Multi-proxy Records Of Terrestrial And Marine Organic Matter Sources And Burial In Marginal Sea Sediment Over Different Time Scales

The identification of the origins of marine sedimentary organic matter plays animportant role when studying the migration/transformation processes of these organicmatters and the contribution of marginal seas on global carbon circles because of theinfluence of both climate change and human activity. The ratio of total organic carbonand total organic nitrogen (C/N Ratio) is one of the traditional indexes fordiscriminating the origin of sedimentary organic matter. Branched and IsoprenoidTetraether index (BIT) and Terrestrial and Marine Biomarker Ratio (TMBR) are twonew proxies proposed in recent years for estimating the relative contributions of TOMon sedimentary organic matters. BIT is based on the ratio of terrestrial soil anaerobicbacteria biomarker of branched glycerol dialkyl glycerol tetraethers (branchedGDGTs) and marine Thaumarchaeota biomarker of crenarchaeol. TMBR is based onthe ratio of terrestrial high plants biomarkers and marine algae biomarkers. Both thetwo indexes with certain terrestrial and marine end-values have been successfullyused for identifying the sources of marine sedimentary organic matter. In this paper,multi-indexes involving C/N ratio, BIT and TMBR have been proposed to evaluatethe relative contributions of TOM/MOM on the sedimentary organic matter and todiscuss the environmental factors influencing the burial of sedimentary organic matterin the site of DH11located in the Mud Area of Southern Cheju Island over the last100years and in the site of KCES1located in the Japan Sea during the last48ka BP.For site DH11, the mass accumulation rates (MARs) records of total organiccarbon (TOC) and marine biomarkers reveal a relatively stable trend for the burial ofMOM before1950s and an increasing trend for the burial of MOM and TOM after the1950s. The calculated TOM contribution using a binary mixture model based on C/Nratio, BIT and TMBR index varies from22%to30%,5.1%to12%and8.0%to26%, respectively. The differences on TOM contribution could be attributed to differentsources of organic matters used in these indexes. Low TOM contributions indicatethat MOM dominants in sedimentary TOC at site DH11. The decreasing of C/N ratio,BIT and TMBR indexes since1950s suggests the decline of TOM contributionbecause of more rapidly increasing of MOM than TOM. Enhanced East Asian WinterMonsoon and Kuroshio, and increased nutrient inputs may be attributed to theincreasing MOM contribution during the past50years.The records of marine biomarkers at KCES1station present that the buried MOMis at a low level during48-14ka BP and then increase after14ka BP. Low levels ofnutrient resulted from limited water mass exchange between the Tsushima WarmCurrent and the Japan Sea, and the strong stratification caused by low sea level lead tolow productivity in the Japan Sea and then low buried MOM during48-14ka BP. Theincreasing MOM after14cal ka BP is attributed to the invasion of the TsushimaWarm Current to the Japan Sea and the nutrient supply from the deep water becauseof the vertical mixing of seawater. The abnormally decreasing of buried TOC andMOM during10-6ka BP is attributed to the poor preservation efficiency of theorganic matter as a result of the increased advection of sea water. The TOM recordsreveal that More TOM is buried during the glacial period, but fewer duringinterglacial period. This is due to the shift of the mouth of Huanghe River andChangjiang Rriver to eastside because of declining of sea level during the glacialperiod and the high dust supply for the strengthened winter East Asian monsoon. AfterLGM period, the weakened winter East Asian monsoon and the increased sea levellead to shifting the mouth of the rivers westwardly and then the abrupt declining ofTOM. During14-11.5ka BP, the invasion of Tsushima Warm water into the Japan Seawith large amounts of terrigenous materials from East China Sea, cold and dryenvironment during YD and the enhanced winter monsoon have also resulted in theincreased TOM burial. Since8ka BP, the burial of TOM contains relatively stable forthe stable sea level and environment of the Japan Sea. In addition, the calculatedTOM contribution using a binary mixture model based on TMBR and BIT indexvaries from10%to71%and2.3%to12%, both suggesting the higher contribution of TOM on the buried organic matter during glacial period but lower contribution duringinterglacial period.Despite of the difference on the implications of the indices of C/N, BIT andTMBR and then the estimation on the contribution of TOM to the buried organicmatter, the comparison between these indexes, and especially their implications andinfluencing factors, can be better utilized for identifying the sources of marinesedimentary organic matter.