Multiple stressors in the coastal ocean

近海海洋环境科学国家重点实验室（厦门大学）State Key Laboratory of Marine Environmental Science (Xiamen University)

近海海洋环境科学国家重点实验室（厦门大学）State Key Laboratory of Marine Environmental Science (Xiamen University)

Minhan Dai (戴民汉)

Collaborators: JW Liu, WP Jing, XH Guo, ZQ Yin

PICES Annual Meeting, Oct. 16, 2013, Nanaimo, Canada

Overview • Ocean Acidification (OA): Another CO2 problem has

emerged– yet coastal ocean more complex

• Coastal ecosystems under multiple forcings: temp rising + O2 decline+ acidification within a similar time frame

• Need consider the hydrodynamics: e.g., Upwelling/Submarine Groundwater Discharge

• OA observation system & multidisciplinary researches essential and consider the multiple stressors at a system level

Outline

• Coastal Ocean Acidification

• Multiple stressors in the Coastal Ocean

• Concluding Remarks

Ocean Acidification: another CO2 problem: increase in [H+] or drawdown of pH

From PMEL

pH = -log (H+) = -log gH{H+} CaCO3 saturation state: = [Ca2+][CO3

2-]/Ksp’, a > 1 ~supersaturated

When CO2 invades sea water:

• [HCO3-]increases

• [CO32-]decreases

• Ω decreases • a small part of HCO3

-

formed dissociates into carbonates + H+ (“ocean acidification”)

Calcification rate vs. arag in coral reef systems

Shamberger et al. (2011)

Why Coastal Ocean?

• Characterized by complex circulations, abundant river/groundwater input, dynamic sediment boundary and high productivity: large gradients chemically and biologically

• A unique physical-biogeochemical ecosystem links the land and the open ocean but vulnerable

• Boundary processes across the land-margin and margin-ocean are key drivers

An updated province –based global shelf air-sea CO2 flux:

~ 0.36 pg/yr

Dai et al., GRL, 2013

Coastal ocean mitigates more CO2 than the open ocean

pH dynamics in different marine

systems

Hofmann et al. (2011) High-Frequency Dynamics of Ocean pH: A Multi-Ecosystem Comparison. PLoS ONE 6(12): e28983. doi:10.1371/journal.pone.0028983

OA in coastal ocean more dramatic A NE Pacific Coastal Site

(Tatoosh Island, 2000-2008)

- Wootton et al., PNAS, 2008

pH more variable in coastal systems

OnOn--Site ObservationSite ObservationOnOn--Site ObservationSite Observation

Jiang et al., L&O, 2011

MEL-SMMC CO2-A

– Anthropogenic CO2

– Upwellings of low pH waters

– Respirations

– Ground water

Cases: main drivers of OA in coastal ocean

The South China Sea

(Station SEATS, 1998-2009)

- Arthur Chen, MEBC-SCS Conference Abstract, 2010

http://mebc-scs.marine.nsysu.edu.tw/images/Text/Abstract_Chen.pdf

Anthropogenic CO2-driven pH changes in the South China Basin

Surface pH decreasing: －0.002 yr-1

pCO

2 (

atm

)

350

360

370

380

390

pHSW

8.03

8.04

8.05

8.06

Year1998 2000 2002 2004 2006 2008 2010 2012

ar

ag

3.52

3.56

3.60

3.64

3.68

Predicted anthropogenic CO2 induced pH decrease－

0.0019 yr-1

Air pCO2 2 atm yr-1

At TAlk=2200 mol kg-1; Temp=29.0 oC; S=33.5;

PO4=0.01 M; Si(OH)4=2 M

– Anthropogenic CO2

– Upwellings of low pH waters

– Respirations

– Ground water

Examples: OA in coastal ocean

Aragonite Saturation Depth (arag = 1.0) in the Global Oceans

- Feely et al., 2004 Coastal Upwelling System

Western NP vs. Eastern NP

Case I: Continental shelf off the Oregon-California border

(Upwelling in the Eastern NP)

Distribution of the depths of the undersaturated water (arag < 1.0; pH < 7.75) on the continental shelf of western North America.

