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

从晚更新世，特别是从最后一次冰消期的古记录表明，地下热量积累之前的不稳定性的北方冰盖表现为IRD排放到北大西洋。然而，这种地下热量积累背后的确切机制及其对冰山大量排入北大西洋（称为海因里希事件）的作用却知之甚少。因此，拟议项目的主要目标是破译北大西洋高纬度地区地下热量和盐分异常积累的起源（这也是从本提案的初步研究中推断出来的），严格检验地下热量和盐分平流是否对北方冰盖的不稳定起了根本作用，并从机理上了解所涉过程。这些目标将通过生成地下温度和盐度记录来实现，这些记录跟踪了北大西洋中高纬度地区的地下水文地理和过去500 kyr期间低时间分辨率（2 kyr）的IRD计数，并辅以IRD沉积增加事件的高分辨率（250年）记录。为了重建地下温度和盐度，将为地点U1313生成Mg/Ca和180深居浮游有孔虫物种Globorotalia truncatulinoides（右旋），而温跃层物种Neogloboquadrina pachyderma（左旋）将用于地点984。选定的岩心（IODP站点U1313和ODP站点984）位于连接副热带环流和副极地环流的拟议热通道中，其特征是（i）高沉积速率，（ii）整个研究间隔的连续沉积（即，（iii）丰富和保存完好的温跃层居住的浮游有孔虫和底栖有孔虫的出现，以及（iii）高分辨率的年龄模型，这是实现本建议目标的必要先决条件。总的来说，拟议的记录将允许阐明整个北大西洋的地下热量和盐预算的时间和空间变化及其对冰盖稳定性的作用。在过去的500 kyr中总共重建了16次海因里希事件，新生成的记录也将允许验证在特定事件期间地下热量和盐预算的变化是否作为冰盖不稳定的反馈机制发挥了根本作用，因此终止。

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.