The Argo profiling float project will enable, for the first time, continuous global observations of the temperature, salinity, and velocity of the upper ocean in near‐real time.This new capability will improve our understanding of the ocean's role in climate, as well as spawn an enormous range of valuable ocean applications. Because over 90% of the observed increase in heat content of the air/land/sea climate system over the past 50 years occurred in the ocean [Leuitus et al., 2001], Argo will effectively monitor the pulse of the global heat balance.The end of 2003 was marked by two significant events for Argo. In mid‐November 2003, over 200 scientists from 22 countries met at Argo's first science workshop to discuss early results from the floats. Two weeks later, Argo had 1000 profiling floats—one‐third of the target total—delivering data. As of 7 May that total was 1171.

Profiling floats with optical sensors can provide important complementary data to satellite ocean color determinations by providing information about the vertical structure of ocean waters, as well as surface waters obscured by clouds. Here we demonstrate this ability by pairing satellite ocean color data with records from a profiling float that obtained continuous, high-quality optical data for 3 yr in the North Atlantic Ocean. Good agreement was found between satellite and float data, and the relationship between satellite chlorophyll and floatderived particulate backscattering was consistent with previously published data. Upper ocean biogeochemical dynamics were evidenced in float measurements, which displayed strong seasonal patterns associated with phytoplankton blooms, and depth and seasonal patterns associated with an increase in pigmentation per particle at low light. Surface optical variables had shorter decorrelation timescales than did physical variables (unlike at low latitudes), suggesting that biogeochemical rather than physical processes controlled much of the observed variability. After 2.25 yr in the subpolar North Atlantic between Newfoundland and Greenland, the float crossed the North Atlantic Current to warmer waters, where it sampled an unusual eddy for 3 months. This anticyclonic feature contained elevated particulate material from surface to 1000-m depth and was the only such event in the float's record. This eddy was associated with weakly elevated surface pigment and backscattering, but depthintegrated backscattering was similar to that previously observed during spring blooms. Such seldom-observed eddies, if frequent, are likely to make an important contribution to the delivery of particles to depth.

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This Community White Paper (CWP) examines the present Sea Surface Salinity (SSS) observing system, satellite systems to measure SSS and the requirements for satellite calibration and data validation. We provide recommendations for augmenting the in situ observing network to improve the synergism between in situ and remote sensing measurements. The goal is have an integrated (in situ-satellite) salinity observing system to provide necessary the global salinity analyses to open new frontiers of ocean and climate research. It is now well established that SSS is one of the fundamental variables for which sustained global observations are required to improve our knowledge and prediction of the ocean circulation, global water cycle and climate. With the advent of two new satellites, the ocean observing system will begin a new era for measuring and understanding the SSS field. The SMOS (Soil Moisture and Ocean Salinity) and Aquarius/SAC-D (Scientific Application Satellite-D) missions planned to be launched between late 2009 and late 2010, are intended to provide ~150-200 km spatial resolution globally, and accuracy ~0.2 psu, or better, on monthly average. The challenge for the next decade is to combine these satellite and in situ systems to generate the optimal global SSS analysis for climate and ocean research. The in situ data provide surface calibration and validation for the satellite data, while the satellites provide more complete spatial and temporal coverage. The first priority is the maintenance of the existing in situ SSS observing network. In addition, we propose specific enhancements, ideally to include (1) deploying ~ 200 SSS sensors on surface velocity drifters and moorings in key regions, and (2) adding higher vertical resolution near-surface profiles to ~100 Argo buoys to address surface stratification, mixing and skin effects. Plans during the next few years to deploy a significant fraction of these enhanced measurements are identified.