Future Ocean Productivity: Impact of Greenland Ice Sheet Melt Scenario

1. Future oceanproductivity: the impact of an extreme Greenlandicesheetmelt scenario Laurent Bopp Institut Pierre-Simon Laplace / CNRS & Ecole Normale Supérieure Paris , France Acknowledgements: L. Kwiatkowski, J. Naar, D. Defrance, O. Aumont, D. Couespel and IPSL CMC, …

2. Future oceanproductivity Open oceanproductivityisprojected to fallgloballydepending on RCP scenario (medium confidence). The estimateddecreasewilloccurby up to 9% by 2100 under the RCP8.5 business-as-usualclimate scenario (relative to 1990, lowconfidence) (IPCC, 2014). Net PrimaryProductivity Model Uncerftainties NPP = Net Primary Production (by phytoplankton)

3. Future oceanproductivity / regional Large regionalcontrasts–low agreement in manyregions, both on the sign of change and on the mechanismsinvolved Change in NPP (RCP85 scenario, model-mean, gC/m2/y) (IPCC SROCC, 2019)

4. Future oceanproductivity / regional : IPCC SROCC Large regionalcontrasts–low agreement in manyregions, both on the sign of change and on the mechanismsinvolved North Atlantic : relative agreement on the sign of change – on the role of increased stratification & reducednutrientsupply. Change in NPP (RCP85 scenario, model-mean, gC/m2/y) (IPCC SROCC, 2019)

5. Q: Response of N Atl NPP to Greenland Flash Melting ? CMIP5 Earth System Models do no includeany interactive IceSheetModels Revision of Greenland contribution to sea-levelrise in the 21st century and beyond (IPCC SROCC) Indications from the past (Heinrich Events) showingdecreased NPP in the N Atl in response to hosing Mariotti et al. CP 2012 Marioti et al. CP 2012

6. How: Use of IPSL Earth System Model and GreenlandMelt Scenarios IPSL Earth System Modelsincluding Marine Biogeochemistry w/ PISCES Freshwaterhosing simulations : 0.05 Sv – 0.43 cm (GrIS50) 0.075 Sv – 65 cm (GrIS75) 0.1 Sv – 86 cm (GrIS100) 0.2 Sv– 173 cm (GrIS200) DeFrance et al. PNAS 2017 Marioti et al. CP 2012

7. Results (1) : Amplification of North Atlantic Productivitydecline Large impact on NPP in the NorthAtlantic (up to more than 2x the reductionfrom RCP85) Abrupt response in the first 15 yrs of the simulation

8. Results (1) : Amplification of North Atlantic Productivitydecline DNPP DMLD (GrIS200 – RCP85) As expected, the responseislargelydriven by enhanced stratification caused by freshwater input

9. Results (2) : ReducedProductivity in the South Atlantic –Unexpected Almost -20% decrease in the South Atlantic, largelyconfined to Benguela Upwelling System

10. Results (2) : ReducedProductivity in the South Atlantic –Unexpected UpwerllingFavourableWinds NutrientSupply Theseenhanced NPP declines are related to atmosphericteleconnections and ocean-atmospherecoupling(Defrance et al. 2017). With an intensificaition of the polewarddisplacement of τupw

11. Limits / Conclusions A classicalexample of a Physical « tipping point » affecting Marine Biogeochemistry / Ecosystems Interesting far-fieldeffectsthroughatm/oceanteleconnections But : VeryIdealized simulations (more « what-if » type, with > 1m of Greenlandmelting) Neglectedprocesses (no nutrient in freshwatere.g.) Long-term extensions ? More abrupt scenarios ? Kwiatkowski, Naar, Bopp, Aumont, Defrance, Couespel, in rev, GRL

13. The Greenlandicesheetmeltwater simulations presentedherein are, by design, highly 385 idealised. Moreover, the magnitude of Greenlandfreshwaterdischarge, 389 particularly in the GrIS75, GrIS100 and GrIS200 simulations, isnotablyhighcompared to 390 bothrecent observations (Schrama & Wouters, 2011) and previousestimates of melt rates 391 under RCP8.5 (Vizcaino et al., 2015; Fürst et al., 2015; Aschwanden et al., 2019). Nonetheless, althoughunlikely, even the mostextrememeltwater simulation is 397 arguably plausible givenpaleorecords of sealevelrise (Fairbanks, 1989; Deschamps et al., 398 2012). Unrepresented processes : nutrient in freshwater fluxes