Over the past 2.8 million years, large ice sheets have repeatedly grown and decayed in Northwest Europe and evidence of these fluctuations is preserved in glacial sediments off the coast of Norway. Icebergs released by these ice sheets often scraped across the seafloor, sculpting iceberg scours in the sediments.
An exceptional ancient buried seafloor has been discovered, which exhibits iceberg scours with spiral shapes. This geometry shows that the icebergs were moved by a combination of the tide and an ancient version of the North Atlantic Current (NAC). Referring to these landforms, researchers from the University of Manchester were able to reconstruct the speed of the current from 430,000 years ago. These findings indicate that as the European ice sheets shrank, the NAC was approximately 50% slower than its present-day speed. This is significant because the NAC plays a crucial role in transporting heat from the tropics to Northwest Europe. Any change in the strength of the NAC would influence the climate of Northwest Europe.
The majority of research in this field has concentrated on the last glaciation, which is already well-documented. However, by investigating much older glaciation records, scientists will be far better equipped to accurately reconstruct historic glacial fluctuations and the rates and mechanisms of past climate change. This data should provide a metric to predict future changes.
- What methods and equipment are required to reconstruct a historic ocean current?
This research used 3D seismic reflection data to image buried seafloor surfaces offshore Norway.
On this buried seafloor, a number of exceptionally well-preserved landforms allowed the relative ratio between different ocean and tidal currents to be investigated and compared with the present day ratio in the same area. This landform record sits well with isolated geochemical data from offshore boreholes and allows for the ocean setting to be reconstructed.
- What insights do historic glacial fluctuation patterns provide when it comes to predicting future climate change?
A key part of predicting climatic change in the future is the ability to recreate conditions that are known to have occurred in the past, i.e. if the numerical models used to predict climate change cannot recreate the past, then we can have little faith in what they predict for the future. The ocean currents presented here provide an insight into what large-scale ice sheet melting can do to ocean currents in the North Atlantic.
These changes directly influence the climate and developing a better understanding of these changes is crucial. The time period to which these spiral features are dated is also one of the best fitted time periods for understanding what the climate system is doing as ice sheets rapidly melt; a situation that increasing evidence suggests is occurring due to anthropogenic warming of the atmosphere.