B R S S E M I N A R S E R I E S P R E S E N T S :

Friday 8 July

Ocean uptake of CO2:Are the Oceans Acidifying?

Dr Steve Widdicombe,Plymouth Marine Laboratories, UK

This presentation will introduce the process of ocean acidification, highlight someof the key environmental concerns and discuss some of the mitigation strategiesthat have been suggested. With world primary energy demand projected to rise atan average of 1.7% annually over the next 30 years this means an increase in therelease of CO2. Of all the predicted impacts attributed to this inevitable rise inatmospheric CO2 concentration (and the associated rise in temperature), one ofthe most pressing is the acidification of surface waters through the absorption ofthe atmospheric CO2 and its reaction with seawater to form carbonic acid. It ispredicted that this process may lead to a surface ocean pH reduction of 0.7 unitsby the end of the century. It is clear that the growing emissions of CO2 from humanprocesses could pose a distinct threat to the global environment. Howeverquantifying the consequences of CO2 release is problematic as many physical andbiogeochemical processes combine to create a complex set of interactions.

11.00am - 12:00noon (morning tea at 10:45am)Edmund Barton Conference Centre (in the courtyard)

Edmund Barton BuildingKings Avenue, Canberra

Bookings not required.Parking can be a problem, we suggest taking a taxi.

For further details, please call the BRS Seminar Coordinator on 6272 3440.

For further information on BRS Seminars or to obtain papers/presentations supplied byprevious seminar presenters, please visit our website at: www.brs.gov.au/brsseminars

Reviewing the Impact of Increased Atmospheric CO2 onOceanic pH and the Marine Ecosystem:

“Ocean Acidification”

Dr Steve WiddicombePlymouth Marine Laboratory

Benthic Ecologist

I have worked at PML for the past 15 years

Main interests are the factors that affect the communities that live in/on the seafloorand the ecosystem functions these communities perform.

Particular area of expertise is the use of large experiments to explore theseinterests.

The Plymouth Marine Laboratory [PML] is an independent and impartial collaborativecentre of the UK Natural Environment Research Council [NERC].

First involvement with ocean acidification was 4 years ago through a EuropeanNetwork of Excellence “CO2 GeoNet”

I now run 2 large interdisciplinary projects exploring the potential impacts of oceanacidification and the ecological risks associated with geological storage.

Carbon in the Ocean

Pre industrially, the oceansand the organisms that live inthem contained about 38 000Gt C (1 Gt = 1015 grams or 1billion tonnes)

Oceans are a carbon sink andtake up 2 Gt C per year

This 95% of all the carbon thatis in the oceans, atmosphereand on land.

6 Gt C per year released into the atmosphereby human activities

Atmospheric concentrations are higher today than at any timefor at least the last 420 000 years

Burning fossil fuels is releasing CO2 that wouldotherwise be locked up in geological reservoirs.

About one half (48%) of all the CO2 produced by fossil fuel burningand cement production in the past 200 years (1800 – 1994) hasbeen absorbed by the oceans.

A total of 118 ± 18 Gt C (1800 – 1994)

Today that figure is nearer 140 Gt C(over 500 Gt CO2)

Human impact on the carbon cycle

Oceanic AcidificationAtmosphere

CO2 (g) CO2 + H2O ´(H2CO3)´ HCO3

- + H+ ´ CO32- + 2H+

Surface Ocean

CO2 dissolves into the seawater to form Dissolved Inorganic Carbon(DIC) which consists of:

1. aqueous CO2 (including carbonic acid) – 1%

2. bicarbonate HCO3- - 91%

3. carbonate CO32- - 8%

All 3 forms of DIC are important for biological processes (e.g.photosynthesis and calcification)

DIC operates as a natural buffer to the addition of hydrogen ions –known as the “carbonate buffer”

BUT we now know there is a limit to how much CO2 the carbonatebuffer can deal with.

Henry’s Law

Oceanic pH

Acid solutions have an excess of H+ ions and a pH less than 7

Alkaline solutions have an excess of OH- ions and a pH more than 7

The term pH describes the acidity of a liquid.

pH = -log10[H+]

H20 _ H+ + OH-

Concentration of H+ and OH- are roughly equal (10-7 mole per litre)This means a neutral solution has a pH = 7

This measure is negative logarithmic – if H+ concentration increase10 fold, pH decreases by one unit.

Wolf-Gladrow, Riebesell, Burkhardt, Bijma (1999) Tellus 51B, 461

The Oceans are becoming more acid as they take up more CO2

Oceanic pH

The oceans are currently alkaline pH 8.1 ± 0.3

CO2 + H2O ´ HCO3- + H+ ´ CO3

2- + 2H+

Net effect of dissolving CO2 in seawater is to increase H2CO3, H+ andHCO3

- concentrations & decrease CO32- concentrations.

