Interannual variability of meridional ocean heat transport at 26.5°N and impacts on North Atlantic heat content
William E Johns1, Jian Zhao2, Gerard D McCarthy3, David Smeed4, Christopher S Meinen5, Molly O'Neil Baringer6, Eleanor Frajka-Williams7, Darren Rayner3, Elaine McDonagh8 and Brian King8, (1)Rosenstiel School for Marine and Atmospheric Sciences, University of Miami, Miami, FL, United States, (2)Woods Hole Oceanographic Institution, Woods Hole, MA, United States, (3)National Oceanography Centre, Southampton, United Kingdom, (4)National Oceanography Center, Soton, Southampton, United Kingdom, (5)Atlantic Oceanographic and Meteorological Laboratory, Physical Oceanography Division, Miami, FL, United States, (6)Atlantic Oceanographic and Meteorological Laboratory, Miami, FL, United States, (7)University of Southampton, Southampton, United Kingdom, (8)National Oceanography Centre Southampton, United Kingdom
Abstract:
Since April 2004, continuous estimates of the oceanic meridional heat transport in the Atlantic have been derived from the RAPID-MOCHA observing system along 26.5°N. Several improvements in the methodology for both the AMOC and heat transport calculation have been implemented recently, which have been applied retrospectively to the entire time series. These include improvements in the surface extrapolation of interior geostrophic velocities, adoption of the TEOS-10 equation of state, updated Gulf Stream temperature transport calibration, and weekly optimal interpolation of Argo and RAPID mooring data to estimate the interior temperature transport.
The mean values for the AMOC strength and northward heat transport from the 10-year time series obtained thus far (2004-2014) are 17.0 Sv and 1.24 PW, respectively. Both the AMOC strength and the heat transport have decreased in recent years compared to values observed prior to 2009; the 5-year means for the pentad 2009-2013 were 15.6 Sv (1.14 PW) compared to values of 18.7 Sv (1.34 PW) for the pentad 2004-2008. The decline in the heat transport of 0.2 PW between these periods is significant: it is equivalent to a net decrease in surface heat flux of ~7 W/m2 over the whole North Atlantic, and represents a net deficit in heat delivery to the North Atlantic of 1.0 PW during the last 5 years, nearly equivalent to one year's worth of the typical heat transport. Observations of ocean heat content (OHC) from Argo data show that the North Atlantic OHC reached a decadal peak in about 2007 and has since declined, consistent with the lower recent heat transport values recorded by the 26.5°N array.
