Holocene hydroclimatic changes at three windward montane wetland sites on the Island of Hawai‘I

Authors: Olivia Marohnic*, University of Hawaii At Manoa, David Beilman, Department of Geography and Environment, University of Hawaii at Manoa, James Juvik, Department of Geography, University of Hawaii at Hilo
Topics: Paleoenvironmental Change, Climatology and Meteorology, Water Resources and Hydrology
Keywords: paleoclimate, paleohydrology, tropical Pacific, Hawaii, late Holocene, sediment geochemistry
Session Type: Poster
Day: 4/5/2019
Start / End Time: 3:05 PM / 4:45 PM
Room: Lincoln 2, Marriott, Exhibition Level
Presentation File: No File Uploaded

Few terrestrial records of long-term environmental change for Hawai‘i, and detailed paleoclimate records for the Holocene are still needed. This study presents high-resolution (16-80 yr cm-1) radiocarbon-dated sediment proxy data from three montane wetlands on the windward side of the Island of Hawaii, which share similar elevations and mean temperatures but which span a range in annual rainfall (281-607 cm yr-1). Physical and geochemical characteristics of organic sediments are interpreted as ecohydrological proxies, including ẟ13C values, carbon-to-nitrogen ratios, sediment density, and rates of sediment and carbon accumulation. Onset of peat formation around 7-8 kya at multiple sites shows consistently wetter conditions. An increase in carbon accumulation rates (by ~10 gC/m2/yr) and decrease in ẟ13C (1-2 ‰) at around 3-4 kya, at the same time as a third site initiates peat formation, suggests a peak in wetness at this time. From ~2.5kya to present, all proxies shift towards a drier signal (decreased carbon accumulation rates, increased ẟ13C, C:N ratio in one of the cores), indicating a shift back to relatively drier conditions. At the site with the highest resolution over the last 4 kya (averaging 16 yr cm-1), multivariate analysis of n-alkane chain length distributions from modern Hawaiian bog plants and organic sediments shows little discernible change in plant input over time, suggesting that changes in ecohydrological proxies were driven by changes in regional climate. This evidence compared to other paleoclimate proxies across the Hawaiian Islands point to a millennial scale central-Pacific/Hawaiian wet period around ~4-2.5 kya.

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