Cenozoic Antarctic climate evolution based on molecular and isotopic biomarker reconstructions ...

306 Pages·2017·11.83 MB·English

by  Bella Duncan

Cenozoic Antarctic climate evolution based on molecular and isotopic
biomarker reconstructions from geological archives in the
Ross Sea region

by

Bella Jane Duncan

A thesis
submitted to the Victoria University of Wellington
in fulfilment of the requirements for the degree of
Doctor of Philosophy
In Geology

Victoria University of Wellington
2017

Geology! the helicopter rises,
the scientists crowd around,
and Emily’s drill goes down

through a thousand years of ice:
ghost of a dog, ghost of a pony
Oates going deeper and deeper

Below the surface
*
still perfectly himself
still gone for some time,
lost in whatever Emily might find

of sediments and algae,
the movement and retreat
of seasons, time passing
in samples and traces
-beech and conifer-
stuff from the core

to take home and question
and even then perhaps
not quite be sure…
*
May the years of her life
look after her
Emily’s gone to Antarctica

From Hoosh by Bill Manhire

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Abstract
During the Cenozoic Era (the last 65 Ma), Antarctica’s climate has evolved from ice free
conditions of the ‘Greenhouse world’, which at its peak (~ 55 Ma) supported near-tropical forests,
to the ‘Icehouse’ climate of today with permanent ice sheets, and a very sparse macroflora. This
long-term cooling trend is punctuated by a number of major, abrupt, and in some cases,
irreversible climate transitions. Reconstructing past changes in vegetation, sea surface
temperature, hydroclimate and the carbon cycle require robust geological proxies that in turn can
provide insights into climatic thresholds and feedbacks that drove major transitions in the
evolution of Antarctica’s ice sheets. Biomarkers allow climate and environmental proxy
reconstructions for this region, where other more traditional paleoclimate methods are less
suitable. This study has two aims. Firstly to assess the suitability and applicability of biomarkers
in Antarctic sediments across a range of depositional settings and ages, and secondly to apply
biomarker-based climate proxies to reconstruct environmental and climate conditions during key
periods in the development of the Antarctic Ice Sheets.
The distribution and abundances of n-alkanes are assessed in Oligocene and Miocene sediments
from a terrestrial outcrop locality in the Transantarctic Mountains, and two glaciomarine
sediment cores and an ice-distal deep marine core from the western Ross Sea. Comparisons are
made with n-alkane distributions in Eocene glacial erratics and sedimentary rocks of the
Mesozoic Beacon Supergroup, both likely sources of reworked material. A shift in dominant
chain length from n-C to n-C occurs between the Late Eocene and Early Oligocene,
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considered a response to a significant climate cooling. Samples from glaciofluvial environments
onshore, and subglacial and ice-proximal environments offshore display a reworked n-alkane
distribution, characterised by low carbon preference index (CPI), high average chain length
(ACL) and high n-C /n-C values. Whereas, samples from lower-energy, more benign
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lacustrine and ice-distal marine environments predominantly contained contemporary material.
Palynomorphs and biomarker proxies based on n-alkanes and glycerol dialkyl glycerol
tetraethers (GDGTs) are applied to a Late Oligocene and Early Miocene glaciomarine succession
spanning the large transient excursion of the Mi-1 glaciation (~23 Ma) in DSDP Site 270 drill
core from the central Ross Sea. While the Late Oligocene is marked by relatively warm
conditions, regional cooling initiated a transition into Mi-1. This was likely driven by a
combination of decreasing atmospheric CO and an orbital geometry favouring low seasonality
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and cool summers, leading to an intensification of proto-Antarctic bottom water production as
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the Ross Sea deepened and cooled. Mi-1 manifests as a regionally cool period, with minimum
subsurface temperatures of ~4°C and onshore mean summer temperatures of ~8°C. A negative
n-alkane δ13C excursion of up to 4.8‰ is interpreted as a vegetation response to cold, restricted
growing seasons, with plants driven to lower altitudes and more stunted growth forms. However,
ocean temperatures remained too warm for marine-based ice sheets to advance onto the outer
continental shelf and over-ride the drill site. The large increase in ice volume associated with this
event, implied by global δ18O records, was probably held on a higher, terrestrial West Antarctica
of greater extent than present day. The relative lack of ice rafted debris during Mi-1, suggests the
presence of a marginal marine-terminating ice sheet with fringing ice shelves to the south of
DSDP site 270, calving icebergs lacking a basal debris layer, similar to those calving from the
Ross Ice Shelf today. This extensive ice cover may explain a large decrease in marine n-alkanes
at this time restricting marine productivity on the continental shelf. The biomarker data for the
Early Miocene in DSDP 270 indicates a relative warming in both terrestrial and marine
temperatures following the transient Mi-1 glacial expansion, but an overall baseline cooling of
climate between Late Oligocene and the Early Miocene in the Ross Sea embayment.
Isoprenoid GDGTs are used to reconstruct a Cenozoic subsurface ocean temperature compilation
for the Ross Sea, a key source region of ocean deep water. The ocean temperature TEXL
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calibration and BAYSPAR in standard subsurface mode were considered, through comparison
with independent microfossil and sedimentological data, the most appropriate for use in this
region. Ocean temperatures cool prior to the Eocene/Oligocene transition and remain cool for the
rest of the Cenozoic, with the exception of short periods of relative warmth in the Late Oligocene
and Mid-Miocene Climate Optimum, and long-term trends broadly mirror that of the
foraminiferal δ18O record from the deep Pacific. The Δ Ring Index is used to assess non-thermal
influences on GDGT distributions, and displays a long term shift from more positive to more
negative deviations. This correlates with %GDGT-0, and also relates to a declining trend in the
Methane Index, which reflect the contribution of methanogenic and methanotrophic archaea.
These changes suggest that these archaea contributed more to the archaeal community in the
early to mid Cenozoic, potentially indicating a more anoxic depositional environment in the Ross
Sea. The Branched to Isoprenoid Tetraether index (BIT) steadily declines over the Cenozoic,
reflecting increasingly hyper-arid conditions onshore, with less active glaciofluvial systems,
limited soil development and less ice-free land.

