G03_02

Time-series measurements of dissolved organic and inorganic radiocarbon from Switzerland’s two largest lakes

White M¹, Mittelbach B¹, Rhyner T¹, Haghipour N¹, Blattmann T¹, Jacquin C², Schubert C³, Wessels M⁴, Dubois N^1,3, Eglinton T¹

¹Department of Earth Sciences, ETH Zürich, Zürich, Switzerland, ²Department of Process Engineering, Eawag, Dübendorf, Switzerland, ³Department Surface Waters Research & Management, Eawag, , Switzerland, ⁴Institut für Seenforschung der LUBW, Langenargen, Germany

The Radiocarbon Inventories of Switzerland (RICH) project aims to construct the first national-scale census of carbon across aquatic, terrestrial, and atmospheric reservoirs. Within the Swiss carbon cycle, inland waters play a crucial role with lakes integrating carbon from various sources within their catchment in addition to that fixed by local primary productivity. Here we present measurements of dissolved organic and inorganic radiocarbon from monthly water column samplings of Switzerland’s two largest lakes: Lake Constance and Lake Geneva. Such high-resolution temporal measurements can uncover the nature and drivers of seasonal carbon dynamics in these well-studied lake ecosystems. Comparison of water column profiles from river proximal and river distal sites within each lake will constrain fluvial influence. In addition to isotope data, measurements of the optical properties of dissolved organic matter will aid in untangling sources and cycling of lake water DOC. Preliminary results show that the average radiocarbon signature of DIC in both lakes is depleted relative to atmospheric CO₂, suggesting a ca. 15% contribution from weathering of petrogenic (rock-derived) carbon.