20th Century Rapid Warming: Study Shows How Volcanoes Have Driven the Reversal of 900 Years of Cooling in the Gulf of Maine

A new study that combines an investigation of shells from long-lived quahogs and climate model simulations recently showed that fast 20th-century warming in the Gulf of Maine has inverted long-term cooling that took place there during the past 900 years.

As indicated in a EurekAlert! report, the warming is probably because of increased atmospheric greenhouse gas concentrations and changes in North Atlantic circulation.

The paper specified that given the future forecasts of atmospheric greenhouse gas concentrations and strength, "this warming trend in the Gulf of Maine is likely to continue," resulting in continued and possibly worsening ecologically and economically devastating temperature rises in the region in the future.

According to the paper's lead author Nina Whitney, what this paper reveals, both from the clams and the climate model simulations as well is that in the late 1800s, there were some pretty dramatic changes, and the Gulf of Maine started warming, reversing 900 years of cooking that volcanoes had mainly driven.

Ocean Circulation

Whitney is a National Oceanic and Atmospheric Administration Climate and Global Change Postdoctoral Fellow in the Physical Oceanography department at the Woods Hole Oceanography Institution and obtained her Ph.D. at Iowa State University, where the research presented in this study started.

Both the clams and the climate model simulations indicate that greenhouse gas forcings are not just likely causing surface temperature shifts affecting the Gulf of Maine but leading to changes as well in ocean circulation.

She added that the different ocean currents' pathways and strengths bringing water into the Gulf of Maine have changed as the region has warmed.

Scientists reconstructed three centuries of hydrographic variability in the Gulf of Maine by discerning geochemical records of nitrogen, oxygen, and previously published radiocarbon isotopes from Arctica islandica shells.

Investigating Changes in Ocean Conditions

As specified in the study published in the Communications Earth & Environment journal, the researchers dated the ocean quahogs, which can live up to approximately 500 years and grow their shells in yearly increments relatively analogous to tree rings, were dated by the researchers served as the ocean conditions' good recorders.

Essentially, the chemical signatures from the shells offered the study authors a multi-proxy method to investigate changes in ocean conditions.

Moreover, Oxygen isotopes served as a proxy for seawater temperature and salinity. Nitrogen, as well as radiocarbon isotopes, were proxies for water mass sources.

Scientists put the geochemical results into a more comprehensive temporal and spatial context by examining fully-coupled climate prototype simulations from the Community Earth System Model-Last Millennium Ensemble.

Warming in the Gulf of Maine

Caroline Ummenhofer, the co-author of the paper and associate scientist in WHOI's Physical Oceanography Department, explained the observed rate of warming, specifically in the Gulf of Maine, over the past 100 years had outpaced average global ocean warming.

She added this "extensive consequences for the ecosystems and fisheries of the region and thus for the local economy, as stated in a related ScienceDaily report.

According to Alan Wanamer, co-author of the paper and professor in the Department of Geological and Atmospheric Sciences at Iowa State University, such findings are essential as they "reveal the recent warming in the Gulf of Maine" and offer the possible causes of such warming.

Related information about warming oceans is shown on the Australian Academy of Science's YouTube video below:

Check out more news and information on Global Warming in Science Times.