Phytoplankton in polar regions
BIO 4400 2009 Bente Edvardsen
Arctic and Antarctic - similarities
• Cold
• Low light during long polar winter, continuous
light during summer
• Seasonal dynamics dominated by annual
formation and melting of ice
• Cold high-density bottom water formation
during freezing of sea water, brine expultion
and reduction of ice salinity.
differences
Arctic
Southern Ocean
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•
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Latitude: 70-80°N
Enclosed by land
Ocean size: 15 mill km2
Ice cover: 14 mill km2 winter
7 mill km2 summer
Pack ice last longer and is
thicker (av. 3.5 m)
• Influenced by many large river
systems
• Av. depth 1800 m and large
part over shallow shelf
• Nutrient controlled
phytoplankton production
during the summer
Latitude: 50 - 60 or 70°S
Circumpolar open system
Ocean size: 36 mill km2
Ice cover: 20 mill km2 winter
4 mill km2 summer
Most pack ice is one year
and thinner (av. 1.5 m)
• Little terrestrial influence
• Narrow shelf, pack ice over
deep water (4000-6500 m)
• High nutrient, low chlorophyll
areas that may be limited by
iron
Arctic
Ocean
Southern
Ocean
The maximum and
minimum extent of
sea ice cover.
Irradiance per 24 h
latitude
theoretical values for irradiance at different
latitudes
from Sakshaug et al. 1992
Norwegian, Greenland and
Barents Seas
Barents Sea
Water circulation in the Barents Sea
Polar front
Barent Sea: Distribution of temperature at 100 m
depth during August-September
Variation in ice cover distribution
(extreme)
Barents sea: Median values for end of April in two
periods
from Blindheim
2004
Pack ice= ice formed at sea
Ice assemblages
Melosira arctica in the Arctic
ocean
Ice microalgal
assemblages
from Sakshaug et al. 1992 modified from Horner
Microalgal communities in the ice
(skrugard-sammfunnet)
from Syvertsen 1991
Ice algae
the comb effect
for trapping and
colonisation of ice
algae
Algae in the ice
will avoid vertical
mixing and some
grazing
fra Syvertsen 1991
Algal communities near and on the
ice in the Arctic
= Fragilariopsis oceanica
=Attheya septentrionalis
from Syvertsen 1991
Melosira arctica
Plankton- and ice
algae in the Arctic
from Syvertsen 1991
plankton sub-ice
Nitzschia frigida
Ice algae
communities in
the Barents Sea
the ice edge effect –
productive zone 20-50
km along the ice edge
from Syvertsen 1991
Microalgal development
in the Barents Sea
SPRING
snow
from Sakshaug
et al. 1992
multi year ice
one year ice
Microalgal development in the Barents Sea
snow
SUMMER
from Sakshaug et
al. 1992
Algal succession in the Barents
Sea
the ice-edge effect
TIME
prebloom
ice edge
bloom
nutrient
depleated
Zooplankton
spawning
overwintering zooplankton
migrating up
algae sinking
new generation of
zooplankton developing
Capelin feeding
from Sakshaug et al. 1992
marginal ice zone / ice edge
Antarctic: 100-200 km
Arctic: 20-50 km
Timing of vernal blooming- Arctic
Ice-edge bloom
• Stratification depends on salinity (as in
fjords)
• may start in April, 6-8 weeks before the
vernal bloom in the Norwegian Sea
Stability and production in the
Barents Sea
North of polar front
• strong stratification (freshwater stabilization; 20-30 m)
throughout summer
• regenerated production after the spring maximum
South of polar front
• weaker stratification (temperature stabilisation)
• wind driven vertical mixing throughout summer
keep up nutrient supplies
calm
phytoplankton N
South of the
polar front;
turbulence and
”blooming”
(model),
Barents Sea
with wind
Algal groups in the Barents Sea
Diatoms -> 100 000 cells L-1
Prymnesiophyceans;
• Phaeocystis pouchetii
-> million cells litre-1
other flagellates
Biogeography
Species with preference for cold water have
competing advantages in the Arctic, but are
also present in temperate waters
1. Nitzschia frigida (also in Oslofjorden)
2. Melosira arctica (also in the Baltic Sea)
3. Thalassiosira gravida og Thalassiosira
hyalina (also in Skagerrak)
Subsurface algae and bacteria
Summary – Barents Sea
• Hydrography; atlantic water meets polar
water (polar front)
• Melting cause a brackish upper water
layer that stabilise the water mass
• Spring bloom associated to the ice edge
• Ice algae in and under the ice
• South of the polar front: recurrent periods
with wind cause vertical mixing also in the
summer and bring up nutrients.
