Abstract
Abstract. Iron is a key limiting micro-nutrient for marine primary productivity. It can be supplied to the ocean by atmospheric dust deposition. Volcanic ash deposition into the ocean represents another external and so far largely neglected source of iron. This study demonstrates strong evidence for natural fertilisation in the iron-limited oceanic area of the NE Pacific, induced by volcanic ash from the eruption of Kasatochi volcano in August 2008. Atmospheric and oceanic conditions were favourable to generate a massive phytoplankton bloom in the NE Pacific Ocean which for the first time strongly suggests a connection between oceanic iron-fertilisation and volcanic ash supply.
Highlights
Volcanic ash represents a so far largely neglected component of the surface ocean biogeochemical iron-cycle and marine primary productivity (MPP) which can be limited by the availability of macro-nutrients like nitrate and phosphate
Moderate-resolution Imaging Spectroradiometer (MODIS) Aqua data are the optimal choice because the current study aims to show the build-up of Chl-a induced by fertilisation from ash released from Kasatochi using a time series of ocean colour data, which would be impossible in the case of Sea-viewing Wide Field-of-view Sensor (SeaWiFS) because of the mentioned data gap
MODIS Aqua 8-day composites of with maximum Chl-a that has been reached in the years 2002 Chl-a for 2008 and averaged data from 2002 to 2007 are ilto 2007, the number of pixels with increased concentration lustrated in Fig. 5 as a function of time along the N–S tranduring August 2008 is reduced to 40%, but a strong increase sect from 40◦ N to 60◦ N for the longitudes 165◦ W, 155◦ W, remains located over the open NE Pacific
Summary
Volcanic ash represents a so far largely neglected component of the surface ocean biogeochemical iron-cycle and marine primary productivity (MPP) which can be limited by the availability of macro-nutrients like nitrate and phosphate. The bloom detected by satellite observations occurs shortly after volcanic ash fall from the eruption of Kasatochi volcano (Aleutian Islands) in August 2008 Iron supply to such an iron-limited region increases chlorophyll-a (Chl-a) – used as proxy for surface ocean biomass – considerably and affects the climate relevant ocean-atmosphere exchange of chemical trace species (O’Dowd et al, 2004; Turner et al, 2004), e.g. carbon dioxide, organic carbon aerosols and dimethyl sulfide forming sulphate aerosols.
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