Evolution of the paleo-Daesan Bay (Nakdong River, South Korea) as a result of Holocene sea level change

Abstract

To explore sea level transgression in low-lying inland areas and its possible influence on prehistoric cultures, we investigated the physical and geochemical features of 20-m-long sedimentary cores from the previously seawater-filled Daesan Basin located in the middle reach of the present Nakdong River in Korea as proxies for seawater transgression deep inland areas due to Holocene sea level rise. Based on the relationships among grain size, total sulfur content (TS%), and carbon/sulfur (C/S) ratio, the first transgressive event was detected at ca. 8500 cal yr BP, caused by seawater influx along the present Nakdong River. Higher TS% (0.8–1%) and interbedded fossil oysters at 8000–6000 cal yr BP indicate marine environments, supporting a paleo-Daesan Bay with water depth of ~10–8 m. The common peaks in TS%, in both inland paleo-Daesan Bay and a present coastal area (Suncheon Bay) in southern Korea (e.g., at 3200 and 4700 cal yr BP), may indicate intervals of higher salinity, which suggests simultaneous responses to changes in sea level or hydroclimate. The duration of marine environment (paleo-Daesan Bay) in the remote inland from ca. 8000–3200 cal yr BP provides an analog for inland paleo-bay studies in East Asia.

Holocene millennial-scale variability of coastal environments on the southern coast of Korea and its controlling factors

“…Based on the average values, these fluctuations can be roughly divided into five periods with reduced C/S ratios, suggesting higher salinity and more intensified anoxic conditions: 8900–8200, 7950–6500, 5200–4300, 3500–2600, and 2000–1100 cal yr BP.

Figure 7.( A–C ) Comparison of changes in the C/S ratio of core STP17-14 (this study) with those of core STP16-20 from Goheung Bay on the southern coast of Korea (Lim et al, 2019) and core STP18-06 from Daesan Plain (paleo-Daesan Bay), located at the middle reach of the Nakdong River, Korea (Lim et al, 2022). See Fig.

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“…Our results demonstrate the possible utility of δ 13 C TOC , δ 34 S TS , C/S ratios, and highresolution SR records for tracing past coastal environment changes, including anoxic conditions. With regard to anticipation of global warming and coastal responses, temperature increases in (Lim et al, 2019) and core STP18-06 from Daesan Plain (paleo-Daesan Bay), located at the middle reach of the Nakdong River, Korea (Lim et al, 2022). See Fig.…”

“…To examine whether these fluctuations occurred locally or regionally, we compared the time series of C/S ratios in this study with those from Goheung Bay on the southern coast of Korea (Lim et al, 2019) and from the previously seawater-filled Daesan Basin (paleo-Daesan Bay) located in the middle reach of the present Nakdong River, Korea (Lim et al, 2022). Based on the relationship between salinity and C/S ratio (Berner, 1984;Berner and Raiswell, 1984;Woolfe et al, 1995 and references therein) and differences from present river and innercontinental sediments (e.g., Liu et al, 2021Liu et al, , 2022Chang et al, 2022), the C/S ratios at the three sites (cores STP16-20 [Lim et al, 2019], STP17-14 [this study], and STP18-06 [Lim et al, 2022]) revealed frequent coastal environmental changes in terms of anoxic conditions (Fig. 7).…”

“…Figure7. (A-C) Comparison of changes in the C/S ratio of core STP17-14 (this study) with those of core STP16-20 from Goheung Bay on the southern coast of Korea(Lim et al, 2019) and core STP18-06 from Daesan Plain (paleo-Daesan Bay), located at the middle reach of the Nakdong River, Korea(Lim et al, 2022). See Fig.1for details.…”

“…Study areas (Gwangyang Bay and Goheung Bay) and coring sites on the southern coast of Korea. (A-D) Coring sites: STP17-14 (this study), STP16-20(Lim et al, 2019), STP17-13(Park et al, 2019), and STP18-05(Lim et al, 2022). (E and F) Testing past geomorphological changes between 1920 and 2013.…”