Methane dynamics in the Baltic Sea: investigating concentration, flux, and isotopic composition patterns using the coupled physical–biogeochemical model BALTSEM-CH<sub>4</sub> v1.0
oleh: E. Gustafsson, E. Gustafsson, B. G. Gustafsson, B. G. Gustafsson, M. Hermans, M. Hermans, C. Humborg, C. Stranne, C. Stranne, C. Stranne
| Format: | Article |
|---|---|
| Diterbitkan: | Copernicus Publications 2024-09-01 |
Deskripsi
<p>Methane (CH<span class="inline-formula"><sub>4</sub></span>) cycling in the Baltic Sea is studied through model simulations that incorporate the stable isotopes of CH<span class="inline-formula"><sub>4</sub></span> (<span class="inline-formula"><sup>12</sup></span>C–CH<span class="inline-formula"><sub>4</sub></span> and <span class="inline-formula"><sup>13</sup></span>C–CH<span class="inline-formula"><sub>4</sub></span>) in a physical–biogeochemical model. A major uncertainty is that spatial and temporal variations in the sediment source are not well known. Furthermore, the coarse spatial resolution prevents the model from resolving shallow-water near-shore areas for which measurements indicate occurrences of considerably higher CH<span class="inline-formula"><sub>4</sub></span> concentrations and emissions compared with the open Baltic Sea. A preliminary CH<span class="inline-formula"><sub>4</sub></span> budget for the central Baltic Sea (the Baltic Proper) identifies benthic release as the dominant CH<span class="inline-formula"><sub>4</sub></span> source, which is largely balanced by oxidation in the water column and to a smaller degree by outgassing. The contributions from river loads and lateral exchange with adjacent areas are of marginal importance. Simulated total CH<span class="inline-formula"><sub>4</sub></span> emissions from the Baltic Proper correspond to an average <span class="inline-formula">∼1.5</span> mmol CH<span class="inline-formula"><sub>4</sub></span> m<span class="inline-formula"><sup>−2</sup></span> yr<span class="inline-formula"><sup>−1</sup></span>, which can be compared to a fitted sediment source of <span class="inline-formula">∼18</span> mmol CH<span class="inline-formula"><sub>4</sub></span> m<span class="inline-formula"><sup>−2</sup></span> yr<span class="inline-formula"><sup>−1</sup></span>. A large-scale approach is used in this study, but the parameterizations and parameters presented here could also be implemented in models of near-shore areas where CH<span class="inline-formula"><sub>4</sub></span> concentrations and fluxes are typically substantially larger and more variable. Currently, it is not known how important local shallow-water CH<span class="inline-formula"><sub>4</sub></span> hotspots are compared with the open water outgassing in the Baltic Sea.</p>