Stable carbon and nitrogen isotope variations in sedimentary organic matter in the Sea of Japan since 37 ka: Paleoceanographic implications

doi:10.13745/j.esf.sf.2022.1.6

Abstract

Abstract:

Stable carbon and nitrogen isotopes in sedimentary organic matter (δ¹³C and δ¹⁵N) have been widely used in the organic matter source tracing and reconstruction of paleoproductivity and paleoenvironment. A pronounced feature of sedimentary δ¹³C and δ¹⁵N in the Sea of Japan is their synchronous negative excursions during the Last Glacial Maximum (LGM), yet the causes and mechanisms of this phenomenon are poorly understood. In this study, we investigated the evolutionary history of sedimentary δ¹³C and δ¹⁵N since 37 ka in core LV53-23-1 retrieved from the Oki Ridge of the central Sea of Japan. According to the results, sedimentary δ¹³C and δ¹⁵N ranged from 26.3‰ to 22.5‰ and 1.6‰ to 6.1‰, respectively, with the lower values coinciding with the deposition of dark laminated mud during the LGM (26.5-17 ka), indicating an increased contribution of terrestrial organic matter. Both δ¹³C and δ¹⁵N showed positive excursions during Heinrich Statidal 1 (17-14.5 ka), indicating distinct oceanic environmental changes in the Sea of Japan, which corresponds to the Tsushima Strait flooding and the Tsushima Warm Current invasion into the Sea of Japan at that time. After 14.5 ka sedimentary δ¹⁵N reached ~5‰, comparable to the average δ¹⁵N of nitrate in seawater. We estimated the relative contributions of organic sources using a binary mixing model. The contribution of terrigenous organic matter ranged between 65% to 80% in the LGM, while marine source contributed between 60% to 80% since 14.5 ka. Besides, sedimentary δ¹⁵N depletion during the LGM can be caused by (1) improved nitrogen fixation in the surface water of the Sea of Japan due to higher dust-borne Fe supply, and (2) decreased effects of early diagenesis on sedimentary δ¹⁵N due to prevailing suboxic or anoxic environment. Taken together, the variations of sedimentary δ¹³C and δ¹⁵N in the Sea of Japan since 37 ka are controlled by eustatic sea level and global climate changes, which modulate the organic source, nutrient supply, primary productivity, and redox conditions in water column and sediment.

Key words: stable carbon and nitrogen isotopes, sedimentary organic matter sources, sea level, last glacial period, Sea of Japan

CLC Number:

P736.4

ZOU Jianjun, ZONG Xian, ZHU Aimei, DOU Ruxi, LIN Jinhui, FENG Xuguang, DONG Zhi, Sergey A. GORBARENKO, ZHENG Liwei, SHI Xuefa. Stable carbon and nitrogen isotope variations in sedimentary organic matter in the Sea of Japan since 37 ka: Paleoceanographic implications[J]. Earth Science Frontiers, 2022, 29(4): 123-135.

Figures/Tables 10

Fig.1 Location of the study area and surface circulation in and around the Sea of Japan

Table 1 Age control points of core LV53-23-1

层位 /cm	测试材料和地层标志层	AMS ¹⁴C 年龄/a	日历年龄/ka	沉积速率 /(cm·ka^-1)
31	TL1		11.40
40	N.pachyderma+G.bulloides	12 000±50	13.32	4.69
60	N.pachyderma s.+G.bulloides	15 200±45	17.58	4.69
80	N.pachyderma sin	19 100±85	22.18	4.35
110	N.pachyderma sin	23 500±140	26.91	6.34
128-131	A-Tn		29.40	7.24
158	N.pachyderma+G.bulloides	29 300±270	32.80	7.94
208	N.pachyderma+G.bulloides	34 200±200	38.33	9.04

Fig.2 Temporal profiles of sedimentary organic proxies of core LV53-23-1

Fig.3 Scatter plots of (a) TOC vs. TN, (b) TOC vs. mean grain size (adapted from [47]), and (c) TOC vs. chlorin (adapted from [25])

Fig.4 Scatter plots of (a) δ15N vs. δ13C, δ15N vs. chlorin (adapted from [25]), and (c) δ13C vs. TOC/TN

Fig.5 Comparisons of temporal profiles between sedimentary organic matter δ13C, δ15N in core LV53-23-1 and in (a) sediment trap (adapted from [51-52]) or (b) in other cores (adapted from [7,8,39])

Fig.6 Discrimination plots for sedimentary organic sources. (a) TOC/TN vs. δ13C. (b) δ15N vs. δ13C.

Fig.7 Comparisons of temporal profiles between sedimentary organic matter δ13C, δ15N and other sedimentary proxies of core LV53-23-1

Fig.8 Comparisons of temporal profiles between sedimentary organic matter δ13C, δ15N and climate and environmental proxies

Fig.9 A Schematic illustration of the environmental evolutions in the Sea of Japan during the Last Glacial Maximum (a) and since 14.5 ka (b)

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