# State Research Center of the Russian Federation -- the Arctic and Antarctic Research Institute of the Russian Federal Service for Hydrometeorology and Environmental Monitoring

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## International Arctic Research Center, University of Alaska, Fairbanks

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## HYDROCHEMICAL ATLAS OF THE ARCTIC OCEAN

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## St. Petersburg

### Fairbanks

2001

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# Contents

1.  Introduction................................................................................................3

    1.  Electronic climatic hydrochemical Atlas of the Arctic
        Ocean.................................... 3

    2.  How to use the
        Atlas....................................................................................
        4

    3.  List of
        participants.......................................................................................
        5

    4.  References to Section
        1..................................................................................5

2.  Hydrochemical investigations in the Arctic
    Ocean...................................................6

    1.  History of
        investigations..............................................................................\...6

    2.  Methods of measurement and determination
        accuracy..............................................9

    3.  References to Section
        2.................................................................................13

3.  Data
    processing...........................................................................................15

    1.  Hydrochemical
        information............................................................................15

        1.  Data
            sources..........................................................................................15

        2.  Spatial and temporal distribution of
            observations.............................................\...16

    2.  Control of hydrochemical
        data.........................................................................23

        1.  Data
            input..........................................................................................\....23

        2.  Formal data control in the database of hydrochemical
            elements...........................\...24

            1.  Control of station
                passports........................................................................24

            2.  Control of maximum station observation
                depths................................................24

        3.  Regional
            control....................................................................................\...24

        4.  Control of variability
            limits.........................................................................26

        5.  Expert
            control......................................................................................\...26

    3.  Statistical
        characteristics................................................................................27

    4.  Objective
        analysis........................................................................................38

    5.  References to Section
        3...................................................................................40

4.  Presentation of hydrochemical
    information............................................................42

    1.  Data set of initial
        measurements........................................................................42

4.2. Gridded climatic fields of the objective
analysis...................................................\...43

4.3. Profiles, transects and
fields...........................................................................\...43

5.  Climatic distribution of hydrochemical characteristics in the Arctic
    Ocean.......................48

    1.  Vertical
        profiles............................................................................................48

    2.  Transects....................................................................................................48

5.3. Mean values and dispersions at the standard
depths..................................................49

4.  Maps of climatic distribution of the hydrochemical characteristics
    at the standard depths......49

Appendixes

Appendix 1. Tables of determination methods

Appendix 2. Metadata

1.  **Introduction**

    1.  Electronic Climatic Hydrochemical Atlas of the Arctic Ocean

Chemical composition of water determines its physical properties and
character of processes proceeding in it: freezing temperature, volume of
evaporation, density, color, transparency, filtration capacity, etc.
Presence of chemical elements in water solution confers waters special
physical properties exerting significant influence on their circulation,
creates necessary conditions for development and inhabitance of flora
and fauna, and imparts to the ocean waters some chemical features that
radically differ them from the land waters (Alekin & Liakhin, 1984).

Hydrochemical information helps to determine elements of water
circulation, convection depth, makes it easier to distinguish water
masses and gives additional knowledge of climatic variability of ocean
conditions. Hydrochemical information is a necessary part of biological
research. Water chemical composition can be the governing
characteristics determining possibility and limits of use of marine
objects, both stationary and moving in sea water.

Subject of investigation of hydrochemistry is study of dynamics of
chemical composition, i.e. processes of its formation and hydrochemical
conditions of water bodies (Alekin & Liakhin 1984). The hydrochemical
processes in the Arctic Ocean are the least known. Some information on
these processes can be obtained in odd publications. A generalizing
study of hydrochemical conditions in the Arctic Ocean based on
expeditions conducted in the years 1948-1975 has been carried out by
Rusanov et al. (1979).

The "Atlas of the World Ocean: the Arctic Ocean" contains a special
section "Hydrochemistry" (Gorshkov, 1980). Typical vertical profiles,
transects and maps for different depths -- 0, 100, 300, 500, 1000, 2000,
3000 m are given in this section for the following parameters: dissolved
oxygen, phosphate, silicate, pH and alkaline-chlorine coefficient. The
maps were constructed using the data of expeditions conducted in the
years 1948-1975. The illustrations reflect main features of distribution
of the hydrochemical elements for multi-year period and represent a
static image of hydrochemical conditions. Distribution of the
hydrochemical elements on the ocean surface is given for two seasons --
winter and summer, for the other depths are given mean annual fields.

Aim of the present Atlas is description of hydrochemical conditions in
the Arctic Ocean on the basis of a greater body of hydrochemical
information for the years 1948-2000 and using the up-to-date methods of
analysis and electronic forms of presentation of hydrochemical
information. The most wide-spread characteristics determined in water
samples were used as hydrochemical indices. They are: dissolved oxygen,
phosphate, silicate, pH, total alkalinity, nitrite and nitrate. An
important characteristics of water salt composition -- "salinity" has
been considered in the Oceanographic Atlas of the Arctic Ocean (1997,
1998).

Presentation of the hydrochemical characteristics in this Hydrochemical
Atlas is wider if compared with that of the former Atlas (Gorshkov,
1980). Maps of climatic distribution of the hydrochemical elements were
constructed for all the standard depths, and seasonal variability of the
hydrochemical parameters is given not only for the surface, but also for
the underlying standard depths up to 400 m and including. Statistical
characteristics of the hydrochemical elements are given for the first
time. Detailed accuracy estimates of initial data and map construction
are also given in the Atlas. Calculated values of mean-root deviations,
maximum and minimum values of the parameters demonstrate limits of their
variability for the analyzed period of observations. Therefore, not only
investigations of chemical statics are summarized in the Atlas, but also
some elements of chemical dynamics are demonstrated.

Digital arrays of the hydrochemical elements obtained in nodes of a
regular grid are the new form of characteristics presentation in the
Atlas. It should be mentioned that the same grid and the same boxes were
used in the Atlas, as those that had been used by creation of the
US-Russian climatic Oceanographic Atlas. It allows to combine
hydrochemical and oceanographic information of these Atlases.

The first block of the digital arrays contains climatic characteristics
calculated using direct observational data. These climatic
characteristics were not calculated in the regions without observations,
and the information arrays for these regions have gaps. The other block
of climatic information in a gridded form was obtained with the help of
objective analysis of observational data. Procedure of the objective
analysis allowed us to obtain climatic estimates of the hydrochemical
characteristics for the whole water area of the Arctic Ocean including
the regions not covered by observations. Data of the objective analysis
can be widely used, in particular, in hydrobiological investigations and
in modeling of hydrochemical conditions of the Arctic Ocean.

Array of initial measurements is a separate block. It includes all the
available materials of hydrochemical observations in the form, as they
were presented in different sources. While keeping in mind that this
array contains some amount of perverted information, the authors of the
Atlas assumed it necessary to store this information in its primary
form. Methods of data quality control can be developed in future in the
process of hydrochemical information accumulation. It can be supposed
that attitude can vary in future to the data that were rejected
according to the procedure accepted in the Atlas.

The hydrochemical Atlas of the Arctic Ocean is the first specialized and
electronic generalization of hydrochemical observations in the Arctic
Ocean and finishes the program of joint efforts of Russian and US
specialists in preparation of a number of atlases for the Arctic. The
published Oceanographic Atlas (1997, 1998), Atlas of Arctic Meteorology
and Climate (2000), Ice Atlas of the Arctic Ocean prepared for
publication and Hydrochemical Atlas of the Arctic Ocean represent a
united series of fundamental generalizations of empirical knowledge of
Arctic Ocean nature at climatic level.

The Hydrochemical Atlas of the Arctic Ocean was elaborated in the result
of joint efforts of the SRC of the RF AARI and IARC. Dr. Ye. Nikiforov
was scientific supervisor of the Atlas, Dr. R. Colony was manager on
behalf of the USA and Dr. L. Timokhov -- on behalf of Russia.

1.2. How to Use the Atlas.

The software Ocean Data View (Schlitzer, 2001) should be used for
visualization of hydrochemical information. This software allows one to
construct schemes of station location, profiles, transects, distribution
maps of hydrochemical characteristics. All the possibilities and methods
of their use are given in HELP -- files of these software.

1.3. List of Participants.

1.  Leading research associate, Dr. Nikiforov Ye.G. (Sections 1, 3, 5)

2.  Principal research associate, Dr. Timokhov L.A. (Sections 1, 3, 4)

3.  Department head, Dr. Priamikov S.M. (Sections 1, 5).

4.  Dr. R. Colony (Section 1)

5.  Laboratory head Sokolov V.T. (Sections 2, 3).

6.  Senior Research Associate Karpiy V.Yu. (Sections 1-5).

7.  Senior Research Associate Lebedev N.V. (Sections 1-5).

8.  Senior Research Associate, Dr. Pivovarov S.V. (Sections 2, 3, 5).

9.  Principal research associate, Dr. Pokrovsky O.M. (Section 3).

10. Research Associate Nitishinsky M.A. (Sections 3, 5)

11. Research Associate Garmanov A.L. (Sections 2, 4).

12. Junior Research Associate Novikhin A.Ye. (Sections 3, 5)

13. Junior Research Associate Kirillova Ye.P. (Sections 3, 5).

14. Technician Karpiy S.V. (Web Design).

1.4. References to Section 1.

Alekin O.A., Liakhin Yu. I.: Chemistry of the Ocean. -- L.,
Gydrometeoizdat, 1984, 343 p.

Atlas of the oceans. The Arctic ocean. -- Published by GUNIO, Ministry
of Defense of the USSR, 1980, 184 p.

Joint US-Russian Atlas of the Arctic Ocean, Oceanography Atlas for the
Winter Period. Ed. by F. Tanis, L. Timokhov. Environmental Working
Group, University of Colorado, Boulder, CD-ROM, 1997.

Joint US-Russian Atlas of the Arctic Ocean, Oceanography Atlas for the
Summer Period. Ed. by F. Tanis, L. Timokhov. Environmental Working
Group, University of Colorado, Boulder, CD-ROM, 1998.

Rusanov V.P., Yakovlev N.I., Buynevich A.G.: Hydrochemical conditions of
the Arctic Ocean. -- Proc. of the AARI, 1979, v. 355, 144 p.

Schlitzer R. Ocean Data View software, 2001 -- www. AWI-Bremerhaven. de

**2. Hydrochemical Investigations in the Arctic Ocean**

2.1. History of Investigations

Arctic seas of the Siberian shelf and the Arctic Basin were absolutely
unexplored in hydrochemical aspect till the 20-s of the XX-th century.
Some amount of determinations were made by expeditions of A.
Nordenskiold on board of "Vega" (1878-1879), F. Nansen on board of
"Fram" (1893-1896), H. Sverdrup and F. Malmgren on board of "Maud"
(1918-1921).

Hydrochemical observations for parameters of sea water related with
biochemical processes (nutrients, elements of the carbonate system)
began in the 20-s because of fishery intensification. Amount of
information significantly increased during the Second International
Polar Year (1932-1933), and principle of international coordination was
introduced in practice of investigations of the Arctic seas. Annual
observations were carried out in the Chukchi Sea in the years 1932-1938
by Soviet and US expeditions.

Systematical hydrochemical study of the Kara and Laptev Seas began in
the 30-s after establishment of the Main Administration of the Northern
Sea Route. Study of the East Siberian and Chukchi Seas began somewhat
later.

Materials collected up to the year 1941 by the marine expeditions of the
Arctic Institute allowed to obtain the first comparative hydrochemical
characteristics of the Arctic seas (for example, by then there were
10.000 determinations of dissolved oxygen and more than 12.000
determinations of alkalinity in the Kara Sea, and several thousand
determinations in the Laptev and Chukchi Seas).