Southern Ocean
Hydrography
Antarctic bottom water
Deep ocean circulation
F/F G.O. Sars on cruise to the Southern Ocean
2008
Leg 2: 25 scientists from 8 countries + 12 crew
18 February- 24 March 2008
Stations for CTD, nutrients, chl a and phytoplankton, leg 2.
Aims - phytoplankton
Phytoplankton in the food web
•
Abundance and distribution
•
Species and size composition
•
Co variation with nutrients temp. salinity stability
•
Food preferences in krill
Biodiversity
•
Biodiversity of protists, with emphasis on nano and pico-plankton
•
Distribution, abundance and ecology of certain taxa
Sampling for phytoplankton
-36 stations, up to 8 depths
• Nutrients (N, P, Si)
• Chlorophyll a
• Chlorophyll a size
fractions
• Phytoplankton
quantitative sample
• Phytoplankton net haul
• Pico-nanoplankton
• DNA
• Cultures
Phytoplankton net haul, vertically 0-100m
Methods- biodiversity
DNAisolation
sampling
algal cultures
PCR
cloning
454-sequencing
electron microscopy
phylogenetic
analyses
DNA sequencing
Results:
74
73
72
71
69
68
AKES 2008
66
65
62
63
61
59
58
56
55
53
51
Fluorescence along 15oE
0
0.8
50
0.7
0.6
0.4
3
3
Chl a (mg/m )
Chl a (mg/m )
0
0,1
0,2
0,3
0,4
0,5
0
0
0,1
0,2
0,3
0.3
200
50
50
100
100
150
200
Contours at [0:0.05:.8] µug/l
46
48
50
150
st. 62
54
st. 73
200
250
52
0.2
Depth
250
300
0,4
0
0.1
250
56
Latitude °S
58
60
62
64
66
0
Fluoresence / µug/l
150
Fluorescens
0.5
Depth
DypPressure
(m)/ dbar
100
74
73
72
71
69
68
66
AKES 2008
65
62
63
61
59
58
56
55
53
51
Hydrography
0
12
15oE
temperature
High levels of N, P
and Si south of
51oS (>15,1,30 mg
L-1)
1000
6
4
Theta / °C, p ref = 0 dbar
8
500
Pressure / dbar
Depth (m)
10
2
0
-2
74
66
73
72
64
71
62
69
68
60
66
58
65
56
Latitude °S
AKES 2008
62
63
61
54
59
52
58
56
55
51
53
Contours at [-2:0.5:6 7:1:12 ] °C
46
48
50
1500
0
35.2
salinity
35
34.8
34.4
34.2
1000
34
33.8
33.6
1500
Contours at [33.5:0.1:34.8 35 35.2 ]
46
48
50
52
54
56
58
60
62
64
66
Salinity /
34.6
Pressure / dbar
Depth (m)
500
Quantitative phytoplankton counts
Small pico- and nanoflagellates and
monads. and small diatoms dominated
in the open ocean during this summer
cruise.
1400
1200
Diatoms
1000
Cells/mL
Cryptophytes
800
Ciliates
600
Dinoflagellates
400
nanoflagellates and
monads >3 my
200
0
67- 30m
69 - 5m 72 - 50m 73 - 30m 78 - 30m
Station and depth
78 - 5m 78 - 75m
83 30m
Pico-nanoflagellates
(SEM)
haptophytes, cryptophytes,
prasinophytes, choanoflagellates
etc.
Microalgae in net haul
diatoms
Corethron pennatum
Fragilariopsis kerguelensis
Rhizosolenia antennata f. antennata
Asteromphalus parvulus
Chaetoceros
flexuosus
Microalgae in net haul - diatoms
Chaetoceros
criophilus
Chaetoceros dichaeta
Nanoplankton
LM
SEM
Phaeocystis antarctica
Dactyliosolen cf. tenuijunctus
(haptophyte)
(diatom)
Pico-nanoplankton (LM og SEM)
Fragilariopsis nana
Fragilariopsis pseudonana
Fragilariopsis spp. (st. 63, TEM)
F. separanda
F. rhomboides
F. nana
F. ritscheri
F. kerguelensis
Some conclusions on from the
G.O. Sars cruise in 2008
• Chlorophyll levels were low (<1 mgL-1) with a
maximum at 20-100 m depth
• High levels of N, P, Si in open ocean during
summer
• Higher algal abundance in the polar front region
and near the continent, despite lower stability
here, probably due to higher Fe-levels
• Nano- and picoflagellates and small diatoms
dominated in numbers
• Diatoms dominated in the net hauls