The ocean is warming at an alarmingly fast rate. One ocean basin in particular, the typically cool Gulf of Maine and surrounding areas in the Northwest Atlantic Ocean, is now believed to be among the fastest-warming regions of the entire global ocean.
Scientists at NCEI and the Cooperative Institute for Satellite Earth System Studies recently published a study in Limnology and Oceanography that aims to better understand this region’s long-term climate trends and how they connect to the Gulf Stream decadal variability.
The Gulf of Maine stretches from Cape Cod to Nova Scotia and is a key intersection between cold water masses from the Arctic and warm water masses from the Gulf Stream. The study observed ocean data points in the Gulf of Maine, the nearby Scotian Shelf, the Slope Water region (a water mass between the Gulf Stream and the continental shelf north of Cape Hatteras, North Carolina), and north of the Gulf Stream’s path.
The data points to continuous slow warming within all four regions over the past five decades. However, this relatively slow temperature rise has sharply accelerated in the last ten years, coinciding with a strengthened northward infiltration of warm subsurface water in the summer months. Such strong northward migration of warm water has not been seen in the four preceding decades, making the current rapid warming unique.
The study discovered that contrary to common belief, the Scotian Shelf and Slope Water region have recently been warming much faster than the Gulf of Maine. This implies that the probable cause of the faster warming in the most recent decade was caused by a substantial and rapid change in the Gulf Stream region.
While this study did not focus on the cause of the region’s warming, there have been a number of studies published in the past several years that have addressed the causation-response connections.
Although not exactly the subject of the study, some implications of what is discussed may be important for understanding the causes and effects of warming in the Slope Water region. The warming trend in this basin likely has, among others, two important causes. First is the overall warming of the global ocean as greenhouse gas concentrations rise. Second is the melting of ice in Greenland and the Arctic Ocean, which provides pulses of freshwater that can alter ocean circulation patterns in the region.
A weakening of the Atlantic Meridional Overturning Circulation (AMOC) leads to the Gulf Stream shifting northward and the cold current flowing into the Gulf of Maine becoming weaker, pushing warmer water into the region.
Sharp regional warming may cause severe impacts on marine species in the area. Herring populations are declining and researchers and anglers are seeing an increase in species usually found in warmer waters, such as butterfish and squid. Not only does this impact the fishing industry, but this change affects wildlife such as puffins that have to adapt their chick feeding behaviors as the newly common butterfish are too large for hatchlings to swallow.
Reference:Seidov, Dan, A. Mishonov, and R. Parsons, “Recent warming and decadal variability of Gulf of Maine and Slope Water,” Limnology and Oceanography, doi:10.1002/lno.1189