UVM Theses and Dissertations
Format:
Print
Author:
Nelson, Alice H.
Title:
Dept./Program:
Geology
Year:
2013
Degree:
MS
Abstract:
Paraglacial environments are landscapes that have been exposed by retreating glaciers, where geomorphic change and sediment redistribution is thought to occur rapidly. In my Master's Thesis, I use the concentration of in situ ¹⁰Be, which is a cosmogenically produced isotope, to trace the relative contribution of different sediment sources to Greenland's paraglacial sediment budget. Over the course of two field seasons, we visited three different paraglacial landscapes along the Greenland Ice Sheet margin near Kangerlussuaq, Narsarsuaq, and Tasiilaq. In total, we collected 62 sediment samples from glacial (n=19) and ice-free terrain (n=10), from channels where sediment is sourced from a mixture of glacial and ice-free terrain (n=28), from Holocene fluvial terraces (n=4), and from one aeolian sand dune.
The concentration of in situ ¹⁰Be in sediment ranges from 1,600 to 34,000 atoms g⁻¹ and we are able to use in situ ¹⁰Be concentration as a sediment source tracer because the ¹⁰Be concentration in sediment sourced from glacial terrain is characteristically different from that sourced from ice-free terrain. The ¹⁰Be concentration in sediment from ice-free terrain is significantly higher than the ¹⁰Be concentration in sediment from glacial and mixed sources and is also higher than the concentration in terrace sediment deposited earlier during the Holocene.
In Kangerlussuaq and Tasiilaq, we constrained the exposure age of the ice-free landscape from previously published cosmogenic and radiogenic dating work, and in Narsarsuaq, we augmented previous research with exposure ages calculated from the in situ ¹⁰Be concentration in bedrock (n=5) and boulder (n=6) samples. Ice-free portions of our field areas have had -7 to 11 thousand years of recent subaerial exposure to cosmic radiation and thus, ¹⁰Be concentration in sediment sourced from ice-free terrain is significantly higher than in glacial sediment, which is sourced from a landscape that has been shielded from cosmic rays for much of the last 3.5 million years. We calculated that the low concentrations of ¹⁰Be measured in glacial sediment must have accumulated at depth, and have been inherited from a prolonged period of exposure that pre-dates the Greenland Ice Sheet.
The similarity in ¹⁰Be concentration in sediment from-glacial and mixed fluvial sources indicates that the Greenland Ice Sheet is the dominant source of sediment moving through the paraglacial landscape and into the fjords. The similarity in concentration between glacial sediment and terrace sediment indicates that glacially-sourced sediment also dominated the fluvial system earlier during the Holocene. Our findings imply that the ¹⁰Be concentration in marine sediment sourced from Greenland will be controlled by the efficacy and timing of ice sheet erosion rather than the extent of paraglacial landscape exposure. ure. These findings will help inform a larger research project in which ¹⁰Be concentration in ocean core sediment will be used to create a 5 to 6 million year record of Greenland glaciation.
The concentration of in situ ¹⁰Be in sediment ranges from 1,600 to 34,000 atoms g⁻¹ and we are able to use in situ ¹⁰Be concentration as a sediment source tracer because the ¹⁰Be concentration in sediment sourced from glacial terrain is characteristically different from that sourced from ice-free terrain. The ¹⁰Be concentration in sediment from ice-free terrain is significantly higher than the ¹⁰Be concentration in sediment from glacial and mixed sources and is also higher than the concentration in terrace sediment deposited earlier during the Holocene.
In Kangerlussuaq and Tasiilaq, we constrained the exposure age of the ice-free landscape from previously published cosmogenic and radiogenic dating work, and in Narsarsuaq, we augmented previous research with exposure ages calculated from the in situ ¹⁰Be concentration in bedrock (n=5) and boulder (n=6) samples. Ice-free portions of our field areas have had -7 to 11 thousand years of recent subaerial exposure to cosmic radiation and thus, ¹⁰Be concentration in sediment sourced from ice-free terrain is significantly higher than in glacial sediment, which is sourced from a landscape that has been shielded from cosmic rays for much of the last 3.5 million years. We calculated that the low concentrations of ¹⁰Be measured in glacial sediment must have accumulated at depth, and have been inherited from a prolonged period of exposure that pre-dates the Greenland Ice Sheet.
The similarity in ¹⁰Be concentration in sediment from-glacial and mixed fluvial sources indicates that the Greenland Ice Sheet is the dominant source of sediment moving through the paraglacial landscape and into the fjords. The similarity in concentration between glacial sediment and terrace sediment indicates that glacially-sourced sediment also dominated the fluvial system earlier during the Holocene. Our findings imply that the ¹⁰Be concentration in marine sediment sourced from Greenland will be controlled by the efficacy and timing of ice sheet erosion rather than the extent of paraglacial landscape exposure. ure. These findings will help inform a larger research project in which ¹⁰Be concentration in ocean core sediment will be used to create a 5 to 6 million year record of Greenland glaciation.