Pyroclastic Eruption Boosts Organic Carbon Fluxes Into Patagonian Fjords

Abstract

Fjords and old‐growth forests store large amounts of organic carbon. Yet the role of episodic disturbances, particularly volcanic eruptions, in mobilizing organic carbon in fjord landscapes covered by temperate rainforests remains poorly quantified. To this end, we estimated how much wood and soils were flushed to nearby fjords following the 2008 eruption of Chaitén volcano in south‐central Chile, where pyroclastic sediments covered >12 km2 of pristine temperate rainforest. Field‐based surveys of forest biomass, soil organic content, and dead wood transport reveal that the reworking of pyroclastic sediments delivered ~66,500 + 14,600/−14,500 tC of large wood to two rivers entering the nearby Patagonian fjords in less than a decade. A similar volume of wood remains in dead tree stands and buried beneath pyroclastic deposits (~79,900 + 21,100/−16,900 tC) or stored in active river channels (5,900–10,600 tC). We estimate that bank erosion mobilized ~132,300+21,700/−30,600 tC of floodplain forest soil. Eroded and reworked forest soils have been accreting on coastal river deltas at >5 mm yr−1 since the eruption. While much of the large wood is transported out of the fjord by long‐shore drift, the finer fraction from eroded forest soils is likely to be buried in the fjords. We conclude that the organic carbon fluxes boosted by rivers adjusting to high pyroclastic sediment loads may remain elevated for up to a decade and that Patagonian temperate rainforests disturbed by excessive loads of pyroclastic debris can be episodic short‐lived carbon sources.

Reflections on the history of research on large wood in rivers

“…Given this complexity, it is not surprising that rivers draining Chaiten and Calbuco volcanoes have differed substantially in abundance and flux of large wood, and both landscapes remain very dynamic even 10 years after eruption. Eruptions can account for large fluxes of carbon from terrestrial to river to estuarine environments (Ulloa et al ., 2015b; Mohr et al ., 2017). The carbon footprint of the 2008 Chaitén eruption on the Rayas River was more significant than the measured geomorphic impacts on channel geometry for the first 5 years following disturbance; a modest post‐eruptive geomorphic response in this river has been a poor indicator of its biogeochemical response (Ulloa et al ., 2015b).…”

Environmental and coastline changes controlling Holocene carbon accumulation rates in fjords of the western Strait of Magellan region

“…Regional to local factors as climate conditions and the altitudinal distribution of the vegetation zone influence the transport of OC terr , which often depends on precipitation rates and locallly associated water pathways (Lamy et al, 2010). Moreover, damages of terrestrial ecosystems after the deposition of tephra from explosive volcanic eruptions cause enhanced plant decay up to a millennium scale leading to increased delivery and deposition of OC terr (Kilian et al, 2006;Korup et al, 2019;Mohr et al, 2017).…”

High-resolution stalagmite stratigraphy supports the Late Holocene tephrochronology of southernmost Patagonia

“…Matrix effects between NIST610/NIST612 and CaCO3 were considered to contribute less than 10% error. Measured isotopes were 27 Al, 29 Si, 31 P, 34 S, 43 Ca, 88 Sr, 90 Zr and 238 U. Element concentrations have been stoichiometrically normalized to 400,000 ppm 43 Ca, assuming that the stalagmite is composed of 100% CaCO3.…”