Lagrangian connectivity of the upper limb of the overturning circulation studied with high-resolution ocean models

• Main Author: Rühs, Siren
• Format: Thesis
• Language: English
• Published: 2018
• Subjects: Drake Passage; Indian; Pacific
• Online Access: https://oceanrep.geomar.de/id/eprint/44981/; https://oceanrep.geomar.de/id/eprint/44981/1/Dissertation_SirenRuehs_LagrangianConnectivityOverturningCirculation_Complete.pdf; https://macau.uni-kiel.de/receive/diss_mods_00023871

Lagrangian connectivity studies with ocean models comprise the analysis of sets of virtual fluid particle trajectories to identify connecting pathways, as well as associated timescales and transports between distinct oceanic regions. They constitute a powerful tool in physical oceanography and a unique means to coherently study seawater pathways associated with the global overturning circulation (GOC). However, there are several open questions related to the (partially unresolved) impact of small-scale flow variability on large-scale Lagrangian connectivity measures. This doctoral dissertation addresses different aspects of the question how high-resolution ocean models can help improving our understanding of the spreading of water masses associated with the global overturning circulation, by: (i) reviewing the theoretical background of Lagrangian connectivity studies with ocean models, thereby highlighting the importance to distinguish Lagrangian analyzes of simulated purely advective volume transport trajectories from Lagrangian modeling approaches to estimate advective-diffusive tracer trajectories; (ii) investigating Lagrangian volume transport pathways and along-track tracer changes of the GOC’s upper limb in the South Atlantic (study 1) and Indian Ocean (study 2) with high-resolution models; and (iii) assessing the performance of near-surface particle dispersal simulations in the extended Agulhas Current system by means of lateral eddy diffusivity estimates (study 3). The major aim of study 1 was to revisit the relative importance of the different sources for the GOC’s upper limb in the South Atlantic, that are, waters entering from the Indian Ocean through the Agulhas Current system versus waters entering from the Pacific through Drake Passage. To do so, backward trajectory calculations from the North Brazil Current have been employed. They revealed a substantially higher volumetric contribution of waters originating at Drake Passage than estimated by previous Lagrangian studies with coarser resolution ...