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

过去几十年来，北极迅速变暖，导致海冰范围和厚度急剧减少，其速度超过了气候模型的模拟。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，海冰建模的不确定性很大，因为由于仪器和卫星记录较短，一般不会超过1970年代后期，因此对海冰的长期变化性知之甚少。为了准确地模拟并预测北极气候的未来演变，必须更好地了解过去几个世纪的逐年温度和海冰变化，特别是在工业革命之前，当时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，如树木年轮或冰核在陆地上。然而，直到最近，在亚北极和北冰洋还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，在浅海海底长寿命的珊瑚藻类堆积可以用来重建过去650年来北极的气候和冰的变化。在大面积海冰覆盖期间，很少有光线到达海底，导致光合藻类的年生长率低。相反，当海冰覆盖率低时，藻类的年生长率增加。通过测量藻类的生长和地球化学成分，可以逐年重建过去的海冰覆盖率和温度。珊瑚藻在整个北冰洋都很普遍，它们可以在那里生活几个世纪，附着在浅海底，同时在它们的方解石骨架中形成年度生长带。 该提案的总体目标是开发一个多世纪记录网络，记录过去的海水温度、海冰的季节性持续时间和珊瑚藻骨骼的海洋化学，以更好地了解亚北极-北极海洋环境的历史变化。重建工作将集中在最近从加拿大北极地区、格陵兰岛和斯匹次卑尔根群岛收集的样本上，这些关键地点的特点是季节性温度和海冰波动强烈。这项研究将为即将发生的影响航运、基础设施和资源开发从而影响北方社区的变化提供急需的基线数据和历史视角。

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.