Vol. 60, n.3, September 2019
Comments on computations about the Mediterranean Outflow composition
Received: 25 November 2018; accepted: 17 January 2019
The Mediterranean Outflow (MO) is composed of four major intermediate and deep Mediterranean Waters (MWs) that mix with two major Atlantic Waters (AWs) in the Strait of Gibraltar. There is an ancient debate about whether, all along the Strait, these mixed MWs either totally mix together and give a homogeneous MO or remain individualised and give a heterogeneous MO. I do not address herein this scientific debate, which needs a large amount of data analyses that I will present in papers to come, but I comment on the available computations performed to specify the MO composition. In particular, a recent objective analysis of hydrological profiles aims at specifying, for each sample in either the Mediterranean Sea or the Strait, the percentages of the major MWs and AWs involved in the mixing while claiming using a clustering method classically used to specify water masses characteristics. I show that: i) the performed computations have nothing to do with such a method, ii) the used Euclidean distance cannot provide any sound result, iii) such an analysis always identifies one intermediate MW as having the largest percentage everywhere in the Strait and, more generally, iv) no statistical objective computation can provide sound results in regions where hydrological characteristics are rapidly evolving. I suggest that the sole reliable type of hydrological analyses in such a place is based, as I have done in the past, on the AWs-MWs mixing lines slopes and positions according to processes I am now able to specify, and I conclude that all available data sets account for the MO heterogeneity all along the Strait.
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