Source: Geophysical Research Letters
The island prefecture of Hokkaido, Japan’s second largest island, has a rich cultural history of hunter-gatherers on land and at sea. Over thousands of years through the Holocene and into the 19th century, the prevalence of these cultures across the island has risen and fallen. Climatic oscillations and changing seas were probably important factors in these cultural changes, a new study shows.
Historically, Hokkaidō was home to two main types of subsistence cultures: land hunter-gatherers, such as the Zoku-Jomon and Satsumon peoples, and seafarers like the Okhotsk people. The Zoku-Jomon and Satsumon peoples gathered and probably managed millet, barley, and beans, while the Okhotsk mainly fished, hunted sea mammals such as seals, and harvested other sea foods. Each group is ancestral to the contemporary Ainu people.
Historical records and archaeological evidence of these three cultures span thousands of years, from 8,000 years before the present to the end of the 19th century, when modern lifestyles began to replace the culture of hunters- pickers. Historians and scientists thought changes in which cultures were dominant and where they were located could be linked to climate, but evidence to strongly connect the dots was lacking.
In search of an answer, paleoclimatologists Masanobu Yamamoto and Osamu Seki, both from Hokkaidō University in Japan, turned to a peat bog on Rishiri Island, north of Hokkaidō, to test whether its deep peat deposits might hold clues to past climates. With students in tow, the two researchers extracted 5-meter bog cores comprising mainly peat moss commonly found in subpolar bogs around the world. Researchers carbon dated the nucleus and analyzed the oxygen isotopic composition of cellulose in peat moss and grasses, because oxygen isotopes in plants are related to climatic factors such as rainfall, humidity and water source.
The authors used oscillations in cellulose oxygen isotopes to reconstruct 4,400 years of the position of summer westerly winds, which influence the summer monsoon, and a regional ocean current called the Tsushima Hot Stream, which provides warm, moist air to the region. They discovered a large shift in oxygen isotopes around 2,300 years ago, suggesting a shift in the climate of northern Hokkaido from mainly control of westerly winds and monsoons to control of the hot current. from Tsushima.
Changes in the location of the sea-dependent Okhotsk culture correlated with the strength of the warm Tsushima Current, which cut off nutrients that stimulated growth throughout the food chain. As climatic controls changed, so did the cultures of Hokkaidō – from about 1,600 to 1,100 years ago, the marine culture of Okhotsk developed as the warm Tsushima Current is weakened. But as Tsushima’s warm current grew stronger and nutrients dwindled, inland cultures flourished and developed.
Inland Zoku-Jomon and Satsumon cultures were more sensitive to summer westerly winds and the monsoon season. When westerly winds shifted north, hot, humid summers persisted.
“Most people think that climate change affects human societies, but we still don’t have a good understanding of the mechanisms and processes of how this happens,” Yamamoto said. “I think this [study] is a very important step for our field. Examining cultures like these, which have close and direct ties to their environment and climate, is a useful way to learn how different societies are responding to climate change, he added. (Geophysical Research Letters, https://doi.org/10.1029/2021GL0966112022)
—Rebecca Dzombak (@bdzombak), science writer