The Bering Strait and the Southern Ocean winds' grip on the world climate.

摘要

The Bering Strait's Grip on the World Climate. The Holocene interglacial period of the last 10,000 years and the penultimate interglacial ∼125,000 years ago have been characterized by distinctly stable climates. Here, we propose that the switch between the stable and unstable systems is the opening and closure of the Bering Strait (BS). A semi-global analytical ocean model (which includes both wind and thermohaline processes) is used to show that, during interglacial periods perturbations in North Atlantic Deep Water (NADW) formation are damped out because of a novel BS freshwater feedback mechanism. This new feedback mechanism is due to the strong winds in the Southern Ocean which, with an open BS, quickly [O(10) years)] flush any low salinity anomalies out of the Atlantic and into the Pacific Ocean. During glacial periods, the stabilizing feedback is prevented by the closure of the BS which traps the anomalies within the Atlantic, causing long lasting perturbations.; The Island Wind-Buoyancy Paradox. In recent years, a variety of studies have suggested that the meridional overturning circulation is at least partially controlled by the Southern Ocean winds. However, the overturning requires transformation of water masses, a process driven by buoyancy fluxes. This seems paradoxical as the wind and buoyancy fluxes are generally thought to be independent.; The paradox is resolved qualitatively, using salinity and temperature mixed dynamical-box models and a temperature slab model, and quantitatively, employing a numerical model. The salinity and temperature box models and the slab model suggest that stronger southern winds will tend to weaken the vertical and horizontal salinity stratification so that it is easier for the conversion of deep to surface water (and vice versa) to take place.; The (process orientated) numerical model is adapted to include a thermodynamic parameterization for the surface heat and freshwater fluxes. In response to stronger southern winds, the thermocline thickens in the north, releases more heat to the atmosphere and, therefore, converts more surface to deep water.