Cycles of limited in number, but, nevertheless, special observations
were done in this period in some expeditions. These observations have
been carried out in order to reveal influence exerted by ice melting and
freezing on hydrochemical conditions of these seas, including chemical
properties of sea ice, study of a possibility to use hydrochemical
characteristics as reagents of water mass origin and propagation, study
of river runoff influence on hydrochemical conditions of the seas. With
this in mind, spatial distribution have been studied of alkaline and
sulfate coefficients, pH, concentration of dissolved oxygen, as well as
of complete set of nutrients and electric conductivity of sea water.
These observations have given some material for estimation of daily and
seasonal oscillations of hydrochemical element concentrations.

In particular, alkalinity increase of sea water were revealed both in
melting zones, as well as in water areas with strong influence of river
runoff. However, concentration of dissolved oxygen in the melting zones
was increased in the surface layer because of intensive development of
phytoplankton, production of oxygen, and often over-saturation of
seawater by oxygen (Wiese, 1938). The author revealed that ice edge in
the polar seas is a frontal zone according to hydrochemical and
biological indications.

Selective rejection of salt out of brine captured by ice takes place by
freezing and successive ice thickness growth, it causes a relative
concentration decrease of carbonates and sulfates in surface waters.
This fact is also approved by study of chemical composition of sea ice
(Laktionov, 1930). Deterioration of normal relationships between salt
components of seawater is a consequence of this fact.

By ice melting, these processes are reversal in those water areas, where
the ice has drifted during polar winter (i.e. for 7-9 months).

Deficit of dissolved oxygen is observed in the water areas influenced by
river runoff, because of inflow of a large amount of organic matters and
intensive oxidation. As this takes place, active reaction of environment
strongly shifts to the acid side (pH values decrease up to 7.5 and
lower) (Laktionov, 1936).

Therefore, results of hydrochemical investigations of this period
revealed wide possibilities for their implementation in diagnostics of
water mass origin and dynamics in the Arctic seas and Arctic Basin.

A large amount of complete analysis of sea and salty water composition
has also been performed. Using this material P. Lobza (1947) has studied
a relationship between water salinity and chlorine concentration. She
revealed significant deviations of the chlorine coefficient in the
Arctic seas from the White Sea to the Chukchi Sea from that accepted in
the formula of Knudsen-Sorensen for the ocean water (Fig. 2.1):

$S = 0\text{.}\text{030} + 1\text{.}\text{8050}\text{Cl}$.

According to her determinations, there is a growth of the chlorine
coefficient in the salty waters (S\< 25 psu) from 1.807 by S=25 psu (it
is for 0.002 higher than the value for the ocean) to 1.845 by S=10 psu.
Therefore, salinity (and density) of the waters freshened by river
runoff can be up to 2% higher, than it follows from the formula for the
ocean. However, at a later time, interest to this problem has
significantly weakened because of insufficient accuracy and
labor-intensity of the used analytical methods.

![](media/image1.png){width="6.691666666666666in"
height="3.7604166666666665in"}

Fig. 2.1 Dependence of the chlorine coefficient K~Cl~ of water salinity
in the Arctic seas influenced by river runoff.

according to P. Lobza (1940)

the formula of Knudsen-Sorensen

data of analytical determinations

Investigations were continued in the 80-s using high precision methods
of determination of chloride activity in sea water (in particular, with
the help of chloride electrodes (Melnikov, 1984; 1989). It has been
found that noticeable oscillations of inter-element relationship
appeared by low water temperatures (- 1.8 $$ 4^0^ C) exerting influence
on accuracy of water salinity determination using two methods --
electrometric and argentometric.

Both these methods give underestimated values for the surface waters
(upper layer of 10 m) in all four Arctic seas in summer. Difference
between actual and measured values can be rather significant: dispersion
of the deviations is 0.03-0.12 psu for the first method, and 0.05-0.18
psu for the second one.

Chemical processes exert significant influence on relative composition
of the surface waters in winter. These processes develop by ice
formation and changes of ice cover state, for example, it is brine
rejection in the under-ice water layer. That is why, both indirect
methods of salinity determination give overestimated results. As this
takes place, $\Delta S$ values exceeding 0.02 psu were observed in
30-40% of cases, they were equal practically to zero in 20-30% of cases.

Overestimated results are common in the waters of the Arctic seas
underlying the upper layer of 10 m. However, errors do not exceed 0.02
psu in 80% of cases.

The hydrochemical observations were substantially reduced during the
Second World War, they were continued only after the war in marine
expeditions of the Arctic and Antarctic Research Institute (AARI).

Since 1946, the annual summer hydrochemical observations were performed
in marine oceanographic expeditions "Ice Patrol" in the Arctic seas, at
first in the Chukchi Sea and later on in the Kara, Laptev and East
Siberian Seas. The observations were carried out at standard transects.
Aspiration to unification of methods of chemical analysis of sea water,
all-embracing character of investigations and their higher level were
typical for the post-war period. Materials of these expeditions were
used in many research works and became a basis for drawing of maps of
mean distribution of hydrochemical parameters in the Arctic seas (Atlas
of the Arctic Ocean, 1980; Atlas of the Arctic, 1985).

The most large-scale and systematic hydrochemical observations using a
fixed grid were performed in the 70-s and in the beginning of 80-s
according to the plan of the Natural Experiment in Study of Interaction
of the Ocean and Atmosphere (Trioshnikov et al., 1968). In this period,
hydrological and accompanying hydrochemical observations were organized
as plan hydrological surveys of sea water areas. This work was carried
out using vessels in summer and aircraft in winter, covering the entire
sea water area and the Arctic Basin. Observations at "North Pole"
drifting stations were continued simultaneously. Number of hydrochemical
determinations increased in this period to several tens of thousand for
previously poor covered areas. It allowed to study hydrochemical
conditions in the seas, Arctic and North European Basin using a serious
statistical basis.

The "Ice Patrol" marine expeditions were stopped in the 80-s. Summer
observations in the Kara Sea were carried out by the research vessels
"Academician Shuleikin" and "Professor Multanovsky". Summer surveys of
ice free parts of the sea were completed by observations in sea ice made
by the research icebreaker "Otto Shmidt". The vessels of the "Shuleikin"
type were equipped by modern sounding complexes, plastic bottles were
used for sampling, nutrient concentration in sea water was determined
with the help of AutoAnalyzer AKEA. Use of modern analytical and
sampling equipment allowed to improve significantly quality of
hydrochemical information.

Vast amount of information on hydrochemical conditions in coastal and
river mouth zones of the Arctic seas was collected by sledge-tractor
expeditions of Arctic departments of the USSR Hydrometeorological
Service and in coastal observatories (Zubakina, 1974, Miskevich, 1979,
Sidorov, 1992).

It should be mentioned that chemical analysis of water samples were
performed using unified instructions. It guaranteed comparability of
data obtained in different expeditions.

International cooperation in study of the Arctic seas received wide
impetus in the 90-s. Several Russian-Norwegian and Russian-German
expeditions were carried out in the Kara Sea. Russian-French expeditions
SPASIBA (Letolle et al., 1997) worked in the Laptev Sea in September
1989 and in August-September 1991. A series of multidisciplinary
Russian-German expeditions was performed in the Laptev Sea in 1992-1999
in accordance with the program "Laptev Sea System", some of these
expeditions were unique (Kassens & Karpiy, 1994; Kassens & Dmitrenko,
1995). This expedition for the first time was carried out in autumn in
1995 in the period of intensive ice formation (Kassens, 1997). In 1996
propagation of river water in seashore near estuary during flood on Lena
was studied for the first time (Dmitrrenko et al., 1999). Joint
US-Russian expeditions with participation of Japanese specialists were
performed in this period of time in the Chukchi Sea and in the eastern
part of the East Siberian Sea. The main specific feature of the
expeditions in this period of research is simultaneous collection of
information in different branches of science and study of the Arctic
seas as unit systems.

Of course, data of expeditions performed in different years are not of
the same quality. Information obtained since the 60-s is more reliable,
because of presence of a definite experience of hydrochemical
observations in the Arctic, and implementation of optical devices
instead of the visual methods of analysis. The most accurate data have
been obtained in the expeditions on the vessels of the "Shuleikin" type
and in international expeditions in the 90-s.

There were no foreign publications in hydrochemistry of the Russian
Arctic seas till the middle of the 90-s. Foreign research vessels have
worked usually in the Chukchi and Beaufort Seas. However, a US
icebreaker made an oceanographic survey in the East Siberian and Laptev
Seas in the summer of 1963, and in the Kara Sea in 1965. Results of
these observations have been later published (Codispoti & Richards,
1968). Nevertheless, many scientists were interesting in processes on
the wide Siberian shelf (Anderson, 1995; References to this Section).
Problems of biological productivity of the Arctic seas have attracted a
maximum attention, as well as influence of river runoff (Anderson et
all., 1983; Schlosser et all., 1994; Dai & Martin 1995 and others),
interaction of the shelf and the Arctic Basin (Legendre et all., 1996;
Schauer et all., 1997).

International cooperation in study of the Kara and Laptev Seas has given
results. New data have been obtained on water mass distribution in the
northern troughs of the Kara Sea (Augstein, 1997; Pivovarov et al.,
1999). The hydrochemical observations performed in the Russian-French
expeditions SPASIBA were used in a number of articles devoted to
influence of the Lena river on the south-eastern part of the Laptev Sea.

The most complete review of investigation results of hydrochemical water
structure of the marginal Arctic seas of the Siberian shelf and of the
Arctic Basin were made by V. Rusanov et al. (1979), geochemical
processes in the Eurasian shelf seas were studied by Ye. Romankevich et
al. (1982) and V. Smagin (1995). Hydrochemical division into districts
for these water areas has been carried out, and variability limits of
the main hydrochemical elements and their structure have been
determined.

2.2. Methods of Measurement and Determination Accuracy.

Hydrochemical Atlas of the Arctic Ocean unites data collected in
expeditions of different scientific and industrial organizations of
different countries for a long period of time. Naturally, methods of
chemical analysis of seawater were constantly refined during such a long
period of time. Chemical analysis of sea water was performed in the USSR
using unified instructions and standard methods which had been
elaborated in the following methodical centers: the State Oceanographic
Institute (SOI), the Hydrochemical Institute (HCI), the Arctic and
Antarctic Research Institute (AARI), and others. It ensured the
possibility to compare data obtained in different expeditions by
different organizations.

These instructions for performance of chemical analysis of sea water
were periodically changed, because of perfection of analytical equipment
and in order to meet more strict requirements to determination accuracy
and to ensure consistency of the Russian methods with the international
standards. These changes can be traced analyzing successive editions of
the "Guidance for Chemical Analysis of Sea Waters" published in 1950,
1959, 1977, 1993, however, the principle remains invariable that all the
observations regardless of expedition or region of field work should be
carried out using the last accepted "Guidance" or "Guiding Document".

As a rule, concentrations of only main biohydrochemical indices were
determined in the Arctic expeditions from all the variety of chemical
elements and their compositions dissolved and suspended in seawater.
They are as follows: nutrients (dissolved mineral forms of nitrogen,
phosphorus, silicon), dissolved oxygen and some parameters of the
carbonate system (pH and alkalinity). Choice of these chemical elements
and parameters was determined by the fact that they were used for
estimation of biological productivity of marine environment, and that
many of them were indicators of water mass origin.

The Winkler method (Guidance 1993), which had shown itself to advantage,
was used for determination of *oxygen*. Measurement error within the
range of concentrations typical for the Arctic seas does not exceed 0.05
ml/l, the total error equals 3.4%. Tables of oxygen solubility in sea
water have varied repeatedly in the course of long period of
observations. It made difficult to perform joint analysis of the data
obtained in different time. Calculations of sea water saturation by
oxygen in the Hydrochemical Atlas of the Arctic Ocean were carried out
using the formulas recommended by the Oceanographic Commission according
to the UNESCO formula (Tables 1976).

Mineral nutrients are a nourishment base for life of phytoplankton.
Dissolved inorganic forms of nitrogen (nitrites, nitrates, ammonium
nitrogen), phosphorus (phosphates) and silicon (silicates) are the most
important for algae.

