During the Last Glacial Maximum (LGM), around 20,000 years ago, the North Atlantic Ocean's subtropical gyre (STG) was much deeper and stronger than it is today. A gyre is a large system of rotating ocean currents. Today, the STG reaches depths of about 1 kilometer, but during the ice age, it extended down to 2.0-2.5 kilometers. This was due to stronger winds and cooler temperatures, which caused more water to sink and create denser water masses.

Scientists discovered this by studying tiny organisms called foraminifera, which lived in the ocean and left behind fossils in the seafloor. By analyzing the oxygen isotopes in these fossils, scientists could determine past water temperatures and the depth of the gyre. They found that the STG, including the powerful Gulf Stream, was not only deeper but also transported more water during the ice age.

These findings are important because they help us understand how ocean currents have changed over time and how they affect climate. The deeper and stronger gyre played a crucial role in moving heat from the tropics to higher latitudes, which impacted global climate patterns. This research also helps scientists improve their climate models, making predictions about future climate changes more accurate.

The North Atlantic's subtropical gyre was much more intense during the last ice age, driven by stronger winds and cooler conditions, which had significant effects on global ocean circulation and climate.