North Atlantic Footprint of Summer Greenland Ice Sheet Melting on Interannual to Interdecadal Time Scales: A Greenland Blocking Perspective

Recent rapid melting of the summer Greenland ice sheet (GrIS) and its impact on Earth's climate has attracted much attention. In this paper, we establish a connection between the melting of GrIS and the variability of summer sea surface temperature (SST) anomalies over the North Atlantic on interannual to interdecadal time scales through changes in subseasonal Greenland blocking (GB). It is found that the latitude and width of GB are important for the spatial patterns of the GrIS melting. The melting of the GrIS on interdecadal time scales is most prominent for the positive Atlantic multidecadal oscillation phase (AMO(+)) because the high-latitude GB and its large width, long lifetime, and slow decay are favored. However, the North Atlantic mid-high latitude warm-cold-warm (cold-warm-cold) tripole, referred to as the NAT(+) (NAT(-)) pattern, on interannual time scales tends to strengthen (weaken) the role of AMO(+) in the GrIS melting, especially on the northern or northeastern periphery of Greenland, by promoting (inhibiting) high-latitude GB and increasing (decreasing) its width. It is further revealed that AMO(+) (NAT(+)) favors the persistence and width of GB mainly through producing weak summer zonal winds and a small summer meridional potential vorticity gradient (PVy) in the North Atlantic mid-high latitudes at 55 degrees-70 degrees N (55 degrees-65 degrees N) compared to the role of negative AMO (NAT(-)). The event frequency and zonal width of GB events and their poleward shift are favored by the combination of NAT(+) with AMO(+). In contrast, the combination of NAT(-) and AMO(+) tends to suppress reduced summer zonal winds and PVy, thus inhibiting the event frequency of GB events and their poleward shift and zonal width. SIGNIFICANCE STATEMENT: Rapid melting of the summer Greenland ice sheet (GrIS) has been observed to frequently occur, especially after the year 2000, leading to a rise in sea level and other effects on Earth's climate. The physical cause of the rapid melting of the GrIS is an important area of research. We establish a connection between the summer melting of the GrIS and different sea surface temperature (SST) modes in the North Atlantic via changes in Greenland blocking. Although the positive Atlantic multidecadal oscillation (AMO(+)) phase favors the overall melting of GrIS, the phase of the North Atlantic tripole (NAT) SST pattern modulates the strength and location of the GrIS melting. The positive NAT phase (NAT(+)) with a warm-cold-warm tripole structure in the North Atlantic mid-high latitudes and AMO(+) combine to result in a strong warm SST anomaly in the high latitudes of the North Atlantic north of 60 degrees N, which promotes the melting of GrIS on the western, northern, and northeastern peripheries of Greenland via high-latitude Greenland blocking with an increased zonal width. The combination of the negative NAT phase (NAT(-)) with a cold-warm-cold tripole structure and AMO(+) tends to suppress this effect. Thus, our results provide a new understanding of why the melting of GrIS shows a strong variability in strength and region.