Ecology  of  Marine  Phytoplankton  •  Tuesday  5  Nov  2013  

–  Introduc@on  to  marine  phytoplankton  –  Type  II  func@onal  response:  

•  Encounter-­‐handling  processes  •  Wednesday  6  Nov  2013  

–  Seasonal  blooms  –  Cell  size  and  equilibrium  resource  compe@@on  

•  Thursday  7  Nov  2013  –  Equilibrium:  Top  down  control  and  co-­‐existence  –  Resource  supply  ra@os  and  co-­‐existence  

•  Nitrogen  fixers  

LECTURE  NOTES  WILL  BE  POSTED  AT  hVp://ocean.mit.edu/~mick/ENS-­‐S06-­‐2013  

Introduc@on  to  Marine  Phytoplankton  

•  What  are  phytoplankton?  •  Where  are  they  in  the  ocean?  •  Why  do  we  care  about  them?  •  What  is  the  role  of  diversity?  

Chapter  5  of  R.G.  Williams  and  M.J.  Follows,  Ocean  Dynamics  and  the  Carbon  Cycle,  CUP  (2011)  

Marine  ecosystem:    Photosynthesis  and  respira@on  

Phytoplankton  are  phototrophs:  Primary  producers  of  organic  carbon  

Diatom:  Coscinidiscus  radiatus  

carbo- hydrate

protein

pigment

CO2

N NO3

-

light O2

iron

•  Several  elements  to  build  func@onal  molecules  •  Average  elemental  ra@o  C:N:P:O2      ≈    106:16:1:-­‐170  

•  “Redfield  ra@o”  

P PO43-

DNA/RNA

Where  do  they  live?  

Data:  AMT  15                          Anna  Hickman,  NOC  Southampton  

Surface  ocean  chlorophyll  from  space  

NASA    MODIS  Global  marine  primary  produc@on  ~  50  Pg  C  year-­‐1  

Why  do  they  live  there?  

Carbon  is  plen@ful    Supply  of  N,  P,  Fe,  …  etc  is  limi@ng  for  reproduc@on  

Marine  nitrogen  cycle  

The  ocean’s  physical  structure  and  circula@on  

The  ocean’s  physical  structure  and  circula@on  

The  ocean’s  physical  structure  and  circula@on  

Equator                                                                                          Pole  

Why  do  they  live  there?  

Figure:  Anna  Hickman  in    Williams  and  Follows  (2011)  

Dashed  line  indicates  light  at  1%  of  surface  incident  flux  

Surface  ocean  chlorophyll  from  space  

NASA    MODIS  

Why  do  we  care  about  phytoplankton?  

•  Marine  food  web  and  fisheries  •  The  ocean  store  of  carbon  dioxide  

Copepods  (zooplankton)  

Sir  Alister  Hardy  

Zooplankton  hun@ng  phytoplankton  

hVp://www.youtube.com/watch?v=Y3QVBFFTNaA&feature=related  

Hardy’s  herring  food  web  

Fisheries  

Fisheries  

Major  fisheries  

chlorophyll  

The  ocean  carbon  cycle    

hVp://jameswight.files.wordpress.com/2012/09/global-­‐carbon-­‐cycle-­‐cropped.jpg  

600    

38,000    

2000    

5,000     74,000,000    

Petagrams  C  

Sinking  organic  par@cles  

Marine  snow  (Richard  LampiV)  

Zooplankton  fecal  pellets  (Debbie  Steinberg)  

•  Downward  flux  aVenuated  by  zooplankton  and  heterotrophic  microbes  

•  Globally,  ~20%  of  primary  produc@on  sinks  out  of  sunlit  Eupho@c  layer  •  10  Pg  C  year-­‐1  

•  <1%  reaches  sea  floor  •  Small  frac@on  buried    

•  Net  oxygen  produc@on      

Changes  in  produc@vity  of  oceans  implicated  in  past  changes  of  atmospheric  CO2  

