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 expultionand reduction of ice salinity.

differencesArctic• 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 productionduring the summer

Southern Ocean• 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

ArcticOcean

SouthernOcean

The maximum and minimum extent ofsea ice cover.

Irradiance per 24 h

theoretical values for irradiance at different latitudes

from Sakshaug et al. 1992

latitude

NorwegianNorwegian, , GreenlandGreenland and and BarentsBarents SeasSeas

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

Barents sea: Median values for end of April in twoperiods

(extreme)

from Blindheim 2004

Pack ice= ice formed at sea

Melosira arctica in the Arcticocean

Ice assemblages

from Sakshaug et al. 1992 modified from Horner

Ice microalgalassemblages

Microalgal communities in the ice

from Syvertsen 1991

(skrugard-sammfunnet)

Ice algae

fra Syvertsen 1991

the comb effectfor trapping and colonisation of icealgae

Algae in the icewill avoid verticalmixing and somegrazing

Algal communities near and on the ice in the Arctic

from Syvertsen 1991

= Fragilariopsis oceanica =Attheya septentrionalis

Plankton- and icealgae in the Arctic

from Syvertsen 1991

plankton sub-ice Nitzschia frigida

Melosira arctica

Ice algaecommunities in the Barents Sea

from Syvertsen 1991

the ice edge effect –productive zone 20-50 km along the ice edge

Microalgal developmentin the Barents Sea

from Sakshaug et al. 1992

SPRINGsnow

multi year ice one year ice

Microalgal development in the Barents Sea

from Sakshaug et al. 1992

SUMMERsnow

Algal succession in the BarentsSea

from Sakshaug et al. 1992

the ice-edge effect

prebloom

Zooplankton spawning

overwintering zooplankton migrating up

ice edgebloom

nutrientdepleated new generation of

zooplankton developing

Capelin feedingalgae sinking

TIME

marginal ice zone / ice edgeAntarctic: 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 theBarents Sea

North of polar front• strong stratification (freshwater stabilization; 20-30 m)

throughout summer• regenerated production after the spring maximumSouth of polar front• weaker stratification (temperature stabilisation)

• wind driven vertical mixing throughout summer keep up nutrient supplies

South of the polar front; turbulence and ”blooming”(model), Barents Sea

phytoplankton Ncalm

with wind

Algal groups in the Barents Sea

Diatoms -> 100 000 cells L-1

Prymnesiophyceans; • Phaeocystis pouchetii

-> million cells litre-1

other flagellates

BiogeographySpecies 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 thesummer and bring up nutrients.

Southern Ocean

Hydrography

Antarctic bottom water

Deep ocean circulation

F/F G.O. Sars on cruise to the Southern Ocean2008

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

• Nutrients (N, P, Si)• Chlorophyll a• Chlorophyll a size

fractions• Phytoplankton

quantitative sample• Phytoplankton net haul• Pico-nanoplankton• DNA• Cultures

-36 stations, up to 8 depths

Phytoplankton net haul, vertically 0-100m

algal culturessampling

DNA-isolation

Methods- biodiversity

electron microscopy

PCR

DNA sequencingphylogenetic

analyses

cloning454-sequencing

Fluo

rese

nce

/ µug

/l

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

51

53

55

56

58

59

61

62

63

65

66

68

69

71

72

73

74

Latitude °S

Pre

ssur

e / d

bar

AKES 2008

Contours at [0:0.05:.8] µug/l46 48 50 52 54 56 58 60 62 64 66

300

250

200

150

100

50

0

Fluorescence along 15oE

0

50

100

150

200

250

0 0,1 0,2 0,3 0,4 0,5

Chl a (mg/m3)

Depth

Fluo

resc

ens

Dyp

(m)

0

50

100

150

200

250

0 0,1 0,2 0,3 0,4

Chl a (mg/m3)

Depth

st. 62 st. 73

Results:

Thet

a / °

C, p

ref =

0 d

bar

-2

0

2

4

6

8

10

12

51

53

55

56

58

59

61

62

63

65

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68

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74

Latitude °S

Pre

ssur

e / d

bar

AKES 2008

Contours at [-2:0.5:6 7:1:12 ] °C46 48 50 52 54 56 58 60 62 64 66

1500

1000

500

0

Sal

inity

/

33.6

33.8

34

34.2

34.4

34.6

34.8

35

35.2

51

53

55

56

58

59

61

62

63

65

66

68

69

71

72

73

74

Pre

ssur

e / d

bar

AKES 2008

Contours at [33.5:0.1:34.8 35 35.2 ] 46 48 50 52 54 56 58 60 62 64 66

1500

1000

500

0

Dep

th(m

)D

epth

(m)

temperature

salinity

Hydrography

15oEHigh levels of N, P and Si south of51oS (>15,1,30 mg L-1)

Quantitative phytoplankton counts

0

200

400

600

800

1000

1200

1400

67- 30m 69 - 5m 72 - 50m 73 - 30m 78 - 30m 78 - 5m 78 - 75m 83 30m

Station and depth

Cel

ls/m

L

Diatoms

Cryptophytes

Ciliates

Dinoflagellates

nanoflagellates andmonads >3 my

Small pico- and nanoflagellates and monads. and small diatoms dominatedin the open ocean during this summer cruise.

Pico-nanoflagellates(SEM)

haptophytes, cryptophytes, prasinophytes, choanoflagellates

etc.

Rhizosolenia antennata f. antennata Asteromphalus parvulus

Fragilariopsis kerguelensis

Corethron pennatum

Microalgae in net hauldiatoms

Chaetoceros dichaeta

Chaetoceroscriophilus

Chaetocerosflexuosus

Microalgae in net haul - diatoms

Nanoplankton

Phaeocystis antarctica

(haptophyte)

Dactyliosolen cf. tenuijunctus

(diatom)

LM SEM

Pico-nanoplankton (LM og SEM)

Fragilariopsis nana

Fragilariopsis pseudonana

Fragilariopsis spp. (st. 63, TEM)

F. nana

F. kerguelensis

F. separanda

F. rhomboides F. ritscheri

Some conclusions on from theG.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 stabilityhere, probably due to higher Fe-levels

• Nano- and picoflagellates and small diatomsdominated in numbers

• Diatoms dominated in the net hauls