Radiocarbon ages of dissolved and particulate organic matter in small water bodies of the Lena Delta

Gesine.Mollenhauer [ at ]


The term “Permafrost” describes soil or rock, whose temperature stays at or underneath 0 for at least two years. 50% of the globally estimated, soil-stored organic carbon is to be found in permafrost of the northern hemisphere. Due to global warming more and more of this permanently frozen soil thaws. This leads to thermokarst processes, which create lakes and small ponds. Those lakes and ponds lead to more thawing of the soil around them. The long stored old organic material can be leached out by this thawing processes and either dissolve or float as particles in the water column. Carbon, which is released in big arctic rivers, has been analyzed. Often, the particulate organic carbon (POC) carried by rivers is older than the dissolved organic Carbon (DOC). The radiogenic carbon signature of DOC shows a very young signature. Due to mineralization and metabolism by microorganisms large amount of DOC leave the flows as CO2 and CH4. Concentrations of DOC in artic lakes have been analyzed while the origin of this DOC was completely unclear. Also, DOC from ponds has not been analyzed concerning their radiogenic carbon signature yet. This bachelor thesis focuses on this gap of research and will attempt to answer the following questions: Do relations between the sizes of water bodies, the concentrations and radiogenic signature of DOC exist? What happens with dissolved and particulate carbon in lakes and ponds? Why carbon in artic rivers is so young? The samples for this thesis were taken during field expeditions in August 2016 and July 2017. These expeditions took place in the central part of the Delta Lena. Samples were taken on the geological first terrace unit and on the third terrace unit. To cover the first terrace unit, lakes and ponds on Samoylov were sampled. To cover the third terrace unit, lakes and outflows on Kurungnakh were sampled. To extract DOC the water samples were evaporated using a Rotary-Evaporator and afterwards analyzed in an AMS called MICADAS. The resulting concentrations and radiogenic carbon signatures lead to the perception, that bigger lakes have a lower concentration of DOC with more enriched amounts of 14C while smaller ponds have a higher concentration with a more depleted ratio. DOC, which was leached into the waterbodies either gassed out due to mineralization or metabolisms by microorganisms. Bigger amounts of POC are especially leached into waterbodies due to heavy rain events, the thawing process in early summer and floods. The enriched Δ14C-signature of the Lena can be explained with the release of larger amounts of carbon with enriched Δ14C-values from the first terrace. Additionally, older organic Carbon is instable and degrades fast.

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Hammes, J. S. (2019): Radiocarbon ages of dissolved and particulate organic matter in small water bodies of the Lena Delta , Bachelor thesis, Universität Bonn.

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