Local and downstream relationships between Labrador Sea Water volume and North Atlantic meridional overturning circulation variability

Author Posting. © American Meteorological Society, 2019. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Climate 32(13), (2019): 3883-3898, doi:10.1175/JCLI-D-18-0735.1.
While it has generally been understood that the production of Labrador Sea Water (LSW) impacts the Atlantic meridional overturning circulation (MOC), this relationship has not been explored extensively or validated against observations. To explore this relationship, a suite of global ocean–sea ice models forced by the same interannually varying atmospheric dataset, varying in resolution from non-eddy-permitting to eddy-permitting (1°–1/4°), is analyzed to investigate the local and downstream relationships between LSW formation and the MOC on interannual to decadal time scales. While all models display a strong relationship between changes in the LSW volume and the MOC in the Labrador Sea, this relationship degrades considerably downstream of the Labrador Sea. In particular, there is no consistent pattern among the models in the North Atlantic subtropical basin over interannual to decadal time scales. Furthermore, the strong response of the MOC in the Labrador Sea to LSW volume changes in that basin may be biased by the overproduction of LSW in many models compared to observations. This analysis shows that changes in LSW volume in the Labrador Sea cannot be clearly and consistently linked to a coherent MOC response across latitudes over interannual to decadal time scales in ocean hindcast simulations of the last half century. Similarly, no coherent relationships are identified between the MOC and the Labrador Sea mixed layer depth or the density of newly formed LSW across latitudes or across models over interannual to decadal time scales.
FL and MSL are thankful for the financial support from the National Science Foundation (NSF) Physical Oceanography Program (NSF-OCE-12-59102, NSF-OCE-12-59103). The NCAR contribution was supported by the National Oceanic and Atmospheric Administration (NOAA) Climate Program Office (CPO) under Climate Variability and Predictability Program (CVP) Grant NA13OAR4310138 and by the NSF Collaborative Research EaSM2 Grant OCE-1243015. NCAR is sponsored by the NSF. NPH is supported by NERC programs U.K. OSNAP (NE/K010875) and ACSIS (National Capability, NE/N018044/1). Y-OK is supported by NOAA CPO CVP (NA17OAR4310111) and NSF EaSM2 grant (OCE-1242989). AR is supported by NASA-ROSES Modeling, Analysis and Prediction 2016 NNX16AC93G-MAP. RZ is supported by NOAA/OAR. Argo data were collected and made freely available by the International Argo Program and the national programs that contribute to it (http://www.argo.ucsd.edu, http://argo.jcommops.org). The Argo Program is part of the Global Ocean Observing System (http://doi.org/10.17882/42182). Data from the RAPID-MOCHA-WBTS array funded by NERC, NSF and NOAA are freely available from www.rapid.ac.uk/rapidmoc. We thank Stephen Griffies for providing access to the GFDL-MOM025 COREII simulation output and Matthew Harrison and Xiaoqin Yan for their comments on the manuscript. We also thank the anonymous reviewers for their valuable comments.
2020-06-11