*Nitrite concentration* was determined in seawater using the
colorimetric method. Nitrite concentration is not high, therefore
analysis error can be 20% and above. For determination of *nitrate
concentration*, the method was used of their reduction to nitrite in a
column of coppered fine-crystalline cadmium with subsequent
determination of nitrite concentration using the colorimetric method.
The total error within the range of concentrations observed in the
Arctic seas varies from 3.1 to 7.4% (Guidance, 1993). The method error
does not exceed 4.4% while using Autoanalyzers.

Ammonium nitrogen was determined using the colorimetric method with the
total error varying from 2.8 to 11.4% within the range of concentrations
from 15 to 500 $\mu$g/l.

Concentration of dissolved *inorganic silicon* was determined using the
colorimetric method and scale of colors with errors up to 20% and above
(Guidance, 1954) and device methods with errors 4.6-5.8% depending on
concentration (Guidance, 1993). Use of Autoanalyzers allowed to obtain a
higher accuracy and presentation of results (Koroleff, 1983).

Concentration of dissolved *inorganic phosphorus (orthophosphate)* and
total phosphorus was determined in seawater (Guidance, 1993). Error of
the colorimetric analysis equals 4-5% depending on concentration and
used devices. The term "phosphate" is often used in scientific
literature on chemical oceanography instead of the term orthophosphate
as a synonym.

The carbonate system of sea water is a buffer system, it supports a weak
alkaline medium and plays a significant role in hydrobiological and
physiological processes.

A pH scale with a set of indicators was usually used for pH
determination in sea water (The Buch method). Accuracy of pH
determination was significantly improved with implementation of
potentiometers in practice of hydrochemical observations. The total
error equals 0.04 conventional units (Guidance, 1993).

The volumetric-analytical and potentiometric methods were used for
determination of *total alkalinity* of sea water. Error of these methods
is about 0.5% (Guidance, 1993). The alkaline-saline coefficient and
relative alkalinity are ratios of the total alkalinity to salinity and
chlorinity of sea water, respectively. These indices were taken up in
chemical oceanography, because using their values one can differ sea
freshening caused by river runoff and that caused by precipitation and
ice melting.

Detailed information about instructions and Guiding Documents used by
investigators for performance of chemical analysis in specific
expeditions or research vessel cruises are given below in Table 2.1.

It should be mentioned that there were some *specific conditions* of
performance of hydrochemical observations in the Arctic. These
conditions might cause violation of methodical requirements and
appearance of systematic and accidental errors. They are as follows:
severe climatic conditions, insufficiently well equipped ship
laboratory, especially at small ships; overtime of analysts, and others.
In the airborne "Sever" expeditions, water samples were analyzed in base
laboratories 6-12 hours after sampling, and often transportation of the
samples took much more time. Therefore, information about laboratory was
certainly recorded in books for registration of primary hydrochemical
observations. All the hydrochemical observations were subjected to a
strict control and estimation by a methodical commission of the AARI
hydrochemical laboratory.

List of instructions and methods used for hydrochemical determinations
are given in Tables 2.1 and 2.2.. The table "Information on methods of
hydrochemical analysis used in expeditions of the AARI and other
organizations in the Arctic Ocean" is given in Appendix 1. Name of these
expeditions, period of their performance, name of research vessel or
other platform and number of stations carried out in each expedition are
given in this table. Numbers divided by oblique stroke are given in the
columns related with hydrochemical parameters. The left side gives a
number of used guidance, instruction or other methodical document (Table
2.1), the right side gives a method number for determination of this
specific element (Table 2.2) mentioned in the guidance.

##### Table 2.1

List of guiding documents and instructions used by hydrochemical
investigations.

+-----+----------------------------------------------------------------+
| No. | ## Guidances, instructions                                     |
+-----+----------------------------------------------------------------+
| 1   | Instruction for performance of hydrochemical investigations of |
|     | sea water. The Main Administration of the Northern Sea Route,  |
|     | M. 1944                                                        |
+-----+----------------------------------------------------------------+
| 2   | Guidance for chemical analysis of sea waters (edited by P.     |
|     | Voronkov). Hydrometeoizdat, L. 1950                            |
+-----+----------------------------------------------------------------+
| 3   | Guidance for chemical analysis of sea waters. Published by the |
|     | Main Administration of the Northern Sea Route, 1954            |
+-----+----------------------------------------------------------------+
| 4   | Guidance for marine hydrochemical investigations.              |
|     | Hydrometeoizdat, L. 1959                                       |
+-----+----------------------------------------------------------------+
| 5   | Guidance for methods of chemical analysis of sea waters.       |
|     | Hydrometeoizdat, L. 1977                                       |
+-----+----------------------------------------------------------------+
| 6   | Methodical instructions No. 30 SOI, M. 1966                    |
+-----+----------------------------------------------------------------+
| 7   | Provisional instruction for determination of nutrients. AARI,  |
|     | 1968                                                           |
+-----+----------------------------------------------------------------+
| 8   | Instruction for determination of silicon in sea water. AARI    |
+-----+----------------------------------------------------------------+
| 9   | Provisional methodical instructions for quantitative           |
|     | determination of mineral phosphorus in sea water. SOI, M. 1971 |
+-----+----------------------------------------------------------------+
| 10  | Provisional methodical instructions for quantitative           |
|     | determination of silicon (with chlorine tin) in marine         |
|     | environment. SOI, M. 1971                                      |
+-----+----------------------------------------------------------------+
| 11  | Provisional instruction for quantitative determination of      |
|     | dissolved oxygen in sea water. SOI, M. 1972                    |
+-----+----------------------------------------------------------------+
| 12  | Provisional methodical instructions for determination of       |
|     | oxygen in the Arctic waters. AARI                              |
+-----+----------------------------------------------------------------+
| 13  | Instruction of the All-Union Arctic Institute. Kondyrev,       |
|     | Bruevich                                                       |
+-----+----------------------------------------------------------------+
| 14  | Instruction for hydrochemical determinations in the sea. S.    |
|     | Bruevich, 1938                                                 |
+-----+----------------------------------------------------------------+
| 15  | Guidance for chemical analysis of sea waters. St. Petersburg,  |
|     | Hydrometeoizdat, 1993, GD 52.10.243-92                         |
+-----+----------------------------------------------------------------+

Table 2.2.

### Methods of chemical analysis

  --------------- ---------------------------------------------------------------
  Hydrochemical   
  parameters and  
  methods of      
  their analysis  

  Oxygen          

  1               Iodinemetric (the Winkler method)

  pH              

  1               Colorimetric

  1 /a            Subjective (standard scale)

  2               Electrometric (рН-meter)

  Total           
  alkalinity      

  1               Automatic titration with HCl (Acidometric,
                  Volumetric-analytical method)

  2               Back titration method

  3               Electrometric (рН-meter)

  Phosphate       

  1               Colorimetric (color equalization according to the Denige-Atkins
                  with chlorine tin)

  1 /a            Subjective (Gener's cylinder)

  1 /b            Objective (photoelectrocolorimeter (PEC), spectrophotometer)

  2               Colorimetric (according to the Morphy-Riley with ascorbic acid)

  2 /a            Objective (photoelectrocolorimeter, spectrophotometer)

  Silicate        

  1               Colorimetric (according to the Dienert-Wandenbulke method with
                  Moor salt)

  1 /a            Subjective (Gener cylinder)

  1 /b            Objective (photoelectrocolorimeter, spectrophotometer)

  2               Colorimetric (All-Union Institute of Fishery and
                  Oceanography) - PEC

  3               Colorimetric (Mullin-Riley for small concentrations) - PEC

  4               Autoanalizer АКЕА (DATEX manual)

  Nitrite         

  1               Colorimetric (color equalization according to the Griss-Ilosway
                  method)

  1 /a            Subjective (Gener cylinder)

  1 /b            Objective (photoelectrocolorimeter, spectrophotometer)

  2               Autoanalizer АКЕА (DATEX manual)

  Table 2.2 (to   
  be continued)   

  Hydrochemical   
  parameters and  
  methods of      
  their analysis  

  Nitrate         

  1               Colorimetric (dephenilamin oxidation method)

  1 /a            Subjective (standard scale)

  2               Colorimetric (reduction using the methods of Wood, Armstrong,
                  et al.)

  2 /b            Objective (photoelectrocolorimeter, spectrophotometer)

  3               Autoanalizer АКЕА (DATEX manual)
  --------------- ---------------------------------------------------------------

For example, numbers "4/1b" in the column of silicon determination (Si)
means the following. The chemical analysis has been carried out in
accordance with the Guidance for marine hydrochemical investigations
(Hydrometeoizdat, L. 1959) given in Table 2.2.1 as number 4, the
measurements have been made using the colorimetric method (color
equalization according to the Dienert-Wandenbulke with Moor salt), in
doing so, the measurement of optical density has been performed using
photoelectrocolorimeter or spectrophotometer (see Table 2.2.2, column
"silicate", item 1b).

2.3. References to Section 2

Anokhin V.N., Melnikov S.A.: Physical-chemical properties of sea water
and variation of its salt composition in the under-ice layer. -- In:
Vertical structure and dynamics of the under-ice layer. Hydrometeoizdat,
L., 1989, pp. 25-35.

Wiese W.Yu.: Hydrochemical conditions in the marginal ice zone of the
Arctic seas. -- Problems of the Arctic, 1943, No. 2, pp. 13-31

Zubakina A.N.: Some hydrochemical specific features of estuary zones of
Anabar, Lena, Yana, Indigirka. -- Proc. of the SOI, 1974, v. 118, pp.
44-55

Lobza P.G.: Chemistry of the Kara Sea. Skeleton of the salt
composition. - Proc. of the AARI, 1947, v. 197, 180 p.

Laktionov A.F.: Hydrochemical conditions in the Laptev Sea. 1936

Laktionov A.F.: On properties of sea ice. -- Proc. of the Institute of
North Investigations, 1930, v. 49

Melnikov S.A.: Study of concentrations of some elements of salt
composition in the waters of the shelf zone of the East Siberian Sea
using ion-selective potentiometry. -- Pro. Of the AARI, 1984, v. 368,
pp. 87-98

Miskevich I.V.: Extremely low levels of oxygen concentration in the
waters of estuary sea-shore of the Lena delt. -- Deposited in the
All-Union Institute of Scientific and Technical Information --
International Data Center, 1979, 10p.

Trioshnikov A.F., Borisenkov Ye.P., Nikiforov Ye.G., Mustafin F.M.,
Chaplygin Ye.I., Spaikher A.O.: Natural experiment in study of
interaction of the ocean and atmosphere. -- Problems of the Arctic and
Antarctic, 1968, v. 28, pp. 5-20.

Romankevich Ye.A., Daniushevskaya A.I., Beliaeva A.N., Rusanov V.P.:
Biochemistry of organic matters in Arctic seas. -- "Nauka", M., 1982,
240p.

Rusanov V.P., Yakovlev N.I., Buynevich A.G.: Hydrochemical conditions of
the Arctic Ocean. -- Proc. of the AARI, 1979, v. 365, 144 p.

Sidorov I.S., Gudkov A.Yu.: Influence of oxygen regime on living
conditions of zoobenthos in coastal regions of the Laptev Sea. --
Oceanography, 1992, v.32, No.5, pp. 902-904.

Smagin V.M.: Hydrochemical investigations of polar regions. - Problems
of the Arctic and Antarctic, 1995, v. 70, pp. 183-192.

Anderson L.G., Dyrssen D., Jones E.P., Lowings M.G. Inputs and outputs
of salt, freshwater, alkalinity, and silica in the Arctic Ocean //
Deep-Sea Res. -- 1983. -- No. 1. -- P. 87--94.

Anderson L.G. Chemical oceanography of the Arctic Ocean and its shelf
seas // In: Arctic Oceanography: Marginal ice zones and continental
shelves coastal and estuarine Studies. -- 1995. -- Vol. 49. -- P.
183--202.

