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- Azarian, Clara, et al.
(författare)
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Marine heatwaves and global warming impacts on winter waters in the Southern Indian Ocean
- 2024
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Ingår i: Journal of Marine Systems. - 0924-7963. ; 243
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Tidskriftsartikel (refereegranskat)abstract
- In the Southern Ocean, the term “winter waters” (WWs) refers to a water mass characterized by a subsurface layer of minimum temperature that plays an important ecological role for marine ecosystems, and in particular for top predators. Given that the Southern Ocean is experiencing warming and intense marine heatwaves (MHWs), particularly at subantarctic latitudes, we investigate here how different levels of warming might impact the presence, depth and minimum temperature of WWs in the Indian sector of the Southern Ocean. In particular, we assess how WWs are impacted by surface MHWs using in situ Argo hydrographic observations and biologging data. The results indicate that WWs are substantially reduced, deeper and warmer during the presence of MHWs. Using the most recent climate projections, we find a significant, but scenario-dependent, southward shift of WWs under global warming. Potential impacts of such WW shifts on pelagic ecosystems, at different timescales (from daily to decadal), are discussed.
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| 5. |
- Boyd, Philip W., et al.
(författare)
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The role of biota in the Southern Ocean carbon cycle
- 2024
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Ingår i: NATURE REVIEWS EARTH & ENVIRONMENT. - 2662-138X. ; 5:5, s. 390-408
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Forskningsöversikt (refereegranskat)abstract
- The Southern Ocean, although relatively understudied owing to its harsh environment and geographical isolation, has been shown to contribute substantially to processes that drive the global carbon cycle. For example, phytoplankton photosynthesis transforms carbon dioxide into new particles and dissolved organic carbon. The magnitude of these transformations depends on the unique oceanographic and biogeochemical properties of the Southern Ocean. In this Review, we synthesize observations of biologically mediated carbon flows derived from the expanded observational network provided by remote-sensing and autonomous platforms. These observations reveal patterns in the magnitude of net primary production, including under-ice blooms and subsurface chlorophyll maxima. Basin-scale annual estimates of the planktonic contribution to the Southern Ocean carbon cycle can also be calculated, indicating that the export of biogenic particles and dissolved organic carbon to depth accounts for 20-30% (around 3 Gt yr-1) of the global export flux. This flux partially compensates for carbon dioxide outgassing following upwelling, making the Southern Ocean a 0.4-0.7 Gt C yr-1 sink. This export flux is surprisingly large given that phytoplankton are iron-limited with low productivity in more than 80% of the Southern Ocean. Solving such enigmas will require the development of four-dimensional regional observatories and the use of data-assimilation and machine-learning techniques to integrate datasets. The Southern Ocean represents a substantial carbon sink and heavily influences global carbon fluxes. This Review describes how an expanding suite of observations are providing increasing insight into the contribution of biota and plankton to the carbon cycle in the Southern Ocean. Increasing coverage from a suite of observations from autonomous platforms will reduce uncertainties on estimates of key processes in the regional carbon cycle that determine the magnitude of the Southern Ocean carbon sink.Episodic storms enhance chlorophyll stocks, presumably owing to enhanced iron supply from depth, but also drive concurrent carbon dioxide outgassing, with unknown cumulative effects on the regional carbon cycle.The influence of climate change on the Southern Ocean and Antarctica is expected to alter the partitioning of basin-scale net primary production between open water, sea ice and under ice.Observations from profiling robotic floats are providing important insights into how the fate of phytoplankton carbon drives regional patterns in export flux in the ocean's interior over multiple annual cycles.The inability to remotely measure dissolved iron or dissolved organic carbon concentrations makes it difficult to understand pivotal processes in the Southern Ocean carbon cycle.Models using data assimilation are already providing promising guidelines on how to deploy autonomous platforms to address key questions around the regional carbon cycle.
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- Burchard, Hans, et al.
