Impact of skeletal dissolution and secondary aragonite on trace element and isotopic climate proxies in Porites corals
Impact of skeletal dissolution and secondary aragonite on trace element and isotopic climate proxies in Porites corals
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DOI：
10.1029/2007pa001462
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发表时间：
2007-12
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影响因子：
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通讯作者：
E. Hendy;M. Gagan;J. Lough;M. McCulloch;P. deMenocal
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作者：
E. Hendy;M. Gagan;J. Lough;M. McCulloch;P. deMenocal
1986年从澳大利亚大堡礁中部一个活生生的大型波利特人聚居地采集的珊瑚岩芯中发现了最近溶解和次生文石充填的限制区域。次生文石针，≥20μm长，覆盖1972年至1974年底沉积的骨骼表面，使堆积密度增加10%。在这个区域上方可以观察到溶解，而更老的骨骼是原始的。我们通过与在附近珊瑚礁采集的8个当代Porite殖民地的类似记录进行比较，研究了这两种类型的早期海洋成岩作用对骨骼地球化学和珊瑚古气候重建的影响。次生文石的过度生长导致了骨骼密度、镁/钙、锶/钙、U/Ca、δO和δC的异常。次生文石始终与每个海表面温度指标(δO-SST-1.6°C；SR/Ca-SST-1.7°C；Mg/Ca-SST-1.9°C；U/Ca-SST-2.8°C)的冷温异常有关。通过不一致的淋溶作用，溶解也会产生冷却的SST人工制品，但仅限于微量元素比率(Mg/Ca-SST-1.2°C；Sr/Ca-SST-1.2°C；U/Ca-SST-2.1°C)。在海水中溶解珊瑚骨架的优先顺序是：Mg>；Ca>；sr>；U；因此，有必要对重建古气候的珊瑚材料进行严格的筛选，以检测溶解和次生矿物的存在。不同成岩作用模式产生的表面SST异常之间的良好一致性意味着，单一珊瑚内的示踪剂复制不能用于验证气候代理解释。然而，不同珊瑚群体之间记录的重复性很差，这提供了强烈的非气候人工产物，如溶解和次生文石。版权所有2007年，美国地球物理联盟。
Restricted zones of recent dissolution and secondary aragonite infilling were identified in a coral core collected in 1986 from a living massive Porites colony from the central Great Barrier Reef, Australia. Secondary aragonite needles, ≥20 μm long, cover skeletal surfaces deposited from 1972 to late 1974 and increase bulk density by 10%. Dissolution is observed above this zone, whereas older skeleton is pristine. We investigate the impact of both types of early marine diagenesis on skeletal geochemistry and coral paleoclimate reconstructions by comparison with similar records from eight contemporary Porites colonies collected at nearby reefs. Secondary aragonite overgrowth causes anomalies in skeletal density, Mg/Ca, Sr/Ca, U/Ca, δ O, and δC. The secondary aragonite is consistently associated with a cool temperature anomaly for each of the sea surface temperature (SST) proxies (δO-SST -1.6°C; Sr/Ca-SST -1.7°C; Mg/Ca-SST -1.9°C; U/Ca-SST -2.8°C). Dissolution, through incongruent leaching, also causes cool SST artifacts but only for trace element ratios (Mg/Ca-SST -1.2°C; Sr/Ca-SST -1.2°C; U/Ca-SST -2.1°C). The sequence of preference with respect to dissolution of coral skeleton in seawater is Mg > Ca > Sr > U. Rigorous screening of coral material for paleoclimate reconstructions is therefore necessary to detect both dissolution and the presence of secondary minerals. The excellent agreement between apparent SST anomalies generated by different modes of diagenesis means that replication of tracers within a single coral cannot be used to validate climate-proxy interpretations. Poor replication of records between different coral colonies, however, provides a strong indication of nonclimatic artifacts such as dissolution and secondary aragonite. Copyright 2007 by the American Geophysical Union.