3D Bivariate Spatial Modelling of Argo Ocean Temperature and Salinity

TL;DR

This paper develops a flexible 3D nonstationary covariance model for jointly analyzing ocean temperature and salinity, capturing their vertical and horizontal dependence from Argo data, improving understanding of ocean stratification and climate effects.

Contribution

It introduces a novel multivariate nonstationary covariance model in 3D space that effectively captures the joint spatial dependence of temperature and salinity across ocean depths.

Findings

The proposed models accurately describe complex vertical cross-covariance structures.

Including both variables improves prediction accuracy for each.

Results align with known ocean stratification patterns.

Abstract

Variables contained within the global oceans can detect and reveal the effects of the warming climate as the oceans absorb huge amounts of solar energy. Hence, information regarding the joint spatial distribution of ocean variables is critical for climate monitoring. In this paper, we investigate the spatial correlation structure between ocean temperature and salinity using data harvested from the Argo program and construct a model to capture their bivariate spatial dependence from the surface to the ocean's interior. We develop a flexible class of multivariate nonstationary covariance models defined in 3-dimensional (3D) space (longitude $\times$ latitude $\times$ depth) that allows for the variances and correlation to change along the vertical pressure dimension. These models are able to describe the joint spatial distribution of the two variables while incorporating the underlying vertical structure of the ocean. We demonstrate that the proposed cross-covariance models describe the complex vertical cross-covariance structure well, while existing cross-covariance models including bivariate Mat\'{e}rn models poorly fit empirical cross-covariance structure. Furthermore, the results show that using one more variable significantly enhances the prediction of the other variable and that the estimated spatial dependence structures are consistent with the ocean stratification.