Reconstructing centuries of Arctic climate and sea ice conditions using annually-banded coralline algae

在过去的几十年里，北极的快速变暖导致了海冰范围和厚度的急剧下降，其速度超过了气候模式所模拟的速度。如果目前的趋势持续下去，预测表明北极夏季海冰可能在未来几十年内消失。然而，海冰模拟的不确定性很大，因为由于仪器和卫星记录较短，对海冰的长期变化了解甚少，一般不会超过20世纪70年代末。为了准确地模拟并预测北极气候的未来演变，有必要更好地了解过去几个世纪的气温和海冰的年际变化，特别是在工业革命之前，人类开始通过排放化石燃料影响气候和海洋化学。这种重建通常是通过使用代理档案来实现的，比如树木年轮或陆地上的冰芯。然而，直到最近，亚北极和北冰洋都没有这样的代理档案。在一项突破性的研究中，我的研究小组现在发现，浅海海底长寿命的珊瑚藻积聚可以用来重建过去650年里北极的气候和冰的变化。在广泛的海冰覆盖期间，很少有光到达海底，导致光合藻类的年增长率很低。相反，当海冰覆盖率低时，藻类的年增长率会增加。通过对藻类生长和地球化学组成的逐年测量，可以重建过去的海冰覆盖和温度。珊瑚藻的堆积在整个北冰洋都很普遍，它们可以附着在浅海底生活几个世纪，同时在它们的钙质骨骼中形成每年的生长带。

Rapid Arctic warming during the past decades has contributed to a dramatic decline of sea-ice extent and thickness at a pace greater than simulated by climate models. If current trends persist, projections suggest that Arctic summer sea-ice may disappear within the next decades. However, the uncertainties in sea-ice modelling are large as long-term sea-ice variability is poorly understood due to short instrumental and satellite records, generally not extending beyond the late 1970s. In order to accurately model and therefore project future evolution of Arctic climate, it is essential to have a better understanding of year-to-year temperature and sea-ice variability during the past centuries, particularly prior to the industrial revolution when humans started impacting climate and ocean chemistry by the emission of fossil fuels. Such reconstructions are typically achieved by using proxy archives, such as tree rings or ice cores on land. Until recently though, no such proxy archive was known from the Subarctic and Arctic Ocean. In a breakthrough study my research group has now discovered that long-lived coralline algal buildups on the shallow sea floor can be used to reconstruct Arctic climate and ice variability during the past 650 years. During times of extensive sea ice cover little light reaches the seafloor resulting in low annual growth rates of the photosynthetic algae. In contrast, when sea ice cover is low annual algal growth rates increase. By measuring algal growth and geochemical composition year-by-year into the past sea ice cover and temperatures can be reconstructed. Coralline algal buildups are widespread throughout the entire Arctic Ocean where they can live for centuries attached to the shallow seafloor while forming annual growth bands in their calcitic skeletons. The overarching goal of this proposal is to develop a network of multicentury records of past seawater temperature, seasonal duration of sea-ice, and ocean chemistry from the skeletons of coralline algae to better understand historic changes in subarctic-arctic marine environments. Reconstructions will focus on recently collected samples from the Canadian Arctic, Greenland, and Spitsbergen - key sites that are characterised by strong seasonal temperature and sea-ice fluctuations. This research will provide much needed baseline data and a historic perspective for upcoming changes that will impact shipping, infrastructure and resource development and therefore Northern communities.