Changing Hydrographic, Biogeochemical, and Acidification Properties in the Gulf of Maine as Measured by the Gulf of Maine North Atlantic Time Series, GNATS, Between 1998 and 2018. Issue 6 (7th June 2022)

• Record Type: Journal Article
• Authors: Balch, William M.; Drapeau, David T.; Bowler, Bruce C.; Record, Nicholas R.; Bates, Nicholas R.; Pinkham, Sunny; Garley, Rebecca; Mitchell, Catherine
• Is Part Of: Journal of geophysical research. Volume 127:Issue 6(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-06-07
• Subjects: Gulf of Maine -- primary production -- time series -- phytoplankton -- nutrients -- ocean acidification; Geobiology -- Periodicals; Biogeochemistry -- Periodicals; Biotic communities -- Periodicals; Geophysics -- Periodicals; 577.14
• DOI: 10.1029/2022JG006790
• Languages: English
• ISSNs: 2169-8953

Abstract

Abstract: The Gulf of Maine North Atlantic Time Series (GNATS) has been run since 1998, across the Gulf of Maine (GoM), between Maine and Nova Scotia. GNATS goals are to provide ocean color satellite validation and to examine change in this coastal ecosystem. We have sampled hydrographical, biological, chemical, biogeochemical, and bio‐optical variables. After 2008, warm water intrusions (likely North Atlantic Slope Water [NASW]) were observed in the eastern GoM at 50–180 m depths. Shallow waters (<50 m) significantly warmed in winter, summer, and fall but cooled during spring. Surface salinity and density of the GoM also significantly increased over the 20 years. Phytoplankton standing stock and primary production showed highly‐significant decreases during the period. Concentrations of phosphate increased, silicate decreased, residual nitrate [N*; nitrate‐silicate] increased, and the ratio of dissolved inorganic nitrogen:phosphate decreased, suggesting increasing nitrogen limitation. Dissolved organic carbon (DOC) and its optical indices generally increased over two decades, suggesting changes to the DOC cycle. Surface seawater carbonate chemistry showed winter periods where the aragonite saturation (Ωar ) dropped below 1.6 gulf‐wide due to upward winter mixing of cool, corrosive water. However, associated with increased average GoM temperatures, Ωar has significantly increased. These results reinforce the hypothesis that the observed decrease in surface GoM primary production resulted from a switch from Labrador Sea Water to NASW entering the GoM. A multifactor analysis shows that decreasing GoM primary production is most significantly correlated to decreases in chlorophyll and particulate organic carbon plus increases in N* and temperature. Plain Language Summary: 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. Key Points: A 20‐year Gulf of Maine (GoM) time series shows surface cooling in spring months but warming in all other seasons Primary production declined over 20 years, mostly associated with changes in chlorophyll, particulate organic carbon, temperature, and residual nitrate (nitrate‐silicate) Deep intrusions of warm, saline North Atlantic Slope Water occurred post‐2008 into the GoM