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

Multiple stressors in the coastal ocean

Minhan Dai (戴民汉)

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

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) 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

When CO2 invades sea water: - • [HCO3 ]increases 2- • [CO3 ]decreases From PMEL • Ω decreases + + - pH = -log (H ) = -log gH{H } • a small part of HCO3 CaCO3 saturation state:  formed dissociates into 2+ 2- +  = [Ca ][CO3 ]/Ksp’, carbonates + H (“ocean a > 1 ~supersaturated acidification”)

Calcification rate vs. arag in coral reef systems

Shamberger et al. (2011) Why Coastal Ocean?

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

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 OnOn--SiteSite ObservationObservation

pH more variable in coastal systems

Jiang et al., L&O, 2011 MEL-SMMC CO2-A Cases: main drivers of OA in coastal ocean

– Anthropogenic CO2 – Upwellings of low pH waters – Respirations – Ground water Anthropogenic CO2-driven pH changes in the South Basin Predicted anthropogenic The South China Sea CO2 induced pH decrease－ (Station SEATS, 1998-2009) 0.0019 yr-1

390 Surface pH decreasing: －0.002 yr-1 380  atm)

( 370 2

CO 360 p 350 8.06

8.05 SW

8.04 pH

3.68 8.03 3.64

arag 3.60  3.56 3.52 - Arthur Chen, MEBC-SCS Conference Abstract, 1998 2000 2002 2004 2006 2008 2010 2012 2010 Year http://mebc- -1 scs.marine.nsysu.edu.tw/images/Text/Abstract_Chen.pdf Air pCO2 2 atm yr At TAlk=2200 mol kg-1; Temp=29.0 oC; S=33.5; PO4=0.01 M; Si(OH)4=2 M Examples: OA in coastal ocean

– Anthropogenic CO2 – Upwellings of low pH waters – Respirations – Ground water 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.

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. - Feely et al., 2008 Case II: The Northern South China Sea (NSCS) Shelf (Upwelling in the Western NP) Field work-2008 summer Leg 1 ( Transects 1-7; Jun 30 - Jul 8)

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

2525 Mainland China 2424 S401c S401b

N) S401a o 2323 S201a estuary

2222 6 7 5 Latitude ( Latitude 2 4 1 3 2121

2020 112112 113113 114114 115115 116116 117117 118118 119119 120120 121121 122122 Longitude (oE) Leg 1 Surface Leg 2 24 24 31 Temp. (oC) Temp. (oC) 30 Upwelling Centers (UC): 23 23 29 Low Temperature 28 22 22 27 High DIC 26 Low arag 21 UC 1 21 UC 2 25 24 UC 2 > UC 1

20 20 23 114 115 116 117 118 119 120 114 115 116 117 118 119 120 24 24 DIC DIC 2040 -1 -1 1990 Surface arag values: 23 (mol kg ) 23 (mol kg ) 1940 1890 2.3 ~ 3.9 22 22 1840 Lowest 2.3 in UC 2 1790 21 21 1740 Oversaturation state 1690

20 20 1640 114 115 116 117 118 119 120 114 115 116 117 118 119 120 24 24 3.9 arag arag Upwelled waters were 3.7 23 23 3.5 transported 3.3 northward from the 22 22 3.1 position of UC 2 to the 2.9 position of UC 1 [Gan 21 21 2.7 2.5 et al., 2009].

20 20 2.3 114 115 116 117 118 119 120 114 115 116 117 118 119 120 arag in the upwelling

Leg 1 Leg 2 3.4 3.4 Transect 2 3.2 Transect 3 3.2 Lowest values in UC 1 and Transect 4 3.0 Transect 5 3.0 UC 2 were largely imprints 2.8 2.8 of upwelled subsurface 2.6 2.6 waters enriched with both arag arag   2.4 2.4 anthropogenic CO2 and Transect 2 2.2 Transect 4 2.2 respired CO2; 2.0 Stations S401a-c 2.0 (a) Transect 5 (c) 1.8 1.8 During the northward -80 -60 -40 -20 0 20 40 -80 -60 -40 -20 0 20 40 transport of the upwelled DIC (mol kg-1) DIC (mol kg-1) water, however, arag -80 -60 -40 -20 0 20 40 -80 -60 -40 -20 0 20 40 750 750 increased whereas fCO2 Transect 2 700 Transect 4 700 decreased with increasing 650 Stations S401a-c 650  Transect 5 DIC. The consistent 600 600 biological production atm) atm)  

