Dissolved Oxygen measurements

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Dissolved Oxygen measurements - solas

Dissolved Oxygen measurements

Pablo Serret,

Carol Robinson, Vas Kitidis


Objective 1

To determine the role of upwelling on the supply, loss and air-sea

exchange of trace and biogenic gases

‣ Constrain ocean-atmospheric flux and offshore transport estimates for oxygen

using helium isotope measurements of transfer velocity.

Objective 2

To determine the photochemical and biological fate of upwelled and

recently produced DOM and its role in air-sea exchange of trace and

biogenic gases

‣ Estimate rates of biological oxidation of DOM, and study the interplay of

microbial and photochemical degradation.


Objective 3

To determine the impact of nutrient enriched water on the spatial and

temporal variability of plankton community structure and activity and

resultant influence on biogenic gas flux

‣ Constrain rates of, and study the effect of the expected change in microbial

plankton community (evolving from a “new production community” towards a

regenerating food-web), and DOM availability on

• Gross Production (GP),

• Dark Community Respiration (DCR) and

• Net community Production (NCP), GP-DCR, an indicator of the metabolic

balance of a community


Marine Plankton Net Metabolism

CO 2

CO 2

PHOTOSYNTHESIS

PRIMARY

PRODUCERS

The relationship

SOLAS – JGOFS

www.uea.ac.uk/env/solas

O 2

O 2

NCP

A bottle

HETEROTROPHS

biogenic

C

CO 2

After Mitsuo Uematsu

COMMUNITY

RESPIRATION

One m 2 of water column

A parcel of water

A province

An ocean basin

The global ocean

?

A food web

A community

An ecosystem

The marine plankton biota

Scaling rules ?


Objective 3

To determine the impact of nutrient enriched water on the spatial and temporal variability of plankton

community structure and activity and resultant influence on biogenic gas flux

‣ Constrain rates of, and study the effect of the expected change in microbial plankton

community (evolving from a “new production community” towards a regenerating food-web)

and DOM availability on GP, DCR and NCP.

some questions, hypotheses:

Constrain the integrated metabolism and evolution

GP:R relationships will change along the filament/history

GP:R relationships will differ between in and out the

filament

Can we generalise the relative role of nutrients-GP, DOM-

R, and community structure on NCP ?

Is GP:R (ideally, food web dynamics) scale-dependent ?

How much DOM remains available to “feed” the open

ocean ?

IIM-CSIC


Previous experience

Measured dissolved O2 and P:R in

Open Ocean (inc. AMT 6, 11 and 15)

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Previous experience

Measured

dissolved O2

and P:R in

Coastal Upwelling:

S Bay of Biscay, 1994-95

(Serrret et al. 1999, MEPS)

NW Iberia:

OMEX 898

(Teira et al. 2001, MEPS)

TPR, 2002

(Cermeño et al. 2006, Est.Coast.Shelf.Sci.)

Impresión, 2004

IIM-CSIC

Para ver esta película, debe

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un descompresor TIFF (sin comprimir

CERSAT-

IFREMER


Previous P:R measurements in the region:

•June 1998, AMT 6, Robinson and Serret (eg Serret et al., 2001, L&O; Robinson et al., 2002, DSR I)

•September 2000, AMT11, Serret (Serrret et al. 2006, DSRII)

•September 2003, AMT 13, Gist and Robinson

•September 2004, AMT 15, Serret

60

Surface GP rates (mmol O2 m -3 day -1 )

60

Surface DCR rates (mmol O2 m -3 day -1 )

25

Surface NCP rates (mmol O2 m -3 day -1 )

50

40

NWA Up

N gyre

S gyre

Temp

50

40

NWA Up

N gyre

S gyre

Temp

20

15

NWA Up

N gyre

S gyre

Temp

30

30

10

20

20

5

10

10

0

min median mean max

0

min median mean max

0

min median mean max

-5

Same scale

Surface rates from coastal upwelling region shown, for

comparison, with surface rates from other oceanic regions

(measured during AMT 12-14, April 2003- June 2004)


AMT

Heterotrophic

Non-heterotrophic

Non- AMT

Heterotrophic

Non-heterotrophic

Net heterotrophy in the North Atlantic subtropical gyre (NAST).

