How well can we derive Global Ocean Indicators from Argo data?

Abstract

Argo deployments began in the year 2000 and by November 2007, the array reached its initial goal of 3000 floats operating worldwide. In this study, Argo temperature and salinity measurements during the period 2005 to 2010 are used to estimate Global Ocean Indicators (GOIs) such as global ocean heat content (GOHC), global ocean freshwater content (GOFC) and global steric sea level (GSSL). We developed a method based on a simple box averaging scheme using a weighted mean. Uncertainties due to data processing methods and choice of climatology are estimated. This method is easy to implement and run and can be used to set up a routine monitoring of the global ocean. Over the six year time period, trends of GOHC and GSSL are 0.54 ± 0.1 W m -2 and 0.75 ± 0.15 mm yr -1, respectively. The trend of GOFC is barely significant. Results show that there is significant interannual variability at global scale, especially for GOFC. Annual mean GOIs from the today's Argo sampling can be derived with an accuracy of ±0.11 cm for GSSL, ±0.22 × 10 8 J m -2 for GOHC, and ±700 km 3 for GOFC. Long-term trends (15 yr) of GOIs based on the complete Argo sampling for the upper 1500 m depth can be estimated with an accuracy of ±0.04 mm yr -1 for GSSL, ±0.02 W m -2 for GOHC and ±20 km 3 yr -1 for GOFC - under the assumption that no systematic errors remain in the observing system. © Author(s) 2011.