The world’s oceans have a significant impact on the climate as heat and CO2 stores. Using sediment samples and model calculations, a study now shows that the surface water in the North Pacific was even warmer than it is today during the last Ice Age. The ocean ensured mild temperatures in the Bering Strait between Asia and America and created good living conditions for the first people to colonize the American continent.
How did the first people come to America? According to the best-established theory, they reached the new continent from East Asia during the last Ice Age via a land bridge in the Bering Sea that existed at the time. But thick ice sheets prevented them from penetrating further inland North America, and climate changes made the land bridge disappear. This created an isolated population that lived in what is now Alaska for several millennia. Fossil pollen and insects suggest that the climate there was relatively mild at the time. But how was that possible given the icy temperatures in neighboring regions?
Ocean currents for a mild climate
A team led by James Rae from the University of St Andrews has now found a plausible answer to this question: “Our data show that the Pacific had a warm current system during the last Ice Age, similar to the Atlantic today, which is responsible for the mild climate in Northern Europe cares, ”says Rae. In order to obtain information about the temperature, the content of salt and nutrients and the currents of the Pacific during the last ice age, the researchers examined sediment samples from the deep sea. The composition of the millennia-old deposits told them that the Pacific used to have stronger intermingling currents that brought warm water from subtropical regions to the north.
The surface water in the northern area of the Pacific was therefore warmer, more salty and poor in nutrients than it is today. “The warm currents may have created a much more pleasant climate in this region than was previously thought,” says Rae’s colleague William Gray. “That could have created a mild climate in the coastal regions of the North Pacific, which created temperate ecosystems on land and in the water, and enabled people to survive in the otherwise harsh climatic period.”
Oceans as carbon stores
The researchers’ data also shows that the Pacific likely stored more CO2 during the Ice Age than it does today. “The Pacific contains 30 times more carbon than the atmosphere,” they explain. “If we do not understand how the ocean behaves under different climatic conditions, we are missing an important part in understanding the global climate system.” Today’s North Pacific contains many nutrients in the upper water layers and releases CO2 into the atmosphere. In the last ice age, on the other hand, the better mixing of the water layers and the lower nutrient content apparently led to CO2 from the atmosphere being stored in the Pacific.
As the researchers’ model calculations show, the ocean’s ability to store CO2 depends crucially on its currents. The currents are in turn influenced by the climate. “Our work shows how dynamic the earth’s climate system is,” says co-author Robert Wills from the University of Washington in Seattle. “Changes in the circulation of the oceans and the atmosphere can have a major impact on how well people can live in different environments. This is also relevant to understanding how different regions will be affected by the future effects of climate change. “
Source: James Rae (University of St Andrews) et al., Science Advance, doi: 10.1126 / sciadv.abd1654