Recovery Rate of a Salt Marsh From the 1700 CE Cascadia Subduction Zone Earthquake, Netarts Bay, Oregon.

Since the 1700 CE Cascadia Subduction Zone earthquake and associated coseismic subsidence and tsunami, vegetated intertidal habitats have reestablished across Pacific Northwest estuaries, yet timescales and mechanisms of recovery are uncertain. We investigated the timescale of salt marsh reestablishment in Netarts Bay, Oregon following the 1700 CE earthquake using a combination of excess 210Pb, 14C, stratigraphic constraints, and Bayesian age‐depth modeling. Coseismic subsidence lowered the area to low/mid marsh, which persisted for 200 years before transition to modern high marsh. The modern high marsh now appears in dynamic equilibrium with modern sea level rise. In addition to serving as a methodological proof of concept for dating the past 300 years, these results provide insight into intertidal morphodynamic response to large perturbations along tectonically active margins. Plain Language Summary: The last major earthquake along the Pacific Northwest (PNW) coast occurred in 1700, causing widespread destruction of salt marshes through elevation loss and burial by tsunami sand. In the ∼300 years following the earthquake, PNW salt marshes that were lost during the earthquake have reestablished; however, we are unsure of the timeframe over which they grew back. Salt marshes provide valuable services, including flood protection, habitat, pollution filtration, and carbon burial. Thus, improved understanding of their growth patterns is important—especially in response to large, destructive events such as those that will occur with increasing frequency under accelerating climate change (like hurricanes). Through a combination of different age dating techniques and statistical analyses, we determined that the reestablishment of a salt marsh in Netarts Bay, Oregon took ∼200 years. Following the next major PNW earthquake, which will undoubtedly occur under accelerated sea level rise, some salt marshes and their services may be lost permanently. Key Points: 14C, excess 210Pb, and Bayesian statistics can produce decadal age‐depth models over the last ∼300 yearsFollowing the 1700 CE Cascadia Subduction Zone earthquake high marsh reestablishment took ∼200 years in Netarts [ABSTRACT FROM AUTHOR]