Exploring Recent Changes of Ocean Salinity Distributions in the Context of Climate Change

由于水文循环仍然是气候系统中最不为人所知的方面之一，而淡水强迫是气候模式之间差异的最可能原因，因此拟议的研究将为评估地球气候正在发生和未来的变化提供重要的观测基础。在过去50年中，海洋盐度分布一直在变化，积累的观测记录开始显示出一些接近全球范围的趋势。近几十年来，各种研究分别记录了印度洋-太平洋、大西洋和地中海热带和亚热带地表水的盐度增加；而在同一时期，在两个半球高纬度地区通风的中深水团变得越来越新鲜。拟议的研究将调查这些明显的大尺度和半对称的海洋盐度分布变化是否可以提供行星水文循环变化的证据。它将参与将观测到的海洋淡水损失率与气候模式模拟的结果进行比较。根据模式预测，水文循环可能对温盐环流（THC）具有重要的气候影响，本研究将评估观测到的盐度和淡水分布变化对海洋密度的影响。利用新的气候学产品和工具，将对南纬30度至北纬90度的太平洋、大西洋、北极和北欧海域进行海洋性质含量变化的系统普查。盐的体积积分将用于确定仪器记录中海洋淡水输送的一级变化，并估计通风海洋层的E-P异常。这些异常将与来自其他来源的最新蒸发和降水气候学产品进行比较。将卑尔根耦合模型与观测相结合，与法国巴黎海洋动力学与气候实验室（LODYC）的研究人员共同研究盐度最大值水域随时间变化的形成和俯冲速率。观测分析还将与NOAA地球物理流体动力学实验室（GFDL）耦合海洋-大气模型的结果进行比较。这些比较将评估模式预测的盐度变化与观测到的变化相似的程度，并提供观点，说明它们是否代表了气候系统背景变率的一个重要信号。最后，根据模式模拟确定的THC阈值，将评估北大西洋北部发生的水柱急剧变新鲜的幅度。更广泛的影响：这项研究的更广泛的影响可能是三重的。首先，它将在来自几个小组的研究人员之间建立合作，即来自WHOI、GFDL和LODYC的建模者和观测者。其次，模式数据的比较将构成校准气候模拟的有力工具，并可能成为进一步的模式实验诊断水文变化机制的重要刺激。第三，更大的研究界将受益于这项工作将产生的HydroBase质量控制数据库和网格气候学产品的扩展。

Because the hydrologic cycle remains one of the least well understood aspects of the climate system, and freshwater forcing the most probable cause for differences among climate models, the proposed research will provide an important observational foundation for evaluating ongoing and future changes in Earth's climate. Over the past fifty years, ocean salinity distributions have been changing and the accumulating observational record is beginning to suggest some trends of near global extent. Various studies have individually documented salinity increases in tropical and subtropical surface waters of the Indo-Pacific, Atlantic and Mediterranean in recent decades; while over the same time period, the intermediate and deep water masses, ventilated at higher latitudes in both hemispheres, have become increasingly fresh. The proposed research will investigate whether these apparently large-scale and hemispherically symmetric shifts in ocean salinity distribution can provide evidence of a change in the planetary hydrologic cycle. It will engage in comparing the observed rates of freshwater gains and losses in the ocean to results from climate model simulations. Reflecting model predictions that the hydrologic cycle may have climatically important effects on the thermohaline circulation (THC), the study will evaluate the impacts of the observed changes in salinity and freshwater distributions on ocean density. A systematic census of ocean property content changes will be conducted for the Pacific, Atlantic, Arctic, and Nordic Seas from 30 degrees S to 90 degrees N utilizing new climatology products and tools. Volumetric integrals of salt will be used to identify first order changes in ocean freshwater transports over the instrumental record and to estimate E-P anomalies for the ventilated ocean layers. These anomalies will be compared to the latest evaporation and precipitation climatology products derived from other sources. Combining the Bergen Coupled Model with observations, the time-dependent formation and subduction rates for Salinity Maximum Waters will be investigated in conjunction with researchers at Laboratoire d' Oceanographie Dynamique et de Climatologie (LODYC) in Paris, France. The observational analyses will also be compared to results from NOAA's Geophysical Fluid Dynamics Laboratory (GFDL) coupled ocean-atmosphere models. These comparisons will assess the degree to which the model projected changes in salinity resemble the observed changes and provide perspective on whether they represent a signal of any significance against the background variability of the climate system. Finally, the amplitude of the dramatic freshening of the water column that has occurred in the northern North Atlantic will be assessed in the context of threshold values for the THC, as determined from model simulations. Broader Impacts: The broader impacts of this study are likely to be threefold. First, it will establish collaboration among researchers from several groups, i.e., modelers and observationalists from WHOI, GFDL, and LODYC. Second, the model-data comparisons will constitute a powerful tool for calibrating climate simulations and may be a significant stimulus for further model experiments to diagnose the mechanisms of hydrologic changes. Third, the larger research community will benefit from the expansion of the HydroBase quality-controlled database and gridded climatology products which will result from this work.