Corser Bog Organic Geochemistry and Stable Isotope Ratios

To constrain the effect of climate and peatland type on carbon accumulation, we reconstructed these parameters from a Holocene-length core of a Sphagnum-dominated peatland near Cordova, AK, USA. We determined peat type using a combination of peat texture and density, macrofossils, distributions of leaf-wax biomarkers, and soil pH reconstructions based on distributions of branched glycerol dialkyl glycerol tetraether lipids (brGDGTs). We produced an independent record of hydroclimate and temperature change using hydrogen isotope ratios of leaf-wax biomarkers and distributions of brGDGTs. Carbon accumulation rates were constrained with 14 AMS 14C dates from identified macrofossils and ash-free bulk density. In the early Holocene, the site was a shallow pond with evidence for emergent macrophytes, Sphagnum, and algae growing in a warm, moist climate. At 9.2 kyr (1 kyr=1000cal. yrBP), the site became a Sphagnum-dominated bog. Under mid-Holocene warm, evaporative climate conditions, the site became sedgedominated. As climate cooled and effective precipitation increased, Sphagnum was able to gain dominance abruptly at ~3.5kyr. Large changes in the vegetation assemblage and hydrology and climate are contemporaneous with significant changes in the rate of carbon accumulation. Carbon accumulated most rapidly when Sphagnum dominated and effective moisture was high and most slowly when sedges were dominant and conditions were warmer and drier. Estimates of future climate change indicate warmer, more evaporative conditions that, in the past, favored a sedge-dominated environment, suggesting that this peatland and those similar can contribute to a positive feedback to warming by transitioning to less efficient carbon sinks.为厘清气候与泥炭地类型对碳累积过程的影响，我们从美国阿拉斯加州科尔多瓦附近一处以泥炭藓（Sphagnum）为主导的覆盖全新世的泥炭岩芯中，重建了相关参数。我们综合泥炭质地与容重、大化石、叶蜡生物标志物分布，以及基于支链甘油二烷基甘油四醚脂类（branched glycerol dialkyl glycerol tetraether lipids, brGDGTs）分布的土壤pH重建结果，判定泥炭类型。我们依托叶蜡生物标志物的氢同位素比值与brGDGTs的分布特征，独立构建了水文气候与温度变化序列。碳累积速率通过14个取自已鉴定大化石的加速器质谱（AMS）¹⁴C测年数据，结合无灰容重进行限定。全新世早期，该区域为浅塘，生长有挺水大型植物、泥炭藓与藻类，对应温暖湿润的气候环境。在9.2 kyr（1 kyr=1000 cal. yrBP，即1千年等于1000个校准年BP）时，该区域转变为以泥炭藓为主导的沼泽。全新世中期，在温暖且蒸发强烈的气候条件下，该区域演变为以莎草为主导的泥炭地。随着气候变冷、有效降水增加，泥炭藓在约3.5 kyr时突然重新占据主导地位。植被组合、水文条件与气候的剧烈变化，均与碳累积速率的显著改变同步发生。当泥炭藓占据主导且有效湿度较高时，碳累积速率最快；而当莎草占据主导、环境温暖干燥时，碳累积速率最慢。未来气候变化预估结果显示，气候将变得更为温暖且蒸发更强——这一环境在过去曾利于莎草主导的泥炭地发育——这表明该泥炭地及其同类生态系统，可通过转变为碳汇效率更低的生态系统，对气候变暖产生正反馈效应。