Stable isotope record and lithic fragments distribution in sediments of MIS9-14 of the North Atlantic

Stable isotope and ice-rafted debris records from three core sites in the mid-latitude North Atlantic (IODP Site U1313, MD01-2446, MD03-2699) are combined with records of ODP Sites 1056/1058 and 980 to reconstruct hydrographic conditions during the middle Pleistocene spanning Marine Isotope Stages (MIS) 9-14 (300-540 ka). Core MD03-2699 is the first high-resolution mid-Brunhes record from the North Atlantic's eastern boundary upwelling system covering the complete MIS 11c interval and MIS 13. The array of sites reflect western and eastern basin boundary current as well as north to south transect sampling of subpolar and transitional water masses and allow the reconstruction of transport pathways in the upper limb of the North Atlantic's circulation. Hydrographic conditions in the surface and deep ocean during peak interglacial MIS 9 and 11 were similar among all the sites with relative stable conditions and confirm prolonged warmth during MIS 11c also for the mid-latitudes. Sea surface temperature (SST) reconstructions further reveal that in the mid-latitude North Atlantic MIS 11c is associated with two plateaus, the younger one of which is slightly warmer. Enhanced subsurface northward heat transport in the eastern boundary current system, especially during early MIS 11c, is denoted by the presence of tropical planktic foraminifer species and raises the question how strongly it impacted the Portuguese upwelling system. Deep water ventilation at the onset of MIS 11c significantly preceded surface water ventilation. Although MIS 13 was generally colder and more variable than the younger interglacials the surface water circulation scheme was the same. The greatest differences between the sites existed during the glacial inceptions and glacials. Then a north - south trending hydrographic front separated the nearshore and offshore waters off Portugal. While offshore waters originated from the North Atlantic Current as indicated by the similarities between the records of IODP Site U1313, ODP Site 980 and MD01-2446, nearshore waters as recorded in core MD03-2699 derived from the Azores Current and thus the subtropical gyre. Except for MIS 12, Azores Current influence seems to be related to eastern boundary system dynamics and not to changes in the Atlantic overturning circulation.本研究整合了北大西洋中纬度3个岩芯位点的稳定同位素与冰筏碎屑记录，涉及综合大洋钻探计划（Integrated Ocean Drilling Program, IODP）U1313站、MD01-2446孔、MD03-2699孔，并结合大洋钻探计划（Ocean Drilling Program, ODP）1056/1058站与980站的相关记录，重建了更新世中期对应海洋同位素阶段（Marine Isotope Stages, MIS）9至14（即300~540 ka）的水文环境。MD03-2699孔是首个来自北大西洋东部边界上升流系统的高分辨率中布容期记录，完整覆盖了MIS 11c与MIS 13时段。本次研究的站位阵列涵盖了盆地东西边界流体系，并实现了亚极地与过渡水团的南北断面采样，由此得以重建北大西洋环流上层支的输运路径。在间冰期鼎盛阶段的MIS 9与MIS 11时期，各站位的表层与深层海洋水文环境均呈现相对稳定的相似特征，证实中纬度地区MIS 11c时期同样存在持续暖期。海表温度（Sea Surface Temperature, SST）重建结果进一步显示，北大西洋中纬度地区的MIS 11c时期存在两个温度平台，其中较年轻的那个温度略高。热带浮游有孔虫类群的出现指示东部边界流体系在MIS 11c早期存在增强的次表层北向热输运，这引发了关于其对葡萄牙上升流系统影响程度的科学问题。MIS 11c起始阶段的深层水通风过程显著早于表层水通风。尽管MIS 13整体较后续的间冰期更为寒冷且环境波动更强，但其表层水循环模式与其他时段一致。各站位间的最大差异出现在冰期起始阶段与冰期时期，此时一条南北走向的水文锋面将葡萄牙近岸与远岸海水分隔开来。结合IODP U1313站、ODP 980站与MD01-2446孔的记录相似性可知，远岸海水源自北大西洋流；而MD03-2699孔记录的近岸海水则来源于亚速尔流，进而隶属于亚热带环流圈。除MIS 12外，亚速尔流的影响似乎与东部边界流体系动力学相关，而非大西洋翻转环流的变化。