Argon and neodymium concentrations of ODP Site 145-884

A large sediment deposit known as the Meiji Drift, located in the northwestern Pacific Ocean, is thought to have formed from deep water exiting the Bering Sea, although no notable deep water forms there presently. We determine the terrigenous sources since 140 ka to the drift using bulk sediment 40Ar-39Ar and Nd isotopic analyses on the silt-sized (20-63 µm) terrigenous fraction from Ocean Drilling Program (ODP) Site 884 to reconstruct paleo-circulation patterns. There are large changes in both isotopic tracers, varying on glacial-interglacial cycles. During glacial intervals, bulk sediment 40Ar-39Ar ages range between 40 and 80 Ma, while Nd isotopic values range from epsilon-Nd = -1 to +2. During interglacial intervals, sediments become much younger and more radiogenic, with bulk sediment ages falling to 2-15 Ma and Nd isotopic values ranging between epsilon-Nd = +5 and +9. These data and quantitative comparison to potential source rocks indicate that the young Kamchatkan and Aleutian Arcs, lying NW and NE of the Meiji Drift, contribute the majority of sediment during interglacials. Conversely, older source rocks, such as those drained by the Yukon River and northeast Russia are the dominant origin of sediments during glacials. Mixing model calculations suggest that as much as 35-45% of the sediment deposited in the Meiji Drift during glacials is from the Bering Sea. It remains unclear whether thermohaline-type circulation or focussing of Bering Sea flow lead to the glacial-interglacial sediment source changes observed here.