Historical and Future Ocean Acidification changes around Australia

Transcription

1 Historical and Future Ocean Acidification changes around Australia Andrew Lenton, Bronte Tilbrook, Richard Matear, Tristan Sasse, Yukihiro Noriji, Kathy McInnes and Julian O Grady

2 The ocean plays a critical role the Global Carbon Cycle Sabine et al, 2004 Le Quéré et al, % of the total anthropogenic emissions 2

3 What is Ocean Acidification? Carbon Dioxide past Past By 2100, atmospheric CO 2 will exceed the highest levels in the last 45 Million years Ocean acidification is a predictable and measurable consequence of rising atmospheric CO 2. 3

4 Why do we care about OA? 4

5 Historical Changes: Motivation Reconstruct changes in ocean acidification around Australia since the pre-industrial to present day Important for: (i) characterizing the mean state around Australia in the present day (ii) correctly attribution observed responses over the historical period; (ii) assess how well climate models (e.g. IPCC AR5) capture observed changes in ocean acidification (iii) provide important boundary conditions for high-resolution regional models e.g. ereefs 5

6 However Observations are limited We reconstruct the changes in ocean chemistry through: Ocean sea surface temperatures HadiSST Ocean sea surface salinity CSIRO Atlas of Regional Seas (CARS) Reconstructed oceanic pco 2 history the value of surface seawater Neural Network approach based on observations (Sasse, et al 2013) and the atmospheric history Alkalinity for this we needed to develop a new alkalinity-salinity relationship 6

7 Alkalinity-Salinity Relationship More than 2700 observations since 1993 In the absence of long-term salinity observations we use climatological salinity 7

8 Assessing the Aragonite Saturation State Uncertainty of 0.1 in aragonite staturation state and 0.02 in ph Captures well the seasonality and mean state except at coastal sites e.g. Ningaloo

9 Mean state and Seasonal Variability Lenton et al, 2016 Large-scale pattern is driven by ocean chemistry and warming ph Large-seasonal variability: driven by mixing and warming (for aragonite) Implications for observations and understanding change

10 Historical Changes around Australia Lenton et al, 2016 Reconstructed changes over the last 140 years - based on observations and atm hist. Reduction of 0.48 units in aragonite saturation state and of 0.09 in ph (0.1 global) The changes and variability in aragonite saturation state and ph are spatially different, implying that biological responses and impacts are also quite different independent! 10

11 Projected Changes assessing with NRS Q: (i) How well do ESMs represent the Oceans around Australia in terms of OA? (ii) How does OA change into the future Based on a suite of 6 CMIP6 ESMS - 1 degree resolution The median over the historical Period ( ) Lenton et al,

12 Projected Changes Around Australia Lenton et al, 2015 Corals not hist. found V.Marg Marg Healthy Corals on the Great Barrier Reef and around part of Australia will experience marginal conditions are expect by 2030 under RCP4.5 & RCP 8.5, and by 2100 values lower than corals are historically found -> move to net loss? While ph changes >0.3 units are projected until RCP 8.5 (3 x Historical Change) likely around most of Australia significant impacts on the marine ecosystem. 12

13 Summary Ocean acidification is a predictable and measureable consequence of rising atmospheric carbon dioxide As atmospheric CO 2 levels continue to rise so will magnitude and rate of ocean acidification - ecosystem services provided by the oceans will be impacted. Ocean chemistry changes are observed around Australia NRS are critical to assessing these changes at annual, seasonal and longer-term. The responses to ph and Aragonite saturation state are different biological implications. In the future much larger changes are projected not very far away, next years, but temperature is changing also organisms face multiple stressors. Data Availability All Historical Reconstruction Data available at IMOS Projections data please contact me 13

14 Andrew Lenton Senior Research Scientist CSIRO Oceans and Atmosphere Flagship t e andrew.lenton@csiro.au