Collaborative Research: Mode Water Formation in the Lofoten Basin: A Key Element in the Meridional Overturning Circulation

该奖项是根据2009年《美国复苏和再投资法案》(公法111-5)资助的。过去十年，北大西洋深对流区--拉布拉多海和格陵兰海--在推动大西洋子午线翻转环流(AMOC)及其相关的向极地热量输送方面所扮演的核心角色受到了严重质疑。特别是，现在已经知道，在这些区域发生的下沉相对较少，只有有限的表面浮力损失，而且，供给AMOC的致密水团并不是这些区域的直接产物。就北欧海而言，格陵兰-苏格兰溢流水组成了AMOC最深的分支，只含有少量格陵兰海水，相反，主要是循环的温暖、含盐的大西洋水域逐步转化的产物。然而，这种转变发生的途径和过程在很大程度上是未知的。在这一转变中扮演核心角色的是罗福滕盆地，它毗邻格陵兰海，位于大西洋流入的两个主要分支之间。温暖、咸化的大西洋海水在通过这个盆地时发生了强烈的变性，仅这个盆地就占了北欧海域表面浮力损失的很大一部分。这导致了一种中间对流产物--罗福滕盆地模式水的形成。与拉布拉多海水和格陵兰海水不同，罗福滕盆地模式水可以迅速从盆地输出，是溢出水的直接来源。然而，尽管它很重要，但该盆地及其中间水团形成的基本动力学特征尚未得到解决。智力价值这个项目的主要智力价值在于它对阐明AMOC的一个关键方面的重要性，即罗福滕盆地的模式水形成及其在北欧海洋转化途径中的作用。这个项目是及时的，因为越来越多的证据表明，格陵兰海的深对流本身对AMOC的影响有限，同时，我们对中间/密集转化路径的理解也有了很大提高。通过使用拉布拉多海作为参照点，调查人员预计将有助于对存在不同地形和不稳定边界流情况下的对流转化有更普遍的理解。观测和模拟相结合的研究将调查罗福滕盆地的模式水的形成及其最终的输出。剖面系泊和直接部署在盆地内的RAFOS浮标将澄清每年的改造、再分层和扩散的周期。分析现有的水文、浮标和遥感数据将有助于指导实地工作，并将使更大范围和更长期的可变性的调查成为可能。将使用各种模型来研究罗福滕盆地和北欧海其他地方的转化过程的动态。最终的结果将是对大气-海洋通量和海洋动力学之间的相互作用有一个新的理解，沿着AMOC的这个关键分支。更广泛的影响这个项目寻求增加我们对地球气候系统中的一个关键过程--北欧海洋变化路径的了解，该过程不仅影响北欧海洋气候变化，而且还影响北冰洋的温暖流入，北冰洋是一个正在经历快速变化的地区。该项目是与几个挪威和其他欧洲集团合作精心规划的，以便最大限度地利用资源和促进国际合作。它包括两个研讨会，以及在整个项目中交换数据、想法和人员。最后，它汇集了一组不同的个人投资主管，他们将为这一问题带来互补的技能，并包括培训一名博士后，他们将从该项目多样化和国际化的科学环境中受益匪浅。

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).The traditionally central role played by the deep convective regions of the North Atlantic - the Labrador Sea and the Greenland Sea - in driving the Atlantic Meridional Overturning Circulation (AMOC) and its associated poleward heat transport has been severely questioned over the last decade. In particular, it is now known that relatively little sinking and only a limited surface buoyancy loss occurs in these regions and, furthermore, that the dense water masses feeding the AMOC are not a direct product of these regions. In the case of the Nordic Seas, the Greenland-Scotland overflow waters comprising the deepest branch of the AMOC contain only small amounts of Greenland Sea Water, and are instead largely the product of the progressive transformation of the circulating warm, salty Atlantic Waters. Yet the pathways and processes through which this transformation occurs are largely unknown. Emerging as playing a central role in this transformation is the Lofoten Basin, which sits adjacent to the Greenland Sea between the two main branches of the Atlantic inflow. The warm, salty Atlantic waters are strongly modified as they transit through this basin, which alone accounts for a substantial fraction of the surface buoyancy loss over the Nordic Seas. This leads to the formation of an intermediate convected product, the Lofoten Basin Mode Water. Unlike Labrador Sea Water and Greenland Sea Water, the Lofoten Basin Mode Water can be rapidly exported from the basin, and is a direct source for the overflows waters. Despite its importance, however, the basic dynamical features of this basin and of its intermediate water mass formation have yet to be addressed. Intellectual MeritThe principal intellectual merit of this project is its importance for elucidating a key facet of the AMOC, namely, mode water formation in the Lofoten Basin and its role in the Nordic Seas transformation pathway. The project is timely since there is growing evidence that the Greenland Sea's deep convection by itself has a limited impact on the AMOC and, at the same time, our understanding of intermediate/dense transformation pathways has greatly improved. By using the Labrador Sea as a reference point, the investigators anticipate contributing to a more universal understanding of convective transformation in the presence of varied topography and an unstable boundary current. The combined observational and modeling study will investigate mode water formation in the Lofoten Basin and its eventual export. A profiling mooring together with RAFOS floats deployed directly within the basin will clarify the annual cycle of transformation, restratification, and dispersal. Analysis of existing hydrographic, float, and remote sensing data will help to guide the field work, and will enable the investigation of larger-scale and longer-term variability. A variety of models will be employed to study the dynamics of the transformation process in the Lofoten Basin and elsewhere in the Nordic Seas. The net result will be a new understanding of the interaction between air-sea fluxes and ocean dynamics along this crucial branch of the AMOC. Broader ImpactsThis project seeks to increase our understanding of a key process in the Earth's climate system, the Nordic Seas transformation pathway, which affects not only the AMOC but, also, the warm inflow into the Arctic Ocean, a region currently undergoing rapid change. The project has been carefully planned in collaboration with several Norwegian and other European groups so as to optimize resources and foster international collaboration. It includes two workshops, as well as exchange of data, ideas, and personnel throughout the project. Finally, it brings together a group of diverse PIs, who will bring complementary skills to this problem, and includes training of a post-doc who will greatly benefit from the diverse and international scientific environment of this project.