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| The masssinkingofphytoplanktoncellsfollowingbloomsisanimportantsourceofcarbontotheocean's
interior,withsomespeciescontributingmoretothe flux ofparticulateorganiccarbon(POC)thanothers.
During the2008NorthAtlanticBloomExperimentintheIcelandBasin,weexaminedplankton
community compositionfromsurfacewatersandfromsedimenttrapsatdepthsdownto750m.
Samples collectedwithneutrallybuoyantLagrangiansedimenttrapscapturedamajor flux event.
Diatoms comprised Z99% ofcell flux intothesedimenttraps,withvegetativecellsandrestingsporesof
the genus Chaetoceros contributing 50–95% ofcell flux. Restingsporesofonespecies,identified as
Chaetoceros aff. diadema, weredominant,comprising35–92% ofcell flux. The flux ofrestingspores
rangedfrom2to63mgCm2 day1 and wassignificantly correlatedwithPOC flux (p¼0.003).Overthe
course of10days,the flux ofrestingsporesincreasedby26fold,suggestingthatthecellssankenmasse,
possibly inaggregates.Incontrast,vegetativecellsof C. aff. diadema sampled fromsurfacewatersduring
the periodprecedingthe flux eventgenerallycomprised o1% ofthediatomcommunityandnever
exceeded5.2%.Restingsporesof C. aff. diadema wererarelyobservedinsurfacewatersbuttheir
concentrations increasedwithdepth(to200m)belowthemixedlayer.Thisincreaseinrestingspore
abundance, coupledwithincreaseddissolvedsilicicacidconcentrationsatdepth,suggestthatthe
morphological changesassociatedwithsporeformationmayhaveoccurredinthemesopelagiczone,
while cellsweresinking.Thevaluesofvariable fluorescence (Fv/Fm) measuredonsedimenttrapmaterial
dominated byrestingsporeswereamongthehighestvaluesmeasuredinthestudyareaatanydepth.
This, incombinationwiththerapidgerminationofrestingsporesinship-boardincubations,suggests
that vegetativecellswerenotphysiologicallystressedduringsporeformation.Thedegradation-resistant,
heavilysilicified restingsporevalvesexplainthehighrelativecontributionof C. aff. diadema resting
spores tototalplanktoncarbonatdepth.Thesedataemphasizetheephemeralnatureoforganiccarbon
flux eventsintheopenoceanandhighlighthownon-dominantspeciesandtransientlifestagescan
contribute moretocarbon flux thantheirmoreabundantcounterparts. | |
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