A multi-decadal meridional displacement of the Subpolar Front in the Newfoundland Basin

Abstract

Abstract.Observations since the 1950s show a multidecadal cycle of a meridional displacement of the Subpolar Front (SPF) in the Newfoundland Basin (NFB) in the North Atlantic. The SPF displacement is associated with corresponding variations in the path of the North Atlantic Current. We use the ocean general circulation model MPIOM with enhanced horizontal and vertical resolutions and forced with NCEP/NCAR reanalysis data to study the relation of the SPF displacement to atmospheric forcing, intensities of the subpolar gyre (SPG) and Meridional Overturning Circulation (MOC), and Labrador Sea Water (LSW) volume. The simulations indicate that the SPF displacement is associated with a circulation anomaly between the SPG and the subtropical gyre (STG), an inter-gyre gyre with a multidecadal time scale. A sensitivity experiment indicates that both wind stress curl (WSC) and heat fluxes (which match LSW changes) contribute to the circulation anomalies in the frontal region and to the SPF displacement. An anticyclonic inter-gyre gyre is related to negative WSC and LSW anomalies and to a SPF north of its climatological position, indicating an expanding STG. A cyclonic inter-gyre gyre is related to positive WSC and LSW anomalies and a SPF south of its climatological position, indicating an expanding SPG. Therefore, the mean latitudinal position of the SPF in the NFB (a "SPF index") could be an indicator of the amount of LSW in the inter-gyre region. Spreading of LSW anomalies intensifies the MOC, suggesting our SPF index as predictor of the MOC intensity at multi-decadal time scales. The meridional displacement of the SPF has a pronounced influence on the meridional heat transport, both on its gyre and overturning components.

North Atlantic Sub‐Polar Gyre Climate Index: A New Approach

“…The NASPG weakens in response to increasing SSH with 1‐year lag before 2000 ( r SSH =−0.7, 1‐year lag). Barrier et al, (, and reference therein) associated the weakening of the NASPG in 1995–1996 with the abrupt shift of the NAO index; Núñez‐Riboni et al () on the other hand attributed the weakening of the NASPG in the 1990s to changes in buoyancy fluxes. If we also consider the NAO to represent the atmospheric forcing, only after 2000 the weakening of the NASPG occurs in correspondence with NAO changes ( r nao =−0.58, −3‐year lag).…”

“…Breckenfelder et al () defined the SPF at the latitude of the steep slope of the 27.68‐kg/m 3 isopycnal, Desbruyéres et al () defined its position from the longitude at which the 8 °C isotherm intersects the 200‐m horizon at 53°N, and Núñez‐Riboni et al () defined the SPF as the mean latitude at 500‐m depth of the region between 30°W to 50°W and 35°N to 55°N where the magnitude of the horizontal density gradient is larger than its space mean plus 1/4 of its standard deviation. The movement of the SPF following Breckenfelder et al () correlates with the variations of the NASPG area ( r =0.5, with −1‐year lag), following Desbruyéres et al () it correlates with posS in the period 1959–2000 ( r =0.64) and with the area in the period 2001–2017 ( r =0.62, 1‐year lag), lastly following Núñez‐Riboni et al () SPF correlates with the area in 1959–2000 ( r =−0.58, −1‐year lag) and with Ψ v , posE, posS, and area in 2001–2017 ( r =0.7 without a lag, 0.61 with 4‐year lag, 0.73 with 2‐year lag, and 0.7 with 4‐year lag, respectively). In the eastern North Atlantic the SPF and water mass properties in general are more variable, so as noted previously by Foukal and Lozier () the SPF movements might not be captured by the variability of one latitude.…”

Sea-surface dynamics and palaeoenvironmental changes in the North Atlantic Ocean (IODP Site U1313) during Marine Isotope Stage 19 inferred from coccolithophore assemblages

“…The subpolar gyre is a region of strong interaction between ocean and atmosphere and, at multidecadal time scales, its variability has been documented to be mainly triggered by the North Atlantic Oscillation (NAO; Eden and Jung, 2001;Núñez-Riboni et al, 2012), a climatic phenomenon in the North Atlantic affecting the atmospheric masses between the pressure centres of the Azores High (AH) and Icelandic Low (IL) (Fig. 1a).…”

Coupling between the North Atlantic subpolar gyre vigor and forest fire activity in northern Scandinavia

“…5d and 6d). The ocean circulation pattern emerging between the subpolar and subtropical gyres correspond to the so-called intergyre gyre (Marshall et al, 2001b, a;Núñez Riboni et al, 2012), defined as the leading empirical orthogonal function (EOF) of the sea surface height (Núñez Riboni et al, 2012). The oceanic circulation pattern is in turn coupled to decadal-to-multidecadal variability in the NAO.…”

“…Accordingly, Labrador Sea water propagates southwards, indicating an expanding subpolar gyre. Hence, the polar front in the North Atlantic is displaced southwards, resulting in cold, subpolar water advection into the subtropical region in the Newfoundland Basin (Núñez Riboni et al, 2012).…”