Geomorphology of the Belize Barrier Reef margin: a survey for IODP drilling

作为沿伯利兹堡礁沿着进行IODP钻探的先决条件，计划沿约100米至约100米之间的前礁区沿着选定部分，利用多波束和浅层地震技术进行详细的水深测量研究。20-150米水深的主要礁缘。到目前为止，没有详细的和全球定位系统控制的水深测量和连续的高分辨率地震数据的堡礁边缘存在。根据将获得的数据，我们打算选择合适的地点进行IODP钻探。我们假设，冰后期低位和海侵礁标志着明确的地形线性构造/阶地沿着平台边缘。我们的目标是定位前礁遗址，这将适合恢复冰后期（20-10 kyr BP）和下伏的旧更新世沉积物沿着一系列的核心横贯。此外，还计划举办一次国际讲习班，将感兴趣的科学家聚集在一起，探讨为印度洋钻探方案制定钻探建议的可能性。随后的IODP提案可能有四个潜在的目标，包括重建冰后期海平面上升，分析和量化冰后期珊瑚礁的组成和结构，以响应海平面和气候变化，并获得在该时间窗内的温度和碳酸盐饱和度的环境数据。此外，更新世的珊瑚礁的起源和古生态学方面可能会进行调查，这取决于旧更新世演替的恢复。在模拟的21世纪海平面上升的增加，冰后期淹没的珊瑚礁序列沿着伯利兹边缘可能被用于未来的海平面预测。在印度-太平洋地区，人们已经获得了几个高分辨率和科学可靠的冰后期珊瑚礁海平面记录（休恩半岛、塔希提岛、大堡礁），而在热带西大西洋（巴巴多斯、东加勒比）只有一个这样的记录。然而，巴巴多斯的记录很奇怪，因为在最近从塔希提岛（IODP航段310）和大堡礁（IODP航段325）获得的海平面数据中，只检测到融水脉冲（MWP）1A和1B。此外，丰富的冰后期微生物岩相发现在大溪地和大堡礁显然是没有在巴巴多斯迄今未知的原因。从这些简单的生物体（细菌）的代理数据（厚度，体积）在很大程度上是环境控制，大概更容易解释为代理数据（sclerochronology，d18 O，Sr/Ca）从encymatically控制珊瑚礁的框架建设者，如珊瑚。微生物岩的丰度是否与腹地的性质、碳酸盐饱和度和海平面上升速度有关一直存在争议。总之，来自热带大西洋的第二个冰后期珊瑚礁档案肯定有助于回答这些公开和有争议的问题，并限制冰后期西大西洋海平面上升的性质。

As precondition for IODP drilling along the Belize Barrier Reef, a detailed bathymetric study using multibeam and shallow seismic techniques is planned along selected section of the forereef area between ca. 20-150 m water depth of this major reef margin. To date, no detailed and GPS-controlled bathymetry and continuous high-resolution seismic data of this barrier reef margin exists. Based on the data to be acquired, we intend to select suitable sites for IODP drilling. We hypothesize that postglacial lowstand and transgressive reefs mark clear topographic lineaments / terraces along the platform margin. We aim at locating fore-reef sites, which will be suitable to recover postglacial (20-10 kyr BP) and underlying older Pleistocene deposits along a series of core traverses. Furthermore, an international workshop is planned to bring together interested scientists in order to explore the possibilities of developing a drill proposal for the IODP. The subsequent IODP proposal could have four potential objectives including the reconstruction of postglacial sea-level rise, to analyze and quantify postglacial reef composition and architecture as response to sea-level and climate change, and to obtain environmental data on temperature and carbonate saturation during that time window. In addition, aspects of Pleistocene reef initiation and paleoecology may be investigated, depending on recovery in older Pleistocene succession. In the light of the modelled 21st century increase in sea-level rise, postglacial drowned reef sequences along the Belize margin can potentially be used for future sea-level projections. In contrast to the Indo-Pacific region where several highly resolved and scientifically robust reef-based postglacial sea-level records have been acquired (Huon Peninsula, Tahiti, Great Barrier Reef), there is only one such record in the tropical western Atlantic (Barbados, eastern Caribbean). The Barbados record is curious however, in the light of the fact that of meltwater pulses (MWP) 1A and 1B only the former has been detected in the recently acquired sea-level data from Tahiti (IODP leg 310) and the Great Barrier Reef (IODP leg 325). Also, abundant postglacial microbialite facies found in the Tahiti and Great Barrier is apparently absent in Barbados for hitherto unknown reasons. Proxy data (thickness, volume) from these comparably simple organisms (bacteria) are largely environmentally controlled and presumably easier to interpret as proxy data (sclerochronology, d18O, Sr/Ca) from encymatically controlled reefal framebuilders such as corals. It has been debated whether microbialite abundance is linked to the nature of the hinterland, carbonate saturation, and rate of sea-level rise. In summary, a second postglacial reefal archive from the tropical Atlantic would certainly help to answer these open and debated questions and to constrain the nature of postglacial sea-level rise in the western Atlantic.