- Feely et al., 2008

Due to the upwelling process, the corrosive water reaches all the way to the surface in the inshore waters near the Oregon-California border.

- Feely et al., 2008

• Upwelling from depths of 150 to 200 m onto the shelf; • First observation of surface undersaturated waters with respect to aragonite (in open ocean surface waters until 2050); • ~30 mol kg-1 of anthropogenic CO2 lowered arag by ~0.2 units.

Case II: The Northern South China

Sea (NSCS) Shelf (Upwelling in the Western NP)

Leg 1 ( Transects 1-7; Jun 30 - Jul 8)

Leg 2 (Transects 5-2; Jul 9 - Jul 12)

Field work-2008 summer

112 113 114 115 116 117 118 119 120 121 12220

21

22

23

24

25

Longitude (oE)

Latit

ude

(oN

)

Mainland China

Pearl River estuary

1

23

45

6 7

S201aS401a

S401bS401c

113 114 115 116 117 118 119 120 121 12211220

21

22

23

24

25

Upwelling Centers (UC): Low Temperature High DIC Low arag

UC 2 > UC 1

Upwelled waters were transported northward from the position of UC 2 to the position of UC 1 [Gan et al., 2009].

Surface arag values: 2.3 ~ 3.9 Lowest 2.3 in UC 2 Oversaturation state

114 115 116 117 118 119 12020

21

22

23

24

114 115 116 117 118 119 12020

21

22

23

24

114 115 116 117 118 119 12020

21

22

23

24

114 115 116 117 118 119 12020

21

22

23

24Leg 1 Leg 2

Temp. (oC)

23

24

25

26

27

28

29

30

31

114 115 116 117 118 119 12020

21

22

23

24

2.3

2.5

2.7

2.9

3.1

3.3

3.5

3.7

3.9arag

114 115 116 117 118 119 12020

21

22

23

24

arag

Temp. (oC)

1640

1690

1740

1790

1840

1890

1940

1990

2040DIC (mol kg-1)

DIC (mol kg-1)

Surface

UC 2UC 1

Leg 1 Leg 2

arag in the upwelling

DIC (mol kg-1)

-80 -60 -40 -20 0 20 40

ar

ag

1.8

2.0

2.2

2.4

2.6

2.8

3.0

3.2

3.4

Transect 2Transect 4Stations S401a-cTransect 5

-80 -60 -40 -20 0 20 40

fCO

2 (

atm

)

350

400

450

500

550

600

650

700

750Transect 2Transect 4Stations S401a-cTransect 5

DIC (mol kg-1)

-80 -60 -40 -20 0 20 40

ar

ag

1.8

2.0

2.2

2.4

2.6

2.8

3.0

3.2

3.4Transect 2Transect 3Transect 4Transect 5

-80 -60 -40 -20 0 20 40

fCO

2 (

atm

)

350

400

450

500

550

600

650

700

750

Transect 2Transect 3Transect 4Transect 5

Leg 1 Leg 2

(a)

(b)

(c)

(d)

Lowest values in UC 1 and UC 2 were largely imprints of upwelled subsurface waters enriched with both anthropogenic CO2 and respired CO2;

During the northward transport of the upwelled water, however, arag increased whereas fCO2 decreased with increasing DIC. The consistent biological production gradually consumed CO2 and raised [CO3], resulting in the increasing arag pattern in the upwelled water.

NDIC (mol kg-1)1940 1950 1960 1970 1980 1990 2000

NTA

lk (

mol

kg-

1 )

2212

2214

2216

2218

2220

2222

2224

2226

Salinity34.0 34.1 34.2 34.3 34.4

Ca2

+ /N

Ca2

+ (

mol

kg-

1 )

9700

9800

9900

10000

10100

(a) (b)

y=(-0.18±0.06)x+(2577±129) r=0.89

y=(-0.14±0.00)x+(2482±2) r=1.00

y=(265.5±12.5)x+(948.3±428.7) r=0.99

Behaviors of DIC, TAlk and Ca2+ in the upwelled water

• NDIC variations ~30 mol kg-1; NTAlk variations ~6 mol kg-1

• Slopes of NTAlk against NDIC were close to －0.16

• Conservative behavior of Ca2+

No significant impact of the upwelling on the net community calcification!

