a. Sample location.
b. Thick section layering photo-
graphed in natural light.
c. Modified ice crystal boundaries photographed in natural light (right) and
between crossed polarizers (left).
Figure 19. Sample F6, taken from the ice accretion panel on the main deck
hatch (scales in millimeters). Dark circles in thin sections are air bubbles.
mation of 120 triple junctions. These changes have
The mean crystal cross section measured 0.31 mm2,
not been accompanied by any significant preferred ori-
which converts to a root-mean-square diameter of
entation of the component crystals. Crystal cross sec-
0.56 mm. In this particular section, the grains appear
tions and derived diameters averaged 0.58 mm2 and
substantially immersed in brine, forming channel-like
0.76 mm, respectively. Bubble diameters averaged 0.27
networks similar to what was observed in samples
mm. Large numbers of irregularly shaped structures,
M6 and M12 in Figure 10. The ice also contained
including some that encircle crystals, are identified as
many rounded, presumed bubbles of air with a
mean diameter of 0.27 mm. A mean density of 0.871
Mg m3 was measured in conjunction with a bulk
Sample M5. This sample (Fig. 21) was retrieved
salinity of 10.3‰.
from the 5-in. gun housing, as was sample M3,
Sample M6. This sample (Fig. 22) was obtained
but was located at a more elevated level, 0.9 m above
the deck on the front face of the gun housing and about
from the same general location (vertical port side fac-
7.5 hours later than sample M3. This later sampling
ing of the 5-in. gun mount) as samples M7, M9, and
time is clearly evident in both the ice thickness,
M10. This sample was only 0.8 cm thick. A relatively
only 0.6 cm, and the microstructural characteristics
low salinity of 7.9‰ was measured, together with a
density of 0.799 Mg m3. Generally, rounded grains
of sample M5. This ice has a granular texture of
well-rounded grains, exhibiting the smallest crystal size
characterize the crystalline texture of this sample. Thin
of any sample of accreted ice collected on the cruise.
section observations give the impression of grains im-