Formation of salinity maximum water and its contribution to the overturning circulation in the North Atlantic as revealed by a global general circulation model

Abstract

[1] The formation of salinity maximum water in the North Atlantic is investigated using a simulated passive tracer and its adjoint. The results reveal that most salinity maximum water in the North Atlantic comes from the northwestern part of the subtropical gyre, and direct contribution from the evaporation-precipitation maximum region via the surface Ekman current is minor. Water originating from the evaporation-precipitation maximum region has to recirculate in the subtropical gyre before entering the sea surface salinity maximum region from the northwest. Once subducted, some portion (~10%) of the salinity maximum water enters the equatorial region in the shallow subtropical cell, but most (~70%) of it appears to turn northward to join the North Atlantic Deep Water. The latter pathway involves a three-dimensional circulation. When the warm, fresh surface water flows northward along the western boundary, it turns eastward in the northern subtropical gyre. As a result of the large excess of evaporation over precipitation, this water gradually gains its salinity on the route, until it reaches the sea surface salinity maximum region in the central subtropical gyre. From there, the salinity maximum water is subducted and flows back to the western boundary in the depth range of the thermocline. With its high-salinity nature, a major portion of this water penetrates into the subpolar region and directly contributes to the deep thermohaline circulation.Citation: Qu, T., S. Gao, and I. Fukumori (2013), Formation of salinity maximum water and its contribution to the overturning circulation in the North Atlantic as revealed by a global general circulation model,

Salinity and Temperature Balances at the SPURS Central Mooring During Fall and Winter

“…The SPURS-1 field campaign took place over a one-year period during [2012][2013] in the North Atlantic Ocean subtropical gyre, near the location where SSS is highest on average ( Figure 1a). The relatively salty waters found at the surface here are subducted and carried downward and southward in a "river of salt" by large-scale currents (Schmitt and Blair, 2015, in this issue) and eventually westward into the Gulf Stream and northward into the subpolar oceans (e.g., Qu et al, 2013). The overarching goal of the SPURS field campaign and associated modeling activities is to improve understanding of the physical processes influencing the formation and evolution of the salinity maximum.…”

Poleward Shift in Ventilation of the North Atlantic Subtropical Underwater

“…STUW has relatively short residence time (<10 years), and its connection to the tropical and subpolar regions via interior pathways can impart the subtropical salinity influence to both the equatorial thermocline (Fine et al, 2001;Gu & Philander, 1997;McCreary & Lu, 1994;Zhang et al, 2003) and the North Atlantic Deep Water (Burkholder & Lozier, 2011;Qu et al, 2013). Because of these broad-scale impacts of STUW, there has been growing interest in the cause of its decadal trends.…”

Potential Vorticity Structure in the North Atlantic Western Boundary Current from Underwater Glider Observations

“…Qu et al (2013) used a simulated passive tracer and its adjoint to show that this salinity maximum water forms at the surface in the northwestern subtropical gyre, then subducts as it circulates around the gyre. The largest cross-stream property gradients occurred along isopycnals that were observed to outcrop locally at least once during the observational period (the densest such isopycnal at a given cross-stream position is indicated by the dashed line in Fig.…”