Sources and high burial efficiency of fossil organic carbon in small bays and implication for coastal carbon cycle

Ke Liu; Xiaotong Xiao; Hailong Zhang; Yujue Wang; Yang Ding; Zicheng Wang; Meixun Zhao

doi:10.1016/j.scitotenv.2024.170207

Sources and high burial efficiency of fossil organic carbon in small bays and implication for coastal carbon cycle

Sci Total Environ. 2024 Mar 15:916:170207. doi: 10.1016/j.scitotenv.2024.170207. Epub 2024 Jan 19.

Authors

Ke Liu¹, Xiaotong Xiao², Hailong Zhang³, Yujue Wang⁴, Yang Ding³, Zicheng Wang⁵, Meixun Zhao⁶

Affiliations

¹ Frontiers Science Center for Deep Ocean Multispheres and Earth System, Key Laboratory of Marine Chemistry Theory and Technology, Ministry of Education, Ocean University of China, Qingdao 266100, China; Laoshan Laboratory, Qingdao 266237, China; National Marine Environmental Monitoring Center, Dalian 116000, China.
² Frontiers Science Center for Deep Ocean Multispheres and Earth System, Key Laboratory of Marine Chemistry Theory and Technology, Ministry of Education, Ocean University of China, Qingdao 266100, China; Laoshan Laboratory, Qingdao 266237, China. Electronic address: xtxiao@ouc.edu.cn.
³ Frontiers Science Center for Deep Ocean Multispheres and Earth System, Key Laboratory of Marine Chemistry Theory and Technology, Ministry of Education, Ocean University of China, Qingdao 266100, China; Laoshan Laboratory, Qingdao 266237, China.
⁴ State Key Laboratory of Estuarine and Coastal Research, East China Normal University, Shanghai 200062, China.
⁵ Frontiers Science Center for Deep Ocean Multispheres and Earth System, Key Laboratory of Marine Chemistry Theory and Technology, Ministry of Education, Ocean University of China, Qingdao 266100, China.
⁶ Frontiers Science Center for Deep Ocean Multispheres and Earth System, Key Laboratory of Marine Chemistry Theory and Technology, Ministry of Education, Ocean University of China, Qingdao 266100, China; Laoshan Laboratory, Qingdao 266237, China. Electronic address: maxzhao@ouc.edu.cn.

PMID: 38244624
DOI: 10.1016/j.scitotenv.2024.170207

Abstract

Coastal seas receive and store large amounts of organic carbon (OC) from land and ocean, thereby playing a crucial role in the global carbon cycle. Understanding factors that influencing OC sources and burial efficiencies in coastal areas have been challenging. We selected the Jiaozhou Bay (JZB) and its surrounding rivers heavily affected by human activities as a case study small bay. We presented bulk parameters of grain size, sediment surface area (SSA), TOC content and carbon isotopes (δ¹³C_org and Δ¹⁴C_org), terrestrial biomarkers (∑C₂₇ + C₂₉ + C₃₁n-alkanes) and marine biomarkers (brassicasterol and dinosterol) in surface sediments and suspended particulates. Our results showed low TOC and biomarker contents in the Dagu River Estuary from the west of the JZB associated with coarse sediments and lower SSA. To estimate the OC proportions, we applied a three-end member mixing model based on TOC δ¹³C_org and biomarker ratios and obtained the OC contribution from phytoplankton (average 52 %), soil (average 34 %) and wetlands (average 14 %). A transect from east to west of the JZB was selected to further assess the OC age composition based on radiocarbon isotopic (¹⁴C) measurements for a new perspective. The lower Δ¹⁴C_org values in the east revealed fossil OC contributions from human activities, such as petroleum pollutant inputs from sewage outlets. Based on a dual‑carbon isotope (δ¹³C_org and Δ¹⁴C_org) mass balance mixing model, the OC contributions were 40 %, 34 %, 14 %, 12 % from fossil carbon, phytoplankton, wetlands and soil, respectively. The very high burial efficiency of fossil OC in JZB (111 ± 19 %) indicated that small bays such as the JZB could be an important sedimentary carbon sink.

Keywords: Anthropogenic activities; Burial efficiency; Jiaozhou Bay; Organic carbon; Source.