Ocean Science | 2021
Water masses in the Atlantic Ocean: characteristics and distributions
Abstract
Abstract. A large number of water masses are presented in the Atlantic Ocean,\nand knowledge of their distributions and properties is important for\nunderstanding and monitoring of a range of oceanographic phenomena. The\ncharacteristics and distributions of water masses in biogeochemical space\nare useful for, in particular, chemical and biological oceanography to\nunderstand the origin and mixing history of water samples. Here, we define\nthe characteristics of the major water masses in the Atlantic Ocean as\nsource water types (SWTs) from their formation areas, and map out their\ndistributions. The SWTs are described by six properties taken from the\nbiased-adjusted Global Ocean Data\nAnalysis Project version 2 (GLODAPv2) data product, including both conservative\n(conservative temperature and absolute salinity) and non-conservative\n(oxygen, silicate, phosphate and nitrate) properties. The distributions of\nthese water masses are investigated with the use of the optimum\nmulti-parameter (OMP) method and mapped out. The Atlantic Ocean is divided\ninto four vertical layers by distinct neutral densities and four zonal\nlayers to guide the identification and characterization. The water masses in\nthe upper layer originate from wintertime subduction and are defined as\ncentral waters. Below the upper layer, the intermediate layer consists of\nthree main water masses: Antarctic Intermediate Water (AAIW), Subarctic\nIntermediate Water (SAIW) and Mediterranean Water (MW). The North Atlantic\nDeep Water (NADW, divided into its upper and lower components) is the\ndominating water mass in the deep and overflow layer. The origin of both the\nupper and lower NADW is the Labrador Sea Water (LSW), the Iceland–Scotland\nOverflow Water (ISOW) and the Denmark Strait Overflow Water (DSOW). The\nAntarctic Bottom Water (AABW) is the only natural water mass in the bottom\nlayer, and this water mass is redefined as Northeast Atlantic Bottom Water\n(NEABW) in the north of the Equator due to the change of key properties,\nespecially silicate. Similar with NADW, two additional water masses,\nCircumpolar Deep Water (CDW) and Weddell Sea Bottom Water (WSBW), are\ndefined in the Weddell Sea region in order to understand the origin of AABW.