OC metabolism: 106CO2+122H2O+16HNO3+H3PO4↔ (CH2O)106(NH3)16H3PO4+138O2, TAlk/DIC=－0.16 IC metabolsim: Ca2++2HCO3

-↔CaCO3+CO2+H2O, TAlk/DIC=2

Summary for the NSCS upwelling

• Upwelling delivered low arag waters onto the shelf, but arag values are still > 1.0;

• Enhanced OC production during the upwelling further increased arag;

• The patterns of arag are largely controlled by water circulation and biological activities at present;

• Oversaturation for now.

Shellfish 79%

Seaweed 11%

Fish 5%

Crustacean 5%

Composition of mariculture yields of China in 2002 [Zhang et al., 2005]

• Corrosive waters with < 1.0 may be possible on most of wide shelves including the NSCS shelf!

• How the calcifying organisms, including many species of shellfish of economic importance to coastal regions, deal with this intermittent exposure of corrosive waters?

China is the largest mariculture country, contributing to 68.81% of the total global yields (FAO, 2006);

Shellfish is the most important composition.

Production of shell fish in 2008 was ~ 10 MT

Context

Aragonite Saturation Depth (arag = 1.0) in the Global Oceans

- Feely et al., 2004

Source Water Depth ~150 m ~150 m

Source Water pH ~7.95 < 7.75

Source Water arag ~1.9 < 1.0

Aragonite Saturation Depth

~500 m in the Western NP

100-300 m in the Eastern NP

The contrasting scenarios between the two cases are related to the different “acidity” of source waters of upwelling.

– Anthropogenic CO2

– Upwellings of low pH waters

– Respirations/nutrification

– Ground water

Examples: OA in coastal ocean

Aerobic respiration

(CH2O)106(NH3)16H3PO4 + 138 O2 + 18 HCO3

– 124 CO2 + 140 H2O + 16 NO3

– + HPO42–

Nitrification

NH4+ + 1.89 O2 + 1.98 HCO3–

0.984 NO3– + 0.016 C5H7O2N

+1.90 CO2 + 2.93 H2O

Fig A from Zhang Cao Fig B from Guo et al., 2008, CSR

Pearl River Estuary

Respiration + Nitrification induced pH drawdown in the Pearl River

DO saturation (%)

Dep

th (m

)

– Anthropogenic CO2

– Upwellings of low pH waters

– Respirations

– Ground water

Examples: OA in coastal ocean

Acidification in Hainan Coral Reef

Low pH in Sanya fringing reef system

2-6 2-7 2-8 2-9 2-10 2-11 2-12 2-13 2-14

pH

_to

tal

sca

le_

@2

5℃

7.7

7.8

7.9

8.0

8.1

8.2

pH Sanya Coral Reef

pH Sanya Bay

2012-

Major processes related to OA in the coastal ocean

River Plume

High TA Input pH ↑

Low TA Input pH ↓

Coastal Upwelling High CO2 pH ↓

Upwelling + OM Respiration CO2 ↑ pH ↓

OA pH ↓ Eutrophication CO2 ↓ pH ↑

Photosynthesis CO2 ↓ pH ↑ Respiration CO2 ↑ pH ↓

Coastal ocean has large natural variability due to changes in physical and biological conditions and various anthropogenic impacts including:

Basics about coastal OA

• OA in coastal ocean? pH change in coastal ocean may be more complex, driven by anthropogenic CO2, riverine/groundwater input (eutrophication & respiration) and water circulation (upwelling of low pH/DO waters), and other biogeochemical reactions under low/no DO.

• Physical dynamics must be considered.

• OA observation is essential to set the stage of OA in coastal ocean

• Coastal ocean is particularly facing multiple stressors

Outline

• Coastal Ocean Acidification

• Multiple stressors in the Coastal Ocean

• Concluding Remarks

Multiple stressors in marine ecosystems

Doney et al., 2010

Multiple forcings & responses: offset? Amplifying?

–Eutrophication-hypoxia + OA +temp?

–SGD + upwelling +….

Multiple stressors: case 1

Enhanced OA by hypoxia and effect of temp?

