Observations of South Pacific Tropical Water (SPTW) have revealed variability on interannual time scales and a trend of increasing salinity over several decades. SPTW identified by a shallow salinity maximum forms in the eastern South Pacific and is transported in the subtropical gyre and along the equator. Variability of SPTW may affect the circulation and water properties in the equatorial region, in particular if the salinity and temperature anomalies are not density compensated. SPTW has a significant interior equatorward pathway, and thus a relatively short (5-15 years) residence time and high formation rate. As a consequence, the contribution of SPTW to the equatorial Pacific is expected to be faster and stronger than its North Pacific counterpart. This project will initiate a more complete understanding of how the equatorial ocean is ventilated through the subduction of South Pacific waters and how variability in this ventilation contributes to climate variability.
The overall research objectives of the project are: to identify variability in SPTW, and to assess downstream impacts of this variability. The relationship of SPTW variability to interannual and longer term atmospheric forcing will be investigated. Depending on the extent and magnitude of the SPTW variability, it is hypothesized that there will be a dynamical signature in the downstream circulation and thermal structure of the tropical South Pacific. The research includes the analysis of available Argo floating profiles and WOCE/CLIVAR tracer (salinity, potential vorticity, oxygen, CFC, SF6, tritium, helium-3, 14C, etc.) data, as well as results from the OGCM for the Earth Simulator (OFES), and simulated passive and adjoint tracers from the Estimating the Circulation and Climate of the Ocean (ECCO).
Intellectual merit: The project will utilize all available hydrographic (mainly Argo) and tracer observations to identify the variability of SPTW. The combined use of observations with results from high-resolution GCMs will allow for a comprehensive, physically consistent interpretation of this variability and its downstream impacts on the tropical Pacific Ocean circulation and thermal structure. In addition, the simulated passive tracer and its adjoint will provide unambiguous means to identify the SPTW pathways and in particular to assess the influence of meso-scale eddies and small scale processes. The SPTW contributes to the Equatorial Undercurrent and water upwelled in the eastern equatorial Pacific, both having direct relevance to ENSO. The derived assessment of the SPTW downstream impacts will enhance the understanding of ocean?s role in climate variability, and provide new information for the predictability and prediction of interannual and longer time scale variability such as ENSO and PDO in the Pacific.
Broader impacts: The project will lead to improved skills for use with ENSO and climate prediction; advance science while promoting education by the training of a postdoctoral fellow and a graduate student in the analysis of observational data and model outputs; enhance infrastructure for research and education by establishing collaborations between different disciplines and different institutions; and benefit the society by the use of existing observations and results from high-resolution GCMs to assess climate change. One of the PIs participates in the program Mentoring Physical Oceanography Women to Increase Retention, and is on the implementation committee of an NSF Advance grant to the University of Miami.