[Eoas-seminar] REMINDER TODAY EOAS Colloquium speaker this Friday 3:30 in CAR 101

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Fri Mar 8 13:01:03 EST 2019

Please join us Today, Mar 9 for our EOAS speaker at 3:30 in CAR 101:

Jeffrey W. Krause
Dauphin Island Sea Lab, Dauphin Island, AL 36528
Department of Marine Sciences, University of South Alabama, Mobile, AL 36688

The North Atlantic spring phytoplankton bloom: a new spin on an old story

Diatoms’ contribution to primary productivity and organic matter export are significant in the high-latitude North Atlantic marine ecosystems.  Unlike other abundant phytoplankton groups, diatoms have an obligate silicon requirement; therefore, silicon availability has the potential to regulate major high-latitude events like the spring bloom.  Waters in the high-latitude sector of the Atlantic (e.g. coastal Greenland, Faroe Islands, Barents Sea, Svalbard) have lower pre-bloom silicic acid concentrations than nitrate.  Given diatoms require Si and N in near unity, the deplete Si relative to N sets a potential control on diatom productivity in this system, such that Si could limit diatom biomass yield in a bloom.  Recent publications have reported 20-year declines in silicic acid concentrations between ~60 – 75 °N latitude in the Atlantic.   Despite the clear changes in Si availability, there are no reported data for the magnitude of diatom Si uptake and whether ambient silicic acid limits silicon uptake by diatoms or their growth.  Here we report data from the West Greenlandic Nuup Kangerlua fjord during the development of the spring bloom over two months at a time-series site.  This site is influenced by the subpolar mode water, Greenland coastal water and early-season glacial melt water.  The ambient silicic acid persistently limited the rate of Si uptake by diatoms and eventually limited their growth at the bloom peak.  Temporally concurrent with growth limitation by silicic acid availability, diatom settling velocity increased to pre-bloom levels, reflective of physiological stress, and an increase in the number of dead cells among the total diatom assemblage.  These data suggests that silicon availability plays an important role in terminating the spring bloom in this region when diatoms are favored to dominate the bloom sequence.
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