338 PART IV SYNTHESIS

0100200300400−10

−5

0

∆T (

°C)

01002003004000

1

2

age (thousand years)

dust

con

c (p

pmv)

0100200300400150

200

250

300

XC

O2

(ppm

v)(a) atmospheric carbon dioxide

(b) temperature change

(c) dust concentration

Figure 13.8 Changes associated withglacial–interglacial variations as recordedin the Vostok ice core from Antarcticaover the last 400 000 years. Each year,snow accumulates and is eventuallypacked down into ice; the bubbles of airtrapped in the ice provide informationabout long-term changes in the planet: (a)atmospheric mixing ratio XCO2 (ppmv)measured in bubbles of gas trapped in theice, which can be viewed as representinga global change, since carbon dioxide iswell mixed in the atmosphere; (b) localtemperature change (◦C) as indicated bythe isotopic composition of the water inthe ice; and (c) concentration ofwindborne dust deposited in the ice;higher dust concentrations might reflectstronger continental sources or changesin wind strength and circulation, which islikely to be similar for the delivery ofdustborne iron to the remote SouthernOcean. Data from Petit et al. (1999).

up less of the emitted carbon. After the oceanand atmosphere have equilibrated, but prior tosediment interactions, there is an exponentialrelationship between atmospheric CO2 and theintegrated amount of carbon being emitted.This simple balance suggests that if the knownfossil-fuel reservoirs of 4000 Pg C are consumed(without any compensating carbon capture), thenatmospheric XCO2 increases to 1000 ppmv on a mil-lennial timescale (after a larger transient peak).Over the subsequent tens of thousands of years,atmospheric carbon dioxide is eventually reducedby interaction of the ocean–atmosphere systemwith the carbonate sediments.

Next we consider some possible drivers of pastglacial–interglacial cycles using the same simpli-fied model framework.

13.3 Glacial–interglacial changesin atmospheric CO2

There have been striking glacial–interglacial vari-ations in atmospheric carbon dioxide over nearly

the last million years, as revealed by analysis of icecores from Greenland and Antarctica (illustratedin Fig. 13.8a). Prior to the industrial era, atmo-spheric carbon dioxide consistently reached amaximum of 280 to 300 ppmv during interglacialperiods and declined to a minimum of about180 ppmv during glacial periods. These changesin atmospheric carbon dioxide are positively cor-related with variations in Antarctic temperatures(Fig. 13.8b).

For the transition at 240 000 years ago, theAntarctic temperature changes lead the atmo-spheric carbon dioxide changes by 800 ± 200years and are followed by deglaciation in thenorthern hemisphere over the subsequent ∼4200years (Caillon et al., 2003). For the changes at130 000 years, the Antarctic temperature andatmospheric carbon dioxide changes are closelycoupled, both increasing over 8000 years, againthe changes preceding melting of the northernhemisphere ice sheets and any reorganisation ofnutrients in the North Atlantic (Broecker andHenderson, 1998). Hence, glacial–interglacialchanges might be initiated by physical changes

Thousands  of  years  ago  

Diverse  types  of  phytoplankton  

Pico-­‐cyanobacteria  

•  Key  traits:  – Smallest  photo-­‐autotrophs  

•  Smallest  is  Prochlorococcus  <1μm  radius  

– Small  genome  •   ~1.7-­‐9  Mbp    •  (c.f.    12-­‐57  Mbp  eukaryo@c  phyto)  

–  Dominate  popula@on  in  low-­‐nutrient  subtropical  waters  

Prochlorococcus:  image  C.  Ting  

0.1  micron  

Prochlorococcus  dominate  low  nutrient  subtropical  gyres  

AMT  15  

Nitrate

Prochlorococcus

Synechococcus

Johnson  et  al,  Science  (2006)  Phytoplankton:  log(cells  ml-­‐1)  Nitrate  (micromoles  kg-­‐1)  

