Hallberg and Gnanadesikan 2001, 2006 Meredith and Hogg 2006) this process is referred to as eddy saturation. From diagnostics of high-resolution numerical models, strengthening winds may lead to little overall increase in strength of the large-scale Southern Ocean horizontal circulation, usually inferred from zonal Antarctic Circumpolar Current (ACC) transports, where the wind energy instead increases eddy kinetic energy at the mesoscale (e.g. There is a debate over the expected response of the Southern Ocean circulation to altered wind forcing. However, the paleoclimatic inferences of implied upwelling have often been interpreted in terms of wind-induced changes in the Eulerian-mean circulation, rather than accounting for the partial compensation from the ocean eddy circulation. Stronger winds have also been proposed as strengthening upwelling and initiating the deglacial rise in atmospheric CO 2 (Anderson et al. Changes in the zonal symmetry of Southern Hemisphere winds have recently been implicated in the reinvigoration of the Southern Ocean carbon sink (Landschützer et al. 2007, 2008), which increases the exposure of natural carbon-rich deep waters to the surface, opposing anthropogenic carbon uptake. 2007), increased upwelling (Lenton and Matear 2007) and a stronger Eulerian-mean overturning (Lovenduski et al. For example, stronger winds have been invoked in the present day as driving a weakening in the sink of anthropogenic carbon, inducing enhanced surface mixing (Le Quéré et al. 2010) and the present day (Frölicher et al.

2015): atmospheric CO 2 can be drawn down by subduction of upper ocean waters, as well as increased by outgassing of CO 2 from natural carbon-rich waters.Ĭhanges in physical forcing over the Southern Ocean have been invoked as explaining changes in atmospheric CO 2 for the past (Sigman and Boyle 2001 Toggweiler et al. By providing the window for the global deep ocean to communicate with the atmosphere, these different physical transport pathways lead to a delicate carbon balance over the Southern Ocean (Morrison et al.

The Southern Ocean plays a fundamental role in the climate system, ventilating much of the global ocean by forming subtropical mode, intermediate and bottom waters, as well as uniquely returning deep waters to the surface (Marshall and Speer 2012). This metric can be used to interpret the long-term effect of Southern Ocean dynamics on the natural carbon cycle and atmospheric CO 2, alongside other metrics, such as involving the proportion of preformed nutrients and the extent of sea ice cover. Increased residual upwelling drives elevated atmospheric CO 2 at a rate of typically 1–1.5 parts per million/10 6 m 3 s −1 by enhancing the communication between the atmosphere and deep ocean. The skill of the metric is assessed by employing suites of idealized ocean model experiments, including parameterized and explicitly simulated eddies, with online biogeochemistry and integrated for 10,000 years to equilibrium. The metric encapsulates the combined, net effect of winds and air–sea buoyancy forcing on both the upper and lower overturning cells, which have been invoked as explaining atmospheric CO 2 changes for the present day and glacial-interglacial changes. Here, we develop a dynamically-motivated metric, the residual upwelling, that measures the primary effect of Southern Ocean dynamics on atmospheric CO 2 on centennial to millennial timescales by determining the communication with the deep ocean. There has been a widespread focus on explaining atmospheric CO 2 changes in terms of changes in wind forcing in the Southern Ocean. The Southern Ocean plays a pivotal role in climate change by exchanging heat and carbon, and provides the primary window for the global deep ocean to communicate with the atmosphere.

Icycle on thin ice unblocked