Mechanism of interannual variability of ocean bottom pressure in the South Pacific

Abstract

The study of ocean bottom pressure (OBP) is useful for understanding the variability that contributes to sea level change. Previous studies have reported the strong OBP anomalies in the Southern Ocean on different timescales. In this study, the characteristic and mechanisms of the energetic interannual OBP variability in the southeastern Pacific are examined using 14 years of Gravity Recovery and Climate Experiment (GRACE) data. It is found that the OBP anomalies are positive (negative) related to the convergence (divergence) of Ekman transport forced by local winds variability. Such local winds are attributed to atmospheric teleconnections, particularly the second Pacific-South American (PSA2). The sea level pressure (SLP) anomalies associated with the positive phase of PSA2 shows a wavenumber-3 structure in the high latitude of South Pacific, which benefits a strong and persistent anticyclone over the southeastern Pacific, leading to the positive OBP anomalies there. Moreover, El Niño–Southern Oscillation (ENSO) plays an important role in the concurrent OBP variability during austral spring (August–November) and leads the austral autumn (March–June) OBP variability by 1 season. These results highlight the influence of atmospheric teleconnections on interannual OBP variability and are validated by a mass conservation (non-Boussinesq) ocean model, which is expected to not only better understanding of OBP mechanisms in a longer time, but also predict OBP variation in the global scale.