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Reconstructing precipitation in the tropical South Pacific from dinosterol 2H/1H ratios in lake sediment

January 15, 2019

The South Pacific Convergence Zone (SPCZ) is the Southern Hemisphere’s largest precipitation feature supplying freshwater to 11 million people. Despite its significance, little is known about the location and intensity of SPCZ precipitation prior to instrumental records, hindering attempts to predict precipitation changes in a warming world. Here we use sedimentary molecular fossils to establish a tool for extending the historical record of precipitation. Freshwater lake sediments and water samples were collected from 30 lakes that span a 4.6 mm d−1 range in precipitation rates from the Global Precipitation Climatology Project (GPCP). δ2Hlakewater values from 29 lakes ranged from −29 to +23‰ and were inversely correlated (r = −0.51, p < 0.001) with precipitation rates, likely due to the combination of the amount of precipitation plus evaporation. δ2H values of the dinoflagellate sterol dinosterol in surficial sediments from 21 lakes ranged from −316‰ in the Solomon Islands to −245‰ in French Polynesia. These δ2Hdinosterolvalues were significantly correlated (r = 0.71, p < 0.001) with δ2Hlakewaterand inversely correlated (r = −0.77, p < 0.001) with mean annual precipitation rates with a sensitivity of −12.1 ± 2.6‰ (mm d−1)−1. Fractionation between dinosterol and lake water (εdinosterol/lakewater) decreased at the driest lake sites (r =  − 0.70, p < 0.001). The empirical relationship between δ2Hdinosterol and GPCP rainfall, although indirect, provides a means of quantitatively reconstructing past precipitation in the SPCZ region with an uncertainty of less than 3.1 mm d−1, which compares favorably to the 1.5 mm d−1 uncertainty for the satellite-gauge based GPCP precipitation data.

Publication Year 2019
Title Reconstructing precipitation in the tropical South Pacific from dinosterol 2H/1H ratios in lake sediment
DOI 10.1016/j.gca.2018.10.028
Authors Ashley E. Maloney, Daniel B. Nelson, Julie N. Richey, Matthew Prebble, David A. Sear, Jonathan D. Hassall, Peter G. Langdon, Ian W. Croudace, Atun Zawadzki, Julian P. Sachs
Publication Type Article
Publication Subtype Journal Article
Series Title Geochimica et Cosmochimica Acta
Index ID 70202161
Record Source USGS Publications Warehouse
USGS Organization St. Petersburg Coastal and Marine Science Center