Seasonal trends in the Southeast Florida current and shelf CO2 fluxes

An anthropogenically driven increase in atmospheric CO2 concentrations is known to drive an increase in the globally integrated ocean carbon sink. However, there is significant regional and seasonal variability, and significant changes in seasonal cycle amplitudes have been predicted. Three decades of sea surface observations collected from the southeast Florida Current and shelf waters reveal behavior over seasonal and interannual timescales for a region important to global carbon storage and transport. The strong temperature dependence of fCO2 in the region dominates the seasonal cycle of air-sea flux, although biophysical processes are also important. The possibility of wet and dry seasonal asymmetric trends through time were evaluated, but no statistically significant trends were found. The results indicate that uptake in the region has not changed over the last three decades after accounting for sampling bias and demonstrate the importance of robust seasonally unbiased data sets in conducting climate studies. Even in this highly sampled region, data distribution biases were found, mainly in the early 1990s. Seasonally biased data are thus not only a problem for polar regions but can also affect flux calculations in sub-tropical regions. Although not statistically significant to date, different responses in different seasons with time may lead to seasonal amplification and a decoupling of the annual mean and the seasonal means in the future. •The region is a weak sink for CO2, contrary to the results of an earlier study.•No long-term annual trend of CO2 fluxes was found.•Long-term seasonal trends and asymmetries were statistically insignificant.•Seasonal cycle dominated by temperature rather than biophysical processes.