Hypoxia in the East China Sea off the Changjiang (Yangtze River) Estuary

Li & Zhang, 2002

(Wang, 2006)

(Zhu et al., 2011)

DO< 2 mg/L, ~10000 – 20000 km2

Taiwan: ~32,260 km2

SST anomaly of global ocean in 20th century

The enhanced warming over the global subtropical western boundary currents in the 20th century might be attributable to the poleward shift of their mid-latitude extensions and/or intensification in their strength.

All data points with S > 31 and depth > 10 m are selected.

Enhanced OA by respiration in hypoxic zone off the Changjiang estuary

Survey in Aug. 2011

The offshore water:

S = 33.2716

T = 26.7065

P = 10.471 dbar

DO = 208.31 μmol/kg

DIC = 1937.25 μmol/kg

TA = 2227.98 μmol/kg

NO3+NO2 = 0 μmol/kg

Silicate = 0 μmol/kg

Phosphate = 0 μmol/kg

pCO2_Calculted = 420 μatm

Considering the slight TA change during respiration by TA:O=-17/138; DIC:DO=106/138

7.2

7.4

7.6

7.8

8.0

8.2

-50 0 50 100 150 200 250

pHT

O2 (μmol/kg)

Pre-industry

OAPI-P = -0.138Present

pHT = 8.05

OA'PI-P =

-0.209

pHT=

7.65

OA'P-F =

-0.360

OAP-F = -0.238

OA

Hypoxia

280 ppm

420 ppm

800 ppm

Model 1: S, T, P, and Nutrients Constant

BC: Buffering Capacity; PI: preindustrial pCO2 (280 ppm); P: present pCO2 (420 ppm ); F: future pCO2 (year 2100, 800 ppm)

Consider the slight TA change during respiration by TA:O=-17/138; DIC:O=106/138

Model 2: S, P, Nutrients Constant, T Changes

7.2

7.4

7.6

7.8

8.0

8.2

-50 0 50 100 150 200 250

pHT

O2 (μmol/kg)

Pre-industry

OAPI-P = -0.138

Present

pHT = 8.05

OA'PI-P =

-0.203

pHT=

7.65

OA'P-F =

-0.318

OAP-F = -0.230

OA

Hypoxia

280 ppm, T-0.76oC

420 ppm, T constant

800 ppm, T+4oC

Consider the temperature change but no effect of temperature on respiration Tpreindustry: T-076oC Tyear 2100 : T+4oC

The values beside the “/” come from the model 1 (left) and model 2 (right)

7.2

7.4

7.6

7.8

8.0

8.2

-50 0 50 100 150 200 250

pHT

O2 (μmol/kg)

OA'PI-P = -0.209/-0.203

pHT= 7.65

OA'P-F = -0.360/-0.318

Pre-industry

OAPI-P = -0.138/-0.138

Present

pHT = 8.05

OAP-F = -0.238/-0.230

OA

Hypoxia

280 ppm

420 ppm

800 ppm

280 ppm, T-0.76oC800 ppm, T+4oC

Model 1 vs 2: Higher temperature buffers the effect of ocean acidification

Because the effect of temperature on CR, pH will drop 0.21unit (RespF-RespP) in the future than at present

7.2

7.4

7.6

7.8

8.0

8.2

-50 0 50 100 150 200 250

pHT

O2 (μmol/kg)

Pre-industry

OAPI-P = -0.138

Present

pHT = 8.05OA'PI-P = -0.187

pHT= 7.82

OA'P-F = -0.438

OAP-F = -0.230

OA

Hypoxia

280 ppm, T-0.76oC

420 ppm, T constant

800 ppm, T+4oC

Considering the effect of temperature on respiration

Reminder

Subsurface enhancement of oxygen consumption and/or ocean acidification will depend on the seasonal hydrodynamics (if transport to the open ocean)

Multiple stressors: case 2

Coastal Coral system under the impact of groundwater, upwelling

and anthropogenic CO2?

