Abstract
Changes in the climate system over recent decades have had profound impacts on the mean state and variability of ocean circulation, while the Nordic Sea overflow has remained stable in volume transport during the last two decades. The changes of the overflow flux depend on the pressure difference at the depth of the overflow outlet on both sides of the Greenland-Scotland Ridge (GSR). Combining satellite altimeter data and the reanalysis hydrological data, the analysis found that the barotropic pressure difference and baroclinic pressure difference on both sides of the GSR had a good negative correlation from 1993 to 2015. Both are caused by changes in the properties of the upper water, and the total pressure difference has no trend change. The weakening of deep convection can only change the temperature and salt structure of the Nordic Sea, but cannot reduce the mass of the water column. Therefore, the stable pressure difference drives a stable overflow. The overflow water storage in the Nordic Sea is decreasing, which may be caused by the reduction of local overflow water production and the constant overflow flux. When the upper interface of the overflow water body in the Nordic Sea is close to or below the outlet depth, the overflow is likely to greatly slow down or even experience a hiatus in the future, which deserves more attention.
Highlights
As an important driver of thermohaline circulation, the Nordic Sea overflow has a profound impact on environmental changes in the Arctic and even the world
Z where Ptrop represents the barotropic pressure and Pclin is the baroclinic pressure; ρ0 = 1028 kg/m3 is the surface seawater density; g = 9.8 m/s2 is the gravitational acceleration; ζ is the sea level height, and here is taken as Sea Level Anomaly (SLA); ρ is the seawater density, which is derived from the temperature and salt data of EN4; z is the calculated pressure depth, and unless otherwise specified, it is taken as 840 m, which is the maximum depth of the Greenland-Scotland Ridge (GSR) sill
Based on the satellite altimeter data and the reanalysis hydrological data, we obtained a slight increase in the pressure difference between the two sides of the GSR from 1995 to 2015
Summary
As an important driver of thermohaline circulation, the Nordic Sea overflow has a profound impact on environmental changes in the Arctic and even the world. The total pressure difference is equal to the barotropic presalthough there is a decreasing trend in atmospheric forcing from 1993 to 2016, the depth of sure difference plus the baroclinic pressure difference, depending on the local and reconvection in the Greenland Sea in winter has a deepening tendency This is due to the mote physical processes, such as convection, mixing, and circulation, which further deincrease in the salinity of seawater in the upper 1500 m, which results in the weakening of termine the overflow flux of the Nordic Sea [4].
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