Rapid detection of climate scale environmental variability in the Gulf of Maine

The Gulf of Maine buoy array of the Northeastern Regional Association of Coastal Ocean Observing Systems (NERACOOS) has been providing continuous oceanographic measurements for over a decade. NERACOOS is one of the eleven regional associations of the US Integrated Ocean Observing System (IOOS). The buoys are deployed and maintained by the Physical Oceanography Group of the University of Maine, initially as part of the Gulf of Maine Ocean Observing System. Analysis of this large timeseries (over 10⁵ samples for a single depth) shows statistically significant warming trends at all depths for all locations, providing the first depth-resolved rates of temperature variability for the U.S. East Coast from continuous data. Analysis steps include quality control of the data, calculation and averaging of daily means and anomalies, according to the decorrelation timescale (~ 20 days) and calculation of rates of change with linear regression. Use of the decorrelation timescale allows for optimal determination of errors by assessing the number of unique samples within the large dataset, in which observations are closely correlated to adjacent records. There are significant relationships between temperature variability and time (p<;0.05), and all rates of change are positive and significant (p<;0.05), although the temperature variability explained by time alone is low (average 12%). Warming rates are not consistent with depth; the greatest rates are observed mid water column at the deepest locations. Long-term historical time-series indicate that between 1940 and 1950 the Gulf of Maine warmed at approximately 0.25 °C yr^-1, followed by over a decade of cooling at a similar rate, all superimposed on an overall warming trend of 0.01 °C yr^-1. The period of rapid warming recorded by the NERACOOS buoys since 2004, of similar magnitude to the 1940-50 warming trend, may represent another cycle of decadal variability or perhaps in- icate a shift in the long-term warming trend. If current warming trends continue, the Gulf of Maine ecosystem is projected to undergo a transition in species composition and food web structure. Direct effects of warming include changes in thermal habitat (affecting growth, molting and reproduction cycles) and species shifts in local spatial distribution and biogeographic range. While the transition states and their timing cannot be well predicted, the present understanding points to particular impacts on a number of important species that reside at the southern extent of their biogeographic range in the Gulf of Maine. The difficulty in prediction of ecosystem states and impacts reinforces the need to observe not only temperature and hydrographic characteristics, but also lower-level ecosystem productivity, diversity and abundance of key dominant species in the coastal zone, an area not well observed by current sampling strategies. Sustained high temporal frequency, fixed location time series are critical to detection of physical variability in as short a timeframe as possible. Without comparable sampling of ecological variability, we will not have the capacity for timely detection of ecosystem responses. Knowledge of the extent of change in the Gulf of Maine coastal ecosystem will contribute to informed decisions for adaptive management and development of Gulf of Maine ecosystem resources.