Australia: The Land Where Time Began

A biography of the Australian continent 

Atlantic Overturning Circulation Recent Slowing as a Recovery from Earlier Strengthening

There has been a substantial weakening of the Atlantic meridional overturning circulation (AMOC) over the past decade (Smeed et al., 2014). There may already have been some weakening over the past century (Rahmstorf et al., 2014), and it is projected by global climate models that further weakening will occur in response to anthropogenic climate change (Collins et al., 2013). There could be significant impacts on surface climate that result from such weakening (Jackson et al., 2015). An increase in overturning up to the mid-1990s, to be followed by a decrease, has often been found by model simulations based on historical conditions (Danabasoglu et al, 2015). Therefore, it is not clear if the weakening that has been observed over the past decade is a persistent weakening or merely part of decadal variability (Roberts, Jackson & McNeall, 2014). In this study Jackson et al. used a state-of-the-art global-ocean reanalysis product, GloSea5, which covers the years 1989-2015 and matches closely observations of the AMOC at 26.5o N, which captured the interannual variability as well as the decadal trend with unprecedented accuracy. The 10 years of observations, April 2004 to February 2014, are placed by the reanalysis into a longer-term context, and suggests that the decreased overturning circulation is consistent with a recovery after a previous increase. It was found by Jackson et al. that the most likely cause of these variations are density anomalies propagating southwards from the Labrador Sea. Their conclusion is that it is probable that decadal variability played a key role in the decline of the AMOC that was observed over the past decade.

Sources & Further reading

Jackson, L. C., K. A. Peterson, C. D. Roberts and R. A. Wood (2016). "Recent slowing of Atlantic overturning circulation as a recovery from earlier strengthening." Nature Geosci 9(7): 518-522.


Author: M. H. Monroe
Last Updated 14/08/2016
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