Promong phytoplankton blooms in the open ocean · Mesoscale eddies and Rossby waves ... Addion of...
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Promo%ng phytoplankton blooms in the open ocean: Results from nutrient addi0on experiments Dr. Claire Mahaffey Dr. Karin Bjorkman and Prof. David Karl
Transcript of Promong phytoplankton blooms in the open ocean · Mesoscale eddies and Rossby waves ... Addion of...
Promo%ngphytoplanktonbloomsintheopenocean:
Resultsfromnutrientaddi0onexperiments
Dr.ClaireMahaffeyDr.KarinBjorkmanandProf.DavidKarl
Introduc7on• Fixa7onofCO2byphytoplankton(PRIMARYPRODUCTION)dependentupontwofactors:lightandnutrients
SEASURFACECOLOURASAPROXYFORCHLOROPHYLLACONCENTRATIONS
60%ofsurfaceocean:carbonfixa7onlimitedby
nutrientsupply
YET:subtropicalgyresaccountforupto50%of
totalorganiccarbonexportofglobalocean
(Sub)tropicaloceanenvironment
Nitrate
0.2‐2µm
2‐10µm
>10µm
0.2‐2µm
2‐10µm
>10µm
CarbonfixaGon
Phytoplanktonbiomass(Chlorophylla)
• Permanentlystra7fied
• Nutrientimpoverishedsurfaceocean
• Picoplankton(<2μm)responsiblefor>90%ofchlorophyllaand>70%ofcarbonfixa7on
Communitysizestructureandexport
FromKarl,1999
>10μmcellsize <2μmcellsize
HIGHEXPORTPRODUCTION
LOWEXPORTPRODUCTION
Bloomsin“oceandeserts”
• Summer7meincreaseinwatercolumnstability• MesoscaleeddiesandRossbywaves(Churchetal.,2008,Wilsonetal.,2003)• Winter7mesupplyofphosphorus(Doreetal.,2008)
WHATDRIVESTHESEBLOOMS?
• Episodicbloomsofdiatomsandnitrogenfixingcyanobacteria(Churchetal.,2008,Doreetal.,2008,
Whydoweneedtounderstandbloomsinoceandeserts?
• Oceandesertsrepresent60%oftotaloceanarea(EppleyandPeterson,1979)• Responsiblefor~50%ofglobaloceancarbonexport(Emersonetal.,1997)
• Periodicbloomsdriveupto50%ofannualexport(Karletal.,1997,Doreetal.,2008)
HOWEVER:• Fewdirectobserva7onsofbloomsduetotheirstochas7cnature• Uncertaintysurrounding:
‐ Speciescomposi7onandsuccession‐ Carbonfixa7onandfate‐ Speedofdevelopment‐ Reproducibility
Oceanfer7lisa7on• Addi7onofnutrientcocktailordeep‐seawatertosurfaceoceantos7mulatecarbonfixa7onandsequestra7on
Nutrientaddi7onexperiments
• Dissolvednutrients• Biomassparameters(chlorophylla)• Communitysizestructure,0.2,2and10μm• Speciescomposi7on(pigmentsandflowcytometry)• Ratemeasurements(carbonfixaGon)
Stn. ALOHA (22°45’ N, 158°W)
5%vol:vol
QuesGon:Inanutrientlimitedsystem,canwepredictablys7mulateaphytoplanktonbloombyaddingnutrient‐richdeepseawater:
‐increaseinbiomass(chlorophylla)
‐increaserateofcarbonfixa7on
‐changecommunitysizestructurefromsmall(0.2‐2μm)tolarge(>10μm)cells
‐increasethepoten7alforexportoforganiccarbon?
