Adinrichs et al.
Baltic and North Seas Climatology
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3altic Sea (402404 profiles‘
North Sea (792741 profiles
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FIGURE 1 | Annual (A) and monthly (B) frequency of marine observational profiles for the BNSC area of the North and Baltic Sea (1873-2015}
data density is highest at the surface and that a low data density
characterizes the deep areas of the BNSC region (ie., especially
the North Atlantic).
Quality Control
Srroneous observations have to be filtered out during the
creation of the climatology. Here, we follow the data quality
control strategy implemented for the automated quality control
of the global hydrographic archive for the compilation of the
WOCE-Argo global hydrographic climatology (Gouretski, 2018).
The number of profiles in the BNSC region (after sorting out
duplicates) accounts to more than 1 million and reveals that a
check of all these observations with respect to their quality is only
possible with an automatic procedure.
The quality control consists of eight different single checks
described in the following.
1. Crude range check
In general: Temperature and salinity in the North and Baltic
Sea have a characteristic range. Temperature values below
—2°C and above 25°C and salinity values above 38 PSU can
zertainly be regarded as erroneous for the regarded area.
Those values are flagged by this check.
Depth dependent: Additionally, this check is based on the
frequency distributions of temperature and salinity as a
function of depth, and based on this, defines characteristic
value ranges for single depth levels. The purpose of this check
is to reject crude outliers, which passed the overall range check
for temperature and salinity.
Maximum observed depth
Each instrument or station type has a characteristic maximum
depth level to which observations are recorded. If this value is
exceeded in a profile, all values are flagged. Information about
the instrument or station type, if available, is stored in the
meta data.
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3.
Constant value
Ifa profile shows a certain number (N) of consecutive constant
values in a defined depth interval, those values will be flagged.
The number N depends on the instrument type.
Spikes
Spikes are an unnatural change of the parameter value from
one depth level to another and therefore have to be flagged.
For this purpose, parameter-specific threshold values defining
a spike are taken into account as well as the distance between
the consecutive depth levels regarded for this check.
Vertical gradient
Ranges for the vertical parameter gradient are defined. For this
purpose, corresponding frequency distributions are created
based on the observational data and ranges for the vertical
gradient are defined at a set of levels. For neighboring depth
levels with observed parameter values, a vertical gradient can
be calculated. In case this lies outside the vertical gradient
range for this depth level, both observations are flagged.
Number of extrema
The procedure aims at checking the shape of the vertical
profile. The number of local extrema (for T and S separately)
is found for each observed profile. If the number of identified
extrema is more than three, all observed values for this
profile are flagged. The extrema are taken into account only
if the difference between the parameter values at the neighbor
minimum and maximum points exceed predefined tolerances.
The tolerances for these differences do not depend on depth
and are set to 0.5°C and 0.5 PSU for temperature and salinity.
Comparison with digital bathymetry
For this check the digital bathymetry GEBCO2 (Weatherall
et al., 2015) is used. If the digital bathymetry indicates solely
“land” near the hydrographic station, it is assumed that
the position of that hydrographic station is erroneous and
all observed values of the profile are flagged. If the digital
bathymetry indicates the presence of “sea” points in a certain
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Alk 9019 1 VMalııme 7 | Article 15£
