| 1. |
- Silvano, Alessandro, et al.
(författare)
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Observing Antarctic Bottom Water in the Southern Ocean
- 2023
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Ingår i: Frontiers in Marine Science. - 2296-7745. ; 10
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Forskningsöversikt (refereegranskat)abstract
- Dense, cold waters formed on Antarctic continental shelves descend along the Antarctic continental margin, where they mix with other Southern Ocean waters to form Antarctic Bottom Water (AABW). AABW then spreads into the deepest parts of all major ocean basins, isolating heat and carbon from the atmosphere for centuries. Despite AABW's key role in regulating Earth's climate on long time scales and in recording Southern Ocean conditions, AABW remains poorly observed. This lack of observational data is mostly due to two factors. First, AABW originates on the Antarctic continental shelf and slope where in situ measurements are limited and ocean observations by satellites are hampered by persistent sea ice cover and long periods of darkness in winter. Second, north of the Antarctic continental slope, AABW is found below approximately 2 km depth, where in situ observations are also scarce and satellites cannot provide direct measurements. Here, we review progress made during the past decades in observing AABW. We describe 1) long-term monitoring obtained by moorings, by ship-based surveys, and beneath ice shelves through bore holes; 2) the recent development of autonomous observing tools in coastal Antarctic and deep ocean systems; and 3) alternative approaches including data assimilation models and satellite-derived proxies. The variety of approaches is beginning to transform our understanding of AABW, including its formation processes, temporal variability, and contribution to the lower limb of the global ocean meridional overturning circulation. In particular, these observations highlight the key role played by winds, sea ice, and the Antarctic Ice Sheet in AABW-related processes. We conclude by discussing future avenues for observing and understanding AABW, impressing the need for a sustained and coordinated observing system.
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| 2. |
- De Boer, Agatha M., et al.
(författare)
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Control of the glacial carbon budget by topographically induced mixing
- 2014
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Ingår i: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 41:12, s. 4277-4284
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Tidskriftsartikel (refereegranskat)abstract
- Evidence for the oceanic uptake of atmospheric CO2 during glaciations suggests that there was less production of southern origin deep water but, paradoxically, a larger volume of southern origin water than today. Here we demonstrate, using a theoretical box model, that the inverse relationship between volume and production rate of this water mass can be explained by invoking mixing rates in the deep ocean that are proportional to topographic outcropping area scaled with ocean floor slope. Furthermore, we show that the resulting profile, of a near-linear decrease in mixing intensity away from the bottom, generates a positive feedback on CO2 uptake that can initiate a glacial cycle. The results point to the importance of using topography-dependent mixing when studying the large-scale ocean circulation, especially in the paleo-intercomparison models that have failed to produce the weaker and more voluminous bottom water of the Last Glacial Maximum.
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| 3. |
- Jüling, André, et al.
(författare)
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Multidecadal variability in the climate system : phenomena and mechanisms
- 2020
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Ingår i: The European Physical Journal Plus. - : Springer Science and Business Media LLC. - 2190-5444. ; 135:6
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Forskningsöversikt (refereegranskat)abstract
- An open and fundamental issue in climate dynamics is the origin of multidecadal variability in the climate system. Resolving this issue is essential for adequate attribution of human-induced climate change. The purpose of this paper is to provide a perspective on multidecadal variability from the analysis of observations and results from model simulations. Data from the instrumental record indicate the existence of large-scale coherent patterns of multidecadal variability in sea surface temperature. Combined with long time series of proxy data, these results provide ample evidence for the existence of multidecadal sea surface temperature variations. Results of a hierarchy of climate models have provided several mechanisms of this variability, ranging from pure atmospheric forcing, via internal ocean processes to coupled ocean-atmosphere interactions. An important problem is that current state-of-the-art climate models underestimate multidecadal variability. We argue that these models miss important processes in their representation of ocean eddies and focus on a robust mechanism of multidecadal variability which is found in multi-century simulations with climate models having a strongly eddying ocean component.
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