A DEGLACIAL AND HOLOCENE RECORD OF CLIMATE VARIABILITY IN SOUTH-CENTRAL ALASKA FROM STABLE ISOTOPES AND PLANT MACROFOSSILS IN PEAT

Peat cores have frequently been used as paleoecological and paleoclimate archives, but relatively few studies have used stable isotopes in peat to interpret paleoclimate. Here, we use stable oxygen isotope analyses of organic remains, in addition to plant macrofossils and peat carbon (C) accumulation rates, from a Kenai Peninsula, Alaska lowland peat core to examine deglacial and Holocene climate variability in south-central Alaska. Our findings show relatively higher δ¹⁸O (by ~5-10‰) during the Bølling-Allerød (B-A) Warming (~14 to 12.9 ka) and the early Holocene (11.6 to ~8.7 ka) and relatively lower values during cooler intervals such as the Younger Dryas (13 to 11.6 ka) and Little Ice Age. Higher δ¹⁸O values are coeval with high rates of C accumulation. The large amplitude changes observed in this peat record, along with the weak correlation between dominant peat type and δ¹⁸O values, suggest that the oxygen isotopic signal is related to both changes in temperature and moisture. The timing and magnitude of shifts in δ¹⁸O in the Kenai peat record are consistent with other regional δ¹⁸O lake records, implying climate is the main driver of shifts in the Kenai peat record. Our observed ¹⁸O enrichment during the relatively warm B-A and warm early Holocene implies a weakened Aleutian Low, a semi-permanent low-pressure system that delivers moisture to the region during winter months, resulting in a drier early Holocene climate. Although ¹⁸O enrichment may indicate heightened evaporation during the early Holocene, rapid C accumulation in Kenai Peninsula cores suggests high moisture availability. Therefore, it is more likely that increased summer moisture allowed for the proliferation of peatlands on the Kenai and across Alaska. This pattern is consistent with modern seasonal isotopic differences in southern Alaska, with winter precipitation in this region exhibiting relatively lower δ¹⁸O values compared with summer values. In order to achieve warm/wet conditions in the summer in this region of Alaska, ridging over Alaska and troughing farther west than normal would need to occur. While this is a rare scenario under modern climate, it is possible that such a pattern persisted during the early Holocene, with greater storm tracks originating from the East Siberian Sea and a higher-than-normal Pacific subtropical high.