Air bubble to clathrate hydrate transformation in polar ice sheets: A reconsideration based on the new data from Dome Fuji ice core

Abstract

[1] Mapping the spatial distribution of air bubbles and clathrate hydrates in thick sections of Antarctic ice from Dome Fuji station reveals a considerable redistribution of the inclusions in terms of number and volume in the bubbleto-hydrate transition zone. Analysis of the data indicated that more than 10% of the hydrates nucleated outside the preceding bubbles and more than 30% of the bubbles completely expired due to the gas outflow toward the coexisting hydrates. These features of the gas-hydrate-ice nonequilibrium system are of major importance for modeling the global bubble-to-hydrate transformation in polar ice sheets and thus the results may help improve our ability to extract paleoclimatic information from air inclusions in ice cores.

Studies of hydrate nucleation with high pressure differential scanning calorimetry

“…At low subcoolings this can have a very low probability since the critical radius can be appreciable. In the case of hydrate formation from air inclusions in ice cores, nucleation can take thousands of years (Ohno et al, 2004;Salamantin et al, 1998Salamantin et al, , 2001Shimanda and Hondoh, 2004). At higher subcoolings, the difference in free energy between the parent and daughter phase increases, this shifts the critical nucleus to lower radii.…”

How air bubbles form in polar ice.

“…4, a) along the edges of ice crystals similar in shape to equilibrium polyhedrons that fill the whole space, like tetrakaidecahedrons of Lord Kelvin and Robert Williams [Maeno and Ebinuma, 1983]. Pores in fi rn close off and the air remaining in the pore volume becomes 1 -δD (‰) according to diff erent estimates: [Jouzel et al, 2007] (a), [Watanabe et al, 2003] (b), [Petit et al, 1999] (c) (δD scales are inverse); 2 -number of air bubbles per unit mass (N, g -1 ), according to diff erent estimates: this study (a), [Ohno et al, 2004] (b), [Lipenkov and Salamatin, 2014] (c). Horizontal dash lines are average N in LGM ice deposited in Holocene climate.…”

“…1.08 60 [Ohno et al, 2004] 22 Dome A 80°22′ S, 77°22′ E -58.5 2.32 0.41 2933 1.50 75 This study N o t e. T is snow temperature at the depth where it becomes seasonally invariable (10-15 m); b is snow accumulation rate; d s is relative density of snow on ice sheet surface; τ c * and τ c are, respectively, ages of ice at the fi rn/ice transition, measured and calculated using equation 11; A c is calculated ice grain size at the fi rn/ice transition; 〈r c 〉 and s are, respectively, mean radius of air bubbles at the fi rn/ice transition and its variance; N is measured number of air bubbles per unit mass, with two-sigma error. N and A c values for LGM ice are additionally quoted for Vostok, Concordia and Dome Fuji cores (Fig.…”

“…The fi rst data thus obtained for ice cores from the Concordia and Kohnen research stations agree, within an exper-imental error, with the measurements by the author used in this study. Figure 2 shows measured numbers of air bubbles from the Vostok [Lipenkov and Salamatin, 2014], Dome Fuji [Ohno et al, 2004], and Concordia (this study) ice cores. According to isotope analysis of ice, the depth profi les of air bubble properties presented in Fig.…”

“…No. Drill site Coordinates [Gow and Williamson, 1975] 9 KM200 68°15′ S, 94°05′ E -30.5 26.4 0.49 175 174 1.93 65 [Lipenkov et al, 1999] 10 WAIS 79°28′ S, 112°05′ W -31.0 20.2 0.42 -217 2.14 15 [Fegyveresi et al, 2011] 11 NGRIP 75°06′ N, 42°19′ W -31.5 17.5 0.35 -272 2.40 20 [Kipfstuhl et al, 2001] 12 GRIP 72°35′ N, 37°38′ W -31.7 21.2 0.41 220 224 2.09 50 [Pauer et al, 1999] 13 KM260 68°46′ S, 94°28′ E -33.5 6.9 0.51 455 535 3.39 0.41 0.37 52 [Lipenkov et al, 1999] 14 KM325 69°18′ S, 95°01′ E -37.0 14.0 0.49 356 339 1.91 0.38 0.35 45 [Lipenkov et al, 1999] 15 KM400 69°57′ S, 95°37′ E -39.9 15.4 0.47 389 342 1.59 0.36 0.33 49 [Lipenkov et al, 1999] 16 Talos [Lipenkov, 2000] 21 Dome Fuji 77°19′ S, 39°42′ E -57.3 3.1 0.34 2424 2249 1.39 20 [Ohno et al, 2004] Dome Fuji (LGM)…”