Phenology metrics for ocean waters with application to future climate change in the Northwest Atlantic Ocean

Abstract

Phenology metrics quantify the timing of seasonal events; future climate projections of changes to these metrics can be used in long-term ecosystem-based approaches to ocean resource management. Here a set of phenology metrics for ocean waters is presented. These metrics include three common ones: the onset of spring, the length of the growing season, and the onset of stratification. In addition, five novel metrics have been derived, including two that are based on the duration of thermal stress, defined as the amount of time that the future climate spends above the present climate maximum temperature; two that provide pelagic and demersal development indices by measuring the difference in time for a given number of present climate surface or bottom temperature degree days to arrive in the future; and a fifth metric that represents the absolute difference in a scalar quantity between the future and present climates. Spatial maps of the changes in these metrics for the mid-21st century have been derived from a high-resolution simulation of the Northwest Atlantic Ocean. A focus of this study was the application of the metrics to predict changes in ecosystem components in the future. Eight applications are presented for the Northwest Atlantic Ocean shelf region, describing predictions of shifts in the timing of inshore lobster migration; increased mortality, earlier spawning times and increased length-at-age for cod; reduced egg development times for shrimp; thermal stress on herring; and changes in habitat conditions for halibut and snow crab. This set of phenology change metrics serves as a starting point to illustrate the diverse ecosystem-related calculations possible using future climate ocean model output.