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

作为沿伯利兹堡礁进行IODP钻井的先决条件，计划在该主要珊瑚礁边缘约20-150米水深之间的前礁区域选定部分使用多波束和浅层地震技术进行详细的测深研究。到目前为止，还没有详细的gps控制的深海测量和连续的高分辨率地震数据。根据获得的数据，我们打算选择合适的地点进行IODP钻探。我们假设冰期后的低水位和海侵礁标志着台地边缘清晰的地形地貌/阶地。我们的目标是定位礁前遗址，这些遗址将适合恢复冰期后（20-10 kyr BP）和沿着一系列岩心穿越的下伏更老更新世沉积物。此外，计划举办一次国际讲习班，召集感兴趣的科学家，探讨为国际开发计划署拟订钻探建议的可能性。随后的IODP提案可能有四个潜在目标，包括重建冰川后海平面上升，分析和量化冰川后珊瑚礁组成和结构对海平面和气候变化的响应，以及获得该时间窗内温度和碳酸盐饱和度的环境数据。此外，根据古更新世演替的恢复，可以研究更新世礁的形成和古生态学的各个方面。根据模拟的21世纪海平面上升的增加，伯利兹边缘的冰后淹没礁序列可能被用于未来的海平面预测。在印度-太平洋地区，已经获得了几个高度确定的、科学上可靠的基于珊瑚礁的冰川后海平面记录（Huon半岛、塔希提岛、大堡礁），与此相反，热带西大西洋地区（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 leg 310）和大堡礁（IODP leg 325）获得的海平面数据中，只检测到1A和1B的融水脉冲（MWP）。此外，在塔希提岛和大堡礁发现的丰富的冰川后微生物岩相在巴巴多斯显然不存在，原因迄今尚不清楚。来自这些相对简单的生物（细菌）的替代数据（厚度、体积）在很大程度上是受环境控制的，可能更容易解释为来自珊瑚等受环境控制的珊瑚礁框架构建者的替代数据（年代学、d18O、Sr/Ca）。微生物岩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期后珊瑚礁档案肯定有助于回答这些公开和有争议的问题，并限制西大西洋冰期后海平面上升的性质。

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.