CO2 Uptake in the Pacific From 1985 to 2018: A Comparative Assessment of Observation- and Model-Based Estimates

Abstract

As a contribution to the second REgional Carbon Cycle Assessment and Processes effort, we compare net and anthropogenic sea-air CO₂ fluxes, CO₂ accumulation rates in the ocean interior and their trends in the Pacific Ocean by analyzing results from state-of-the-art observation-based estimates and global ocean biogeochemistry models (GOBMs) over the period 1985–2018. The ensemble-mean net CO₂ fluxes integrated over the Pacific (44°S–62°N) are −0.41 ± 0.12 PgC yr⁻¹ from pCO₂ products and −0.51 ± 0.16 PgC yr⁻¹ from GOBMs. The anthropogenic CO₂ flux from GOBMs (−0.71 ± 0.10 PgC yr⁻¹) is 1.4 times as large as the net CO₂ flux, with particularly large anthropogenic uptake in the equatorial region (−0.34 ± 0.03 PgC yr⁻¹) significantly offsetting the large natural CO₂ outgassing there (+0.72 ± 0.06 PgC yr⁻¹). The basin-wide net CO₂ uptake has increased at similar mean rates of −0.09 ± 0.06 and −0.08 ± 0.02 PgC yr⁻¹ decade⁻¹ in pCO₂ products and GOBMs, respectively, comparable with the increase in anthropogenic CO₂ uptake of −0.10 ± 0.01 PgC yr⁻¹ decade⁻¹ in GOBMs. However, a notable mismatch in the trend of the net CO₂ flux change that exists between pCO₂ products (+0.00 ± 0.02 PgC yr⁻¹ decade⁻¹) and GOBMs (−0.04 ± 0.01 PgC yr⁻¹ decade⁻¹) in the equatorial region is yet to be resolved. The rate of anthropogenic CO₂ accumulation from GOBMs is +0.76 ± 0.17 PgC yr⁻¹. This is nearly balanced with the anthropogenic CO₂ flux and is also encompassed by the previous observation-based estimates.