ROV basierte Untersuchung der räumlichenVariabilität der Lichttransmission durcharktisches Meereis im Sommer
2012
The energy balance of the Arctic is of high importance to the climate system of
our planet also outside the arctic. The sea ice cover as boundary layer between
ocean and atmosphere plays a crucial role in the partitioning of incident energy
between differend compartments of the climate system. While sea ice reflects
most of the incident light, some part is penetrating through the ice. Extent,
thickness and albedo of sea ice have been observed for many years. In contrast,
there exist only few measurements of transmitted light, as acces under the ice is
difficult. Few data exist especially on the spatial variability of transmitted light.
This work presents the first measurements of transmitted light onboard a
remotely operated vehicle (ROV) under sea ice in the central Arctic. Several
profiles of transmitted light were measured during the cruise ARK-XXVI/3
(TransArc 2011) of the german research icebreaker Polarstern in 2011 (beginning
in the eurasian basin, over the pole to the canadian basin and towards russian
shelf seas). Two spectroradiometers with different angular response characteristics
were used for the first time for simultaneous measurements. The amount
of data enables statistically significant conclusions on a huge databasis and an
approach to spatial variability of the light conditions under sea ice. Transmittances
for different ice types could be derived and the variability within an ice
type described.
One of the main results of the work is that first year sea ice transmits three
times more light than multi year sea ice. Spatial variability on single floes exceeds
one order of magnitude, but is mainly influenced by surface properties. Due to
the lack of a surface scattering layer melt ponds transmit considerably more
light than the surrounding bare ice. From the ratio between the two different
sensors we can deduce, that the scattering-coefficient of sea ice is dependent on
direction and that the light field under the ice is not isotropic, as it was assumed
earlier.
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