30ka以来南海东北部陆坡坡底沉积有机质的长链正构烷烃特征及其古植被意义

为探寻南海深海平原区的有机质组成特征、来源及其所反映的古气候/环境演化信息, 对南海东北部深水区的ZSQD289沉积柱状样品进行了正构烷烃组成及其单体稳定碳同位素的相关分析, 结合孢粉鉴定结果, 重点探讨该沉积区末次冰期以来陆源输入变化、源区的古植被演化及其气候响应因素。结果表明:30ka以来, 南海东北部深海陆坡坡底的沉积有机质以洋/陆混源为特征, 且以海洋自生生产力贡献为主, 其生源贡献存在明显的冰期/间冰期旋回变化特征, 冰期时陆源有机质输入明显高于全新世间冰期; 其陆源有机质应该主要由台湾南部河流输入, 在低海平面时通过海底峡谷搬运至此, 其过程中可能受到西太平洋底流和黑潮的影响。该沉积源区植被演化经历了C3/C4植物互为消长的变化过程, 但30ka以来主要还是以C3植物占优势, 由此推测末次冰期以来源区(台湾岛南部)不存在明显的干旱化, 冰期虽然温度较低但气候比较湿润。

THE n-ALKANE RECORDS FROM SEDIMENTS IN THE BASE OF SLOPE (NEAR ABYSSAL PLAIN) OF THE NORTH-EASTERN SOUTH CHINA SEA (SCS) OVER THE LAST 30ka: IMPLICATIONS FOR PALEOVEGETATION

To investigate organic sources and paleo-environmental response on geological time scales in the Abyssal Plain of the South China Sea(SCS), we selected the sediment core ZSDQ289(20°52'N, 119°52.3'E) with length 847cm, collected from the base of slop in the northeastern SCS in 2011. The core has relatively uniform lithology and steady deposition which is composed of gray and dark gray siliceous and calcareous clay with thin sandsilt interbed. Its data frame was established by linear interpolation method according to the oxygen isotope curve of Globigerinoides ruber shells and the AMS14 C data of G. ruber shells and organic matters. The top age of the core is about 1ka and its bottom age is about 30ka. The content of n-alkanes and their compound-specific stable carbon isotopes were analyzed at a relatively low resolution to trace the glacial-interglacial variations, with 46 samples covering a total of 30ka, which has been investigated concerning their organic matter composition, terrigenous sources contribution and paleo-climatic/environmental change since 30ka.Alkane proxies of L22-/H23+ and C31/C17 ratios indicated that the sediment organics were contributed from mixed marine and terrestrial sources and dominated by the marine contribution over the past 30ka. The L22-/H23+ ratios decreased while C31/C17 increased obviously during glacial period. The average total content of long-chain n-alkane(nC25~nC33), representing terrestrial high plants contribution, were higher by around 0.17μg/g in glacial period than those in interglacial period. In addition, the past C3/C4 plants composition of terrestrial contribution was reconstructed using compound-specific stable carbon isotopes of long-chain n-alkanes combined with some other appraisal proxies(eg. C31/C27, ACL, and pollen data). The calculated results from a binary end-member model showed that the C4 % contribution ranges from 29.78 % to 52.58 %, and the average C4 % in glacial and interglacial period is 42.59 % ±3.73 % and 36.66 % ±4.22 %, respectively. Obviously the vegetation composition of the provenance(the southern Taiwan Island)of core ZSQD289 was dominated by C3 plants throughout the past 30ka, which indicated that the provenance was not dry even during the last glacial period as the temperature was low.