Sensitivity of Future ocean acidification to Land carbon uptake

Chair: Joellen Russell

Richard Matear (1), Andrew Lenton (1)

1 CSIRO, Hobart, Tasmania, Australia

Background
The future land carbon uptake under the various emission scenarios is highly uncertain 1, 2 with the potential to significantly impact future climate change projections 3. Previous studies have focus on how the land carbon uptake may impact the future climate 4 but by modifying the atmospheric CO2 concentrations the land uptake will also influence the future trajectory for ocean acidification. Ocean acidification (OA) has the potential to significantly impact marine ecosystem by reducing calcifications rates 5, altering phytoplankton composition6, changing fish behaviour7 and affecting larval recruitment8.

Methods
Making accurate projection of ocean acidi- fication is essential to assessing the future impact of ocean acidification. Here, we use the CO2 emissions scenarios for 4 Representative Concentration Pathways (RCPs) with an Earth Sys- tem Model to project the future trajectory of ocean acidification.

Findings
We show that simulated response on the land carbon uptake has a significant impact on the onset of under-saturated conditions in the Southern Ocean and Arctic Ocean, the suitable habitat for tropical coral and the deepwater saturation state. The impact is most significant for the middle emission scenario (RCP4.5) when the time negative ocean acidification condition is advanced.

Conclusions
• rate of OA related to land carbon uptake (climate-carbon feedback)

• sensitivity is largest for the middle emissions scenarios (RCP4.5 and 6) and could accelerate the impact of ocean acidification. Such acceleration increases OA impacts but perhaps it will also undermine the ability of marine biota to adapt to the changing environment

• need to do ESM simulations to make future OA projections (relevance to AR6) and reduce the uncertainty in the climate-carbon feedback

References
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4.Friedlingstein, P. et al. Climate-carbon cycle feedback analysis: Results from the C4MIP 11 model intercomparison. J Climate 19, 3337–3353 (2006).

5.Stojkovic, S., Beardall, J. & Matear, R. J. CO2concentrating mechanisms in three southern hemisphere strains of Emiliania huxleyi. Journal Of Phycology 49, 670–679 (2013).

6.Lohbeck, K. T., Riebesell, U. & Reusch, T. B. H. Adaptive evolution of a key phytoplankton species to ocean acidification. Nature Geoscience 5, 346–351 (2012).

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