The timing and amplitude of Pleistocene sea-level lowstands and deglacials from U-Th chronology of Great Barrier Reef corals (Expedition 325)

对过去海平面的研究对于寻求了解地球气候的研究人员来说非常感兴趣。海平面代表了陆地上冰层所锁住的水量。因此，对海平面的研究可以告诉我们过去的气候状态--低海平面反映了地球历史上冰盖更大的寒冷冰期;高海平面反映了温暖的间冰期。我们对现代冰盖如何应对人为变暖的认识还不全面。围绕冰盖行为的最重要问题之一是确定对变暖的反应的崩溃率，这将影响未来海平面上升的速度。解决这个问题的一种方法是检查过去的海平面上升率与已知的冰盖崩溃时期的非人为条件下第四纪冰川间冰期过渡。化石珊瑚提供了过去海平面的间接测量，因此回答了过去海平面如何（以及何时）变化的问题。珊瑚只生活在海平面以下，也可以确定它们生长在海平面以下多远。这一水深估计是基于我们发现的珊瑚类型以及我们发现的与它们相关的其他动物群和植物群。沿着我们发现珊瑚的海拔高度，这个水深估计使我们能够重建过去海平面的高度。这个重建的海平面所代表的时间也可以从珊瑚中测量出来。我们利用在珊瑚生长过程中自然结合到珊瑚骨骼中的铀（及其放射性衰变产物-钍）来计算珊瑚的年龄。这种U-Th测年技术可以找到珊瑚的年龄从1到60万年。然而，在调查过去的海平面时存在一个问题，因为过去的海平面比现在低得多（在最近的冰川时期，海平面为c。120米低于现代水平）。海平面低时生长的珊瑚很难接近，现在海平面已经上升到现代水平-它们在水下深处。为了解决这个问题，并从更深的地方恢复样本，将有一个IODP钻探考察大堡礁。这次考察将钻探以前现场调查中通过形态学确定的化石珊瑚礁。这些珊瑚礁化石位于水深44至123米的地方，保存着来自较低海平面的珊瑚档案。我们的计划是从这些化石礁中取样，使用U-Th测年法确定它们的年龄，然后重建冰川时期海平面低的时候的海平面。这些对低海拔的估计将用于调查驱动地球自然气候系统的机制。在这方面，从低海平面到高海平面的变化的时间和速率特别重要，使我们能够测试潜在强迫（地球绕太阳轨道的变化，或内部气候强迫，如大气CO2浓度）和气候响应（海平面）之间的任何超前滞后关系。

The study of past sea level is of great interest to researchers seeking to understand the Earth's climate. Sea level is a proxy for the amount of water locked up on the land as ice sheets. The study of sea level therefore can tell us about the past state of the climate - low sea levels reflect colder, glacial, periods in Earth history when ice sheets were larger; high sea levels reflect warmer, interglacial, intervals. Our knowledge of how modern ice sheets will respond to anthropogenic warming is not yet comprehensive. One of the most important questions surrounding ice sheet behaviour is the determination of collapse rates in response to warming, which will influence future rates of sea level rise. One way to approach this question is to examine past rates of sea level rise associated with known periods of ice sheets collapse under the non-anthropogenic conditions Quaternary glacial-interglacial transition. Fossil corals provide an indirect measurement of past sea level and therefore answering questions about how (and when) it has changed in the past. Coral only live below sea level and it is also possible to determine how far below sea level they grew. This water depth estimation is based on the types of coral we find and the other fauna and flora we find associated with them. Along with the elevation that we recovered the coral from, this water depth estimation enables us to reconstruct the height of past sea level. The time that this reconstructed sea level represents can also be measured from the coral. We use the uranium (and the product of its radioactive decay - thorium) naturally incorporated into the coral's skeleton during growth to calculate an age for the coral. This U-Th dating technique can find the age of corals from 1 to 600,000 years old. There is, however, a problem in investigating past sea levels which were much lower than present (during the most recent glacial period sea level was c. 120m below modern levels). The corals that grew when sea level was low are hard to access now sea level has risen to its modern level - they are deep underwater. To solve this problem and recover samples from deeper localities, there will be an IODP drilling expedition to the Great Barrier Reef. This Expedition will drill into fossil coral reefs that have been identified by their morphology by a previous site survey. These fossil reefs are at water depths of 44 to 123m and preserve an archive of corals from lower sea levels. It is our plan to take samples from these fossil reefs, use U-Th dating to determine their ages, and then reconstruct sea level for glacial periods while sea level was low. These estimates of low stand sea level will be used to investigate mechanisms that drive the Earth's natural climate system. The timing and rate of changes from low to high sea level are particularly important in this respect, allowing us to test any lead-lag relationship between a potential forcing (changes in the Earth's orbit around the Sun, or internal climate forcing such as atmospheric CO2 concentration) and climatic response (sea level).