( 550 550 ( gradually consumed CO2 2 2 500 500 and raised [CO ], resulting CO CO 3 f f 450 Transect 2 450 in the increasing arag Transect 3 400 Transect 4 400 pattern in the upwelled (b) Transect 5 (d) 350 350 water. Behaviors of DIC, TAlk and Ca2+ in the upwelled water

2226 10100 y=(-0.18±0.06)x+(2577±129) r=0.89 )

2224 -1 )

-1 10000 2222 y=(265.5±12.5)x+(948.3±428.7) mol kg

2220 r=0.99  ( mol kg 9900  2218 2+

2216 y ± x ± /NCa =(-0.14 0.00) +(2482 2) 9800 NTAlk ( NTAlk r=1.00 2+ 2214 Ca (a) (b) 2212 9700 1940 1950 1960 1970 1980 1990 2000 34.0 34.1 34.2 34.3 34.4 NDIC (mol kg-1) Salinity • NDIC variations ~30 mol kg-1; NTAlk variations ~6 mol kg-1 • Slopes of NTAlk against NDIC were close to －0.16 OC metabolism: 106CO2+122H2O+16HNO3+H3PO4↔ (CH2O)106(NH3)16H3PO4+138O2, TAlk/DIC=－0.16 2+ - IC metabolsim: Ca +2HCO3 ↔CaCO3+CO2+H2O, TAlk/DIC=2 • Conservative behavior of Ca2+

No significant impact of the upwelling on the net community calcification! 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. Context • 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 Seaweed Fish Crustacean 11% 5% 5% the total global yields (FAO, 2006); Shellfish is the most important composition. Shellfish 79% Production of shell fish in 2008 Composition of mariculture was ~ 10 MT yields of China in 2002 [Zhang et al., 2005] 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 ~500 m in the 100-300 m in the Saturation Depth Western NP Eastern NP The contrasting scenarios between the two cases are related to the different “acidity” of source waters of upwelling. Examples: OA in coastal ocean

– Anthropogenic CO2 – Upwellings of low pH waters – Respirations/nutrification – Ground water Respiration + Nitrification induced pH drawdown in the Pearl River Aerobic respiration

(CH2O)106(NH3)16H3PO4 + 138 – O2 + 18 HCO3  124 CO2 + – 2– Pearl River Estuary 140 H2O + 16 NO3 + HPO4

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 DO saturation (%)

Depth (m) Examples: OA in coastal ocean

– Anthropogenic CO2 – Upwellings of low pH waters – Respirations – Ground water Acidification in Coral Reef

Low pH in fringing reef system

8.2 ℃ 8.1 8.0 7.9 pH Sanya Coral Reef 7.8 pH pH_total scale_@25 pH_total 7.7 2012- 2-6 2-7 2-8 2-9 2-10 2-11 2-12 2-13 2-14 Major processes related to OA in the coastal ocean

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

River Plume

High TA Input pH ↑ Eutrophication CO2 ↓ pH ↑ OA pH ↓ Low TA Input pH ↓

Photosynthesis CO2 ↓ pH ↑ Respiration CO2 ↑ pH ↓

Upwelling + OM Respiration

CO2 ↑ pH ↓ Coastal Upwelling

High CO2 pH ↓ 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 ( River) Estuary

(Wang, 2006)

Li & Zhang, 2002 DO< 2 mg/L, ~10000 – 20000 km2 Taiwan: ~32,260 km2

(Zhu et al., 2011) 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. Enhanced OA by respiration in hypoxic zone off the Changjiang estuary

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

Survey in Aug. 2011

The offshore water: TA = 2227.98 μmol/kg S = 33.2716 NO3+NO2 = 0 μmol/kg T = 26.7065 Silicate = 0 μmol/kg P = 10.471 dbar Phosphate = 0 μmol/kg DO = 208.31 μmol/kg pCO2_Calculted = 420 μatm DIC = 1937.25 μmol/kg Model 1: S, T, P, and Nutrients Constant

8.2 Pre-industry OAPI-P = -0.138 Present 8.0 pHT = 8.05

OAP-F = -0.238 T 7.8 OA'PI-P = -0.209 pH 7.6 pHT= 7.65 280 ppm 7.4 OA 420 ppm OA'P-F = 800 ppm -0.360 7.2 -50 0 50 100 150 200 250 Hypoxia O2 (μmol/kg)

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

BC: Buffering Capacity; PI: preindustrial pCO2 (280 ppm); P: present pCO2 (420 ppm ); F: future pCO2 (year 2100, 800 ppm) Model 2: S, P, Nutrients Constant, T Changes

