Current Conditions of the Northeast U.S. Shelf Ecosystem: Spring 2023 Update

“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. See archived reports here.

Summary 

• During the last half of 2022, 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. In some areas, temperature was approximately 3°C above mean levels.
• Fall phytoplankton blooms were generally above average inclusive of Georges Bank, Gulf of Maine, and the Scotian Shelf ecoregions.
• Chlorophyll concentration increased in the second half of 2022 reversing a decadal trend of decline.
• The fall thermal transition continues to shift to progressively later in the year, raising concern over the timing of production cycles in the food web.

Temperature

Daily Sea Surface Temperature for the Last Half of 2022

Daily sea surface temperatures were at or generally above average conditions during the last half of 2022. The Georges Bank, Gulf of Maine, and Scotian Shelf ecoregions had the largest departures from average conditions; mid-summer temperatures were approximately 3°C above the average. In the Middle Atlantic Bight ecoregion, 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 2022

Sea surface temperatures for the last half of 2022 continued at high levels in all ecoregions. On Georges Bank, this temperature data series was among the highest levels in the time series in 2022. In other segments of the ecosystem, temperature continued high level trends. The linear trends in all the ecoregions appear to be significant. 

Sea Surface Temperature Distribution for the Last Half of 2022

The spatial distribution of sea surface temperature by ecoregions were generally above normal, with the highest temperature anomalies observed in August and November. There were some negative anomalies observed in the Middle Atlantic Bight in October. Some of the highest anomalies were associated with the southern flank of Georges Bank, an effect related to recent movement of Gulf Stream position.

Trends in Variability of Sea Surface Temperature for the Last Half of 2022

Sea surface temperature variability (the standard deviation) for the last half of 2022 declined on Georges Bank and was near the mean in the other 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 of 2022

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 are based on historical shipboard measures and augmented with other data in recent years. The temperature for the last half of 2022 was among the highest temperatures in the time series. 

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 later fall transition dates appears significant in all the Northeast Shelf ecoregions. The transition day was the latest in the time series for the George Bank ecoregion.

Chlorophyll Concentration

Weekly Chlorophyll for the Last Half of 2022

Chlorophyll concentration was generally below average during the late summer and early fall of 2022. With the exception of the Middle Atlantic Bight, there were signs of significant late season bloom activity.

Chlorophyll Concentration Trends for the Last Half of the Year

Average chlorophyll concentrations during the last half of the year appear to have rebounded in 2022 after a period of decline in all ecoregions. The most dramatic increase appears to have occurred in the Gulf of Maine with chlorophyll concentration at a record high. It is noteworthy that we have identified a change point in chlorophyll concentration in all areas within the last decade or so.

Fish Distribution from Autumn Survey Data

The species of the Northeast Shelf ecosystem have shown changes in distribution over recent decades. Individual species have shifted distribution due to a number of reasons and these shifts can be characterized in a number of different ways. Three metrics that have been used to characterize distribution on the Northeast Shelf include: 

• Position in the ecosystem along an axis oriented from the southwest to the northeast referred to as the “along-shelf” distance
• Depth of occurrence
• Distance from the coastline

Along-shelf distances range from 0 to 1360 kilometers, which relates to positions along the axis from the origin in southwest to northeast. Depth ranges from 0 to -260 meters, which relates to depth of occurrence. Distance to the coast ranges from 0 to 110 km. These indices are based on 48 of the most abundant taxa. Along-shelf distance has increased over time reflecting a shift in species distribution to the Northeast. The 2022 distance was among the highest in the time series. Depth of occurrence has also increased over time reflecting a greater use of deeper habitats. There is no significant trend in distance to the coastline. The map position of the center of gravity for these species moved slightly to the southwest in 2022 from its extreme northeastern position in 2021.