The emerging issue of hypoxia in Canadian coastal waters

DFO national science workshopMont-Joli, Québec, Canada

November 21, 2006

Denis GilbertOcean and Environmental Science BranchMaurice-Lamontagne Institute Department of Fisheries and Oceans (DFO)Mont-Joli, Québec, Canada

Talk outline• Eastern Canada: St. Lawrence Estuary, Emerald

Basin, Bedford Basin• Western Canada: Strait of Georgia, station Papa,

Oregon events give forewarning for Vancouver Island

• Global synthesis: 14 papers planned by SCOR Working group 128 on coastal hypoxia

Denis Gilbert, IML, 2006-11-21

Regions considered in this talk

StationPapa

Oregoncoast

Strait ofGeorgia

St. LawrenceEstuary

EmeraldBasin

BedfordBasin

Denis Gilbert, IML, 2006-11-21

-75 -70 -65 -60 -55 -50 -45 -40

35

40

45

50

55F

Oxygensaturation (%)

10

20

30

40

50

60

70

80

90

100

110

-75 -70 -65 -60 -55 -50 -45 -40

35

40

45

50

55C

Temperature ( C)

-2

0

2

4

6

8

10

12-75 -70 -65 -60 -55 -50 -45 -40

35

40

45

50

55D

Salinity

33.5

34

34.5

35

35.5

36

-75 -70 -65 -60 -55 -50 -45 -40

35

40

45

50

55E

O2 concentration

( mol L-1)

50

100

150

200

250

300

350

400

Water properties on

the27.25 kg/m3

density surface

Gilbert et al. (2005, L&O, 50: 1654-1666)

T

O2

S

O2sat.

Temperature and oxygen in LSLE (300 m+)

Gilbert et al. (2005, L&O, 50: 1654-1666)

33 33.5 34 34.5 35 35.5 36 36.5-2

0

2

4

6

8

10

12

14

Salinity

Pot

enti

al t

empe

ratu

re

( C

)

27.627.427.227

26.8

1931-1935

1980-2003

NACWLCWMixing lineT-S at Cabot Strait

Water mass mixing: NACW – LCW

1931-193572% LCW, 28% NACW

1980-200353% LCW, 47% NACW

Gilbert et al. (2005, L&O, 50: 1654-1666)

-70 -68 -66 -64 -62 -60 -58 -5645

46

47

48

49

50

51

52

Longitude

Latit

ude

Denis Gilbert, IML, 17-Jan-2006

Oxy

gen

satu

ratio

n (%

)

0

20

40

60

80

100

Near-bottom oxygen measured during the 2004-2005 stock assessment surveys

Gilbert et al. (2006, Naturaliste Canadien)

Near-bottom oxygen in 2004-2005:Interpretation for cod

-70 -68 -66 -64 -62 -60 -58 -5645

46

47

48

49

50

51

52

Longitude

Latit

ude

Denis Gilbert, IML, 17-Jan-2006

Oxy

gen

satu

ratio

n (%

)0

20

40

60

80

100

21% saturation = LC_5028% saturation = LC_0528% < O2 < 70% reduced growth O2 > 70% : optimal growth

Plante et al (1998, J. Fish Biology, 53: 1342–1356)Chabot et Dutil (1999, J. Fish Biology, 55: 472–491)

Color coding

Oxygen levels selected by various species

Gilbert et al. (2006, Naturaliste Canadien)

Northwest Atlantic water masses

Pershing et al. 2001, Oceanography, 14: 76-82

Mode 1

Mode 2

T-S-O2-nutrients timeseries at 150m depth in Emerald Basin

Drinkwater et al 2002NAFO SCR 02/42

Denis Gilbert, IML, 2006-11-21

Bedford Basin monitoring station

Bill Li, BIO

Bedford Basin monitoring station (continued)

Bill Li, BIO

Mid-depth Intrusion

Oxygen (ml/l)

April 2000

NO ( mol/l) 3

Straits of Juan de Fuca and Georgia

Diane Masson & Patrick Cummins, IOS

The Strait of Georgia

Diane Masson & Patrick Cummins, IOS

Deep, centralBasin

Longitude

Latit

ude

Temperature and oxygen trends - Strait of Georgia

Temperature trend (°C/year)

Diane Masson & Patrick Cummins, IOS

Decreased solubility due to warmer water only accounts for 25% of oxygen decrease (i.e. saturation is decreasing !)

