How local ocean dynamics affect Hawaiian ecosystems

Abstract

The Hawaiian Islands are characterized by complex ocean dynamics over a range of spatial scales. These processes have important consequences for ecosystems but, due to coarse resolution, are typically poorly represented in global climate models. Using a regional model, this project investigates local physical processes around the Hawaiian Islands, how they are projected to change in the future, and their impacts on coastal ecosystems. We find that internal tides are a significant source of temperature variability around the Hawaiian Islands. This effect is shown to persist under future stratification and may help to buffer coral reefs from warming temperatures. Mesoscale eddies are known to impact productivity locally. We demonstrate that cyclonic eddies can also have far-reaching, remote impacts on productivity around the Hawaiian Islands. Using dynamically-downscaled climate projections, we find that, without considerable emissions reductions or rapid adaptation, Hawaiian corals will be exposed to severe heat stress throughout the second half of the 21st century. Regional dynamics drive spatial variability in projected heat stress. For example the island-modified wind field generates mesoscale eddies and spatial variability in surface heat flux, both of which contribute to spatial patterns in long-term warming trends. This results in spatial patterns in the rate at which corals will need to adapt to avoid permanent severe heat stress. Together these results show how regional dynamics on a range of timescales impact coastal ecosystems around the Hawaiian Islands. These dynamics also modify how climate change will impact Hawaii’s coastal regions, highlighting the importance of resolving local dynamics in climate projections.