The curious convection teleconnection question: links between Weddell Sea and Labrador Sea deep convection on multi-decadal timescales

Many climate models show strong variability in preindustrial Southern Ocean (SO) sea surface temperatures, heat fluxes, sea-ice, salinity, and mixed layer depths, all associated with open-ocean deep convection through polynyas. The CM2MC model, a coarse-resolution 3° version of GFDL's ESM2M model, and the 1°GFDL ESM2G model (as well as other 1^o CMIP5 models we have analyzed) demonstrate regular out-of-phase multi-decadal variability of Weddell Sea (WS) open-sea convection and Labrador deep convection in long control simulations with no anthropogenic CO2 forcings. Convection events in the two regions are out-of-phase; we explore differences in the oceanic teleconnection pathways in the lower and higher resolution models and potential interactions between the Northern and Southern convective evens. In the higher resolution ESM2G model, the Labrador convection dominates Atlantic Meridional Overturning Circulation (AMOC) multi-decadal variability, with a southward propagation of signals from the North Atlantic to about 40°S on an approximately 20-year timescale. The accumulation of heat in the (Circumpolar Deep Water) CDW helps "precondition" the WS region, acting to destratify the water column at the site of polynya formation and initiate deep convection. In the 3°low resolution model, Antarctic Bottom Water (AABW) formation and the Antarctic Circumpolar Current (ACC) strength increase, while Antarctic Intermediate Water (AAIW) formation and AMOC strength decrease in decades with strong WS Convection. AMOC responds strongly to the WS convection and resulting decreases in SO Westerlies, with AMOC signals propagating northward on a 20- to 30-year timescale all the way to the North Atlantic, affecting in turn the Labrador Sea density properties and convection.

We hypothesize that the fundamentally different teleconnection signals and the strong relevance of the WS convection for AMOC in the lower resolution model is in part due to a strong response to WS convection of SO westerlies and AAIW formation. The role of SO westerlies decreases in higher resolution models, increasing the relative impact of the Labrador convective events on AMOC. The see-saw mechanism between Southern Ocean Meridional Overturning circulation (SMOC) and AMOC is also identified and contrasted between these 2 model types.