1. Climate change and marine ecosystems
Oxygen 
Hypoxia
Oxygen minimum zone (OMZ)
Dead zones
pCO2  pH 
Acidification
Corals
Southern ocean
Upwelling zones
Estuaries
(see Liz’s 11/09 and 11/28 lectures for review of carbonate chemistry and gas dissolution)

2. Main processes affecting dissolved gas distribution in ocean:
Mixing at the surface (equilibrium with atmosphere)
Respiration produces CO2, takes up O2
Photosynthesis Produces O2, takes up CO2
Solubility: colder, fresher water holds more gas than warmer, saltier water. Pressure increases the solubility of gas.
Thermohaline circulation

3. Dissolved Oxygen (DO) Hypoxia (low oxygen): DO < 2.0 mg/L
DO <0.5 mg/L in deep water (below mixed layer)
1 mg/L = 0.7 mL/L DO at STP
Main causes of hypoxia:
High primary productivity  bacterial decomposition
Warming
Stratification
Advection of low-O2 water
Sources: photosynthesis, mixing at the surface, and sinking of cold, fresh water at the poles
Temperature effect: Colder, fresher water holds more dissolved oxygen than warmer, saltier water
Pressure effect: Pressure increases oxygen solubility

4. “Oxygen Minimum Zone” (OMZ) Defined as region where DO<0.5 mL/L
Recall that oxygen reaches a minimum at mid-depth

5. There is life in the OMZ, but special adaptations are needed to tolerate low DO
Slow metabolism
Small bodies
Larger gills/lungs
Efficient blood pigments
Vampire squid has low metabolism, small body, large gills, more efficient blood pigments

6. OMZ has expanded over last 50 years
Eastern tropical
North Atlantic Ocean
Eastern equatorial
Pacific Ocean
Expanding oxygen minimum zone reduces the “refuge” available to animals trying to escape warm surface waters. Few surface dwellers have adaptations for tolerating hypoxia.
White lines: DO=1.4 mg/L
White lines: DO=1 mg/L
Dissolved oxygen concentration (mmol/kg shown in color) versus time (1960–2008) and pressure (1 dbar ~ 1 m).
Stramma et al. 2008

7. Persistent hypoxia over large area creates Dead zones
Large input of nutrients generates a phytoplankton bloom
Dead phytoplankton sink and are attacked by bacteria that remineralize them while using up available oxygen
Hypoxia leads to death of larger animals (fish, crabs, etc.)
Two main causes:
Eutrophication (e.g., Gulf of Mexico)
Upwelling (e.g., Oregon)

8. (In the Gulf of Mexico)

9. Eutrophication-induced “dead zone” occurs each summer in Gulf of Mexico
-First appeared in 1950’s
-Size of Connecticut on average
-Has grown as big as New Jersey
>200,000 metric tons of fish and zooplankton lost annually to hypoxia
Texas LA MS
Dead zone first reported in 50’s, mapped since the 80’s. Growing in size and duration
States increasing in size: Rhode Island (1.5K sq mi), Delaware (2.5K sq. mi), Connecticut (5.5K sq. mi), New Jersey (8.7 sq. mi), New Hampshire (9.3 sq mi)

10. Oregon dead zone linked to climate change

11. Upwelling-induced
The upwelled water is lower in dissolved oxygen as the OMZ gets larger and deep waters become more hypoxic

12. Dead zone first appeared in 2002, now a regular summer feature
globalchange.gov
Dead zone first appeared in 2002, now a regular summer feature
Growing larger, more persistent, moving north
2006 dead zone was the size of Rhode Island

13. Carbonate system maintains an equilibrium
Carbonate + CO2 + water  bicarbonate + H ion
Equilibrium concentrations (not to scale)

14. Carbonate system maintains an equilibrium
Add CO2
Push equation
to the right
All concentrations must change

15. Carbonate system maintains an equilibrium
Reach new equilibrium with
Lower concentrations of CO32-
Higher concentrations of H+
Remember that increasing H+ leads to lower pH. Stomach ACID has a very low pH of 2 to 3.   
 CaCO3
 pH
New Equilibrium concentrations

16. Graphical representation of carbonate system

17. Ocean Acidification Ocean pH is projected to drop by ~0
Ocean Acidification Ocean pH is projected to drop by ~0.4 by 2100 Corresponds to a 50% drop in [CO32-]
now
Rost et al (redrawn from Wolf and Gladrow 2008)

18. [CO32-] needed to form calcium carbonate CaCO3
Aragonite Calcite
Hard corals Soft corals
Pteropods Coccolithophores
Snail and bivalve larvae Some adult snails and bivalves
Some adult snails Sponges
Foraminifera
Sea urchins
Barnacles
Sponges
Reduction in [CO32-] makes it harder for marine organisms to make calcium carbonate body parts (skeletons, shells, spicules, spines, etc.)

