Relevance of surface freshwater flux for global ocean circulation and Atlantic freshwater content variability

• Main Author: Liu, Xin
• Other Authors: Stammer, Detlef (Prof. Dr.)
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: Staats- und Universitätsbibliothek Hamburg Carl von Ossietzky 2017
• Subjects: large-scale ocean circulation; freshwater content variability; freshwater flux; climate change; GECCO2; 550 Geowissenschaften; 38.90 Ozeanologie; Ozeanographie; ddc:550; Antarctic; Southern Ocean; The Antarctic; Antarc*
• Online Access: http://nbn-resolving.de/urn:nbn:de:gbv:18-90625; https://ediss.sub.uni-hamburg.de/handle/ediss/7623

Over the next century changes in the ocean will occur as a consequence of an intensified water cycle and the associated surface freshwater flux changes under global warming. One objective of this thesis is concerned with the dynamical ocean response to the associated surface volume flux anomalies. The other objective is to detect the contributions of surface freshwater flux and freshwater transport to the regional freshwater content variations in the Atlantic, specifically at interannual and decadal time scales. To address the first objective, the model configuration of the German contribution to the Estimating the Circulation and Climate of the Ocean (GECCO2) is used with two salinity boundary conditions (virtual salt flux version and volume flux version). Both versions are forced first by the present-day freshwater flux and then by the additional freshwater flux anomalies, which are estimated over the period 2081−2100 relative to 1986−2005 under the Representative Concentration Pathway (RCP) 8.5 scenario from the Max-Planck-Institute Earth System Model. The resulting differences between the two salinity boundary conditions show that the adjustment of ocean circulation involves a barotropic response as predicted from the Goldsbrough-Stommel theory. In comparison to the present-day Goldsbrough-Stommel circulation, the corresponding barotropic circulation driven by the RCP8.5 freshwater flux anomalies intensifies by about 20% globally with a stronger intensification about 50% in the Southern Ocean. The barotropic circulation anomaly induced by the intensified volume flux reaches to 0.6 Sv in the Antarctic Circumpolar Current region. The adjustment also involves changes in the meridional overturning circulation, mirroring the convergence and divergence of the mass transport driven by surface volume flux. The subsequent pathway of fresh water and the spreading of volume flux match with each other in the shallow cells but diverge substantially with depth. Associated with the circulation changes are the changes in ...