Simulating the atmospheric CO₂ concentration across the heterogeneous landscape of Denmark using a coupled atmosphere–biosphere mesoscale model system

• Main Authors: A. S. Lansø, T. L. Smallman, J. H. Christensen, M. Williams, K. Pilegaard, L.-L. Sørensen, C. Geels
• Format: Article
• Language: English
• Published: Copernicus Publications 2019-04-01
• Series: Biogeosciences
• Online Access: https://www.biogeosciences.net/16/1505/2019/bg-16-1505-2019.pdf

<p>Although coastal regions only amount to 7&thinsp;% of the global oceans, their contribution to the global oceanic air–sea <span class="inline-formula">CO₂</span> exchange is proportionally larger, with fluxes in some estuaries being similar in magnitude to terrestrial surface fluxes of <span class="inline-formula">CO₂</span>.</p> <p>Across a heterogeneous surface consisting of a coastal marginal sea with estuarine properties and varied land mosaics, the surface fluxes of <span class="inline-formula">CO₂</span> from both marine areas and terrestrial surfaces were investigated in this study together with their impact in atmospheric <span class="inline-formula">CO₂</span> concentrations by the usage of a high-resolution modelling framework. The simulated terrestrial fluxes across the study region of Denmark experienced an east–west gradient corresponding to the distribution of the land cover classification, their biological activity and the urbanised areas. Annually, the Danish terrestrial surface had an uptake of approximately <span class="inline-formula">−7000</span>&thinsp;GgC&thinsp;yr<span class="inline-formula">⁻¹</span>. While the marine fluxes from the North Sea and the Danish inner waters were smaller annually, with about <span class="inline-formula">−1800</span> and 1300&thinsp;GgC&thinsp;yr<span class="inline-formula">⁻¹</span>, their sizes are comparable to annual terrestrial fluxes from individual land cover classifications in the study region and hence are not negligible. The contribution of terrestrial surfaces fluxes was easily detectable in both simulated and measured concentrations of atmospheric <span class="inline-formula">CO₂</span> at the only tall tower site in the study region. Although, the tower is positioned next to Roskilde Fjord, the local marine impact was not distinguishable in the simulated concentrations. But the regional impact from the Danish inner waters and the Baltic Sea increased the atmospheric concentration by up to 0.5&thinsp;ppm during the winter months.</p>