## 5 Discussion
### Sea-Surface Characteristics during the MIS4-MIS3  
The C24 cooling event centered at 106.5 ka in core Hu90-08 corresponds to the sharp rise in the %_N. pachyderma_ in the eastern subpolar gyre (Figure 6). A similar peak in %_N. pachyderma_ at 109.5 ka also found in core 37 JPC, although there appears to be an offset in age between the two records (i.e., 37 JPC and Hu90-08), most likely due to the use of outdated age model [56] in core 37 JPC. An intermediate IRD peak at 88 ka with a concomitant rise in the %_N. pachyderma_ (Figure 6) is correlated to the cooling event C21 for the first time in the western subpolar gyre. The lighter \(\delta^{18}\)O event appears to follow the IRD event suggesting freshening of the sea-surface. The IRD/g and %_N. pachyderma_ peaks identify H2, H4, and H5 [57] with the concomitant light \(\delta^{18}\)O, although there are differences in \(\delta^{18}\)O during each H-event (Figure 7). One of the striking features is the covariation of the foraminifers/g with that of the abrupt rise in IRD/g, consistent with the hypothesis of a near-collapse of the productivity [58; 58]. The highest concentration (85%) of _N. pachyderma_ but significant reduction in _N. incompta, T. quinqueloba, G. bulloides, and G. inflata_ during H-events (Figure 5) suggests an incursion by the polar water. Moreover, the decline of _N. pachyderma_ but an increase in _N. incompta_ immediately after the H-events reflects rapid changeover by the subpolar to transitional water at site Hu90-08. The lighter _N. pachyderma_\(\delta^{18}\)O suggests a sea-surface freshening during the H2, H4, and H5, consistent with the records at other regional sites (Figures 1 and 7). [PERSON] et al. [38] reported SSTs, sea-surface salinities, and sea-ice covers during the H0, H1, and H2, including the LGM (Figure 1; Table 1). The authors reported 0 \({}^{\circ}\)C and <5 \({}^{\circ}\)C SSTs during February and August, respectively, with sea-ice cover ranging from 4 to 12 months/year. Our data are consistent with the broader temperature aspect of [PERSON] et al. [38] when the transfer function of %_N. pachyderma_ to SST [59] is applied. [PERSON] et al. [19] also reported the concentration of _N. pachyderma_ (Figure 7e), which remained \(\sim\)95% during the MIS3 in the Irminger Basin, suggesting an absolute dominance by the polar water mass. By developing a Heinrich variable (RM), [PERSON] et al. [10] reported the intensity of ice-rafting on the sea-surface, matching with the summer and winter SSTs. However, the exact mechanism by which the ice-rafting (i.e., meltwater discharge) and the rise in the SSTs were linked remains unclear. The IRD records at Hu90-08 (Figure 7) are consistent with the H1, H2, H4, and H5 ice-rafting records from the nearby core SU90-11 [60], except for two minor IRD peaks within the MIS4 in Hu90-08. An increasing trend from 20 to 85.5% in _N. pachyderma_ between 54 and 10 ka (Figure 7), a mirror image to the %_N. incompta_ might reflect a gradual sea-surface cooling and more frequent incursions by the polar water during the winter and spring times [10; 59]. This longer-scale inverse covariation between the %_N. pachyderma_ and %_N. incompta_ was frequently interrupted by the H-events. In contrast to the incursion by the polar water, the increase in %_N. incompta_ (Figure 5) suggests frequent incursions by the warm and salty water due to the NAC inflow, most likely during the late spring and summer. The high-frequency variability in %_T. quinqueloba_ ranging from 0.86 to 19.55%suggests occasional intrusions by the subpolar water [27] at site Hu90-08, most likely due to the penetration of the glacial Labrador Current [1,61]. In contrast to the records at site Hu90-08, the %_N. pachyderma_ peaks in the millennial-scale records of CH69-K09 due to its higher temporal resolution are narrower, implying that the impact of H-events-induced meltwater lasted for a short period. Granted that there might be a mismatch between the age models of cores, however, a close inspection reveals much more subtle changes.