Fall Thermal Transition Date
Phenology is the climate influence related to the timing between plant and animal production cycles. Many marine organisms time their reproductive cycles to best utilize seasonal phytoplankton blooms, like the spring and fall blooms, and in turn temperature plays a role in the development of these blooms. One measure to characterize the change in the timing of thermal forcing is the date of arrival of a fall transition temperature, which will vary by region and is meant to mark the occurrence of the average temperature between summer and winter. The date of arrival of the fall thermal transition temperature has reflected progressively later fall seasonal conditions over the past few decades (see figures, blue line is time series smoother, red dashed line marks 2016 data). The transition has shifted by nearly a month in the northern part of the ecosystem as seen in the data for the Scotian Shelf where the transition date was around November 20 during the 1980s and is now close to December 20. The shift at the southern end of the ecosystem was not as large. The seasonal shift fall transition in the Middle Atlantic Bight was the latest in the time series occurring in early December.