Augstein E. (Ed.) The expedition ARCTIC '96 of RV "Polarstern" (ARK XII)
with the Arctic Climate System Study (ACSYC) // Reports on Polar
Research. -- 1997. -- No. 234. -- 54 p.

Codispoti L.A., Richards F.A. Micro-nutrient distributions in the East
Siberian and Laptev seas during summer 1963 // Arctic. -- 1968. -- No.
21. -- P. 67--83.

Kassens H., Karpiy V.Y. Russian-German cooperation: The Transdrift I
expedition to the Laptev Sea // Reports on Polar Research. -- 1994. --
No. 151. -- 168 p.

Kassens H., Dmitrenko I. The TRANSDRIFT II Expedition to the Laptev Sea
// Reports on Polar Research. -- 1995. -- No. 182. -- P. 1--180.

Kassens H. (Ed.) Laptev Sea System: Expeditions in 1995 // Reports on
Polar Research. -- 1997. -- No. 248. -- 210 p.

Legendre L., Rivkin R.B., Michel C. Food web structure and biogenic
carbon export on the continental shelves of the Arctic Ocean // Mem.
Nat. Inst. Pol. Res. -- 1996. -- No. 51. -- P. 41--65.

Letolle R., Martin J.M., Thomas A.J., Gordeev V.V., Gusarova S., Sidorov
I.S. ^13^O abundance and dissolved silicate in the Lena delta and Laptev
Sea (Russia) // Marine Chemistry. -- 1993. -- No. 43. -- P. 47--64.

Pivovarov S.V., Hölemann J.A., Kassens H., Antonow M., Dmitrenko I.
Dissolved oxygen, silicon, phosphorous and suspended matter
concentration during the spring breakup of the Lena River. -- In.: H.
Kassens et al., (Eds.) Land-ocean system in the Siberian Arctic:
dynamics and history. Springer. -- 1999. -- P. 251--264.

Schauer U., Muench R.D., Rudels B., Timokhov L. Impact of Arctic shelf
waters on the Nansen Basin intermediate layers // Journal of Geophysical
Research. -- 1997. -- Vol. 102. -- No. C2. -- P. 3371--3382.

Schlosser P., Bauch D., Fairbanks R., Bonisch G. Arctic river-runoff:
Mean residence time in the shelves and in the halocline // Deep-Sea Res.
-- 1994. -- Vol. 41. -- No. 7. -- P. 1053--1068.

Wiese,W. Zur Kenntnis der Salze der Meeresises - Annal. der Hydrol. und
marit. Meteorolog., 1930.

**3. Data Processing**

3.1. Hydrochemical Information

3.1.1. Data Sources

Observations carried out by expeditions on drift ice, icebreakers in ice
and research vessels on open water in the water area of the Arctic Ocean
(Fig. 3.1) formed a data set of initial hydrochemical measurements.
Period of observations was chosen since 1948 till 2000.

![](media/image2.wmf){width="6.6in" height="6.6in"}

Fig. 3.1. Water areas for which data of hydrochemical measurements were
collected for the years 1948-2000.

Data of the AARI and of the National Oceanographic Data Center-- World
Data Center - A(NODC) were used for creation of the complete historical
data set of Russian and western observations. The NODC data set was
collected from different sources including the Russian ones (See
Appendix 2).

Significant part of the AARI hydrochemical information was stored on
paper. Therefore, the data typing was organized first of all.

The collected data were united in a data set of initial measurements
(See Section 4.1.). The data set included 21.264 stations with 163.127
observation depths. Structure of hydrochemical information was
non-uniform. Observation data were presented in different formats,
different measurement units of hydrochemical characteristics were used,
indices of expeditions and vessels were often changed, there was
duplication of data.

The data set of initial measurements was subjected to analysis for the
data duplication. Presence of duplicated data is a serious problem of
oceanographic databases, collected from different sources, because the
present-day system of information collection and exchange allows
repeated data input in data sets.

Check and exclusion of duplicated stations from the database was
realized in two ways: using automatic check of data coincidence, during
the expert control of hydrochemical information.

The automatic control provides data scan for coincidence of coordinates
(with accuracy of 0.5^/^ of latitude and longitude), date and time of
station performance, and information at the first standard depths. If
coordinates and time of stations coincide, or, in the absence of time,
information at the first standard depth coincides, then station with
more useful information (time of observation, station depth, greater
number of parameters at greater number of observation depths, presence
of temperature and salinity measurements at the first observation depth,
etc.) is selected for further processing and analysis. This method
rather quickly allows to get rid of duplicating oceanographic stations
(BarKode, 1999), however, there is a danger of a loss of some useful
information.

Additional check for duplicates was made by the expert method. Data
samplings were made for that purpose, these data were obtained by
different expeditions at different time in specific regions of the
Arctic Ocean. In presence of duplicated data, they were compared using
the expert method. The most reliable and complete data sets were left in
the database, and the questionable and incomplete duplicated data sets
were eliminated.

The data set of initial measurements has reduced for 18.52% after
preliminary analysis and duplicated data elimination. The obtained data
set was used for description of specific features of spatial and
temporal distribution of hydrochemical observations.

Metadata are given in Appendix 2.

3.1.2. Spatial and Temporal Distribution of Observations

Information on amount of stations for the years 1948-1993 in the joint
database is given in Section 3. Location of oceanographic stations,
where measurements of hydrochemical characteristics were carried out, is
shown in Fig. 3.2-3.8. Fig. 3.9 and 3.10 demonstrate distribution of
stations with element determination for different years.

Scale of temporal averaging for the Arctic Basin was chosen as follows.
Seasonal variations of oceanographic characteristics in the Arctic Basin
manifest themselves in the upper 200 m layer. Winter season lasts for 9
months, beginning in September and finishing in the end of May. Ice
thickness growth and salinity increase in the upper layer are observed
in the central part of the ocean till June. Therefore, May can be
considered as the last month of the winter period.

In the southern parts of Arctic seas duration of the winter season is
somewhat shorter. Transition to spring processes happens in river mouths
and separate fiords in the second half of May.

![](media/image3.wmf){width="3.1102362204724407in"
height="3.1102362204724407in"}![](media/image4.wmf){width="3.1102362204724407in"
height="3.1102362204724407in"}

Fig. 3.2. Location of stations with oxygen observations in the Arctic
Basin and Arctic seas for the years 1948-2000: a) winter (November- May)
-- 3017 stations; b) summer (July-September) -- 8748 stations.

![](media/image5.wmf){width="3.1102362204724407in"
height="3.1102362204724407in"}![](media/image6.wmf){width="3.1102362204724407in"
height="3.1102362204724407in"}

Fig. 3.3. Location of stations with silicate observations in the Arctic
Basin and Arctic seas for the years 1948-2000: a) winter (November- May)
-- 4430 stations; b) summer (July-September) -- 6966 stations.

![](media/image7.wmf){width="3.1102362204724407in"
height="3.1102362204724407in"}![](media/image8.wmf){width="3.1102362204724407in"
height="3.1102362204724407in"}

Fig. 3.4. Location of stations with phosphate observations in the Arctic
Basin and Arctic seas for the years 1948-2000: a) winter (November- May)
-- 1626 stations; b) summer (July-September) -- 3284 stations.

![](media/image9.wmf){width="3.1102362204724407in"
height="3.1102362204724407in"}![](media/image10.wmf){width="3.1102362204724407in"
height="3.1102362204724407in"}

Fig. 3.5. Location of stations with nitrite observations in the Arctic
Basin and Arctic seas for the years 1948-2000: a) winter (November- May)
-- 1423 stations; b) summer (July-September) -- 2553 stations.

![](media/image11.wmf){width="3.1102362204724407in"
height="3.1102362204724407in"}![](media/image12.wmf){width="3.1102362204724407in"
height="3.1102362204724407in"}

Fig. 3.6. Location of stations with nitrate observations in the Arctic
Basin and Arctic seas for the years 1948-2000: a) winter (November- May)
-- 256 stations; b) summer (July-September) -- 1461 stations.

![](media/image13.wmf){width="3.1102362204724407in"
height="3.1102362204724407in"}![](media/image14.wmf){width="3.1102362204724407in"
height="3.1102362204724407in"}

Fig. 3.7. Location of stations with pH~B~ observations in the Arctic
Basin and Arctic seas for the years 1948-2000: a) winter (November- May)
-- 2247 stations; b) summer (July-September) -- 6848 stations.

![](media/image15.wmf){width="3.1102362204724407in"
height="3.1102362204724407in"}![](media/image16.wmf){width="3.1102362204724407in"
height="3.1102362204724407in"}

Fig. 3.8. Location of stations with alkalinity observations in the
Arctic Basin and Arctic seas for the years 1948-2000: a) winter
(November- May) -- 1420 stations; b) summer (July-September) -- 1567
stations.

![](media/image17.wmf){width="4.541732283464567in"
height="2.015354330708661in"}![](media/image18.wmf){width="4.527165354330709in"
height="2.013779527559055in"}![](media/image19.wmf){width="4.509055118110236in"
height="2.015354330708661in"}![](media/image20.wmf){width="4.522834645669291in"
height="2.013779527559055in"}

Fig. 3.9. Number of stations in the working base of hydrochemical
determinations in the Arctic Ocean for different years (1948-2000) of
concentration: a) dissolved oxygen, b) silicate, c) phosphate, d)
nitrite

![](media/image21.wmf){width="4.936614173228347in"
height="2.0866141732283463in"}![](media/image22.wmf){width="4.936614173228347in"
height="2.085433070866142in"}![](media/image23.wmf){width="4.936614173228347in"
height="2.085433070866142in"}

Fig. 3.10. Number of stations in the working base of hydrochemical
determinations in the Arctic Ocean for different years (1948-2000) of
concentration: a) nitrate, b) pH~B~, c) alkalinity

3.2. Control of Hydrochemical Data

3.2.1. Data Input

Data from the primary paper sources were placed in computer and added
the files already containing station passport, meteorological and ice
information, water temperature and salinity at observation depths.

The following permissible ranges of parameter variations were accepted
by the first computer-aided control:

a)  station passport

-   station number should be positive,

-   coordinates should change within the limits from 0 to 90^0^ and from
    0 to 59^/^ for latitude, from 0 to 360^0^ and from 0 to 59^/^ for
    longitude; symbols S or N are given to latitude, and symbols E and W
    are given to longitude (longitude greater, than 180^0^, was later
    converted to the western one),

-   use of a field of the "data" type realizes full control of date
    appropriateness up to the control of a leap-year in case typing "29
    February", time: hours -- from 0 to 23, minutes -- from 0 to 59;

-   sea depth should exceed zero;

-   air temperature should vary from --55 to +50^0^ C;

-   wind speed should vary from 0 to 40 m/sec, wind direction -- from 0
    to 360^0^;

-   atmospheric pressure should vary from 800 to 1200 mb;

-   ice concentration should be within the limits from 0 to 10
    conventional units, direction to the ice edge -- from 0 to 360^0^,
    and distance to it should not be negative.

b)  oceanographic data:

-   observation depth should be less or equal sea depth in the station
    passport,

-   water temperature -- from --2.20 to + 30^0^ C,

-   salinity -- from 0 to 36 psu,

-   oxygen -- from 0 to 20 ml/l,

-   pH~B~ -- from 7 to 9 conventional units,

-   alkalinity -- from 0 to 9.999 mg-eq/l,

-   phosphates -- from 0 to 99.9 $\mu$g/l,

-   silicate -- from 0 to 7000 $\mu$g/l,

-   nitrite -- from 0 to 30 $\mu$g/l,

-   nitrate -- from 0 to 700 $\mu$g/l.

Collation of the typed data with the primary paper sources was carried
out after their input. One specialist typed the data, and the other one
collated the input data with the primary paper sources.

After load, all the oceanographic information was subjected to a more
strict computer-aided control. In the process of control system
elaboration, notions were used outlined in different publications
(Belkin, 1991; Boyer & Levitus, 1994; BarKode, 1999) and some other
additional provisions. Control was carried out using 14 criteria:
station coordinates, date and time of observations, correspondence of
depths, correspondence of input data to general distribution
regularities of temperature, salinity and hydrochemical parameters in
the World Ocean and in the Arctic Ocean, in particular.

