| Summary: | Sixteen years of surface water CO2 data from autonomous systems on cruise ships sailing in the Caribbean Sea and Western North Atlantic show marked changes on interannual timescales. The measured changes in fugacity (≈partial pressure) of CO2 in surface water, fCO2w, are based on over a million observations. Seasonally the patterns are similar to other oligotrophic subtropical regions with an amplitude of fCO2w of ≈40 μatm with low wintertime values, causing the area to be a sink, and high summertime values making it a source of CO2 to the atmosphere. On annual scales there was negligible increase of fCO2w from 2002 to 2010 and a rapid increase from 2010 to 2018. Correspondingly, the trend of air‐sea CO2 flux from 2002 to 2010 was strongly negative (increasing uptake or sink) at −0.05 ± 0.01 (mol m−2 year−1) year−1 and positive (decreasing uptake) at 0.02 ± 0.02 (mol m−2 year−1) year−1 from 2010‐2018. For the whole period from 2002 to 2018, the fCO2w lagged the atmospheric CO2 increase by 24 %, causing an increase in CO2 uptake. The average flux into the ocean for the 16 years is −0.20 ± 0.16 mol m−2 year−1 with the uncertainty reflecting the standard deviation in annual means. The change in multiannual trend in fCO2w is modulated by several factors, notably changes in sea surface temperature and ocean mixed layer depth that, in turn, affected the physical and biological processes controlling fCO2w DOC | NOAA | Climate Program Office (CPO). Grant Number: 100007298 Global Ocean Monitoring and Observations. Grant Number: 100007298 SI
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