Distribu@on  of  Prochlorococcus  from  a  sta@s@cal  model  

Flohman  et  al,  PNAS  (2013)  

Diatoms  

•  Key  traits:  – Few  microns  –  100’s  microns  

– Silicate  frustule    – Fast  growing  “opportunists”  – Blooms  owen  lead  to  high  sinking  flux  

Chaetoceros  

Coscinidiscus  radiatus  

Dinoflagellates  

Cera5um  

Dinophysis  acuminata  •  Key  traits:  

– 10  to  100  micron  – Generally  no  mineral  component  – Grow  rela@vely  slowly    –  (Most?)  mixotrophic  

Dinoflagellates  

Coccolithophores  

•  Key  traits:  – Calcifica@on  

•  Ca2+  +  CO32-­‐  ó  CaCO3  

– ~5-­‐50  microns  – Ubiquitous  

•  Low  abundance  in  subtropics  •  Blooms  in  subpolar  oceans  

Coccolithophores  Ca2+  +  CO3

2-­‐  ó  CaCO3  

Calcifica@on:    Alison  Taylor  UNC  

Why  form  coccoliths?  

Coccolithophores  from  space  

Surface  ocean  Par@culate  Inorganic  Carbon  (PIC,  mineral  CaCO3)  from  space    

(Balch  et  al,  JGR,  2005)  Jan-­‐Mar   Apr-­‐Jun  

Jul-­‐Sep   Oct-­‐Dec  

•  Key  traits:  –  Size:  micron-­‐scale  unicellulars  to  mm  scale  colonial  Trichodesmium  

–  Fix  nitrogen:  break  N2  bond  using  enzyme  nitrogenase  

– Nitrogenase  demands    •  Control  of  intra-­‐cellular  O2  

–  Slow  maximum  growth  rate  •  High  iron  requirement  

Trichodesmium  (image:  A.  Hynes)  

1  μm  Croccosphaera  watsonii  (image:  WHOI)  

Nitrogen  fixers  (diazotrophs)  

Iron  supply  from  dust  

Rubin,  Berman-­‐Frank  &  Shaked,  Nature  Geoscience  (2011)  

Nitrogen  fixing  phytoplankton  Use  dissolved  N2  gas  as  N  source  •  Benefit:  Free  from  nitrogen  limita@on  •  Cost:  Slow  growth  rate  

Biogeography  of  Trichodesmium:    LaRoche  and  Breitbarth  (2005)  

Biogeography  on  Atlan@c  Meridional  Transect  

-­‐  diatoms  -­‐  coccolithophores      

–  pico-­‐cyanobacteria          -­‐  Prochlorococcus  

                           -­‐  Synechococcus    

Aiken  et  al  (2000)  

Size  structure  

Size  on  AMT:  Ward  et  al.  J.  Plankton  Res.  (2013)  

picophytoplankton  (<2  μm)  

microphytoplankton  (>20  μm)  

nanophytoplankton  (2-­‐20  μm)  

total  chl  a  (mg  chl  m-­‐3)   total  chl  a  (mg  chl  m-­‐3)  

Herbland  &  Lebou@er  (1981),  PlaV  et  al  (1983),    Chisholm  (1992),  …  

Distribu@on  of  size  classes  es@mated  

from    remote  sensing  

Uitz  et  al,  J.  Geophys.  Res.  (2006)  

Subsequent  lectures:  •  Simple  parameteriza@ons  of  growth  and  loss  processes  

•  What  causes  phytoplankton  blooms?  – Which  kind  of  phytoplankton  dominate  blooms  and  why?  

•  Why  are  Prochlorococcus  so  prevalent  in  the  subtropical  oceans?  

•  How  do  small  and  large  phytoplankton  co-­‐exist?  •  How  do  slow  growing  nitrogen  fixers  compete  and  co-­‐exist  in  the  subtropical  oceans?