High Nitrate

1
Lecture 14 High Nitrate Low Chlorophyll (HNLC)
Ocean Areas
Where are they? What are their characteristics? Wh
at are the main controls on biomass and
production?
2
High-Nitrate Low-Chlorophyll (HNLC) Regions
Subarctic Pacific HNLC
mg Chl/m2
North Atlantic Non-HNLC
NO3, Levitus et al, 1994
Day of Year
Frost, 1993 Parsons Lalli, 1988

• Characterized by
• NO3 gt 2 mM
• Chl lt 1 mg/m3 no blooms!
• Primary production lower than expected

3
Magnitude of the f-ratio related to food web
structure For Example In HNLC ocean
regions small plankton ( 1 mm) small
zooplankton microzooplankton (e.g.
protozoa) small, non-sinking fecal pellets large
recycling production and grazing tightly
coupled small new production small export
flux Iron stimulates larger diatoms grazed by
mesozooplankton time lags leads to larger new
production Larger export flux
See Landry et al, (1997) for more detail. Paper
is in Course Pack.
4
Model for Predicting New Production
(Eppley and Peterson (1979)

• Ventral North Pacific
• Eastern Mediterranean
• Southern California bight
• Eastern Tropical Pacific
• Costa Rica Dome
• Peru Upwelling

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Differences Between HNLC Regions
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Oceanic New Production f-ratio

• Primary Production (PP) depends on two N-sources
• 1) Regenerated by food web
• e.g. NH4 Other DON
• 2) "New" inputs to euphotic zone
• e.g. Deep Water (NO3), Atmos (N2) and
  Terrestrial
• New Production (NP) f PP
• f "f-ratio New/( New Regenerated)
• Typically

NP r NO3 m mol m-2 d-1
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Data Sources

• Observations span several years seasons

Subarctic Pacific 12 Cruises (Canadian
JGOFS) Varela Harrison, 1999 Diana
Varela Frank Whitney Philip Boyd Equatorial
Pacific 9 Cruises (US France JGOFS
Others) Aufdenkampe et al., 2001
--- NO3 2 mMol
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Pacific Map
SeaWifs Multiyear Mean
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Measuring Oceanic New Production
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f-ratio vs Primary Production
--- Eppley Peterson, 1979 l Subarctic
l Equatorial
f-ratio
Primary Production mmol C/m2 d

• Historical regression does not explain
  observations (plt0.01)

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Observed New Production f-ratios
Subarctic Pacific
Equatorial Pacific
N 30
N 40
NP range 0.5 7.7 0.4
6.3 mmol N/m2d ? 0.38 0.15
0.25 0.16
(0.17 0.79) (0.06 0.85)

• Order of magnitude range in NP
• f-ratio error 40-65 big range within region
• Different f-ratios between regions (plt0.01)

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What Controls New Production in HNLC
Regions? Variability in NP 10 x PP (e.g.
EqPac f-ratios 0.06 to 0.85) Hypotheses 1)
Trace metal (Fe) limits growth rates. 2) Grazing
controls biomass. 3) Temperature and Light (esp.
for high latitudes) 4) Ammonium inhibition 5)
Silicate limitation 6) Mixing losses