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 CO 2 fluxes, CO 2 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 CO 2 fluxes integrated over the Pacific (44°S–62°N) are −0.41 ± 0.12 PgC yr −1 from p CO 2 products and −0.51 ± 0.16 PgC yr −1 from GOBMs. The anthropogenic CO 2 flux from GOBMs (−0.71 ± 0.10 PgC yr −1 ) is 1.4 times as large as the net CO 2 flux, with particularly large anthropogenic uptake in the equatorial region (−0.34 ± 0.03 PgC yr −1 ) significantly offsetting the large natural CO 2 outgassing there (+0.72 ± 0.06 PgC yr −1 ). The basin‐wide net CO 2 uptake has increased at similar mean rates of −0.09 ± 0.06 and −0.08 ± 0.02 PgC yr −1 decade −1 in p CO 2 products and GOBMs, respectively, comparable with the increase in anthropogenic CO 2 uptake of −0.10 ± 0.01 PgC yr −1 decade −1 in GOBMs. However, a notable mismatch in the trend of the net CO 2 flux change that exists between p CO 2 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 CO 2 accumulation from GOBMs is +0.76 ± 0.17 PgC yr −1 . This is nearly balanced with the anthropogenic CO 2 flux and is also encompassed by the previous observation‐based estimates.