Late-Holocene salinity changes in Lake Ogawara, Pacific coast of northeast Japan, related to sea-level fall inferred from sedimentary geochemical signatures

Fumiko Watanabe Nara*, Takahiro Watanabe, Tetsuya Matsunaka, Shin ichi Yamasaki, Noriyoshi Tsuchiya, Koji Seto, Kazuyoshi Yamada, Yoshinori Yasuda

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

4 Citations (Scopus)

Abstract

This study aimed to provide important insights into Pacific Ocean sea-level changes by clarifying salinity changes in Lake Ogawara on the Pacific coast of northeast Japan, which became brackish in the late Holocene. Radiocarbon (14C) dating, tephrochronology, and geochemical signatures, including bromine (Br), iodine (I), total sulfur (TS), total organic carbon (TOC), and total nitrogen (TN), were applied to continuous sediment core from Lake Ogawara to estimate salinity changes. The core has two tephra layers, the Towada eruption (To-a; approximately 915 CE) and the Changbaishan eruption (B-Tm; 946 CE). An age model for the core was established using plant macro remain 14C ages constrained by a B-Tm tephra. The depletion of marine-derived elements (Br, I, and TS) was observed in 2200–2000 cal BP layers, indicating a paleosalinity change from saline to brackish conditions caused by falling sea levels during the late Holocene. Variations in Br, I, TOC, and TN concentrations were significantly changed compared to those below the B-Tm layer. High correlations between Br and TOC and I and TOC above the B-Tm tephra layer to the surface indicated an organic source for the halogens post the Changbaishan eruption, indicating a change to the hydrological system of the lake's watershed. The increasing variation in the C/N atomic ratio in the post-B-Tm sediments also supported this hydrological change. Two recorded significant volcanic eruptions could have triggered these changes to the Lake Ogawara water inflow system.

Original languageEnglish
Article number110907
JournalPalaeogeography, Palaeoclimatology, Palaeoecology
Volume592
DOIs
Publication statusPublished - 2022 Apr 15

Keywords

  • B-Tm tephra
  • Brackish lake
  • C
  • Halogens
  • Sea-level changes
  • Tohoku

ASJC Scopus subject areas

  • Oceanography
  • Ecology, Evolution, Behavior and Systematics
  • Earth-Surface Processes
  • Palaeontology

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