Arctic land-ocean organic carbon flux variability and its drivers monitored using ESA CCI ECVs

bennet.juhls [ at ]


Dramatically changing climate in the Arctic is changing the hydrology and the biogeochemistry of rivers. Vice versa, river water can be a powerful indicator for the impact of climate change since river biogeochemistry and discharge integrate upstream terrestrial and aquatic environmental processes over a defined watershed. In Arctic catchments, permafrost is warming and thawing, releasing much organic carbon that was previously frozen, thus inactive in the carbon cycle. Long-term global Climate Change Initiative (CCI) remote sensing based datasets are a powerful tool to observe changes across terrestrial, coastal and marine environments in high frequency and throughout long time series. In this study, we show the potential of CCI Ocean Color data to retrieve the optical properties of the dissolved organic matter (CDOM) and relate them to riverine organic carbon fluxes on a pan-Arctic scale for the last 23 years. Further, we relate riverine discharge and terrestrial CCI and ERA5 Essential Climate Variables (ECVs) to environmental processes that drive the seasonal and interannual variability as well as long-term trends. Arctic river water is optically dominated by coloured dissolved organic matter allowing rather simple band ratio retrievals a better performance compared to complex retrieval algorithms (e.g. semi-analytical & neural networks). Here, we use a ratio between 665nm and 512 nm and calibrate this with an extensive in situ dataset. The results show that extraction of CCI Ocean Color band ratio in the fluvial-marine transition zones, in combination with known relationships between optical properties of organic matter and its concentrations, provides excellent estimates for dissolved organic carbon (DOC) when compared to in situ data. The seasonal and interannual variability in DOC export by Arctic rivers is dominantly driven by large-scale precipitation anomalies within the river catchments. CCI Permafrost ECVs such as permafrost extent, active layer thickness and ground temperature show alarming trends of thaw for 1997 to 2018, whose influence on the long-term export of OC from land to the Arctic Ocean is unexplored so far. Continuing degradation of permafrost in the catchments in conjunction with projected increases in river discharge will have an impact on the global carbon cycle, aquatic ecosystems and the global climate that is currently difficult to assess due to the lack of time series and process studies. Long-term global ECVs constitute a cornerstone of such assessments and will help quantifying impacts of thawing terrestrial permafrost on aquatic ecosystems and the Arctic Ocean in particular.

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Conference (Poster)
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Event Details
Living Planet Symposium, 23 May 2022 - 27 May 2022, Bonn, Germany.
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Juhls, B. , Overduin, P. P. , Runge, A. , El Kassar, J. and Grosse, G. (2022): Arctic land-ocean organic carbon flux variability and its drivers monitored using ESA CCI ECVs , Living Planet Symposium, Bonn, Germany, 23 May 2022 - 27 May 2022 .

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