ASYNC - Resolving asynchronous responses of North Atlantic climate to deglacial changes in ocean circulation

拟议的项目将检验一种假设，即大西洋经向翻转环流（AMOC）-一种对地球气候起主要控制作用的表层和深层洋流系统-的逐渐变化导致北大西洋气候在从最后一个冰河时代过渡到目前的温暖间冰期（约20 000 - 10 000年前）期间发生突变。格陵兰冰芯记录显示了明确的证据，表明这一时期的特点是在不到十年的时间里发生了重大的气候突变，这是由于与高纬度北大西洋向北的表面热输送减少及其向南的深层回流有关的AMOC制度的变化。至关重要的是，在过去的几十年中，由于来自北极的融水和冰输出通量的增加而导致AMOC的异常减弱，从而引发了一个问题：当前AMOC的下降是否预示着一个新的突变阶段，类似于冰芯和海洋沉积物中记录的突变，北大西洋气候对高纬度地表和深海环流变化的响应时间是多少？因此，解决和量化耦合的海洋-大气系统内的异步变化是必不可少的，以提高我们对气候过程的理论理解和气候模式的预测能力，以及确定在何种条件下发生气候突变。ASYNC是由剑桥大学领导的一个国际合作项目，将解决这一根本问题。该项目将利用独特的北大西洋沉积物记录，生成一套精确定年和数十年分辨率的海洋环流和气候变化代用记录。ASYNC是第一个有针对性的努力，通过以连续的方式精确地整合基本的时间尺度来比较高分辨率的北大西洋代理记录。海洋记录将与格陵兰冰芯年表同步，方法是利用来自海底沉积物和已发表冰芯的数十年分辨宇宙成因10 Be记录，独立和连续地重建入射宇宙射线通量的全球同步变化。拟议的项目将产生新的宇宙成因10 Be、海冰、融水排放、以及来自三个北大西洋海洋沉积物岩心的底层和表层水通风重建。古海洋学重建，特别是底层水通风记录，反映了向南的深层组件的AMOC，将直接比较的事件记录在冰芯气候重建从格陵兰岛。ASYNC将共同建立第一个连续同步记录大气、海洋和海冰变化的网络，解决北大西洋海洋扰动在气候系统上的时空传播问题，这些问题贯穿于最后一次冰川消退（约20，000 - 10，000年前）的主要气候转变。ASYNC的结果将推进目前对以下问题的理解：i）气候档案中气候突变的性质和时间，ii）AMOC和气候对格陵兰冰盖和北极海冰融水强迫的非线性响应，iii）北大西洋地区快速气候变化的海洋前兆。

The proposed project will test the hypothesis that gradual changes in Atlantic Meridional Overturning Circulation (AMOC) -a system of surface and deep ocean currents that exerts a primary control on Earth's climate, led to abrupt shifts in North Atlantic climate during the transition out of the last ice age and into the present warm interglacial (~20,000-10,000 years ago). Greenlandic ice-core records show clear evidence that this period was characterised by major abrupt climate shifts in less than a decade, which have been attributed to changes in the AMOC regime associated with reduced northward surface heat transport in the high-latitude North Atlantic and its deep southward return flow. Critically, the anomalous weakening of the AMOC in the last decades caused by enhanced fluxes of meltwater and ice export from the Arctic in response to Arctic change prompts the question: Is the current decline in AMOC heralding a new phase of abrupt change similar to those recorded in ice cores and ocean sediments, and what is the response time of North Atlantic climate to changes in high-latitude surface and deep ocean circulation?Resolving and quantifying asynchronous changes within the coupled ocean-atmosphere system is hence essential to improve our theoretical understanding of climate processes and predictive capacity of climate models, as well as identifying under which conditions abrupt climate change occurs. ASYNC is an international collaborative project led by the University of Cambridge that will tackle this fundamental problem. The project will avail of unique North Atlantic Ocean sediment records to generate a suite of precisely dated and multidecadally-resolved proxy records of ocean circulation and climate change. ASYNC represents the first targeted effort to compare high resolution North Atlantic proxy records by precisely integrating the underlying timescales in a continuous fashion. The marine records will be synchronised to the Greenland ice-core chronology via independent and continuous reconstructions of globally synchronous variations in the incoming cosmic ray flux using multidecadally-resolved cosmogenic 10Be records from seafloor sediments and published ice cores.The proposed project will result in new cosmogenic 10Be, sea ice, meltwater discharge, and bottom- and surface-water ventilation reconstructions from three North Atlantic marine sediment cores. The palaeoceanographic reconstructions, and in particular the bottom-water ventilation records, which reflect the southward deep component of AMOC, will be directly compared to events recorded in ice-core climate reconstructions from Greenland. Together, ASYNC will result in the first network of continuously synchronised records of atmospheric, oceanic and sea ice change that will resolve the temporal and spatial propagation of North Atlantic ocean perturbations on the climate system across the major climatic transitions that punctuated the last deglaciation (~20,000-10,000 years ago). Results from ASYNC will advance the current understanding of i) the nature and timing of abrupt climate shifts across climate archives, ii) nonlinear responses of AMOC and climate to gradual Greenland Ice Sheet and Arctic sea ice meltwater forcing, and iii) ocean precursors of rapid climate change in the North Atlantic region.