Anomalous Pacific‐Antarctic Ridge Volcanism Precedes Glacial Termination 2

Abstract

We present results from a well‐dated sediment core on the Pacific‐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 glacial‐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 mid‐ocean ridge volcanism during glacial terminations.

Influence of late Pleistocene sea-level variations on midocean ridge spacing in faulting simulations and a global analysis of bathymetry

“…The hypothesis that Pleistocene variations in sea level influence melt supply is supported by several lines of evidence. Proxies of ridge hydrothermal circulation indicate a response to sea-level change ( 17 – 19 ), as do variations in the abundance of sediment-hosted volcanoclastics ( 20 ). Axis-parallel variations in crustal thickness along the East Pacific Rise of 200 to 800 m vary with wavelengths that are consistent with the sea-level hypotheses ( 21 ).…”

Rapid heat discharge during deep-sea eruptions generates megaplumes and disperses tephra

“…Dispersal distances for these tephras are inferred to reach several km. Older tephra-bearing sediments recovered from sediment cores taken on the flanks of MORs also indicate similar dispersal scales 29 , 30 . These tephras provide evidence for explosive pyroclastic eruption styles 15 , 19 , something that has traditionally been considered extremely rare due to the high hydrostatic pressure 31 , 32 (we note that some debate exists as to the potential for tephra to be generated by magmatic fragmentation of fluid magma 15 versus other brecciation processes such as thermal granulation 33 and/or hydrovolcanic fragmentation 28 ).…”

“…This inference can potentially be tested by future in situ observations of syn-eruptive hydrothermal processes 65 and continued sampling and chemical analysis of megaplume fluids. Application of our inversion method to paleo-tephra deposits recovered from marine sediment cores 29 , 30 could, in principle, provide new inroads toward constraining the long-term (≳10 ka) time-averages of the flux of mass and heat from the crust to the oceans associated with seafloor volcanic events.…”

Rapid heat discharge during deep-sea eruptions generates megaplumes and disperses tephra

“…Dispersal distances for these tephras are inferred to reach several km. Older tephra-bearing sediments recovered from sediment cores taken on the flanks of MORs also indicate similar dispersal scales 29,30 . These tephras provide evidence for explosive pyroclastic eruption styles 15,19 , something that has traditionally been considered extremely rare due to the high hydrostatic pressure 31,32 (we note that some debate exists as to the potential for tephra to be generated by magmatic fragmentation of fluid magma 15 versus other brecciation processes such as thermal granulation 33 and/or hydrovolcanic fragmentation 28 ).…”