Tracing the provenance and evolution of Asian dust fluxes during the Holocene: A geochemical study of sediment archives from Adak Island, Alaska

Asian dust plumes export micronutrients eastward to the Pacific Ocean and are substantial for regulating the marine biogeochemical cycles and productivity. Previous studies from the Gulf of Alaska (a high-nutrient and low-chlorophyll zone) revealed that the dominant nutrient supply during the last deglaciation was primarily sourced from iceberg meltwater instead of local Alaskan dust fluxes. However, attention to distal dust sources from Asia was limited, possibly due to resolution constraints. To address this, we consider here two chronologically well-constrained (by tephrochronology and radiocarbon dating) sedimentary archives from Adak Island (Andrew and Heart lakes), in the central Aleutian Islands, Alaska. These records preserve a high-resolution environmental and climatic history for the last ~10 ka and might also include a continuous record of Asian dust plume sources. Terrigenous materials in these sediments originate from either local weathered basalt units and volcanic ash or from distal Asian dust, comprising erosional products of the granitoid terrane. We studied the siliciclastic fraction of the sediments recovered from both lakes and employed elemental analyses along with radiogenic isotopes (Sr, Nd and Pb) to identify and quantify possible allochthonous dust sources. Our preliminary observations from major and trace elemental ratios and statistical analyses (PCA and factor loadings) suggest that, indeed, there are two dominant sources for terrigenous sediments. The enriched LREE and flat HREE pattern, together with a positive Eu anomaly, further support the mixed source (mafic to felsic) of the sediment supply to the lakes. Additionally, the Chemical Index of Alteration (CIA) and other elemental ratios in both lakes suggest a sharp decreasing trend ca. 4 ka followed by an increasing trend ca. 3.5 ka, which is asynchronous with the increased input of Asian dust and the neoglacial cooling event during this interval. The isotopic and other geochemical studies are in progress, which will further validate these findings.