Acidification in Coral Reef Environment

12'

13'

14'

15'

16'

17'

18 18'

109 20'21' 22' 23' 24' 25' 26' 27' 28' 29' 30' 31'

5m

5m10m

10m

10m

10m

20m

20m

30m30m

Sanya River

Dongmao Island

Sanya City

Ximao Island

Luhuitou Byland

Hainan Island, China

Sanya Bay

107 109 111 11317

19

21

23

Sanya National Coral Reef Reserves:

• fringing reef

• length ~ 3 km and width ~ 250~500 m

Acidification in Hainan Coral Reef

Low pH in Sanya fringing reef system

2-6 2-7 2-8 2-9 2-10 2-11 2-12 2-13 2-14

pH

_to

tal s

cale

_@2

5℃

7.7

7.8

7.9

8.0

8.1

8.2

pH Sanya Coral Reef

pH Sanya Bay

2012-

De

pth

(m

)

0.5

1.0

1.5

2.0

2.5

2-6 2-7 2-8 2-9 2-10 2-11 2-12 2-13 2-14

22

4R

a d

pm

(1

00

L)-1

0

30

60

90

120

Salin

ity

33.3

33.4

33.5

33.6

33.7

33.8

224Ra Sanya Bay

Salinity Sanya Bay

2012-

Tidal-driven Submarine Groundwater Discharge (SGD) in Sanya fringing reef

Low salinity and high 224Ra during spring tide indicates the intrusion of SGD

Upwelling in Sanya Coral Reef

108 110 112

18

19

20

DD203DD202

SY

Salinity (PSU)33.0 33.3 33.6 33.9 34.2 34.5 34.8

Pote

ntia

l Tem

p(℃

)

05

101520253035

DD203DD202SY-Coral Reef

Salinity (PSU)32.0 32.4 32.8 33.2 33.6 34.0 34.4

Pote

ntia

l Tem

p (℃

)

23

24

25

26

27

28

SY-Coral Reef

SY station is located at the edge of coral reef ecosystem.

Average depth of SY station: 14m

Upwelled water

Contribution of SGD to acidification

Large diurnal changes of pH and pCO2 in spring tide when SGD was significant: up to 70% of the changes.

The aragonite saturation decreased to 1.77 during low tide of spring tide, a potential threat to coral reef systems.

2-6 2-7 2-8 2-9 2-10 2-11 2-12 2-13 2-14

arag

onite

satu

ratio

n

1

2

3

4

5

2012-

Threats to coral reef around Hainan

Upwelling

Hainan Island

Coral reefs in Hainan waters account for more than 98% of the total area of that in China (Wu et al., 2012).

Current and Future Scenarios

In 2100

• air pCO2=750 atm

• pH=7.6~7.8

• CaCO3 saturation down to 1.62~2.06.

Multiple stresses to coastal coral reefs

Upwelling low pH

Groundwater table High tide

Low tide

Tidal pumping

Groundwater low pH

Anthropogenic CO2

Rising air temperature

Upwelling low pH

Groundwater table ↑↓？ High tide

Low tide

Tidal pumping

Anthropogenic CO2

Sea level?

Rising air temperature

Precipitation↑↓？

Groundwater ？low pH

Multiple stresses to coastal coral reefs: future changes?

Gordian Knot?

from Boyd, 2013, Nature Climate Change, 3, 530-533

Summary

• Coastal ecosystem are clearly under multiple stressors

– Hypoxic zones

– Coral reef systems

• The ecosystem responses/feedbacks to multiple stressors are complex.

Concluding remarks • Penetration of CO2 in the coastal ocean has emerged

• The geochemistry of acidification is based on very well defined knowledge – yet coastal ocean more complex

• Coastal ecosystems under multiple forcings: temp rising + O2 decline+ acidification within a similar time frame

• Need consider the hydrodynamics: e.g., Upwelling/SGD

• OA observation system & multidisciplinary researches essential

CHOICE-C: Carbon Cycling in China Seas- budget, controls and ocean acidification

A national program funded by Ministry of Science and Technology through National Basic Research Program of

China (973 Program) & a SOLAS endorsed program

Jan 2009-Aug 2013

http://973oceancarbon.xmu.edu.cn

Cocean

Air-sea CO2 flux

Processes

Ecological effects

Future trend

Thank you for your audience!

Funding sources: NSF-China, MOST