An assessment of Southern Ocean water masses and sea ice during 1988–2007 in a suite of interannual CORE-II simulations

• DOI: 10.1016/j.ocemod.2015.07.022
• Publication Date: 2015-08-12T04:30:37Z
• Authors: Stephanie M. Downes; Riccardo Farneti; Petteri Uotila; Stephen M. Griffies; Simon J. Marsland; David Bailey; Erik Behrens; Mats Bentsen; Daohua Bi; Arne Biastoch; Claus Böning; Alexandra Bozec; Vittorio M. Canuto; Eric Chassignet; Gokhan Danabasoglu; Sergey Danilov; Nikolay Diansky; Helge Drange; Pier Giuseppe Fogli; Anatoly Gusev; Armando Howard; Mehmet Ilicak; Thomas Jung; Maxwell Kelley; William G. Large; Anthony Leboissetier; Matthew Long; Jianhua Lu; Simona Masina; Akhilesh Mishra; Antonio Navarra; A.J. George Nurser; Lavinia Patara; Bonita L. Samuels; Dmitry Sidorenko; Paul Spence; Hiroyuki Tsujino; Qiang Wang; Stephen G. Yeager
• Keywords: Atmospheric Science; 550; : Southern Ocean; Sea ice; 0207 environmental engineering; 02 engineering and technology; 551; Geotechnical Engineering and Engineering Geology; Oceanography; Southern Ocean, CORE-II experiments, Water masses, Sea ice; Ocean model intercomparison; Water masses; CORE-II experiments; 13. Climate action; Computer Science (miscellaneous); 14. Life underwater

We characterise the representation of the Southern Ocean water mass structure and sea ice within a suite of 15 global ocean-ice models run with the Coordinated Ocean-ice Reference Experiment Phase II (CORE-II) protocol. The main focus is the representation of the present (1988–2007) mode and intermediate waters, thus framing an analysis of winter and summer mixed layer depths; temperature, salinity, and potential vorticity structure; and temporal variability of sea ice distributions. We also consider the interannual variability over the same 20 year period. Comparisons are made between models as well as to observation-based analyses where available. The CORE-II models exhibit several biases relative to Southern Ocean observations, including an underestimation of the model mean mixed layer depths of mode and intermediate water masses in March (associated with greater ocean surface heat gain), and an overestimation in September (associated with greater high latitude ocean heat loss and a more northward winter sea-ice extent). In addition, the models have cold and fresh/warm and salty water column biases centred near 50°S. Over the 1988–2007 period, the CORE-II models consistently simulate spatially variable trends in sea-ice concentration, surface freshwater fluxes, mixed layer depths, and 200–700 m ocean heat content. In particular, sea-ice coverage around most of the Antarctic continental shelf is reduced, leading to a cooling and freshening of the near surface waters. The shoaling of the mixed layer is associated with increased surface buoyancy gain, except in the Pacific where sea ice is also influential. The models are in disagreement, despite the common CORE-II atmospheric state, in their spatial pattern of the 20-year trends in the mixed layer depth and sea-ice.