Present and future variations in Antarctic firn air content
Present and future variations in Antarctic firn air content
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DOI：
10.5194/tc-8-1711-2014
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发表时间：
2014-09
期刊：
影响因子：
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通讯作者：
S. Ligtenberg;P. K. Munneke;M. Broeke
中科院分区：
文献类型：
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作者：
S. Ligtenberg;P. K. Munneke;M. Broeke
一个积雪致密化模式（FDM）被用来评估空间和时间（1979-2200年）的变化，在深度，密度和温度的积雪层覆盖的南极冰盖（AIS）。一个时间依赖的版本的FDM相比，更常用的稳态FDM的结果。虽然两个模型的平均AIS雪空气含量（FAC）是相似的（22.5米），大的空间差异被发现：在冰盖内部，稳态模型低估了FAC高达2米，而FAC高估了5-15米沿着冰盖边缘，由于显着的表面融化。应用稳态FAC值将表面高程转换为冰厚（即，假设接地线处的漂浮）可能导致接地线处的冰排放量被低估，因此，相对于1992-2011年期间的协调估计，当前AIS质量损失被低估了23.5%（或16.7 Gt/年）。测量的时间也很重要，因为在33年（1979-2012年）内模拟了1-2 m的FAC变化。直到2200年，南极FAC预计将改变由于增加积累，温度和表面融化的组合。后两个结果在FAC的减少，由于（i）更多的再冻结融水，（ii）更高的致密化率，（iii）更快的积雪到冰的过渡在积雪层的底部。然而，这些影响被增加的降雪所抵消，导致FAC增加4-14%。只有在受融化影响的地区，未来的FAC模拟下降，在南极半岛和德龙宁毛德地的冰架上变化最大（-50%至-80%）。在AIS上积分，降水量的增加导致冰和空气的体积增加相似（到2100年都约为150 km 3 yr −1）。总的来说，这一体积增加相当于地表海拔每年+2.1厘米的变化，这表明在未来利用卫星测高进行质量平衡研究时，考虑积雪深度的变化仍然很重要。
A firn densification model (FDM) is used to assess spatial and temporal (1979–2200) variations in the depth, density and temperature of the firn layer covering the Antarctic ice sheet (AIS). A time-dependent version of the FDM is compared to more commonly used steady-state FDM results. Although the average AIS firn air content (FAC) of both models is similar (22.5 m), large spatial differences are found: in the ice-sheet interior, the steady-state model underestimates the FAC by up to 2 m, while the FAC is overestimated by 5–15 m along the ice-sheet margins, due to significant surface melt. Applying the steady-state FAC values to convert surface elevation to ice thickness (i.e., assuming flotation at the grounding line) potentially results in an underestimation of ice discharge at the grounding line, and hence an underestimation of current AIS mass loss by 23.5% (or 16.7 Gt yr −1 ) with regard to the reconciled estimate over the period 1992–2011. The timing of the measurement is also important, as temporal FAC variations of 1–2 m are simulated within the 33 yr period (1979–2012). Until 2200, the Antarctic FAC is projected to change due to a combination of increasing accumulation, temperature, and surface melt. The latter two result in a decrease of FAC, due to (i) more refrozen meltwater, (ii) a higher densification rate, and (iii) a faster firn-to-ice transition at the bottom of the firn layer. These effects are, however, more than compensated for by increasing snowfall, leading to a 4–14% increase in FAC. Only in melt-affected regions, future FAC is simulated to decrease, with the largest changes (−50 to −80%) on the ice shelves in the Antarctic Peninsula and Dronning Maud Land. Integrated over the AIS, the increase in precipitation results in a similar volume increase due to ice and air (both ~150 km 3 yr −1 until 2100). Combined, this volume increase is equivalent to a surface elevation change of +2.1 cm yr −1 , which shows that variations in firn depth remain important to consider in future mass balance studies using satellite altimetry.