A photomicrograph of a section of the hinge of an Arctica islandica shell, taken at 20x magnification. These rings of these shells allowed scientists to accurately date them and use to assess ocean conditions at a given time. Credit: Maya Feldberg-Bannatyne.
Key points:
- Scientists reconstructed 300 years of hydrographic variability in the Gulf of Maine using clam shells.
- The Gulf of Maine took about 900 years to cool by 2°C and only 100 years to warm by 2°C.
- The warming is likely due to increased atmospheric greenhouse gas concentrations and changes in western North Atlantic circulation, and will only worsen in time.
The shells of long-lived clams, in combination with climate simulations, have revealed that for the first time in 900 years, the waters of the Gulf of Maine have warmed.
“Both the clams and the climate model simulations suggest that greenhouse gas forcings are not only likely causing surface temperature changes affecting the Gulf of Maine, but also causing changes in ocean circulation. The pathways and the strengths of different ocean currents bringing water into the Gulf of Maine have changed as the region has warmed,” said Nina Whitney, lead author of the paper and postdoctoral fellow at the Woods Hole Oceanographic Institution (WHOI).
Whitney and her team used chemical signatures from the shells of arctica islandica, or ocean quahog/clams, to study changes in ocean conditions. Arctica islandica are the perfect samples as they can live up to about 500 years and grow their shells in annual increments, similar to tree rings. For the study, oxygen isotopes detected in the shells served as a proxy for seawater temperature and salinity, while nitrogen and radiocarbon isotopes were proxies for water mass source.
Combined with climate model simulations from the Community Earth System Model-Last Millennium Ensemble, the researchers found that the rate of warming since the early 20th century in the Gulf of Maine stands out in the context of the last 1000 years, and reverses a long-term multi-century cooling trend that occurred up to the late 1800s.
“The reality is that it took about 900 years to cool by 2°C and only 100 years to warm by 2°C. Unfortunately, warming in the Gulf of Maine will likely continue and worsen in the coming decades with negative impacts on the entire ecosystem,” said says Alan Wanamaker, study co-author and professor in the department of geological and atmospheric sciences at Iowa State University.
The open-access study is published in Communications Earth & Environment.
Information provided by WHOI.