Impacts of Ice-Ocean Stress on the Subpolar Southern Ocean:Role of the Ocean Surface Current

The mechanical influences involved in the interaction between the Antarctic sea ice and ocean surface current(OSC)on the subpolar Southern Ocean have been systematically investigated for the first time by conducting two simulations that include and exclude the OSC in the calculation of the ice-ocean stress(IOS), using an eddy-permitting coupled ocean-sea ice global model. By comparing the results of these two experiments, significant increases of 5%, 27%, and 24%, were found in the subpolar Southern Ocean when excluding the OSC in the IOS calculation for the ocean surface stress,upwelling, and downwelling, respectively. Excluding the OSC in the IOS calculation also visibly strengthens the total mechanical energy input to the OSC by about 16%, and increases the eddy kinetic energy and mean kinetic energy by about38% and 12%, respectively. Moreover, the response of the meridional overturning circulation in the Southern Ocean yields respective increases of about 16% and 15% for the upper and lower branches;and the subpolar gyres are also found to considerably intensify, by about 12%, 11%, and 11% in the Weddell Gyre, the Ross Gyre, and the Australian-Antarctic Gyre, respectively. The strengthened ocean circulations and Ekman pumping result in a warmer sea surface temperature(SST), and hence an incremental surface heat loss. The increased sea ice drift and warm SST lead to an expansion of the sea ice area and a reduction of sea ice volume. These results emphasize the importance of OSCs in the air-sea-ice interactions on the global ocean circulations and the mass balance of Antarctic ice shelves, and this component may become more significant as the rapid change of Antarctic sea ice.

鄂西渝东地区页岩岩石物理参数试验研究

研究页岩气储层岩石的物理参数及其地球物理响应特征对其资源评价具有重要意义。基于鄂西渝东地区海相页岩露头标本，在实验室内测量页岩的密度、声波速度、渗透率和复电阻率。结果表明，研究区页岩具有低密度、低渗透率、相对中高电阻率的特征，但页岩极化率相差较大，最高达40．8％，最低14．5％，分为高极化率、中极化率和低极化率3个层次。研究区页岩的矿物成分主要为石英和黏土，但下志留统龙马溪组页岩的脆性矿物含量更高，下寒武统水井沱组页岩方解石和白云石含量相较于龙马溪组更高。

A Bayesian Inference Approach to Reduce Uncertainty in Magnetotelluric Inversion: A Synthetic Case Study

The deterministic geophysical inversion methods are dominant when inverting magnetotelluric data whereby its results largely depends on the assumed initial model and only a single representative solution is obtained. A common problem to this approach is that all inversion techniques suffer from non-uniqueness since all model solutions are subjected to errors, under-determination and uncertainty. A statistical approach in nature is a possible solution to this problem as it can provide extensive information about unknown parameters. In this paper, we developed a 1D Bayesian inversion code based Metropolis-Hastings algorithm whereby the uncertainty of the earth model parameters were quantified by examining the posterior model distribution. As a test, we applied the inversion algorithm to synthetic model data obtained from available literature based on a three layer model (K, H, A and Q). The frequency for the magnetotelluric impedance data was generated from 0.01 to 100 Hz. A 5% Gaussian noise was added at each frequency in order to simulate errors to the synthetic results. The developed algorithm has been successfully applied to all types of models and results obtained have demonstrated a good compatibility with the initial synthetic model data.

On the Multiscale Oceanic Heat Transports Toward the Bases of the Antarctic Ice Shelves

The mass balance of the Antarctic Ice Sheet(AIS)is important to global sea-level change.The AIS loses mass mainly through basal melting and subsequent calving of the Antarctic ice shelves.However,the simulated basal melting rates are very uncertain in ice sheet models,partially resulting from the poor understanding of oceanic heat transports.In this article,we review the recent progress in understanding and simulating such heat transports.Regulated by major circulation features,Circumpolar Deep Water(CDW)is much closer to the Bellingshausen-Amundsen Seas and the Cooperation Sea(60°E to 90°E)and the sector further east to 160°E.The ice shelves within these sectors are experiencing enhanced basal melting resulting from tropical forcing and intensified westerlies.Around West Antarctica,the isopycnal structure favors the delivery of CDW across slopes and shelves,while around East Antarctica,the persistent and strong westward Antarctic Slope Current(Front)acts to prevent warm-water intrusion.Both eddies and troughs favor heat transport to the fronts of the ice shelves and even into the cavities.The sharp contrast between the water column thicknesses on both sides of ice shelf fronts blocks the barotropic inflows and can excite topographic Rossby waves.Inside the cavities,the heat fluxes to the bases of the ice shelves are controlled by the cavity geometry,the circulations in the cavities,and the properties of the water masses beneath the ice shelves.Limited direct observations of cavities have promoted the development of various models.To improve basal melting simulations,meltwater plume models have been developed to study meltwater-laden mixed layer dynamics by increasing the vertical resolution,with recent advanced studies considering the vertical structures of frazil ice concentration and velocity.To reduce the uncertainties in the simulated and projected basal mass loss of the Antarctic ice shelves,future efforts should be devoted to improving the bathymetry and cavity geometry,investigating small-scale processes and parameterizing these processes in coupled climate-ice sheet models,and quantifying the feedback from the mass loss of the AIS.