The impact of ice layers on gas transport through firn at the North Greenland Eemian Ice Drilling (NEEM) site, Greenland

摘要

Typically, gas transport through firn is modeled in the context of anidealized firn column. However, in natural firn, imperfections are present,which can alter transport dynamics and therefore reduce the accuracy ofreconstructed climate records. For example, ice layers have been found inseveral firn cores collected in the polar regions. Here, we examined theeffects of two ice layers found in a NEEM, Greenland firn core on gastransport through the firn. These ice layers were found to have permeabilityvalues of 3.0 and 4.0 × 10−10 m2, and are therefore notimpermeable layers. However, the shallower ice layer was found to besignificantly less permeable than the surrounding firn, and can thereforeretard gas transport. Large closed bubbles were found in the deeper icelayer, which will have an altered gas composition than that expected because theywere closed near the surface after the water phase was present. The bubblesin this layer represent 12% of the expected closed porosity of this firnlayer after the firn-ice transition depth is reached, and will thereforebias the future ice core gas record. The permeability and thickness of theice layers at the North Greenland Eemian Ice Drilling (NEEM) site suggest that they do not disrupt the firn-airconcentration profiles and that they do not need to be accounted for in gas transportmodels at NEEM.