Regensburg 2007 – wissenschaftliches Programm
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UP: Fachverband Umweltphysik
UP 4: Ozeanographie, Hydro- und Kryosphäre
UP 4.2: Vortrag
Montag, 26. März 2007, 12:00–12:15, H48
Dispersion in North Atlantic Deep Water transfer between the northern source region and the South Atlantic — •Oliver Huhn and Wolfgang Roether — Institut für Umweltphysik, Universität Bremen
North Atlantic Deep Water (NADW) represents the Atlantic part of the deep, southward return arm of the oceanic ”conveyor belt“, which moderates Europe’s climate and effects most of the water transfer from the ocean surface into the deep waters globally. The transfer starts from the NADW formation regions, which in the case of upper NADW (approx. 1500 - 2000 m depth) is the Labrador Sea (far NW Atlantic). NADW is found concentrated toward the continental slope of the Americas, but subject to meandering, and to recirculation into, and mixing with, the waters of the interior Atlantic. Individual water parcels thus follow a complex ensemble of trajectories. We have obtained characteristics of that ensemble by fitting the free parameters of a suitable function using extensive observations of the transient tracers CFC-11, CFC-12, CCl4, and tritium. A tracer transfer function of ocean-surface concentrations to those in newly formed NADW was derived as a precursory step. In the upper NADW we obtain RMS transfer-time dispersions on the way from the Labrador Sea of 31 years at 6 ∘N rising to 53 years at 20 ∘S, compared to mean transfer times ranging 46 to 79 years (±20 %); furthermore, approximately 10 % to 40 % of the water is old, tracer-free water admixed on the way. Similar results have been obtained for lower NADW (approx. 2500 - 4000 m). The combination of tritium and CFC observations is particularly suited to constrain the dispersion, since it acts on the concentrations of these tracers in an opposite way. The tracer-adjusted transfer functions allow quantification of the NADW transport of pollutants and other compounds delivered to the NADW formation region. The results can furthermore check mean transfer times and large-scale dispersion of the NADW part of dynamic ocean circulation models.