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

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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.