Diane Masson & Patrick Cummins, IOS

Coupled atmosphere-ocean-ice & biogeochemistry model suggest …

• Oxygen levels will decline in the intermediate and deep ocean

• Oxygen decline reflects changes due to solubility, ocean dynamics and ocean biology

• An expansion of low oxygen regions like the eastern equatorial Pacific (≈20% increase)

• We need better global observations to monitor oxygen changes

Richard Matear, CSIRO, Australia

Pacific oceanoxygen

distribution

Matear and Hirst 2003, GBC

Observed

Modelled

Ice-ocean-atmosphere coupled model with

biogeochemistry predicts a 20%

increase in global volume of hypoxic

waters

Matear and Hirst (2003, GBC)

Station Papa

0

25

50

75

100

125

150

175

Mar-86 Mar-90 Mar-94 Mar-98 Mar-02

Oxy

gen

(µm

ol/k

g)

-7.05 µmol/kg/y

28

32

36

40

44

Mar-86 Mar-90 Mar-94 Mar-98 Mar-02

Nitr

ate

(µm

ol/l)

200 m

300 m

400 m

600 m+0.76 µmol/kg/y

Frank Whitney, IOS

At Ocean Station Papa, oxygen has been declining steadily since 1994. As oxygen is consumed through the remineralization of detrital materials, nitrate and CO2 are produced. The interior of the ocean is currently nutrient rich but oxygen depleted. This trend is linked with widespread changes being observed in the North Pacific.

Dead zones off Oregon Coast in July and August: 2002, 2004 and 2005

Grantham et al. (2004, Nature, 429:749-754)

Argo floats with oxygen sensors

Denis Gilbert, IML, 2006-11-21

Argo profilingfloat 4900637

0 10 20 30 40 50 60 70 80 90 100 110-2000

-1800

-1600

-1400

-1200

-1000

-800

-600

-400

-200

0

Oxygen saturation (%)

05-Nov-2006 11:44:00 , r4900637_062

De

pth

(m

)

0 5 10 15Temperature (C)

32 32.5 33 33.5 34 34.5 35Salinity

23 24 25 26 27 28Density (kg m-3)

Near Vancouver IslandLatitude: 46.431 °NLongitude: 128.25 °W

Papers proposed by SCOR WG 128 on hypoxia

• Global coverage of hypoxic zones (Nancy Rabalais, USA)• Oxygen trends over past 100 years (Denis Gilbert, Canada)• Historical record from sediments (Andy Gooday, U.K.)• Upwelling-dominated systems (Pedro Monteiro, South Africa)• Systems with high anthropogenic N & P inputs (unknown author)• Recovery following remediation efforts (Michael Kemp, USA)• Benthic-pelagic coupling (Jack Middelburg, Netherlands)

Denis Gilbert, IML, 2006-11-21

Papers proposed by SCOR WG 128 on hypoxia (continued)

• Greenhouse gas emission – N20 & CH4 (Wajih Naqvi, India)• Impacts of global warming (Richard Matear, Australia)• Effects on nekton and plankton (Werner Ekau, Germany)• Microbial communities (Osvaldo Ulloa, Chile)• Knowledge gaps and future research (unknown lead author)• Designing hypoxia observing systems (unknown lead author)• Overall summary of all papers (Jing Zhang, China)

Denis Gilbert, IML, 2006-11-21

SUMMARY (1/2)• St. Lawrence Estuary, Emerald Basin and Strait of

Georgia oxygen levels are influenced by interannual variations in water properties over the upper continental slope.

• Bedford Basin undergoes short periods of hypoxia followed by quick recovery during episodic bottom water renewal events.

Denis Gilbert, IML, 2006-11-21

SUMMARY (2/2)• Enhanced upper ocean stratification may be responsible for

reduced winter ventilation at station Papa. We may witness episodes of more severe hypoxia off Vancouver Island within the next decade.

• Coastal hypoxia is an issue of growing concern around the world. Other countries (Denmark, Sweden, U.S.) are considering and/or implementing mitigation measures to restore key ecosystem functions and services.

Denis Gilbert, IML, 2006-11-21