作为全球碳循环的重要环节之一,甲烷厌氧氧化作用(Anaerobic Oxidation of Methane,AOM)不仅是微生物生态学领域最具科学魅力、充满学术争议的问题之一,也是调节地质历史时期地球环境和气候变化的重要因素之一。近年来,针对包括海洋在内的各种环境中的AOM展开了大量的研究,然而迄今为止,对该反应的运作机制仍缺乏足够了解,其中包括该作用对海洋环境和气候系统在过去、现在和未来的影响机理和程度问题,这说明对于甲烷最重要汇的了解还存在着盲区。以现代海洋地质环境中的AOM为研究对象,综述了其产生机理、反应底物、电子受体、以及涉及到其中的微生物等方面的最新研究成果,探讨了该作用对于地球环境、气候的影响意义及地质学启示,并尝试展望了需要进一步研究的几点方向,希望藉此能引起广大研究者的兴趣与重视。
Sedimentary sequence and sediment provenance are important factors when it comes to the studies on marine sedimentation. This paper studies grain size distribution, lithological characteristics, major and rare earth elemental compositions, micropaleontological features and ^(14)C ages in order to examine sedimentary sequence and sediment provenance of the core BH6 drilled at the mouth of the Yellow River in Bohai Sea. According to the grain size and the micropaleontological compositions, 4 sedimentary units have been identified. Unit 1(0–8.08 mbsf) is of the delta sedimentary facies, Unit 2(8.08–12.08 mbsf) is of the neritic shelf facies, Unit 3(12.08–23.85 mbsf) is of near-estuary beach-tidal facies, and Unit 4(23.85 mbsf–) is of the continental lake facies. The deposits from Unit 1 to Unit 3 have been found to be marine strata formed after the Holocene transgression at about 10 ka BP, while Unit 4 is continental lacustrine deposit formed before 10 ka BP. The provenances of core BH6 sediments show properties of the continental crust and vary in different sedimentary periods. For Unit 4 sediments, the source regions are dispersed while the main provenance is not clear, although the parent rock characteristics of a few samples are similar to the Luanhe River sediments. For Unit 3, sediments at 21.1–23.85 mbsf have been mainly transported from the Liaohe River, while sediments above 21.1 mbsf are mainly from the Yellow River and partially from the Liaohe River. For Unit 2, the sediments have been mainly transported from the Yellow River, with a small amount from other rivers. For Unit 1, the provenance is mainly the Yellow River catchment. These results help in better understanding the evolution of the Yellow River Delta.
SONG ShengFENG XiuliLI GuogangLIU XiaoXIAO XiaoFENG Li
Based on 17 AMS 14 C age data,we reconstructed high-resolution records of sea surface primary productivity(PP) in the southern Okinawa Trough(MD05-2908) over the last 6.8 ka BP using the calcareous nannofossil carbon isotope and the relative percentage contents of Florisphaera profunda indexes.The underlying mechanism controlling the sea surface PP was then discussed.The sea surface PP,indicated by the coccolith δ 13 C and %Fp conversional equations,decreased with some fluctuations since 6.8 ka BP.This decrease may be connected to the decreased terrigenous input resulting from the reduced East Asian Summer Monsoon(EASM) precipitation.Both the periods of 4-2 ka BP(PME) and 6.8-4.8 ka BP were characterized by relatively higher PP.The former was mainly controlled by the weakening of the Kuroshio Current,whereas the latter mainly resulted from the greater terrigenous input associated with the stronger EASM.
