Coral Geochemical Records Track Millennial-Scale Ecosystem Change and Resilience in the Tropical Eastern Pacific

Abstract

Along the coastal Tropical Eastern Pacific (TEP), regions of strong seasonal upwelling bring cold, nutrient-rich waters, controlling ecological conditions and sustaining millions of people through large-scale fisheries. The TEP is also important for the regulation of global climate and is affected by large-scale environmental processes such as ENSO. How the nutrient dynamics of this region will respond to climate change and what the implications will be for coastal ecology remains unknown. Environmental records are needed that capture intra and inter-decadal variation and extend over millennia where these biotic and abiotic processes interact. Here, we develop a new sampling approach and construct two coral skeleton records (n = >600) from reef matrix cores that extend six millennia, from the upwelling Gulf of Panamá and the non-upwelling Gulf of Chiriquí. We ask what effects millennial-scale climate patterns have on upwelling in the region, and how the magnitude of upwelled nutrients influences ecological productivity and even human habitation. We combined multiple proxies using climatic (carbonate δ18O), nutrient (skeletal-organic matrix δ15N), diagenetic (taphonomic scoring), ecological (benthic community composition), and temporal (U-Th dates) data. Using Generalised Additive Models to assess variability, we find strong divergences in the nutrient (δ15N; range >5 ‰) records between Gulfs, while δ18O (range ~2‰) is more stable. The greatest variation in δ15N values occurs during times of high reef accretion whereas δ18O is constant, suggesting that nutrients, not temperature, are driving reef productivity. Taphonomic, taxonomic, and age data reveal periodic shifts and collapses of coral communities that differ between Gulfs. We end by drawing connections between these ecological shifts to the episodic human habitation documented during the late-Holocene and hypothesize what this may mean for ecosystem resilience and environmental management under future climate.