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

Masanobu Yamamoto,Kazuyoshi Yamada,Pavel Tarasov,Fangxian Wang,Tomohisa Irino,Tsuyoshi Haraguchi,Kenta Suzuki,Xuan-Yu Chen,Katsuya Gotanda,Hitoshi Yonenobu

doi:10.3389/feart.2021.704332

Abstract

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 Highviachanges 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.

Highlights

The summer climate of northern Japan is influenced by the summer position of the westerly winds and the strength of the Tsushima Warm Current (TWC)
A northward shift in the position of the westerly jet increases the δD of precipitated water, and the associated higher fraction of summer-to-annual precipitation further increases the δD. These results suggest that the position of the westerly jet controls the amount of precipitation, as well as the δD of precipitated water over a long timescale
The glycerol dialkyl glycerol tetraethers (GDGTs)-based mean annual temperature (MAT), the average chain length (ACL), and the δ13C and δD of long-chain n-fatty acids indicated that climate was cold in the Oldest Dryas period and warm during 10–6 ka (Figure 4)

Summary

INTRODUCTION

The summer climate of northern Japan is influenced by the summer position of the westerly winds and the strength of the Tsushima Warm Current (TWC). Three precise tephra ages have been incorporated into the model for providing additional chronological constraints, given the identification of these tephra layers in the RK12 sediment core of Lake Kushu (Chen et al, 2016; Chen et al, 2019). These include B-Tm tephra (composite core depth—150.5 cm; 1,004 cal yr BP; Oppenheimer et al, 2017), Ko-g tephra (core depth—1,169 cm; 95.4% probability range—6,651–6,446 cal yr BP; Chen et al, 2021) and Ma-f∼j tephra (core depth—1,277 cm; 95.4% probability range—7,550–7,128 cal yr BP; Chen et al, 2021). Based on a multi-proxy approach (diatoms, aquatic pollen, algae, geochemistry), Schmidt et al (2019) reconstructed three phases of lake basin development, including a marshy phase between 16.6 and 9.4 cal ka BP, a lagoon phase between 9.4 and 5.9 cal ka BP, and a freshwater lake phase after 5.9 cal ka BP, as the sand bar separating the Kushu lagoon from the sea formed

Analytical Methods

DATA AVAILABILITY STATEMENT

CONCLUSION