Abstract
Abstract. A large number of water masses are presented in the Atlantic Ocean, and knowledge of their distributions and properties is important for understanding and monitoring of a range of oceanographic phenomena. The characteristics and distributions of water masses in biogeochemical space are useful for, in particular, chemical and biological oceanography to understand the origin and mixing history of water samples. Here, we define the characteristics of the major water masses in the Atlantic Ocean as source water types (SWTs) from their formation areas, and map out their distributions. The SWTs are described by six properties taken from the biased-adjusted Global Ocean Data Analysis Project version 2 (GLODAPv2) data product, including both conservative (conservative temperature and absolute salinity) and non-conservative (oxygen, silicate, phosphate and nitrate) properties. The distributions of these water masses are investigated with the use of the optimum multi-parameter (OMP) method and mapped out. The Atlantic Ocean is divided into four vertical layers by distinct neutral densities and four zonal layers to guide the identification and characterization. The water masses in the upper layer originate from wintertime subduction and are defined as central waters. Below the upper layer, the intermediate layer consists of three main water masses: Antarctic Intermediate Water (AAIW), Subarctic Intermediate Water (SAIW) and Mediterranean Water (MW). The North Atlantic Deep Water (NADW, divided into its upper and lower components) is the dominating water mass in the deep and overflow layer. The origin of both the upper and lower NADW is the Labrador Sea Water (LSW), the Iceland–Scotland Overflow Water (ISOW) and the Denmark Strait Overflow Water (DSOW). The Antarctic Bottom Water (AABW) is the only natural water mass in the bottom layer, and this water mass is redefined as Northeast Atlantic Bottom Water (NEABW) in the north of the Equator due to the change of key properties, especially silicate. Similar with NADW, two additional water masses, Circumpolar Deep Water (CDW) and Weddell Sea Bottom Water (WSBW), are defined in the Weddell Sea region in order to understand the origin of AABW.
Highlights
The ocean is composed of a large number of water masses without clear boundaries but gradual transformations between each other (e.g. Castro et al, 1998)
The optimum multi-parameter (OMP) model determines the contributions from predefined source water types (SWTs), which represent the values of the “unmixed” WMs in the formation areas, through a linear set of mixing equations, assuming that all key properties of water masses are affected by the same mixing processes
The characteristics of the main water masses in their formation areas are defined in a six-dimensional hydrochemical space in the Atlantic Ocean
Summary
The ocean is composed of a large number of water masses without clear boundaries but gradual transformations between each other (e.g. Castro et al, 1998). The limitation of the analysis based on T –S relationship is obvious; distributions of more (than three) water masses cannot be analysed at the same time with only these two parameters, so physical and chemical oceanographers have worked to add more parameters to the characterization of water masses The concepts and definitions of water masses given by Tomczak (1999) are used, and we seek to define the key properties of the main water masses in the Atlantic Ocean and to describe their distributions. In order to facilitate the analysis, the Global Ocean Data Analysis Project version 2 (GLODAPv2) data product is used to identify and define the characteristics of the most prominent water masses based on six commonly measured physical and biogeochemical properties (Fig. 1). Detailed investigations on temporal variability of water masses, or their detailed formation processes, for instance, may find this study useful but will certainly want to use a more granular approach to water mass analysis in their particular areas
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