1. Atlantic Meridional Overturning Circulation Slowdown Causes Widespread Cooling In The Atlantic Stuart A. Cunningham Scottish Association for Marine Science Stuart.Cunningham@sams.ac.uk Christopher D. Roberts 3, Eleanor Frajka-Williams 2, William E. Johns 4, Will Hobbs 5, Matthew D. Palmer 3, Darren Rayner 1, David A. Smeed 1, Gerard McCarthy 1 1 National Oceanography Centre Southampton, 2 University of Southampton, 3 Met Office, Exeter, 4 RSMAS, University of Miami, 5 IMAS, Hobart.

2. OHC error ~=0.2x10 22 J A cold subtropical North Atlantic

3. Spatial and Temporal Pattern of Ocean Heat Content in the North Atlantic (1991-2010 seasonal cycle removed & 0 to 2000 m) Enhanced Ocean Data Assimilation and Climate Prediction EN3 v2a gridded objective analysis of quality-controlled sub-surface temperature observations (Ingleby and Huddleston 2007, http://www.metoffice.gov.uk/hadobs/en3/). http://www.metoffice.gov.uk/hadobs/en3/

4. OHC (10 22 J) : Feb 2004

5. OHC (10 22 J) : Aug 2004

6. OHC (10 22 J) : April 2005

7. OHC (10 22 J) : Aug 2005

8. OHC (10 22 J) : Sept 2006

9. OHC (10 22 J) : May 2007

10. OHC (10 22 J) : Oct 2009

11. OHC (10 22 J) : March 2010

12. OHC (10 22 J) : Jan 2011

13. OHC (10 22 J) : Sept 2011

14. Observing the AMOC and Associated Heat Flux 41°N Johns, W. E., et al., (2011). "Continuous, array-based estimates of Atlantic Ocean heat transport at 26.5°N." J. Clim. 24(10): 2429-2449. Hobbs, W. R. and J. K. Willis (2012). "Midlatitude North Atlantic heat transport: A time series based on satellite and drifter data." J. Geophys. Res. 117(C01008): doi:10.1029/2011JC007039.

15. Subtropical Atlantic Heat Budget (0-2000m) S’ 26.5°N N’ 41.0°N F’ surface flux 0 m 2000 m

16. Meridional Heat Transport and Divergence 1/4/04 to 31/3/09MeanSD 26.5°N1.260.11 41°N0.480.11 41-26.5°N-0.770.2 1/4/08 to 31/3/10MeanSD 26.5°N0.850.26 41°N0.350.14 41-26.5°N-0.50.23

17. Ocean Heat Content

18. ERA-Interim surface flux anomalies

19. Relative Heat Content Change Palmer & Haines (2009): Estimating oceanic heat content change using isotherms, J.Clim, 22,

20. What generates the MLD (  >14°C) temperature anomalies?

21. Summary 1.Sustained cooling in upper 2 km of subtropical Atlantic between 2010-2012. 2.OHC change partitioned equally between the seasonal mixed layer >14°C and deep ocean. 3.Reduced AMOC at 26.5°N is the largest contributor to reduced MHT divergence. 4.In seasonal mixed layer heat loss is due to atmospheric heat loss (60%) and MHT divergence (40%). 5.Results emphasise the role for the ocean in the North Atlantic climate system on seasonal to interannual timescales and suggest a role for the AMOC in setting sub- surface temperature anomalies. 6.These anomalies have previously been linked to re-emerging SST patterns and subsequent NAO anomalies.

23. Need to do a bit about re-emergence/SST patterns and link to NAO (Taws). Then say we identify the OHC change due to divergence as responsible.

24. OHC Errors

26. Ekman and Geostrophic Heat Transport Variability

27. Interannual Variability What happened to the MOC in 2009-10? Table of annual changes (Std of annual means): Layer2004-20082009 (change) Mean [Sv]Std [Sv]Mean [Sv] MOC18.10.8812.2 (-5.9) Gulf Stream31.80.2630.7 (-1.1) Ekman2.90.361.1 (-1.8) Upper mid-ocean-16.60.95-19.6 (-3.2) UNADW (1100-3000m)-11.90.18-10.7 (1.2) LNADW (3000-5000m)-7.80.69-3.8 (4.0)

28. RAPID MOC: 2009-2010, Ekman constant What happened to the MOC in 2009-10, not directly due to Ekman? Table of annual changes (Ekman fixed): Layer2004-20082009 (change) Mean [Sv]Std [Sv]Mean [Sv] MOC18.70.8914.3 (-4.4) Gulf Stream31.80.2630.7 (-1.1) Ekman3.60.03.6 (0) Upper mid-ocean-16.70.91-19.9 (+3.2) UNADW (1100-3000m)-12.20.32-11.5 (-0.7) LNADW (3000-5000m)-8.00.66-4.7 (-3.3) Longer duration (18-month) slowdown of the MOC: seen in the Gulf Stream, upper mid-ocean and LNADW.

29. MOC timeseries and related data products are available from www.noc.soton.ac.uk/rpdmocwww.noc.soton.ac.uk/rpdmoc Data from individual instruments are available from www.bodc.ac.ukwww.bodc.ac.uk Gulf Stream, MOC, Ekman & Upper Mid-Ocean Transports (10-day & 3-month, low-pass filtered) Gulf Stream MOC Ekman Upper Mid-Ocean LNADW (3-5km) UNADW (1.1-3km)

30. Meridional Heat Transport Time Series Johns, et al. (2011), Continuous array-based estimates of Atlantic Ocean Heat Transport at 26.5N, JClim

31. Meridional Heat Transport at 26.5°N Contribution to Q net by spatially correlated v,T variability across interior from argo data.. Q GS → Cable voltage calibrated for temperature transport, (Shoosmith et al., 2005) r = 0.94, σ = 0.1 PW Q Ek → ECMWF ERA Interim wind stress (daily) Reynolds SST (weekly) Q WBW → Directly calculated from moored CM’s/thermistors in Abaco WB array Q INT → Zonally-averaged interior transport profile from endpoint geostrophic moorings Seasonally-varying interior hyrdographic climatology (Hydrobase, R. Curry) merged with argo data.

32. Ocean Heat Content

33. RAPID @ 26.5°N 1.26±0.11 PW 04-09 Hobbs & Willis @ 41°N 0.48±0.11 PW 04-09 TF08 error bars Coupled models (CM2.1, CCSM4) Radiation balance residual (NCEP,ECMWF,TF08)l Global hydro inverse (Ganachaud) Air-sea flux climatology (Large) RAPID & 41N: Direct Residual Radiation Balance, Climatologies and Direct Estimates Atlantic Ocean Heat Transport Estimates

34. Overturning and Gyre Heat Transport

38. Atlantic Meridional Overturning Circulation Slowdown Causes Widespread Cooling In The Atlantic Stuart A. Cunningham Scottish Association for Marine Science, Oban Stuart.Cunningham@sams.ac.uk Christopher D. Roberts 3, Eleanor Frajka-Williams 2, William E. Johns 4, Will Hobbs 5, Matthew D. Palmer 3, Darren Rayner 1, David A. Smeed 1, Gerard McCarthy 1 1 National Oceanography Centre Southampton, 2 University of Southampton, 3 Met Office, Exeter, 4 RSMAS, University of Miami, 5 IMAS, Hobart.