Tech Briefs Magazine - October 2023 - Comsol-29A

RESEARCH SPOTLIGHT
dissolution should arrest the
dissolution of suspended
calcite grains, because of the
supersaturation it generates.
» HELPING OTHER
HUMANS MEND
THE SEAS
FIGURE 4 The tendency for calcite dissolution above, at, and below the sediment-water
interface (a). A dissolving pteropod shell affects the boundary zone around the sediment-
water interface (b).
FIGURE 5 Simulation results showing how the presence
of a pteropod in the seafloor sediment affects the
dissolution rates of nearby calcite grains. Lighter-colored
areas indicate where dissolution is occurring more rapidly.
The white lines indicate the saturation line, or isocontour,
where calcite is at equilibrium with its dissolution
byproducts, meaning there should not be any net
dissolution or precipitation.
The seawater that mingles with solids near the sediment-
water interface plays a crucial role in this process. The
boundary between the seafloor and the water is varied, and
seawater circulates around solids, even below the apparent
line of separation. Capturing the gradated boundary between
seawater and sediment is
one of the advantages of
Sulpis' 3D model. As the
pteropod shell dissolves,
the surrounding seawater
becomes saturated with
aragonite. This zone of
saturated seawater mixed
with sediment is indicated by
the red shading in Figure 4b.
It is this aragonite-saturated
seawater that chemically
interacts with - and protects
- the calcite left behind by
other organisms.
Figure 4a shows the
seawater saturation state
with respect to calcite, which
is its ability to be dissolved
throughout this transition
zone between sea and
sediment. At 1.5 mm above
the seafloor, seawater is
undersaturated, and any
calcite grains should dissolve
quite readily. The black line
shows that in the absence of
any aragonite source, calcite
dissolution should continue at
the sediment-water interface.
The red line indicates the
zone where pteropod shell
Having developed a
new means of analyzing
underwater micrometerscale
biochemical processes,
Sulpis is now exploring how
his work can guide further
research. " Our next step has
been to try to replicate these
processes in the lab, with
calcite and pteropod shells in
beakers. So far, experimental
results are similar to what the
simulation shows, " he says.
" The goal now is to use this
information to better interpret
what we can observe in situ. "
Toward this end, Sulpis and
his colleagues have obtained a
grant from the Dutch Research
Council (NWO) to directly
study how aragonite producers
shape their environment.
Of course, the organism
whose activity has the greatest
impact on its environment is
the human. Anthropogenic
acidification threatens the
life-sustaining tapestry that
ocean creatures weave among
their parts of Earth. With this
in mind, the broader project
of understanding carbonate
cycles takes on added urgency.
" Compared to how much CO2
we are adding to the oceans,
only a tiny amount is being
neutralized, " says Sulpis.
" Maybe the carbonate cycle
process can do the job, but
it may take several thousand
years to do so! "
Taking a more immediate
perspective, Sulpis is eager
for fellow humans to apply
his research and analysis to
protecting the sea butterflies'
world - and ours. " Our
models are all open access, "
he says, " and I hope others
can make use of what we
have created. "
COMSOL NEWS 29a
Tech Briefs Magazine - October 2023

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