Bloomresponse
• 70‐100%nutrientassimila7on
• 20±4foldincreaseinchlorophyll• 23±7foldincreaseincarbonfixa7on
0
20
40
60
80
100
120
0 20 40 60 80 100 120 140 160
Percen
t(%)a
ssim
ilaGon
Time(hrs)
nitrate
phosphate
Series4
Series5
SizestructureCarbonfixaGon
0.2–2μm
2–10μm>10μm
Chlorophylla
INITIAL INITIALFINAL FINAL
• 3cruises
Bloomresponse
• 70‐100%nutrientassimila7on
• 20±4foldincreaseinchlorophyll• 23±7foldincreaseincarbonfixa7on0
20
40
60
80
100
120
140
160
HOT161 HOT183 HOT191
Prim
aryprod
ucGon
(ugCL‐1 d
‐1)
Cruise
SizestructureCarbonfixaGon
0.2–2μm
2–10μm>10μm
Chlorophylla
INITIAL INITIALFINAL FINAL
• 3cruises
Bloomresponse
• 70‐100%nutrientassimila7on
• 20±4foldincreaseinchlorophyll• 23±7foldincreaseincarbonfixa7on
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
HOT161 HOT183 HOT191
Chloroph
yll(ugL‐1)
Cruise
SizestructureCarbonfixaGon
0.2–2μm
2–10μm>10μm
Chlorophylla
INITIAL INITIALFINAL FINAL
• 3cruises
Non‐bloomresponse• 7cruises
• <50%ofnutrientsassimilated
• 4±1foldincreaseinchlorophyll
• 5±1foldincreaseincarbonfixa7on
SizestructureCarbonfixaGon
0.2–2μm
2–10μm>10μm
Chlorophylla
INITIAL INITIAL
0
20
40
60
80
100
120
0 50 100 150 200
Percen
t(%)a
ssim
ilaGon
Time(hrs)
nitrate
phosphate
Series4
Series5
Series7
Series8
FINAL FINAL
Non‐bloomresponse• 7cruises
• <50%ofnutrientsassimilated
• 4±1foldincreaseinchlorophyll
• 5±1foldincreaseincarbonfixa7on
SizestructureCarbonfixaGon
0.2–2μm
2–10μm>10μm
Chlorophylla
INITIAL INITIAL
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
HOT163 HOT164 HOT165 HOT167 HOT174 HOT175 HOT186
Chloroph
ylla(u
gL‐1)
Cruise
FINAL FINAL
Non‐bloomresponse• 7cruises
• <50%ofnutrientsassimilated
• 4±1foldincreaseinchlorophyll
• 5±1foldincreaseincarbonfixa7on
SizestructureCarbonfixaGon
0.2–2μm
2–10μm>10μm
Chlorophylla
INITIAL INITIAL
0
20
40
60
80
100
120
140
160
Prim
aryprod
ucGon
(ugCL‐1 d
‐1)
Cruise
FINAL FINAL
Experimentsummary
Parameter Bloomresponse Non‐bloomresponse
Nutrients 70‐100%assimila7on <50%assimilated
Chlorophyll 20±4foldincrease 4±1foldincrease
Carbonfixa7on 23±7foldincrease 5±1foldincrease
Sizecomposi7on Dominatedby>10um Dominatedby0.2–2um
Months MaytoJuly SeptembertoJanuary
Bloomresponse,Summer(MaytoJuly)–rapidandcompleteassimila7onofnutrientsandbloomforma7on
Non‐bloomresponse,Winter(SeptembertoJanuary)–slowandincompleteassimila7onofnutrientsandnobloomformed
Poten7alcarbonfixed• Nitrateadded =2μM• Maximumpoten7alcarbonfixed =174±19μgCL‐1
Accumulatedcarbonfixedduringsummerandwinterincuba7ons
*Expressedaspercent(%)ofmaximumpoten7alcarbonfixed(174μgCL‐1)
Comparingsummerandwintercarbonpoten7al:
3xcarbonfixedforwholecommunity 10xmorecarbonfixedbylargecells(>10μm)
Season Wholecommunity* >10umcells*
Summer 115±18 59±15
Winter 31±4 5±1
Whatarethemechanismsdrivingthisvaria7onincommunityresponse?
• Ini7alnutrientcondi7ons• Communitystructureandcomposi7on• Sizecomposi7on
NOSIGNIFICANTDIFFERENCEBETWEENWINTERAND
SUMMERCRUISES
0
20
40
60
80
100
120
140
0 2 4 6 8 10 12
Mized
LayerDep
th(m
)
Months
• Watercolumnstabilityandstructure
SeasonalalteraGonofwatercolumnstabilitymaycauseFINE‐SCALEchangesin
nutrientfieldsandcommunitystructure
Poten7almechanisms
‐0.100
‐0.080
‐0.060
‐0.040
‐0.020
0.000
0.020
0.040
0.060
0.080
‐10
‐8
‐6
‐4
‐2
0
2
4
6
8
0 1 2 3 4 5 6 7 8 9 10 11 12 13
• Watercolumnsweepingbyexportevents
• Summer‐7mebloomsdrivelargeexportevent
• “Sweep”thewatercolumnofseedpopula7onscapableofrapidassimila7onofnutrients
• LightfluxEm‐2d‐1‐Summer: 47.3±2.3‐Winter: 31.2±3.1
SIGNIFICANTDIFFERENCEINLIGHTFLUX
Par7clefluxanomalymeasuredat150m
Conclusions
• Addi7onofnutrient‐richdeepseawatertosurfacephytoplanktoncommunitygeneratedbloomsduringsummeronly
• Mechanismsunderlyingvaria7oninphytoplanktoncommunityresponsebetweensummerandwinterremainsuncertain
• IMPLICATIONS:– finescaleupwelling,e.g.mesoscaleeddies
– Ar7ficialfer7lisa7onoftheopenocean
Thankyou
Carbonpumps• Solubilitypump:‐seawatertemperature
‐thermohalinecircula7on
• Biologicalpump
