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| 2. |
- Arndt, D. S., et al.
(författare)
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State of the Climate in 2016
- 2017
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Ingår i: Bulletin of The American Meteorological Society - (BAMS). - 0003-0007 .- 1520-0477. ; 98:8, s. S1-S280
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Tidskriftsartikel (refereegranskat)abstract
- In 2016, the dominant greenhouse gases released into Earth's atmosphere-carbon dioxide, methane, and nitrous oxide-continued to increase and reach new record highs. The 3.5 +/- 0.1 ppm rise in global annual mean carbon dioxide from 2015 to 2016 was the largest annual increase observed in the 58-year measurement record. The annual global average carbon dioxide concentration at Earth's surface surpassed 400 ppm (402.9 +/- 0.1 ppm) for the first time in the modern atmospheric measurement record and in ice core records dating back as far as 800000 years. One of the strongest El Nino events since at least 1950 dissipated in spring, and a weak La Nina evolved later in the year. Owing at least in part to the combination of El Nino conditions early in the year and a long-term upward trend, Earth's surface observed record warmth for a third consecutive year, albeit by a much slimmer margin than by which that record was set in 2015. Above Earth's surface, the annual lower troposphere temperature was record high according to all datasets analyzed, while the lower stratospheric temperature was record low according to most of the in situ and satellite datasets. Several countries, including Mexico and India, reported record high annual temperatures while many others observed near-record highs. A week-long heat wave at the end of April over the northern and eastern Indian peninsula, with temperatures surpassing 44 degrees C, contributed to a water crisis for 330 million people and to 300 fatalities. In the Arctic the 2016 land surface temperature was 2.0 degrees C above the 1981-2010 average, breaking the previous record of 2007, 2011, and 2015 by 0.8 degrees C, representing a 3.5 degrees C increase since the record began in 1900. The increasing temperatures have led to decreasing Arctic sea ice extent and thickness. On 24 March, the sea ice extent at the end of the growth season saw its lowest maximum in the 37-year satellite record, tying with 2015 at 7.2% below the 1981-2010 average. The September 2016 Arctic sea ice minimum extent tied with 2007 for the second lowest value on record, 33% lower than the 1981-2010 average. Arctic sea ice cover remains relatively young and thin, making it vulnerable to continued extensive melt. The mass of the Greenland Ice Sheet, which has the capacity to contribute similar to 7 m to sea level rise, reached a record low value. The onset of its surface melt was the second earliest, after 2012, in the 37-year satellite record. Sea surface temperature was record high at the global scale, surpassing the previous record of 2015 by about 0.01 degrees C. The global sea surface temperature trend for the 21st century-to-date of +0.162 degrees C decade(-1) is much higher than the longer term 1950-2016 trend of +0.100 degrees C decade(-1). Global annual mean sea level also reached a new record high, marking the sixth consecutive year of increase. Global annual ocean heat content saw a slight drop compared to the record high in 2015. Alpine glacier retreat continued around the globe, and preliminary data indicate that 2016 is the 37th consecutive year of negative annual mass balance. Across the Northern Hemisphere, snow cover for each month from February to June was among its four least extensive in the 47-year satellite record. Continuing a pattern below the surface, record high temperatures at 20-m depth were measured at all permafrost observatories on the North Slope of Alaska and at the Canadian observatory on northernmost Ellesmere Island. In the Antarctic, record low monthly surface pressures were broken at many stations, with the southern annular mode setting record high index values in March and June. Monthly high surface pressure records for August and November were set at several stations. During this period, record low daily and monthly sea ice extents were observed, with the November mean sea ice extent more than 5 standard deviations below the 1981-2010 average. These record low sea ice values contrast sharply with the record high values observed during 2012-14. Over the region, springtime Antarctic stratospheric ozone depletion was less severe relative to the 1991-2006 average, but ozone levels were still low compared to pre-1990 levels. Closer to the equator, 93 named tropical storms were observed during 2016, above the 1981-2010 average of 82, but fewer than the 101 storms recorded in 2015. Three basins-the North Atlantic, and eastern and western North Pacific-experienced above-normal activity in 2016. The Australian basin recorded its least active season since the beginning of the satellite era in 1970. Overall, four tropical cyclones reached the Saffir-Simpson category 5 intensity level. The strong El Nino at the beginning of the year that transitioned to a weak La Nina contributed to enhanced precipitation variability around the world. Wet conditions were observed throughout the year across southern South America, causing repeated heavy flooding in Argentina, Paraguay, and Uruguay. Wetter-than-usual conditions were also observed for eastern Europe and central Asia, alleviating the drought conditions of 2014 and 2015 in southern Russia. In the United States, California had its first wetter-than-average year since 2012, after being plagued by drought for several years. Even so, the area covered by drought in 2016 at the global scale was among the largest in the post-1950 record. For each month, at least 12% of land surfaces experienced severe drought conditions or worse, the longest such stretch in the record. In northeastern Brazil, drought conditions were observed for the fifth consecutive year, making this the longest drought on record in the region. Dry conditions were also observed in western Bolivia and Peru; it was Bolivia's worst drought in the past 25 years. In May, with abnormally warm and dry conditions already prevailing over western Canada for about a year, the human-induced Fort McMurray wildfire burned nearly 590000 hectares and became the costliest disaster in Canadian history, with $3 billion (U.S. dollars) in insured losses.
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| 3. |
- Arndt, D. S., et al.
(författare)
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STATE OF THE CLIMATE IN 2017
- 2018
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Ingår i: Bulletin of The American Meteorological Society - (BAMS). - : American Meteorological Society. - 0003-0007 .- 1520-0477. ; 99:8, s. S1-S310
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Forskningsöversikt (refereegranskat)
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| 4. |
- 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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| 7. |
- 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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| 8. |
- 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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| 9. |
- 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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| 10. |
- 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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