Impacts of Climate Change on the Ascension Island Marine Protected Area and Its Ecosystem Services.

This is the first projection of marine circulation and biogeochemistry for the Ascension Island Marine Protected Area (AIMPA). Marine Protected Areas are a key management tool used to safeguard biodiversity, but their efficacy is increasingly threatened by climate change. To assess an MPA's vulnerability to climate change and predict biological responses, we must first project how the local marine environment will change. We present the projections of an ensemble from the Sixth Coupled Model Intercomparision Project. Relative to the recent past (2000–2010), the multi‐model means of the mid‐century (2040–2050) project that the AIMPA will become warmer (+0.9 to +1.2°C), more saline (+0.01 to +0.10), with a shallower mixed layer depth (−1.3 to −0.8 m), a weaker Atlantic Equatorial Undercurrent (AEU) (−1.5 to −0.4 Sv), more acidic (−0.10 to −0.07), with lower surface nutrient concentrations (−0.023 to −0.0141 mmol N m−3 and −0.013 to −0.009 mmol P m−3), less chlorophyll (−6 to −3 µg m−3) and less primary production (−0.31 to −0.20 mol m−2 yr−1). These changes are often more extreme in the scenarios with higher greenhouse gases emissions and more significant climate change. Using the multi‐model mean for two scenarios in the years 2090–2100, we assessed how five key ecosystem services in both the shallow subtidal and the pelagic zone were likely to be impacted by climate change. Both low and high emission scenarios project significant changes to the AIMPA, and it is likely that the provision of several ecosystem services will be negatively impacted. Plain Language Summary: Ascension Island is a small remote volcanic island in the equatorial Atlantic Ocean. The seas around Ascension Island have been protected from commercial fishing since 2019. We used the marine component of computer simulations of the Earth's climate to try to understand the future of the Ascension Island Marine Protected Area (AIMPA). Over the next century, the AIMPA region will become warmer, more saline, more acidic, less productive, and with lower nutrient and chlorophyll concentrations in the surface waters. The most important current of the region, the Atlantic Equatorial Current, is also projected to weaken in all scenarios. These changes are likely to negatively impact the ability of the AIMPA to provide ecosystem services such as healthy ecosystems, fish stocks, the removal of carbon dioxide from the air, and attract tourism. This work is important because it is the first projection of the climate around the AIMPA since it was created, and it has allowed local policymakers to understand how the changing climate is likely to affect their environment and ecosystem services. Key Points: We present the first projection of the future marine circulation and biogeochemistry of the Ascension Island Marine Protected Area (AIMPA)The AIMPA will become warmer, more saline, more acidic, with less surface nutrients, primary production and chlorophyllThe AIMPA's capacity to provide ecosystem services will be significantly negatively impacted under a high emission scenario [ABSTRACT FROM AUTHOR]