the surface temperature.
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| 5. |
- de Boer, Agatha M., et al.
(författare)
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The Impact of Southern Ocean Topographic Barriers on the Ocean Circulation and the Overlying Atmosphere
- 2022
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Ingår i: Journal of Climate. - 0894-8755 .- 1520-0442. ; 35:18, s. 5805-5821
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Tidskriftsartikel (refereegranskat)abstract
- Southern Ocean bathymetry constrains the path of the Antarctic Circumpolar Current (ACC), but the bathymetric influence on the coupled ocean–atmosphere system is poorly understood. Here, we investigate this impact by respectively flattening large topographic barriers around the Kerguelen Plateau, Campbell Plateau, Mid-Atlantic Ridge, and Drake Passage in four simulations in a coupled climate model. The barriers impact both the wind and buoyancy forcing of the ACC transport, which increases by between 4% and 14% when barriers are removed individually and by 56% when all barriers are removed simultaneously. The removal of Kerguelen Plateau bathymetry increases convection south of the plateau and the removal of Drake Passage bathymetry reduces convection upstream in the Ross Sea. When the barriers are removed, zonal flattening of the currents leads to sea surface temperature (SST) anomalies that strongly correlate to precipitation anomalies, with correlation coefficients ranging between r = 0.92 and r = 0.97 in the four experiments. The SST anomalies correlate to the surface winds too in some locations. However, they also generate circumpolar waves of sea level pressure (SLP) anomalies, which induce remote wind speed changes that are unconnected to the underlying SST field. The meridional variability in the wind stress curl contours over the Mid-Atlantic Ridge, the Kerguelen Plateau, and the Campbell Plateau disappears when these barriers are removed, confirming the impact of bathymetry on surface winds. However, bathymetry-induced wind changes are too small to affect the overall wave-3 asymmetry in the Southern Hemisphere westerlies. Removal of Southern Hemisphere orography is also inconsequential to the wave-3 pattern.
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| 6. |
- de Lavergne, C., et al.
(författare)
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A Parameterization of Local and Remote Tidal Mixing
- 2020
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Ingår i: Journal of Advances in Modeling Earth Systems. - 1942-2466. ; 12:5
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Tidskriftsartikel (refereegranskat)abstract
- Vertical mixing is often regarded as the Achilles' heel of ocean models. In particular, few models include a comprehensive and energy-constrained parameterization of mixing by internal ocean tides. Here, we present an energy-conserving mixing scheme which accounts for the local breaking of high-mode internal tides and the distant dissipation of low-mode internal tides. The scheme relies on four static two-dimensional maps of internal tide dissipation, constructed using mode-by-mode Lagrangian tracking of energy beams from sources to sinks. Each map is associated with a distinct dissipative process and a corresponding vertical structure. Applied to an observational climatology of stratification, the scheme produces a global three-dimensional map of dissipation which compares well with available microstructure observations and with upper-ocean finestructure mixing estimates. This relative agreement, both in magnitude and spatial structure across ocean basins, suggests that internal tides underpin most of observed dissipation in the ocean interior at the global scale. The proposed parameterization is therefore expected to improve understanding, mapping, and modeling of ocean mixing. ©2020. The Authors.
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| 7. |
- de Lavergne, C., et al.
(författare)
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Toward global maps of internal tide energy sinks
- 2019
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Ingår i: Ocean Modelling. - : Elsevier BV. - 1463-5003 .- 1463-5011. ; 137, s. 52-75
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Tidskriftsartikel (refereegranskat)abstract
- Internal tides power much of the observed small-scale turbulence in the ocean interior. To represent mixing induced by this turbulence in ocean climate models, the cascade of internal tide energy to dissipation scales must be understood and mapped. Here, we present a framework for estimating the geography of internal tide energy sinks. The mapping relies on the following ingredients: (i) a global observational climatology of stratification; (ii) maps of the generation of M-2, S-2 and K-1 internal tides decomposed into vertical normal modes; (iii) simplified representations of the dissipation of low-mode internal tides due to wave-wave interactions, scattering by small-scale topography, interaction with critical slopes and shoaling; (iv) Lagrangian tracking of low-mode energy beams through observed stratification, including refraction and reflection. We thus obtain a global map of the column-integrated energy dissipation for each of the four considered dissipative processes, each of the three tidal constituents and each of the first five modes. Modes >= 6 are inferred to dissipate within the local water column at the employed half-degree horizontal resolution. Combining all processes, modes and constituents, we construct a map of the total internal tide energy dissipation, which compares well with observational inferences of internal wave energy dissipation. This result suggests that tides largely shape observed spatial contrasts of dissipation, and that the framework has potential in improving understanding and modelling of ocean mixing. However, sensitivity to poorly constrained parameters and simplifying assumptions entering the parameterized energy sinks calls for additional investigation. The attenuation of low-mode internal tides by wave-wave interactions needs particular attention.
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| 8. |
- Gülk, Birte, 1994, et al.
