A Lacustrine Biomarker Record From Rebun Island Reveals a Warm Summer Climate in Northern Japan During the Early Middle Holocene Due to a Stronger North Pacific High

The summer climate of northern Japan since the last glacial period has likely been determined by atmospheric and oceanic dynamics, such as changes in the North Pacific High, the position of the westerlies, the Kuroshio Current, the Tsushima Warm Current (TWC), and the East Asian summer monsoon. However, it is unclear which factor has been most important. In this study, we analyzed leaf wax δ13C and δD and glycerol dialkyl glycerol tetraethers (GDGTs) in sediments from Lake Kushu, Rebun Island, northern Japan, and discuss changes in climate over the past 17,000 years. The GDGT-based temperature, the averaged chain length, δ13C and δD of long-chain n-fatty acids indicated that the climate was cold during the Oldest Dryas period ∼16 ka and warm in the early Middle Holocene from ∼9 to 6 ka. This climate change is consistent with the sea surface temperature in the Kuroshio–Oyashio transition, but inconsistent with changes in the TWC in the Sea of Japan. The results imply that the summer climate of northern Japan was controlled mainly by changes in the development of the North Pacific High via changes in the position of the westerly jet and East Asian summer monsoon rainfall, whereas the influence of the TWC was limited over a millennial timescale.

Marine Reservoir Effects Deduced from 14C Dates on Pottery Residues, Bones, and Molluskan Shells from the Hamanaka 2 Archaeological Site, Rebun Island, Hokkaido, Japan

This article investigates the marine reservoir effects from apparent age differences among molluskan shells, birds, and sea mammals from the Hamanaka 2 archaeological site, Rebun Island, Japan, which was occupied during the latter half of the Late Jomon period (1300−1200 cal BC). The radiocarbon ages were younger in the order of charred wood<marine molluskan shells<Alcidae<Japanese sea lion≤charred materials on potsherds. According to data from molluskan shells from the site, the local marine reservoir correction (ΔR) for the Soya Warm Current, which flows near Rebun Island, was 172±39 14C yr. ΔR values of bone collagen for Alcidae (a family of seabirds) and Japanese sea lion were 289 and 389 14C yr, respectively. A ΔR value of 447±55 14C yr was obtained on charred material from the inner surfaces of potsherds at Hamanaka 2. The different reservoir effects relate to the differences in the diets or habitats of the shellfish, sea lion, and seabird remains at the site.