The Southern Ocean connects the Indian, Pacific and Atlantic Oceans and provides a direct pathway to exchange mass, heat and salt across the World Ocean, therefore playing an important role in the climate system. Due to the complexity of its structure and the general inadequacy of its sampling, both in time and space, it remains a challenge to describe and visualize the three dimensional pattern of its circulation and the associated tracer distribution (temperature, salinity, oxygen or nutrients). This work contributes to the understanding of the thermohaline structure of the ocean and especially of the Southern Ocean by introducing a novel decomposition method, the Functional Principal Component Analysis applied on combined T-S vertical profiles. We first normalize hydrographic profiles by using a functional spline representation and then, the statistical method of dimension reduction and feature extraction reveals the main spatial patterns of the T-S variations. Applied to the Southern Ocean, the first two modes explain ~92% of the combined T–S variance, thus providing a surprisingly good approximation of the thermohaline properties. The vertical modes present circumpolar patterns that can be closely related to the stratification regimes that define the circumpolar fronts. Notably the Polar Front is located at the natural boundary between the region controlled by the first (thermal) mode to the north and the second (haline) mode to the south. A mapping of the fundamental zonation is provided with an estimate of the width of the water mass boundaries. As a validation of this method, the Antarctic Polar Front is investigated further in the Indian sector using the same statistical framework. We show that the Polar Front latitudinal position varies seasonally upstream of the Kerguelen Plateau. This meandering is confirmed by hydrographic data gathered by elephant seals equipped with miniaturized sensors. Finally, the potential of the method is illustrated with an application to the World ocean where the first three vertical modes explain to 93% of the combined T-S variance and are related to very robust structures of the World Ocean.
LOCEAN-IPSL, CNRS / Université P. et M. Curie, Paris, France
Tue, 26/02/2019 - 3:05pm
RC-4082, The Red Centre, UNSW