IAP2-22-465

Controls on organic carbon burial in fjords – a case study from an extreme glacial lake outburst flood in Elliott Creek (BC, Canada)

Previous work suggests that marine fjords are responsible for burying globally significant amounts of organic carbon (OC). Understanding the burial of terrestrial OC in fjords is important on a global scale, as previous work estimated that just the fine-grained fjord sediments are responsible for burying ~11% of global organic carbon flux into the oceans (Smith et al. 2015). More recently it was shown that coarse-grained sediment deposited by small rivers floods will significantly increase that amount of OC burial in fjords (Hage et al, 2020, 2022). Exceptionally large and infrequent floods, like glacial lake outburst floods (GLOFs), are likely to transport and bury larger amounts OC into coarse-grained fjord deposits, however their role remains poorly constrained due to their infrequent nature. Yet, constraining the full OC burial budget in marine sediments is important as these sediments are the second largest sink of atmospheric CO2 and thus contributes to long-term regulation of climate (Gaillardet et al., 1999).

An exceptional GLOF occurred on 28th Nov 2020 at Elliot Creek (BC, Canada, Figure 1) that now provides us a unique opportunity to study the OC burial efficiency of such extreme events. Reconstruction from the measured 4.9 Mw seismic activity that coincided with the event indicates the original landslide dislodged 30 million tonnes of sediment and triggered a ~100m high displacement-wave in the glacial lake. This wave in turn broke through the lake’s moraine-dam, releasing large amounts of water, which powerfully scoured Elliott Creek before entering into the fjord. The event posed a hazard to marine traffic and coastal structures and destroyed significant salmon, wildlife and forest resources of Homalco First Nations. The Elliot Creek event moved large volumes of sediment and OC, which are ultimately deposited in the fjord. Fortuitously, Bute Inlet was previously the site of an extremely detailed time series of seabed surveys, as it was mapped ten times in between 2008 up to 2020 (Heijnen et al., 2022). Recent work by our group at Bute Inlet has shown how turbidity currents transport young terrestrial OC from the river mouth down to the deeper fjord waters. The extensive background data on the bathymetry, the current dynamics and the geochemical signatures of the OC in the fjord under normal conditions now enable a unique opportunity to study the OC burial of large GLOFs.

This project aims to test two hypotheses, which are: 1) large GLOFs can transport vast amounts of sediment and OC to the distal lobe and (2) young terrestrial organic matter can be efficiently buried in these deep water fjord sediment. Here, efficiency refers to direct transport from source to sink, as opposed the normal conditions in which OC only reaches this sink through many staggered smaller transport events.

Click on an image to expand

Image Captions

Figure 1: A) overview of Bute Inlet fjord, B) Indication of the Glacial Lake Outburst Flood (GLOF) location in Elliot Creek, C) helicopter images taken several days after the GLOF occurred.

Methodology

The hypotheses will be tested by mapping the GLOF-related deposits throughout the fjord and characterising their OC components. Field data collection is already carried out by previous projects where post-GLOF bathymetric surveys were done, and samples were collected. Now, these bathymetry data need to be worked up to produce series of difference maps to identify post-GLOF deposition and erosion since 2020.

Sediment and organic carbon characterisation will include grain-size analysis, XRD, total organic carbon, C-N-S, stable carbon isotope and radiocarbon composition. Combination of all routine organic geochemistry (TOC, CNS, d13C and 14C) and textural data will be used for initial fingerprinting of OC (marine or terrestrial source).

Throughout the project, student will be in touch and working closely with other project partners, including Canadian Geological Survey, Hakai Institute and Homalco First Nations

Project Timeline

Year 1

The first year of the projects will mainly focus on preparing bathymetry difference maps and identifying GLOF depocentres. First textural and mineralogical sediment characterisation will towards the end of the Year-1. This analysis will include clay mineralogy, sandstone petrography and grain size analysis.
Year-1 will also include visit to field area for land-based sampling and meeting with project partners including Canadian Geological Survey, Hakai institute and Homalco First Nations.

Year 2

Year-2 will mainly focus on organic carbon characterisation of GLOF deposits. Majority of the year-2 will be dedicated to laboratory work including identification of total organic carbon (TOC), C-N-S values of the sediment and isotopic composition of organic carbon fraction (d13C). Radiocarbon dating will also be used if long cores become available through ongoing projects on Bute Inlet and if old sediments need to be dated.

Year 3

Organic carbon characterisation will continue into Year-3. Data interpretation and writing-up the dissertation should commence in the second half of year-3.

Year 3.5

The last 6 months of the studentship will mainly focus on writing up the dissertation as well as dissemination of the findings.

Training
& Skills

During the lifespan of the project, student will develop skills on
– spatial data handling and analysis (Bathymetry, difference maps, GIS skills)
– sedimentary lab and petrography (clay mineralogy, sandstone petrography, grain size and textural analysis)
– organic carbon identification and lab techniques (TOC, CNS, stable isotopes)

References & further reading

Gaillardet, J., Dupré, B., Louvat, P., Allègre, C. J., 1999, Global silicate weathering and CO2 consumption rates deduced from the chemistry of large rivers, Chemical Geology, 159, 1–4, p3-30.
Hage, S., Galy, V.V., Cartigny, M.J., Heerema, C., Heijnen, M.S., Acikalin, S., Clare, M.A., Giesbrecht, I., Gröcke, D.R., Hendry, A. and Hilton, R.G., 2022. Turbidity currents can dictate organic carbon fluxes across river‐fed fjords: An example from Bute Inlet (BC, Canada). Journal of Geophysical Research: Biogeosciences, p.e2022JG006824.

Hage, S., Galy, V.V., Cartigny, M.J.B., Acikalin, S., Clare, M.A., Gröcke, D.R., Hilton, R.G., Hunt, J.E., Lintern, D.G., McGhee, C.A. and Parsons, D.R., 2020. Efficient preservation of young terrestrial organic carbon in sandy turbidity-current deposits. Geology, 48(9), pp.882-887.

Heijnen, M.S., Clare, M.A., Cartigny, M.J., Talling, P.J., Hage, S., Pope, E.L., Bailey, L., Sumner, E., Lintern, D.G., Stacey, C. and Parsons, D.R., 2022. Fill, flush or shuffle: How is sediment carried through submarine channels to build lobes?. Earth and planetary science letters, 584, p.117481.

Smith, R.W., Bianchi, T.S., Allison, M., Savage, C. and Galy, V., 2015. High rates of organic carbon burial in fjord sediments globally. Nature Geoscience, 8(6), pp.450-453.

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