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Lagrangian pathways of upwelling in the Southern Ocean
Author(s) -
Viglione Giuliana A.,
Thompson Andrew F.
Publication year - 2016
Publication title -
journal of geophysical research: oceans
Language(s) - English
Resource type - Journals
eISSN - 2169-9291
pISSN - 2169-9275
DOI - 10.1002/2016jc011773
Subject(s) - mixed layer , upwelling , outcrop , geology , advection , pycnocline , oceanography , seamount , structural basin , ocean gyre , residence time (fluid dynamics) , climatology , oceanic basin , ocean general circulation model , ocean current , lagrangian , climate change , geomorphology , subtropics , general circulation model , physics , geotechnical engineering , fishery , biology , mathematical physics , thermodynamics
The spatial and temporal variability of upwelling into the mixed layer in the Southern Ocean is studied using a 1/10°ocean general circulation model. Virtual drifters are released in a regularly spaced pattern across the Southern Ocean at depths of 250, 500, and 1000 m during both summer and winter months. The drifters are advected along isopycnals for a period of 4 years, unless they outcrop into the mixed layer, where lateral advection and a parameterization of vertical mixing are applied. The focus of this study is on the discrete exchange between the model mixed layer and the interior. Localization of interior‐mixed layer exchange occurs downstream of major topographic features across the Indian and Pacific basins, creating “hotspots” of outcropping. Minimal outcropping occurs in the Atlantic basin, while 59% of drifters outcrop in the Pacific sector and in Drake Passage (the region from 140°W to 40°W), a disproportionately large amount even when considering the relative basin sizes. Due to spatial and temporal variations in mixed layer depth, the Lagrangian trajectories provide a statistical measure of mixed layer residence times. For each exchange into the mixed layer, the residence time has a Rayleigh distribution with a mean of 30 days; the cumulative residence time of the drifters is 261 ± 194 days, over a period of 4 years. These results suggest that certain oceanic gas concentrations, such as CO 2 and 14 C, will likely not reach equilibrium with the atmosphere before being resubducted.