T03_P06

DOC radiocarbon measurements at the AWI-MICADAS facility, current method developments and improvements

Grotheer H^1,2, Gentz T¹, Höhn M¹, Kattein L¹, Schlagenhauff S¹, Hefter J¹, Mollenhauer G^1,2

¹Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, Bremerhaven, Germany, ²University Bremen, Dept. of Geosciences and MARUM, Bremen, Germany

Reliable radiocarbon ages of dissolved organic carbon (DOC) are a perquisite to obtain improved understanding of current carbon cycle dynamics. Dissolved organic matter (DOM) is an extremely complex natural organic mixture consisting of tens of thousands of individual compounds with a large variety of chemical and physical properties. Because of this complexity and the presence of sea salt, radiocarbon sample preparation for marine DOC is very challenging as available methods for extraction and purification (SPE, or ultra-filtration) depend on either physical or chemical properties and thus only consider a fraction of the DOC pool amenable to the preparation method. Consequently, the sample preparation selectivity hampers our wholistic understanding of the DOC pool, its cycling and reactivity. Today the only method available considered to reliably report bulk DOC radiocarbon composition is ultraviolet oxidation (UVox), where irrespectively of chemical or physical properties DOC molecules are quantitatively oxidized to CO₂. However, UVox is only available at a few very specialized laboratories, is very time consuming and tedious. 

We will report on ongoing method developments for processing marine DOC by utilizing a modified, commercially available Gräntzel thin-film flow-through reactor enabling fast sample processing. The offline UVox system is coupled via a custom-built zeolite trap to the existing GIS infrastructure of the MICADAS system. Technical details, reproducibility tests and current blank levels will be reported.