Export and mesopelagic particle flux during a North Atlantic spring diatom bloom

Spring diatom blooms are important for sequestering atmospheric CO2 below the permanent thermocline in the form of particulate organic carbon (POC). We measured downward POC flux during a sub-polar North Atlantic spring bloom at 100 m using thorium-234 (234Th) disequilibria, and below 100 m using neutrally buoyant drifting sediment traps. The cruise followed a Lagrangian float, and a pronounced diatom bloom occurred in a 600 km2 area around the float. Particle flux was low during the first three weeks of the bloom, between 10 and 30 mg POC m−2 d−1. Then, nearly 20 days after the bloom had started, export as diagnosed from 234Th rose to 360–620 mg POC m−2 d−1, co-incident with silicate depletion in the surface mixed layer. Sediment traps at 600 and 750 m depth collected 160 and 150 mg POC m−2 d−1, with a settled volume of particles of 1000–1500 mL m−2 d−1. This implies that 25–43% of the 100 m POC export sank below 750 m. The sinking particles were ungrazed diatom aggregates that contained transparent exopolymer particles (TEP). We conclude that diatom blooms can lead to substantial particle export that is transferred efficiently through the mesopelagic. We also present an improved method of calibrating the Alcian Blue solution against Gum Xanthan for TEP measurements.

[1]  T. Trull,et al.  Sinking particle properties from polyacrylamide gels during the KErguelen Ocean and Plateau compared Study (KEOPS): Zooplankton control of carbon export in an area of persistent natural iron inputs in the Southern Ocean , 2008 .

[2]  O. Schofield,et al.  Effects of phytoplankton physiology on export flux , 2008 .

[3]  J. Newton,et al.  Export flux of particulate organic carbon from the central equatorial Pacific determined using a combined drifting trap-234Th approach , 1996 .

[4]  I. Salter,et al.  Particle export from the euphotic zone: Estimates using a novel drifting sediment trap, 234Th and new production , 2008 .

[5]  David Archer,et al.  Association of sinking organic matter with various types of mineral ballast in the deep sea: Implications for the rain ratio , 2002 .

[6]  A. Alldredge,et al.  Preface: Aggregation in marine system , 1995 .

[7]  L. Coppola,et al.  An assessment of particulate organic carbon to thorium-234 ratios in the ocean and their impact on the application of 234Th as a POC flux proxy , 2006 .

[8]  J. T. Turner.  Zooplankton fecal pellets, marine snow and sinking phytoplankton blooms , 2002 .

[9]  R. Feely,et al.  Acantharian Fluxes and Strontium to Chlorinity Ratios in the North Pacific Ocean , 1987, Science.

[10]  J. Sarmiento,et al.  Decadal variability in North Atlantic phytoplankton blooms , 2009 .

[11]  H. Dam,et al.  Coagulation efficiency, organic-matter glues and the dynamics of particles during a phytoplankton bloom in a mesocosm study , 1995 .

[12]  K. Buesseler,et al.  Carbon and nitrogen export during the JGOFS North Atlantic Bloom experiment estimated from 234Th: 238U disequilibria , 1992 .

[13]  David M. Karl,et al.  VERTEX: carbon cycling in the northeast Pacific , 1987 .

[14]  W. Moore,et al.  Determination of natural radioactive tracers , 2007 .

[15]  A. Alldredge,et al.  Rapid formation and sedimentation of large aggregates is predictable from coagulation rates (half-lives) of transparent exopolymer particles (TEP) , 1995 .

[16]  André W. Visser,et al.  Intensive aggregate formation with low vertical flux during an upwelling‐induced diatom bloom , 1998 .

[17]  Reiner Schlitzer,et al.  Depth‐dependent elemental compositions of particulate organic matter (POM) in the ocean , 2003 .

[18]  P. Froelich,et al.  A simple method for the rapid determination of biogenic opal in pelagic marine sediments , 1989 .

[19]  Bruce E. Logan,et al.  The role of particulate carbohydrate exudates in the flocculation of diatom blooms , 1994 .

[20]  L. Balistrieri,et al.  Organic carbon to 234Th ratios of marine organic matter , 2006 .

[21]  P. Boyd,et al.  Shedding light on processes that control particle export and flux attenuation in the twilight zone of the open ocean , 2009 .

[22]  U. Passow.  Transparent exopolymer particles (TEP) in aquatic environments , 2002 .

[23]  K. Buesseler.  The decoupling of production and particulate export in the surface ocean , 1998 .

[24]  C. Benitez‐Nelson,et al.  Insights into particle formation and remineralization using the short‐lived radionuclide, Thoruim‐234 , 2010 .

[25]  B. Bodungen,et al.  Abundance, encystment and sedimentation of acantharia during autumn 1990 in the East Greenland Sea , 1993 .

