Phytoplankton and Upper Ocean
Biogeochemical Cycles Along Line P
Angelica Peña
Institute of Ocean Sciences, Fisheries & Oceans Canada.
Contribution: Diana Varela, Department of Biology & School of Earth and
Ocean Sciences, University of Victoria
Biogeochemical Cycles
Atmosphere
Biogeochemical
Advection / Mixing
Nutrients
Sinking Particles
Biological
Pump
Remineralization
C N P Si O
Sampling Stations – Line P
50° N, 145°W
4250m
48° 39’ N, 126° 40’ W
1300m
48° 34.5 N, 125.5°W
120m
Line-P Sampling
• Weathership era: 1956-1981
• SUPER (Subarctic Pacific Ecosystem Research)
program: 1984-88
• VERTEX (Vertical exchange) program
• WOCE (World Ocean Circulation Experiment) 1991-1997
• CJGOFS (Canadian Joint Global Ocean Flux Study)
1992-1997
• SERIES (Subarctic ecosystem response to iron
enrichment study) 2002
Sampling along Line P
Longitude (W)
-124
P4
-128
Chlorophyll
P12
-132
P16
-136
P20
-140
-144
P26
-148
1960
1970
1980
1990
2000
Longitude (W)
-124
P4
-128
P12
-132
P16
-136
-140
P20
-144
P26
-148
1960
1970
1980
Time
1990
2000
Nutrients
Observations from the weathership era
A High Nitrogen – Low Chlorophyll
(HNLC) region
– High nitrate concentration all year around
– Chlorophyll concentration are low all year
(<0.5 mg m-3) – no spring bloom
– Modest annual cycle in primary production
– Annual cycle in mesozooplankton abundance
– Surface oxygen supersaturation in
spring/summer
NO3 Minimum ~ ½ Winter Maximum
OSP: 1966–76 (0-20 m)
Frost, 1993, Prog.Ocgy.32.
[adapted from Parslow, 1981]
Recognized as a region of
High Nitrogen – Low Chlorophyll (HNLC)
Chlorophyll a at OSP, Weathership Era
• no spring bloom
• average 0.3-0.4 mg-Chl m-3
• all obs. < 2 mg-Chl m-3
Miller et al., 1991
L&O, 36(8)
(via Parslow, 1981)
All data - all depths
Annual Cycle:
NO3¯ → P P →
Mesozooplankton
(1988)
Oceanogr. Mar. Biol. Annu. Rev., 26, 317-359.
Primary productivity (0-50m)
OSP 1960-66, redrawn from:
McAllister, 1969.
J. Fish. Res. Board Can. 26.
Denman & Pena, 2002.
Deep-Sea Res. II, 49.
Mesozooplankton wet weight
OSP 1956-80, data from:
Fulton, J.D., 1983. Can. Data
Rept. Fish. Aquat. Sci. 374.
Chlorophyll-a (mg m-2)
NE Subarctic Pacific – HNLC region
0
60
120
180
Integrated over 0-50m (1961-1967)
Production (mg-C m-2 h-1
Average 0-50m
240
300
360
0
60
Day of the Year
120
180
240
300
360
Day of the Year
Upper 20 m (1966-1976)
0
60
120
180
240
Day of the Year
(Frost, 1993)
300
360
0
60
120
180
240
Day of the Year
300
360
SUPER program
Why there are no phytoplankton blooms in the
NE subarctic Pacific?
• Phytoplankton biomass controlled by
mesozooplankton grazing – “Major Grazer
Hypothesis”
• Mixing and Micrograzer Hypothesis –micrograzers
control phytoplankton biomass. This interaction is
not broken down by deep mixing in winter months.
Phytoplankton dominated by small-size
organism
Fe deficiency limits phytoplankton growth at
OSP
NO3
Chl a
PO4
Water collected
6 August 1987
No Fe added
→
little Chl a increase, little NO3 & PO4 drawdown
5 nmol kg-1 Fe added
→
large Chl a increase & NO3 , PO4 drawdown
Martin & Fitzwater, 1988. Nature 331.
