Collaborative Research: Fresh water and heat fluxes to the Arctic Ocean modeled with tree-ring proxies

北冰洋海冰几十年来一直在减少。随着冰层的消退，更多的开放水域被暴露出来，这减少了从北极反射回来的光线，并导致北极进一步变暖和海冰消失。这种反馈有助于放大整个北冰洋地区的变暖，这正在改变河水和大气循环之间的常规联系，从而改变流入北冰洋的热量和能量。现代对北冰洋河流流动的观测，以及对相关热量收支的估计，很少能追溯到几十年前。这些记录太短，不能完全量化淡水流量和热量预算的长期趋势，这使得理解这些趋势背后的过程变得困难。这项研究通过利用北极地区的树木年轮记录和河流测量数据来重建和研究流向北冰洋的水、热和能量的几个世纪的波动，从而帮助填补这一空白。这项研究使用了大量现有的和新收集的树木年轮数据，加上长时间的河流测量数据，来开发和测试重建北极第二大河流叶尼塞河的水流和热量收支。河流水文时空变化的因果归因需要考虑变化的积雪融化、永久冻土的融化以及大坝和水库对自然流态的改变。这一考虑因素是用新汉普郡大学水平衡模型进行评估的。通过使用更新到2020年的多层仪器和模型数据(例如，气候、水文、人为、一般环流模型(GCM)的输出)，该团队正在使用来自西伯利亚的300多个树木年轮记录来重建过去300年的河流流量和水温。除了传统的树木年轮宽度测量外，热传输重建还探索了树木年轮木材解剖中河流温度变化的信号。总体而言，这项工作正在确定北极地区过去河流能量通量变化的气候驱动因素。研究人员将测量时期的径流特征，以及重建时期的年、数十年和百年变率，放在GCM预测的下个世纪径流变化的背景下。虽然叶尼塞河是研究的直接焦点，但一个广泛的目标是将方法、方法和工具扩展到其他泛北极地区。为了协助其他研究人员，该小组正在开发一个新的在线工具箱(TRRIMS，树环区域综合水文气候建模和分析系统)。该工具合成了叶尼塞河热量和流量的年轮信号，并采用非参数统计量进行空间重建。TRIMS在线工具加强了研究和教育的基础设施，使社会能够了解北极扩大造成的自然灾害和环境变化。这项研究还促进了北极的国际科学合作，以促进探索北极系统变化背后的生物地球化学、地球物理和生态过程的国际和跨学科合作。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Arctic Ocean sea ice has been declining for several decades. As the ice retreats, more open water is exposed, which reduces the amount of light reflected back from the Arctic and leads to further Arctic warming and sea ice loss. This feedback contributes to the amplification of warming across Arctic regions, which is changing the regular connections between river water and atmospheric circulation, and consequently the heat and energy flowing into the Arctic Ocean. Modern observations of Arctic river flow, and estimates of associated heat budgets, rarely extend back more than several decades. These records are too short to fully quantify the long-term trends in freshwater flow and heat budgets, which makes it difficult to understand the processes underlying those trends. This research helps fill that gap by utilizing tree-ring records and river gauge data in the Arctic to reconstruct and study multi-century fluctuations of water, heat and energy flow to the Arctic Ocean.This research uses a wide array of existing and newly collected tree-ring data, coupled with a long record of river gauge data, to develop and test reconstructions of water flow and heat budgets for the Yenisei River, the second largest river of the Arctic. Causal attribution of spatial-temporal variations of river hydrology requires consideration of changing snowmelt, thawing permafrost, and modification of natural flow regimes by dams and reservoirs. This consideration is assessed with the New Hampshire University Water Balance Model. With the engagement of multiple layers of instrumental and modeled data updated to 2020 (e.g., climatic, hydrologic, anthropogenic, General Circulation Model (GCM) outputs) the team is using over 300 tree-ring records from Siberia to reconstruct river discharge and water temperature for the last 300 years. In addition to conventional tree-ring width measurements, the heat transport reconstruction explores the signal for river temperature variation in the wood anatomy of tree rings. Overall, this effort is identifying climatic drivers of past river energy flux variations in the Arctic. The researchers place runoff features of the gauged period, as well as the annual, multi-decadal, and centennial variability from the reconstructed periods, in the context of GCM projected runoff changes for the next century. While the Yenisei River is the direct focus of the research, a broad goal is an extension of the approach, methods, and tools to other pan-Arctic regions. To assist other researchers, the team is developing a new online toolbox (TR-RIMS, Tree-Ring Regional Integrated hydroclimatic Modeling and analysis System). The tool synthesizes tree-ring signals for the heat and volume of Yenisei River and adopts a non-parametric statistics for the spatial reconstruction. The online TR-RIMS tool enhances the infrastructure for both research and education and enable societal understanding of natural hazards and environmental change induced by the Arctic amplification. The research also promotes international scientific collaboration in the Arctic to boost international and interdisciplinary collaboration exploring biogeochemical, geophysical and ecological processes underlying Arctic system change.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.