8.2 Pre-industry OAPI-P = -0.138 Present 8.0 pHT = 8.05

OA'PI-P = OAP-F = -0.230 T 7.8 -0.203 pH 7.6 280 ppm, T-0.76oC pHT= 7.65 420 ppm, T constant o 7.4 800 ppm, T+4 C OA'P-F = OA -0.318 7.2 -50 0 50 100 150 200 250 Hypoxia O2 (μmol/kg) Consider the slight TA change during respiration by TA:O=-17/138; DIC:O=106/138 Consider the temperature change but no effect of temperature on respiration o o Tpreindustry: T-076 C Tyear 2100 : T+4 C Model 1 vs 2: Higher temperature buffers the effect of ocean acidification

8.2 Pre-industry OAPI-P = -0.138/-0.138 Present

8.0 pHT = 8.05

OA'PI-P = -0.209/-0.203 OAP-F = -0.238/-0.230

T 7.8 pH 7.6 280 ppm pHT= 7.65 420 ppm 800 ppm o 7.4 OA 280 ppm, T-0.76 C o OA'P-F = 800 ppm, T+4 C -0.360/-0.318 7.2 -50 0 50 100 150 200 250 Hypoxia O2 (μmol/kg)

The values beside the “/” come from the model 1 (left) and model 2 (right) Considering the effect of temperature on respiration

8.2 Pre-industry OAPI-P = -0.138 Present OA'PI-P = -0.187 8.0 pHT = 8.05

OAP-F = -0.230

T 7.8 pHT= 7.82 pH 7.6 OA'P-F = -0.438 280 ppm, T-0.76oC 7.4 OA 420 ppm, T constant 800 ppm, T+4oC

7.2 -50 0 50 100 150 200 250 Hypoxia O2 (μmol/kg)

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

18 18' Hainan Island, China 5m 17' Sanya City Sanya National Coral 10m Sanya Bay 5m 16' Sanya River Reef Reserves: 15' 10m Ximao Island

14' 20m Dongmao Island • fringing reef 13' 23 20m 10m 21 Luhuitou 12' 19 Byland 30m 10m • length ~ 3 km and 17 107 109 111 113 30m 109 20'21' 22' 23' 24' 25' 26' 27' 28' 29' 30' 31' width ~ 250~500 m

Acidification in Hainan Coral Reef

Low pH in Sanya fringing reef system

8.2 ℃ 8.1 8.0 7.9 pH Sanya Coral Reef 7.8 pH Sanya Bay pH_total scale_@25 pH_total 7.7 2012- 2-6 2-7 2-8 2-9 2-10 2-11 2-12 2-13 2-14 Discharge (SGD) in Sanya fringing reef Sanya reef in fringing (SGD) Discharge Tidal-driven Submarine Groundwater SubmarineGroundwater Tidal-driven tideindicates theintrusion of SGD Low salinityand high 224 -1 2012- Ra dpm (100 L) Depth (m) 120 0.5 1.0 1.5 2.0 2.5 30 60 90 0 - - - - -0 21 -2 21 2-14 2-13 2-12 2-11 2-10 2-9 2-8 2-7 2-6 224 Ra during springRa Salinity 224 Ra Sanya Bay Sanya Bay 33.3 33.4 33.5 33.6 33.7 33.8

Salinity 20 Upwelling in Sanya Coral Reef 19 DD202 DD203 SY station is located at the edge of 18 SY coral reef ecosystem.

108 110 112 Average depth of SY station: 14m

28 35 ) ) 30 ℃ 27 ℃ 25 26 20 25 Upwelled water 15 10 DD203 24 DD202 Potential Temp( Potential

Potential Temp ( Temp Potential 5 SY-Coral Reef SY-Coral Reef 23 0 32.0 32.4 32.8 33.2 33.6 34.0 34.4 33.0 33.3 33.6 33.9 34.2 34.5 34.8 Salinity (PSU) Salinity (PSU) 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.

5

4

3

2 aragonite saturation aragonite 1 2012- 2-6 2-7 2-8 2-9 2-10 2-11 2-12 2-13 2-14 Threats to coral reef around Hainan

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

Hainan Island

Upwelling 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

Rising air temperature

Anthropogenic CO2 Groundwater table High tide

Tidal pumping Low tide Groundwater low pH Upwelling low pH Multiple stresses to coastal coral reefs: future changes?

Rising air temperature

Precipitation↑↓？

Anthropogenic CO2 Groundwater table ↑↓？ High tide

Tidal pumping Sea level? Low tide Groundwater ？ low pH Upwelling low pH 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 Thank you for your audience! 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

Air-sea CO2 flux

Processes

Ecological Cocean effects

Future trend

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

Funding sources: NSF-China, MOST