High spatial-resolution monitoring of surface CO2 concentrations in Lake Michigan

Determining the net flux of CO₂ and O₂ between large bodies of water and the atmosphere is difficult, because this measurement requires data with high temporal and spatial resolution. To achieve this objective, we have installed a CO₂/O₂ gas monitoring system on the Lake Express ferry that crosses Lake Michigan up to six times daily, from the Port of Milwaukee in Wisconsin to Muskegon, Michigan between April and November. Each cross of the lake is about two and a half hours. Mounting on the Lake Express will allow coverage of approximately 130 km of spatial sampling per trip or up to 780 km per day. Sampling is alternated between sampling the CO₂ and O₂ in the lake surface water and in the atmosphere. GPS coordinates are recorded while sampling the water and atmosphere to obtain an accurate position for all gas measurements taken along the transect. Data are logged every 5 seconds, with a 30 s block mean calculated. Roughly 10000 data points are logged daily