Protocol for the Assessment and Correction of Moored Surface Water and Air pCO2 Measurements from the Ocean Observatories Initiative Endurance Array

As part of the NSF-funded Ocean Observatories Initiative (OOI) Coastal and Global Scale Arrays, surface buoy pCO₂ measurements are made using the Pro-Oceanus CO₂-Pro Atmosphere pCO₂ sensor. This sensor measures the partial pressure of CO₂ gas in both surface water and air, allowing for surface flux calculations. Both the air and water measurements and the flux estimates are available through the OOI Data Portal. Additionally, the most recent 60 days worth of OOI Endurance Array surface buoy pCO2 data will be available starting this Fall 2019 via the NANOOS Visualization System (NVS, http://nvs.nanoos.org/) and the Global Ocean Acidification Observing System Data Portal (GOA-ON, http://portal.goa-on.org/).

In the OOI Endurance Array, surface water and air pCO₂ measurements are made at four locations over the Oregon and Washington shelf and slope. These locations lie within the northern California Current Marine Ecosystem. We will report on the surface water and air pCO₂ data returned for the first four years of Endurance Array operations and describe a protocol based on cross-comparisons to independent, shipboard (both CTD samples and underway flow-thru systems) pCO₂ measurements and an observation-based global monthly gridded sea surface pCO₂ estimate with an associated monthly climatology (Landshützer et al. 2017) for assessing and correcting instrument offsets and drift and improving the quality and scientific applicability of the OOI Endurance Array pCO₂ measurements. This protocol is applicable to the same suite of measurements made by this sensor deployed in the OOI Pioneer and Global Arrays.