The Croker Carbonate Slabs, in the UK sector of the Irish Sea, has shallow (70 to 100 m) water, strong (> 2 knot) tidal currents, coarse mobile surficial sediments and the most extensive methane-derived authigenic carbonate (MDAC) known in European waters. Multi-disciplinary studies (2004 to 2015) were commissioned specifically to document the benthic habitat, and have resulted in the designation of this site as a Marine Protected Area (MPA) under the European Commission’s Habitats Directive as an example of “Submarine structures formed by leaking gases”. However, this paper is focussed on the geoscience aspects of the site: the mineralogy and isotopic composition of the MDAC, its formation and age. It considers the implications of these findings with respect to the timing of the deglaciation of the area since the Last Glacial Maximum (LGM), and the environmental implications of the seepage of methane from the site over a period of at least 17,000 years. Carbon isotope ratios (δ13 C − 34 to − 54‰) confirm that the carbonate minerals (high-Mg calcite and aragonite) result from the anaerobic oxidation of methane. Widespread shallow gas within post-glacial sediments is sourced from underlying coal-bearing Carboniferous strata. Geophysical (side-scan sonar and multi-beam echo sounder) and visual surveys show that the MDAC occurs as isolated lumps, continuous pavements, and cliffs < 6 m tall, which post-date the post-glacial sediments, but are in places covered by a veneer of coarse mobile surficial sediments. U-Th dates (17,000 ± 5500 to 4000 ± 200 BP) suggest continual MDAC formation since the last glacial maximum, and constrain the postglacial sea level rise in this part of the Irish Sea; the site must have been submarine before MDAC formation started, whether or not methane was escaping. Visual and acoustic evidence of gas seepage is limited, but methane concentrations in the water are high (< 21.4 nmol l−1) and suggest present-day export to the atmosphere. It is also implied that significant methane release to the atmosphere occurred immediately after the retreat of the ice that covered the site during the LGM until 21.9 to 20.7 ka BP.

中文翻译：

---

Croker 碳酸盐板：爱尔兰海中大量甲烷衍生的自生碳酸盐——性质、起源、寿命和环境意义

Croker Carbonate Slabs 位于爱尔兰海的英国部分，具有浅水（70 至 100 m）、强大（> 2 节）的潮汐流、粗糙的可移动表面沉积物和已知最广泛的甲烷衍生自生碳酸盐 (MDAC)在欧洲水域。多学科研究（2004 年至 2015 年）专门用于记录底栖栖息地，并导致该地点被指定为欧盟委员会栖息地指令下的海洋保护区 (MPA)，作为“由泄漏气体”。然而，本文侧重于该地点的地球科学方面：MDAC 的矿物学和同位素组成、其形成和年龄。它考虑了这些发现对自末次盛冰期 (LGM) 以来该地区冰川消退时间的影响，以及在至少 17,000 年的时间里，该地点的甲烷渗漏对环境的影响。碳同位素比（δ13 C - 34 至 - 54‰）证实碳酸盐矿物（高镁方解石和文石）来自甲烷的厌氧氧化。冰川后沉积物中广泛存在的浅层气体来自下伏的含煤石炭纪地层。地球物理（侧扫声纳和多波束回声测深仪）和目视调查显示 MDAC 以孤立的块状、连续的路面和 <6 m 高的悬崖出现，这些悬崖比冰后沉积物的年代晚，但在某些地方被覆盖由一层粗糙的可移动表面沉积物覆盖。U-Th 日期（17,000 ± 5500 至 4000 ± 200 BP）表明自上次冰期最大值以来持续形成 MDAC，并限制爱尔兰海这部分地区的冰后海平面上升；无论甲烷是否逸出，该地点在 MDAC 形成之前一定是海底的。气体渗漏的视觉和听觉证据有限，但水中的甲烷浓度很高（< 21.4 nmol l-1），表明目前已排放到大气中。还暗示在 LGM 期间覆盖该地点的冰退缩后立即发生了大量的甲烷释放到大气中，直到 21.9 至 20.7 ka BP。