Chlorophyll a, a pigment produced by phytoplankton, can be measured to determine the amount of phytoplankton present in water bodies. From a human perspective, high values of chlorophyll a can be good (abundance of nutritious diatoms as food for fish) or bad (Harmful Algal Blooms that may cause respiratory distress for people), based on the associated phytoplankton species.
Description of time series:
This time series shows the average concentration levels of chlorophyll ɑ for Alaska’s Eastern Bering Sea region. During the last five years there has been no significant trend while values have remained within the 10th and 90th percentiles of all observed data in the time series.
Description of gauge:
The gauge value of 65 indicates that between 2016 and 2020 the average concentration levels of chlorophyll a in Alaska’s Eastern Bering Sea region were slightly higher than the long term median of all chlorophyll ɑ concentration levels between 1998 and 2020.
0–10: Chlorophyll a was significantly lower than the long term median state.
10–25: Chlorophyll a was considerably lower than the long term median state.
25–50: Chlorophyll a was slightly lower than the long term median state.
50: Chlorophyll a was at the long term median state.
50–75: Chlorophyll a was slightly higher than the long term median state.
75–90: Chlorophyll a was considerably higher than the long term median state.
90–100: Chlorophyll a was significantly higher than the long term median state.
Indicator and source information:
The data for this Chlorophyll a annual indicator were provided by the NOAA Fisheries Coastal and Oceanic Plankton Ecology, Production, and Observations Database (COPEPOD). COPEPOD determined the annual Large Marine Ecosystem (LME) chlorophyll a concentrations using mapped, monthly composites of chlorophyll a concentration as calculated from radiance measurements ("ocean color") made by the SeaWiFS and MODIS-Aqua satellite sensors. These monthly composites were obtained from NASA (https://oceancolor.gsfc.nasa.gov/). Annual means for each LME for each year were calculated from the average of the LME 12 monthly means in that year. The overall “National Annual Mean mean was calculated as the average of all LME annual means. See the Data Background section for more details. Source: https://www.st.nmfs.noaa.gov/copepod/about/about-copepod.html.
To learn more about satellite-based chlorophyll a measurements within NOAA or to supplement the time series data shown here, please visit NOAA CoastWatch for more information and assistance.
Data background and limitations:
Satellite chlorophyll a, 9 km mapped, monthly composited data from SeaWiFS and MODIS-Aqua NASA products were spatially re-binned into 0.5 degree latitude by 0.5 degree longitude boxes (nominally about 50 km2 near the equator) then those ~50 km2 box values were averaged over the area of a given LME, resulting in 12 values per LME, one value for each month. The annual LME chlorophyll a amount reported here is the average of those 12 monthly values. This technique was done for each LME from North America and Hawaii. The overall “National Annual Mean mean was calculated as the average of all the LME annual means. Note that chlorophyll a is often plotted on a logarithmic scale to accentuate proportional changes. In other words, small changes in concentration when amounts are relatively low could mean a very big proportional change in the phytoplankton whereas the same change in absolute concentration when concentrations are relatively large is less meaningful.