Variability in sea ice carbonate chemistry: A case study comparing the importance of ikaite precipitation, bottom ice algae, and currents across an invisible polynya
- 1Department of Geography, University of Calgary, Calgary, Alberta, Canada
- 2Centre for Earth Observation Science, University of Manitoba, Winnipeg, Manitoba, Canada
- 3Arctic Eider Society, Sanikiluaq, Canada
- 4SmartIce Sea Ice Monitoring & Information Inc., St. John’s, Canada
- 5Department of Geography, University of Victoria, Victoria, British Columbia, Canada
- anow at: College of Life and Environmental Sciences, University of Exeter, Exeter, United Kingdom
- bnow at: Institute for Marine and Antarctic Studies, University of Tasmania, Hobart, Australia
- 1Department of Geography, University of Calgary, Calgary, Alberta, Canada
- 2Centre for Earth Observation Science, University of Manitoba, Winnipeg, Manitoba, Canada
- 3Arctic Eider Society, Sanikiluaq, Canada
- 4SmartIce Sea Ice Monitoring & Information Inc., St. John’s, Canada
- 5Department of Geography, University of Victoria, Victoria, British Columbia, Canada
- anow at: College of Life and Environmental Sciences, University of Exeter, Exeter, United Kingdom
- bnow at: Institute for Marine and Antarctic Studies, University of Tasmania, Hobart, Australia
Abstract. The carbonate chemistry of sea ice is known to play a role in global carbon cycles, but its importance is uncertain in part due to disparities in reported results. Variability in physical and biological drivers is usually invoked to explain differences between studies. In the Canadian Arctic Archipelago, “invisible polynyas” – areas of strong currents, thin ice, and potentially high biological productivity – are examples of extreme spatial variability. We used an invisible polynya as a natural laboratory to study the effects of inferred initial ice formation conditions, ice growth rate, and algal biomass on the distribution of carbonate species by collecting enough cores to perform a statistical comparison between sites located within, and just outside of, a polynya near Iqaluktuttiaq (Cambridge Bay, Nunavut, Canada). At both sites, the uppermost 10-cm ice horizon showed evidence of CO2 offgassing, while carbonate distributions in the middle and bottommost 10-cm horizons largely followed the salinity distribution. In the polynya, the upper-ice horizon had significantly higher bulk total inorganic carbon (TIC), total alkalinity (TA), and salinity, potentially due to freeze-up conditions that favoured frazil ice production. The middle-ice horizons were statistically indistinguishable between sites, suggesting that ice growth rate is not an important factor for the carbonate distribution under mid-winter conditions. The thicker (non-polynya) site experienced higher algal biomass, TIC, and TA in the bottom horizon. Carbonate chemistry in the bottom horizon could be explained by the salinity distribution, with the strong currents at the polynya site potentially playing a role in desalinisation; biology did not have a noticeable impact. We did see evidence of calcium carbonate precipitation, but with little impact on the TIC : TA ratio, and little difference between sites. Because differences were constrained to relatively thin layers at the top and bottom, vertically averaged values of TIC, TA, and especially the TIC : TA ratio were not meaningfully different between sites. This provides some justification for using a single bulk value for each parameter when modeling sea ice effects on ocean chemistry at coarse resolution. Exactly what value to use (particularly for the TIC : TA ratio) likely varies by region but could potentially be approximated from knowledge of the source seawater and sea ice salinity. Further insights await a rigorous intercomparison of existing data.
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Brent G. T. Else et al.
Status: closed
-
RC1: 'Comment on tc-2021-320', Sebastien Moreau, 15 Nov 2021
The comment was uploaded in the form of a supplement: https://tc.copernicus.org/preprints/tc-2021-320/tc-2021-320-RC1-supplement.pdf
- AC1: 'Reply on RC1', B.G.T. Else, 31 Jan 2022
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RC2: 'Comment on tc-2021-320', Eric Mortenson, 02 Dec 2021
General comments
The study presents a comparison of the ice carbonate system throughout the ice column between two sites exhibiting different biological (ice algal) and physical (currents, snow cover) conditions. One of the main results is emphasis on the importance of brine drainage over secondary processes like primary productivity and ikaite precipitation in characterizing the ice-carbonate system. They acknowledge that air-sea exchange and ikaite precipation may be important near the surface, and that primary productivity be important near the bottom, but the much thicker middle of the ice column has a stronger influence when averaging over the entire ice column.
The challenge to the main result above is the TIC and TA deficits in the surface ice, as shown in the S:TIC and S:TA plots (fig 7). Although this layer is small relative to the entire ice column (therefore making the deficits not as important when considering the entire ice column), why are the nDIC:nTA slopes (fig 8) so close to the ikaite precipitation slope?
I think the answer is that the different horizons are improperly weighted in fig 8. I.e., with the exception of the “high-resolution” core, there are an equal number of measurements for the relatively thin surface and bottom layers as there are for the thicker middle layer. I suggest making separate regression lines for each layer for the 2 cores, and stating that the thicker middle layer dominates the bulk characteristics (per unit area).