19. Ω = saturation state for CaCO3
- Depth where Ω = 1 is the saturation horizon, aka lysocline
- If Ω <1, carbonate ion is undersaturated, water is corrosive
Saturation state = thermodynamic potential for mineral to form or dissolve
Karag = 10^-8.3
Kcalc = 10^-8.5
Lysocline occurs at depth where saturation state = 1
aragonite dissolves more easily (at higher pH) than calcite

20. Projected pH varies with climate scenario
Projected pH varies with climate scenario. Map hides important regional variation.
RCP 2.6
70% reduction in CO2 from 2010 to 2100
RCP 8.5
300% increase in CO2 from 2010 to 2100
IPCC AR5 2013

21. When deep water first forms in North Atlantic, its pCO2 is in equilibrium with atmosphere. Water is fairly cold.
Eventually the deep water returns to the surface, and its pCO2 re-equilibrates with the atmosphere.
The deep water sinks to depths and travels south through the Atlantic, picking up CO2 from respiration.
The deep water travels North through the Pacific. It continues to pick up CO2 from respiration.
Deep water travels around Antarctica. It picks up more CO2 from respiration and can hold more as it gets colder.

22. Atlantic Ocean Pacific Ocean Temperature Depth (m) Depth (m)
Organisms in Pacific more vulnerable to acidification than organisms in Atlantic. Pacific mixed layer is shallower, and deep water has been cut off longer.
Atlantic Ocean
Depth (m)
South pole Equator North Pole
Pacific Ocean
Depth (m)
South pole Equator North Pole
Temperature

23. (dissolution occurs at <100% or
Pacific Atlantic
2011-
2030
% saturation
of aragonite
(dissolution occurs at <100% or
~100Ωarag)
2080-
2099
CCD is around 5000 m in Atlantic and m in Pacific
black line = projected saturation horizon
(depth below which aragonite is undersaturated)
IPCC Report 2007

24. Aragonite will be under-saturated at mid- to high latitudes by 2100
Aragonite will be under-saturated at mid- to high latitudes by Reef-building corals live in shallow water at low latitudes and are less at risk than high-latitude or deep-water corals.
% saturation of aragonite
(dissolution at <100%)
black line: projected saturation horizon
IPCC Report 2007

25. Reef-building
coral distribution
Most live between 30o N and 30o S
Lots of light here
Cold-water coral distribution
Some at very high latitudes
Some in deep sea (no zooxanthellae)

26. Coral calcification rate is lower and more affected by pH in dark than in light
Leclercq et al. 2001

27. Acidification vs. Bleaching
Aragonite saturation state Maximum monthly SST
Patterns are reversed because of temperature effects: Heat causes bleaching but also reduces the dissolved CO2 concentration.
Healthy
Marginal
Severe
Severe
Marginal
Healthy
Guinotte et al. 2003

28. Aragonite will be under-saturated at mid- to high latitudes by 2100
Aragonite will be under-saturated at mid- to high latitudes by Polar organisms are at great risk.
% saturation of aragonite
(dissolution at <100%)
Aragonite saturation horizon is different from carbonate compensation depth (CCD) that Liz talked about. It’s more like the lysocline, where dissolution begins to exceed formation. But saturation horizon is shallower for aragonite.
black line: projected saturation horizon
IPCC Report 2007

29. Emiliana huxleyi have thinner coccoliths and lower sinking velocities at high pCO2 in lab
Kleypas et al. 2006
Biermann & Engel 2010

30. Pteropods in Southern Ocean already showing reduced calcification
“Sea butterfly,” Limacina helicina
Bednaresk et al. (2012) reported finding pteropods in Scotia Sea (Atlantic part of Southern Ocean) with degraded shells

31. California Current upwelling brings cold, (hypoxic), acidified water near shore
Summer 2007
(Beginning of La Niña)
Colors indicate depth of saturation horizon. Below this depth,
Ω < 1 and pH < 7.75
Blue: 200 m
Red/pink: < 40 m
Feely et al. 2008

32. <-Offshore California coast ->
Aragonite
saturation state pH
pCO2
Data from May/June 2007, during La Niña
Feely et al. 2008

33. low buffering capacity high buffering capacity
Estuarine pCO2
River
pCO2 ≈ 1000’s of μatm
low buffering capacity
Lower pH
Ocean
pCO2 ≈ μatm
high buffering capacity
Higher pH
CO2 sources
Atmosphere (not at equilibrium)
*Plankton respiration
**Benthic respiration
CO2 sources
Atmosphere (equilibrium)
Plankton respiration
pCO2
Tidal height pH
time

34. Collapse of Olympia oyster in Puget Sound, WA linked to ocean acidification
Olympia oysters in being harvested at low tide
Olympia oyster larva
A $110 Million/year business
Starting in 2005, few larvae survived
Fishery has all but collapsed WA

35. Puget Sound is an estuary in an upwelling region (double whammy)
Data from oyster hatchery
Biomass doubles
Complete mortality
No gain in biomass
Relative production is change in biomass from D-stage to competency
Barton et al. 2012