Publication Date:
2020-06-11
Description:
To date, observations on a single location indicate
that cryogenic gypsum (Ca{SO4} *2H2O) may constitute an
efficient but hitherto overlooked ballasting mineral enhancing
the efficiency of the biological carbon pump in the Arctic
Ocean. In June–July 2017 we sampled cryogenic gypsum
under pack ice in the Nansen Basin north of Svalbard
using a plankton net mounted on a remotely operated vehicle
(ROVnet). Cryogenic gypsum crystals were present at
all sampled stations, which suggested a persisting cryogenic
gypsum release from melting sea ice throughout the investigated
area. This was supported by a sea ice backtracking
model, indicating that gypsum release was not related to a
specific region of sea ice formation. The observed cryogenic
gypsum crystals exhibited a large variability in morphology
and size, with the largest crystals exceeding a length of 1 cm.
Preservation, temperature and pressure laboratory studies revealed
that gypsum dissolution rates accelerated with increasing
temperature and pressure, ranging from 6%d-1 by
mass in polar surface water (-0.5 °C) to 81%d-1 by mass in
Atlantic Water (2.5°C at 65 bar). When testing the preservation
of gypsum in formaldehyde-fixed samples, we observed
immediate dissolution. Dissolution at warmer temperatures
and through inappropriate preservation media may thus explain
why cryogenic gypsum was not observed in scientific
samples previously. Direct measurements of gypsum crystal
sinking velocities ranged between 200 and 7000md-1, suggesting
that gypsum-loaded marine aggregates could rapidly
sink from the surface to abyssal depths, supporting the hypothesized
potential of gypsum as a ballasting mineral in the
Arctic Ocean.
Repository Name:
EPIC Alfred Wegener Institut
Type:
Article
,
peerRev
Format:
application/pdf
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