NOAA/WDS Paleoclimatology - North Atlantic IRD, d18O, and Foraminifera Data during the Last Glacial Cycle

Past studies of marine sediments of the North Atlantic documented millennial-scale sea-surface cooling related to the Dansgaard-Oeschger events that have influenced the oceanic fronts and surface hydrology during the last glacial cycle. Most studies have focused on using ice-rafting, single or a few planktonic foraminifers’ abundance, and geochemistry to assess environmental changes, however, detailed planktonic foraminiferal assemblage data in the North Atlantic Transition Zone (NATZ) and subpolar gyre (SPG) for the full glacial cycle are scarce. Here we report planktonic foraminiferal abundances, oxygen isotopes, and ice rafted debris (IRD) counts from two sediment cores, Hu90-08 and Hu71-377, collected from the Milne seamount of southwestern SPG (SW SPG) and NATZ, respectively. Further, we have used the published micropaleontological (planktonic foraminiferal assemblage) data from the eastern and western SPG to provide an integrated reconstruction of changes in the surface water masses and dynamics of the Polar, Arctic, and subarctic fronts (PF, AF, and SAF). During the Heinrich iceberg-rafting events, when meltwater flooded the North Atlantic surface, the PF, AF, and SAF shifted southward, and the polar/subpolar water masses briefly invaded the western and eastern SPG and NATZ. During the last deglaciation-Holocene, the regions of cores Hu90-08 and Hu71-377 were mainly influenced by the warm North Atlantic Current, and the SAF was located north of both cores. In the early MIS3 (60-40 ka), the oceanic frontal system shifted northward from its position during MIS4. The SPG and NATZ gradually warmed, and the subpolar species Globigerina bulloides in cores Hu90-08, Hu71-377, and CH69-K09 increased in the middle of MIS3 (i.e., 38-30 ka), suggesting continuous warming of the sea surface temperature (SST) hydrological environment while the oceanic frontal systems continued to move northward. This hydrological environment rapidly cooled in the late MIS3-MIS2 (30-19 ka), with the PF shifted southward to the mid-latitude (~45°N) during the last glacial maximum. Despite the overall warmth of the SWwestern SPG (near the Newfoundland Basin) compared to the eastern SPG during MIS5, the North Atlantic-wide cooling events C21 and C24 are still identified in the SWwestern SPG. Further, the planktonic foraminiferal abundances in cores EW93-37JPC (i.e., scarce Neogloboquadrina pachyderma and abundant Globigerinoides inflata) and Hu90-08 reveal relatively warm MIS5e conditions compared to the Holocene. However, the decrease in the abundance of G. inflata suggests that the SWwestern SPG was influenced by the seasonal subpolar waters and possibly a short southward shift in the oceanic frontal systems between 124 and 120 ka.