Coral reefs and sea-level change
Coral reefs and sea-level change
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DOI：
10.1016/j.margeo.2013.12.006
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发表时间：
2014-06
期刊：
影响因子：
2.9
通讯作者：
C. Woodroffe;J. Webster
中科院分区：
文献类型：
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作者：
C. Woodroffe;J. Webster
珊瑚礁因其地质保存和适合定年，为以前的海平面位置提供了重要的证据。对这一证据的解释假定了对珊瑚礁地貌、现代珊瑚礁生物分布和影响它们的环境因素的理解。化石礁梯田形成于末次间冰期，海洋氧同位素（MIS） 5e亚阶段（~ 128-116 ka），普遍存在于许多热带海岸线上，关于该高水位期间海平面达到的高度一直存在争议。来自许多末次间冰期遗址的观测表明，海平面至少比现在的海平面高3米，这意味着冰盖的范围比现在要小。在对构造活动部位进行隆升校正时，通常采用6米的标高。最近的汇编表明海拔可达8-9米，但从海平面以下发现最后一次间冰期的珊瑚礁上观察到的资料很少。在MIS 5e期间的海平面振荡已经从几个地点得到解释，最近的研究推断在间冰期结束时海平面迅速上升了几米。这些解释对于目前确定珊瑚年代和推断其古水深的精度是有限的。考虑到全新世珊瑚礁遗址之间的海平面变化，以及在均衡或弯曲调整中观察到的地理变化，将末次间冰期海平面变化限制在小于1-2米的不确定性范围内仍然存在争议，这并不奇怪。隆升边缘的珊瑚礁化石也为MIS阶段5c和5a提供了明确的证据，而Huon半岛的珊瑚礁化石表明了与Heinrich事件相关的波动（MIS 3）。解译结果显示，不同地点之间存在相当大的差异，在以前的间冰期，海平面时间和海拔高度的不确定性仍然较大。未来对保存在快速下沉边缘的化石礁的广泛序列的研究可以解决这些不确定性。水下珊瑚礁已经提供了关于上次冰川消退期间海平面上升的重要信息。在巴巴多斯岛和塔希提岛以及休恩半岛周围的岩心，已经产生了一幅大致一致的冰融化图像，反映了上一次冰川极大期以来的海平面上升变化。这些研究表明，珊瑚礁对与融水脉冲相关的海平面快速上升很敏感，一些珊瑚礁被淹没，而另一些则退缩了。综合海洋钻探计划（IODP）对塔希提岛和最近的大堡礁的考察，扩大了这些记录，但冰川融水脉冲的时间、性质和影响的细节仍然难以捉摸。全新世珊瑚礁的研究表明了不同的生长策略；一些跟上了海平面上升的速度，而另一些则在海平面下降时赶上了。全新世海平面似乎经历了一个逐渐上升的过程，直到现在横跨加勒比海，为珊瑚礁的垂直增生提供了容纳空间；而在印度-太平洋，海平面自7 ka以来一直接近目前的水平，许多礁滩是在海洋虹吸引起的海平面轻微下降后出现的。礁滩上的微环礁可能提供了过去海平面位置的最清晰证据，但如果没有它们，就需要新的生物或其他海平面指标来更好地约束古水深。迫切需要从其他关键的珊瑚礁位置进行进一步的研究，不仅要破译驱动过去海平面变化及其地理变异的过程，而且要更好地了解珊瑚礁在未来海平面上升的背景下将如何应对。
Coral reefs provide significant evidence for former sea-level positions because of their geological preservation and suitability for dating. Interpretation of this evidence presumes an understanding of reef geomorphology, modern reef organism distributions, and environmental factors influencing them. Fossil reef terraces, formed during the last interglacial, marine oxygen isotope (MIS) substage 5e (~ 128–116 ka), are prevalent on many tropical shorelines and there has been ongoing debate as to the height reached by sea level during that highstand. Observations from numerous last interglacial sites suggest that sea level was at least 3 m above present sea level, implying less extensive icesheets than at present. An elevation of 6 m has commonly been adopted when correcting tectonically active sites for uplift. Recent compilations suggest elevations up to 8–9 m, but incorporate few observations from reefs where the last interglacial is found below sea level. Oscillation of sea level during MIS 5e has been interpreted from several sites, with recent studies inferring rapid rise of several metres at the end of the interglacial. These interpretations are at the limits to the precision with which corals can currently be dated and their palaeo-water depths inferred. It is not surprising that constraining last interglacial sea-level changes within uncertainties of less than 1–2 m remains controversial, considering sea-level variations recognised between reef sites in the Holocene, and observed geographical variation in isostatic or flexural adjustments. Fossil coral reefs on uplifting margins also provide clear evidence for MIS substages 5c and 5a, and those on Huon Peninsula indicate fluctuations related to Heinrich events (MIS 3). Interpretations show considerable variability between sites, with still greater uncertainties about sea-level timing and elevation during previous interglacials. Future study of extensive sequences of fossil reefs preserved on rapidly subsiding margins could address these uncertainties. Submerged reefs have already yielded important information about sea-level rise during the last deglaciation. Coring around Barbados and Tahiti, as well as on the Huon Peninsula, has produced a broadly consistent picture of ice melt, reflecting eustatic change since the last glacial maximum. These studies have shown the sensitivity of reefs to rapid sea-level rise associated with meltwater pulses, with some reefs drowning while others back-stepped. Integrated Ocean Drilling Program (IODP) expeditions to Tahiti, and recently the Great Barrier Reef, extended these records, but details of timing, nature and impact of deglacial meltwater pulses remain elusive. Studies of Holocene reefs have indicated different growth strategies; some kept up with sea level, while others caught up when sea level decelerated. Holocene sea level appears to have experienced a gradual rise up to present across the Caribbean, providing accommodation space for reefs to accrete vertically; whereas in the Indo-Pacific sea level has been near its present level since 7 ka, with many reef flats emergent following a slight fall of sea level caused by ocean siphoning. Microatolls on reef flats provide perhaps the clearest evidence of past sea-level position, but, in their absence, novel biological or other sea-level indicators are required to better constrain palaeo-water depths. There is an urgent need for further research from additional key reef locations, not only to decipher processes driving past sea-level change and its geographical variability, but also to better understand how coral reefs will respond in the context of future sea-level rise.