Please use this identifier to cite or link to this item: http://hdl.handle.net/20.500.12136/1821
|Title:||The nature of the medieval warm period - little Ice Ace Transition in an annually resolved speleothem record from Voli Voli Cave, Fiji|
García Antón, Elena
|Publisher:||American Geophysical Union|
|Citation:||AGU Fall Meeting, 2011|
|Abstract:||The modern tropical Fiji climate is characterised by seasonal rainfall controlled by the position of the South Pacific Convergance Zone, which is closest to the islands during the wet summer season and weakens when migrating north during the drier winter season. Annual rainfall is strongly modulated on decadal timescales by ENSO with higher rainfall associated with La Nina events with dry spells sometimes leading to drought conditions during El Nino events. A laminated speleothem from Voli Voli cave Fiji spans a 1500 year interval across the transition from the Medieval Warm Period into the Little Ice Age. Fabrics change from calcite with thin clay layers at the base to white laminated calcite and the older record is characterised by elevated δ13C values then a rapid decrease in δ13C, dated at 1200-1300 AD, coinciding with the onset of clean calcite deposition. δ18O values define a simpler trend that monotonically decreases by ≈1‰ across the transition but high resolution micromilling at 100 micron resolution reveals smooth oscillations in δ18O and a key question is whether these cycles are annual or multi-annual features. To understand relationships between local cave processes and seasonal weather patterns, a program of cave monitoring has been underway since 2009. Voli Voli cave is a descending passage that terminates near a fissured cliff facing the SE trade winds; these are more persistent during the winter and weaken during the summer and cave monitoring shows that high cave air CO2 levels decline near the cave termination as a result of weak incoming ventilation by atmosphere driven by wind strength or chimney ventilation. The high resolution δ13C record shows regular peaks that are correlated with cycles in P and Sr and are interpreted as annual markers driven by rainfall and seasonal ventilation. The smooth δ18O cycles are quasi-decadal features possessing a similar frequency to ENSO with an amplitude of 2-3‰ equivalent to an amount-effect related change in annual precipitation of ≈50%. Clay layers are associated with micro hiatuses suggesting periods of drought which are much more frequent prior to the AD 1300 transition which is known to have had a widespread impact on societies in the Pacific Basin resulting in increased conflict, shifts in settlements and changes in subsistence strategies. The Voli Voli record provides new evidence of an underlying climatic change and further work will provide insight into long term trends in intradecadal ENSO periodicity and intensity in terms of δ18O cycles that can be related directly to precipitation amount and sea surface temperature, improving understanding of the impact of short-lived climate changes on past and future societies.|
|Appears in Collections:||Congresos, encuentros científicos y estancias de investigación|
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