(författare)
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Variability and Remote Controls of the Warm-Water Halo and Taylor Cap at Maud Rise
- 2023
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Ingår i: Journal of Geophysical Research: Oceans. - 2169-9275 .- 2169-9291. ; 128:7
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Tidskriftsartikel (refereegranskat)abstract
- The region of Maud Rise, a seamount in the Weddell Sea, is known for the occurrence of irregular polynya openings during the winter months. Hydrographic observations have shown the presence of a warmer water mass below the mixed layer along the seamount's flanks, commonly termed the warm-water Halo, surrounding a colder region above the rise, the Taylor Cap. Here we use two observational data sets, an eddy-permitting reanalysis product and regional high-resolution simulations, to investigate the interannual variability of the Halo and Taylor Cap for the period 2007–2022. Observations include novel hydrographic profiles obtained in the Maud Rise area in January 2022, during the first SO-CHIC cruise. It is demonstrated that the temperature of deep waters around Maud Rise exhibits strong interannual variability within the Halo and Taylor Cap, occasionally to such an extent that the two features become indistinguishable. A warming of deep waters by as much as 0.8°C is observed in the Taylor Cap during the years preceding the opening of a polynya in 2016 and 2017, starting in 2011. By analyzing regional simulations, we show that most of the observed variability in the Halo is forced remotely by advection of deep waters from the Weddell Gyre into the region surrounding Maud Rise. Our highest-resolution simulation indicates that mesoscale eddies subsequently transfer the properties of the Halo's deep waters onto the Taylor Cap. The eddies responsible for such transfer originate in an abrupt retroflection along the inner flank of the Halo.
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| 9. |
- Harcourt, R., et al.
(författare)
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Animal-borne telemetry: An integral component of the ocean observing toolkit
- 2019
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Ingår i: Frontiers in Marine Science. - : Frontiers Media SA. - 2296-7745. ; 6:JUN
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Tidskriftsartikel (refereegranskat)abstract
- Animal telemetry is a powerful tool for observing marine animals and the physical environments that they inhabit, from coastal and continental shelf ecosystems to polar seas and open oceans. Satellite-linked biologgers and networks of acoustic receivers allow animals to be reliably monitored over scales of tens of meters to thousands of kilometers, giving insight into their habitat use, home range size, the phenology of migratory patterns and the biotic and abiotic factors that drive their distributions. Furthermore, physical environmental variables can be collected using animals as autonomous sampling platforms, increasing spatial and temporal coverage of global oceanographic observation systems. The use of animal telemetry, therefore, has the capacity to provide measures from a suite of essential ocean variables (EOVs) for improved monitoring of Earth's oceans. Here we outline the design features of animal telemetry systems, describe current applications and their benefits and challenges, and discuss future directions. We describe new analytical techniques that improve our ability to not only quantify animal movements but to also provide a powerful framework for comparative studies across taxa. We discuss the application of animal telemetry and its capacity to collect biotic and abiotic data, how the data collected can be incorporated into ocean observing systems, and the role these data can play in improved ocean management. © 2019 Harcourt, Sequeira, Zhang, Roquet, Komatsu, Heupel, McMahon, Whoriskey, Meekan, Carroll, Brodie, Simpfendorfer, Hindell, Jonsen, Costa, Block, Muelbert, Woodward, Weise, Aarestrup, Biuw, Boehme, Bograd, Cazau, Charrassin, Cooke, Cowley, de Bruyn, Jeanniard du Dot, Duarte, Eguíluz, Ferreira, Fernández-Gracia, Goetz, Goto, Guinet, Hammill, Hays, Hazen, Hückstädt, Huveneers, Iverson, Jaaman, Kittiwattanawong, Kovacs, Lydersen, Moltmann, Naruoka, Phillips, Picard, Queiroz, Reverdin, Sato, Sims, Thorstad, Thums, Treasure, Trites, Williams, Yonehara and Fedak.
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| 10. |
- Klocker, Andreas, et al.
(författare)
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Deep-Reaching Global Ocean Overturning Circulation Generated by Surface Buoyancy Forcing
- 2023
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Ingår i: Tellus, Series A: Dynamic Meteorology and Oceanography. - 0280-6495 .- 1600-0870. ; 75:1, s. 392-409
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Tidskriftsartikel (refereegranskat)abstract
- In contrast with the atmosphere, which is heated from below by solar radiation, the ocean is both heated and cooled from above. To drive a deep-reaching overturning circulation in this context, it is generally assumed that either intense interior mixing by winds and internal tides, or wind-driven upwelling is required; in their absence, the circulation is thought to collapse to a shallow surface cell. We demonstrate, using a primitive equation model with an idealized domain and no wind forcing, that the surface temperature forcing can in fact drive an interhemispheric overturning provided that there is an open channel unblocked in the zonal direction, such as in the Southern Ocean. With this geometry, rotating horizontal convection, in combination with asymmetric surface cooling between the north and south, drives a deep-reaching two-cell overturning circulation. The resulting vertical mid-depth stratification closely resembles that of the real ocean, suggesting that wind-driven pumping is not necessary to produce a deep-reaching overturning circulation, and that buoyancy forcing plays a more important role than is usually assumed.
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