Pöppelmeier Frerk, Jeltsch-Thömmes Aurich, Lippold Jörg, Joos Fortunat, Stocker Thomas F
Climate and Environmental Physics, Physics Institute, University of Bern, Bern, Switzerland.
Oeschger Centre for Climate Change Research, University of Bern, Bern, Switzerland.
Nat Geosci. 2023;16(4):349-356. doi: 10.1038/s41561-023-01140-3. Epub 2023 Apr 3.
Uncertainties persist in the understanding of the Atlantic meridional overturning circulation and its response to external perturbations such as freshwater or radiative forcing. Abrupt reduction of the Atlantic circulation is considered a climate tipping point that may have been crossed when Earth's climate was propelled out of the last ice age. However, the evolution of the circulation since the Last Glacial Maximum (22-18 thousand years ago) remains insufficiently constrained due to model and proxy limitations. Here we leverage information from both a compilation of proxy records that track various aspects of the circulation and climate model simulations to constrain the Atlantic circulation over the past 20,000 years. We find a coherent picture of a shallow and weak Atlantic overturning circulation during the Last Glacial Maximum that reconciles apparently conflicting proxy evidence. Model-data comparison of the last deglaciation-starting from this new, multiple constrained glacial state-indicates a muted response during Heinrich Stadial 1 and that water mass geometry did not fully adjust to the strong reduction in overturning circulation during the comparably short Younger Dryas period. This demonstrates that the relationship between freshwater forcing and Atlantic overturning strength is strongly dependent on the climatic and oceanic background state.
在对大西洋经向翻转环流及其对诸如淡水或辐射强迫等外部扰动的响应的理解方面，不确定性依然存在。大西洋环流的突然减弱被视为一个气候临界点，在地球气候从上一个冰河时代被推动出来时，这个临界点可能已经被跨越。然而，由于模型和代理数据的局限性，自末次盛冰期（22000 - 18000年前）以来环流的演变仍然受到的限制不足。在这里，我们利用来自追踪环流各个方面的代理记录汇编以及气候模型模拟的信息，来约束过去20000年的大西洋环流。我们发现了末次盛冰期期间大西洋翻转环流浅薄且微弱的连贯图景，这调和了明显相互矛盾的代理证据。从这个新的、多重约束的冰川状态开始的末次冰消期的模型 - 数据比较表明，在海因里希事件1期间响应微弱，并且在相对较短的新仙女木期期间，水体几何形状并未完全适应翻转环流的强烈减弱。这表明淡水强迫与大西洋翻转强度之间的关系强烈依赖于气候和海洋背景状态。
