Temperature-salinity correlations and spiciness in oceanic variability

Density gradients are an important factor in determining the ocean circulation. Temperature (T) and salinity (S) make competing contributions to these density variations. Thermohaline variability has the maximum effect on density fluctuations when T and S anomalies are negatively correlated and a minimal effect when they are positively correlated. Therefore, T-S correlations are an important characteristic of oceanic variability. We analyze the relationship between T and S variability in a hierarchy of oceanic and coupled model integrations, ranging from a two-dimensional (y-z) ocean model to a general circulation model. In addition to statistical correlation analysis, we also compute the diagnostic quantity known as "spiciness", which is defined to be orthogonal to density. We show that although T and S are only weakly correlated near the ocean surface, the interior of the ocean is characterized by strong, positive T-S correlations, or equivalently, large spiciness variations. Our analysis also helps in identifying pathways that link the high latitude ocean to the tropical ocean.