Millennial-scale Variability of a Major East Antarctic Outlet Glacier during the Last Glaciation

45 Pages·2016·7.46 MB·English

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USF Tampa Graduate Theses and Dissertations USF Graduate Theses and Dissertations
10-19-2015
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Michelle Guitard
University of South Florida, [email protected]
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Guitard, Michelle, "Millennial-scale Variability of a Major East Antarctic Outlet Glacier during the Last
Glaciation" (2015). USF Tampa Graduate Theses and Dissertations.
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Millennial-scale Variability of a Major East Antarctic Outlet Glacier during the Last

Glaciation

by

Michelle E. Guitard

A thesis submitted in partial fulfillment
of the requirements for the degree of
Master of Science in Marine Science
with a concentration in Geological Oceanography
College of Marine Science
University of South Florida

Major Professor: Amelia E. Shevenell, Ph.D.
Eugene W. Domack, Ph.D.
Brad E. Rosenheim, Ph.D.

Date of Approval:
November 3, 2015

Keywords: Amery Ice Shelf, radiocarbon, cosmogenic beryllium-10, millennial-scale variability

Copyright © 2015, Michelle E. Guitard
ACKNOWLEDGMENTS

I want to say a huge thank you to those who helped and supported me through my
Masters degree. Thank you to my major advisor, Amelia Shevenell, who works so hard for her
students. She inspires me to work hard and to always keep learning. Thank you to my committee
members, Brad Rosenheim and Eugene Domack, for their insight and guidance on this project.
Thank you also to Amy Leventer at Colgate University, and Yusuke Yokoyama and his lab at the
Atmosphere and Ocean Research Institute, University of Tokyo for their mentorship in the
laboratory and in the field. Thank you to the Australian researchers who have devoted their time
to investigating the Prydz Bay region and for their scientific collaboration. Thank you to the
crew and support staff aboard the Research Vessels Nathaniel B. Palmer and Aurora Australis
for their assistance on cruises NBP01-01, AA-186, and KROCK. Thank you to the faculty, staff
and students of the Paleo Lab at the College of Marine Science for making the lab experience a
great one. Last, but certainly not least, thank you to my friends and family who have supported
me through the triumphs and the tears. Your love and support mean the world to me.
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TABLE OF CONTENTS

List of Tables ................................................................................................................................. iii

List of Figures ................................................................................................................................ iv

Abstract ........................................................................................................................................... v

Introduction .................................................................................................................................... 1
Background ......................................................................................................................... 1
Study Location .................................................................................................................... 2

Methods ........................................................................................................................................... 8
Physical Properties Analyses .............................................................................................. 8
Development of Marine Composite Depth Scale ................................................................ 8
Ramped Pyrolysis Preparation for Radiocarbon Analysis .................................................. 8
Radiocarbon Analysis, Correction and Calibration ............................................................. 9
Beryllium-10 Preparation .................................................................................................... 9

Results and Discussion .................................................................................................................. 11
Physical Properties ............................................................................................................ 11
Radiocarbon ...................................................................................................................... 11
Beryllium-10 .................................................................................................................... 12
Regional Glacial and Oceanic Fluctuations: Timing and Variability ............................... 14

Conclusions ................................................................................................................................... 17

References ..................................................................................................................................... 18

Appendix A: Extended Data ......................................................................................................... 22
Extended Data Figure 1 ..................................................................................................... 22
Extended Data Figure 2 ..................................................................................................... 23
Extended Data Table 1 ...................................................................................................... 24
Extended Data Table 2 ...................................................................................................... 26
Extended Data Table 3 ...................................................................................................... 27
Extended Data Table 4 ...................................................................................................... 28

Appendix B: Supplementary Methods .......................................................................................... 29
Radiocarbon Contamination Correction ............................................................................ 29
Calibration ......................................................................................................................... 31
Beryllium-10 Concentration Corrections .......................................................................... 31
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Beryllium-10 Budget Estimates ....................................................................................... 32

Appendix C: Supplementary Discussion ....................................................................................... 34
Diatom Assemblages ......................................................................................................... 34

Appendices References ................................................................................................................. 36

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LIST OF TABLES

Extended Data Table 1: Percent diatom abundance (%abundance) from NBP01-01
JPC-34, -35, and -36 SMO units .................................................................................. 24

Extended Data Table 2: Prydz Channel 14C and cal BP ages, δ 13C, and %TOC ........................ 26

Extended Data Table 3: NBP01-01 ramped pyrolysis 14C ages, RP temperature range,
uncorrected and corrected F values ............................................................................ 27
m

Extended Data Table 4: Aliquot weight, uncorrected and corrected 10Be abundance with
associated error, and flux for NBP01-01 cores ............................................................ 28

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LIST OF FIGURES

Figure 1: Prydz Channel, East Antarctica, depicting multibeam swath bathymetry, core
locations ......................................................................................................................... 5

Figure 2: NBP01-01 core stratigraphy, magnetic susceptibility (MS), % diatom abundance,
10Be concentration ([10Be]) alongside Prydz Channel composite MS and
radiocarbon (14C) ages ................................................................................................... 6

Figure 3: Improved acid insoluble organic matter (AIOM) radiocarbon (14C) ages derived
from the ramped pyrolysis (RP) technique .................................................................... 7

Figure 4: Oceanic and climatic millennial-scale variability ......................................................... 16

