Coherent regional expressions of Holocene summer temperature on Greenland

Abstract. Proxy time series suggest that Holocene summer warmth peaked asynchronously across Greenland, but the extent to which these differences reflect coherent regional climate patterns remains unclear. We compile 38 quantitative and qualitative summer-temperature proxy time series from Greenland and adjacent seas and apply an uncertainty-weighted factor analysis framework that accommodates heterogeneous proxy types to identify coherent temporal and spatial patterns from 10 ka to present. We compare these proxy-derived factors with those for five proxy-informed paleoclimate reconstructions and a transient model-only baseline. Two factors best represent the proxy network. The leading temporal mode reaches a maximum by 7.2 ka, reflecting early-to-mid Holocene warmth in northern and eastern Greenland, and contrasts with delayed warming in western Greenland. We interpret this pattern as an insolation-driven summer-temperature response modified by meltwater, ocean stratification, and sea-ice dynamics during retreat of the Laurentide and Greenland ice sheets. The second temporal mode peaks by 5.4 ka and is strongest in southern and southwestern Greenland, which may reflect an increased coastal influence of Atlantic-origin heat transported by the Irminger and West Greenland currents. Climate reconstructions reproduce the temporal evolution of the proxy-derived factors more successfully than their spatial patterns. Two paleoclimate reconstructions provide the closest agreement, but no existing reconstruction reproduces the complete regional structure of the proxy network. Despite proxy and chronological uncertainties, this analysis demonstrates that heterogeneous proxies can resolve coherent spatiotemporal patterns in Holocene Greenland climate, providing a basis for mechanistic interpretation and an empirical benchmark for evaluating paleoclimate reconstructions.