Marine Heat Waves
To date, the ocean has absorbed more than 90% of the heat associated with climate change, causing the average ocean temperature to increase world-wide. In Olympic Coast National Marine Sanctuary, water temperatures are expected to increase over the next century, becoming 2°F warmer by 2050. Warmer ocean temperatures hold less oxygen and increase stratification, and can weaken upwelling and reduce ecosystem productivity, factors that all have the potential to affect the distribution of species and modify species ranges.
Marine heatwaves are a “discrete prolonged anomalously warm water event,” specifically when seawater temperatures exceed a seasonally-varying threshold (typically the 90th percentile) for at least five consecutive days. Marine heatwaves are different from long-term increasing ocean temperature, in that marine heatwaves are discrete extreme warming events.
Marine heatwaves are a relatively new phenomenon and research is still emerging on the genesis and impacts of these events. Among other consequences, recent marine heatwaves in the Pacific Northwest have been shown to concentrate toxin levels from harmful algal blooms and shift species distributions for ecologically and commercially important marine resources, while contributing to several mortality events for seabirds and marine mammals on the West Coast.