Variability in sea ice carbonate chemistry: A case study comparing the importance of ikaite precipitation, bottom ice algae, and currents across an invisible polynya
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 Archipe...
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ftcopernicus:oai:publications.copernicus.org:tcd98249 2023-05-15T14:29:03+02:00 Variability in sea ice carbonate chemistry: A case study comparing the importance of ikaite precipitation, bottom ice algae, and currents across an invisible polynya Else, Brent G. T. Cranch, Araleigh Sims, Richard P. Jones, Samantha Dalman, Laura A. Mundy, Christopher J. Segal, Rebecca A. Scharien, Randall K. Guha, Tania 2021-10-27 application/pdf https://doi.org/10.5194/tc-2021-320 https://tc.copernicus.org/preprints/tc-2021-320/ eng eng doi:10.5194/tc-2021-320 https://tc.copernicus.org/preprints/tc-2021-320/ eISSN: 1994-0424 Text 2021 ftcopernicus https://doi.org/10.5194/tc-2021-320 2021-11-01T17:22:28Z 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 CO 2 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. Text Arctic Archipelago Arctic Cambridge Bay Canadian Arctic Archipelago ice algae Nunavut Sea ice Copernicus Publications: E-Journals Arctic Nunavut Canadian Arctic Archipelago Canada Cambridge Bay ENVELOPE(-105.130,-105.130,69.037,69.037) |
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Open Polar |
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Copernicus Publications: E-Journals |
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ftcopernicus |
language |
English |
description |
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 CO 2 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. |
format |
Text |
author |
Else, Brent G. T. Cranch, Araleigh Sims, Richard P. Jones, Samantha Dalman, Laura A. Mundy, Christopher J. Segal, Rebecca A. Scharien, Randall K. Guha, Tania |
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Else, Brent G. T. Cranch, Araleigh Sims, Richard P. Jones, Samantha Dalman, Laura A. Mundy, Christopher J. Segal, Rebecca A. Scharien, Randall K. Guha, Tania Variability in sea ice carbonate chemistry: A case study comparing the importance of ikaite precipitation, bottom ice algae, and currents across an invisible polynya |
author_facet |
Else, Brent G. T. Cranch, Araleigh Sims, Richard P. Jones, Samantha Dalman, Laura A. Mundy, Christopher J. Segal, Rebecca A. Scharien, Randall K. Guha, Tania |
author_sort |
Else, Brent G. T. |
title |
Variability in sea ice carbonate chemistry: A case study comparing the importance of ikaite precipitation, bottom ice algae, and currents across an invisible polynya |
title_short |
Variability in sea ice carbonate chemistry: A case study comparing the importance of ikaite precipitation, bottom ice algae, and currents across an invisible polynya |
title_full |
Variability in sea ice carbonate chemistry: A case study comparing the importance of ikaite precipitation, bottom ice algae, and currents across an invisible polynya |
title_fullStr |
Variability in sea ice carbonate chemistry: A case study comparing the importance of ikaite precipitation, bottom ice algae, and currents across an invisible polynya |
title_full_unstemmed |
Variability in sea ice carbonate chemistry: A case study comparing the importance of ikaite precipitation, bottom ice algae, and currents across an invisible polynya |
title_sort |
variability in sea ice carbonate chemistry: a case study comparing the importance of ikaite precipitation, bottom ice algae, and currents across an invisible polynya |
publishDate |
2021 |
url |
https://doi.org/10.5194/tc-2021-320 https://tc.copernicus.org/preprints/tc-2021-320/ |
long_lat |
ENVELOPE(-105.130,-105.130,69.037,69.037) |
geographic |
Arctic Nunavut Canadian Arctic Archipelago Canada Cambridge Bay |
geographic_facet |
Arctic Nunavut Canadian Arctic Archipelago Canada Cambridge Bay |
genre |
Arctic Archipelago Arctic Cambridge Bay Canadian Arctic Archipelago ice algae Nunavut Sea ice |
genre_facet |
Arctic Archipelago Arctic Cambridge Bay Canadian Arctic Archipelago ice algae Nunavut Sea ice |
op_source |
eISSN: 1994-0424 |
op_relation |
doi:10.5194/tc-2021-320 https://tc.copernicus.org/preprints/tc-2021-320/ |
op_doi |
https://doi.org/10.5194/tc-2021-320 |
_version_ |
1766303146245619712 |