The amount of carbon dioxide (CO₂) being absorbed by the ocean is relevant to the earth's climate. CO₂ values in the coastal ocean and estuaries are not well known because of the instrumentation used. We used a new approach to measure CO₂ across the coastal and estuarine zone. We found that CO₂ and salinity were linked to the state of the tide. We used our CO₂ measurements and model salinity to predict CO₂. Previous studies overestimate how much CO₂ the coastal ocean draws down at our site.