Questionable records were not eliminated from the database, but marked
with special symbols. A system of quality flags was used for this
procedure.

3.2.2. Formal Data Control in the Hydrochemical Database.

3.2.2.1. Control of Station Passports.

*Station coordinates*. According to this control, the stations with
latitude exceeding 90^0^ and longitude beyond the limits of the range
--180^0^ $$ 180^0^ , or with coordinate minutes equal or greater 60 are
marked with flag 23, and they are not used for further work. Such
stations were not revealed in the result of this control.

3.2.2.2. Control of Maximum Station Observation Depths.

*Control of observation depths*. According to this control, the stations
with observation depths exceeding sea depth taken from reference array
of the Arctic Ocean depths are marked with flag 25, and they are not
used for further work. The nearest to this station point from the depth
array was chosen, but not far than 14.1 km. If the observation depth
significantly exceeds sea depth in this point (for 120% for depth range
0-100 m, for 40% for depths greater than 100 m), location of the station
is questionable. Formally, 1085 stations should have been marked
according to this control. Location of the stations that did not pass
the control was studied before station marking with flag 25 (Fig. 3.11).
This location analysis showed that these stations were located in
deepwater regions mainly over the continental slope or in places with
strongly broken relief; in shallow regions, they were located mainly
near shore. Taking into account, that depth interval in places with
strongly broken relief at the distance of 14.1 km is significant, and
grid spacing of the depth array in shallow waters (coastal water areas,
estuaries, bays) did not guarantee necessary representativity, the
stations in these regions were not marked with flag 25 and were used in
further calculations. Group of the stations located over relatively flat
region in the northern part of the Chukchi Sea was performed in the
"Sever" expeditions. Depths at these stations in these expeditions could
have been determined with insufficient accuracy. Taking into account
results of this analysis and, first and foremost, significance of each
station with hydrochemical observations in the Arctic Ocean, poorly
covered by observations, these stations were not marked by flag 25 and
were used for further calculations.

3.2.3. Regional control

Regional control included check of correctness of station coordinates.
It was done at different stages of joint data set preparation. Because
the main part of the data was placed in computer as separate files, each
of these files contained data of a specific cruise of research vessel,
airborne expedition or coastal observations at observatories, regional
control was carried out before file input in the joint database. The
Ocean Data View software (Schlitzer, 2001) gives an opportunity to scan
operatively data of separate expeditions to make sure that vessel route
coincides with schemes of its movement given in expedition reports.
False station coordinates were corrected, and after this correction data
input in the database was performed.

Some problem arose by data check for the data obtained from other
sources and not from the AARI archives. Cruise or expedition reports
were inaccessible. Check technique in these cases consisted of
comparison of research vessel route with time of station performance.
Succession of station performance in time was checked in condition that
vessel speed did not exceed 15 knots. Oceanographic stations falling out
of reasonable schedule of vessel movement at transects were marked as
questionable.

![](media/image24.wmf){width="6.559027777777778in"
height="6.577083333333333in"}

Fig. 3.11. Location of stations that did not pass formally control of
maximum station observation depths (flag 25).

3.2.4. Control of Variability Limits.

Primary computer-aided control of the station passports and variability
limits of the parameters was carried out both by data input and by
loading of data obtained from different sources. Permissible ranges of
different attributes of the station passports and values of the
hydrochemical elements were described above in Section 3.2.1. Values
beyond the limits of these permissible ranges were not eliminated by
loading of data from files with hydrochemical information, but marked
with the according flags of quality and reliability as questionable or
rejected. The hydrochemical parameters vary over a wide range in the
Arctic Ocean, therefore, criteria of control and data estimate for
ranges of their variability in deepwater regions differs from that in
shallow regions. Use of automatic methods of control recommended in
other papers (Belkin, 1991; BarKode, 1999) does not give good results.
That is why, only those data were rejected that were beyond the
reasonable limits of variability of the hydrochemical parameters typical
for the entire World Ocean. Expert data control was carried out
afterwards.

3.2.5. Expert Control.

Expert control is initial and final phase of the procedure of quality
estimate of hydrochemical measurements. Its importance in assessment of
accuracy and representativity of observations in different parts of
water area is specially great by insufficient number of observations and
/or their non-uniform distribution in time and space. It is typical for
this Atlas. The expert control was the most labor-consuming and minute
part of the data set check. In the process of control, the base was
divided into several parts according to regional indications: the Arctic
Basin, the Kara Sea, the Laptev Sea and the region uniting the East
Siberian Sea, the Chukchi Sea and the Beaufort Sea. These samples
include all the available data for the region.

Four different experts did the control. Each of them controlled the data
for his region. Cruise scan of the data was carried out using the Ocean
Data View software (Schlitzer, 2001). In this process, station
coordinates, dates and time of their conduction, correspondence of
depths given in the station passports to bottom relief were checked.
Distribution of the hydrochemical parameters at each station was
analyzed, and it was compared with mean distributions of the same
parameters in same region of seas or the Arctic Basin in the same period
of the year. Correspondence of the loaded hydrochemical information with
general regularities of distribution of the hydrochemical parameters in
the Arctic Ocean and in the Arctic seas, in particular (Rusanov et al.,
1979).

Results beyond the limits of tolerance were rejected, i.e. they were
marked as bad data. Abnormal values of the hydrochemical parameters
within the reasonable limits of hydrochemical element variability, but
not appropriate to our notion of hydrochemical structure of a specific
region, were marked as the questionable data. Number of rejected and
questionable data revealed in the result of the expert control is given
in Table 3.1.

Some problems, that arose by the data expert control, should be
mentioned. First, it is complicated to check the data in such poorly
studied regions as, for example, the East Siberian Sea or the
north-eastern part of the Kara Sea. Second, the Arctic seas are
characterized by complex vertical structure and inlaid distribution of
the hydrochemical parameters, both on the surface, at the standard
depths and, especially, at the near-bottom depths. Reference literature
on structure of water column and variability of the hydrochemical
parameters in shallow regions of the Arctic seas (shelf zone) is limited
and contradictory. All this makes impossible to use unit criteria of
data quality estimates not only for all the Arctic seas, but for
separate regions of each of these seas.

Table 3.1.

Number of data marked as questionable and rejected at the first stage in
the joint data set.

  ------------ -------- -------------- --------- ---------- ------------ ---------------
  Parameter    Total    Questionable   Quest., % Rejected   Rejected,%   Quest..+Rej., %

  Oxygen       111127   1116           1,00      737        0,66         1,67

  Phosphate    43132    976            2,26      1593       3,69         5,96

  Silicate     102750   1305           1,27      2334       2,27         3,54

  Nitrite      26465    184            0,70      1507       5,69         6,39

  Nitrate      16201    239            1,48      1240       7,65         9,13

  pН           74730    562            0,75      321        0,43         1,18

  Alkalinity   19442    124            0,64      203        1,04         1,68
  ------------ -------- -------------- --------- ---------- ------------ ---------------

# The expert control was carried out using C-code specially elaborated for this project by AARI specialists, accounting for knowledge of hydrological and hydrochemical conditions of the Arctic Ocean.

Program of the expert control provided performance of the following
procedures:

1.  Control of correspondence of extreme values of the hydrochemical
    elements determined at all the stations with actual hydrological and
    hydrochemical conditions.

2.  Construction of display plots of vertical distribution (profiles) of
    the elements and determination of those values that form extremes
    that cannot be caused by real processes.

3.  Drawing of experimental maps of gridded distribution of the
    hydrochemical elements of different scale using statistical
    characteristics.

4.  Check of extreme mean values of the elements on the gridded maps
    constructed with the help of objective analysis of observations for
    their correspondence to temporal series in the adjacent grid cells.

5.  Interpolation of separate values of the elements in grid nodes not
    covered by observations.

6.  Output of final data for map drawing of hydrochemical element
    distribution.

In the process of the expert control, the experts decide, what "quality
flag" should be given to distributions. This information is placed and
stored in the archive of distributions.

Therefore, the expert control was carried out after the statistical
control and after gridding of the results of hydrochemical distributions
by the objective analysis. Results of the control were put on maps, and
plots of vertical distribution were constructed only after repeated
performance of the expert control.

3.3. Statistical Characteristics.

Linear interpolation of values of the hydrochemical elements to the
standard depths was carried out before calculation of statistical
characteristics and after the formal and expert control: 0, 5, 10, 15,
25, 50, 75, 100, 150, 200, 250, 300, 400, 500, 750, 1000, 1500, 2000,
2500, 3000, 3500, 4000, 4500 meters (Fig. 3.12).

Number of oceanographic stations with the hydrochemical observations was
analyzed. This analysis revealed that the standard depths were the best
covered by observations. If observations at some station were conducted
at other depths, linear interpolation of the hydrochemical elements to
the standard depths was carried out. This interpolation was conducted
only in the case, when

![](media/image25.wmf){width="5.913779527559055in"
height="2.8133858267716536in"}![](media/image26.wmf){width="5.822834645669292in"
height="2.8133858267716536in"}![](media/image27.wmf){width="5.730708661417323in"
height="2.767322834645669in"}

Fig. 3.12. Distribution of number of oceanographic stations with the
hydrochemical observations for the years 1948-2000 (a -- in the layer
0-110 m, b- in the layer 110-310 m, c -- in the layer 310-4500 m) in the
working base after the formal and expert control.

number of the standard depths between the observations did not exceed
one. If the interpolation was prohibited according to this criterion,
and difference between the observation depth and the nearest standard
depth did not exceed 5% of the layer thickness between the neighboring
standard depths and the observation, then values of the hydrochemical
elements were transferred ("dragged") to the nearest standard depth. For
example, if the upper observation depth was 210 m, and the next one was
305 m, then the interpolation was not conducted for the "mixed" standard
depths 250 and 300 m, because their number (two) exceeded the chosen
criterion (one). However, value from 305 m was "dragged" (transferred)
to the standard depth 300 m in this case. This procedure was not carried
out for the observation depth 210 m. Values of the standard depths and
upper and lower limits for the procedure of transfer are given in Table
3.2

Table. 3.2.

Standard depths and upper and lower limits for the procedure of transfer
of observational depth to the standard depth

  ----------------------- ----------------------- -----------------------
  **Standard depth (m)**  **Upper limit for the   **Lower limit for the
                          procedure of transfer   procedure of transfer
                          of observational depth  of observational depth
                          to the standard depth   to the standard depth
                          (m)**                   (m)**

  5                       4.75                    5.25

  10                      9.75                    10.75

  25                      24.25                   26.25

  50                      48.75                   51.25

  75                      73.75                   76.25

  100                     98.75                   102.5

  150                     147.5                   152.5

  200                     197.5                   202.5

  250                     247.5                   252.5

  300                     297.5                   305

  400                     395                     405

  500                     495                     512.5

  750                     737.5                   762.5

  1000                    987.5                   1025

  1500                    1475                    1525

  2000                    1975                    2025

  2500                    2475                    2525

  3000                    2975                    3025

  3500                    3475                    3525

  4000                    3975                    4025

  4500                    4475                    4525
  ----------------------- ----------------------- -----------------------

Statistical characteristics of the hydrochemical elements were
calculated after the interpolation and transfer of values to the
standard depths for all the standard depths from 0 up to 400 m
separately for two seasons: winter (November-May) and summer
(July-September). Winter and summer values of the hydrochemical elements
were used together for calculations of statistical characteristics at
the standard depths from 400 to 4500 m.

Final calculation of statistical characteristics of the hydrochemical
elements after all the types of control was carried out at the standard
depths in the winter season in squares 200x200 km, in the summer
season - in squares 200x200 km for the Arctic Basin and 100x100 km for
the Arctic seas (Fig. 3.13). Grid of the squares coincides with the
location of the squares for which statistical characteristics of
temperature and salinity were calculated in the Hydrographic Atlas of
the Arctic Ocean (1997, 1998).

