2014clarkncphd.pdf (14.26 MB)
A molluscan record of Late Cenozoic climate and palaeoseasonality from Antarctica and South America
thesis
posted on 2014-12-08, 11:30 authored by Nicola Anne ClarkShallow marine late Neogene and Quaternary sedimentary deposits around coastal
Antarctica and South America contain abundant fossil bivalves, but these have rarely been
utilised for palaeoclimate work. Due to their incremental growth, bivalves contain a wealth
of information relating to the environment they were living in, including temperature (using
δ[superscript 18]O) and productivity (using δ[superscript 13]C). A repeatable method of assessing the preservational
state of fossil bivalves using a combination of techniques has been developed to ensure
only pristine material is analysed for stable isotopes. These include inspection of the
lamellar structure under an optical microscope, observation of luminescence using
cathodoluminescence and identification of internal crystal structure using scanning electron
microscopy. A targeted study of modern pectinid, cardiid and hiatellid bivalves confirm
their suitability for reconstructing sea surface temperatures (SSTs), although in the case of
hiatellids an understanding of the local environment is essential for an accurate
interpretation of oxygen isotope records.
Stable isotope analysis of pristine late Neogene (ca. 6.5 to 2.5 Ma) pectinid bivalves from
James Ross Island, Antarctic Peninsula and pectinid, cardiid and hiatellid bivalves from the
Vestfold and Larsemann Hills in the East Antarctic, record two distinct environmental
signals: 1) warmer than present summer SSTs of up to +4.5°C, consistent with a number of
other shallow-shelf and deeper water marine fossil proxies, including bryozoans,
silicoflagellates and cetaceans, and with General Circulation Model simulations (e.g.
PlioMIP) and, 2) seasonal fluxes of freshwater from local ice sheets, artificially decreasing
δ[superscript 18]O ratios.
Stable isotope analysis of late Pliocene to Quaternary (ca. 3.5 to 0.2 Ma) Chlamys bivalves
and Argopecten purpuratus from the Mejillones Peninsula and Coquimbo, northern Chile,
identify similar SSTs (+13 to +18°C) compared to present and suggest El Niño-Southern
Oscillation (ENSO) variation has been present in the south-eastern Pacific since the late
Pliocene, a signal consistent with climate model predictions.
This study emphasises the importance of developing new climate proxies that identify
seasonal variation, and which can be used in conjunction with other environmental proxies
to provide detailed palaeoclimate data for little studied Neogene successions of the coastal
zones of Antarctica and the south-eastern Pacific.
History
Supervisor(s)
Williams, Mark; Zalasiewicz, JanDate of award
2014-11-01Author affiliation
Department of GeologyAwarding institution
University of LeicesterQualification level
- Doctoral
Qualification name
- PhD