Interannual Variability of the Mixed Layer Winter Convection and Spice Injection in the Eastern Subtropical North Atlantic

Abstract

International audienceThe Argo dataset is used to study the winter upper-ocean conditions in the northeastern subtropical (NEA) Atlantic during 2006–12. During late winter 2010, the mixed layer depth is abnormally shallow and a negative anomaly of density-compensated salinity, the so-called spiciness, is generated in the permanent pycnocline. This is primarily explained by unusual weak air–sea buoyancy flux during the late winter 2010, in contrast with the five other studied winters. Particularly deep mixed layers and strong spiciness anomalies are observed during late winter 2012. The 2010 winter conditions appear to be related to historically low North Atlantic Oscillation (NAO) and high tropical North Atlantic index (TNA). Interannual variability of the eastern subtropical mixed layer is further investigated using a simple 1D bulk model of mean temperature and salinity linear profiles, based on turbulent kinetic energy conservation in the upper-ocean layer, and forced only with seasonal air–sea buoyancy forcing corresponding to fall–winter 2006–12. It suggests that year-to-year variability of the winter convective mixing driven by atmospheric buoyancy flux is able to generate interannual variability of both late winter mixed layer depth and spiciness in a strongly compensated layer at the base of the mixed layer and in the permanent pycnocline

Poleward Shift in Ventilation of the North Atlantic Subtropical Underwater

“…Qiu and Huang (1995) pointed out that the annual excursion of the mixed layer depth greatly exceeds the vertical Ekman pumping. As a result, the subduction rates are governed primarily by the rapid shoaling of the mixed-layer depth in response to surface buoyancy gain (Kolodziejczyk et al, 2015;Liu & Huang, 2011;Trossman et al, 2009). Qu et al (2016) provided additional evidence for the sensitivity of STUW to the mixed layer change: STUW is produced at the intersection of the mixed layer front (or the mixed layer sharp transition zone) and the outcrop isohalines.…”

Atlantic Water Transformation Along Its Poleward Pathway Across the Nordic Seas

“…For instance, AW is a warm and salty water mass compared to cold and fresh polar waters of same density. From a general perspective, spicy waters are formed in the subtropics by the strong evaporation and vertical mixing (Kolodziejczyk et al, ; Yeager & Large, ) before flowing poleward along with western boundary currents (Laurian et al, ). At higher latitudes, those waters play an important role in air‐sea interactions and oceanic heat transport (Kwon et al, ).…”

Surface Salinity in the North Atlantic Subtropical Gyre During the STRASSE/SPURS Summer 2012 Cruise

“…There was weak correlation between temperature and salinity variability in this region and during this season. Kolodziejczyk et al (2014b) indicated that summer 2012 conditions in the salinity maximum were influenced by anomalously salty subsurface waters that originated farther to the northeast at the end of the previous winter and by locally salty surface waters.…”