Publikationsdatum:
2018-08-10
Beschreibung:
Past studies of South Georgia’s climatic history were constrained to land-based sedimentary records, such as peat
bogs and coastal lakes, or to terrestrial geomorphology, such as terminal moraines. Hence, the current state of
knowledge on past climatic changes in South Georgia is characterised by a complete absence of records from
sedimentary marine archives in the fjords or coastal embayments of the region. This study comprises detailed
examination of one of the first marine sediment cores recovered on its northeastern shelf in Royal Bay Glacial
Trough. Alongside the analysis of new acoustic sub-bottom data, it is the first work to deliver extensive insight
into South Georgia’s post-glacial climatic history from a marine perspective. The glacial troughs on the South
Georgia shelf radiate from the coast towards the shelf edge and represent major sediment traps as they form the
only key large-scale depressions in the shelf bathymetry. Sedimentary records, covering a period since at least the
Last Glacial Maximum, are thought likely to be recorded in most of them.
The sediment core of this study covers sedimentation dated from a maximum of 15,346 ±492 cal. yr BP until
the present day. Physical core parameters indicate a major change in climatic conditions around 14,000 cal. yr
BP, the time of the Antarctic Cold Reversal. Holocene climate variabilities are also recorded in the trough infill.
The acoustic data show a major change in sedimentation and a pronounced unconformity at the core site, which
appears to have had a widespread effect over a large area of the shelf. The origin of the unconformity remains
unclear, though several hypotheses, including bottom-current erosion, glacial overriding and earthquake activity,
are proposed and discussed.
Another important finding at the core site is the presence of methane-derived authigenic carbonates. They form
either as secondary precipitates in the subsurface or syndepositional at the seafloor as individual minerals or sediment
cements. The authigenic carbonates are linked to the widespread occurrence of cold methane seeps on the
shelf which are visible today as zones of acoustic blanking and wipe-out structures in the sub-bottom profiles.
These seeps are evidence of major biogenic productivity and carbon drawdown on the South Georgia shelf and
the subsequent decay of organic matter. This finding is an important consideration for future studies as authigenic
carbonate production and methane release have an impact on the isotopic composition of carbonate shells of marine
organisms. Thus, radiocarbon ages recovered from the South Georgia shelf need to be examined critically and
might require additional corrections.
Repository-Name:
EPIC Alfred Wegener Institut
Materialart:
Conference
,
notRev
Format:
application/pdf
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