06 Feb 2023
 | 06 Feb 2023
Status: this preprint is open for discussion.

Hyperspectral imaging sediment core scanning tracks high-resolution Holocene variations in (an)oxygenic phototrophic communities at Lake Cadagno, Swiss Alps

Paul D. Zander, Stefanie B. Wirth, Adrian Gilli, Sandro Peduzzi, and Martin Grosjean

Abstract. Pigments produced by anoxygenic phototrophic bacteria are valuable proxies of past anoxia in lacustrine and marine environments. Pigment measurement typically requires time-consuming and costly chemical extractions and chromatographic analyses, which limits the temporal resolution of paleoenvironmental reconstructions based on sedimentary pigments. Here, we evaluate the potential of in-situ hyperspectral imaging (HSI) core scanning as a rapid, non-destructive method to document high-resolution changes in oxygenic and anoxygenic phototrophic communities at meromictic Lake Cadagno, Switzerland. Three distinct groups of pigments can be detected with the HSI method in the sediments of Lake Cadagno; each pigment group represents a different phototrophic community. Oxygenic phototrophs are indicated by total chloropigments (TChl; chlorophyll-a, -b and derivatives). Two types of anoxygenic phototrophs were distinguished – purple sulfur bacteria (PSB), represented by bacteriochlorophyll-a, and green sulfur bacteria (GSB), represented by bacteriochlorophylls-c, -d, and -e. HSI pigment indices were validated by pigment measurements performed on extracted samples using spectrophotometer and high-performance liquid chromatography (HPLC). Bacteriochlorophylls were present throughout the past 10 kyr, confirming geochemical evidence of nearly continuous stratification and sulfidic conditions at Lake Cadagno. Major shifts in the anoxygenic phototropic communities are recorded at decadal to millennial scales. GSB and PSB communities coexisted from 10.2–3.4 kyr BP, with dominance of PSB over GSB from 8.8–3.4 kyr BP indicating strongly stratified conditions in the lake and strong light radiation at the chemocline. From 3.4–1.3 kyr BP, PSB were mostly absent, and GSB became dominant, implying lower light intensity at the chemocline due to a combination of factors including deforestation in the lake surroundings, increased flood frequency, cooler climatic conditions, and changes in groundwater solute concentrations. The high-resolution HSI data show that frequent flood events and mass movements disturbed the chemocline and the anoxygenic bacterial communities, and that the PSB were particularly sensitive and slow to recover following these disturbance events. This study demonstrates for the first time that HSI can detect GSB related pigments, making the method uniquely valuable as a rapid tool to study samples containing pigments of both oxygenic and anoxygenic phototrophs.

Paul D. Zander et al.

Status: open (until 31 Mar 2023)

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  • RC1: 'Comment on egusphere-2023-151', Anonymous Referee #1, 09 Mar 2023 reply

Paul D. Zander et al.

Data sets

Lake Cadagno sediment core hyperspectral imaging and pigment data tables Zander, P. D., Wirth, S. B., Gilli, A., Peduzzi, S., and Grosjean, M.

Paul D. Zander et al.


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Short summary
This study shows for the first time that hyperspectral imaging can detect bacteriochlorophyll pigments produced by green sulfur bacteria in sediment cores. We tested our method on cores from Lake Cadagno, Switzerland and were able to reconstruct high-resolution variations in the abundance of green and purple sulfur bacteria over the past 12,700 years. Climate conditions, flood events, and land use had major impacts on the lake’s biogeochemical conditions over short and long timescales.