Early response of the northeast subarctic Pacific plankton assemblage to volcanic ash fertilization

Abstract

Fe-poor water collected at Sta. P20 in the Gulf of Alaska in June 2011 was enriched with different concentrations of volcanic ash (0.12, 1.2, and 10 mg L 21 ) from two subduction zone volcanoes, Kasatochi and Chaiten, and incubated onboard under in situ conditions for 6 d. The experimental setup also included a control (no addition) and a positive control (addition of 0.6 nmol L 21 FeSO 4 ). Following a 4 d lag period, there were increases in carbon fixation rates (up to a factor of 10) and chlorophyll a concentrations (up to a factor of 3) in the positive control and in the ash-enriched (1.2 and 10 mg L 21 ) treatments. Diatoms dominated at the end of the incubations, but cyanobacteria, dinoflagellates, pelagophytes, and haptophytes were also stimulated by the presence of ash. Deposition of , 1 mg ash L 21 , which is in the lower range of those estimated to have caused the August 2008 bloom following the eruption of the Kasatochi volcano in the Aleutian Islands, would suffice to trigger a bloom in the Gulf of Alaska.

Volcanic ash supply to the surface ocean—remote sensing of biological responses and their wider biogeochemical significance

“…This was despite deionized water (Milli-Q) leaching experiments with the Eyjafjallajökull ash indicating an upper bound Fe release of 4.6-16 nmol L −1 . Conversely, Mélançon et al (2014) observed changes in chlorophyll-a biomass in the North Pacific that generally matched Fe-only treatment-indicating full relief of Fe stress in both cases, and Browning et al (2014a) who in the Southern Ocean reported responses to ash amendment that were equivalent, or in a number of cases significantly enhanced relative to the Fe-only treatment.…”

“…Arguably the most convincing evidence that natural phytoplankton communities can access Fe supplied from volcanic ash has come from shipboard bioassay experiments that have detected changes in phytoplankton physiology (Achterberg et al, 2013;Browning et al, 2014a), biomass (Achterberg et al, 2013;Browning et al, 2014a;Mélançon et al, 2014), and community structure (Mélançon et al, 2014) that are consistent with relief of phytoplankton Fe limitation (Boyd et al, 2007). However, observed responses have not been consistent in either the magnitude of phytoplankton response to a given ash loading, or the relative response compared to parallel Fe-only treatment experiments.…”

“…Unfortunately, whilst presenting an intriguing hypothesis, direct evidence for marine phytoplankton responding to ash fallout from the eruption was lacking. More recently, multiple studies have reported significant phytoplankton responses to volcanic ash supply; either following a natural deposition event (Hamme et al, 2010;Langmann et al, 2010a;Lin et al, 2011;Achterberg et al, 2013), or through controlled supply of ash to phytoplankton communities in shipboard bottle enrichment experiments (Achterberg et al, 2013;Browning et al, 2014a;Mélançon et al, 2014).…”

“…The Sierra Negra and La Cumbre volcanoes referred to in the text are located in the Galapagos Islands. Also shown are sites of ash addition experiments (blue circles) performed in the North Atlantic (Achterberg et al, 2013), North Pacific (Mélançon et al, 2014) and South Atlantic and Southern Ocean (Browning et al, 2014a), and the location of Ocean Station Papa (OSP, black square). PCC, Puyehue-Cordón Caulle. to originate from large scale Fe fertilization of the remote highnitrate Southern Ocean after the eruption of Mt Pinatubo in 1991 (Figure 1; Sarmiento, 1993;Watson, 1997;after Spirakis, 1991).…”

Organic matter production response to CO 2 increase in open subarctic plankton communities: Comparison of six microcosm experiments under iron-limited and -enriched bloom conditions

“…Phytoplankton growth in these regions is regulated mainly by availability of essential micronutrient iron (Fe) and hence the regions are known as a high nutrient, low chlorophyll (HNLC) region (Boyd et al, 2004;Tsuda et al, 2003Tsuda et al, , 2007. It is also known that sporadic eolian dust deposition events stimulate phytoplankton production in these regions (Iwamoto et al, 2011;Mélançon et al, 2014;Yuan and Zhang, 2006) and this potentially affects the oceanic food webs (Olgun et al, 2013). Thus the regions are characterized as the background conditions of suppressed phytoplankton biomass and activity by low Fe availability with sporadic phytoplankton growth by Fe additions from dust events.…”