Wednesday, July 31, 2013

New paper finds N. Atlantic ocean heat content & sea levels controlled by the natural Atlantic Multidecadal Oscillation [AMO]

A paper published today in the Journal of Geophysical Research Oceans finds ocean heat content and sea levels in the Northern North Atlantic are associated with the cycles of the natural Atlantic Multidecadal Oscillation [AMO, also referred to as AMV]. The authors find the warming evident in sea levels and ocean heat content in the N. Atlantic during the satellite era [since 1979] "represents transition of the AMV from cold to warm phase" and note "an abrupt change 2009–2010 [in N. Atlantic sea levels] reaching a new minimum in 2010." 

The AMO, also sometimes referred to as Atlantic Multidecadal Variability [AMV], is an approximate ~70 year natural climate cycle that is highly correlated to Northern hemisphere and global temperature change.  Increases in greenhouse gases cannot possibly explain these shifts in ocean heat content and sea levels in the N. Atlantic. 

Northern North Atlantic sea surface height and ocean heat content variability

Sirpa H√§kkinen, Peter B. Rhines, Denise L. Worthen

Abstract: The evolution of nearly 20 years of altimetric sea surface height (SSH) is investigated to understand its association with decadal to multidecadal variability of the North Atlantic heat content. Altimetric SSH is dominated by an increase of about 14 cm in the Labrador and Irminger seas from 1993 to 2011, while the opposite has occurred over the Gulf Stream region over the same time period. During the altimeter period the observed 0–700 m ocean heat content (OHC) in the subpolar gyre mirrors the increased SSH by its dominantly positive trend. Over a longer period, 1955–2011, fluctuations in the subpolar OHC reflect Atlantic multidecadal variability (AMV) and can be attributed to advection driven by the wind stress “gyre mode” bringing more subtropical waters into the subpolar gyre. The extended subpolar warming evident in SSH and OHC during the altimeter period represents transition of the AMV from cold to warm phase. In addition to the dominant trend, the first empirical orthogonal function SSH time series shows an abrupt change 2009–2010 reaching a new minimum in 2010. The change coincides with the change in the meridional overturning circulation at 26.5°N as observed by the RAPID (Rapid Climate Change) project, and with extreme behavior of the wind stress gyre mode and of atmospheric blocking. While the general relationship between northern warming and Atlantic meridional overturning circulation (AMOC) volume transport remains undetermined, the meridional heat and salt transport carried by AMOC's arteries are rich with decade-to-century timescale variability.