Freshwater budget and salinity variability in the subpolar and subtropical gyres of the North Atlantic

近年来，盐度和淡水分布变化的研究受到观测资料时空分辨率的限制，盐度异常的研究只能采用5年平均的方法。随着Argo计划的启动，盐度剖面的数量急剧增加，从1999年该计划开始到2014年4月，在全球海洋中收集了190万份Argo剖面。整个Argo阵列大约在2005 - 2007年在北大西洋就位。尽管做出了这样的努力，但空间和时间覆盖范围不足以详细确定北大西洋次极地的盐度变化。我们利用Argo剖面研究了盐度剖面与动力高度的关系。动态高度也用测高法测量，1992年以来获得了高质量的数据。因此，Argo浮标和高度计数据的结合使我们能够将高采样的时间周期（从2005-2007年开始）延长到1992年，即高度计测量的开始。第一阶段利用Argo数据和测高数据，构建了1992-2012年700m高空间（0.25 × 0.25格点）和时间（日）分辨率盐度时间序列。为了计算当地淡水通量对盐度变化的影响，更新后的HOAPS 3气候学HOAPS 3.3于2015年5月发布并应用。继续提案的目标以第一阶段的结果为基础，包括：(i)利用观测（Argo、CTD、高度计）、高分辨率（1/24）模式、GECCO2合成（TP 3.1）和更新的HOAPS气候学（TP 2.1）的结果，分析区域盐度含量的月至多年变化，以及淡水通量和相关过程。分别计算700m以上和混合层地表淡水通量的含量变化及影响。（ii）研究锋面、曲流和涡旋的地表和地下结构的演化和变率，计算涡旋的盐度含量异常，跟踪其路径上的盐度异常，评估所涉及的过程的作用。（iii）计算700m以上涡旋盐度输送的时间序列，特别是进入亚极地西大西洋和穿过MAR进入东大西洋的涡旋盐度输送。（iv）在东北大西洋1900m以下区域检验盐度重建是否有效，并通过增加卫星地表盐度观测，检验盐度剖面重建质量是否有所提高。

Up to recent years, the study of salinity and freshwater distribution changes was hampered by the lack of temporal and spatial resolution of the observations, so that salinity anomalies could only be studied by averaging over 5 years. With the onset of the Argo programme, the number of salinity profiles dramatically increased, and 1.9 million Argo profiles were collected in the global ocean between the onset of the program in 1999 and April 2014. The full Argo array was in place in the North Atlantic around 2005 - 2007. Despite this effort, the spatial and temporal coverage is not sufficient to identify salinity variations in detail in the subpolar North Atlantic. We used the Argo profiles to exploit the relation between the salinity profiles and dynamic height. Dynamic height is also measured by altimetry, and high quality data are available since 1992. A combination of Argo floats and altimeter data thus allowed us to extend the time period with high sampling (starting about 2005-2007) into the past till 1992, the onset of the altimeter measurements. In the first phase, high spatial (0.25 x 0.25 grid) and temporal (daily) resolution salinity time series (1992-2012) in the upper 700m were constructed using Argo data and altimetry. To calculate the influence of local freshwater fluxes on the salinity changes, the updated HOAPS 3 climatology HOAPS 3.3 became available in May 2015 and was applied. The objectives of the continuation proposal are based on the results of the first phase, and are (i) Analyse the monthly to multiannual variability in the regional salinity contents, together with freshwater fluxes and involved processes using observations (Argo, CTD, altimeter), a high resolution (1/24) model, results from the GECCO2 synthesis (TP 3.1) and from the updated HOAPS climatology (TP 2.1). Calculate content changes and influence of surface freshwater fluxes for upper 700m and separately for the mixed layer. (ii) Study the evolution and variability of surface and subsurface structures of fronts, meanders, and eddies, calculate salinity content anomalies in eddies, follow salinity anomalies along their pathways and assess the role of the involved processes (iii) Calculate time series of eddy salinity transports in the upper 700m, especially into the subpolar western Atlantic and across the MAR into the eastern Atlantic, and (iv) check whether the salinity reconstructions are valid in regions shallower than 1900m depth in the Northeast Atlantic, and test whether the quality of the reconstructions of the salinity profile improve by adding satellite observations of surface salinity.