Holocene Changes in Deep Water Circulation Inferred From Authigenic Nd and Hf Isotopes in Sediment Records From the Chukchi‐Alaskan and Canadian Beaufort Margins

Abstract

AbstractThe rare earth element concentrations and radiogenic isotope (Sr‐Nd‐Hf) compositions measured in bulk sediment leachates, together with bulk and clay mineralogical data, from two piston cores recovered in the Canadian Beaufort (AMD0214‐02PC) and Chukchi‐Alaskan (HLY0501‐01JPC) margins were studied to investigate changes in the weathering regimes and deep water circulation during the Holocene. The coupled evolutions of the Nd and Hf isotopic compositions (expressed in epsilon units: ɛNd and ɛHf, respectively) are in good agreement with modern seawater and bulk sediment leachate data from Pacific water, Atlantic water, and the Mackenzie River. This agreement supports the idea that boundary exchange and brine formation likely play a significant role in the ɛNd and ɛHf values of the bottom waters in the western Arctic Ocean. The ɛNd and ɛHf records from the Canadian Beaufort and Chukchi‐Alaskan margins reveal changes toward more radiogenic values from the early to late Holocene. Based on the ɛNd and ɛHf records, we suggest that the unradiogenic values are not controlled by water mass provenance and mixing but rather by provenance and a change in the weathering regime in the Mackenzie and Yukon drainage basins during the early to mid‐Holocene. In contrast, the more radiogenic ɛNd and ɛHf values in the Chukchi‐Alaskan margin and the mineralogical records in the late Holocene have primarily been controlled by an increase in the contributions of seawater and detrital particles from the Bering Sea via the Bering Strait inflow, which is likely related to major changes in the Pacific Ocean‐atmospheric dynamics.