Thesis for the Degree of Doctor of Philosophy - DTU Orbit

302 V. Hansen et al. / Science of the Total Environment 412-413 (2011) 296–303
August
April
Salinity
a b
c d
isotopes species and oxygen is observed (Table 3). These results suggest
that the oxidation conditions of surface water do not influence
the iodine speciation in the studied basins. This situation is also illustrated
by Figs. 4 and 5, which show that despite rather uniform oxygen
concentration in the surface water, there is a large variability in
the iodine isotopes distribution. The different distribution pattern of
iodide and iodate ( 129 I and 127 I) along the surface water of Skagerrak,
Kattegat and Belt Sea (Fig. 1, station 12) is most likely due to the mixing
process between saline North Sea-Atlantic and Baltic Sea fresher
water (Figs. 2 and 3). North Sea surface water with high 129 I and
127 I iodide concentrations and high salinity (Hou et al., 2007) enters
Skagerrak and mixes with the relatively low iodide concentrations
(Figs. 2 and 3) and low salinity (Fig. 5) outflow waters from the Baltic
Sea in the Kattegat through the Belt Sea (station 12, Fig. 1).
4.2. Iodide and iodate in surface water of Arkona Sea and Baltic Proper
In the Arkona Sea, higher 129 I − / 129 IO 3 − happened in August
(Fig. 3c) and could be explained as a reduction of 129 IO3 - along the
water profile from Kattegat through the Belt Sea to 129 I - as found
along the surface water of southern Baltic Sea. However, ratio of
127 I − / 127 IO3 − , shows instead higher values in April (Fig. 2f), indicating
a selective reduction of iodate that may be a significant process governing
the out of equilibrium (freshly added to the environment)
129 I isotope compared to the naturally equilibrated 127 I isotope. As
the Arkona Basin is end-member of relatively saline water, iodide
and iodate concentration are severely affected by the mixing process.
Variability in the relative 129 I − / 127 I − and 129 IO 3 − / 127 IO3 − values
(Fig. 4) between the sampling campaigns (August-2006 and April-
2007) can reflect seasonal and input effects. Addition of huge fresh
water to the system during spring snow and ice melting may preferentially
alter the concentrations and iodine speciation, specifically in
near coastal regions. During August, extensive algal blooming may
on the other hand contribute to increase the iodide species, particularly
near to coastal and shallow water regions. The present distribution
of the studied sampling sites is rather limited and does not
provide enough coverage to deduce specific distribution patterns of
the isotopes in the surface water. Furthermore, addition of data on iodine
speciation in depth profiles of the sampling site will expose better
the interplay between regional water transport and environmental conditions.
Nevertheless, the data presented here has shown for the first
time the extent and general distribution patterns of iodine isotopes species
that add new valuable information for future environmental
analysis.
5. Conclusions
We here present data on iodine isotopes ( 129 I and 127 I) and their
species (iodide and iodate) in surface water collected from 16 locations
in August 2006 and 19 locations in April 2007 in the Baltic Proper,
Kattegat and Skagerrak. From those results we draw the following
conclusions: a) reduction of iodate and oxidation of iodide in Skagerrak
and Kattegat may be a slow process since insignificant change in
129 I and 127 I speciation was found; b) reduction of iodate to iodide
seems to be a relatively fast process in surface water of the southern
Baltic Sea; c) oxidation conditions of the surface water are not exerting
a marked effect on the iodine speciation in the studied basins; d)
seasonal and input effects may alter the concentrations and speciation
modes specifically in near coastal regions.
Acknowledgements
Oxygen (ml/L)
Fig. 5. Distribution of salinity and oxygen in the surface water of Skagerrak, Kattegat and Baltic Sea, during August 2006 and April 2007.
Table 3
Correlation relationship (R 2 ) between iodine species and oxygen and salinity.
127 I −
127 IO3 −
129 I −
129 IO3 −
127 I-
127 IO3 − 129 I − 129 IO3 −
Oxgyen Salinity
0.14 0.44 0.52 −0.03 0.49
0.37 0.36 −0.2 0.55
0.79 −0.08 0.8
−0.04 0.75
Funding for the sampling was provided by the Swedish Meteorological
and Hydrological Institute (SMHI). We thank Lars Andersson
and Bodil Thorstensson and all the crew and scientific team on
board of the research vessel Argos for the help during the sampling
expeditions. X.L. Hou appreciates the support by “BaiRen” Project of
CAS (Grant No. KZCX2-YW-BR-13).