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At several locations around Antarctica, dense water is formed as a result of intense sea ice formation. When this dense water becomes sufficiently denser than the surrounding water, it descends the continental slope and forms Antarctic Bottom Water (AABW). This study presents the AABW formation off the coast of Cape Darnley [Cape Darnley Bottom Water (CDBW)] in East Antarctica, using a nonhydrostatic model. The model is forced for 8 months by a temporally uniform surface salt flux (because of sea ice formation) estimated from Advanced Microwave Scanning Radiometer for Earth Observing System (EOS; AMSR-E) data and a heat budget calculation. The authors reproduce AABW formation and associated periodic downslope flows of dense water. Descending pathways of dense water are largely determined by the topography; most dense water flows into depressions on the continental shelf, advects onto the continental slope, and is steered downslope to greater depths by the canyons. Intense sea ice formation is the most important factor in the formation of AABW off Cape Darnley, and the existence of depressions is of only minor importance for the flux of CDBW. The mechanism responsible for the periodic downslope flow of dense water is further analyzed using an idealized model setup. The period of dense water outflow is regulated primarily by the topographic beta effect. [ABSTRACT FROM AUTHOR]

Cabbeling effect on the water mass transformation in the Southern Ocean is investigated with the use of an eddy-resolving Southern Ocean model. A significant amount of water is densified by cabbeling: water mass transformation rates are about 4 Sv (1 Sv ≡ 106 m3 s−1) for transformation from surface/thermocline water to Subantarctic Mode Water (SAMW), about 7 Sv for transformation from SAMW to Antarctic Intermediate Water (AAIW), and about 5 Sv for transformation from AAIW to Upper Circumpolar Deep Water. These diapycnal volume transports occur around the Antarctic Circumpolar Current (ACC), where mesoscale eddies are active. The water mass transformation by cabbeling in this study is also characterized by a large amount of densification of Lower Circumpolar Deep Water (LCDW) into Antarctic Bottom Water (AABW) (about 9 Sv). Large diapycnal velocity is found not only along the ACC but also along the coast of Antarctica at the boundary between LCDW and AABW. It is found that about 3 Sv of LCDW is densified into AABW by cabbeling on the continental slopes of Antarctica in this study. This densification is not small compared with observational and numerical estimates on the AABW formation rate, which ranges from 10 to 20 Sv. [ABSTRACT FROM AUTHOR]

The energy budget of global thermohaline circulation (THC) is numerically investigated using an ocean general circulation model (OGCM) under a realistic configuration. Earlier studies just discuss a globally integrated energy budget. This study intends to draw a comprehensive picture of the global THC by separately calculating the energy budgets for three basins (the Atlantic, Indo-Pacific, and Southern Ocean). The largest mechanical energy source is a kinetic energy (KE) input to the general circulation by wind. Of that, 0.3 TW is converted to gravitational potential energy (GPE), and 80% of the energy conversion occurs in the Southern Ocean. Almost the same quantity of GPE is supplied by vertical mixing. Injected GPE is almost equally dissipated by convective adjustment and the effect of cabbeling, and a large part of that is consumed in the Southern Ocean. A dominant role of the Southern Ocean in the energy balance of THC and importance of the interbasin transport of GPE are found. Then, the enhancement of the meridional overturning circulation in the Atlantic induced by wind in the Southern Ocean is examined. Calculating the energy budget anomaly enables the authors to identify its mechanism as a component of THC. [ABSTRACT FROM AUTHOR]

We compared the climate response of doubled CO2 equilibrium experiments (2 × CO2) by atmosphere–slab ocean coupled general circulation models (ASGCMs) and that of 1% per year CO2 increase experiments (1%CO2 by atmosphere–ocean coupled general circulation models (AOGCMs) using eight state-of-the-art climate models. Climate feedback processes in 2 × CO2 are different from those in 1%CO2, and the equilibrium climate sensitivity in 2 × CO2 is different from the effective climate sensitivity in 1%CO2. The difference between and is from −1.3 to 1.6 K, a large part of which can be explained by the difference in the ice-albedo and cloud feedback. The largest contribution is cloud SW feedback, and the difference in cloud SW feedback for 2 × CO2 and 1%CO2 could be determined by the distribution of the SAT anomaly which causes differences in the atmospheric thermal structure. An important factor which determines the difference in ice-albedo feedback is the initial sea ice distribution at the Southern Ocean, which is generally overestimated in 2 × CO2 as compared to 1%CO2 and observation. Through the comparison of climate feedback processes in 2 × CO2 and 1%CO2, the possible behaviour of the time evolution of is discussed. [ABSTRACT FROM AUTHOR]

Numerical experiments are conducted using a sea ice-coupled ocean general circulation model (OGCM) forced by two different freshwater flux datasets. These two datasets are the National Centers for Environmental Prediction-National Center for Atmospheric Research (NCEP-NCAR) reanalysis and the European Centre for Medium-Range Weather Forecasts (ECMWF)-based climatological datasets, which are widely used to force OGCMs. It is found that the strength of the simulated Atlantic deep circulation considerably differs between the two experiments. To explain the resulting difference, these two freshwater fluxes are compared and additional experiments are carried out, focusing on the difference at northern high and midlatitudes, at low latitudes, and in the Southern Ocean, separately. An examination of these experiments shows that the difference in the simulated Atlantic deep circulation comes mainly from the difference in the river runoff data, especially at the northern high latitudes. Although the amount of the difference in the river runoff data at northern high latitudes is small, compared with that of the evaporation and the precipitation in other regions, it has a considerable influence on the strength of the Atlantic deep circulation. It indicates that the strength of the Atlantic deep circulation is affected more significantly by the accuracy of the river runoff data than that of the evaporation and the precipitation data. [ABSTRACT FROM AUTHOR]