Australia: The Land Where Time Began |
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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.
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.
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Author: M.H.Monroe Email: admin@austhrutime.com Sources & Further reading |