Abstract Plant wax hydrogen isotopic composition is commonly used to reconstruct the hydrogen isotopic composition of precipitation used by terrestrial vegetation. However, mangroves growing in coastal environments take up a mixture of freshwater and seawater. Biosynthetic fractionation (between source water and plant wax) differs between plant types and as a function of salinity, potentially complicating interpretations of past precipitation in coastal environments. In order to reconstruct Holocene hydrologic and ecologic changes archived within sediments from Blackwood Sinkhole on Abaco Island in The Bahamas, we adopt a multi-proxy approach using plant wax hydrogen isotopic composition (δ2H) to reconstruct paleohydrology, together with plant wax carbon isotopic composition (δ13Cwax), sterol biomarkers and pollen abundances to identify vegetation change. When pollen indicates a stable terrestrial plant community (2950–850 cal yrs BP), variations of δ2H values measured on the plant wax C28 n-alkanoic acid are interpreted in terms of precipitation isotope (δ2Hprecip) changes, with 2H-depletion from 2950 to ∼2100 cal yrs BP and ∼1700 to 1000 cal yrs BP. However, interpretation is complicated at 850 cal yrs BP, when δ2H values decrease (−50‰) concurrent with increased Laguncularia racemosa (white mangrove) and Conocarpus erectus (buttonwood mangrove), and the mangrove-derived biomarker, taraxerol. We develop a pollen-based correction for mangrove inputs, yielding reconstructed precipitation isotope estimates (δ2Hprecip-corr). Low δ2Hprecip-corr values are synchronous with increased abundance of pine pollen, both of which may indicate wetter conditions from 850 cal yrs BP to present. This study provides additional evidence that mangroves can complicate hydrologic reconstructions from n-alkyl terrestrial plant wax biomarkers, and that such complication can be removed by pollen-based correction. After correcting for mangrove inputs, we obtain estimates of δ2Hprecip-corr from −33 to +25‰ throughout the last 2950 years, with uncertainties on the order of 10–20‰.

中文翻译：

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过去 3,000 年来巴哈马沿海落水洞湖中降水和植被变化的植物蜡证据

摘要 植物蜡氢同位素组成常用于重建陆地植被所利用的降水氢同位素组成。然而，生长在沿海环境中的红树林吸收了淡水和海水的混合物。生物合成分馏（源水和植物蜡之间）因植物类型和盐度而异，这可能会使沿海环境中过去降水的解释复杂化。为了重建巴哈马 Abaco 岛 Blackwood Sinkhole 沉积物中的全新世水文和生态变化，我们采用多代理方法使用植物蜡氢同位素组成 (δ2H) 以及植物蜡碳同位素组成重建古水文（ δ13​​Cwax), 甾醇生物标志物和花粉丰度来识别植被变化。当花粉指示稳定的陆生植物群落（2950-850 cal yrs BP）时，在植物蜡 C28 正链烷酸上测量的 δ2H 值的变化被解释为沉淀同位素（δ2Hprecip）变化，从 2950 年到 2H-消耗～2100 cal yrs BP 和～1700 到 1000 cal yrs BP。然而，在 850 cal yrs BP 时，当 δ2H 值降低 (-50‰) 并伴随着总状 Laguncularia Racemosa（白色红树林）和 Conocarpus standus（buttonwood 红树林）以及红树林衍生的生物标志物蒲公英醇增加时，解释很复杂。我们为红树林输入开发了基于花粉的校正，产生重建的降水同位素估计值 (δ2Hprecip-corr)。低 δ2Hprecip-corr 值与松花粉丰度的增加同步，这两者都可能表明从 850 cal yrs BP 到现在的潮湿条件。这项研究提供了额外的证据，表明红树林会使正烷基陆生植物蜡生物标志物的水文重建复杂化，并且可以通过基于花粉的校正来消除这种并发症。在校正红树林输入后，我们获得了过去 2950 年从 -33 到 +25‰ 的 δ2Hprecip-corr 估计值，不确定性约为 10–20‰。