The analysis of the mixing processes involving water masses on the Ross Sea continental shelf is
one of the goals of the CLIMA project (Climatic Long-term Interactions for the Mass balance in Antarctica).
This paper uses extended Optimum MultiParameter analysis (OMP), which is applied to four datasets
collected during the cruises of 1994/95, 1995/96, 1997/98 and 2000/01 in the Ross Sea (Antarctica). Data
include both hydrological, (temperature, salinity, and pressure; T, S, and P, respectively) and chemical
parameters (O2, Si(OH)4, PO4, and NO3+NO2). The OMP analysis is based on the assumption that the mixing
is a linear process which affects all parameters equally so that each sample shows physical/chemical
properties that are the result of the mixing of some properly selected Source Water Types (SWTs). OMP thus
evaluates the best set of contributions by all SWTs to each sample, and allows the spatial distribution and
structure of the water masses in a basin to be evaluated. Ocean circulation may subsequently be inferred by
means of a deeper analysis of the spreading of the water mass. In this study, the “real” Redfield ratios
observed in the Ross Sea were used to correct the equations referring to the chemical parameters in
accordance with the extended version of OMP. The solutions include some physically realistic constraints.
The results allow a detailed description of the water mass distribution, validated through comparison with
some “canonical” thermohaline characteristics of the Ross Sea hydrology. In particular our results verify the
spreading of the HSSW over the entire continental shelf and emphasize the key role it plays in the ventilation
of the deep waters outside the Ross Sea. In addition a description is given of the intrusion of relatively warm
waters coming from the open ocean and flowing at some specific locations at the continental shelf break.