Analysis of carbon burial flux and source in coastal sediments of Lianyungang since the Mid−Holocene

This paper is the result of environmental geological survey engineering.

Objective The influencing factors and driving mechanism of carbon burial in coastal zones and shelf areas are one of the global research hotspots. Previous researches are generally limited to single−hole studies of total organic carbon （TOC）, and systematic study of total carbon (TC) and TOC are rarely conducted. This article systematically studies the factors affecting the carbon burial and preservation of sediments in Lianyungang since the Middle Holocene, which can serve to evaluate the regional carbon storage capacity.

Methods Through the determination of TOC, TC, and TN (total nitrogen) δ¹³C content of sediments, combined with AMS¹⁴C dating, X−ray diffraction, soluble salt, foraminifera and particle size data since the Mid-Holocene, the spatial and temporal distribution characteristics of carbon burial, carbon sources and the main influencing factors of carbon burial were analyzed in the coastal area of Lianyungang.

Results A chronostratigraphic classification was carried out using historical geography combined with AMS¹⁴C dating data, which was divided into three depositional stages: Stage I is 6325−722 a BP period, it is a shelf sedimentary environment, TOC_BF (TOC burial flux) average value is 8.1 g /(m²·a), the average value of TC_BF (TC burial flux) is 24.9 g /(m²·a). Stage II is the coastal shelf−near coastal environment during 722−205 a BP, with an average TOC_BF of 57.0 g /(m²·a) the average value of TC_BF is 271.8 g /(m²·a). Stage Ⅲ is an offshore-intertidal environment during 205−0 a BP. The values of TOC_BF and TC_BF are equivalent to those of stage Ⅱ. Although TOC content of the sediments in stage Ⅰ is slightly higher than that in stages Ⅱ and Ⅲ, the deposition rate of stage Ⅱ and Ⅲ is affected by the source replenishment after the Yellow River captures Huaihe River, and the deposition rate has increased by 5−9 times, so TC_BF and TOC_BF have increased by 8−11 times.

Conclusions TC content of sediment is mainly influenced by the modern circulation controlled by the strong East Asian monsoon, and TC is mainly composed of inorganic carbon with an average share of about 70% and a maximum of 84%. During the period of 6325−3000 a BP, TC content was low, or it was related to the strong East Asian monsoon during this period. The mean grain size values at this stage were also larger than that of other sedimentary stages. The source of TOC is mainly from marine sources, accounting for about 67%. The superficial TOC value is higher, which is related to the short storage time of superficial TOC, part of TOC has not been completely mineralized and decomposed, and the impact of human activities.