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| Titel |
Lipid and compound-specific carbon isotope analysis of Lake Pupuke sediments as indicators of environmental change in the Auckland region over the last 50,000 years |
| VerfasserIn |
Daniel Atkin, Paul Augustinus, Thomas Stephens, Katherine Ficken |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250036981
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| Zusammenfassung |
| Lake Pupuke exists as a fresh water lake located on the North Shore of Auckland City, New
Zealand. Accumulated sediments within Lake Pupuke represent a continuous record from
crater formation ca. 200 Ka to Present, making them an important record of climatic change
in northern New Zealand.
Lipid composition and compound-specific carbon isotope analyses were carried out on
Lake Pupuke sediment cores spanning ca. 50,000 cal. yr BP to Present. Compounds of
interest included n-alkanes, n-alkanols, n-alkanoic acids and botryococcenes. Bulk sediment
and compound-specific carbon isotope records exhibit a positive excursion during the period
18,000 to 27,000 cal. yr BP. This coincides with the Last Glacial Cold Period (LGCP) and in
the absence of native C4 plant species most likely reflects decreased discrimination of the 13C
isotope as a result of low pCO2. Termination of the glacial period occurs ca. 18,000 cal. yr
BP and is defined by a steady increase in organic carbon content with a decrease in bulk and
compound-specific δ13C which continues until ca. 10,000 cal. yr BP. Both aquatic and
terrestrial biomarkers (represented by botryococcene and long chain n-alkyl compounds
respectively) exhibit an increase in δ13C values beginning ca. 7,500 cal. yr BP through
to present day. This is not reflected in the aquatic macrophyte biomarkers (mid
chain length n-alkyl compounds) and may be caused by increased carbon recycling
as a result of greater lake productivity and an increased canopy effect during this
period.
A marked increase in botryococcene biomarkers is noted during the period 7,500 to 9,500
cal. yr BP, reaching total concentrations as high as 19 mg/g. This is accompanied by a relative
increase in C29 and C31 n-alkane terrestrial biomarkers. This zone is also evident to a lesser
degree in the bulk sediment proxies, which exhibit increased carbon content, C/N ratio and
δ13C values. The abundance of botryococcenes would suggest algal blooms of Botryococcus
Braunii. Such blooms usually occur after periods of heavy rain and in association with
dissolved phosphorus. This would suggest a period of increased storminess and
erosion, which would also account for the increase in terrestrial input to the lake. |
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