黄土高原最近4个冰期旋回蜗牛及其卵化石记录的生物繁殖季节的气候变化过程

Seasonality is a fundamental aspect of climate change, with a significant influence on ecology and human societies. Assessing seasonality in different climate states is therefore important. Alternations of the Quaternary glacial-interglacials are significant transitions of climate states. However, oscillations of seasonality during glacial and interglacials are poorly understood. The Chinese loess sequences located in the monsoon-controlled Loess Plateau are among the best archives for seasonality studies, but indictors of seasonality are presently rare. In this project, land snail eggs are developed as a new proxy for seasonal oscillations based on studies of a large amount of surface soil samples and on laboratory-controlled studies of egg-related ecology with emphasis focusing on temperature and moisture, establishing a relationship between changes in the abundance of land snail eggs and seasonal parameters. Then, we will establish sequences of fossil land snail egg assemblage covering the last four glacial-interglacials of the past 450 ka, based on loess-paleosol sections of the Jingyuan, Xifeng and Weinan, by analysis of the abundance of different egg size, and by studies of relationship between abundance of fossil eggs and land snail populations. The characteristics of changes in the abundance of fossil land snail eggs, such as amplitude, duration and periodicities, will be gained. Using the established relationship of land snail eggs and seasonality, seasonal climate oscillations will be reconstructed for the last four glacials and interglacials. Differences in seasonality of each glacial and interglacial and possible driving factors will be discussed. This project would be the first study using land snail eggs to reconstruct oscillations of seasonality and would open new field of research for land snail studies, providing new evidence for and new understanding of the Quaternary oscillations of seasonality.

不同冰期、间冰期的季节性气候变化过程仍不清楚。气候变化幅度最显著的最近4个冰期-间冰期旋回是研究冰期、间冰期季节性气候变化过程的重要时段。除季节长度和幅度外，季节的突发气候事件也是季节性气候变化过程的主要特征，但长期以来因替代指标极少而限制了对其研究。蜗牛繁殖季节的突发气候事件导致的不能孵化的蜗牛卵含量，提供了季节突发气候事件的敏感指标。本项目通过蜗牛培养实验，明确常见蜗牛种类卵的大小和孵化温度湿度范围；通过表土不同蜗牛种类卵含量-气候参数的研究，明确繁殖季节（春季/秋季）突发气候事件反映的是哪些气候参数（季节最低、最高温度，季节最小、最大降水）。以靖远、西峰剖面为主剖面，以渭南剖面为辅，建立最近4个冰期旋回蜗牛卵、蜗牛化石组合序列；研究不同蜗牛种类卵含量变化过程，揭示繁殖季节突发气候事件的强度和发生频次；研究蜗牛化石组合、特征种的演替特点，结合蜗牛-气候转换函数，揭示黄土高原最近4个冰期旋回繁殖季节气候幅度和长度的变化过程及可能原因。

季节气候的长尺度演化过程，对理解冰期-间冰期旋回演化具有重要意义。最近4个冰期-间冰期旋回，气候变化幅度最显著，是研究冰期和间冰期季节气候变化过程的最佳时段之一。遗憾的是，缺少能够敏感反映季节气候变化的代用指标，限制了我们对冰期旋回季节气候演化的理解。蜗牛繁殖季节的突发气候事件导致蜗牛卵不能孵化，因此蜗牛卵具有揭示季节突发气候事件的潜力，但是蜗牛卵化石一直没有引起古气候学家的重视。本项目首次以蜗牛卵为主要研究手段，结合蜗牛组合，通过对93个表土和1387个地层样品计22吨土样中的蜗牛及其卵化石的系统分析研究，揭示冰期旋回季节气候变冷事件的演化及其对蜗牛多样性和壳体形态、种群结构的影响，取得如下认识：1、总结了代表性动物卵的研究进展，发现蜗牛卵具有季节敏感、数量丰富、连续分布的优势，初步建立了表土蜗牛卵数据库，揭示出蜗牛卵丰度的增加与春季最低温有很好的联系，表明蜗牛卵可作为繁殖季节气候变冷事件的代用指标。2、建立了黄土高原3个剖面最近4个冰期-间冰期旋回蜗牛卵化石序列，揭示出季节变冷事件的冰期-间冰期演化规律，表现为，在气候转冷时期，特别是冰增期，季节变冷事件最为强烈，有的盛冰期也较为强烈，但在冰消期没有出现，在冰期内部和间冰期内部也很少出现。这个规律表明季节变冷事件与冰期和间冰期的转换有较密切的联系，进一步的研究或许可帮助预测全新世何时结束这一古气候热点问题。3、蜗牛化石组合揭示出，最近两次冰期气候具有3个演化阶段的结构特点，但这两个冰期的气候变化幅度不同。这种气候变化特点，可能与地球公转轨道参数的不同配置有关。4、首次运用蜗牛证据揭示出，末次冰消期气候转暖背景下，东亚季风雨带向西北推进，增加了黄土高原西北部生态脆弱区蜗牛生物多样性，变暖也导致季节变冷事件减少，蜗牛生长季延长，蜗牛成年体的数量增加，种群年龄结构更加多样化。上述成果为冰期-间冰期气候演化及其对生物多样性和种群结构的影响提供了独特证据和一些新认识。在Quaternary Science Reviews, Science Bulletin, Palaeogeography Palaeoclimatology Palaeoecology, Sciene of the Total Environment, 第四纪研究等刊物上发表论文9篇。

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