This document summarizes research on ocean acidification and carbonate chemistry in the Great Barrier Reef. The research aims to determine how exposure to ocean acidification is changing on the reefs and identify drivers of variability. Observations from sites along the Great Barrier Reef and models show that seasonal changes in carbonate chemistry are linked to a winter source of CO2 on the Great Barrier Reef shelf. Coastal inputs also influence carbonate chemistry. The research uses data from ship surveys, moorings and sampling to improve biogeochemical models of the region from individual reef to whole Great Barrier Reef scales.

1. Bronte Tilbrook, Andy Steven, Craig Neill, Mark Baird, Mathieu Mongin and
Yukihiro Nojiri (NIES, Japan)
Blue Planet Symposium, Cairns, 27-29 May 2015
CSIRO OCEANS AND ATMOSPHERE FLAGSHIP
Ocean acidification and carbonate
chemistry of the Great Barrier Reef

2. Ocean acidification
• Ocean CO2 uptake is
decreasing seawater pH
and dissolved carbonate/
aragonite saturation state
• Coral growth decreases as
seawater aragonite
saturation states decrease

3. 3
Less coral growth
Weaker reefs
Habitat loss
Biodiversity decline
Resilience of reef
system to other
stresses (warming,
fishing pressure)
reduced
Economic loss

4. Great
Barrier
Reef
Aragonite Saturation State
Great Barrier Reef carbonate chemistry
Atmospheric
CO2
Aragonite
Saturation
State
pH
Preindustrial
280 ppm
4.5 8.20
Present
395 ppm
3.7 8.09
~2035
450ppm
3.3 8.05
~2100
840ppm
~2.3 ~7.8
Heron Island

5. Great Barrier Reef carbonate chemistry

6. OBJECTIVES:
 Determine exposure of reefs to ocean acidification and how this is
changing
 Identify drivers of variability in carbonate chemistry/acidification. Offshore
& coastal inputs? Reef and inter-reef regions?
 Improve predictions of the response of ecosystems on the GBR to ocean
acidification
Great Barrier Reef biogeochemical observing system

7. Great Barrier Reef and Coral Sea observations and models
Transfuture 5
RTM Wakmatha

8. GBR source water: Coral Sea
Transfuture 5
Aragonite Saturation State

9. Coastal inputs: IMOS Yongala reference site
Yongala
Cyclone Yasi
and major floods
Offshore

10. INSHORE-OFFSHORE CHANGES:
STILL CALCIFYING
 Reef waters indicate net calcification (net growth)
2250 2300 2350
0
20
40
60
80
100
Total Alkalinity, normalised (micromol/kg)
GBR
Coral Sea

11. SEASONAL CHANGE IS OCCURRING
ALONG THE LENGTH OF THE GBR
Salinity
Aragonite Saturation
State
 transport of Coral Sea Water onto the GBR shelf are important
control on the water chemistry
 largest net calcification signal is in the North GBR

12. SEASONAL CHANGES ARE LINKED
TO A WINTER CO2 SOURCECarbonlevels
(TCO2normalised)
 GBR-shelf source of CO2 that is not related to
dissolution (e.g. remineralisation and CO2 uptake)

14. Hydrodynamic/Biogeochemical models
• GBR 4 km model (eReefs/BGC)
• Inner GBR 1 km model (eReefs/BGC)
• Heron Island model development – reef scale
test bed. Used to assess feedback of different
reef communities to modifying water chemistry
and role of water transport and residence time.
Future: Model-data integration from individual reef to
whole of GBR
GBR and offshore sampling
• Ship of opportunity
• IMOS moorings and reference site
• inshore sampling (e.g. coastal carbon
cluster)
• reef scale sampling at Heron Island
test site to parametise reef scale
model of calcification and production

15. Presentation title | Presenter name 15 |
Integra
Support for research:
DEPARTMENT OF THE
ENVIRONMENT