000K  utf8
1100  $c2024
1500  eng
2050  urn:nbn:de:gbv:8:3-2024-00024-3
3000  Roch, Marisa
4000  On the Changing Upper-Ocean Stratification$dTrends and Variability of the Upper-Ocean Structure during the Argo Observation Period$hChristian-Albrechts-Universität zu Kiel  [Roch, Marisa]
4030  Kiel$nChristian-Albrechts-Universität zu Kiel
4209  The warming climate is causing an increasing ocean stratification as a consequence of intensified ocean surface warming. Changes in ocean stratification affect e.g., ocean ventilation, mixed layer entrainment, heat exchange and air-sea interactions. In turn, these changes play a role for carbon uptake, oxygen distribution and nutrient fluxes that are crucial for marine ecosystems. How exactly these physical and biological processes will be affected remains uncertain and the effects of stratification changes probably vary among regions. Taking advantage of the excessive Argo observation dataset from 2006-2022, this thesis examines the decadal variability and recent changes of the upper-ocean stratification and surface mixed layer for the period of the most intense warming to-date. In particular, the southeastern tropical Atlantic Ocean (10°S-20°S, 5°W-15°E) shows continuous warming and freshening of the mixed layer for the period of 2006-2020. The resulting surface density reduction affects the upper-ocean stratification that strengthened by 30%. A procedure is developed to determine the vertical stratification maximum from the Argo array on global scales. Globally, the summer and winter vertical stratification maxima intensify by 7-8% from 2006-2021 while the mixed layer deepens by 4 m, proposing a de-coupling of the upper-ocean from the ocean interior. Changes in the upper-ocean structure impact the potential vorticity (PV) of the water column. This thesis establishes a relation between the decadal variability of North Atlantic Oscillation (NAO) and a zone of high PV in the northeastern tropical Atlantic, which plays a role for the subtropical-tropical pathways. During positive NAO phases, intensified trade winds result in isopycnal heave and squeezing of density layers that strengthen the PV. Analyses of the Sverdrup streamfunction and geostrophic velocities indicate enhanced thermocline flow via the western boundary toward the equator.
4950  https://nbn-resolving.org/urn:nbn:de:gbv:8:3-2024-00024-3$xR$3Volltext$534
4961  https://macau.uni-kiel.de/receive/macau_mods_00004305
5051  550
5550  Argo Observations
5550  Climate Variability
5550  Mixed Layer Deepening
5550  Mixed Layer Warming
5550  Potential Vorticity
5550  Upper-Ocean Stratification
5550  Upper-Ocean Structure