A summary of temperature, chlorophyll and other oceanographic conditions on the Northeast U.S. Continental Shelf during the first 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.
Daily sea surface temperatures were at or above average conditions during the first half of 2020. The Georges Bank and Gulf of Maine ecoregions had the largest departures from average conditions. Winter temperatures were approximately 2°C above the long-term average. In the Mid-Atlantic, temperatures fluctuated below the mean for the second half of the spring. In all areas except for the Mid-Atlantic Bight, temperatures moderated well above the mean by mid-year.
Average sea surface temperatures for the first 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. Spring temperatures in all areas appear to have experienced a change in level around the year 2010, increasing the mean temperature by 1°C.
The 6-month spring sea surface temperature average was above normal. However, monthly sea surface temperature imagery shows that temperatures were below normal in the Mid-Atlantic during the month of May. They returned to normal or above average in June in most parts of the region.
Sea surface temperature variability (the standard deviation within each ecoregion) for the first half of 2020 increased in the more northern Northeast Shelf ecoregions. The increase in variability appears to be significant in the Gulf of Maine and Scotian Shelf but not significant in the other areas. There were no clear-cut patterns in any change points in variability between areas.
We derived the long-term temperature time series 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. It generally matched the conditions during the warm period of the late 1940s and early 1950s.
Phenology is the seasonal timing of plant and animal production cycles. Many marine organisms time their reproductive cycles to make best use of seasonal phytoplankton blooms, such as the spring and fall blooms. In turn, temperature plays a role in the development of blooms. Identifying the initiation date of the spring transition temperature, which varies by region, is likely related to different forcing factors. The spring thermal transition date was relatively constant from 1982 to approximately 2010 for the Northeast Shelf ecoregions. A change point appeared in the northern areas around 2010, when the transition date advanced approximately two weeks. In recent years, the trend toward earlier spring transition dates appears significant in northern segments of the ecosystem—the Gulf of Maine and Scotian Shelf ecoregions.
Phytoplankton blooms, measured as chlorophyll concentration, are a major component of the food web. They are a primary food source for zooplankton and filter feeders such as shellfish. Chlorophyll concentration was generally below average during the first half of 2020. In areas that typically have a spring bloom, such as Georges Bank and the Gulf of Maine, chlorophyll concentration varied below the long-term average through the bloom period. The chlorophyll concentration for the Middle Atlantic Bight and Scotian Shelf also tended to be below the long term mean. The only area with the semblance of a bloom was Georges Bank. The peak in chlorophyll would suggest the bloom start was typical of previous bloom events.
Average chlorophyll concentrations during the first half of the year appear to have decreased in recent years in all subareas of the ecosystem. With the exception of Georges Bank, the declining trends were significant. It is noteworthy that we have identified a change point in chlorophyll concentration in all areas within the last decade or so.
As weather and earth system models have improved, so have monthly forecasts over seasonal scales ranging up to 7 months in advance. For each of the Northeast Shelf ecoregions, we provide forecasts from an ensemble of six forecast models. They start with estimates for July 2020 and end in January 2021. The forecasts suggest that the Northern ecoregions will have above average sea surface temperatures, while the Middle Atlantic Bight will experience less elevated temperatures.
Learn more about these ecosystem forecasts
Blacktip sharks. Credit: iStock.
Releasing a sandbar shark on a shark survey.
Stump Point area in Hayes, Virginia, part of the Middle Peninsula, on a flyover with SouthWings. Credit: Scott Lerberg, Chesapeake Bay National Estuarine Research Reserve Virginia
The Fishadelphia team. Credit: Dr. Talia Young.