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Date of Award

Summer 2024

Document Type

Masters Thesis

Department or Program Affiliation

Geology

Degree Name

Master of Science (MS)

Department

Geology

First Advisor

Ponton, Camilo

Second Advisor

Pfeiffer, Allison

Third Advisor

Love, Brooke

Abstract

The dynamics of the Cordilleran Ice Sheet (CIS) over the last glacial period are complex, with several instances of ice retreat and readvance before the final retreat. This study demonstrates that in western Washington, marine sediment cores can be used to reconstruct continental ice cover. Here, I present a reconstruction of terrestrial landscape evolution within the Puget Sound during the last deglaciation, using geochemical analyses of organic matter from marine sediment cores. I measured the carbon isotope composition in bulk organic matter (d13Corg) and concentrations of leaf wax biomarkers (n-alkanes and fatty acid methyl esters) from three marine sediment cores off the coast of Washington State. Sedimentary organic matter is predominantly terrestrial in origin in all three cores and constitutes 75-95% of the total organic matter. The end of glacial sedimentation is marked by a positive carbon isotope excursion (2.3 - 6.9‰ in magnitude) and by an increase in concentration of leaf wax biomarkers, that most likely represents a period of rapid ice sheet retreat in the Puget Lowlands. Using biomarker abundances to produce an estimate for terrestrial organic matter (%Terr) and an isotope mass balance mixing model, I determined the isotopic excursion represents a change in source of vegetation cover among C3plant varieties. My calculations suggest that shrubs and forbs were more abundant than trees in the Puget Lowlands during the last glacial period. Furthermore, I propose the positive isotopic excursion marks the drainage of Glacial Lake Russell into the Strait of Juan de Fuca and the reorganization of continental drainage pathways as the Puget Lobe of the CIS retreated north.

Type

Text

Keywords

stable isotopes, biomarkers, Puget Lobe, Cordilleran Ice Sheet, carbon, n-alkanes, Fatty Acids, vegetation cover, Pacific Northwest plants

Publisher

Western Washington University

OCLC Number

1452262148

Subject – LCSH

Land cover--Washington (State)--Puget Sound; Phytogeography--Washington (State)--Puget Sound; Drift--Washington (State)--Puget Sound; Marine sediments--Washington (State)--Puget Sound--Analysis; Drift--Washington (State)--Puget Sound

Geographic Coverage

Puget Sound (Wash.)

Format

application/pdf

Genre/Form

masters theses

Language

English

Rights

Copying of this document in whole or in part is allowable only for scholarly purposes. It is understood, however, that any copying or publication of this document for commercial purposes, or for financial gain, shall not be allowed without the author’s written permission.

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