Global Overturning Circulation


Conceptual models have clarified scientific understanding of the ocean’s deep stratification and meridional overturning circulation (MOC), while making predictions that may be tested via observations and numerical modeling. One example is the one-dimensional advection-diffusion “abyssal recipes” balance, first posited by Munk in 1966. However, we now recognize that the observed diapycnal diffusivity is, in many places, an order of magnitude smaller than Munk’s estimate. This has highlighted the importance of along isopycnal transport in the ocean interior, in particular in the Southern Ocean where deep isopycnals outcrop or are “ventilated” at the ocean surface.

Our group's research on this topic has been aimed at building upon existing conceptual models of the global overturning. In particular, we note that the ocean’s overturning circulation inherently has a three-dimensional structure, yet modern quantitative estimates of the overturning typically represent the sub-surface circulation as a two-dimensional, two-cell streamfunction that varies with latitude and depth, which suppresses information about zonal mass and tracer transport. We are working to explore the dynamics of the ocean’s modern “figure-of- eight” circulation that cycles through multiple basins.

Furthermore, the ocean’s role in regulating atmospheric carbon dioxide on glacial–interglacial timescales remains an unresolved issue in paleoclimatology. Recent understanding of the deep ocean circulation and stratification is suggests that that the major changes invoked in ocean physics are dynamically linked. In particular, the expansion of permanent sea ice in the Southern Hemisphere results in a volume increase of Antarctic-origin abyssal waters and a reduction in mixing between abyssal waters of Arctic and Antarctic origin.

Related Publications:

Thompson, A.F., A.L. Stewart & T. Bischoff, 2015. A multi-basin residual-mean model for the global overturning circulation. /submitted to J. Phys. Oceanogr.

Burke, A., A.L. Stewart, J.F. Adkins, R. Ferrari, M.F. Jansen & A.F. Thompson, 2015. The glacial mid-depth radiocarbon bulge and its implications for the overturning circulation. /Paleoceanography/, 30, 1021-1039.

Stewart, A.L. & A.F. Thompson, 2015. The neutral density temporal residual mean overturning ciculation. /Oc. Model./, 90, 44-56.

Ferrari, R., M. Jansen, J.F. Adkins, A. Burke, A.L. Stewart & A.F. Thompson, 2014. An ocean tale of two climates: Modern and Last Glacial Maximum. /Proc. Natl. Ac. Sci./, 111, 8753-8758. [PDF]

Stewart, A.L., R. Ferrari & A.F. Thompson, 2014. On the evolution of conceptual models of the ocean's deep stratification and overturning. /Journal of Physical Oceanography/, 44, 891-899. [PDF]

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