14, left panels) is due to the North Atlantic contribution (Fig. 14 right panels). At 26°N, the intensity of the overturning component of mass transport is much weaker both in CM5_RETRO (7.3 Sv) and in CM5_piStart (8.7 Sv) than what is suggested
by observations (e.g. 18.7 ± 5.6 Sv Cunningham et al., 2007). At this location, intensification from CM5_RETRO to CM5_piStart configuration amounts to 15%, and this value is similar for all subtropical latitudes. Further north, differences are smaller (8.0 Sv in CM5_RETRO vs 8.4 Sv in CM5_piStart. AG-014699 purchase at 45°N) and values are again weaker than values inferred from observations (14–15 Sv in Ganachaud and Wunsch, 2000 and Talley et al., 2003), as already commented in several studies (Dufresne et al., 2013, Marti et al., 2010 and Swingedouw et al., 2007). Finally, the barotropic streamfunction (Fig. 15) confirms www.selleckchem.com/products/ink128.html that the Antarctic Circumpolar Current (ACC) is stronger in CM5_piStart than in CM5_RETRO after 400 years of simulation. Beyond the Southern Ocean, major changes are found in the Pacific, with a basin-wide positive anomaly in CM5_piStart in the northern mid-latitudes and a negative one in the south. Given the lack of significant differences in the wind stress curl structure and intensity in both simulations (not shown), these differences could be due to changes in the
oceanic bathymetry. The black lines in Fig. 15 (bottom panel) indeed show that several areas, including the North Pacific, are much deeper in CM5_piStart than in CM5_RETRO. This modification was implemented simultaneously as the partial steps formulation: the last level of the model in abyssal plains was increased in CM5_piStart to improve realism of the topography. This deeper bathymetry in CM5_piStart induces a decrease of the potential vorticity expressed as f/H where f stands for the Coriolis factor and H the local depth of the ocean. This is consistent with the generally positive anomalies in the barotropic streamfunction in the northern Pacific
second in CM5_piStart and the negative ones in the south ( Fig. 15 bottom panel). In the North Pacific, the intensity of both gyres (maximum of the streamfunction of the each gyre) is nevertheless weaker in CM5_piStart (55 Sv vs. 59 Sv in CM5_RETRO for the subtropical gyre, 21 Sv vs. 27 Sv in CM5_RETRO for the subpolar gyre). The change from one model to the next is similar but smaller in the other basins, except for the North Atlantic, where the subpolar gyre is intensified (18 Sv in CM5_piStart, vs. 16 Sv in CM5_RETRO) in CM5_piStart in spite of small changes in bathymetry. This intensification is due to the intensification of the deep convection in this area (not shown) that compensates a decrease of deep convection in the Nordic Seas linked to the increase of sea-ice extent.