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 2017 data). The transition has shifted by nearly a month in the northern part of the ecosystem as seen in the data for the Gulf of Maine and Georges Bank where the transition date was in November during the 1980s and is now occurring in December. The 2017 Scotian Shelf occurred so late that it was off scale for the detection algorithm. The shift at the southern end of the ecosystem was not as large with the transitions in the Middle Atlantic Bight largely confined to the month of November.