Dissolved Inorganic Carbon and δ13C of the Hawaiian Ocean Time Series from 1990-2021

As humans continue to produce large amounts of CO2 via the burning of fossil fuels, the concentrations and isotopic signature of the ocean’s dissolved inorganic carbon (DIC) is changing. Utilization of DIC and its δ13C as a tracer for anthropogenic carbon at Station ALOHA has not been examined since 2017. This study modeled DIC and δ13C between 1990 and 2021 and compared them to observed measurements to show that anthropogenic carbon has reached at least 200 m at Station ALOHA. Samples were collected in December of 2021 from the R/V Thomspon and analyzed in the Quay Stable Isotope Laboratory. Using historical salinity, wind, temperature, and pCO2 data, expected DIC concentrations of the surface ocean were modeled. Over the last half decade DIC concentrations in the surface layer have increased by 20.32 μmol/kg due to anthropogenic burning of fossil fuels and the accumulation of carbon dioxide into the surface ocean at Station ALOHA has increased by 0.2 μmol/kg/yr since 2017. The average δ13C values for the water column between 0 m and 1020 m have decreased by 0.63 ‰ and 0.12 ‰ on average since 1997 and 2012 respectively. The enrichment of Carbon-12 and the increase of DIC concentrations points towards increasing anthropogenic output of carbon dioxide