(författare)
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Linking Ocean Mixing and Circulation
- 2024
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Ingår i: BULLETIN OF THE AMERICAN METEOROLOGICAL SOCIETY. - 0003-0007 .- 1520-0477. ; 105:7
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Tidskriftsartikel (refereegranskat)abstract
- Walter Munk, in his famous abyssal recipes, showed more than half a century ago that the strength of the global overturning circulation is closely linked to diapycnal mixing. Since then, oceanographic research has succeeded in identifying more and more processes generating mixing and overturning circulation: internal-wave mixing, boundary mixing, wake eddies, gravity currents, double diffusion, and many more. The same dependence was also observed in other marine systems at smaller scales, including marginal and semienclosed seas and estuaries. Numerical models describing these mechanisms often include discretization errors that become evident in particular in the form of spurious numerical mixing, which may trigger artificial circulation patterns at all scales. The Warnemünde Turbulence Days (WTD, http://www.io-warnemuende.de/wtd.html) have been established in 2003 to provide a regular international forum for discussing new developments in marine turbulence. Since then, the WTD have been organized on a biannual basis with the 11th WTD taking place during 17–20 September 2023 in Rostock. We invited contributions discussing all aspects of mixing in the ocean, especially, however, those that focus on the relation of mixing and circulation at all relevant scales.
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- Clayson, C. A., et al.
(författare)
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Super sites for advancing understanding of the oceanic and atmospheric boundary layers
- 2021
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Ingår i: Marine Technology Society Journal. - 0025-3324. ; 55:3, s. 144-145
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Tidskriftsartikel (refereegranskat)abstract
- Air–sea interactions are critical to large-scale weather and climate predictions because of the ocean’s ability to absorb excess atmospheric heat and carbon and regulate exchanges of momentum, water vapor, and other greenhouse gases. These exchanges are controlled by molecular, turbulent, and wave-driven processes in the atmospheric and oceanic boundary layers. Improved understanding and representation of these processes in models are key for increasing Earth system prediction skill, particularly for subseasonal to decadal time scales. Our understanding and ability to model these processes within this coupled system is presently inadequate due in large part to a lack of data: contemporaneous long-term observations from the top of the marine atmospheric boundary layer (MABL) to the base of the oceanic mixing layer. We propose the concept of “Super Sites” to provide multi-year suites of measurements at specific locations to simultaneously characterize physical and biogeochemical processes within the coupled boundary layers at high spatial and temporal resolution. Measurements will be made from floating platforms, buoys, towers, and autonomous vehicles, utilizing both in-situ and remote sensors. The engineering challenges and level of coordination, integration, and interoperability required to develop these coupled ocean–atmosphere Super Sites place them in an “Ocean Shot” class. © 2021, Marine Technology Society Inc.. All rights reserved.
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- Coadou Chaventon, Solange, et al.
(författare)
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Oceanic Fronts Driven by the Amazon Freshwater Plume and Their Thermohaline Compensation at the Submesoscale
- 2024
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Ingår i: JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS. - 2169-9275 .- 2169-9291. ; 129:7
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Tidskriftsartikel (refereegranskat)abstract
- Upper ocean fronts are dynamically active features of the global ocean playing a key role in the air-sea exchanges of properties and their transport in the ocean interior. With scales ranging from the submesoscale (0.1-10 km) to the mesoscale (10-100s km) and a temporal variability from hours to months, collecting in situ observations of these structures is challenging and this has limited our understanding of their associated processes and impacts. During the EUREC4A-OA/ATOMIC field experiment, which took place in the northwest tropical Atlantic in January-February 2020, a large number of uncrewed platforms, including five Saildrones, were deployed to provide a detailed picture of the upper-ocean fine-scale variability. This region is strongly influenced by the outflow of the Amazon River, even in winter, which is the minimum outflow season. Here, the generation of fine-scale horizontal thermohaline gradients is driven by the stirring of this freshwater river input by large anticyclonic eddies, the so-called North Brazil Current Rings. Vertical shear estimates using the Saildrones ADCP show that partial temperature compensation occurs along restratifying submesoscale salinity-dominated fronts. The distribution of surface along-track gradients, as sampled by different horizontal length-scales, reveals the prevalence of submesoscale fronts. This is supported by a flattening of the spectral slopes of surface density at the submesoscale. This study emphasizes the need to resolve the upper ocean at high spatial resolution to understand its impact on the broader circulation and to properly represent air-sea interactions. Plain Language Summary Oceanic eddies and filaments that range between 10 and 100 km in size can be identified in the study region of the northwestern tropical Atlantic using ocean color as viewed from space (a proxy for chlorophyll-a). The ocean color maps show that these eddies and filaments are associated with the detachment from the shelf of a freshwater Amazon plume and its interaction with the larger oceanic motions O(100 km). Field observations from different measurements acquired from research vessels and five uncrewed surface vehicles (USVs) reveal the prevalence and scale of upper ocean fronts, whose magnitude results from the combined effect of temperature and salinity. The Amazon freshwater plume is key to the formation of strong salinity-driven density fronts. However, when looking at O(1 km) scales, we detect horizontal temperature variations along slumping fronts that partially counteract the effect of salinity. This leads to a damping of the lateral density fronts. This study contributes to the development of a detailed picture of the ocean fine scales, which is necessary to improve our understanding of air-sea interactions over frontal regions.
