Causes and Mechanisms of Global Warming/Climate Change

Comparison of the average mean surface air temperature around the world during 1951–1978 with that for 2010–2019 shows that the bulk of the warming is around the North Atlantic/Arctic region in contrast to the Antarctic ice sheet. Obviously, the temperature change is not global. Since there is a substantial difference between solar heat absorption between the equator and the poles, heat must be moving to the North Pole by surface ocean currents and tropical cyclones. The cold, dry Arctic air coming from Siberia picks up heat and moisture from the open oceans, making the sea water denser so that the warm water sinks slowly down to c. 2000 m. A deep-water thermohaline flow (THC) transports the excess hot (c. 18°C) water south to Antarctica. It is replaced by a cold (c. 2°C) surface water from that area. The latter quickly cool western Europe and Siberia, and glaciers start to advance in Greenland within about 10 years. The THC flow decreases in Interglacials, causing the increased build-up of heat in the Northern Hemisphere (c. 60% currently stored in the Atlantic Ocean), and the ice cover in the Arctic Ocean thaws. Several such cycles may take place during a single major cold event.

Relating thermohaline simulation of salt dissolution to land collapse at a Transylvanian salt diapir, Romania

<p>The presented study estimates salt dissolution caused by groundwater around a salt diapir in the Transylvanian Basin, which is facing land-collapse hazards related to historic salt mining activities. Because the amount of salt dissolution is controlled by the concentration gradients and fluxes near vulnerable areas of the salt dome, specific attention has been given to hydrogeological boundary conditions. They include the hydraulic role of possible more permeable fault zones along the salt dome, and the potential access to the salt diapir of over-pressurized subsaturated groundwater within regional scale sandstone layers. A structural three-dimensional (3D) model of the salt diapir, the adjacent basin sediments, and the mining galleries was developed based on existing maps, borehole data, own field observations, and geological publications of the Transylvanian Basin. The salt dissolution potential was simulated with 2D vertical thermohaline flow and transport model scenarios along the southeastern flank of the diapir. Results showed that the following factors increase the salt dissolution capacity along the upper 180 m of the diapir: (1) the presence of more permeable Quaternary alluvial sediments in connection with a fault zone of higher permeability along the diapir, and (2) the presence of more permeable sandstone units within the Miocene sediments in the east of the diapir, which provide freshwater access to the upper parts of the diapir. Thermohaline simulation with viscosity variation of the fluid, instead of a constant viscosity, influences the resulting salt fluxes by up to 50% within studied temperature ranges of 10 to 60°C in the model domain. The range of theoretical dissolution rates along the upper 180 m of the diapir supports the hypothesis that cavern collapse is more likely to occur where cavern side walls have already been mined to almost no remaining side walls of rock salt, which is the case in the southeastern part of the diapir. A past land collapse from 2010, which formed a 70-90 m wide saline lake, has occurred in this area southeast of the diapir appearing to be the more vulnerable to land collapse.</p><p>Zechner, E., Dresmann, H., Mocuţa, M., Danchiv, A., Huggenberger, P., Scheidler, S., Wiesmeier, S., Popa, I., Zlibut, A. (2019): Salt dissolution potential estimated from two-dimensional vertical thermohaline flow and transport modeling along a Transylvanian salt diapir, Romania, Hydrogeol. J., 27, 1245-1256, https://doi.org/10.1007/s10040-018-1912-1.</p>

Physics and Dynamics of the Oceans

This chapter focuses on the physics and dynamics of the ocean. It describes the variability of salinity and surface temperature, as well as the vertical temperature structure of the ocean, with the thermocline separating the variable top layer from the deeper ocean. It then describes the key forces in the ocean, as well as the geostrophic balance due to the Coriolis force and density differences. It derives the equations for the change of velocity with depth, the Ekman flow. Barotropic flow and baroclinic flow are elucidated and the general circulation of the ocean, with gyres and the effect of vorticity on their structure, is shown. The thermohaline circulation of the ocean with surface flow and returning deep ocean flows is described. Next, a simple model is used to show how salinity interacts with the thermohaline flow. Finally, as an example of ocean–land interaction, the El Niño phenomenon is described.

Localization of Multidecadal Variability. Part II: Spectral Origin of Multidecadal Modes

In a companion paper, the authors have shown that in an idealized Atlantic–Pacific Ocean configuration with a conveyor-type overturning circulation, localized multidecadal variability occurs in the Atlantic. Results suggest that the multidecadal variability originates from the instability of the three-dimensional thermohaline circulation and that the physics of the spatial patterns of the SST anomalies can be understood from a study of an Atlantic-only configuration. Specific internal (multidecadal) modes, which obtain a positive growth factor depending on the background thermohaline flow, are associated with the instability. In this paper, the spectral origin of these internal modes is studied using eigensolution continuation techniques. As in the single-hemispheric case, multidecadal modes arise through mergers of so-called SST modes. In the double-hemispheric case studied here, there actually are two types of multidecadal modes that lead to oscillatory behavior. Depending on the background conditions, one of these oscillatory flows is preferred.