Dispert, Astrid (2007) Decadal temperature changes across the Antarctic Circumpolar Current. (Diploma thesis), Christian-Albrechts-Universität zu Kiel, Kiel, Germany, 86 pp.

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Abstract

Changes in the large-scale hydrographic structure of the Southern Ocean are examined by utilizing the rapidly- expanding ARGO float dataset, in comparison to a historical hydrograhic database (BOA). By invoking and comparing different schemes of considering the historical and modern profiles in narrow meridional bins over both regional and global extent, and by contrasting zonal averages on isobaric and isopycnal surfaces with averages taken along approximate streamlines of the ACC, the study contributes to a synthesis and refinement of previous suggestions of a warming trend in the upper-to-mid-depth Southern Ocean, elucidating the 3D structure of this signal and shedding some light on possible origins. The inspection of the tendencies in meridional cross-sections reveal several, distinct patterns of change during the last four decades. The first two, a deep-reaching warming of uCDW at the southern flank of the ACC, and a pronounced decrease of density (i.e., subsidence and southward shift of isopycnals) in the northern portion of the ACC, appear consistent with a dynamical response of the ACC and its associated meridional overturning to an increasing SAM index and westerly wind stress. The other main signal seen in the regional and global averages is a prominent and extended warming trend at constant depth in the mode waters north of the ACC, corresponding to a cooling and freshening on isopycnal surfaces. Inspection of the temporal tendencies of this process suggests the presence of the mid-depth warming trend at least since the 1960-70s, and give some indications of deviations from a monotonous trend.

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