Hiilemann et al.: Dissolved and Particulate Major and Trace Elements
109
subsequent drainage of the brine to the underlying water column has a strong impact on the
biological community living in and under the ice. In addition, ice related trace element cycling
can significantly modify the transport of metals from the rivers to the sea and the dispersion of
hazardous metals and metalloids in the Arctic environment.
Geochemistry of ice-rafted sediments as a tracerfor ice drift patterns
The modem sedimentary regime in the Laptev Sea is dominated by the fluvial input of the rivers
draining the Siberian platform. Especially the sediment inputs by the Lena river in the east and
the Khatanga river in the west control the mineralogical and geochemical compositions of
suspended matter and surficial sediments in the southern Laptev Sea. The Khatanga, like the
Yenisey, drains a plateau with Triassic flood basalts. Basalts have a unique geochemical
signature compared to granite, shales or average continental crust, because they are enriched in
e.g. Mg, Ca and depleted in elements like K, and the REE. This should make the normalized
element contents (e.g. MgI AI, Cal AI, KI AI and REEl AI ratio) a good tracer for the fluvial input
from the Khantanga river. This assumption is supported by geochemical and mineralogical field
data from the Laptev Sea. As an example, highest Mg/AI and CaiAI ratios in the surficial
sediments were observed in the SW Laptev Sea near the mouth of the Khatanga (Holemann et
a!., unpub!. data). Suspensions from this river system are also characterized by high amounts
of Mg-bearing pyroxene (Lisitzyn, 1996) that are also found in the sediments of the SW Laptev
Sea (Behrens et a!., 1996).
The geochemical data from the SW and SE Laptev Sea (Table I) indicate that the MgI Al and
Cal Al ratios observed in ice-rafted sediments reflect this general distribution pattern with higher
ratios in the western and lower ratios in the eastern Laptev Sea. In contrast KI Al and REEl Al
are higher in ice-rafted sediments from the SE Laptev Sea (Figure 5). This supports the
hypothesis that the geochemical signature of ice-rafted sediments from the Laptev Sea mainly
reflect the chemical composition of river-borne sediments and, thus, make the geochemical
fingerprint of ice-rafted sediments a useful tracer for the reconstruction of ice drift patterns in
the Laptev Sea and the Transpolar Drift.
The major difference between ice from the southern Laptev Sea and the northern Laptev Sea
is that IRS contents in newly formed ice in offshore regions are generally lower. At low particle
contents « 2 mg kg· l ) the particle assemblage is characterized by a higher proportion of
autochthonous organic matter, like ice algae. In contrast to mineral particles, organic particles
have different chemical compositions and a higher capacity for complexation and chelation.
This can explain the higher content of particulate S, Cu, Ni and Pb in new ice with low particle
contents.
As a consequence the geochemical fingerprint of "clean", newly formed ice from the
northern, deeper parts of the Laptev Sea seems to be determined mainly by biological
processes. However, a maximum content of As (> 0.47 /lmol g.l) was measured in lowparticle new ice in the northern Yana valley, a region that is characterized by As enrichment in
surficial seafloor sediments (Holemann et a!. 1995; Holemann et a!. subm.). Elevated contents
of arsenic (> 0.80 /lmol g.l) were also measured within the pack ice of the Transpolar Drift
(Wollenburg, unpub!. data) and in sea ice north off the Laptev Sea (- 0.40 /lmol g.l;
Holemann, unpub!. data) during the Polarstern cruise ARK XIII. Tn contrast, pack ice from
stations near the East Siberian Sea stations showed contents lower than 0.13 /lmol gl
This gives further evidence that resuspension of seafloor sediments in the northern Laptev
Sea is an active entrainment process resulting in the incorporation of sediments into the growing
ice cover. The mechanism should be more pronounced during winter storm periods with strong
resuspension of sediments in the ice-free polynya region and frazil ice formation due to
supercooling of the water column.
109
subsequent drainage of the brine to the underlying water column has a strong impact on the
biological community living in and under the ice. In addition, ice related trace element cycling
can significantly modify the transport of metals from the rivers to the sea and the dispersion of
hazardous metals and metalloids in the Arctic environment.
Geochemistry of ice-rafted sediments as a tracerfor ice drift patterns
The modem sedimentary regime in the Laptev Sea is dominated by the fluvial input of the rivers
draining the Siberian platform. Especially the sediment inputs by the Lena river in the east and
the Khatanga river in the west control the mineralogical and geochemical compositions of
suspended matter and surficial sediments in the southern Laptev Sea. The Khatanga, like the
Yenisey, drains a plateau with Triassic flood basalts. Basalts have a unique geochemical
signature compared to granite, shales or average continental crust, because they are enriched in
e.g. Mg, Ca and depleted in elements like K, and the REE. This should make the normalized
element contents (e.g. MgI AI, Cal AI, KI AI and REEl AI ratio) a good tracer for the fluvial input
from the Khantanga river. This assumption is supported by geochemical and mineralogical field
data from the Laptev Sea. As an example, highest Mg/AI and CaiAI ratios in the surficial
sediments were observed in the SW Laptev Sea near the mouth of the Khatanga (Holemann et
a!., unpub!. data). Suspensions from this river system are also characterized by high amounts
of Mg-bearing pyroxene (Lisitzyn, 1996) that are also found in the sediments of the SW Laptev
Sea (Behrens et a!., 1996).
The geochemical data from the SW and SE Laptev Sea (Table I) indicate that the MgI Al and
Cal Al ratios observed in ice-rafted sediments reflect this general distribution pattern with higher
ratios in the western and lower ratios in the eastern Laptev Sea. In contrast KI Al and REEl Al
are higher in ice-rafted sediments from the SE Laptev Sea (Figure 5). This supports the
hypothesis that the geochemical signature of ice-rafted sediments from the Laptev Sea mainly
reflect the chemical composition of river-borne sediments and, thus, make the geochemical
fingerprint of ice-rafted sediments a useful tracer for the reconstruction of ice drift patterns in
the Laptev Sea and the Transpolar Drift.
The major difference between ice from the southern Laptev Sea and the northern Laptev Sea
is that IRS contents in newly formed ice in offshore regions are generally lower. At low particle
contents « 2 mg kg· l ) the particle assemblage is characterized by a higher proportion of
autochthonous organic matter, like ice algae. In contrast to mineral particles, organic particles
have different chemical compositions and a higher capacity for complexation and chelation.
This can explain the higher content of particulate S, Cu, Ni and Pb in new ice with low particle
contents.
As a consequence the geochemical fingerprint of "clean", newly formed ice from the
northern, deeper parts of the Laptev Sea seems to be determined mainly by biological
processes. However, a maximum content of As (> 0.47 /lmol g.l) was measured in lowparticle new ice in the northern Yana valley, a region that is characterized by As enrichment in
surficial seafloor sediments (Holemann et a!. 1995; Holemann et a!. subm.). Elevated contents
of arsenic (> 0.80 /lmol g.l) were also measured within the pack ice of the Transpolar Drift
(Wollenburg, unpub!. data) and in sea ice north off the Laptev Sea (- 0.40 /lmol g.l;
Holemann, unpub!. data) during the Polarstern cruise ARK XIII. Tn contrast, pack ice from
stations near the East Siberian Sea stations showed contents lower than 0.13 /lmol gl
This gives further evidence that resuspension of seafloor sediments in the northern Laptev
Sea is an active entrainment process resulting in the incorporation of sediments into the growing
ice cover. The mechanism should be more pronounced during winter storm periods with strong
resuspension of sediments in the ice-free polynya region and frazil ice formation due to
supercooling of the water column.