After addressing the above, as well as fixing the minor comments below, I would recommend this article for publication in The Cryosphere.
Cheers,
Eric Mortenson
Specific comments
-84: I suggest adding underlined: …and under-ice seawater temperature and currents…
-104: I suggest adding underlined: …a function of under-ice seawater nutrient concentration and turbulence, …
-259-260: Note that the respective magnitudes of tidal amplitudes and of tidally-induced currents are not necessarily related (e.g., currents can be quite strong at the mouth of an enclosed bay with a small opening, due to small amplitude changes in the enclosed bay)
-323: As mentioned just above this line, snow cover has a strong effect on light penetration, it would be nice to see a number for (or quantitative comparison to) Dalman’s snow cover measurement.
Table1/2: It would be nice to see these separated by date, in addition to the totals, at least for mean and standard deviation
Technical corrections
-Please be consistent using either DIC or TIC, but not both.
-Just a stylistic comment, why use “horizons”, instead of strata or levels?
-102-103, twice there are “(“ with no ending parentheses, replace with commas maybe
-Lines 119 and 125, Please spell Mortensen with “-son”
-To me, it seems a bit clearer if the paragraph on all cores collected (lines 187-196) came before the paragraph on individual core carbon sampling (lines 177-186)
-Line 372: Nomura, Nomura should be Nomura, 2014
-Line 433: remove “to” at end of line
-Tables 1 and 2 appear to be identical, but with slightly different captions.
-Fig. 1: I recommend changing the font color for POLY to white to improve visibility
- AC2: 'Reply on RC2', B.G.T. Else, 31 Jan 2022
Status: closed
-
RC1: 'Comment on tc-2021-320', Sebastien Moreau, 15 Nov 2021
The comment was uploaded in the form of a supplement: https://tc.copernicus.org/preprints/tc-2021-320/tc-2021-320-RC1-supplement.pdf
- AC1: 'Reply on RC1', B.G.T. Else, 31 Jan 2022
-
RC2: 'Comment on tc-2021-320', Eric Mortenson, 02 Dec 2021
General comments
The study presents a comparison of the ice carbonate system throughout the ice column between two sites exhibiting different biological (ice algal) and physical (currents, snow cover) conditions. One of the main results is emphasis on the importance of brine drainage over secondary processes like primary productivity and ikaite precipitation in characterizing the ice-carbonate system. They acknowledge that air-sea exchange and ikaite precipation may be important near the surface, and that primary productivity be important near the bottom, but the much thicker middle of the ice column has a stronger influence when averaging over the entire ice column.
The challenge to the main result above is the TIC and TA deficits in the surface ice, as shown in the S:TIC and S:TA plots (fig 7). Although this layer is small relative to the entire ice column (therefore making the deficits not as important when considering the entire ice column), why are the nDIC:nTA slopes (fig 8) so close to the ikaite precipitation slope?
I think the answer is that the different horizons are improperly weighted in fig 8. I.e., with the exception of the “high-resolution” core, there are an equal number of measurements for the relatively thin surface and bottom layers as there are for the thicker middle layer. I suggest making separate regression lines for each layer for the 2 cores, and stating that the thicker middle layer dominates the bulk characteristics (per unit area).
After addressing the above, as well as fixing the minor comments below, I would recommend this article for publication in The Cryosphere.
Cheers,
Eric Mortenson
Specific comments
-84: I suggest adding underlined: …and under-ice seawater temperature and currents…
-104: I suggest adding underlined: …a function of under-ice seawater nutrient concentration and turbulence, …
-259-260: Note that the respective magnitudes of tidal amplitudes and of tidally-induced currents are not necessarily related (e.g., currents can be quite strong at the mouth of an enclosed bay with a small opening, due to small amplitude changes in the enclosed bay)
-323: As mentioned just above this line, snow cover has a strong effect on light penetration, it would be nice to see a number for (or quantitative comparison to) Dalman’s snow cover measurement.
Table1/2: It would be nice to see these separated by date, in addition to the totals, at least for mean and standard deviation
Technical corrections
-Please be consistent using either DIC or TIC, but not both.
-Just a stylistic comment, why use “horizons”, instead of strata or levels?
-102-103, twice there are “(“ with no ending parentheses, replace with commas maybe
-Lines 119 and 125, Please spell Mortensen with “-son”
-To me, it seems a bit clearer if the paragraph on all cores collected (lines 187-196) came before the paragraph on individual core carbon sampling (lines 177-186)
-Line 372: Nomura, Nomura should be Nomura, 2014
-Line 433: remove “to” at end of line
-Tables 1 and 2 appear to be identical, but with slightly different captions.
-Fig. 1: I recommend changing the font color for POLY to white to improve visibility
- AC2: 'Reply on RC2', B.G.T. Else, 31 Jan 2022
Brent G. T. Else et al.
Brent G. T. Else et al.
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