Summary/Abstract
A 20-year coastal time series, the Gulf of Maine North Atlantic Time Series, has included regular oceanographic measurements across the Gulf of Maine (GoM), one of the fastest warming ocean water bodies on Earth. Physical, chemical, biological, biogeochemical, and bio-optical measurements demonstrate: (a) unexpected, statistically-significant surface cooling in spring months along with surface warming in all other seasons, (b) deep warm water in the GoM after 2008, likely associated with intrusions of warm, saline N. Atlantic Slope water, (c) declines in phytoplankton primary production over 20 years, most significantly associated with chlorophyll, particulate organic carbon, temperature, and residual nitrate (the excess of nitrate over silicate), (d) deep mixing events in winter bring corrosive water to the surface, making it more likely to dissolve carbonates of shell formers and (e) dissolved organic carbon and its colored constituents progressively increased in the GoM, yet this does not correlate significantly with the drop in primary production. These results link the control of GoM productivity to waters originating outside of the GoM in the Northwest Atlantic.