Air–sea fluxes of CO2 and CH4 from the Penlee Point Atmospheric Observatory on the south-west coast of the UK

摘要

We present air–sea fluxes of carbon dioxide (CO), methane (CH),momentum, and sensible heat measured by the eddy covariance method from therecently established Penlee Point Atmospheric Observatory (PPAO) on the south-west coast of the United Kingdom. Measurements from the south-westerly direction(open water sector) were made at three different sampling heights(approximately 15, 18, and 27 m above mean sea level, a.m.s.l.), each from adifferent period during 2014–2015. At sampling heights  ≥  18 m a.m.s.l., measured fluxes of momentum and sensible heat demonstratereasonable ( ≤  ±20 % in the mean) agreement with transfer ratesover the open ocean. This confirms the suitability of PPAO for air–seaexchange measurements in shelf regions. Covariance air–sea CO fluxesdemonstrate high temporal variability. Air-to-sea transport of COdeclined from spring to summer in both years, coinciding with the breakdownof the spring phytoplankton bloom. We report, to the best of our knowledge,the first successful eddy covariance measurements of CH emissions from amarine environment. Higher sea-to-air CH fluxes were observed duringrising tides (20 ± 3; 38 ± 3;29 ± 6 µmole m d at 15, 18, 27 m a.m.s.l.)than during falling tides (14 ± 2; 22 ± 2;21 ± 5 µmole m d), consistentwith an elevated CH source from an estuarine outflow driven by localtidal circulation. These fluxes are a few times higher than the predictedCH emissions over the open ocean and are significantly lower thanestimates from other aquatic CH hotspots (e.g. polar regions,freshwater). Finally, we found the detection limit of the air–sea CHflux by eddy covariance to be 20 µmole m d overhourly timescales (4 µmole m d over 24 h).