Argo: The Global Array of Profiling Floats

The Argo network of autonomous profiling floats will provide the first global views of the time-varying temperature (T) and salinity (S) fields of the upper ocean. Argo will serve a broad community of scientific and operational users, with objectives falling into several categories. It will provide a quantitative description of the evolving physical state of the upper ocean and the patterns of ocean climate variability, including heat and freshwater storage and transport. The data will enhance the value of the Jason altimeter through measurement of the subsurface vertical structure of T and S, plus reference velocity, with sufficient coverage and resolution for interpreting altimetric sea surface height variability. Argo data will be used for initializing ocean and coupled forecast models, for data assimilation and for dynamical model testing. A primary focus of Argo is seasonal-to-decadal climate variability and predictability, but many applications for high-quality global ocean analyses are anticipated

Global Ocean Warming and Sea Level Rise

The ocean observing system has progressed considerably over the past 50 years, enabling more accurate estimation of global ocean heat content and its impact on sea level (thermosteric sea level). For the entire 50-year record, estimates of global thermosteric sea level rise are about 0.4 mm/yr, much less than the total sea level rise of 1.8 mm/yr for the same period. However, this estimated 50-year heating rate may be biased low due to undersampling of the oceans, particularly in the Southern Hemisphere during the early decades. For the period 1993 – 2003, with high precision satellite altimetry and a quasi-global upper ocean thermal network, thermosteric sea level rise was about 1.6 mm/yr for the layer 0-750 m, out of a total sea level rise of 2.8 mm/yr. Considerable regional and interannual variability are evident. The large increase in the estimated heating rate relative to the earlier period may have been due partly to decadal variability and partly to improved global coverage by the measurements. The recent implementation of the global Argo array has now made it possible to estimate 1-year averages of thermosteric sea level with accuracy of 0.5 mm, and hence the error in 10-year change is less than 0.1 mm/yr. Global salinity measurements, also made by Argo, provide an important constraint on the oceanic freshwater budget, one component of which is the melting of continental ice that causes eustatic sea level rise. Data assimilation techniques offer the promise of more robust estimates of ocean thermal expansion but to date there are considereable poorly explored differences between the various approaches. GRACE gravity data can be used to estimate changes in mass of the ocean. GRACE, satellite altimetry and steric changes agree well for the annual cycle but there is significant disagreement on trends over the 3 year period from 2002 to 2006. Coupled ocean-atmosphere models are the central tool for computing future ocean thermal expansion. Many of these models no longer rely on flux corrections. However, different models produce significantly different amounts of thermal expansion. Some aspects of the regional distribution of sea level rise projected by these models are similar. The only high resolution coupled ocean-atmosphere model available produces similar results to the medium resolution version of the same model, but the high resolution model has finer scale features and also has an increase in eddy sea-level variability

Guidelines towards an integrated ocean observation system for ecosystems and biogeochemical cycles

The observation of biogeochemical cycles and ecosystems has traditionally been based on ship-based platforms. The obvious consequence is that the measured properties have been dramatically undersampled. Recent technological advances in miniature, low power biogeochemical sensors and autonomous platforms open remarkable perspectives for observing the “biological” ocean, notably at critical spatio-temporal scales which have been out of reach until present. The availability of this new observation technology thus makes it possible to envision the development of a globally integrated observation system that would serve both scientific as well as operational needs. This in situ systemm should be fully designed and implemented in tight synergy with two other essential elements of an ocean observation system, first satellite ocean color radiometry and second advanced numerical models of biogeochemical cycles and ecosystems