Academic Journal
Sea-ice dynamics strongly promote Snowball Earth initiation and destabilize tropical sea-ice margins
| العنوان: | Sea-ice dynamics strongly promote Snowball Earth initiation and destabilize tropical sea-ice margins |
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| المؤلفون: | Voigt, A., Abbot, D. S. |
| المصدر: | eISSN: 1814-9332 |
| سنة النشر: | 2018 |
| المجموعة: | Copernicus Publications: E-Journals |
| الوصف: | The Snowball Earth bifurcation, or runaway ice-albedo feedback, is defined for particular boundary conditions by a critical CO 2 and a critical sea-ice cover (SI), both of which are essential for evaluating hypotheses related to Neoproterozoic glaciations. Previous work has shown that the Snowball Earth bifurcation, denoted as (CO 2 , SI) * , differs greatly among climate models. Here, we study the effect of bare sea-ice albedo, sea-ice dynamics and ocean heat transport on (CO 2 , SI) * in the atmosphere–ocean general circulation model ECHAM5/MPI-OM with Marinoan (~ 635 Ma) continents and solar insolation (94% of modern). In its standard setup, ECHAM5/MPI-OM initiates a~Snowball Earth much more easily than other climate models at (CO 2 , SI) * ≈ (500 ppm, 55%). Replacing the model's standard bare sea-ice albedo of 0.75 by a much lower value of 0.45, we find (CO 2 , SI) * ≈ (204 ppm, 70%). This is consistent with previous work and results from net evaporation and local melting near the sea-ice margin. When we additionally disable sea-ice dynamics, we find that the Snowball Earth bifurcation can be pushed even closer to the equator and occurs at a hundred times lower CO 2 : (CO 2 , SI) * ≈ (2 ppm, 85%). Therefore, the simulation of sea-ice dynamics in ECHAM5/MPI-OM is a dominant determinant of its high critical CO 2 for Snowball initiation relative to other models. Ocean heat transport has no effect on the critical sea-ice cover and only slightly decreases the critical CO 2 . For disabled sea-ice dynamics, the state with 85% sea-ice cover is stabilized by the Jormungand mechanism and shares characteristics with the Jormungand climate states. However, there is no indication of the Jormungand bifurcation and hysteresis in ECHAM5/MPI-OM. The state with 85% sea-ice cover therefore is a soft Snowball state rather than a true Jormungand state. Overall, our results demonstrate that differences in sea-ice dynamics schemes can be at least as important as differences in sea-ice albedo for causing the spread in climate ... |
| نوع الوثيقة: | text |
| وصف الملف: | application/pdf |
| اللغة: | English |
| Relation: | https://cp.copernicus.org/articles/8/2079/2012/ |
| DOI: | 10.5194/cp-8-2079-2012 |
| الاتاحة: | https://doi.org/10.5194/cp-8-2079-2012 https://cp.copernicus.org/articles/8/2079/2012/ |
| رقم الانضمام: | edsbas.1ECB22B6 |
| قاعدة البيانات: | BASE |
| DOI: | 10.5194/cp-8-2079-2012 |
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