Marine Isotope Stage 19: analogue for the present interglacial

过去的间冰期具有与现在的间冰期（全新世）相似的轨道几何特征，为评估近千年来气候系统不同组成部分的自然演化和人为干扰程度提供了基础。虽然人类对植被和景观的改造贯穿整个全新世，但可以说对全球环境最重大的干扰是过去两个世纪以来人类排放温室气体（GHG）的开始。然而，在他的“早期人为假设”中，Ruddiman（2003）提出，人类在工业时代之前数千年就开始改变温室气体浓度，森林砍伐和水稻农业的集约化分别导致大气中CO2和CH4水平的增加。更具体地说，这些气体的浓度表现为全新世早期的峰值，随后下降，但CO2和CH4的下降趋势分别在8千年和5千年后逆转。Ruddiman通过与前四个间冰期的自然趋势进行类比，提出全新世温室气体浓度的演化是异常的，但轨道结构的差异和它们精确同步的不确定性强调了这种比较的局限性。最近，根据轨道参数的相位和整体气候演化，大约78万年前被称为海洋同位素阶段（MIS） 19的时期被确定为与当前间冰期最相似的时期。为评价全新世温室气体演化和植被演替提供了更为合适的试验台。然而，尽管有这种潜力，MIS 19仍未得到充分研究。拟议的项目旨在通过生成最详细的记录（~200年的分辨率），从ODP站点977在Alboran海，南伊比利亚边缘的MIS 19期间的植被和水文变化，并将其与正在进行的古海洋学代用物分析相结合，目前由西班牙联盟GRACCIE正在进行分析。近年来，伊比利亚边缘的西部和南部地区已成为通过联合花粉和古海洋学代理分析直接将海洋和陆地记录联系起来的关键地区，这些分析是在与大陆相邻的同一海洋档案中恢复的。这可以直接比较海洋和陆地的变化，绕过时间尺度和相关性的不确定性。结果将确定：(1)MIS 19间冰期在海面条件下的持续时间和与植被变化的精确相位；(2)该地区全新世已有植被变化趋势（MIS 19 vs -à-vis）；(3) MIS 19c末大气甲烷浓度峰值期间的植被性质和水文变化；(4)间冰期前后及间冰期内植被和侵蚀对短期气候变率的响应和影响。如果MIS 19 - MIS 1的类比是正确的，这些结果将对评估：(i)在没有人为强迫的情况下，当前间冰期的自然长度；（ii）过去一千年来，人类活动对该地区自然植被趋势的影响程度；（iii）全新世甲烷演化的根本原因。

Past interglacials characterized by an orbital geometry similar to the current interglacial (Holocene) provide a basis for assessing the natural evolution of different components of the climate system and the extent of anthropogenic interference during recent millennia. While human modification of vegetation and landscapes has been underway throughout the Holocene, arguably the most significant interference with global environments has been the onset of anthropogenic emissions of greenhouse gases (GHG) over the past two centuries. However, in his 'early anthropogenic hypothesis', Ruddiman (2003) proposed that humans began modifying greenhouse gas concentrations thousands of years before the industrial era, with forest clearance and intensification of rice agriculture leading to increases in atmospheric CO2 and CH4 levels, respectively. More specifically, the concentrations of these gases show early Holocene peaks followed by declines, but the downward trend was reversed after 8 and 5 thousand years ago for CO2 and CH4, respectively. By drawing analogies with natural trends in the previous four interglacials, Ruddiman suggested that the Holocene evolution of GHG concentrations was anomalous, but differences in orbital configurations and uncertainties over their precise synchronization have underlined the limitations of such comparisons. More recently, the period around 780 thousand years ago, known as Marine Isotope Stage (MIS) 19 has been identified as the closest analogue to the current interglacial on the basis of the phasing of orbital parameters and overall climate evolution. As such, it provides a more appropriate testbed for evaluating the Holocene evolution of GHG and vegetation succession. However, despite this potential, MIS 19 remains substantially understudied. The proposed project aims to address this imbalance by generating the most detailed record (~200-yr resolution) of vegetation and hydrological changes during MIS 19 from ODP Site 977 in the Alboran Sea, S Iberian margin and combine it with ongoing analyses of palaeoceanographic proxies from the same samples, currently underway by the Spanish Consortium GRACCIE. In recent years, the western and southern parts of the Iberian margin have emerged as critical areas for linking marine and terrestrial records directly through joint pollen and palaeoceanographic proxy analyses in the same marine archive recovered adjacent to the continent. This allows a direct comparison between ocean and terrestrial changes, bypassing timescale and correlation uncertainties. The results will establish:(1) the duration of the MIS 19 interglacial in sea surface conditions and the precise phasing with vegetation changes;(2) Vegetation trends during MIS 19 vis-à-vis those already observed in the region during the Holocene;(3) the nature of vegetation and hydrological changes during the peak in atmospheric methane concentrations at the end of MIS 19c;(4) the response of vegetation and impact on erosion to short-term climate variability during the intervals before and after the interglacial as well as within it.If the MIS 19 - MIS 1 analogy is correct, these results will have implications for assessing: (i) the natural length of the current interglacial, in the absence of anthropogenic forcing; (ii) the extent to which human impact over the past millennia has overprinted natural vegetation trends in the region; (iii) the underlying causes for the Holocene evolution of methane.