[26]  D. Caron,et al.  Planktonic sarcodines (Acantharia, Radiolaria, Foraminifera) in surface waters near Bermuda: abundance, biomass and vertical flux , 1995 .

[27]  S. Henson,et al.  Timing of nutrient depletion, diatom dominance and a lower-boundary estimate of export production for Irminger Basin, North Atlantic , 2006 .

[28]  O. Ragueneau,et al.  Si and C interactions in the world ocean: Importance of ecological processes and implications for the role of diatoms in the biological pump , 2006 .

[29]  David A. Siegel,et al.  A bottom-up view of the biological pump : modeling source funnels above ocean sediment traps , 2008 .

[30]  C. Brown,et al.  Distribution of calcifying and silicifying phytoplankton in relation to environmental and biogeochemical parameters during the late stages of the 2005 North East Atlantic Spring Bloom , 2009 .

[31]  Manfred Ehrhardt,et al.  Methods of seawater analysis , 1999 .

[32]  P. Boyd,et al.  Size-fractionated primary production and nitrogen uptake during a North Atlantic phytoplankton bloom : implications for carbon export estimates , 2001 .

[33]  P. Boyd,et al.  Phytoplankton production and biomass estimates in the northeast Atlantic Ocean, May–June 1990 , 1995 .

[34]  Richard A. Krishfield,et al.  Factors controlling the flux of organic carbon to the bathypelagic zone of the ocean , 2002 .

[35]  S. Thomalla,et al.  Particulate organic carbon export from the North and South Atlantic gyres: The 234Th/238U disequilibrium approach , 2006 .

[36]  Alice L. Alldredge,et al.  A dye-binding assay for the spectrophotometric measurement of transparent exopolymer particles (TEP) , 1995 .

[37]  S. Honjo,et al.  Annual biogenic particle fluxes to the interior of the North Atlantic Ocean; studied at 34°N 21°W and 48°N 21°W , 1993 .

[38]  Alice L. Alldredge,et al.  Aggregation of a diatom bloom in a mesocosm: The role of transparent exopolymer particles (TEP) , 1995 .

[39]  H. Dam,et al.  Sedimentation of phytoplankton during a diatom bloom : Rates and mechanisms , 1996 .

[40]  R. B. Pearce,et al.  Estimating carbon, silica and diatom export from a naturally fertilised phytoplankton bloom in the Southern Ocean using PELAGRA: a novel drifting sediment trap , 2007 .

[41]  M. Brzezinski,et al.  The origin of transparent exopolymer particles (TEP) and their role in the sedimentation of particulate matter , 2001 .

[42]  M. Charette,et al.  234Th sorption and export models in the water column: A review , 2006 .

[43]  P. Wassmann,et al.  Does Phaeocystis spp. contribute significantly to vertical export of organic carbon? , 2007 .

[44]  D. Johns,et al.  Sedimentation of acantharian cysts in the Iceland Basin: Strontium as a ballast for deep ocean particle flux, and implications for acantharian reproductive strategies , 2010 .

[45]  A. Engel.  The role of transparent exopolymer particles (TEP) in the increase in apparent particle stickiness (α) during the decline of a diatom bloom , 2000 .

[46]  Bruce E. Logan,et al.  The abundance and significance of a class of large, transparent organic particles in the ocean , 1993 .

[47]  G. Wasserburg,et al.  238 U, 234 U and 232 Th in seawater , 1986 .

[48]  R. Lampitt.  Evidence for the seasonal deposition of detritus to the deep-sea floor and its subsequent resuspension , 1985 .

[49]  S. Wakeham,et al.  The role of biominerals in the sinking flux and preservation of amino acids in the Southern Ocean along 170°W , 2003 .

[50]  J. R. Beers,et al.  THE PRESERVATION OF ACANTHARIANS IN FIXED PLANKTON SAMPLES1 , 1970 .

[51]  H. Ducklow,et al.  Plankton succession and carbon cycling at 47°N 20°W during the JGOFS North Atlantic Bloom Experiment , 1993 .

[52]  S. Fowler,et al.  An assessment of the use of sediment traps for estimating upper ocean particle fluxes , 2007 .

[53]  S. Wakeham,et al.  A new, mechanistic model for organic carbon fluxes in the ocean based on the quantitative association of POC with ballast minerals , 2001 .

[54]  D. M. Nelson,et al.  sedimentary fluxes on the Ross Sea continental shelf , 1996 .

[55]  M. Sieracki,et al.  Plankton community response to sequential silicate and nitrate depletion during the 1989 North Atlantic spring bloom , 1993 .

[56]  P. Tréguer,et al.  Si/C decoupling in the world ocean: is the Southern Ocean different? , 2002 .