Gulf of Maine Temperature-Salinity Curves From the Early 1900s (Henry Bigelow) Compared to the Present (GNATS)

Gabrielle Martinez, American Society of Limnology and Oceanography, Kensington, United States and William M Balch, Bigelow Lab for Ocean Sciences, East Boothbay, ME, United States
The Gulf of Maine (GoM) is a continental shelf sea in the Northwest Atlantic with high primary
productivity. The hydrological cycle is intensifying due to climate change, with increased rates
of warming and precipitation. Climate change appears to be causing changes in both temperature
and salinity in the GoM, as well as the associated seawater density. Such changes could change
the Gulf’s physical oceanography. In order to understand the magnitude of changes in
temperature and salinity over the last century, temperature-salinity plots from the GoM were
compared using data of Henry Bigelow (1912-1915) and the Gulf of Maine North Atlantic Time
Series (GNATS; glider data taken from 2008). Bigelow collected the most data during the
month of August, so we did our comparison with glider data during that month. Our null
hypothesis was that there were no statistically significant changes in the temperature-salinity
relationship in the Gulf of Maine during the month of August over the last century. To determine
statistical significance between the two data sets, Student’s t-tests were run for comparison of
temperature and salinity values. Binning all longitudes and all depths together, temperature and
salinity values were found to be significantly different (p<0.05). The salinity values for modern
Maine Surface Water (depth range 0-50 m) are significantly lower than the salinities in the
early1900s, showing that the surface GoM is getting significantly fresher. Maine Intermediate
Water (typically found between 50-120 m) showed considerable variability, overall, but with
higher salinity below 100 m over the century. The deepest water, Maine Bottom Water (MBW;
found between 120-225 m depth), has the narrowest confidence limits in temperature and salinity
due to less influence by surface seasonal variability. MBW has significantly warmed by 1.028°C
± 0.108 (SE; n=5) since the early 1900s.