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Acknowledgements
This thesis would not have been possible without the support and help of many people. Firstly,
thanks must go to my amazing team of supervisors, Rob McKay, James Bendle and Tim Naish.
Rob, thanks for giving me the chance to do my ideal PhD project. Your support, encouragement
and enthusiasm has made this often stressful process a lot easier. I’m really grateful for all the
opportunities you’ve given me over the last few years, including going along to AGU and other
conferences, enabling lab visits to Birmingham and taking me along on field trips, even if that’s
occasionally involved dealing with some questionable music choices. James, your biomarker
knowledge and advice has been invaluable. Thanks for hosting me in Birmingham, teaching
me a whole lot about organic geochemistry and for enthusiastic discussions on topics as diverse
as compound specific isotope interpretations to possum smiting. Tim, thanks for all your help
and advice in setting the stratigraphic scene for my project, and useful discussions on data
interpretation and the ‘big picture’.
This research would not have been possible without funding support. I’m grateful to Antarctica
New Zealand for the Sir Robin Irvine Scholarship and field support in Antarctica. Victoria
University of Wellington granted me a Fee’s Waiver and Doctoral Submission Scholarship. I
received a SCAR Fellowship which helped cover travel and laboratory costs at the University
of Birmingham. I’m grateful for funding received via a Royal Society of New Zealand
Rutherford Discovery Fellowship (RDF-13-VUW-003) awarded to Rob McKay. An Antarctic
Research Centre Endowed Development Fund grant and SGEES Faculty Strategic Research
grant allowed me to travel to Urbino Summer School in Paleoclimatology. Thanks to NERC
for funding proposal number BRIS/85/1015, awarded as a grant-in-kind to the Bristol NERC-
LSMSF for compound specific GC-ir-MS analyses. I thank the University of Birmingham for
support-in-kind (consumables and technical training during laboratory visits). I’m grateful for
funding this study received from the MBIE Past Antarctic Climates Program (CO5X1001).
Many other people have contributed to this research. Thanks to Richard Levy for your advice,
helpful discussions on DSDP 270 and of course for taking me to Antarctica! I thank Todd
Ventura for being my local organic geochemistry mentor, running my samples for bulk
pyrolysis and for leading the charge on the lab set up. I had a great group helping me in the lab
in Birmingham. Heiko Moossen taught me the methods and provided invaluable knowledge.
Beth Chamberlain, Carrie Walker and Lucy Tyack were my amazing lab support, both when I
was in Birmingham and especially when I was back on the other side of the world. Thanks to
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Joe Prebble for processing and counting the palynomorph samples for DSDP 270, and for
helpful discussions on interpretation. I’m also grateful to Matt Ryan being a palynomorph
diagram whizz so I could make my figures. Denise Kulhanek provided help with the DSDP
270 age model. Thanks to Srinath Krishnan for running my GDGT data and helping me
understand it. Thanks to James Super for additional GDGT help and to Mark Pagani for
accepting and organising my samples to be run at Yale. I’m grateful to Francesca Sangiorgi,
Courtney Warren, Veronica Willmott and Stefan Schouten for willingly providing GDGT data
for AND-1B, AND-2A, CIROS-1 and the McMurdo Erratics. Thanks to the Organic
Geochemistry Unit at the University of Bristol for analysing my samples for compound specific
isotopes. I’ve had many helpful discussions with staff and students in the ARC over the course
of this research, with particular thanks to Chris Kraus for lots of chats on how to interpret
DSDP 270.
It’s been a privilege to spend my PhD (and several years before that!) in the Antarctic Research
Centre. The encouraging and supportive atmosphere created by the ARC staff and students has
been a fantastic environment to work in. I’ve been lucky enough share this journey with some
awesome office mates and fellow postgrads. Thanks to Ben, Georgia, Matt, Katie, Molly,
Heidi, Peter, Condor, Chris, Lauren, Dan, Katelyn and many others. My wider geological
family have shared the ups and downs of uni, life and beer pong over the last decade, with
special mention to Danny, Boots, Kolja and my ‘breakfast date girls’ Cara, Gemma and Katie.
This thesis was partly fuelled by thousands of cups of tea courtesy of Shaun, thanks for
graciously accepting frequently losing the daily quiz and for being a wonderful friend. Thanks
to Shaun, Jenni, Rich and Juliet for many fantastic ‘takeaways and sport’ evenings, roast
dinners, excellent chats and help with baby/toddler wrangling.
No matter where they’ve been in the world, my lovely ladies have always been there for me.
Thanks Tracey, Jaime, Liz, Tessa and Nicole for the love, rants and cider.
My incredible family mean the world to me, and I could never have done this without them.
Hamish, Belinda, Alice, Henry, Pat, Marnie and Nana, thank you so much for your constant
love and support. Mum and Dad, you built the foundations that have allowed me to follow my
dreams in the security that I will always have your unwavering love and encouragement. I can
never thank you enough for your help with Arden, and your devotion to him. Many a stressful
day has been forgotten when I’ve come home to Max and Arden, my little family, my
cheerleaders and my happiness. Thank you for surrounding me with your love, I can’t wait to
keep growing with you.
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This thesis is dedicated to Arden
Above everything, I am most proud to be your mother

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