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Kristofer Döös, Johan Nilsson, Jonas Nycander, Laurent Brodeau, and Maxime Ballarotta

1. Introduction The World Ocean thermohaline circulation is frequently idealized as a conveyor belt transporting heat and freshwater from the Indo–Pacific to the Atlantic ( Broecker 1987 ). This interocean exchange of heat and freshwater, closely associated with the formation of North Atlantic Deep Water (NADW), is of key importance for the climatic and hydrographic differences between the North Atlantic and the North Pacific. It should be noted, however, that the freshwater transport into the

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Alain Colin de Verdière

1. Introduction The fate of the thermohaline circulation (THC) is now a leading research subject, given the threat of global warming and the possible role played by this circulation in the variability of paleoclimates—a research topic pioneered by Broecker (1987) . Because the THC is sensitive to freshwater fluxes, the salinity decrease observed over the subpolar North Atlantic ( Dickson et al. 2002 ; Curry and Mauritzen 2005 ) and the accelerated melting of Greenland ice ( Rignot and

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A. Colin de Verdière

1. Introduction Oscillations in OGCMs under mixed surface boundary conditions (restoring on surface temperature, imposed freshwater flux) have now been widely reported and are found to occur in several frequency bands: decadal, centennial, millennial [see the reviews by Weaver and Hughes (1992) and Dijkstra and Ghil (2005) ]. A strong incentive for a better understanding of the oscillations of the thermohaline circulation (THC) comes from the paleoclimatic evidence originating from ice cores

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Aixue Hu, Bette L. Otto-Bliesner, Gerald A. Meehl, Weiqing Han, Carrie Morrill, Esther C. Brady, and Bruce Briegleb

1. Introduction The thermohaline circulation [(THC), or the meridional overturning circulation (MOC)] is a global-scale, three-dimensional oceanic circulation. It transports warmer and saltier upper-ocean water into the subpolar North Atlantic, where that water loses its heat to the atmosphere and becomes cold and dense, then sinks to the deep ocean in the Labrador Sea and the Greenland–Iceland–Norwegian Seas forming the North Atlantic Deep Water. This deep water flows southward and upwells

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Jan D. Zika, Matthew H. England, and Willem P. Sijp

hydrological cycle. The water masses through which the global conveyor is thought to travel are each defined by unique temperature and salinity properties. Here, we investigate the ocean circulation in temperature–salinity (thermohaline) coordinates. By doing so, we are able to determine whether a global conveyor of the scale previously proposed based on observed tracer fields ( Gordon 1986 ; Broecker 1991 ) exists in a climate model. In addition, we argue that such analysis provides a useful framework

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Laure Zanna and Eli Tziperman

1. Introduction The North Atlantic Ocean sea surface temperature (SST) and salinity (SSS) exhibit variability on different time scales from interannual (e.g., Levitus 1989 ) to interdecadal and decadal ( Kushnir 1994 ) that are often attributed to the variability of the thermohaline circulation (THC). Numerical models also show THC oscillations on decadal time scales (e.g., Bryan et al. 2006 ; Delworth and Greatbatch 2000 ; Jungclaus et al. 2005 ) that can possibly be explained as a small

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Yosef Ashkenazy and Eli Tziperman

1. Introduction The ocean, and the ocean meridional overturning circulation [here referred to as the thermohaline circulation (THC; Wunsch 2002 )] in particular, are normally assumed to play an important role in climate dynamics, including both past climate variability such as the Heinrich ( Heinrich 1988 ) and Dansgaard–Oeschger (DO) events ( Dansgaard et al. 1984 ), and possible future climate change ( Houghton et al. 2001 ). The multiple equilibria of the THC ( Marotzke et al. 1988

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Florian Sévellec, Mahdi Ben Jelloul, and Thierry Huck

1. Introduction One of the expected consequences of global warming is the modification of the water cycle, one of the main forcing mechanisms of the ocean thermohaline circulation. In actuality, freshwater fluxes have a local influence on the surface salinity, and thus on the ocean dynamics. Josey and Marsh (2005) show that sea surface salinity has been modified since the mid-1970s because of increased precipitation in the North Atlantic Ocean subpolar gyre. Modification of ocean salinity in

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Arnaud Czaja

circulation over the North Atlantic and Pacific, differences unambiguously attributable to processes independent of the state of the ocean, might be instrumental in systematically favoring the North Atlantic for higher surface salinities. In doing so, it is hoped that one can break the circular chain of arguments traditionally invoked in discussions of the dynamics of the thermohaline circulation. In essence, we propose to build upon Warren’s (1983) idea that the southwest–northeast tilt of the

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Xiaogang Wu and Mu Mu

1. Introduction In recent years, the climate variation in the world has captured the public’s eye in which the thermohaline circulation (THC) plays an important role. Now, both Past Global Changes (PAGES) and Climate Variability and Predictability (CLIVAR), which are two of the most important international plans in the global climate research, give emphasis to the studies of global THC. THC is considered as a density flow, which is driven by the temperature and salinity of ocean. There have

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