New estimates of sulfate diffusion rates in the EPICA Dome C ice core
To extract climatically relevant chemical signals from the deepest, oldest Antarctic ice, we must first investigate the degree to which chemical ions diffuse within solid ice. Volcanic sulfate peaks are an ideal target for such an investigation because they are high-amplitude, short-duration ( ∼3 ye...
| Published in: | Climate of the Past |
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| Main Authors: | , , , , |
| Format: | Text |
| Language: | English |
| Published: |
2024
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| Subjects: | |
| Online Access: | https://doi.org/10.5194/cp-20-2031-2024 https://cp.copernicus.org/articles/20/2031/2024/ |
| Summary: | To extract climatically relevant chemical signals from the deepest, oldest Antarctic ice, we must first investigate the degree to which chemical ions diffuse within solid ice. Volcanic sulfate peaks are an ideal target for such an investigation because they are high-amplitude, short-duration ( ∼3 years) events with a quasi-uniform structure. Here we present an analysis of the EPICA Dome C sulfate record over the last 450 kyr. We identify volcanic peaks and isolate them from the non-sea-salt sulfate background to reveal the effects of diffusion: amplitude damping and broadening of peaks in the time domain with increasing depth and age. Sulfate peak shape is also altered by the thinning of ice layers with depth that results from ice flow. Both processes must be simulated to derive effective diffusion rates. This is achieved by running a forward model to diffuse idealised sulfate peaks at different rates while also accounting for ice thinning. Our simulations suggest a median effective diffusion rate of sulfate ions of 2.4 ± 1.7 × 10 - 7 <svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="77pt" height="13pt" class="svg-formula" dspmath="mathimg" md5hash="6f0177d04e8f7b18806b1f9a56533080"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cp-20-2031-2024-ie00001.svg" width="77pt" height="13pt" src="cp-20-2031-2024-ie00001.png"/> </svg:svg> m 2 yr −1 in Holocene ice, slightly faster than suggested by previous work. The effective diffusion rate observed in deeper ice is significantly lower, and Holocene ice shows the highest rate of the last 450 kyr. Beyond the Holocene, there is no systematic difference between the effective diffusion rates of glacial and interglacial periods despite variations in soluble ion concentrations, dust loading, and ice grain radii. Effective diffusion rates for 40 to 200 ka are relatively constant and of the order 1 × 10 - 8 <svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="42pt" height="14pt" class="svg-formula" dspmath="mathimg" ... |
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