Coordinates of the squares are given as the Cartesian coordinates of the
Lambert equigraphic azimuth projection calculated using the formulas:

$X = 2R\text{sin}(\frac{\chi}{2})\text{sin}\lambda$

$Y = 2R\text{sin}(\frac{\chi}{2})\text{cos}\lambda$,

here $\chi = \text{90} - \phi$is supplement of latitude, $\lambda$is
longitude, *R*=6371.116 radius of the sphere having the same surface as
the Earth ellipsoid, *X, Y* are grid coordinates.

X-axis is oriented along meridian 0-180 ^0^ , Y-axis is oriented along
meridian 270-90^0^ . Center of the coordinate system is located in the
Pole.

All the maps given in the Atlas are constructed in this coordinate
system. *X* and *Y* axes are subscribed in tens of kilometers.

Calculation of the following statistical characteristics was conducted
using the formulas:

Mean value of a parameter $X = \sum_{}^{}\frac{X_{i}}{N}$;

Dispersion of a parameter $S^{2} = \mu 2$;

Root-mean deviation $S = (S^{2})^{0\text{.}5}$;

Coefficient of skewness $\text{As} = \mu\frac{3}{S^{3}}$

Coefficient of excess $\text{Ex} = \mu\frac{4}{S^{4}} - 3$

$\mu 2 = \frac{\left\lbrack \sum_{}^{}{(X_{i} - X)^{2}} \right\rbrack}{N}$;

$\mu 3 = \frac{\left\lbrack \sum_{}^{}{(X_{i} - X)^{3}} \right\rbrack}{N}$;

$\mu 4 = \frac{\left\lbrack \sum_{}^{}{(X_{i} - X)^{4}} \right\rbrack}{N}$;

here *X* is the parameter mean value, *X~i~* is the parameter observed
value, *N* is the number of observations in a square, *S^2^* is the
parameter dispersion, *S* is the root-mean deviation, *As* is the
asymmetry (skewness), *Ex* is the excess, $\mu 2,\mu 3,\mu 4$ are the
central moments of the second, third and fourth order, respectively.

Of course, calculation of the first three statistical characteristics
has a sense only in the case, when number of measurements exceeds three
(then appropriate estimates can be carried out using the Student
criterion). However, these appropriate statistical characteristics can
be reliably obtained in some points of coastal observations (located in
estuaries and estuary seashores of Ob, Yenisei, Lena, Khatanga).

The parameter mean value in a square was calculated taking into account
preliminary averaging for each year. Extreme values were chosen, and the
other statistical characteristics were calculated using the whole series
of observations in this square.

![](media/image28.wmf){width="3.9098425196850393in"
height="3.927952755905512in"}![](media/image29.wmf){width="3.9098425196850393in"
height="3.927952755905512in"}

Fig.3.13. Grid used for calculation of statistical characteristics of
the hydrochemical elements: a- grid 200x200 km for the winter season
(November-May); b -- 200x200 km (in the Arctic Basin) and 100x100 km (in
the Arctic seas) for the summer season (July-September).

Besides, the equation of mean square regression plane was calculated
using the least square method, scatter of observation points near this
surface is the minimum one, if compared with other surfaces. Equation of
this surface is as follows:

*Z = Ax + By + C,*

here *Z* is the parameter value (in corresponding units of measurement
for this hydrochemical element), *x* and *y* are coordinates (in tens of
kilometers).

The Cartesian coordinates of the square angles (in tens of kilometers)
and values of the statistical characteristics of the hydrochemical
elements are given in the ASCII-files ("Statistics\\Txt" subdirectory)
on CD-ROM. Mask of names of the ASCII- files looks as follows:

**SSN_ELE_1948-2000_HHHH.TXT**,

here:

**SSN** is the season (**WIN** -- winter, **SUM** -- summer);

**ELE** is the hydrochemical element (**OXY** -- dissolved oxygen,

**SIL** -- silicate,

**PO4** -- phosphate,

**NO2** -- nitrite,

**NO3** -- nitrate,

**PHB** -- pH~B~,

**ALK** -- alkalinity**)**;

**1948-2000** -- period of observations;

**HHHH** is the standard depth (m);

**TXT** is the file name extension.

The characteristics demonstrated in Table 3.3. are given in columns of
the files (in order from left to right).

Table 3.3.

Information given in the ASCII-files ("Statistics" Directory) with
calculated statistical characteristics of the hydrochemical elements (in
order from left to right).

+--------------+-------------------------------------+---------+------+
| **Name of    | ## Characteristics                  | *       |      |
| the column** |                                     | *Column |      |
|              |                                     | format  |      |
|              |                                     | in      |      |
|              |                                     | n       |      |
|              |                                     | otation |      |
|              |                                     | SDF     |      |
|              |                                     | (       |      |
|              |                                     | "System |      |
|              |                                     | Data    |      |
|              |                                     | For     |      |
|              |                                     | mat")** |      |
+--------------+-------------------------------------+---------+------+
|              |                                     | **      | **   |
|              |                                     | Initial | Leng |
|              |                                     | and     | th** |
|              |                                     | final   |      |
|              |                                     | p       |      |
|              |                                     | osition |      |
|              |                                     | in      |      |
|              |                                     | line**  |      |
+--------------+-------------------------------------+---------+------+
| XMIN         | Minimum value of X-coordinate (tens | 1-10    | 10   |
|              | of km) for this square              |         |      |
+--------------+-------------------------------------+---------+------+
| XMAX         | Maximum value of X-coordinate (tens | 11-19   | 9    |
|              | of km) for this square              |         |      |
+--------------+-------------------------------------+---------+------+
| YMIN         | Minimum value of Y-coordinate (tens | 20-28   | 9    |
|              | of km) for this square              |         |      |
+--------------+-------------------------------------+---------+------+
| Table 3.3    |                                     |         |      |
| (to be       |                                     |         |      |
| continued)   |                                     |         |      |
+--------------+-------------------------------------+---------+------+
| **Name of    | #### Characteristics                | *       |      |
| the column** |                                     | *Column |      |
|              |                                     | format  |      |
|              |                                     | in      |      |
|              |                                     | n       |      |
|              |                                     | otation |      |
|              |                                     | SDF     |      |
|              |                                     | (       |      |
|              |                                     | "System |      |
|              |                                     | Data    |      |
|              |                                     | For     |      |
|              |                                     | mat")** |      |
+--------------+-------------------------------------+---------+------+
|              |                                     | **      | **   |
|              |                                     | Initial | Leng |
|              |                                     | and     | th** |
|              |                                     | final   |      |
|              |                                     | p       |      |
|              |                                     | osition |      |
|              |                                     | in      |      |
|              |                                     | line**  |      |
+--------------+-------------------------------------+---------+------+
| YMAX         | Maximum value of Y-coordinate (tens | 29-37   | 9    |
|              | of km) for this square              |         |      |
+--------------+-------------------------------------+---------+------+
| NUM_VALUES   | Number of actual, interpolated and  | 38-48   | 11   |
|              | "dragged" values of observations    |         |      |
|              | for this hydrochemical element in   |         |      |
|              | the corresponding*\** season in     |         |      |
|              | this square at this depth           |         |      |
+--------------+-------------------------------------+---------+------+
| NUM_YEARS    | Number of years with observations   | 49-58   | 10   |
|              | for this hydrochemical element in   |         |      |
|              | the corresponding*\** season in     |         |      |
|              | this square at this depth           |         |      |
+--------------+-------------------------------------+---------+------+
| MIN_VALUE    | Minimum value for this              | 59-68   | 10   |
|              | hydrochemical element in the        |         |      |
|              | corresponding*\** season in this    |         |      |
|              | square at this depth                |         |      |
+--------------+-------------------------------------+---------+------+
| MEAN_VALUE   | Mean value for this hydrochemical   | 69-79   | 11   |
|              | element in the corresponding*\**    |         |      |
|              | season in this square at this depth |         |      |
|              | (taking into account preliminary    |         |      |
|              | averaging for each year)            |         |      |
+--------------+-------------------------------------+---------+------+
| MAX_VALUE    | Maximum value for this              | 80-89   | 10   |
|              | hydrochemical element in the        |         |      |
|              | corresponding*\** season in this    |         |      |
|              | square at this depth                |         |      |
+--------------+-------------------------------------+---------+------+
| STAND_DEV    | Mean-root (standard) deviation      | 90-99   | 10   |
+--------------+-------------------------------------+---------+------+
| VARIANCE     | Dispersion (variance)               | 100-108 | 9    |
+--------------+-------------------------------------+---------+------+
| SKEWNESS     | Coefficient of skewness (asymmetry) | 109-117 | 9    |
|              | *\*\**                              |         |      |
+--------------+-------------------------------------+---------+------+
| EXCESS       | Coefficient of excess *\*\**        | 118-125 | 8    |
+--------------+-------------------------------------+---------+------+
| COEF_A       | Coefficient A of the equation of    | 126-139 | 14   |
|              | mean square regression plane *\*\** |         |      |
+--------------+-------------------------------------+---------+------+
| COEF_B       | Coefficient B of the equation of    | 140-153 | 14   |
|              | mean square regression plane *\*\** |         |      |
+--------------+-------------------------------------+---------+------+
| COEF_C       | Coefficient C of the equation of    | 154-167 | 14   |
|              | mean square regression plane *\*\** |         |      |
+--------------+-------------------------------------+---------+------+

> *Note:* *\** *statistical characteristics were calculated at the
> standard depths from 0 to 400 m for each season and for the standard
> depths from 500 to 4500 m both winter and summer values of the
> hydrochemical elements were used together;*
>
> *\*\* value .NULL. in the data columns of the ASCII-files mean absence
> of the calculated statistical characteristics for this square.*

Examples of fields of the statistical characteristics (mean values and
mean-root deviations) at 5 m depth are shown in Fig. 3.14-3.17 for two
elements: dissolved oxygen with the best coverage by observations and
nitrite with the worst coverage.

![](media/image30.wmf){width="6.511805555555555in"
height="6.4944444444444445in"}

Fig. 3.14. Mean concentration of dissolved oxygen (ml/l) and its
mean-root deviation in the Arctic Basin and the Arctic seas (according
to data in the squares 200x200 km) in winter (November-May) for the
years 1948-2000 at 5 m depth.

![](media/image31.wmf){width="6.5159722222222225in"
height="6.498611111111111in"}

Fig. 3.15. Mean concentration of dissolved oxygen (ml/l) and its
mean-root deviation in the Arctic Basin (squares 200x200 km) and the
Arctic seas (squares 100x100 km) in summer (July-September) for the
years 1948-2000 at 5 m depth.

![](media/image32.wmf){width="6.511805555555555in"
height="6.4944444444444445in"}

Fig. 3.16. Mean nitrite concentration ($\mu$mol/l) and its mean-root
deviation in the Arctic Basin and the Arctic seas (according to data in
the squares 200x200 km) in winter (November-May) for the years 1948-2000
at 5 m depth.

![](media/image33.wmf){width="6.511805555555555in"
height="6.4944444444444445in"}

Fig. 3.17. Mean nitrite concentration ($\mu$mol/l) and its mean-root
deviation in the Arctic Basin (squares 200x200 km) and the Arctic seas
(squares 100x100 km) in summer (July-September) for the years 1948-2000
at 5 m depth.

3.4. Objective Analysis

The spectral method of objective analysis, developed by Pokrovsky
(1984), was used as the basic method for construction of decadal
climatic fields of temperature and salinity by realizing of the
US-Russian Oceanographic Atlas of the Arctic Ocean (1997, 1998). The
spectral method of objective analysis has shown the best results in
terms of reconstruction of temperature and salinity characteristics if
compared with the other methods used in the Oceanographic Atlas of the
Arctic Ocean. Moreover, only this method has been capable to reconstruct
oceanographic fields using observations in the summer period in the
absence of data on significant part of the central Arctic Basin. This
method has also given the opportunity to obtain fields of reconstruction
errors. The mentioned advantages of this method were determined by the
fact that it was based on simultaneous spatial and temporal analysis of
observational data by decomposition of these fields with the help of a
combination of empirical spatial and temporal components. This method
combines analytical approach and statistical interpretation of
estimation results.

