Palaeobotanical records from Rebun Island and their potential for improving the chronological control and understanding human–environment interactions in the Hokkaido Region, Japan

Abstract

Rebun Island with Hamanaka and Funadomari among the 43 documented archaeological sites and the environmental archive stored in the Lake Kushu sediment proves to be one of the key areas to study the interplay between ecology, climate and human activities. This paper focuses on the potential of palaeobotanical records from Rebun Island for improving the chronological control and understanding of late Quaternary climate changes and habitation environments of northern hunter-gatherers in the Hokkaido Region of Japan. A set of 57 radiocarbon dates of the RK12 core (Lake Kushu) demonstrates that it represents a continuous environmental archive covering the last c. 17,000 years. The RK12 pollen record reflects distinct vegetation changes associated with the onset of the lateglacial warming about 15,000 cal. yr BP and the cold climate reversal after c. 13,000 cal. yr BP. The onset of the current Holocene interglacial after c. 11,700 cal. yr BP is marked by a major spread of trees. The middle Holocene ( c. 8000–4000 cal. yr BP) is characterized by a major spread of deciduous oak in the vegetation cover reflecting a temperature increase. A decline of oak and spread of fir and pine is recorded at c. 2000 cal. yr BP. After c. 1100 cal. yr BP, arboreal pollen percentages decrease, possibly linked to intensified usage of wood during the Okhotsk and Ainu culture periods. The results of diatom analysis suggest marshy or deltaic environments at the RK12 coring site prior to c. 10,500 cal. yr BP and a brackish lagoon between c. 10,500 and 7000 cal. yr BP. A freshwater lake developed after 6500 cal. yr BP, likely reflecting sea level stabilization and formation of the sand bar separating the Kushu depression from the sea. Plant macrofossil analysis shows use of various wild plants and also domesticated barley during the Okhotsk and Ainu periods.

Diatoms from Lake Kushu: A pilot study to test the potential of a Late Quaternary palaeoenvironmental archive from Rebun Island (Hokkaido Region, Japan)

“…Radiocarbon dates were calibrated against the calibration curve Intcal13 (Reimer et al, 2013), and the model was constructed using the free-shape algorithm (Goslar et al, 2009). The grey silhouettes along the best-fit line represent calibrated 14 C dates taken into account by the model, while the not-filled silhouettes left of the best-fit line represent older 14 C dates rejected by the model (redrawn after Müller et al, 2016). Research question Does RK12 show maximum lacustrine extent between 4.9 and 3.1 ka as suggested by Sato et al (1998) Sato et al (1998)?…”

“…The modern landscape is considerably deforested and Sasa spp. (bamboo grass from the Poaceae family) became widespread on the entire island (Müller et al, 2016). Patchy forests and shrubs occupy the river and spring valleys.…”

“…3). A detailed description of the 14 C data and discussion of the calibration issues and age-depth model for the RK12 core will be presented in a separate paper (Müller et al, 2016).…”

“…Asterisks mark cultures of which remains were found on Rebun Island. Archaeological dates from Müller et al (2016).…”

“…kyr BP), and Historic Ainu (0.7-0.1 cal. kyr BP; Müller et al, 2016) cultures that were recently found on Rebun Island, this area is of special interest for the BHAP research. So far there are 43 sites on Rebun Island, with the oldest residential sites dated to ca.…”