Collaborative Research: Global Ocean Repeat Hydrography, Carbon, and Tracer Measurements, 2015-2020

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Earth's climate is changing, with large natural decadal variability in some regions. Among the most important and basic climate system components are the heat, freshwater, and carbon content and transport of the oceans, which directly interact with other essential components of the climate system in the atmosphere and cryosphere. In turn the associated variability and trends in the ocean's carbon content, carbonate saturation state, oxygen, and nutrients impact its internal biological environment, with notable large-scale regional changes. This joint study of the ocean carbon cycle and circulation is critical to identify critical areas where changes in ocean circulation could have serious consequences for future anthropogenic carbon uptake. Global warming-induced changes in the ocean's transport of heat and freshwater, which could affect the circulation, are being followed through these long-term measurements. Results to date have shown that the abyssal ocean is warming, taking up to 30% of the excess heat in the entire Earth system, leading to changes in circulation patterns and ventilation rates in the upper ocean. The uptake of anthropogenic carbon from the atmosphere to the ocean has been mapped and shows that the oceans are acidifying. Oxygen concentrations are declining in the ocean thermocline, and tropical oxygen minimum zones are expanding. The project is based on the fundamental concept that data collected belong to the community and need to be made quickly and freely available to the community at large through a recognized international data center. The project will continue to promote training and learning for graduate students, postdoctoral scientists, and new scientists in sea-going work. Outreach activities will continue as opportunities arise.The systematic and global re-occupation of select ocean hydrographic sections conducted for the past decade (2003-2014) will be extended into the 2015-2020 period with the continued objective of quantifying changes in the full-depth ocean. The project is in support of the U.S. CLIVAR (CLImate Variability and predictability) and the Carbon Science Programs, and is a component of a global observing system for the physical climate and carbon system. This long-standing project continues to contribute to the following overlapping scientific objectives: Data for Model Calibration, Validation and Model Based Synthesis; Carbon System Studies; Heat and Freshwater Storage and Flux Studies; Deep and Shallow Water Mass and Ventilation Studies; and Calibration of Autonomous Sensors. By integrating the scientific needs of the carbon, tracer and hydrographic communities, major scientific synergies and cost savings will continue to be achieved. In addition to efficiency, the coordinated approach produces scientific advances that exceed those of having individual programs. An average of two sections will be conducted every year, sometime collaboratively with international partner. The measurements made on each section include hydrography (full-depth vertical profiles of salinity, temperature, oxygen, nutrients, currents), Underway surface temperature, salinity, partial pressure of carbon dioxide (pCO2), air-sea fluxes, bathymetry, navigation), carbon system (dissolved inorganic carbon, pCO2. Total Alkalinity, pH, dissolved organic carbon and nitrogen), and transient tracers. This project will collect the data and perform the quality control measures routinely carried out by providers of reference-quality data. Post-cruise data updates, distribution, and archive will continue to be managed by groups with separate funding. This ongoing project is integrated with a larger international effort to monitor the ocean's response to climate change.