Abstract
Maintaining North Atlantic (NA) intra-basin near-surface salinity (NSS) contrast between the high NSS (>37.0) in the subtropical NA (STNA) and low NSS (<35.0) in the subpolar NA (SPNA) has been shown to be important in sustaining the strength of the Atlantic Meridional Overturning Circulation. Evaporation (E) exceeding precipitation (P) in the STNA is primarily responsible for the high NSS there, whereas P dominating E in the SPNA contributes to its low NSS. With a basic understanding of NA intra-basin moisture transport, a correlation analysis was conducted between E-P/NSS over the NA subpolar gyre (SPG) and E-P across the rest of the NA over the 1985–2012 time period. Significant anti-correlations exist between E-P/NSS over the NA SPG and E-P over the central/northern STNA. This suggests that during times of high E over the central/northern STNA there is high (low) precipitation (NSS) over the SPG demonstrating a relationship likely exists between E over the STNA and NSS over the SPG. The maximum anti-correlated area is poleward of the maximum E-P location in the STNA, which is examined. These results provide a first step to ultimately utilizing NSS in the NA as a proxy for estimating changes in the hydrological cycle.
Highlights
Over 77% of global P and 85% of global E occurs over the ocean[7,8,9]
The strength and direction of the divergence of water vapor from the subtropical NA (STNA) varies with seasons[31,32], in all four seasons it is captured and precipitated in four different regions: (i) along the Atlantic Intertropical Convergence Zone (ITCZ), (ii) in the eastern tropical Pacific ITCZ, (iii) off the East Coast of North America, and (iv) in the subpolar North Atlantic (SPNA, approximate area shown in red box of Fig. 2a)
Since the ITCZ dynamics and potential impacts on tropical near-surface salinity (NSS) is outside our focus on the extratropical NSS interconnections, only the subpolar NA (SPNA) and STNA NSS contrasts and their relations to the hydrological cycle are the subject of this study
Summary
Over 77% of global P and 85% of global E occurs over the ocean[7,8,9]. While most of P and E occurs over the ocean, their historical estimates are plagued by large uncertainties in satellite observations[10,11], and assessing long-term change of E minus P (E-P) directly from measurements is not feasible[12,13]. The satellite observation record (~1979-present) is too short to assess long-term water cycle changes when compared to multi-decadal variability, and in situ data pre-1979 is full of large data gaps over the ocean[13]. Models have shown that the inter-basin moisture transport—termed an “Atmospheric Bridge”27 —and resulting NSS contrasts between the Pacific and Atlantic is a key controlling mechanism of the global thermohaline circulation[27,28,29]. This inter-basin salinity amplification is projected to continue[19]. In freshwater “hosing” model simulations[4,27,29,30], high-latitudinal freshening and subtropical-subpolar NSS contrast in the NA have risen as an important if not key factor[3,4] impacting the AMOC, while similar freshening in the Southern Ocean did not inflict noticeable AMOC change[4]
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