Distribution of intermediate water masses in the subtropical northeast Atlantic

摘要

This work presents the quantitative study of climatological distributions ofmid-depth source water types in the northeast (NE) Atlantic using the optimum multiparameter analysis (OMP). It generalises a number of regional resultsfrom particular synoptic sections. The cores of the Mediterranean Water (MW),the modified Antarctic Intermediate Water (mAAIW) and the SubarcticIntermediate Water (SAIW) are detected and spatial variations of theirdepth/density are obtained: as expected, spreading of the water types ispredominantly isopycnic and follows the major mid-depth circulation patterns.In some areas the turbulent transport also makes a considerablecontribution. 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 neutraldensity 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 around27.75 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 foundat 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 fromthe northern Iberian Peninsula and the Bay of Biscay to the northern Azores.The main MW core contains the majority of the outflowing MW. It primarilyoriginates from the Mediterranean undercurrent around Estremadura Promontory,where the Joint Effect of Baroclinicity and Bottom Relief (JEBAR) overridesthe topographic β effect. It is transported west to the Azores Islandsmostly along 39° N. The lower MW core originates in the Gulf ofCádiz, 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 tospread south along both slopes of the Mid-Atlantic Ridge (MAR). SAIW east ofthe MAR mixes with the upper and the main MW cores and re-circulates in acyclonic gyre at 15–25° W and 34–39° N, penetrating asfar south as the Azores Current. The mAAIW core is detected between 27.60 and27.65 kg m?3. Its northernmost spreading limit is between 25 and29° N, but its influence can be observed along the African coast andimmediately west of the Canary Islands up to 32° N. The maximumconcentration of the mAAIW core is found south of the Canary Islands, from wheremAAIW is advected westwards, along with the westward spreading of the deepfraction of MW.