Autonomous seawater pCO₂ and pH time series from 40 surface buoys and the emergence of anthropogenic trends

Abstract. Ship-based time series, some now approaching over three decades long, are critical climate records that have dramatically improved our ability to characterize natural and anthropogenic drivers of ocean CO₂ uptake and biogeochemical processes. Advancements in autonomous ocean carbon observing technology over the last two decades have led to the expansion of fixed time series stations with the added capability of characterizing sub-seasonal variability. Here we present a data product of 40 autonomous moored surface ocean pCO₂ (partial pressure of CO₂) and pH time series established between 2004 and 2013. These time series characterize a wide range of seawater pCO₂ and pH conditions in different oceanic (17 sites) and coastal (12 sites) regimes including coral reefs (11 sites). With well-constrained daily to interannual variability and an estimate of decadal variability, these data suggest the length of time series necessary to detect an anthropogenic trend in seawater pCO₂ and pH varies from 8 to 15 years at the open ocean sites, 16 to 41 years at the coastal sites, and 9 to 22 years at the coral reef sites. Only two open ocean pCO₂ time series, WHOTS in the subtropical North Pacific and Stratus in the South Pacific gyre, are longer than the estimated time of emergence, and deseasoned monthly means show anthropogenic trends of 1.9 ± 0.3 µatm yr⁻¹ and 1.6 ± 0.3 µatm yr⁻¹, respectively. In the future, it is possible that updates to this product will allow for estimating anthropogenic trends at more sites; however, the product currently provides a valuable tool in an accessible format for evaluating climatology and natural variability of surface ocean carbonate chemistry in a variety of regions. Data are available at https://doi.org/10.7289/V5DB8043 and http://www.nodc.noaa.gov/ocads/oceans/Moorings/ndp097.html.