IODP Site Survey of V-Shaped Ridge Features, North Atlantic Ocean

尽管人们普遍认为板块运动是由地幔的热对流维持的，但我们仍然对对流的空间和时间细节知之甚少。因此，任何可以用来限制这种环流性质的观测都是特别有意义的。此外，在重要的古海洋门户，对流环流变化产生的垂直运动可能对古代温盐环流产生重要影响。在北大西洋，位于冰岛以南大洋中脊两侧的V型海脊，长期以来一直被认为是冰岛羽流内瞬时对流行为的直接表现。最近的分析表明，从大洋中脊挖出的岩石的化学成分，加上V形海脊的水深表示，需要热的(30-35摄氏度)羽流物质脉冲，才能在北大西洋下方放射状展开。这些热脉冲与垂直抬升的时间变化有关，而垂直抬升反过来又缓和了北部成分水(即北大西洋深水的古老前身)横跨格陵兰-苏格兰山脊的溢出。因此，地幔对流对全球输送带关键部分的古代温盐环流具有直接和可测量的影响。尽管取得了这些重要进展，但人们对V型脊线的详细结构和化学成分知之甚少。模型依赖于20世纪60年代采集的质量较差的地震反射剖面。我们将获取、处理、解释一组横跨V形山脊的地震反射剖面，并对其进行建模，这些剖面在冰岛西南部表达得最好。辅助的在航数据将包括多波束测深、重力和磁力剖面以及玄武岩的疏浚。我们的调查将实现两个重要目标。首先，在每个拟议的IODP钻井地点，一组高分辨率剖面将对沉积盖层的详细结构以及沉积物-基底界面进行成像，这将构成计划中的钻探段的现场勘测。其次，这些剖面将被用来确定过去1500万年来瞬变羽流行为的详细年表。这一年表将与正在进行的玄武岩地球化学和古海洋学研究结合起来。我们的研究结果将对定量认识北组分水上第三系溢流具有重要意义。

Although there is general agreement that plate motions are maintained by thermal convection of the Earth's mantle, we still know rather little about the spatial and temporal details of the convective flow. Thus any observations that can be used to constrain the nature of this circulation are of particular interest. Furthermore, at significant palaeoceanographic gateways, vertical movements generated by changes in convective circulation are likely to have had an important impact on ancient thermohaline circulation. In the North Atlantic Ocean, the V-shaped ridges, which lie on either side of the mid-oceanic ridge south of Iceland, have long been regarded as a direct manifestation of transient convective behaviour within the Icelandic plume. Recent analysis has shown that the chemistry of rocks dredged from the mid-oceanic ridge combined with the bathymetric expression of the V-shaped ridges require hot (30-35 degrees Centigrade) pulses of plume material to spread out radially beneath the North Atlantic Ocean. These hot pulses are linked with temporal changes in vertical uplift which in turn moderate the overflow of Northern Component Water (i.e. the ancient precursor of North Atlantic Deep Water) across the Greenland-Scotland Ridge. Thus mantle convection has a direct and measurable effect on ancient thermohaline circulation in a key portion of the global conveyor. Despite these important advances, the detailed structure and chemistry of the V-shaped ridges are very poorly known. Models are reliant upon poor quality seismic reflection profiles which were acquired in the 1960s. We will acquire, process, interpret and model a set of seismic reflection profiles across the V-shaped ridges where they are best expressed southwest of Iceland. Ancillary underway data will include multi-beam bathymetric, gravity and magnetic profiling, and dredging of basalts. Our survey will achieve two important aims. First, a set of high resolution profiles which image the detailed structure of sedimentary cover together with the sediment-basement interface at each of the proposed IODP driill sites will constitute a site survey for the planned drilling leg. Secondly, these profiles will be used in their own right to determine the detailed chronology of transient plume behaviour over the last 15 million years. This chronology will be combined with ongoing studies of basalt geochemistry and palaeoceanography. Our results will have an important impact upon the quantitative understanding of Neogene overflow of Northern Component Water.