|Graham and Risk explore carbon dioxide flux through snow in two different snowpacks in Nova Scotia. The focus is on the timescales of CO2 "recovery" (if you will) after wind-induced pressure pumping events (this is similar to the Venturi effect where an increase in speed results in a decrease in pressure).|
It honestly took me a while to figure out the major points of the manuscript, which was in the timescale of the re-establishment of consistent CO2 gradients in the snowpack after disturbances for the use of gradient-based approaches. This is fine, but wasn't entirely apparent from the introduction, where the findings of Bowling, Massman and others could have been written in a way to point to a more clear overarching question. Doing so will lead in my opinion to a much more compelling manuscript.
The text could be more efficient throughout. As a first example, " Datasets have shown that winter..." on line 2 could simply be, "Winter...".
The paper was not particularly well-referenced with a mere 27 references on a topic that has attracted much more attention than this.
line 7 of page 2 isn't entirely accurate. 7% of what? Saturated vapor pressure?
On what basis is the snowpack diffusion approach the most commonly used technique? One may argue that eddy covariance is used much more frequently but also that careful studies of flux through snow using this technique are perhaps a bit lacking.
on page 2 line 34, the major finding of Bowling and Massman is that "enhanced diffusion" is a major mechanism of gas transport through snow, so citing it here isn't the most accurate thing to do.
On page 4, the GMP can be heated as noted, but this impacts the advection when adding heat to a snowpack. It would be forthcoming to estimate the advective flux induced by the GMP sensors for a conservative estimate of their impact on advection. This also creates a risk of melting and freezing snow and encapsulating sensors.
I'm rather confused by section 2.2 in which it seems like only periods that conform to certain assumptions are chosen, which will bias the results in favor of these conditions and not provide a representative estimate of CO2 flux during the snow-covered period. This topic is covered in the discussion, but led to confusion in the results section.
The 1D model development on page 5 was a bit lacking as the role of temperature, pressure, and tortuosity was ignored or described in a cursory manner. The sensitivity analysis in section 2.4 helps assuage some of these concerns but it should be placed after the model description for continuity.
'is considered impossible' is incorrect on line 6, it's just that 3D transport is not modeled in a 1D model.
'under certain conditions' in the results induces curiosity as to what these conditions are. Do they fall under certain classes or conditions?
" These values were a good representation of the CO2 concentration at the snow-air interface." what does this mean?
On page 10 line 27 or so, note the findings of Rains et al. (2016, doi: 10.1016/j.coldregions.2015.10.003) that variations in wind speed at low (multiple hour) frequencies may be more effective than variations in atmospheric pressure for explaining changes in snowpack CO2 concentrations. (see also the upper part of page 12 on multi-measurement comparisons).
in section 4.2, these are essentially the findings of Bowling and Massman (2011) which should be cited.