Current Conditions of the Northeast U.S. Shelf Ecosystem: Spring 2021 Update
A summary of temperature, chlorophyll and other oceanographic conditions on the Northeast U.S. Continental Shelf during the last half of 2020.
“Current Conditions” is a biannual report on ecosystem and fisheries data for the Northeast U.S. continental shelf ecosystem. The report includes measurements of temperature and salinity indicators of seasonal warming and cooling patterns. We derive indicators describing phytoplankton distribution and blooms from satellite remote sensing data. Northeast Fisheries Science Center bottom trawl surveys provide upper trophic level indicators of fish and macroinvertebrate habitat and distribution dynamics. Note that some data elements usually reported in Current Conditions are not available for this report, as some of our surveys did not occur as planned. This would include bottom temperature, surface and bottom salinity, and modeling data related to fish distribution and habitat.
- During the last half of 2020, sea surface temperatures in the Northeast U.S. Shelf Ecosystem continued to be above average following a shift in thermal conditions that began around 2010.
- Fall phytoplankton blooms were generally below average and it is questionable whether a fall bloom developed in any part of the ecosystem
- The fall thermal transition continues to shift to progressively later on the year, raising concern over the timing of production cycles in the food web.
Daily Sea Surface Temperature for the Last Half of the Year
Daily sea surface temperatures were at or generally above average conditions during the last half of 2020. The Georges Bank, Gulf of Maine, and Scotian Shelf ecoregions had the largest departures from average conditions where mid-summer temperatures were approximately 3°C above the average. In the Middle Atlantic Bight areas temperatures fluctuated around one standard deviation above the mean. In all areas, temperatures tended to moderate toward the mean by the end of the year.
Sea Surface Temperature Trends for the Last Half of the Year
Sea surface temperatures for the last half of 2020 continued at high levels in all ecoregions. However, thermal conditions have become more moderate since the record high temperatures observed in 2012. The linear trends in all the ecoregions appear to be significant.
Trends in Variability of Sea Surface Temperature for the Last Half of the Year
Sea surface temperature variability (the standard deviation) for the last half of 2020 increased in the coastal boundary ecoregions. The increase in variability appears to be significant in the Gulf of Maine but not significant in the other areas. There were no clear-cut patterns in any change points in variability between areas.
Long-term Trends of Sea Surface Temperature for the Last Half Year
The long-term temperature time series is derived from the Extended Reconstructed Sea Surface Temperature dataset. It provides a low-resolution depiction of sea surface temperature on the Northeast Shelf since the 1850s. The data is based on historical shipboard measures and augmented with other data in recent years. The temperature for the last half of 2020 was above average and generally matched the conditions during the warm period of the late 1940s and early 1950s.
Fall Thermal Transition Day
Phenology is the climate’s influence on the timing between plant and animal production cycles. Many marine organisms time their reproductive cycles to make best use of seasonal phytoplankton blooms, like the spring and fall blooms. In turn, temperature plays a role in the development of blooms. Identifying the initiation date of the fall transition temperature, which varies by region, can help determine the physical forcing on fall transition events. The fall thermal transition date was relatively constant from 1982 to approximately 2008 for the Northeast Shelf ecoregions. A change point appears in the northern areas around 2008, when the fall transition date advanced approximately two weeks. The trend to earlier fall transition dates appears significant in the Gulf of Maine, Georges Bank, and Scotian Shelf regions.
Weekly Chlorophyll for the Last Half of the Year
Chlorophyll concentration was generally below average during the last half of 2020. In areas that typically have a fall bloom, such as Georges Bank, chlorophyll concentration varied below the long-term average through the bloom period. The chlorophyll concentration for the Gulf of Maine appear above average late in the bloom period suggested a bloom might have occurred.
Chlorophyll Concentration Trends for the Last Half of the Year
Average chlorophyll concentrations during the last half of the year appears to have decreased in recent years in all subareas of the ecosystem. The most dramatic decline appears to have occurred in the Middle Atlantic Bight and Georges Bank areas. It is noteworthy that we have identified a change point in chlorophyll concentration in all areas within the last decade or so.