Drake, T.W., Tank, S.E.,
Zhulidov, A.V., Holmes, R.M.,
Gurtovaya, T. and
Spencer, R.G.M.
2018
Increasing alkalinity export
from large Russian Arctic rivers
Environmental Science & Technology 52:
8302-8308
NOTE:
Drake et al. (2018) note that
"riverine carbonate alkalinity,
in the form of bicarbonate (HCO3-)
and carbonate (CO32-) ions,
represents an important
biogeochemical flux of carbon
from land to ocean."
Over long time scales,
this alkalinity flux
from rivers
"controls the
calcium carbonate
( CaCO3 )
saturation state
in the ocean
and can function
as a sink for
atmospheric
carbon dioxide."
Changes in riverine
carbonate alkalinity
have implications
for ocean
"acidification"
( a decline in oceanic pH
caused by rising
atmospheric CO2 ).
SUMMARY:
Drake et al. admit it is
"difficult to assess
the importance
of any single driver."
But "regardless of the
direct causes, these trends
have broad implications
for the rate of
carbon sequestration
on land, and delivery
of buffering capacity
to freshwater ecosystems
and the Arctic Ocean."
The authors say:
"higher surface
air temperatures
may have direct and
indirect effects on
weathering via
permafrost thaw,
microbial respiration,
and the enhanced
productivity of
surface vegetation."
They say permafrost thaw
"exposes unweathered
mineral surfaces,
increases residence times
of infiltrating water,
and increases mixing
with mineral rich
groundwater,
all of which promote
alkalinity production
and export."
Other reasons that
could also be contributing
to the enhanced alkalinity
export by rivers, include:
(1) biological effects
driven by CO2 fertilization
that enhances below-ground
chemical weathering,
(2) declines in acid deposition,
(3) increased precipitation,
(4) changes in hydrologic
flow paths, and
(5) shifts in vegetation.
DETAILS:
The team of six scientists
examined trends for two
of the largest rivers
in the Arctic, the Ob' and
Yenisei.
For annual discharge rates
to the Arctic Ocean,
the Yenisei and Ob' rivers
are the largest and
third largest, respectively,
and for the globe as a whole
they are the fifth
and 13th largest,
again respectively.
Drake et al. utilized a suite
of pertinent data to estimate
the total annual alkalinity flux
from these two rivers
from which they determined
trends in alkalinity export
from the Ob' and Yenisei
into the Arctic Ocean
over the period 1974-2015.
As shown in the upper charts,
annual discharge rates
at the Ob' River exhibited
no long-term trend,
whereas they experienced
a statistically significant
rise of 14.7% at the
Yenisei River over the
past four decades.
The annual export
of alkalinity
from both rivers
rose dramatically
over the period of study,
with export from the Ob'
and Yenisei increasing
by +134% and +185%,
respectively.
The lower charts reveal
a strong linear correlation
between this parameter
and mean annual temperatures
in the high northern latitudes
(44-90°N).
