Lectu re 14
High Nit rate
Low Chlo rophyll (HNLC)
Ocean A reas
Where are they?
What are their characteristics?
What are the main controls on biomass and production?
High Nitrate Low-C
rpyll H
lo
h
(N
C
L
s
n
io
eg
)R
mg Chl/m2
Subarctic Pacific
HNLC
NO3, Levitus et al, 1994
North Atlantic
Non-HNLC
Day of Year
Frost, 1993; Parsons & Lalli, 1988
Characteized by:
" NO > 2 µM
3
3
" Chl < 1 mg/m & no blooms!
" Primary production lower than expected
Magnitude of the f-ratio related to food web structure:
For Example: In HNLC ocean regions
small plankton (~ 1 µm)
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.
Model for Predicting New Production
(Eppley and Peterson (1979)
1.
2.
3.
4.
5.
6.
Ventral North Pacific
Eastern Mediterranean
Southern California bight
Eastern Tropical Pacific
Costa Rica Dome
Peru Upwelling
Differences Between HNLC Regions
Seasonality
Temperature (oC)
Light
Mixing
Upwelling Iron
Atmospheric Iron
Ammonium (mM)
Silicate
Subarctic
Pacific
High
Equatorial
Pacific
Low
Southern
Ocean
High
10
Moderate
Low
Low
High
25
High
High
High
Moderate
2
Low
Moderate
Moderate
Low
0.5
Moderate
0.1
High
1
High/Low
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 ≈ ρ NO3 [ m mol m-2 d-1 ]
ρ NO3−
f ≈
ρ NO3− + ρ NH 4+
Data Sources
"
Observations span several years & seasons
Subarctic Pacific:
12 Cruises (Canadian JGOFS)
Varela & Harrison, 1999
Diana Varela
Frank Whitney
Philip Boyd
Equatorial Pacific:
--- [NO3] = 2 µMol
9 Cruises (US & France JGOFS
& Others)
Aufdenkampe et al., 2001
Zonal Flux Cruise
April 1996
Hawaii
New
Caledonia
Tahiti
SeaWifs
Multiyear Mean
Measuring Oceanic New Production
Collect
15NO
3
Addition
UW
incubate
on-deck
in-situ
~ 6 hr
NO3 → PO15N
15
filter
Mass spectrometer
f-ratio vs Primary Production
f-ratio
--- Eppley & Peterson, 1979 l Subarctic l Equatorial
Primary Production [mmol C/m2 d]
Historical regression does not explain observations (p<0.01)
"
Observed New Production & f-ratios
Subarctic
Pacific
NP range
[mmol N/m2d]
ƒ
"
"
"
Equatorial
Pacific
N = 30
N = 40
0.5 – 7.7
0.4 – 6.3
0.38 ± 0.15
(0.17 – 0.79)
0.25 ± 0.16
(0.06 – 0.85)
Order of magnitude range in NP
f-ratio error 40-65% & big range within region
Different f-ratios between regions (p<0.01)
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