Insights into glacial processes from micromorphology of silt-sized sediment

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Insights into glacial processes from micromorphology of silt-sized sediment.pdf (4.73 MB)

Date

2023-06-20

Authors

Lepp, Allison P.
Miller, Lauren E.
Anderson, John B.
O'Regan, Matt
Winsborrow, Monica C.M.
Smith, James A.
Hillenbrand, Claus-Dieter
Wellner, Julia S.
Prothro, Lindsay O.
Podolskiy, Evgeny A.

ORCID

Journal Title

Journal ISSN

Volume Title

Publisher

DOI

https://doi.org/10.5194/tc-2023-70

URI

https://hdl.handle.net/1969.6/98052

Abstract

Meltwater plume deposits (MPDs) from marine sediment cores have elucidated clearly connected, yet difficult to constrain, relationships between ice-marginal landform construction, grounding-zone retreat patterns, and subglacial hydrology for several glacial systems in both hemispheres. Few attempts have been made, however, to infer coveted details of subglacial hydrology, such as flow regime, drainage style, and mode(s) of sediment transport through time from grain-scale characteristics of MPDs. Using MPD, till, and ice-proximal diamicton samples collected offshore of six modern and relict glacial systems in both hemispheres, we examine whether grain-shape distributions and microtexture assemblages (collectively, grain micromorphology) of the silt fraction are the result of subglacial meltwater action, or are indistinguishable from glacial proximal and subglacial sediments from the same region. We find that of all grains imaged (n=9,400), three-quarters can be described by one-quarter of the full range of measured shape morphometrics, indicating widespread and efficient abrasive processes in subglacial environments. Microtexture analysis reveals that while grains comprising MPDs show evidence of edge rounding more often than tills, fluvial microtextures occur in modest amounts on grain surfaces. Furthermore, MPDs retain many mechanical (i.e., glacial) textures in comparable abundances to tills. Significant alteration of MPDs from till sources is observed for systems (1) for which intensive, potentially catastrophic, meltwater drainage events in the Holocene are inferred from marine geologic records, and (2) with comparatively less mature till grains and a contribution of supraglacial melt to the bed, indicating that quantifiable grain-shape alteration of MPDs may reflect a combination of young till, high-energy flow of subglacial meltwater, persistent sediment entrainment, and/or long sediment transport distances. We encourage future works to integrate grain micromorphology into site-specific marine sediment analyses, which may distinguish periods of persistent, well-connected subglacial discharge from periods of sporadic or disorganized drainage and provide context needed to estimate sediment fluxes and characterize ice response to subglacial meltwater transmission. In addition, this work demonstrates that glacial and fluvial surface textures are retained on silts in adequate abundance for microtexture analysis.

Description

Keywords

sediment, meltwater plume deposits (MPDs), micromorphology

Sponsorship

The authors acknowledge the captains, crews, and science parties who over the decades collected the dozens of cores sampled for this research. Funding for this research comes from a subcontract to the University of Virginia to LEM as part of the larger collaborative Thwaites Offshore Research grant (NSF OPP Grant 1738942 and Natural Environment Research Council grant nos. NE/S006664/1 and NE/S006672/1). We thank M. Esteves, V. Stanley, and the curatorial staff at the Oregon State University Marine and Geology Repository for their assistance with sample requests. D. Buskard and M. Prakash were instrumental in developing the MATLAB script. The Quanta 650 SEM is housed in the Nanoscale Materials Characterization Facility, and we thank the staff for providing the first author instrument training. Figures use the colorblind-friendly palette “Java” from the MetBrewer color package developed by B. R. Mills (https://github.com/BlakeRMills/MetBrewer). Data analysis and interpretation presented in this study was conducted at the University of Virginia in Charlottesville, Virginia. The University of Virginia was built by enslaved laborers on the unceded lands of the Monacan Nation, who have protected and 545 cultivated these lands for thousands of years. The authors acknowledge and respect their stewardship of the land, past, present, and future.

Rights:

CC BY 4.0 DEED Attribution 4.0 International

Citation

Lepp, A. P., Miller, L. E., Anderson, J. B., O'Regan, M., Winsborrow, M. C. M., Smith, J. A., Hillenbrand, C.-D., Wellner, J. S., Prothro, L. O., and Podolskiy, E. A.: Insights into glacial processes from micromorphology of silt-sized sediment, The Cryosphere Discuss. [preprint], https://doi.org/10.5194/tc-2023-70, in review, 2023.

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