Climate change reversing 900 years of cooling in Gulf of Maine



Gianna Melillo
Wed, August 10, 2022

In an effort to chronicle changing water temperatures in the Gulf of Maine, researchers assessed data collected from shells and simulated variability through climate models.

They found that following a prolonged period of cooling, climate change has contributed to rising temperatures in the region.

These increased temperatures have already taken a toll on local marine life and will likely worsen in the future.

Using data from shells in the western Gulf of Maine along with other proxies for water properties, researchers revealed global warming has been reversing a thousand-year cooling process in the region since the late 1800s.

According to authors, this is likely due to increased atmospheric greenhouse gas concentrations and changes in western North Atlantic water dynamics. Findings were published in Communications Earth and Environment.

Climate model simulations also show “warming over the last century was more rapid than almost any other 100-year period in the last 1,000 years in the region.”

Extreme marine sea surface temperature (SST) heat waves have been documented in the Gulf of Maine in recent years and have taken a toll on the region’s ecosystems, including certain whales, fish and lobster.

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However, little is known about temperature variability or water properties prior to the installment of the Boothbay Harbor (BBH) SST, dating back to 1905. To address this knowledge gap, researchers set out to construct a 300-year data set chronicling hydrographic variability in the Gulf of Maine.

Three sources of chemical proxies were used to assess water changes including shells, oxygen isotopes (to measure temperature and salinity) and nitrogen isotopes (to measure water mass source).

Prior to the documented warming, the region was consistently cooling for many years thanks to volcanic forcings, researchers said. The cooling followed by rapid warming detected in the study is consistent with the Community Earth System Model-Last Millennium Ensemble (CESM-LME), which shows reconstructions of external forcings, like greenhouse gas or solar variability, over the last millennium.

The CESM-LME Northern Hemisphere surface temperature simulations also detail the impact of volcanic forcings prior to 1850 and greenhouse gas and aerosol forcings after 1850, authors said.

In addition, the position of the gulf stream, which helps dictate what proportion of slope water enters the Gulf of Maine, also plays a large role in dictating temperatures.

Future projections of atmospheric greenhouse gas concentrations along with a projected weakening of the Atlantic Meridional Overturning Circulation indicate warming in this region will likely continue, “leading to continued and potentially worsening ecologically and economically devastating temperature increases in the region in the future,” authors concluded.