Atmosphere and Ocean Research Institute, University of Tokyo, Kashiwa, Japan.
Department of Earth and Planetary Science, Graduate School of Science, University of Tokyo, Tokyo, Japan.
Nature. 2018 Jul;559(7715):603-607. doi: 10.1038/s41586-018-0335-4. Epub 2018 Jul 25.
The approximately 10,000-year-long Last Glacial Maximum, before the termination of the last ice age, was the coldest period in Earth's recent climate history. Relative to the Holocene epoch, atmospheric carbon dioxide was about 100 parts per million lower and tropical sea surface temperatures were about 3 to 5 degrees Celsius lower. The Last Glacial Maximum began when global mean sea level (GMSL) abruptly dropped by about 40 metres around 31,000 years ago and was followed by about 10,000 years of rapid deglaciation into the Holocene. The masses of the melting polar ice sheets and the change in ocean volume, and hence in GMSL, are primary constraints for climate models constructed to describe the transition between the Last Glacial Maximum and the Holocene, and future changes; but the rate, timing and magnitude of this transition remain uncertain. Here we show that sea level at the shelf edge of the Great Barrier Reef dropped by around 20 metres between 21,900 and 20,500 years ago, to -118 metres relative to the modern level. Our findings are based on recovered and radiometrically dated fossil corals and coralline algae assemblages, and represent relative sea level at the Great Barrier Reef, rather than GMSL. Subsequently, relative sea level rose at a rate of about 3.5 millimetres per year for around 4,000 years. The rise is consistent with the warming previously observed at 19,000 years ago, but we now show that it occurred just after the 20-metre drop in relative sea level and the related increase in global ice volumes. The detailed structure of our record is robust because the Great Barrier Reef is remote from former ice sheets and tectonic activity. Relative sea level can be influenced by Earth's response to regional changes in ice and water loadings and may differ greatly from GMSL. Consequently, we used glacio-isostatic models to derive GMSL, and find that the Last Glacial Maximum culminated 20,500 years ago in a GMSL low of about -125 to -130 metres.
大约 1 万年的末次冰期最大值是地球最近气候历史上最冷的时期。与全新世相比，大气中的二氧化碳含量低约 100ppm，热带海洋表面温度低约 3 至 5°C。末次冰期最大值始于大约 31000 年前全球平均海平面（GMSL）突然下降约 40 米的时候，并在接下来的 10000 年里迅速融化进入全新世。融化的极地冰盖的质量和海洋体积的变化，以及 GMSL 的变化，是描述末次冰期最大值和全新世之间以及未来变化的气候模型的主要约束条件；但这一转变的速度、时间和幅度仍然不确定。在这里，我们表明大堡礁大陆架边缘的海平面在 21900 年至 20500 年前下降了约 20 米，相对于现代海平面为-118 米。我们的研究结果基于回收和放射性测年的化石珊瑚和珊瑚藻组合，代表了大堡礁的相对海平面，而不是 GMSL。随后，相对海平面以每年约 3.5 毫米的速度上升了大约 4000 年。这一上升与之前在 19000 年前观察到的变暖一致，但我们现在表明，它发生在相对海平面下降 20 米和全球冰量增加之后。我们的记录的详细结构是可靠的，因为大堡礁远离以前的冰盖和构造活动。相对海平面可能受到地球对冰和水负荷的区域变化的影响，与 GMSL 可能有很大的不同。因此，我们使用冰川均衡模型来推导出 GMSL，并发现末次冰期最大值在 20500 年前达到了一个大约-125 至-130 米的 GMSL 低值。
