Climate variability over the circum-Caribbean region during the past 1200 years from oxygen-isotope analyses of lake sediments

在数年到数十年的时间尺度上，可用水的变化，特别是干旱，是社会关注的一个主要问题。在这种时间尺度上，干旱发生频率和程度的变化很可能是未来气候变化的结果，特别是在亚热带地区。包括中美洲东部、墨西哥湾和加勒比地区（以下简称环加勒比地区）在内的地区可能对未来的气候变化特别敏感，特别是在干旱的发生率和严重程度方面：这是我们提出研究的主题。降雨的气象记录太短，无法涵盖多年至数十年时间尺度上过去降雨的全部变化，也无法表明地理格局是否随时间和在不同条件下发生了变化。过去气候的自然“档案”，包括湖泊和海洋沉积物、洞穴沉积物和树木年轮，提供了一个机会，可以将气象记录进一步追溯到过去，并阐明降雨变化的模式和原因。在这项研究中，我们将利用湖泊沉积物中保存的介形虫方解石壳的氧同位素分析来研究过去1200年的降雨变化。我们计划分析已经从墨西哥东部的尤卡坦半岛、牙买加、海地和巴布达收集的湖泊沉积物岩心。这些地点位于从西向东的样带上，据了解，近几十年来，沿着这条样带发生了降雨量的变化。我们的重建工作将得到沿加勒比海周边地区从北向南样带的现有研究的补充，从而使我们能够调查过去降雨的地理模式变化。过去1200年是一个重要的研究时间段，因为它涵盖了气候的显著变化间隔，包括以潮湿气候为主的中世纪气候异常（MCA），干燥的小冰期（LIA）和MCA结束时明显干旱的经典末期，这被认为是尤卡坦半岛重大社会变化的原因。在这段时间内气候的广泛变化是众所周知的，但该地区地理格局的变化，尽管有现有数据的暗示，却很少受到约束。此外，海洋环流和海面温度变化、太阳活动变化和火山爆发等潜在原因之间的联系还没有得到很好的了解。通过对过去1200年的降雨变化进行新的重建，我们将进一步了解这一时期变化的性质和原因。通过将记录的时间跨度扩大到气象数据之外，我们将能够显示降雨变化的地理模式在最近的过去是否保持不变，或者似乎已经发生了变化。除了为加勒比海地区提供重要的古气候数据外，我们的研究还将为考古学家提供急需的气候重建，特别是那些在墨西哥和巴布达研究气候与社会之间联系的考古学家。

Variations in water availability, especially drought, on timescales of years to decades are a major concern for society. Changes in the frequency and magnitude of drought on such timescales are a likely outcome of future climate change, especially in subtropical regions. The area that encompasses the eastern part of Central America, the Gulf of Mexico and the Caribbean (hereafter the circum-Caribbean region) is likely to be especially sensitive to climate change in the future, especially in terms of the incidence and severity of drought: it is this region that is the subject of our proposed research. Meteorological records of rainfall are too short to encompass the full range of variations in past rainfall on timescales of years to decades or to indicate whether geographical patterns have changed through time and under different conditions. Natural 'archives' of past climate, including lake and marine sediments, speleothems (cave deposits) and tree rings, provide an opportunity to extend the meteorological records further back into the past and to shed light on the modes and causes of rainfall variability. In this research, we will investigate changes in rainfall over the past 1200 years using oxygen-isotope analyses of the calcite shells of ostracods preserved in lake sediments. We plan to analyse lake sediment cores that have already been collected from sites in the Yucatan Peninsula of eastern Mexico, Jamaica, Haiti and Barbuda. These sites are located on a west to east transect, along which changes in rainfall are known to have occurred over recent decades. Our reconstructions will be complemented by existing studies along a north to south transect within the circum-Caribbean region, thus allowing us to investigate changes in the geographical patterns of past rainfall. The past 1200 years is an important time period to study as it covers intervals of marked change in climate including the Medieval Climate Anomaly (MCA) of predominantly wet climate, the drier little ice age (LIA) and the terminal classic period of marked drought at the end of the MCA, which is thought to have contributed to major societal change in the Yucatan Peninsula. The broad variations in climate over this interval are quite well known, but changes in the geographical patterns in the region, despite being implied by existing data, are poorly constrained. Furthermore, links to potential causes, such as variations in ocean circulation and sea-surface temperatures, changes in solar activity and volcanic eruptions, are not well understood. By generating new reconstructions of variability in rainfall over the past 1200 years, we will provide further insights in to the nature and causes of change during this period. By extending the timespan of records beyond that of meteorological data, we will be able to show whether geographical patterns of rainfall variability have remained constant over the recent past or, as seems likely, have changed. In addition to providing important palaeoclimatic data for the circum-Caribbean region, our research will generate much-needed reconstructions of climate for archaeologists, especially those working on links between climate and society in Mexico and Barbuda.