Oceanic pH

7.4

7.6

7.8

8

8.2

8.4

8.6

-25 -20 -15 -10 -5 0 5

time (million years before present)

pH

Caldeira and Wickett (2003)

Past (Pearson and Palmer,2000) and predictedvariability of marine pH.

2000 AD

2050 AD

2100 AD

Continued CO2 Emissions and Ocean Acidification

pH has changed by 0.1 pHunits since pre-industrialtimes.

This equates to a 30%increase in the concentrationof hydrogen ions in the last200 years.

0.5 – 2.5km Corals, Molluscs (Pteropods),

Macroalgae

Aragonite

1.5 – 5km Foraminifera, Coccolithophores,

Echinoderms, Molluscs,

Macroalgae

Calcite

Saturation HorizonMarine Groups

Marine organisms that construct calcium carbonate structures dependon the presence of carbonate.

CaCO3 will dissolve unless there is a sufficiently high concentration ofcarbonate (CO3

2-) ions.

CaCO3 becomes more soluble with decreasing temperature andincreasing pressure.

Creates a boundary called a “saturation horizon”.

Calcium Carbonate

Ca2+ + 2HCO3- _ CaCO3 + CO2 + H2O _ H2CO3 + CO3

2- _ 2HCO3-

Some what does a change inpH mean for the oceans andthe organisms that live in it?

Effects on micro organisms

Photosynthesis

Growth and composition

Metal speciation

Nutrient speciation

50% of global primary production is carried out in theoceans by plankton <10mm

- Small _

- Little effect

- Effect unknown

Effect of Reducing pH on Key Nutrients

Changes in speciation of phosphate, silicate and ammonia with pH(from Reebe and Wolf-Gladrow 2001)

Speciation: of key nutrients for phytoplanktonand bacterial growth are pH dependent

Nitrogen: in particularammonia-ammonium, ispH dependent, with theconcentration of NH3 (Aq)decreasing as pHdeclines

Inorganic phosphate: aspH falls to 7.8, theconcentration of H2PO4

-

rises as that of PO43-

decreases

Changes in the relative proportions ofphosphorus, nitrogen and trace metal speciesmay have an effect on plankton diversity

Effects on bacterial processesLow pH inhibition of nitrification

Change in Nitrification Rate with pH

y = 0.1508x2 - 1.5944x + 4.1302

R2 = 0.984

0

0.2

0.4

0.6

0.8

1

1.2

5.5 6 6.5 7 7.5 8 8.5pH

Re

lati

ve

Nit

rifi

ca

tio

nra

te

now

WCS

Experimentally derived response curve (Huesemann et al, 2002)

The shift away from NH3 willinhibit nitrification, which inturn will inhibit denitrification.

Nitrification / Denitrification

-3

-2234 NONOONNHNH �ÆÆ�+

N2

nitrificationDenitrificationto atmosphere

Oxidation of ammonia to nitrate / nitrite

Low pHÁ

Spatial variability in ecosystem response

Denitrification parameterisedfor sandy sediments, mayunder estimate muddysediments.

10% decrease is consistentacross the domain.

60

50

40

30

20

10

60

50

40

30

20

10

6

5

4

3

2

1

Compares with measurements / estimates of15-150 mmol N .m-2.y-1. (Lohse 93,96)

2000 simulation

WCS simulation

Difference in denitrification loss

WCS - 2000

Effects on larger organisms

Decreased motility, inhibition of feeding,

reduced growth, reduced recruitment,

respiratory distress, decrease in population size,

shell dissolution, mortality

increased susceptibility to infection

destruction of chemosensory systems

Effects of Low pH on Zooplankton: the Food of Fish

Yamada & Ikeda 1999; Heath 1995; Shiramura et al. 2002; Kurihara et al. 2004

Evidence to indicate that marine zooplankton(crustacea) passing through plumes of CO2enriched seawater suffer high mortalities – butvery little research

Some zooplankton have calcium carbonate shells(molluscs) and will be vulnerable. This pteropodis an important part of the Antarctic food web

Reduced fertilization of copepod eggs at CO2

levels beyond 1000 ppm (2100 worst casescenario)

Limacina helicina antartica

Adult female copepod bearing eggs

Crustacean zooplankton

Impact on Fish and Squid

Portner and Reipschlager (1996); Portner et al. (2004)

Squid are an important food resourcefor humans, whales etc.

