Units used in CARS and BOA
This page describes the units used for properties represented in
CARS (CSIRO Atlas of Regional
(BLUELink Ocean Archive).
Temperature is in degrees Celsius. However, there are different definitions
of temperature in seawater, and modern observations are reported in a standard
called ITS-90. Ideally BOA and CARS would be standardized on ITS-90, but they
are not. Temperature has been collated and mapped using the values as found
in the source datasets.
Conversions between the standards are discussed
World Ocean Database is the largest data source used in BOA. For
CARS2009, the WOD2005 was used with the July 2008 Update. The documentation for
WOD has this to say:
Temperature measurements have been obtained by means of manual (i.e., visual
readings of temperature from reversing thermometers) and automated (i.e.,
digital recordings of temperature from STDs and CTDs) instruments.
Temperature measurements have been obtained following several International
Temperature Scales (ITSITS-1927; ITS-1948, ITS-1968) to the ITS-1990
(Preston-Thomas, 1990). Temperature data in WOD09 nominal units are in the
scale the measurements were reported in by the originator of the data.
CSIRO data, directly sourced from CSIRO rather than via WOD, is
already standardised (including pre-1990 data) to ITS-90.
WOCE data does identify the standard used for temperature in each
file, so this could (and will in future) be used to standardise on ITS-90.
Salinity is in Practical Salinity Units (PSU). Again, it is used as
found in hte source datasets.
Standards blah blah
World Ocean Database
Salinity measurements have been obtained by manual (e.g., chemical titrations,
chlorinity to salinity formulae, refractometers, salinographs, inductive
salinometers, etc.) and automated (i.e., conductivity to salinity from CTDs)
methods. For the past few decades, bottle salinity sampling and analyses are
normally conducted to calibrate the conductivity to salinity measurements of
CTDs. Salinity measurements have been obtained using reference standard
seawater samples of known salinity (within uncertainty). In 1978 the
practical salinity scale (PSS-1978) was adopted defining salinity in terms of
electrical conductivity ratio (UNESCO, 1981; Lewis and Perkins, 1981; Culkin
and Ridout, 1998). Under the PSS-1978 definition, salinity measurements are
dimensionless (Millero, 1993). Seawater standards provide a means to test the
calibration of salinity measurement instruments and facilitate the
inter-comparison of ocean salinity measurements against samples of known
electrical conductivity ratio (UNESCO, 1981; Mantyla, 1980; 1987; 1994;
Culkin and Smed, 1979; Culkin, 1986; Aoyama et al., 2002; Kawano et al.,
2005; Saunders, 1986). More recently, the concept of absolute salinity
anomaly has been introduced to compute absolute salinity values in terms of
salinity values using the PSS-78 definition (McDougall et al., 2009). In all
cases, WOD09 salinity data are not corrected for ?standard sea water? changes
(Mantyla, 1994) or converted to any salinity scale other than the scale the
measurements were reported in.