The role of North Atlantic subsurface heat accumulation for Late Pleistocene Heinrich Events

晚更新世，特别是最后一次冰川消融以来的古记录表明，在北半球冰盖失稳之前，地下热量积累了，这表现为IRD向北大西洋的排放。然而，这种地下热量积累背后的确切机制及其在冰山大规模排放到北大西洋(称为海因里希事件)中所起的作用，人们却知之甚少。因此，拟议项目的主要目标是破译高纬度北大西洋异常地下热量和盐分积聚的来源(这一提议的初步研究也推断了这一点)，批判性地检验地下热量和盐分平流是否对北半球冰盖的不稳定起了基本作用，并从机理上了解了所涉及的过程。这些目标将通过生成跟踪过去500年北大西洋中高纬度地区的地下水文图和低时间分辨率(2 KYR)的IRD计数的地下温度和盐度记录来实现，并辅之以IRD沉积增加时期的高分辨率(250年)记录。为了能够重建地下温度和盐度，将在U1313号站点生成镁/钙和180种深水浮游有孔虫Globorotalia truncatulinoides(右)，而在984号站点将使用温跃层栖息物种Neogloboquina pachyderma(左)。选定的岩芯(IODP站点U1313和ODP站点984)位于拟议的连接副热带环流和亚极环流的热通道上，其特点是：(I)高沉积速率，(Ii)在研究期间(即最后500ka)持续沉积，(Iii)出现大量和保存良好的温跃层栖息的浮游和海底有孔虫，以及(Iii)高分辨率年龄模型，这是实现本提案目标的必要先决条件。总体而言，拟议的记录将有助于阐明北大西洋次表层热量和盐分收支的时间和空间变异性及其对冰盖稳定性的作用。在过去500KYR总共16次海因里希事件的重建中，新产生的记录还将允许验证特定事件期间地下热量和盐收支的变化是否作为冰盖不稳定从而终止的反馈机制发挥了基本作用。

Paleorecords from the Late Pleistocene and especially from the last deglaciation indicate that subsurface heat accumulated prior to the destabilization of northern hemisphere ice sheets as manifested by IRD discharge to the North Atlantic. The exact mechanisms behind this subsurface heat accumulation and its role for the massive discharge of icebergs into the North Atlantic (known as Heinrich Events) is, however, poorly understood. Therefore, the principal objectives of the proposed project are to decipher the origin of anomalous subsurface heat and salt accumulation in the high-latitude North Atlantic (as also inferred from a preliminary study for this proposal), to critically test if subsurface heat and salt advection played a fundamental role for the destabilization of northern hemisphere ice sheets, and to obtain a mechanistic understanding of the processes involved. These objectives will be reached through the generation of subsurface temperature and salinity records tracking the subsurface hydrography across the mid- to high-latitude North Atlantic and IRD counts during the past 500 kyrs in low temporal resolution (2 kyr), supplemented by high-resolution (250 years) records across episodes of increased IRD deposition. To allow for the reconstruction of subsurface temperatures and salinities, Mg/Ca and 180 of the deep-dwelling planktic foraminiferal species Globorotalia truncatulinoides (dextral) will be generated for Site U1313 while the thermocline-dwelling species Neogloboquadrina pachyderma (sinistral) will be used for Site 984. The chosen cores (IODP Site U1313 and ODP Site 984) are located in the proposed heat pathway connecting the Subtropical Gyre with the Subpolar Gyre and are characterized by (i) high sedimentation rates, (ii) continuous sedimentation across the study interval (i.e., the last 500 ka), (iii) the occurrence of abundant and well-preserved thermocline-dwelling planktic and benthic foraminifera, and (iii) a high-resolution age model, necessary prerequisites for the aims of this proposal. Overall, the proposed records will allow to shed light onto the temporal and spatial variability of the subsurface heat and salt budget across the North Atlantic and its role on ice-sheet stability. Being reconstructed for a total of 16 Heinrich Events across the last 500 kyr, the newly generated records will also allow to verify if variations in the subsurface heat and salt budget during specific events played a fundamental role as feedback mechanism for ice-sheet destabilization and therefore terminations.