Is it supported by nutrients originating in the NWA upwelling?


AMT

Heterotrophic

Non-heterotrophic

Non- AMT

Heterotrophic

Non-heterotrophic

L1 : 3/8 net heterotrophic data points

0

∑ NCP CARPOS = - 1.6 mol O 2

/m 2 /8days

1

Mean Sept NCP 06= -0.2 ± 13.1 mol O 2

/m 2 /day

4

3

6

5

L1

L2

L2 : 6/8 net heterotrophic data points

∑ NCP = - 94.63 mol O 2

/m 2 /8days

Mean NCP = -11.8 ± 5.8 mol O 2

/m 2 /day

150

150

100

50

0

-50

-100

-150

E10 E14 E19 E26 E30 E33 E38 E44

DAY

PNC -R PB

V. Pérez & M. Aranguren

100

50

0

-50

E51 E56 E63 E69 E74 E78 E84 E90

-100

-150

ESTACION

PNC R PB

Net heterotrophy in the North Atlantic subtropical gyre (NAST).

Is it supported by nutrients originating in the NWA upwelling?


In-vitro determination of GP, DCR and NCP (GP-DCR)

using dark/ light bottle incubations.

Water sampled at

pre-dawn cast for

GP, sampled

throughout day for

DCR

Zero, light and dark

replicates filled

simultaneously

Incubated on deck:

Dark

Light (97 to 1%)

Samples titrated to

determine oxygen

concentration

LIGHT – ZERO = NCP

LIGHT + DARK = GP

DARK – ZERO = DCR


Measurement of in-situ oxygen concentrations

to determine “in-situ” rates

•In-vitro incubations determine the “instantaneous” activity of a community

at the time of sampling

•Concerns about unrepresentative sampling e.g. missing episodic bursts of

GP, “bottle effects”, incubation length/conditions, differential rates…

So try to derive respiration from in situ measurements

•Profile of O 2 concentration measured at dusk and

dawn in same body of water as determined by SF 6

•Lagrangian study creates a very large bottle!

•Only respiration during hours of darkness,

difference in concentration gives oxygen

consumed: determine rates.


Measurement of in-situ O2 concentrations

to determine “in-situ” rates

L

1

6 5

4 3

L2

2

1

0

150

100

50

0

-50

-100

E10 E14 E19 E26 E30 E33 E38 E44

-150

DAY

PNC -R PB

R. Varela et al.

U. Vigo

Lagrangian

experiments

CARPOS

(september 2006)


Measurement of in-situ oxygen concentrations

to calibrate oxygen sensors on CTDs and on

underway system

•Calibration samples taken

from a range of depths from

most casts

•Regular (6-8 hourly?)

samples from non-toxic

Winkler conc (umol/l)

300

SS CTD

250

200

150

100

y = 1.0965x + 1.0258

50

R 2 = 0.9984

0

0 50 100 150 200 250

SBE conc (umol/kg)

Linear regression

of calibration

samples taken

from CTD casts

during AMT 17

(Oct-Nov 2005)

0

Depth (m)

-50

-100

-150

-200

-40 -30 -20 -10 0 10 20 30 40

Latitude (°N)

% Oxygen saturation along the AMT 13 transect, Sep-Oct 2003


Measurement of bacterial (


Water required

Productivity cast:

10 litres at 97, 55, 33, 14 and 1% light depths

Other casts:

0.5 litres at all depths

Underway:

0.5 litres every 6-8 hrs

Lab space etc

•Bench space for oxygen system (ca. 1.5 m x 2)

•0.5 m in lab to filter

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