Extended Data Figure 1: Down-section NBP01-01, AA-186, and KROCK core lithology
and normalized magnetic susceptibility data ............................................................... 22

Extended Data Figure 2: Uncorrected Beryllium-10 concentration (10Be), Total Organic
Carbon (TOC), and δ13C for NBP01-01 cores ............................................................. 23

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ABSTRACT
Ongoing retreat of Antarctica’s marine-based glaciers is associated with warm (~2° C)
modified Circumpolar Deep Water intrusion onto the continental shelf, suggesting that Southern
Ocean temperatures may influence Antarctic ice sheet stability. Understanding past cryosphere
response to environmental forcing is crucial to modeling future ice sheet behavior. Of particular
interest is the response of the East Antarctic Ice Sheet (EAIS), which stands to contribute ~20 m
to global sea level. However, marine sediment sequences recording timing and variability of
EAIS fluctuations through the last major climate shift, the Last Glacial Maximum (LGM), are
either missing from the margin or have poor chronological control. Here we present three marine
sediment cores that contain a record of pre-LGM fluctuations of the marine-based Lambert
Glacier-Amery Ice Shelf (LG-AIS) system into Prydz Channel, East Antarctica. Analyses of core
lithology, physical properties, cosmogenic nuclide concentration and diatom assemblage
demonstrate that Prydz Channel was characterized by alternating open-marine and sub-shelf
deposition, implying repeated LG-AIS fluctuations through the LGM. Our radiocarbon
chronology demonstrates that LG-AIS fluctuations occurred on millennial timescales. Our record
corroborates regional marine and terrestrial records, which demonstrate millennial scale
variability in Antarctic Circumpolar Current strength, ice-rafted debris deposition, sea ice extent,
Antarctic atmospheric temperature, and Southern Ocean sea surface temperature. This evidence
suggests that the EAIS was sensitive to sub-orbital climate forcing in the past, and has
implications for modeling future EAIS behavior.
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INTRODUCTION
Background
The response of Antarctica’s ice sheets to ongoing atmosphere and ocean warming is the
largest uncertainty in future sea level rise projections. Whereas much has been learned about the
impact of warming on the marine-based West Antarctic Ice Sheet (WAIS)1,2, recent observations
of East Antarctic Ice Sheet (EAIS) outlet glacier retreat suggest that this ice sheet, with its 19.2
meters of marine-based sea level equivalent, may also respond sensitively to abrupt climate
perturbations, including the warm ocean waters presently destabilizing the WAIS3. To reduce
uncertainty surrounding future sea-level rise, predictive models require reliable ice-proximal
observations of the orbital to millennial-scale EAIS response to past climate change.
Models and observations highlight the sensitivity of Antarctica’s ice sheets to abrupt
oceanic perturbations (e.g. sea level rise and/or ocean warming) in regions of enhanced glacial
flow2. Models that prescribe abrupt warmings and/or sea level rise during the last deglaciation
reveal maximum ice flow and discharge rates via outlet glaciers that drain into the Weddell Sea,
Amundsen Sea, Ross Sea, and Prydz Bay and suggest that abrupt oceanic forcings propagate
rapidly through associated glacial catchments4. Chronologically constrained observations of late
Quaternary (0-40 ka) EAIS variability are limited, but terrestrial records suggest episodes of
thinning and retreat between 40 and 30 ka in catchments associated with Weddell Sea5 and Prydz
Bay6,7 marine-terminating outlet glaciers as well as during millennial-scale Antarctic Isotopic
Maxima (AIM) events, a proxy for atmospheric temperature8. Ice distal Southern Ocean marine
sediment records reveal millennial-scale episodes of warming and IRD deposition, which suggest
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either dynamic ice sheet responses to ocean perturbations and/or fluctuations in seasonal sea ice
extent9.
Because the EAIS extended across the continental shelf in most locations during the last
glaciation, preserved late Quaternary sediments are rare and dating these sequences is complex.
Thus, sub-orbital scale ice sheet variability is inferred from far-field marine records. Due to these
limitations, existing studies of past outlet glacier behavior and forcings focus on understanding
the timing and rates of retreat during the last deglaciation10,11 by radiocarbon (14C) dating the
contact between the sub-glacial diamictites and overlying glacial marine sediments. This
approach yields important paleoclimatic insights and is straightforward if sufficient marine
calcium carbonate (CaCO ) is present, there is minimal sediment reworking, and a local reservoir
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age can be constrained through time. However, the ice-proximal Antarctic margin is a complex
depositional environment; marine sediments are CaCO -poor, reworking is common, and
3
reservoir ages fluctuate. Bulk sedimentary acid insoluble organic matter (AIOM) 14C ages, used
in the absence of CaCO , often overestimate depositional age because they incorporate a matrix
3
of autochthonous marine- and glacially-derived allochthonous organic carbon that encompasses a
spectrum of ages12.
Study Location
Here we present the first accurately-dated detailed late Quaternary (~40-0 ka) record of
EAIS outlet glacier variability. This record, from Prydz Channel, in Prydz Bay, East Antarctica,
fills an important ice-proximal gap between terrestrial Antarctic and Southern Ocean records and
enables direct investigation of late Quaternary EAIS variability. Within Prydz Channel, a 150 km
wide and 700 m deep cross-shelf trough, a set of elongate streamlined ridges trend parallel to the
channel axis. These ridges extend the length (~60 km) and width (40-150 km) of the central
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