Rapid Response of Volcanism to Deglaciation in Southeast Alaska and Evidence for Attendant Climate Impacts

Abstract:

Evidence for increased subaerial volcanism during the last deglaciation has been hypothesized to result from depressurization of magma chambers in response to glacial unloading. However, the direct link between isostatic changes and the initiation of volcanism is obscured by different regional climate histories and timescales of isostatic adjustment. Likewise, the regional and global response to this volcanic forcing is poorly constrained due to the difficulty of obtaining high-resolution records that can capture short-term climate variability.

Marine sediment records from the Southeast Alaska margin have exceptionally high sedimentation rates (up to 1 cm/yr across the last deglacial transition), along with excellent age control (28 ¹⁴C dates), and thus provide a decadal-scale record of 23 tephra layers paired with foraminiferal oxygen isotopes and alkenone temperature reconstructions that record the timing and climate impacts of these eruptions. Major element compositions of eight discrete tephra layers are consistent with a source from the Mt. Edgecumbe Volcanic Field (MEVF).

The onset of the MEVF eruptive sequence is concurrent with the onset of Bølling-Allerød interstadial warmth, the disappearance of ice-rafted detritus, and a period of rapid vertical land motion associated with modeled isostatic rebound in response to glacier retreat. These data support the hypothesis that regional deglaciation can trigger volcanic activity. A series of short-term cooling and surface ocean freshening events are associated with the interval of intense volcanic activity. The Southeast Alaska record thus supports a two-way interaction between climate and volcanism, in which nearly instantaneous volcanic response to ice unloading may enhance climate variability during deglaciation.