Dynamic Holocene Vegetation and North Pacific Hydroclimate Recorded in a Mountain Peatland, Moloka‘i, Hawai‘i

Abstract

The Hawaiian Islands are the only high land in a vast stretch of the North Pacific where past climatological and ecological processes can be reconstructed from terrestrial Earth system archives. We measured hydroclimatic proxies and carbon accumulation in an organic sediment core from the windward montane peatland Pēpē'ōpae on the Island of Moloka'i, Hawai'i using radiocarbon, leaf wax geochemistry, and stable isotopes of carbon and hydrogen in addition to historical pollen records. Following a period of soil development, substantial carbon accumulation began around 10 ka BP (thousands of years before present) under wet conditions. Peat formation was continuous but variable throughout the Holocene, including maxima in carbon accumulation around 9 and 3 ka and a minimum around 1.5 ka that has resulted in a belowground carbon storage today of 144 kg C m −2. From this core we generated a new chronology for previously published pollen spectra from the study site and a Wetness Index that shows increases in dry-adapted taxa in upwind forests during periods of decreased carbon accumulation in the peatland. Shifts in the distribution of sedimentary n-alkane chain lengths in the context of 14 species of modern bog plant n-alkanes suggests litter inputs have been derived from a diverse plant community that changed in dominant species in response to climate. Hydrogen stable isotope ratios of sedimentary C 29 n-alkanes show negative departures around 9 and 3 ka consistent with increases in stormderived rainfall likely related to the position and strength of the northern jet stream. This study is the first to provide a continuous organic sedimentary record of links between hydroclimate, vegetation, and montane belowground carbon sequestration for this part of the North Pacific.

From the Top: Surface-derived Carbon Fuels Greenhouse Gas Production at Depth in a Neotropical Peatland

“…The Changuinola peat deposit is important as an internationally protected wetland and is an example of a pristine undisturbed functioning tropical peatland. This is supported by the age-depth profiles that showed continuous undisturbed peat accumulation over time, and similarities in C and N concentrations and C:N ratios to other ombrotrophic peat domes across the tropics (Beilman et al, 2019;Omar et al, 2022;Dargie et al, 2017;Lähteenoja et al, 2012). This paper contributes a novel characterization of the organic components contributing to surface CO2 fluxes (bulk peat, respiration products, peat chemical composition) to identify the dominant source of C for a tropical peatland.…”

Climate-Induced Forest Mortality in the Tropical Pacific Islands: What Do We Really Know?

“…However, Boehmer and Niemand (2009) highlighted notable parallels between Selling's data and late Holocene climate dynamics. More recently, Beilman et al's (2019) reconstruction of vegetation dynamics in the Holocene found that the return interval of Metrosideros minima (ca. 1,000 years) is substantially longer than the oldest tree age of ca.…”

Characteristics of Lowland Tropical Peatlands: Formation, Classification, and Decomposition

“…For example, biomarkers are molecules compounds derived from biological sources that can retain certain information such as origin, past depositional environment and climate in geological formations. Biomarker studies of non-emergent vascular plants consist of C 21 , C 23 and C 25 n-alkanes, whereas vascular terrestrial plants consist of C 27 , C 29 and C 31 n-alkanes (Meyers and Ishiwatari, 1993;Beilman et al, 2020;Freimuth et al, 2020). Ratnayake et al (2019) examined the biomarker distribution of n-alkanes in several terrestrial ecosystems (Figure 6).…”

“…Tropical peatlands can be identified as a hot spot for carbon and nitrogen burial (Canadell et al, 2007;Ratnayake et al, 2018;Beilman et al, 2020). In recent decades, tropical peatlands are under stress due to human-induced destructions.…”