Upwelling, climate change, and the shifting geography of coral reef development.

The eastern tropical Pacific is oceanographically unfavorable for coral-reef development. Nevertheless, reefs have persisted there for the last 7000 years. Rates of vertical accretion during the Holocene have been similar in the strong-upwelling Gulf of Panamá (GoP) and the adjacent, weak-upwelling Gulf of Chiriquí (GoC); however, seasonal upwelling in the GoP exacerbated a climate-driven hiatus in reef development in the late Holocene. The situation is now reversed and seasonal upwelling in the GoP currently buffers thermal stress, creating a refuge for coral growth. We developed carbonate budget models to project the capacity of reefs in both gulfs to keep up with future sea-level rise. On average, the GoP had significantly higher net carbonate production rates than the GoC. With an estimated contemporary reef-accretion potential (RAP) of 5.5 mm year, reefs in the GoP are projected to be able to keep up with sea-level rise if CO emissions are reduced, but not under current emissions trajectories. With an estimated RAP of just 0.3 mm year, reefs in the GoC are likely already unable to keep up with contemporary sea-level rise in Panamá (1.4 mm year). Whereas the GoP has the potential to support functional reefs in the near-term, our study indicates that their long-term persistence will depend on reduction of greenhouse gases.