| Summary: | We present results from a wellâ€dated sediment core on the Pacificâ€Antarctic Ridge (PAR) that document a ∼15 cm thick layer of basaltic ash shards that precedes the penultimate deglaciation (Termination 2). The glasses have MORB composition consistent with an axial source and their morphologies are typical of pyroclastic deposits created by submarine volcanism. The ash layer was deposited ∼7 km from the PAR axis, a distance that implies buoyant plumes lofted debris high into the water column with subsequent fallout to the core location. We infer plume rise height using grain settling velocities, the water depth at the core site, and deep ocean current speeds from ARGO floats. Rise heights of 1.5 km or less require unrealistically large current speeds to transport grains to the core site. Instead, the data are consistent with a plume rise height of at least 2 km, implying that T2 was an interval of anomalous volcanism along this segment of the PAR. The timing and duration of the ash deposit is consistent with glacialâ€interglacial modulation of ridge magmatism. Volcaniclastic records from additional locations will be necessary to assess whether the PAR record is a rare find or it is representative of midâ€ocean ridge volcanism during glacial terminations. © 2018 American Geophysical Union. Received 14 NOV 2017; Accepted 18 APR 2018; Accepted article online 7 MAY 2018; Published online 16 AUG 2018. DCL and EIS were supported by NSF award OCEâ€1558641 and the University of Connecticut. We are grateful to David Cady at UCONN for assistance with ICPâ€MS analyses and Lora Wingate at the University of Michigan and Jean Lynchâ€Stieglitz at Georgia Tech for assistance with stable isotope analyses. We are also indebted to the Oregon State University Core Repository for the curation of core OC170â€26â€159. The OSU Repository is supported by NSF award OCEâ€1558679. MJL and PDA were supported by NSF awards OCEâ€1558372 and EARâ€1551433. Thanks to Nathan Dalleska at Caltech for assistance with LAâ€ICPâ€MS analyses and ...
|
|---|