Changes of the upper water column at the 45°N North Atlantic since marine isotope stage 3

The 45°N of North Atlantic is located at the central zone of the ice-rafted detritus (IRD) belt of the North Atlantic, where the marine sediments contain rich environmental and climatic information of high-resolution. The sedimentary records there are used for reconstruction of the pale-oceanic environment since the last glacial in this study. IRD contents, planktonic foraminiferal assemblages and their oxygen and carbon isotopes (δ¹⁸O and δ¹³C) from the core Hu71-377, are used as major tools. Combined with AMS¹⁴C dating and oxygen isotope stratigraphy, five Heinrich layers are identified in the MIS3 and MIS2, in which the Heinrich layer 1, 2 and 4 have obvious IRD peaks, high relative abundance of Neogloboquadrina pachyderma and light δ¹⁸O values, but no obvious light δ¹⁸O are observed in the Heinrich layer 3 and 5. The difference in δ¹⁸O between the Heinrich layers 3 and 5 and the Heinrich layers 1, 2 and 4 may suggest the impacts of melt water on the upper water column. Further, the offsets between δ¹³C_N.incompta and δ¹³C_N.pachyderma may also reflect the changes in the mixed layer and thermocline during the Heinrich events. The δ¹³C offsets were close to zero during Heinrich 1 and Heinrich 2, attributing to the vertical mixing of seawater driven by strong winds. And the δ¹³C offsets became larger during Heinrich 4 and Heinrich 5, indicating that the seasonal thermocline became shallower, which supports the inference of the penetration of the North Atlantic Current. What’s more, the planktonic foraminiferal assemblages may reflect the properties of the water masses in the upper water column, especially the relative abundance of N. pachyderma and Neogloboquadrina incompta may indicate the sea surface temperature (SST) changes during MIS3.