Abundance And Composition Of Organic Matter In The Seafloor Surface Sediments From The Offshore Area Surrounding The Leizhou Peninsula

The source of organic matter in the marine sediments on the marginal sea of the continental shelf is very complicated.The source and storage status of organic matter are affected by a variety of environmental factors.Therefore,further understanding of the source and preservation of organic matter from the sediments in the marginal sea is of great significance for the deep understanding of the global carbon cycle.In this paper,the seafloor surface sediments in the offshore area of the Leizhou Peninsula will be used as the research object.The various properties of the sediments?TOC,TN,redox potential,p H value,particle size,the stable isotope of organic carbon and nitrogen?and the composition of n-alkanes will be combined.The content,composition,source and preservation of organic matter in the seafloor surface sediments in the offshore area of the peninsula were analyzed,and the spatial distribution and source of the organic matter in the seafloor surface sediments in the offshore area of the Leizhou Peninsula were discussed,as well as their indication significance to the environment.According to the research results:The TOC and TN content of the seafloor surface sediments in the study area varied from 0 to 0.79%and 0.011%to 0.100%,respectively.The contents of TOC and TN are positively correlated with silt and clay grain-level sediments,indicating strong adsorption capacity of fine-grained sediments to organic matter.TOC and TN have high consistency in spatial distribution:high TOC value area and high TN value area?TOC>0.5%,TN>0.07%?are mainly distributed in the sea area near the Liusha Bay in the southwest of the Leizhou Peninsula;Low TN areas?TOC<0.3%,TN<0.05%?are mainly distributed in the offshore area in the northwest of the Leizhou Peninsula and the offshore area in the southeast of the Leizhou Peninsula.The Liusha Bay is a famous seawater pearl breeding base and shellfish breeding area in China,and its sediment organic matter content is greatly affected by human factors.The TOC/TN ratio of sediments ranged from 5.1 to 14.3,with an average value of9.1.The low-value area is located in the northeast sea area of the Leizhou Peninsula,and the high-value area is located in the offshore area on the west side of the Leizhou Peninsula.The value of?¹³C_org ranges from-22.47‰to-19.18‰,with an average of-20.58‰.There is a large difference in?¹³C_org between the sediments in the eastern and western the Leizhou Peninsula;the sediment?¹³C_org in the eastern sea area of the Leizhou Peninsula is more negative.The measured?¹⁵N value ranges from 3.35‰to6.98‰.The numerical ranges of TOC/TN and?¹³C_org,combined with the terrestrial and marine-derived?¹⁵N distribution ranges and their spatial distribution characteristics,indicate that the organic matter sources in the study area exhibit the characteristics of mixed inputs from marine and terrestrial.The sediment redox potential Eh showed that the sediment in the study area was weakly reduced to a reduced state.The redox potential of the sediment in the high-value area of TOC is low;the sediment Eh in the low-value area of TOC is high.However,the sediments'TOC content has a weak negative correlation with the oxidation-reduction potential Eh;this phenomenon may be due to the fact that the study area is offshore and the sedimentary environment is very complicated.The p H value of sediments in the study area was weakly alkaline,which was negatively correlated with the TOC content of some stations,but weakly negatively correlated with the overall study area.The chain length of n-alkanes in the sediment organic matter is distributed between n C₁₄?n C₄₀,the range of CPI_H is between 1.07?1.66 and the range of OEP is between 1.05?1.62,indicating that the odd-even advantage of high-carbon n-alkanes is not significant,indicating The input of terrestrial organic matter may be insignificant or its sedimentary environment is not conducive to the preservation of terrestrial organic matter or the input of human activities is more obvious.The source of organic matter is mainly sea-source input.Judging from other normal alkane characteristic parameters such as?T/?M,TAR,C₁₇/Pr,C₁₈/Ph,?n-Alk/(n-C₁₆),etc.,the source of organic matter in the seafloor surface sediments in the study area is subject to human activities.The impact is large and the input of terrestrial organic matter is not significant.The Pr/Ph ratio is between 0.26 and 0.96,which may indicate that the entire deposition environment is showing a reduced state.