The poleward enhanced Arctic Ocean cooling machine in a warming climate

As a cooling machine of the Arctic Ocean, the Barents Sea releases most of the incoming ocean heat originating from the North Atlantic. The related air-sea heat exchange plays a crucial role in both regulating the climate and determining the deep circulation in the Arctic Ocean and beyond. It was reported that the cooling efficiency of this cooling machine has decreased significantly. In this study, we find that the overall cooling efficiency did not really drop: When the cooling efficiency decreased in the southern Barents Sea, it increased in the northern Barents and Kara Seas, indicating that the cooling machine has expanded poleward. According to climate model projections, it is very likely that the cooling machine will continue to expand to the Kara Sea and then to the Arctic Basin in a warming climate. As a result, the Arctic Atlantification will be enhanced and pushed poleward in the future

Improving Simulations of the Upper Ocean by Inclusion of Surface Waves in the Mellor-Yamada Turbulence Scheme

The Mellor-Yamada turbulence closure scheme, used in many ocean circulation models, is often blamed for overly high simulated surface temperature and overly low simulated subsurface temperature in summer due to insufficient vertical mixing. Surface waves can enhance turbulence kinetic energy and mixing of the upper ocean via wave breaking and nonbreaking-wave-turbulence interaction. The influences of wave breaking and wave-turbulence interaction on the Mellor-Yamada scheme and upper ocean thermal structure are examined and compared with each other using one-dimensional and three-dimensional ocean circulation models. Model results show that the wave-turbulence interaction can effectively amend the problem of insufficient mixing in the classic Mellor-Yamada scheme. The behaviors of the Mellor-Yamada scheme, as well as the simulated upper ocean thermal structure, are significantly improved by adding a turbulence kinetic energy production term associated with wave-turbulence interaction. In contrast, mixing associated with wave breaking alone seems insufficient to improve significantly the simulations as its effect is limited to the very near-surface layers. Therefore, the effects of wave-turbulence interaction on the upper ocean are much more important than those of wave breaking

Arctic Ocean Freshwater in CMIP6 Coupled Models

In this study we assessed the representation of the sea surface salinity (SSS) and liquid freshwater content (LFWC) of the Arctic Ocean in the historical simulation of 31 CMIP6 models with comparison to 39 Coupled Model Intercomparison Project phase 5 (CMIP5) models, and investigated the projected changes in Arctic liquid and solid freshwater content and freshwater budget in scenarios with two different shared socioeconomic pathways (SSP2-4.5 and SSP5-8.5). No significant improvement was found in the SSS and LFWC simulation from CMIP5 to CMIP6, given the large model spreads in both CMIP phases. The overestimation of LFWC continues to be a common bias in CMIP6. In the historical simulation, the multi-model mean river runoff, net precipitation, Bering Strait and Barents Sea Opening (BSO) freshwater transports are 2,928 ± 1,068, 1,839 ± 3,424, 2,538 ± 1,009, and −636 ± 553 km3/year, respectively. In the last decade of the 21st century, CMIP6 MMM projects these budget terms to rise to 4,346 ± 1,484 km3/year (3,678 ± 1,255 km3/year), 3,866 ± 2,935 km3/year (3,145 ± 2,651 km3/year), 2,631 ± 1,119 km3/year (2,649 ± 1,141 km3/year) and 1,033 ± 1,496 km3/year (449 ± 1,222 km3/year) under SSP5-8.5 (SSP2-4.5). Arctic sea ice is expected to continue declining in the future, and sea ice meltwater flux is likely to decrease to about zero in the mid-21st century under both SSP2-4.5 and SSP5-8.5 scenarios. Liquid freshwater exiting Fram and Davis straits will be higher in the future, and the Fram Strait export will remain larger. The Arctic Ocean is projected to hold a total of 160,300 ± 62,330 km3 (141,590 ± 50,310 km3) liquid freshwater under SSP5-8.5 (SSP2-4.5) by 2100, about 60% (40%) more than its historical climatology

Examination of interannual variability of sea surface temperature in the Indian Ocean using the physical decomposition dethod

The physical decomposition method suggested by Qian (2012) is used to examine the interannual variability of sea surface temperature (SST) and anomaly (SSTA) in the Indian Ocean (IO) for the period 1945.2003. The monthly mean SSTs taken from the global ocean reanalysis produced by the Simple Ocean Data Assimilation (SODA) are decomposed into four terms. The first term is the zonally averaged monthly climatological SST ([Tt(ϕ)]), which features relatively warm surface waters in the tropical IO and relatively colder surface waters over the southern IO. This term also has a relatively low SST pool between the Equator and 20°N. The SST at the center of the pool in summer is about 1-2°C lower than in spring and autumn. The second term is the spatially-varying monthly climatological SSTA (Tt*(λ,ϕ)), due mainly to the topographic effect and seasonal variation in wind forcing. The values of Tt*(λ,ϕ) are negative over the western coastal waters and positive over the eastern coastal and shelf waters in the tropical and northern IO. The third term is the zonally-averaged transient SSTA([T(ϕ,t)']Y). The largest values of [T(ϕ,t)']Y occur over the subtropical and mid-latitudes of the IO, which differs from the SSTA in the tropical waters of the Pacific Ocean. Time series of zonally and meridionally averaged T(ϕ,t)'Y in the tropical-subtropical IO is strongly correlated with the Indian Ocean basin-wide (IOBW) mode. The fourth term is the spatially-varying transient SSTA (T(λ,ϕ,t)*Y']. The REOF analysis of the fourth term demonstrates that the first REOF is correlated strongly with the South Indian Ocean Dipole (SIOD) mode. The second REOF is correlated strongly with the equatorial Indian Ocean dipole (IOD) mode. The third REOF is highly correlated with the tropical IOBW mode

Arctic Ocean Simulations in the CMIP6 Ocean Model Intercomparison Project (OMIP)

oai:publications.copernicus.org:gmdd107357Arctic Ocean simulations in 19 global ocean-sea ice models participating in the Ocean Model Intercomparison Project (OMIP) of the CMIP6 are evaluated in this paper. Our results indicate that no significant improvements were achieved in the Arctic Ocean simulations from the previous Coordinated Ocean-ice Reference Experiments phase II (CORE-II) to the current OMIP. Large model biases and inter-model spread exist in the simulated mean state of the halocline and Atlantic Water layer in the OMIP models. Most of the OMIP models suffer from too thick and deep Atlantic Water layer, too deep halocline base, and large fresh biases in the halocline. The OMIP models largely agree on the inter-annual and decadal variability of the Arctic Ocean freshwater content and volume/heat/freshwater transports through the Arctic Ocean gateways. The models can reproduce observed changes in volume, heat and freshwater transports through the gateways except for the Bering Strait. Overall, the performance of the Arctic Ocean simulations is similar between the CORE2-forced OMIP-1 and JRA55-do-forced OMIP-2.</p