FY 2000

Investigating ocean climate variability: The need for systematic hydrographic observations within CLIVAR/GOOS

Gould, W.J., J.M. Toole, J. Church, S. Wijffels, S. Rintoul, L. Talley, P. Robbins, G.C. Johnson, S. Imawaki, N. Suginohara, K. Hanawa, P. Koltermann, S. Osterhus, H. Freeland, A. Clarke, and H. Mercier

In Proceedings of the International Conference on the Ocean Observing System for Climate, Session 3B, Saint-Raphael, France, 18–22 October 1999, 18 pp (2000)

As the necessity for understanding climate variability is increasingly realised, so too is the need to investigate changes in ocean structure and circulation being recognised. Much of the ocean observing system that is being currently planned, rightly focusses on the upper, seasonally influenced, 200 m or so of the water column with little attention given to monitoring the demonstrated deeper variability. A predominantly upper-ocean focus would leave future generations facing a lack of good-quality, global-scale, deep-ocean data against which to test model predictions, measure the rate (if any) of secular change, and learn about the nature of deep-ocean variability and how it responds to and influences the global climate system. Ship-based hydrographic sampling is one of the oldest observational techniques in physical oceanography; nevertheless it remains the only means of directly measuring the full suite of ocean water properties at high-vertical resolution over the entire water column and hence deriving accurate estimates of net ocean mass and property transports. Here, a subset of previous studies that used hydrographic measurements to describe and build understanding of ocean climate variability are presented as motivation for a programme of repeated sampling within CLIVAR/GOOS. The paper proposes a similar measurement programme that we believe is feasible, cost-effective and vital to future efforts to understand long-term changes in climate.