南沙群岛永暑礁澙湖沉积的晚全新世风暴事件记录

Storm Event Records from the Lagoon Sediment on Yongshu Reef of the Nansha Islands since Late Holocene

位于南沙群岛永暑礁西南小澙湖的南永4井岩芯柱中含多层珊瑚枝和珊瑚砾石的堆积,反映了突发性风暴事件造成的珊瑚碎屑快速搬运和堆积。全新世晚期约4 000 aBP以来,澙湖珊瑚砾堆积记录了1 400870BC、660BC390AD、600770AD和940-1992AD 4个主要的风暴事件频发时期,并且风暴的强度呈阶段性增强。风暴事件还表现出千年和百年尺度的周期性波动,具有1 280 a、370 a、210230 a、140150 a和90 a的准周期,与全新世气候环境的周期性变化相对应,很大程度上受太阳活动周期变化的影响。

The small atoll in the southwest of Yongshu Reef on the Nansha Islands is a typical close lagoon system, where there is a mass of original biogenic clastic deposit. The longest core （NY4） so far was acquired there in 2002. TIMS dating of coral branches and AMS 14C dating of foraminiferas with high precision reveal that the date of the core bottom is about 4000 aBP, corresponding to late Holocene. Sand and coarse silt are the main components in the sediment Of the core, but the coral branches and gravels appear in many layers of the core. Most of them keep the characteristics of fresh surface and edges, that reflects rapid transportation and deposition of the coral clast in lagoon caused by the abrupt storm events. Bulk of the branches and gravels of radii beyond 0.5 cm in the core were measured, and a time-sequence of coral branches and gravels was established. The result of singular spectrum analysis （SSA） on the sequence presents a new main component with a linear variation similar to the original sequence. The main component sequence shows that： storm events in the maritime space of the South China Sea have taken place frequently since 4000 aBP, and main storm events appeared in four periods including 1400 - 870BC, 660BC - 390AD, 600 - 770AD and 940 - 1992AD. The intensity of those storm events enhanced evidently with phases. The result from maximum entropy spectrum analysis on the main component sequence of decade resolution further reveals that： the storm events have represented distinct periodical variations since late Holocene, and the time sequence takes on five quasi-periods, including 1280a,370a,210 -230a,140 - 150a and 90a. The periodic characteristics correspond to the centennial and millennial periods of climatic change during Holocene with a mass of deposit sequence recorded detailedly, such as deep-sea deposit, lake deposit, peat deposit, ice core and tree rings. It can be inferred that the storm events in the South China Sea since late Holocene are correlative with the climatic changes in the Holocene and influenced largely by the periodical variations of solar activity.