Statement_of_Work_1.pdf

STATEMENT OF WORK

Analysis of Diatoms in Sedimentary Deposits of Karluk Lake, Kodiak Island, Alaska, to Evaluate

Sediment Emplacement by Seismic Shaking or Storms

1.0 Introduction and Background

Karluk Lake on Kodiak Island, Alaska, is a ~140 m deep moraine dammed lake that fills a formerly glaciated valley. Sediments beneath the lake floor include unusual sand‐rich deposits that differ from finer‐grained silt and organic sediment deposited normally. In other Alaskan lakes, anomalous sandy lake deposits, identified as turbidites, may record turbidity currents in the lake caused by a number of processes including flooding of tributary streams or strong shaking during earthquakes. To investigate the likely origin of the sandy deposits in Karluk Lake, the USGS is interested in methods to differentiate sediment remobilized in different lake environments (littoral, deltaic, basin slopes) from sediment transported into the lake during flooding of tributary streams.

Diatoms are a class of single‐celled yellow‐brown algae (Bacillariophyceae) found in nearly all environments where there is water and enough light for photosynthesis. Unlike most algal groups, diatoms produce silt‐size preservable hard parts composed of biogenic silica (frustules) that are distinctly ornamented by species and that can be recovered from sedimentary deposits after the organic contents of the cell has decayed. Because certain diatoms species are adapted to specific growth environments (e.g., lakes, streams, wetlands, coastal ocean, moist terrestrial soils), the types of diatoms observed in a sedimentary deposit can be used to reconstruct the environment in which the sediment originally accumulated. Of significance for this project, diatoms are prolific in subarctic freshwater lakes and streams and are known to be diverse and abundant in Karluk Lake (e.g., Terrell, 1987; Finkle, 2013;

Gregory‐Eaves et al., 2003). We propose to document diatoms in modern and fossil deposits of Karluk

Lake to help unravel the stratigraphic record past event‐driven sediment accumulation in deep subbasins of the lake, whether from storm‐driven terrestrial runoff or downslope failure from seismic shaking. These data will help refine the chronology of prehistoric subduction zone earthquakes and major storms in the geologic record of Karluk Lake.

2.0 Scope

The work will include analysis of 70 samples that were collected by USGS personnel at Karluk Lake in

2022. Sample types include plankton tows collected from three long‐term study sites in the lake, surface sediment from environments along the lake shoreline and tributary stream channels, and sediment collected in gravity cores from a range of depths in subbasins of the lake.

Sediment samples will be chemically pretreated and processed to produce microscope slides for quantitative analysis of diatom species composition and abundance. A voucher flora of prominent diatom taxa will be produced.

3.0 Applicable Documents

Finkle, H., 2013, Autonomous salmon lake mapping and limnological assessment of Karluk Lake, 2012:

Alaska Department of Fish and Game Fishery Data Series No. 13‐39, 53 p.

Foged, N., 1981, Diatoms in Alaska: Bibliotheca Phycologica, Band 53, J. Cramer, Vaduz, 317 p.

Gregory‐Eaves, I., Smol, J.P., Douglas, M.S.V., and Finney, B.P., 2003, Diatoms and sockeye salmon

(Oncorhynchus nerka) population dynamics: Reconstructions of salmon‐derived nutrients over the past

2,200 years in two lakes from Kodiak Island, Alaska: Journal of Paleolimnology, v. 30, no. 1, p. 35–53.

Hemphill‐Haley, E., Kelsey, H.M., Graehl, N., Casso, M., Caldwell, Loofbourrow, C., Robinson, M., Vermeer, J., and Southwick, E., 2019, Recent sandy deposits at five northern California coastal wetlands—Stratigraphy, diatoms, and implications for storm and tsunami hazards: U.S. Geological

Survey Scientific Investigations Report 2018–5111, 187 p., accessed February 5, 2020, at http://pubs.er.usgs.gov/publication/sir20185111.

Hemphill‐Haley, E., and Lewis, R.C., 2003, Diatom data from Bradley Lake, Oregon: downcore analyses:

US Geological Survey Open‐File Report, v. 3, p. 190.

Lange‐Bertalot, H., Hofman, G., Werum, M., and Cantonati, M., 2017, Freshwater Benthic Diatoms of

Central Europe (M. Cantonati, M. G. Kelly, & H. Lange‐Bertalot, Eds.): Koeltz Botanical Books, Germany, 942 p.

Reavie, E.D., and Kireta, A.R., 2015, Centric, Araphid and Eunotioid Diatoms of the Coastal Laurentian

Great Lakes: Sampling, Taxonomic Descriptions and Environmental Characteristics: Bibliotheca

Diatomologica, J. Cramer.

Ross, A.E.M., and Goldfinger, C., 2022, A 2700‐yr record of Cascadia megathrust and crustal/slab earthquakes from Upper and Lower Squaw Lakes, Oregon: In Review, accessed November 18, 2022, at https://www.researchsquare.com/article/rs‐2277419/v1.

Spaulding, S.A., Potapova, M.G., Bishop, I.W., Lee, S.S., Gasperak, T.S., Jovanoska, E., Furey, P.C., and

Edlund, M.B., 2021, Diatoms.org: supporting taxonomists, connecting communities: Diatom Research, v.

36, no. 4, p. 291–304.

Terrell, T.T., 1987, The diatom flora (Bacillariophyta) of Karluk Lake, Alaska as determined from sediment cores: Nova Hedwigia, v. 45, no. 3–4, p. 415–422.

Vandekerkhove, E., Van Daele, M., Praet, N., Cnudde, V., Haeussler, P.J., and De Batist, M., 2020, Flood‐ triggered versus earthquake‐triggered turbidites: A sedimentological study in clastic lake sediments

(Eklutna Lake, Alaska): Sedimentology, v. 67, no. 1, p. 364–389.

4.0 Technical Requirements

Sediment samples will be prepared for diatom analysis based on the procedure described in Hemphill‐

Haley et al. (2019) with the addition that Hyrax® will be used as the mounting medium for microscope slides. Diatoms will be identified and counted with a light microscope supplied with Normarksi interference contrast for high‐resolution observation and photomicroscopy. A standard count of 300‐

400 valves per sample will be completed to ensure sound statistical comparisons among samples. The data will be summarized as relative species abundance (%) and valve concentrations in valves/g of sediment. Taxonomic identification will follow published diatom taxonomic references including

Spaulding et al. (2021) and references therein.

5.0 Deliverables

Deliverables will include a report containing (a) a description of methods; (b) voucher flora representing the dominant taxa encountered in the project; (c) spreadsheets containing lists of diatom taxa and quantitative counts for each sample site (MS Excel format); (d) comments on the condition

(preservation) of valves in each sample; and (e) interpretation of the provenance of the sediment sample and probable sediment transport mechanism (storm‐induced flooding or downslope transport by seismic shaking) based on entrained diatoms.