The essence of the method is as follows: measured values of
hydrochemical characteristics *z(t, x)* are considered as a random
function of temporal *(t)* and spatial *(x)* coordinates. The observed
values *z(t, x)* are presented as a sum of a true value

*Z^(r)^(t, x)* of a hydrochemical parameter and an observation error
*e(t,x).* We postulate presence of spatial correlation for
characteristics of *z^(r\ )^~i~* , absence of a systematic error and
correlation between the observation errors *e~i~* and hydrochemical
characteristics

*z^(r\ )^~i~* , spatial and temporal independence of the observation
error and presence of standard deviation $\sigma_{e}^{2}$. This totality
of postulates is reduced to the following model of statistical structure
of the analyzed characteristics.

$z_{i} = z_{i}^{(r)} + e$,

$\langle z_{i}z_{{}_{j}}\rangle = \sigma_{x_{i}x_{j}}$,

$\left\langle z_{i}e_{i} \right\rangle = 0$, (1)

$\left\langle e_{{}_{i}} \right\rangle = 0$,

$\left\langle e_{i}e_{j} \right\rangle = \delta_{\text{ij}}\sigma_{e_{\text{ij}}}^{2}$.

The problem of estimation is formulated for anomalies of the
hydrochemical characteristics *z^/^* , i.e. deviations z of the
corresponding mean values $z^{} = z - \overline{z}$. The mean values
were obtained by temporal averaging and spatial smoothing. Taking into
account, we shall further consider only the above-mentioned deviations,
and they will be marked as *z*.

In order to take into account spatial and temporal connections of
observational data, Pokrovsky (1984) proposed to use a biorthogonal
decomposition of a hydrochemical parameter *z* as follows:

$z(t_{j},x_{i}) = \sum_{}^{}{c_{n}^{j}f_{n}(x_{i}) + e(t_{j},x_{i})}$,
(2)

here *f~n~(x~i~)* is the spatial EOF, *c~n~^j^* is the estimated
coefficient that is usually called the *n-th* principal component.
*x~i~* can be an irregular grid, and values of measured hydrochemical
parameters are given in its nodes.

There are two versions of the spectral analysis (SA). The first variant
of the method supposes interpolation of the spatial EOF in nodes of a
regular grid *x~i~* , where values of characteristics under
consideration will be estimated. The second variant is based on EOF
approximation with the help of a linear combination:

$f_{n}(x_{i}) = \sum_{l}^{}{b_{\text{kl}}P_{l}(x_{i})}$ (3)

of appropriate analytical functions (polynomials, splines, trigonometric
functions, etc.) *P~l~(x~i~).* In this case, we obtain the following
modification of the biorthogonal decomposition (2):

$z(t_{j},x_{i}) = \sum_{}^{}{d_{n}^{j}P_{l}(x_{i}) + e}(t_{j},x_{i})$,
(4)

here $d_{l}^{j} = \sum_{}^{}{b_{\text{kl}}c_{k}^{j}}$.

There are no differences of principle between these mentioned approaches
based on the formulas (2) and (4). In both cases, our problem is in
estimation of a totality of coefficients of the spectral decomposition
$C = \left| c_{n}^{j} \right|$ or $B = \left| b_{k_{l}} \right|$.
Therefore, we shall further consider only the version based on notion
(2) without loss of generality. We shall rewrite formula (2) in the
following matrix form:

$Z = F \cdot C + e$. (5)

Let us introduce designations for the following covariance matrices:

$K_{z} = \left| \sigma_{z_{\text{ij}}}^{2} \right|_{\text{ij}}$ ,

$K_{e} = \left| \sigma_{e_{\text{ij}}}^{2} \right|_{\text{ij}}$,

*(i,j = 1,.....,N).*

The system of linear equations (5) in respect to unknown coefficients
*c~k~^j^* can be solved on the basis of a priori statistical information
(1) using methods of statistical estimation. A formula for the
estimation of the matrix of unknown coefficients C was

obtained in [()]{.mark} on the basis of [()]{.mark}:

[]{.mark}$C = (F^{T} \cdot K_{e}^{- 1} \cdot F + K_{c}^{- 1})^{- 1}F^{T} \cdot K_{e}^{- 1} \cdot Z^{}$,
(6)

here *A^-1^* and *A^T^* are the back and transposed matrices in respect
to *A*, and []{.mark}$$is the sign of matrix multiplication. The matrix
of covariance errors of the decomposition coefficients *K~c~* is a
diagonal matrix composed of the eigenvalues of the covariance matrix
*K~z~* :

$K_{c} = \text{diag}\left| \lambda_{i}^{2} \right|_{i}$,
*i=1,...........,N*.

The matrix *F* is formed by the EOF values, and the matrix *Z* is
composed of a totality of measurement data in the network of
observations *x~i~.*

In order to obtain an estimate of a hydrochemical characteristics in the
nodes of a regular grid *x~i~,* it is necessary to interpolate the EOF
in appropriate nodes of the grid and to obtain a new matrix *F* of the
EOF. Using the obtained matrix F and the estimates of coefficients C,
formula (6) and matrix correlation

[]{.mark}$$[]{.mark}$Z = F \cdot C + \Delta$ , (7)

we shall obtain the estimate of our parameters in the nodes of the
regular grid.

Covariance matrices of estimate errors can be obtained simultaneously
with hydrochemical fields using the following formulas:

$K = (I + (K \cdot (F^{T} \cdot K_{e}^{- 1} \cdot F)))^{- 1} \cdot K_{c}$
,

$K_{z} = F \cdot K_{z} \cdot F^{T}$, (8)

here K~e~ is the covariance matrix of observation error extended on the
regular grid.

The described procedure of hydrochemical field restoration is a
combination of the well-known method of singular decompositions (SVD --
singular value decomposition in the original) and statistical
regularization (Pokrovsky, 1984).

Practical realization of the SA method includes several main stages. The
first stage is an optimal choice of a grid cell (grid spacing and
distribution). Aim of this choice is to cover general spatial regions
(for the time period under consideration), where observations were
carried out. This stage is the basis for EOF calculation of a maximum
dimensionality.

The next stage is a reconstruction of fields in the cells without
observations. Dual character of the coefficients
$\left| c_{k}^{i} \right|$ in formula (2) (in respect to spatial and
temporal dependencies) is the basis for estimate of unknown geophysical
parameters in the "empty cells" without observational data. The
described approach was realized not only in spatial regions with low
spatial data density, but also by restoration of the whole temporal
series of observational data for each cell with observations for at
least in one year. In order to realize this idea more effectively, we
have proposed to perform a preliminary division into districts of the
region under consideration. For that purpose, the analyzed region was
divided into information-uniform zones (IUZ) on the basis of the
previously elaborated method (Pokrovsky & Piatigorsky, 1995). Time
interval of the analysis was divided into uniform sub-intervals. Values
of hydrochemical parameters were statistically interconnected in each of
these sub-intervals. For example, several first EOF's did not change
their signs with the aim that the time correlation function also did not
change its sign within these IUZ's. In the same time, sign could be
changed at the boundaries of the IUZ's and corresponding uniform
intervals at time axis.

The principal temporal modes (the first terms of decomposition (2)) were
used for calculation of mean values in the "empty" grid cells. Mean
values of a hydrochemical parameter can be estimated in each grid cell
with at least one observation for the time period under consideration,
having these temporal modes.

The next stage of the calculation procedure is interpolation of the
fields for one or several years in the given spatial grid. It is
necessary now to interpolate the EOF in the given spatial grid and then
to calculate the coefficients $\left| c_{k}^{i} \right|$ in
decomposition (2). The described procedure should be applied to each
year for the time period under consideration.

The next stage is calculation of mean climatic fields for several years.
Such mean values were calculated in each grid cell on the basis of the
described reconstruction method or by interpolation. In particular, it
is possible to calculate decomposition coefficients using the EOF even
in the case, when there is only one observation in each IUZ, while
having spatial structure of the uniform zones.

### 3.5. References to Section 3.

Alekin O.A., Liakhin Yu. I.: Chemistry of the Ocean. -- L.,
Gydrometeoizdat, 1984, 343 p.

Rusanov V.P., Yakovlev N.I., Buynevich A.G.: Hydrochemical conditions of
the Arctic Ocean. -- Proc. of the AARI, 1979, v. 355, 144 p.

BarKode (Barents and Kara seas oceanographic database). - IACPO Informal
Report No. 5, Murmansk/Tromso, 1999.

Schlitzer R. Ocean Data View software. -- AWI-Bremerhaven, 2001.

Artemyev A.O., Blinov N.I.: On the possibility of restoration of water
temperature field restoration in the Arctic Basin using the method of
optimal interpolation. -- Proc. of the AARI, 1986, v. 408, pp. 117-122.

Gandin L.S.: Objective analysis of meteorological fields. - L.,
Gydrometeoizdat, 1963, 236 p.

Koltyshev A.Ye., Timokhov L.A.: Restoration of oceanographic fields of
the Arctic Ocean. -- Meteorology and Hydrology, 1998, No. 2, pp. 65-72.

Pokrovsky O.M.: Optimization of meteorological satellite sounding of the
atmosphere. - L., Gydrometeoizdat, 1984, 264 p.

Pokrovsky O.M., Piatigorsky A.G.: Use of empirical orthogonal functions
for division into districts of meteorological fields. -- Meteorology and
Hydrology, 1995, No. 6, pp. 12-22.

Rao S.: Linear statistical methods and their applications, M., "Nauka",
1967, 568 p.

Joint US-Russian Atlas of the Arctic Ocean, Oceanography Atlas for the
Winter Period. Ed. by F. Tanis, L. Timokhov. Environmental Working
Group, University of Colorado, Boulder, CD-ROM, 1997.

Joint US-Russian Atlas of the Arctic Ocean, Oceanography Atlas for the
Summer Period. Ed. by F. Tanis, L. Timokhov. Environmental Working
Group, University of Colorado, Boulder, CD-ROM, 1998.

Smith T., Reynolds R., Livezey R., Stokes D.: Reconstruction of
historical sea surface temperatures using empirical orthogonal
functions. -- J. of Climate, 1996, v. 9, pp. 1403-1420.

**4.Presentation of Hydrochemical Information**

4.1. Data Set of Initial Measurements

All the materials of hydrochemical observations, available to the
authors, were accumulated in digital data set of initial measurements in
the same format, as they had been stored in different sources. We had no
opportunity to collect hydrochemical information only from primary
sources. For example, some information was used that had been collected
by NODC from different sources and placed in the Atlas of the World
Ocean 2000. Therefore, the collected data set of initial data is rather
heterogeneous by quality.

The data set of initial measurements was not subjected to quality
control of observations. Therefore, it contains errors of different
type: wrong coordinates, time, measurement errors, wrong measurement
units, errors of operators by data input in tables, etc. According to
our assessment, total percentage of rejects for different
characteristics varies from 5% to 15% (See Table 3.1., Section 3).

Nevertheless, it has been assumed appropriate to place all the initial
information in the Atlas, according to the following arguments. Methods
of measurement quality control can be altered in the process of
hydrochemical information accumulation. It may be supposed that attitude
will vary in future to those data that were rejected according to the
procedure accepted in this Atlas. Therefore, it is important to keep the
information in its primary form for future investigators.

The data set of initial measurements is placed in the directory "Data"
on CD-ROM (ASCII-file AO_CHEM.TXT). This format allow us to use the data
in the mode of the software Ocean Data View (Schlitzer 2001). The Ocean
Data View is attached.

For convenience of possible calculations and data manipulation, the data
set of initial measurements was loaded in the database of hydrochemical
data (DBHD) by management of DBMS VisualFoxPro 3.0. The database is of a
relation character and consists of the following two tables mutually
interconnected by the attribute "unique station number in the DBHD".