At 3 fold increases in atmospheric CO2, fish andother complex animals are likely to havedifficulty reducing internal CO2 concentrations,resulting in accumulation of CO2 andacidification of body tissues and fluids(hypercapnia)

The effects of lower level, long term increases inCO2 on reproduction and development of marineanimals is unknown and of concern

Squid very sensitive because of their highenergy and O2 demand for jet propulsiondecrease in pH of 0.25 having drastic effects(reduction of c. 50%) on their oxygen carryingcapacity

Effects on calcifyingorganisms

Coccolithophores

Others include: Foraminifera, echinoderms and molluscs

and Corals

Coccolithophores: Important Primary Producerson European Shelf Seas

Change in biogeochemistryand ecosystem

Holligan 1993; Archer et al. 2003

Extensive blooms (often 100,000’s km2)of these calcite forming phytoplanktonoccur on shelf seas

Reduction incoccolithophores couldchange phytoplanktonbiodiversity

Largest current producer ofcalcite on Earth

Important role in the global carbon cyclethrough the transport of calcium carbonateto deeper waters and sediments

Coccolithophores aremajor producers ofdimethyl sulphide (DMS)to the atmosphere –thought to be important incloud formation andhence a negativefeedback to climate

Effects of CO2 on Coccolithophores

Gephyrocapsa oceanica

Riebesell et al. Nature (2000)

300 ppm

780-850 ppm

Emiliania huxleyi

pCO2

Reducedcalcification

Coccolithophore model

depth

Julian day

Year 1WeakerstratificationConstant at 30m,

Year 2Strongerstratification,Warmer withdeepening out ofthe euphotic zone

Simulated coccolithophore biomass, compares withobservations of 44 mg C.m-3 at surface, (Burkill, 2002;Widdicombe, 2002).

Based on Tyrrell & Taylor (1996) and Merico et al (2004)

Coccolithophore results

0

400

800

1200

1600

Jan Feb Apr Jun Aug Oct Dec Feb Apr Jun Aug Oct Dec

Y2000

Y2050

Y2100

Ywcs

0

5

10

15

20

Jan Feb Apr Jun Aug Oct Dec Feb Apr Jun Aug Oct Dec

Y2000

Y2050

Y2100

Ywcs

Á Coccolithophore cell biomass (mgC.m-2)

Marked inhibition of coccolithophores is seenwith decreasing pH.

Inhibition strength is sensitive to the physicalconditions prevailing

Stronger light and nutrient limitation in year 2decrease the relative effect of calcificationinhibition

ÁNumber of liths per cell

Inhibition correlates with the degree of lithcoverage and hence the parameterisation ofmortality and grazing relative to the lithcoverage.

Parameterisation penalises <10 liths.cell-1

Warm Water Coral ReefsOnly 1.28 million squarekilometres (less than 1.2%of the worlds continentalshelf area)

BUT many millions ofpeople directly dependanton healthy coral reefs(tourism and fisheries).

Highly diverse ecosystem.

Coral reefsoccur in warm,alkaline, sunlitwaters with higharagonitesaturation.

Corals form a powerful mutualisticsymbiosis with tiny dinoflagellate

algae known as zooxanthellae.

Sitting in the tissues, the algalsymbionts photosynthesize and passmost of their production to the coral.

What are coral reefs ?

In return, the animal provides inorganic nutrients such asammonia and phosphate – from their waste metabolism.

The fate of corals

95% correlation with increases in seatemperature (1-2% above long-termsummer sea temperature maxima) andbleaching.

Backed up experimentally

Almost 30% of warm water corals have disappeared sincethe beginning of the 1980s

Largely due to increasingly frequent and intense periods ofwarm sea temperatures

This causes coral bleaching.

Pre-industrial (pCO2 – 280 ppm) 2060 (pCO2 – 517 ppm)

Required Aragonite saturation for “healthy” coral growth – Average min/max 3.28 – 4.06

High atmospheric CO2 is compounding the problem bylowering the aragonite saturation state of seawater

If atmospheric CO2 concentrations double, calcification rates coulddecrease by 10-30% (Gattuso et al., 1999; Kleypas et al., 1999b).

Some recent studies even suggest a decrease of 54%.

Coral loss = Financial loss

Globally, corals support millions of people through subsistence foodgathering and tourism.

Studies have been based on global warming only.

(Hoegh-Guldberg & Hoegh-Guldberg, 2004)

Reef associated revenue / goods contribute 68% of the grossregional product (AU$ 1.4 billion)

Most dependent region - North Queensland.Of the AU$900 million tourism revenue,AU$800 million was associated with having ahealthy coral reef.

