Abstract
Carbon and nitrogen contents and their isotopic components, and AMS (Accelerator Mass Spectrometry) radiocarbon dating ages, were measured for 57 coastal sediments from Weizhou Island to analyze the distribution of total inorganic carbon (TIC) and its carbon and oxygen isotopic components (δ13Ccarb and δ18Ocarb), total organic carbon (TOC) and total nitrogen (TN) contents and their stable isotopic components (δ13CTOC and δ15NTN), and their environmental significance. The results showed that the oldest age of coastal sediments on Weizhou Island was 2750 cal. a BP (before present), and the average TIC contents of cores A1, A2, B1, C1, and D1 in the intertidal zone were all greater than 5%, where δ13Ccarb and δ18Ocarb were enriched, whereas the TIC contents in cores A3, C2, and D2 of the supra-tidal zone were low, where δ13Ccarb and δ18Ocarb were depleted. Moreover, TIC decreased sharply, 4.95% on average, to close to zero from the estuary to the upstream region in the C1-C2 section. The average C/N ratio was 7.02, and δ13CTOC and δ15NTN were between −14.96‰ and −27.26‰ and −14.38‰ and 4.12‰, respectively. These measurements indicate that the TIC in coastal sediments mainly came from seawater. Cores A1, A2, and B1 in the northern intertidal zone exhibited organic terrestrial signals because of C3 and C4 plant inputs, which indicates that the important source on the northern coast of Weizhou Island came from island land but followed the decrease in C3 plants. The lacustrine facies deposits were mainly distributed in the upper reaches of the river, the northern coastline was advancing toward the sea, and part of the southwestern coastal sediments rapidly accumulated on the shore under the influence of a storm surge. The relative sea level of the Weizhou Island area has continuously declined at a rate of approximately 2.07 mm/a, using beach rock as a marker, since the Holocene.
Highlights
Continental margin sediments contain more than 90% of the carbon buried in the ocean, and the estuary coastal zone, as a sensitive exchange zone for sea–land carbon pools, effectively indicates that the global carbon cycle process is driven by sea level changes [1,2]
We aim to explore the material provenance of Weizhou Island through the changes in total inorganic carbon (TIC), δ13 Ccarb, δ18 Ocarb, C/N, δ13 CTOC, and δ15 NTN to assess the suitability of these proxies as indicators for the inorganic carbon formation process, organic matter source, and environmental evolution process regarding relative sea level fluctuation and dominant vegetation type since the late Holocene
The results of inorganic carbon in the coastal sediments of Weizhou Island show that the average value of TIC is between 0.02% and 10.52%, and polarized between intertidal and supra-tidal
Summary
Continental margin sediments contain more than 90% of the carbon buried in the ocean, and the estuary coastal zone, as a sensitive exchange zone for sea–land carbon pools, effectively indicates that the global carbon cycle process is driven by sea level changes [1,2]. The most importantbyform of inorganic carbon in marine sediments is carbonate, whose or dissolution is controlled the overlying water and pore water ion concentration, pH, temperature, precipitation or dissolution is controlled by the overlying water and pore water ion concentration, CO2 diffusion rate, and biological disturbance [8,9]. Because total inorganic carbon (TIC) mainly comes pH, temperature, CO2 diffusion rate, and biological disturbance [8,9]. Because total inorganic carbon from water evaporation, lighter 12 C and 16 O are preferentially gathered in the reactants under the (TIC) mainly comes from water evaporation, lighter 12C and 16O are preferentially gathered in the isotope dynamic fractionation mechanism.
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