Marine Geology & Seafloor Surveying, Department of Geosciences, University of Malta, Msida, Malta.
Helmholtz Centre for Ocean Research, GEOMAR, Kiel, Germany.
Nat Commun. 2020 Mar 13;11(1):1372. doi: 10.1038/s41467-020-14770-7.
Although offshore freshened groundwater (OFG) systems have been documented in numerous continental margins worldwide, their geometry, controls and emplacement dynamics remain poorly constrained. Here we integrate controlled-source electromagnetic, seismic reflection and borehole data with hydrological modelling to quantitatively characterise a previously unknown OFG system near Canterbury, New Zealand. The OFG system consists of one main, and two smaller, low salinity groundwater bodies. The main body extends up to 60 km from the coast and a seawater depth of 110 m. We attribute along-shelf variability in salinity to permeability heterogeneity due to permeable conduits and normal faults, and to recharge from rivers during sea level lowstands. A meteoric origin of the OFG and active groundwater migration from onshore are inferred. However, modelling results suggest that the majority of the OFG was emplaced via topographically-driven flow during sea level lowstands in the last 300 ka. Global volumetric estimates of OFG will be significantly revised if active margins, with steep coastal topographies like the Canterbury margin, are considered.
尽管已在全球众多大陆边缘记录到了离岸淡化地下水 (OFG) 系统，但这些系统的几何形状、控制因素和就位动力学仍未得到很好的约束。在这里，我们整合了源电磁、地震反射和钻孔数据以及水文模型，以定量描述新西兰坎特伯雷附近一个先前未知的 OFG 系统。OFG 系统由一个主要的和两个较小的低盐地下水体组成。主体从海岸延伸至 60 公里，海水深度为 110 米。我们将盐度的沿架变异性归因于渗透率的非均质性，这是由于有渗透管道和正常断层，以及在海平面低期间由河流补给。推断 OFG 的地下水是由大气降水补给的，并且从陆地上活跃的地下水迁移而来。然而，模拟结果表明，在过去 30 万年的海平面低位期间，OFG 的大部分是通过地形驱动的流动来安置的。如果考虑到像坎特伯雷边缘这样具有陡峭海岸地形的活动边缘，全球 OFG 的体积估计将得到重大修正。
