The ocean response to volcanic iron fertilisation after the eruption of Kasatochi volcano: a regional-scale biogeochemical ocean model study

摘要

In high-nutrient–low-chlorophyll regions, phytoplankton growth is limited bythe availability of water-soluble iron. The eruption of Kasatochi volcano inAugust 2008 led to ash deposition into the iron-limited NE Pacific Ocean.Volcanic ash released iron upon contact with seawater and generated amassive phytoplankton bloom. Here we investigate this event with aone-dimensional ocean biogeochemical column model to illuminate the oceanresponse to iron fertilisation by volcanic ash. The results indicate thatthe added iron triggered a phytoplankton bloom in the summer of 2008.Associated with this bloom, macronutrient concentrations such as nitrate andsilicate decline and zooplankton biomass is enhanced in the ocean mixedlayer. The simulated development of the drawdown of carbon dioxide andincrease of pH in surface seawater is in good agreement with availableobservations. Sensitivity studies with different supply dates of iron to theocean emphasise the favourable oceanic conditions in the NE Pacific togenerate massive phytoplankton blooms in particular during July and Augustin comparison to other months. By varying the amount of volcanic ash andassociated bio-available iron supplied to the ocean, model resultsdemonstrate that the NE Pacific Ocean has higher, but limited capabilitiesto consume CO₂ after iron fertilisation than those observed after thevolcanic eruption of Kasatochi.