Deep Argo’s critical impact on climate change assessment and ocean reanalyses over the full-ocean depth

Deep Argo, the deep-ocean component of the OneArgo program, aims to deliver sustained, full-depth measurements of key ocean variables, such as ocean temperature, salinity, and currents, critical to the Global Ocean Observing System. The capacity of Deep Argo floats to sample autonomously the deepest regions of the ocean every 10 days enables an unprecedented characterization of ocean variability. The Deep Argo data are shared publicly within 24 hours through the Global Telecommunications System. A quality-controlled version is made available within a year on the two Argo Global Data Assembly Centers located in France and the US. The Deep Argo float array has the ability to revolutionize deep-ocean sampling coverage. In less than 7 years, pilot arrays of Deep Argo floats have collected as many deep-ocean profiles in the South Australian, Southwest Pacific, and Brazil basins as  ships collected over the past 70 years. Measurements collected over the last decade have demonstrated Deep Argo’s capability to estimate trends in deep-ocean properties more accurately than from repeat hydrography alone, and with greater temporal and spatial resolution. Deep Argo has resolved circulation pathways of dense water masses formed near Antarctica and in the subpolar North Atlantic with unprecedented details. Deep Argo can close regional sea level budgets at interannual time scale and identify new hotspots of sea level variability due to deep-ocean density change. Enhanced deep-ocean sampling is critical to improve the representation of deep-ocean processes and water mass properties in data assimilative models, validate coupled ocean-atmosphere model and ocean reanalysis, increase consistency of assimilated in situ and satellite observations, and reduce biases in upper-ocean decadal predictions. The Deep Argo fleet counts 200 active floats but a fully-implemented Deep Argo 1200-float array is urgently needed to provide the global coverage required to address societal needs for ocean reanalyzes and forecasts and for estimation of key climate change indicators, such as Earth Energy Imbalance, ocean heat content, and sea level rise.