Distribution of intermediate water masses in the subtropical northeast Atlantic

Abstract

Abstract. This work presents the quantitative study of climatological distributions of mid-depth source water types in the northeast (NE) Atlantic using the optimum multiparameter analysis (OMP). It generalises a number of regional results from particular synoptic sections. The cores of the Mediterranean Water (MW), the modified Antarctic Intermediate Water (mAAIW) and the Subarctic Intermediate Water (SAIW) are detected and spatial variations of their depth/density are obtained: as expected, spreading of the water types is predominantly isopycnic and follows the major mid-depth circulation patterns. In some areas the turbulent transport also makes a considerable contribution. MW in the Atlantic spreads in three cores of different density: the upper MW core (northwest of the line 28° W, 35° N–14° W, 44° N) is found in the neutral density range of 27.65–27.70 kg m−3 at depths of 900–1000 m; the main MW core (between the line above and the line 35° W, 28° N–10° W, 37° N) has neutral density of around 27.75 kg m−3 and is found at 1000–1100 m; the lower MW core (southeast of the line 35° W, 28° N–10° W, 37° N) has neutral density of around 27.80 kg m−3 and is found at 1250–1350 m. The upper MW core has a comparatively low MW content (below 30 %) and is speculated to be transported by the mean flow from the northern Iberian Peninsula and the Bay of Biscay to the northern Azores. The main MW core contains the majority of the outflowing MW. It primarily originates from the Mediterranean undercurrent around Estremadura Promontory, where the Joint Effect of Baroclinicity and Bottom Relief (JEBAR) overrides the topographic β effect. It is transported west to the Azores Islands mostly along 39° N. The lower MW core originates in the Gulf of Cádiz, from where it is transported by the dominating flows southwestwards. The SAIW core is detected between 27.70 and 27.75 kg m−3. It is found to spread south along both slopes of the Mid-Atlantic Ridge (MAR). SAIW east of the MAR mixes with the upper and the main MW cores and re-circulates in a cyclonic gyre at 15–25° W and 34–39° N, penetrating as far south as the Azores Current. The mAAIW core is detected between 27.60 and 27.65 kg m−3. Its northernmost spreading limit is between 25 and 29° N, but its influence can be observed along the African coast and immediately west of the Canary Islands up to 32° N. The maximum concentration of the mAAIW core is found south of the Canary Islands, from where mAAIW is advected westwards, along with the westward spreading of the deep fraction of MW.

Mediterranean Overflow Over the Last 250 kyr: Freshwater Forcing From the Tropics to the Ice Sheets

“…After crossing the Camarinal Sill in the Strait of Gibraltar, at 290 m water depth, this dense MOW cascades down into the Gulf of Cadiz, as an overflow (Legg et al, 2009), accelerating because of its density anomaly and mixes and entrains the overlying fresher eastern North Atlantic central water (ENACW). Because of this mixing, the MOW reduces its salinity and temperature to transform into the MOW that settled within the Atlantic between 500 and 1,500 m ( Figure 1) (Ambar & Howe, 1979;Baringer & Price, 1997;Bashmachnikov et al, 2015;Sanchez-Leal et al, 2017;van Aken, 2001). Most of this mixing and entrainment occurs within the first 100 km along the MOW path after the Strait of Gibraltar and as a result the MOW volume transport increases from 0.8 Sv at the strait to more than 2.7 Sv when the MOW reaches its equilibrium depth in the Atlantic (Baringer & Price, 1997;Legg et al, 2009;Sanchez-Leal et al, 2017).…”

“…MOW mixes in the Atlantic with different water masses (Bashmachnikov et al, 2015;Carracedo et al, 2015Carracedo et al, , 2016Roque et al, 2019) (Figure 1). The ENACW that flows between 400 and 700 m over the MOW is composed by the upper ENACW formed in the subtropical region near the Azores front, and the deep ENACW, also referred to as the polar ENACW, formed by winter cooling in the bay of Biscay (Bashmachnikov et al, 2015;Carracedo et al, 2015;Roque et al, 2019;van Aken, 2001) ( Figure 1a). The upper ENACW and deep ENACW are the subsurface components of the AzC and the Portugal Current, respectively.…”

“…The upper ENACW and deep ENACW are the subsurface components of the AzC and the Portugal Current, respectively. More to the south, the MOW mixes with Antarctic intermediate water (AAIW), which flows northward along the Moroccan margin toward the Gulf of Cadiz between 600 and 1,000 m deep (Bashmachnikov et al, 2015;Carracedo et al, 2015;Roque et al, 2019;van Aken, 2000;Voelker, Colman, et al, 2015).…”

“…Today, the MOW at Gibraltar is pumping water, heat, and salt to the Atlantic interior (Figures 1 and 2). It spreads between 500 and 1,500 m and can eventually reach the high latitudes of the North Atlantic (Bashmachnikov et al, 2015;Bryden & Stommel, 1984;Iorga & Lozier, 1999;Mauritzen et al, 2001;Ozgokmen et al, 2001;van Aken, 2000a). Any change in the physicochemical properties of this water mass in response to Mediterranean pumping of heat and salt may have an important impact on the vertical density gradient Figure 1.…”

Ocean Circulation Over North Atlantic Underwater Features in the Path of the Mediterranean Outflow Water: The Ormonde and Formigas Seamounts, and the Gazul Mud Volcano

“…Following the path of the MOW through the eastern Atlantic, three seafloor elevated features, where CWC have been described (WWF, 2004;Oceana, 2005;Rueda et al, 2016), were selected as target regions for this study: the Gazul mud volcano and the Ormonde and Formigas seamounts (Figure 1). Both Gazul and Ormonde are directly in the pathway of the MOW after it outflows through the Strait of Gibraltar, while Formigas, located further away in the middle of the Atlantic, is influenced by the westward branch of the MOW (Bashmachnikov et al, 2015).…”