Raddatz Jacek, Liebetrau Volker, Rüggeberg Andres, Foubert Anneleen, Flögel Sascha, Nürnberg Dirk, Hissmann Karen, Musiol Johannes, Goepfert Tyler Jay, Eisenhauer Anton, Dullo Wolf-Christian
Institute of Geosciences, Goethe University Frankfurt, Altenhöferallee 1, 60438 Frankfurt, Germany.
GEOMAR Helmholtz Centre for Ocean Research Kiel, Wischhofstr. 1-3, 24148 Kiel, Germany.
Coral Reefs. 2022;41(4):1255-1271. doi: 10.1007/s00338-022-02249-4. Epub 2022 Apr 12.
Similar to their tropical counterparts, cold-water corals (CWCs) are able to build large three-dimensional reef structures. These unique ecosystems are at risk due to ongoing climate change. In particular, ocean warming, ocean acidification and changes in the hydrological cycle may jeopardize the existence of CWCs. In order to predict how CWCs and their reefs or mounds will develop in the near future one important strategy is to study past fossil CWC mounds and especially shallow CWC ecosystems as they experience a greater environmental variability compared to other deep-water CWC ecosystems. We present results from a CWC mound off southern Norway. A sediment core drilled from this relatively shallow (~ 100 m) CWC mound exposes in full detail hydrographical changes during the late Holocene, which were crucial for mound build-up. We applied computed tomography, Th/U dating, and foraminiferal geochemical proxy reconstructions of bottom-water-temperature (Mg/Ca-based BWT), δO for seawater density, and the combination of both to infer salinity changes. Our results demonstrate that the CWC mound formed in the late Holocene between 4 kiloannum (ka) and 1.5 ka with an average aggradation rate of 104 cm/kiloyears (kyr), which is significantly lower than other Holocene Norwegian mounds. The reconstructed BWT and seawater density exhibit large variations throughout the entire period of mound formation, but are strikingly similar to modern in situ observations in the nearby Tisler Reef. We argue that BWT does not exert a primary control on CWC mound formation. Instead, strong salinity and seawater density variation throughout the entire mound sequence appears to be controlled by the interplay between the Atlantic Water (AW) inflow and the overlying, outflowing Baltic-Sea water. CWC growth and mound formation in the NE Skagerrak was supported by strong current flow, oxygen replenishment, the presence of a strong boundary layer and larval dispersal through the AW, but possibly inhibited by the influence of fresh Baltic Water during the late Holocene. Our study therefore highlights that modern shallow Norwegian CWC reefs may be particularly endangered due to changes in water-column stratification associated with increasing net precipitation caused by climate change.
The online version contains supplementary material available at 10.1007/s00338-022-02249-4.
与热带冷水珊瑚类似，冷水珊瑚（CWC）能够构建大型三维珊瑚礁结构。由于持续的气候变化，这些独特的生态系统正面临风险。特别是，海洋变暖、海洋酸化和水文循环的变化可能危及冷水珊瑚的生存。为了预测冷水珊瑚及其珊瑚礁或珊瑚丘在不久的将来将如何发展，一个重要的策略是研究过去的化石冷水珊瑚丘，尤其是浅海冷水珊瑚生态系统，因为与其他深水冷水珊瑚生态系统相比，它们经历的环境变异性更大。我们展示了挪威南部一个冷水珊瑚丘的研究结果。从这个相对较浅（约100米）的冷水珊瑚丘钻取的一个沉积岩芯详细揭示了全新世晚期的水文变化，这些变化对珊瑚丘的形成至关重要。我们应用了计算机断层扫描、钍/铀测年，以及基于有孔虫地球化学指标重建底层水温（基于镁/钙的底层水温）、海水密度的δO，以及两者的组合来推断盐度变化。我们的结果表明，冷水珊瑚丘形成于全新世晚期4千年（ka）至1.5 ka之间，平均堆积速率为104厘米/千年（kyr），这显著低于其他全新世挪威珊瑚丘。重建的底层水温和海水密度在整个珊瑚丘形成期间呈现出很大的变化，但与附近蒂斯勒礁的现代原位观测结果惊人地相似。我们认为底层水温对冷水珊瑚丘的形成没有主要控制作用。相反，整个珊瑚丘序列中强烈的盐度和海水密度变化似乎受大西洋水（AW）流入与上覆的、流出的波罗的海水之间相互作用的控制。斯卡格拉克海峡东北部的冷水珊瑚生长和珊瑚丘形成受到强水流、氧气补充、强边界层以及通过大西洋水的幼体扩散的支持，但可能在全新世晚期受到新鲜波罗的海水的影响而受到抑制。因此，我们的研究强调，由于气候变化导致净降水量增加而引起的水柱分层变化，现代挪威浅海冷水珊瑚礁可能特别濒危。
在线版本包含可在10.1007/s00338 - 022 - 02249 - 4获取的补充材料。