Canadian JGOFS Program
• Functioning of the pelagic ecosystem
• Iron limitation vs grazing control
• Carried out plankton research along Line
P. Sampling at: P4, P12, P16, P20 and P26
(OSP)
Surface nitrate and silicate along Line P
CJGOFS program 1992-1997
(Whitney and Freeland, 1999)
Size-fractionated phytoplankton biomass and
production
1993
1992
1996
1995
1997
1996
(Boyd and Harrison, 1999)
JGOFS I: 1992-1994
1.0
0.8
Mar 93
Feb 94
May 93
May 94
Sep 92
Sep 94
0.6
0.4
0.2
0.0
f-ratio
1.0
0.8
0.6
0.4
0.2
0.0
1.0
0.8
0.6
0.4
0.2
0.0
P4 P12 P16 P20 P26
P4 P12 P16 P20 P26
Station
Average New
Production
27%
JGOFS II: 1995-1997
1.0
0.8
Feb 96
Feb 97
May 96
Jun 97
Aug 95
Aug 96
0.6
0.4
0.2
f-ratio
0.0
1.0
0.8
0.6
0.4
0.2
0.0
1.0
0.8
0.6
0.4
0.2
0.0
P4 P12 P16 P20 P26
P4 P12 P16 P20 P26
Station
Average New
Production
39%
Uptake of three nitrogen sources by two size
fractions of phytoplankton
(Varela and Harrison, 1999)
In vitro iron enrichment experiment
(Suzuki et al., 2002)
(Boyd et al., 1996)
Co-limitation of light and iron
(Maldonado et al., 1999)
Phytoplankton Production at OSP
Martin et al. (1989)
SUPER
CS Wong
Weathership
(Sambroto and
Lorenzen, 1987)
(Welschmeyer et al., 1993)
Average annual cycles of surface nitrate (monthly averages from
1969-1981) and silicate (monthly averages from 1974-1981) at
OSP (Whitney and Freeland, 1990)
Whitney and Freeland, 1999
Annual silicate and nitrate utilization
∆SiO4 (March 31 – August 15)
∆NO3 (March 31 – August 15)
(Wong and Matear, 1999)
SERIES 2002:
Subarctic Ecosystem
Response to Iron
Enrichment Study
brought to life by C.S.
Wong (IOS) and Paul
Harrison (UBC)
SERIES 2002:
Subarctic Ecosystem Response to Iron Enrichment Study from
SeaWiFS Satellite
Concentration (mmol m-3)
SERIES 2002
6
Total Chl (Marchetti)
Chl >20 µm (Marchetti)
5
Total Chl (Saito)
Chl >20 µm (Saito)
4
Chl <20 µm (Saito)
14
12
10
8
6
4
2
0
3
2
1
'Out'
Patch
0
0
5
10
15
20
Days After Enrichment
25
30
Opal flux (mmol-Si m-2 d-1)
C h lo ro p h y ll a (m g m
-3
)
Chl <20 µm (Marchetti)
16
20
0
5
0
5
10
15
20
25
10
15
20
25
16
12
8
4
0
Days Since Fertilization
Cyanobacteria
Large Phytoplankton
Sinking
No Sinking
Grazing
Senescence
(microphagy)
Small Phytoplankton
(<10 μm)
Aggregation
Sinking
Microbial
Food Loop
Accumulation
(microphagy)
Recycled / Total Production
EXPORT
REGENERATION
(Modified from Legendre and Fèvre, 1989)
Natural Fe input
• February 1996 –
hightened biological
activity
• Lateral suppy of
particulate iron from
the continental margin
off the Auletian Islands
in the winter
Lam et al., 2006
OSP – February 2006
Courtesy of Moira Galbrait
Phytoplankton composition – DMS production
Wong et al., in press
Summary
Iron limits phytoplankton production in the HNLC
region of the NE Pacific
Most of the production is regenerated production
Phytoplankton biomass and production along LineP is dominated by small phytoplankton (<20 μm)
Low seasonal variability along Line-P except at the
most coastal station
Most of the temporal variability in phytoplankton
biomass and composition at the oceanic stations
are event scale
Need more study ….
• What controls phytoplankton composition along
Line-P?
• How often there are natural iron input in HNLC
region and what are the effects on the
ecosystem?
• Light limitation on primary production and Colimitation of light and iron
• Importance of interannual, ENSO, and lower
frequency variability on biogeochemical cycles
along Line-P