Ocean acidification - Global warming’s “evil twin” h"p://rsd.gsfc.nasa.gov/rsd/ bluemarble/bluemarble2000.html h"p://www.cc.gatech.edu/~cnieto6/ presenta=on/images/CoralReef1.jpg (quote attributed to R. Feely, NOAA) Ocean acidification - Global warming’s “evil twin” Recap from Tuesday: (quote attributed to R. Feely, NOAA) • Chemical consequences of adding CO2 to the ocean – Depleted CO3= – Define Ω as carbonate saturation – Ω declines as CO3= declines – pH decreases, ocean becoming more acidic – 20 th century decline by about 0.1 • Biological consequences of ocean chemistry changes – Calcification declines in certain plankton – Biosphere 2 studies Ocean acidification - Global warming’s “evil twin” Recap from Tuesday: (quote attributed to R. Feely, NOAA) Hoegh-Guldberg et al. 2007 CO2 increasing in ocean and atmosphere IGBP Global Change Newsletter 73, 2008
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Ocean acidification - Global warming’s “evil twin”
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• N2 is the most common gas in the atmosphere, yet nitrogenis a limiting nutrient for productivity on land and in ocean…
• There are different forms of N; only those where the N-Nbond is broken can be used as nutrients (mainly NO3,NH4).– This is known as fixed nitrogen– N2, N2O are inert forms of nitrogen
• N2 bond is hard to break!• Fixation: formation of nutrient nitrogen from inert• Denitrification, annamox: formation of inert N from fixed N
N fixation and denitrification• Fixation: converts inert N to fixed N (i.e. creates a
source of nutrient N)– In ocean, much N fixation is accomplished by the
cyanobacteria Trichodesmium– Key enzyme is nitrogenase - requires Fe and Mo to be active– Mostly available in microzones around decaying organic matter
• Many bacteria important for primary production are alsoN fixers
Trichodesmium
The cyanobacterium Trichodesmium is an importantsource of marine N fixation. It forms blooms visiblefrom space (left and below) and is also apparent fromdirect observation in the ocean (above right ).
Loss of fixed N• Denitrification: converts NO3 to N2
occurs in O2 minima zones atdepth and in seds where O2depleted by decay
• Anammox (anaerobic ammoniumoxidation): Converts NH4 to N2 -also removes nutrient N– Not recognized until mid-90’s– Potential for large amount in ocean
anoxic regions
Is N cycle in balance?Does fixation balance loss?
Gruber and Sarmiento, Global Biogeochem. Cycles 1997
Marine N cycleWhat controls N in surface ocean?
“it may soon be time to start rewriting the textbooks”--Capone and Knapp, Nature 445, 2007
DECAY
SINKINGPARTICLES
PRIMARYPROD.
Duce et al. 2008
• Large increases sincepreindustrial
• Expect to accelerateregionally
• Large changes in oceanproductivity?
Duce et al. 2008Ratio of fluxes in 2030 compared to 2000
Reactive N deposition Is the picture complete? NO…
• Marine N budgets are not known to within20-50%
• Are fixation and loss processes in balance?Are they related?– May occur in same places
• What are basic controls on fixation anddenitrification?
Ocean phosphate• Most marine productivity relies on recycled PO4