Seawater density depends on both temperature and salinity through the equation of state: increasing temperature decreases density (thermal expansion), while increasing salinity increases density (haline contraction). Water parcels with different temperature-salinity combinations can share the same density if these two opposing effects compensate each other — a relationship visualized as isopycnal (constant density) lines on a temperature-salinity (T-S) diagram.
To find another temperature-salinity combination with the same density as 15°C/35 PSU seawater, both temperature and salinity must change together along an isopycnal curve, since...
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