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| 9. |
- Cronin, Meghan F., et al.
(författare)
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Air-sea fluxes with a focus on heat and momentum
- 2019
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Ingår i: Frontiers in Marine Science. - : Frontiers Media SA. - 2296-7745. ; 6
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Tidskriftsartikel (refereegranskat)abstract
- © 2019 Cronin, Gentemann, Edson, Ueki, Bourassa, Brown, Clayson, Fairall, Farrar, Gille, Gulev, Josey, Kato, Katsumata, Kent, Krug, Minnett, Parfitt, Pinker, Stackhouse, Swart, Tomita, Vandemark, Weller, Yoneyama, Yu and Zhang. Turbulent and radiative exchanges of heat between the ocean and atmosphere (hereafter heat fluxes), ocean surface wind stress, and state variables used to estimate them, are Essential Ocean Variables (EOVs) and Essential Climate Variables (ECVs) influencing weather and climate. This paper describes an observational strategy for producing 3-hourly, 25-km (and an aspirational goal of hourly at 10-km) heat flux and wind stress fields over the global, ice-free ocean with breakthrough 1-day random uncertainty of 15 W m-2 and a bias of less than 5 W m-2. At present this accuracy target is met only at OceanSITES reference station moorings and research vessels (RVs) that follow best practices. To meet these targets globally, in the next decade, satellite-based observations must be optimized for boundary layer measurements of air temperature, humidity, sea surface temperature, and ocean wind stress. In order to tune and validate these satellite measurements, a complementary global in situ flux array, built around an expanded OceanSITES network of time series reference station moorings, is also needed. The array would include 500 - 1000 measurement platforms, including autonomous surface vehicles, moored and drifting buoys, RVs, the existing OceanSITES network of 22 flux sites, and new OceanSITES expanded in 19 key regions. This array would be globally distributed, with 1 - 3 measurement platforms in each nominal 10° by 10° boxes. These improved moisture and temperature profiles and surface data, if assimilated into Numerical Weather Prediction (NWP) models, would lead to better representation of cloud formation processes, improving state variables and surface radiative and turbulent fluxes from these models. The in situ flux array provides globally distributed measurements and metrics for satellite algorithm development, product validation, and for improving satellite-based, NWP and blended flux products. In addition, some of these flux platforms will also measure direct turbulent fluxes, which can be used to improve algorithms for computation of air-sea exchange of heat and momentum in flux products and models. With these improved air-sea fluxes, the ocean's influence on the atmosphere will be better quantified and lead to improved long-term weather forecasts, seasonal-interannual-decadal climate predictions, and regional climate projections.
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| 10. |
- Cronin, M. F., et al.
(författare)
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Developing an Observing Air-Sea Interactions Strategy (OASIS) for the global ocean
- 2022
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Ingår i: Ices Journal of Marine Science. - : Oxford University Press (OUP). - 1054-3139 .- 1095-9289. ; 80:2, s. 367-73
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Tidskriftsartikel (refereegranskat)abstract
- The Observing Air-Sea Interactions Strategy (OASIS) is a new United Nations Decade of Ocean Science for Sustainable Development programme working to develop a practical, integrated approach for observing air-sea interactions globally for improved Earth system (including ecosystem) forecasts, CO2 uptake assessments called for by the Paris Agreement, and invaluable surface ocean information for decision makers. Our "Theory of Change" relies upon leveraged multi-disciplinary activities, partnerships, and capacity strengthening. Recommendations from >40 OceanObs'19 community papers and a series of workshops have been consolidated into three interlinked Grand Ideas for creating #1: a globally distributed network of mobile air-sea observing platforms built around an expanded array of long-term time-series stations; #2: a satellite network, with high spatial and temporal resolution, optimized for measuring air-sea fluxes; and #3: improved representation of air-sea coupling in a hierarchy of Earth system models. OASIS activities are organized across five Theme Teams: (1) Observing Network Design & Model Improvement; (2) Partnership & Capacity Strengthening; (3) UN Decade OASIS Actions; (4) Best Practices & Interoperability Experiments; and (5) Findable-Accessible-Interoperable-Reusable (FAIR) models, data, and OASIS products. Stakeholders, including researchers, are actively recruited to participate in Theme Teams to help promote a predicted, safe, clean, healthy, resilient, and productive ocean.
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