Define water type based on temperature and salinity

Source: R/define_water_type.R

Defines water type based on potential temperature and practical salinity data from a CTD. Default values are for Kongsfjorden

define_water_type(
  dt,
  sal_col = "sal",
  temp_col = "temp",
  WM = kongsfjord_watermasses,
  bind = FALSE
)

Arguments

dt

Dataframe containing temperature and salinity information
sal_col

Character string giving the column name containing salinity data
temp_col

Character string giving the column name containing temperature data. Should be potential temperature, if the default WM is used.
WM

Dataframe giving the water mass definitions.
bind

Should the water type information be cbind with dt (TRUE) or should a character vector containing water type abbreviations returned instead (FALSE; default)

Details

Water-types are useful in summarizing salinity, temperature and density characteristics of water masses. By default, the water types are returned after the definition in Cottier et al. (2005) with slight modifications to avoid overlaps of water types. Density boundaries have not been implemented as these seem to have relatively little meaning on Svalbard after limiting water types using temperature and salinity.

Custom water type classifications can be defined using the WM argument. This argument should be a data frame containing the following column names: type, abb, sal.min, sal.max, temp.min, and temp.max. See the default WM, kongsfjord_watermasses, as an example. Rows in the data frame represent separate water types. The "type" column gives the name of the water mass and the "abb" column the abbreviation of the water mass (used in ts_plot). The water types are defined using rectangular boundaries on salinity (x) - temperature (y) coordinate system. The "sal.min" and "sal.max" columns give the minimum and maximum extent for the x-axis while the corresponding "temp.*" columns define the limits for the y-axis of the rectangles. The rectangles are rendered to polygons inside the function. If water types overlap, the water type that comes first in the WM data frame dominates and defines the water type for a point based on salinity and temperature. Consequently, one point cannot have more than one water type. When making the WM data frame, use Inf and -Inf for water types, which do not have positive and negative limits, respectively.

You can use the TS diagram to check that your custom water types are defined correctly. Note that most sources refer to potential temperatures and practical salinities. Make sure that your data use the same units and standards than the source when defining water types.

MarineDatabase also contains a pre-made WM data frame for the NPI's Rijpfjorden transect (rijpfjord_watermasses). The water types in this classification have been modified from Pérez-Hernández et al. (2017), which was originally made for the same region without the fjord. The changes include addition of Winter Cooled Water from Cottier et al. (2005) and exlusion of density in the categorization. Instead, salinity threshold of 34.87 for Atlantic and Arctic Intermediate Waters (AIW) was used. This decision is purely due to the difficulty of programming polygons in 3D space. It may cause very minor changes in water mass classification at the boundary of AIW and PSW.

References

Cottier F, Tverberg V, Inall M, Svendsen H, Nilsen F, Griffiths C (2005) Water mass modification in an Arctic fjord through cross-shelf exchange: The seasonal hydrography of Kongsfjorden, Svalbard. Journal of Geophysical Research, 110, C12005. doi:10.1029/2004JC002757

Pérez-Hernández M.D., Pickart R.S., Pavlov V. et al. (2017) The Atlantic Water boundary current north of Svalbard in late summer. Journal of Geophysical Research: Oceans, 122, 2269–2290. doi:10.1002/2016JC012486

See also

ts_plot, the kongsfjord_watermasses data.frame ,the rijpfjord_watermasses data.frame

Other ts_plot: ctd_kongsfjord, kongsfjord_watermasses, rijpfjord_watermasses, ts_plot()

Examples

dt <- data.frame(temp = c(1, -1, -0.8), sal = c(34, 34.5, 34.9)) # Make example data
define_water_type(dt) # returned as a factor
#> [1] Other ArW   WCW  
#> Levels: AW TAW IW SW ArW WCW Other
define_water_type(dt, bind  = TRUE) # returned as a data frame
#>   temp  sal watertype
#> 1  1.0 34.0     Other
#> 2 -1.0 34.5       ArW
#> 3 -0.8 34.9       WCW