Atlantic-Pacific asymmetry in deep-water formation
Annual Review of Earth and Planetary Sciences Annual Reviews 46 (2018) 327-352
Abstract:
While the Atlantic Ocean is ventilated by high-latitude deep water formation and exhibits a pole-to-pole overturning circulation, the Pacific Ocean does not. This asymmetric global overturning pattern has persisted for the past 2–3 million years, with evidence for different ventilation modes in the deeper past. In the current climate, the Atlantic-Pacific asymmetry occurs because the Atlantic is more saline, enabling deep convection. To what extent the salinity contrast between the two basins is dominated by atmospheric processes (larger net evaporation over the Atlantic) or oceanic processes (salinity transport into the Atlantic) remains an outstanding question. Numerical simulations have provided support for both mechanisms; observations of the present climate support a strong role for atmospheric processes as well as some modulation by oceanic processes. A major avenue for future work is the quantification of the various processes at play to identify which mechanisms are primary in different climate states.A Model of the Ocean Overturning Circulation with Two Closed Basins and a Reentrant Channel
JOURNAL OF PHYSICAL OCEANOGRAPHY 47:12 (2017) 2887-2906
Submesoscale Instabilities in Mesoscale Eddies
JOURNAL OF PHYSICAL OCEANOGRAPHY 47:12 (2017) 3061-3085
Characterising the chaotic nature of ocean ventilation
Journal of Geophysical Research: Oceans American Geophysical Union 122:9 (2017) 7577-7594
Abstract:
Ventilation of the upper ocean plays an important role in climate variability on interannual to decadal timescales by influencing the exchange of heat and carbon dioxide between the atmosphere and ocean. The turbulent nature of ocean circulation, manifest in a vigorous mesoscale eddy field, means that pathways of ventilation, once thought to be quasi-laminar, are in fact highly chaotic. We characterise the chaotic nature of ventilation pathways according to a nondimensional ‘filamentation number', which estimates the reduction in filament width of a ventilated fluid parcel due to mesoscale strain. In the subtropical North Atlantic of an eddy-permitting ocean model, the filamentation number is large everywhere across three upper ocean density surfaces — implying highly chaotic ventilation pathways — and increases with depth. By mapping surface ocean properties onto these density surfaces, we directly resolve the highly filamented structure and confirm that the filamentation number captures its spatial variability. These results have implications for the spreading of atmospherically-derived tracers into the ocean interior.Relative strength of the Antarctic Circumpolar Current and Atlantic Meridional Overturning Circulation
Tellus A: Dynamic Meteorology and Oceanography Taylor and Francis 69:1 (2017) 1338884-1338884
Abstract:
A simple relationship, based on thermal wind balance, is derived that relates the relative strength of the Antarctic Circumpolar Current (ACC) and Atlantic Meridional Overturning Circulation (AMOC) to the ratios of three depth scales: the e-folding depth of the global stratification, the depth of maximum overturning streamfunction and the maximum depth of the ACC. For realistic values of these depth scales, the relationship predicts a factor 8 ± 4 difference in the volume transports of the ACC and AMOC, consistent with the observation-based ratio of 8 ± 2.