Reef degradation (600ppm by 2100) will cost the local economies ofcoastal Queensland a minimum of AU$2.5 billion over 19 years (2001-2020).

If atmospheric CO2 is higher (800ppm by 2100) financial cost could beas high as AU$14 billion.

The Caribbean

Hawaii

Caribbean reefs provide annual net benefits (fisheries, divetourism and shoreline protection) of between US$ 3.1 billion andUS$ 4.6 billion (Burke et al, 2004)

By 2015, loss of income due to reef degradation, thought to beseveral hundred million dollars per year.

Estimated that coral reefsgenerate US$ 364 millioneach year.

US$304 – snorkelling and diving40 - property7 – non-use2.5 - fisheries

NOTE: these costs do not include the ecological /environmental goods and services provided by the reef.

Cold Water CoralsOften referred to as “deep water” corals butexist at depths between 10m and over 1000m

Distribution probably controlled bytemperature.

Found all over the world.

Exact area unknown but recent studies indicate that cold water coralscould equal or even exceed warm water corals (Freiwald et al., 2004)

Non-photosynthetic, rely on organicmatter from above.

Long lived, slow growing – coloniesup to 8000 years old have been found.

Fossil records show they have beenaround for millions of years.

Support a diverse ecosystem.

Cold water corals such as Lophelia pertusa

Shallowing of thearagonite saturationhorizon will have abig impact on theseecosystems

Freiwald, www.sams.ac.uk, Orr in press

Location of recentlydiscovered Lophelia coralsaround the UK

The Marine Ecosystem

Hetero-trophs

Bacteria

Meso-Micro-

Particulates

Dissolved

Phytoplankton

Consumers

Pico-f

DiatomsFlagell-ates

NO3

PO4

NH4

Si

DIC

Nutrients

Cocco-liths

Meio-benthos

AnaerobicBacteria

AerobicBacteria

DepositFeeders

SuspensionFeeders

Detritus

NutrIents

OxygenatedLayer

ReducedLayer

RedoxDiscontinuity

Layer

AtmosphereO2 CO2 DMS

Ecosystem

Summary

The oceans are absorbing much of the CO2 weproduce and are becoming more acidic as a result.

Ocean acidification is a predictable response, more so than globalwarming.

Ocean acidification and global warming are intrinsically linked – a warmerocean absorbs less CO2

The oceans currently take up 1 tonne of human derived CO2 per year foreach person on the planet.

Almost half of all the human derived CO2 produced in the last 200years is now in the ocean.

Ocean pH has already changed by 0.1 pH units since 1800. (30%increase in hydrogen ions)

pH looks likely to decrease by at least another 0.5 units by 2100

Rate of change in ocean pH is at least 100 times greater than the worldhas experienced for millions of years.

Summary

Seawater pH and carbonate concentrations are critical in marinesystems.

Best scientific information suggests corals (warm and cold) will beadversely affected, along with the communities they support.

Many other organisms dependant on calcification will be affected.

Non-calcifying organisms could also be affected through physiologicalstress, reproductive success and resistance to infection.

Ecosystem functions e.g. nitrogen cycling / eutrophication, will beaffected.

Ecosystems will survive but will they contain the organisms we want orneed?

Ecosystems will be affected.

Sunset over a warming ocean now > 0.1 pH units lower than pre-industrial and which contains over 500 Gt of fossil fuel CO2

Ocean acidification: another argument for control of CO2 emissions

What can we do

about it ???

4 Solutions have beenproposed:

1. Drastically reduce the release of industrial CO2

2. Ocean Fertilisation

3. Ocean sequestration

4. Geological sequestration

0

surface ocean nitrate concentration (mol kg)m -1

5 10 15 20 25 30

Nitrate concentrations in surface water –the “HNLC” regions

Ironex I, Ironex II, Soiree, Eisenex I,Seeds, Series, Sofex, Eisenex II

Iron Fertilisation Experiments

• In the HNLC regions of the open ocean, addition of ironstimulates diatom blooms.

• The ecosystem is transformed from a low-particulate-exportto a high export system.

• There is depletion of inorganic nutrients and dissolved CO2

in the surface.

So is fertilisation the answer ?

• Depending on where fertilisation is done, this depletion canhave serious down stream effects that impact on globalcarbon fixation.

• Enhanced sinking flux leads to lower O2 concentrationsbelow thermocline, potentially N2O production.

From Hanisch(1998)

Typical 1990scartoonsketch ofocean CO2disposalscenarios.

Ocean Sequestration

Deep water sequestration experiments