Distinguishing storm or fire events in historic sediments Willy Amidon, Eric Butler

Introduction

• Lake sediments record past events

• Coring allows study of these records

Previous work

Brown (2000), Noren (2001) used long (6m) cores to reconstruct paleoclimate and environment

- identified coarse, inorganic sediment layers

- interpreted as storm events

OUR PURPOSE: Distinguish fire events from storm events

Goals

Use short cores (< 40cm) to:

• Quantify historic charcoal levels

• Identify historic/prehistoric boundary

• Interpret any “storm” layers found

• Refine lab techniques

Methods of analysis

• Visual logs

- Changes in color, density, grain size, debris

• Loss on Ignition (LOI)

- Identifies trends in organic carbon content

• Charcoal analysis

- Elemental analyzer quantifies elemental carbon (charcoal)

Coring method

• Gravity cores from canoe

• Extrude in the field

• Cores separated into 1 cm intervals

Sample preparation

• Dry samples & weigh

• Digest in nitric acid

- removes organic carbon

• Rinse & dry, weigh

• Elemental analyzer

- measures elemental carbon (charcoal)

Results

• Incomplete digestion (SY)

• Incomplete washing (SY, OG)

Alternate methods

• Visual log on OG core

• LOI on OG core

Results

• Correlation between LOI and organic material

• Suggests a storm/fire layer?

• May also represent logging

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Loss-on-ignition (%)

Coming soon

• Elemental analysis on rewashed samples

- % charcoal content

• Hopeful correlation with LOI and visual log

- Does increase in charcoal correlate with decrease in LOI & color change?

Future work

• Apply procedure to longer cores

• Pb210 dating of macrofossils (wood chips)

• Analyze & compare more short cores