The table of hydrochemical station general attributes (**Headers**)
contains the following:

-   Unique station number in the DBHD (un);

-   Name of vessel or research platform (cruise);

-   Number of the station in the cruise (expedition);

-   Date of station performance (dat);

-   Geographical coordinates of the station (lat, lon);

-   Station depth (depth);

-   Quality flag of the general attributes of this station (fq_st).

The table of hydrochemical data at these stations (**Data_chem**)
contains the following attributes:

-   Unique station number in the DBHD (un);

-   Observation depth (level) \[m\];

-   Reliability flag of the observation depth (fq_level);

-   Concentration of dissolved oxygen at the observation depth (oxy);

-   Reliability flag of the concentration of dissolved oxygen (fq_oxy);

-   pH~B~ \[Buch units\] at the observation depth (phb);

-   Reliability flag of the pH~B~ (fq_phb);

-   Alkalinity (Alk) \[mg-equivalent/l\] at the observation depth (alk);

-   Reliability flag of the alkalinity (fq_alk);

-   Silicate \[$\mu$mol/l\] at the observation depth (sil);

-   Reliability flag of the silicate (fq_sil);

-   Phosphate \[$\mu$mol/l\] at the observation depth (po4);

-   Reliability flag of the phosphate (fq_po4);

-   Nitrite \[$\mu$mol/l\] at the observation depth (no2);

-   Reliability flag of the nitrite (fq_no2);

-   Nitrate \[$\mu$mol/l\] at the observation depth (no3);

-   Reliability flag of the nitrate (fq_no3).

4.2. Gridded Climatic Fields of the Objective Analysis.

The database of the hydrochemical data, that had passed the quality
control, was used for the objective analysis (See Section 3). Working
array contained concentrations of dissolved oxygen, phosphate, silicate,
pH, total alkalinity, nitrite and nitrate for each year at the standard
depths. Geographical coordinates of each station were converted to
coordinates of the Lambert projection which had been also used for
construction of fields of the hydrochemical characteristics in nodes of
the regular grid. Synoptic and meso-scale variations of the
hydrochemical characteristics were not taken into account, they were
considered as a statistical noise. Appropriate filtration was carried
out on the basis of the EOF decompositions described in Section 3.4.

The array of values at the standard depths was subjected to spectral
analysis with a use of procedures described in Section 3.4. Eigenvalues
and values of the principal components were obtained in the result of
this analysis, and gridded climatic fields of the hydrochemical elements
were calculated on their basis. The grid with grid spacing 200 km is
demonstrated in Fig. 4.1.

Distribution fields of phosphate and silicate at 5 m depth are shown as
examples in Fig. 4.2. Maps constructed on the basis of data of the
statistical analysis for boxes with centers located in the grid nodes
are shown for comparison in the same figures. As one can see in these
figures, results of the objective analysis correspond closely to results
of the statistical analysis.

Numerical values of the gridded climatic fields (dissolved oxygen,
phosphate, silicon, pH~B~, total alkalinity, nitrite and nitrate) are
placed in the subdirectory "Gridded_Data\\Txt" as the ASCII-files.

Distribution maps of the hydrochemical elements at depths, constructed
on the basis of objective analysis, are given in WEB-version.

4.3. Profiles, Transects and Fields.

Results of the statistical and objective analysis were used for
construction of vertical and horizontal distributions of the
hydrochemical elements in the Arctic Ocean.

Data of the statistical analysis and data interpolated at the standard
depths were used for construction of vertical profiles.

Climatic values of the elements at the standard depths, obtained using
the objective analysis, were used for construction of the transects
(Fig. 4.3.). Examples of the mean profiles of silicate in Square No. 5
and vertical climatic silicate distribution at Transect No. 12 (See Fig.
4.3) are shown in Fig. 4.4 and 4.5. The vertical profiles of the
elements and their distribution at the transects are given in
WEB-version.

Element values at the standard depths, obtained in the result of the
statistical and objective analysis, were used for construction of
climatic maps.

![](media/image34.wmf){width="6.708333333333333in" height="6.53125in"}

Fig. 4.1. Square grid (a -- 200x200 km) used for calculation of climatic
characteristics of the hydrochemical elements. Characteristics were
calculated for centers of the squares.

![](media/image35.wmf){width="3.2311023622047244in"
height="3.4598425196850395in"}![](media/image36.wmf){width="3.2633858267716533in"
height="3.4598425196850395in"}

a b

![](media/image37.wmf){width="3.2311023622047244in"
height="3.397244094488189in"}![](media/image38.wmf){width="3.2633858267716533in"
height="3.397244094488189in"}c d

> Fig. 4.2. Phosphate \[$\mu$mol/l\] , summer, 5 m depth: a -- mean
> value in squares 200x200 km (*17* -- number of stations); b -- gridded
> field.
>
> Silicate \[$\mu$mol/l\], winter, 5 m depth: c -- mean value in squares
> 200x200 km (*17* -- number of stations); d -- gridded field.

![](media/image39.wmf){width="5.9840277777777775in"
height="6.495138888888889in"}

Fig. 4.3. Scheme of transects and squares, for which vertical profiles
were calculated

![](media/image40.wmf){width="2.4334645669291337in"
height="2.754724409448819in"}![](media/image41.wmf){width="2.4334645669291337in"
height="2.754724409448819in"}

a b

Fig. 4.4. Mean profiles and values (data at the standard depths) of
silicate concentration \[$\mu$mol/l\] (a -- winter, b -- summer) for
square No. 5 200x200 km (See Fig. 4.3).

![](media/image42.wmf){width="6.104166666666667in"
height="4.774305555555555in"}

Fig. 4.5. Silicate distribution \[$\mu$mol/l\], Transect No. 12 (See
Fig. 4.3), winter.

5\. Climatic Distribution of the Hydrochemical Characteristics in the
Arctic Ocean.

5.1. Vertical Profiles.

Vertical distribution of hydrochemical parameters reflects a
complicated, multi-layer water structure in the Arctic Basin and the
Arctic seas.

Water column structure in the Arctic Basin is formed under the influence
of a complex of external and internal factors. The external factors are:
water exchange with the North European Basin through the Fram Strait and
the straits between Svalbard and the Franz-Josef Land, with the Pacific
Ocean through the Bering Strait, with the Baffin Bay through the straits
of the Canadian Archipelago and with the Arctic seas.

The internal factors are: exchange of substance and energy with the
atmosphere and ocean bottom, ice melting and freezing, interaction and
dynamics of water masses within the basin, physical-chemical and
biological processes in water masses.

Extreme values of concentrations of the hydrochemical elements at the
vertical profiles demonstrate different origin of the water masses that
form the water column in the Arctic Basin.

Unfortunately, investigators have not formulated to the present day a
unit approach for description of the Arctic Basin structure and a unit
terminology for water mass marking, though the water masses are the main
element of the structure. It complicates our understanding of obtained
results.

Attention should be paid to the most striking differences in vertical
distributions of the hydrochemical parameters in the Eurasian and
Canadian parts of the Arctic Basin. Minimum oxygen and pH concentrations
and clearly pronounced maxima of nutrients at the intermediate depths
characterize the layer of waters of the Pacific origin mainly
circulating in the Canadian part of the basin.

Vertical distribution of the hydrochemical parameters in the Arctic seas
is characterized as even more complicated and variable. The most general
peculiarities typical for many regions of the Arctic seas are presence
of maximum concentration of oxygen and minimum concentration of silicon
at the intermediate depths in the zones of river runoff influence. Both
these extrema characterize different origin and dynamics complexity of
the small in volume and span of life water masses of the Arctic seas.

5.2. Transects.

Distribution of the hydrochemical parameters at vertical transects
illustrates mean locations of the main elements of the water column
structure in the Arctic Basin.

Extrema of the hydrochemical parameters in the Eurasian part of the
basin are poorly pronounced. The upper quasi-homogeneous layer is
saturated with oxygen up to 100% and is characterized with low
concentrations of nutrients. Oxygen concentration decreases with depth,
however, it is relatively high in deep layers, if compared with the
other oceans, and it testifies for a good ventilation of the near-bottom
layer. Concentration of nutrients increases with depth, and accumulation
of mineral nutrients takes place in the near-bottom waters.

Kernels of low oxygen concentration are clearly seen at the vertical
transects in the Canadian part of the basin, kernels of high nutrient
concentration corresponding to them can be seen approximately at the
same depths. These kernels indicate mean location of the Pacific waters
of winter origin.

5.3. Mean Values and Dispersions at the Standard Depths.

Maps of mean values and dispersions of the hydrochemical parameters at
the standard depths are given in the Atlas. This information allows us
to estimate operatively general variability of the hydrochemical
parameters in a given region and at a given depth. Naturally, the
regions, located in frontal zones separating the water masses, are
characterized by maximum variability. High variability of the
hydrochemical parameters is typical also for the Arctic seas and the
regions of continental slope.

Spatial and temporal irregularity of oceanographic stations with
hydrochemical observations should be taken into account while working
with the maps of mean values and dispersions. Moreover, we should
mention insufficient accuracy and sensibility of methods of
hydrochemical analysis carried out in the Arctic expeditions.

5.4. Maps of Climatic Distribution of the Hydrochemical Characteristics
at the Standard Depths.

Maps of climatic distribution of the hydrochemical parameters at the
standard depths were constructed using all available data, with the
exception of questionable and rejected values. These maps illustrate
general regularities of spatial distribution of the hydrochemical
characteristics in the Arctic Ocean. The most serious problems by map
construction were as follows: spatial and temporal irregularity of
oceanographic stations and significant variability of the hydrochemical
parameters in the frontal zones.

It should be taken into account that observations at 0 m depth (sea
surface) have been performed only in the Arctic seas and only in summer,
and the standard depth 5 m is accepted as the first surface horizon in
the Arctic Basin.

Zones of river runoff influence can be clearly seen at the surface of
the Arctic seas both in winter and in summer on the maps of mean
distribution of silicate, alkalinity and pH. The contour of 10
$\mu$mol/l of silicate distribution is accepted as the boundary of river
runoff influence in the Arctic seas (Rusanov et al., 1979).
Distributions of the other hydrochemical elements at the surface of the
Arctic seas in summer are determined, to a greater extent, by biological
conditions and by a complicated combination of hydrometeorological and
ice conditions. Therefore, even mean fields of these parameters have a
mosaic structure.

Mean distributions of the hydrochemical parameters on the surface of the
Arctic Basin indicate sources and conditions of formation of the surface
waters. The water area of the Arctic Basin was divided into five regions
by silicate concentration on the surface (Rusanov et al., 1979). The
silicate concentration in each region is determined by a combination of
biological, physical-chemical, hydrological and meteorological factors.
The maximum silicate concentrations are observed in the region adjacent
to the Chukchi Sea, and the minimum ones -- in the western sector of the
Arctic Basin, the surface waters in this region are formed under the
influence of the Atlantic Ocean. The increased silicate concentrations
in the region of the North Pole are related with upwelling of the
Pacific waters from the underlying layers (Rusanov et al., 1979).

Phosphate and nitrate distribution in the Arctic Basin is very similar
to that of silicate.

Differences in nutrient distributions in the Eurasian and Canadian
sub-basins are most clearly pronounced at the intermediate depths
(standard depths: 100, 150, 200 m), where the Pacific intermediate
waters of winter origin are located. It should be mentioned that
boundaries, separating the Pacific waters and the over- and underlying
waters, are located at different depths in different regions of the
Arctic Basin. Moreover, the depths, where these waters are deposited,
vary with time. Therefore, interchange of regions with increased and
decreased concentrations is often observed in distribution fields of the
hydrochemical parameters.

Distributions of the hydrochemical parameters at deep and near-bottom
horizons are more monotonous. Differences in mean concentrations between
the Eurasian and Canadian sub-basins are pronounced not so clear.