Methanesulfonic acid (MSA) migration in polar ice: data synthesis and theory

Abstract

Abstract. Methanesulfonic acid (MSA; CH 3 SO 3 H) in polar ice is a unique proxy of marine primary productivity, synoptic atmospheric transport, and regional sea-ice behavior. However, MSA can be mobile within the firn and ice matrix, a post-depositional process that is well known but poorly understood and documented, leading to uncertainties in the integrity of the MSA paleoclimatic signal. Here, we use a compilation of 22 ice core MSA records from Greenland and Antarctica and a model of soluble impurity transport in order to comprehensively investigate the vertical migration of MSA from summer layers, where MSA is originally deposited, to adjacent winter layers in polar ice.We find that the shallowest depth of MSA migration in our compilation varies over a wide range (∼ 2 to 400 m) and is positively correlated with snow accumulation rate and negatively correlated with ice concentration of Na + (typically the most abundant marine cation). Although the considered soluble impurity transport model provides a useful mechanistic framework for studying MSA migration, it remains limited by inadequate constraints on key physicochemical parameters -most notably, the diffusion coefficient of MSA in cold ice (D MS ). We derive a simplified version of the model, which includes D MS as the sole parameter, in order to illuminate aspects of the migration process. Using this model, we show that the progressive phase alignment of MSA and Na + concentration peaks observed along a high-resolution West Antarctic core is most consistent with 10 −12 m 2 s −1 < D MS < 10 −11 m 2 s −1 , which is 1 order of magnitude greater than the D MS values previously estimated from laboratory studies. More generally, our data synthesis and model results suggest that (i) MSA migration may be fairly ubiquitous, particularly at coastal and (or) highaccumulation regions across Greenland and Antarctica; and (ii) can significantly change annual and multiyear MSA concentration averages. Thus, in most cases, caution should be exercised when interpreting polar ice core MSA records, although records that have undergone severe migration could still be useful for inferring decadal and lower-frequency climate variability.

A Comparison of 36Cl Nuclear Bomb Inputs Deposited in Snow From Vostok and Talos Dome, Antarctica, Using the 36Cl/Cl− ratio

“…According to Wagnon et al (), this results from an increase in the Cl − concentration toward the surface which can be explained by HCl mobility in snow. Gas migration in polar ice has also been evidenced for other elements, such as nitric acid (HNO 3 , Mayewski & Legrand, ), or methanesulfonic acid (Osman et al, ). Both the HCl migrating from the deeper part of the snow pit and the newly deposited chlorine will thus accumulate within the upper meters (Figure b, blue line).…”

Pervasive diffusion of climate signals recorded in ice-vein ionic impurities

“…In the GRIP runs, we use the depth-age scale t (z) and velocity w(z) from a Dansgaard-Johnsen model with the ice thickness H = 3029 m, the kink at 1000 m above the bed, and surface accumulation rate a = 0.23 m yr −1 ice equivalent. In the EPICA runs, we use t (z) and w(z) from the model w (Ritz, 1992) with H = 3275 m, n = 1.7, a = 0.023 m yr −1 , and the basal melt rate m base = 0.0008 m yr −1 , which yields a depth-age scale approximating the one published by Parrenin et al (2007). Smoothed versions of T (z) and d g (z) measured at the ice-core sites are used (Fig.…”

Examining links between dust deposition and phytoplankton response using ice cores

“…A potentially more precise age estimate of the base of the SGC can be provided by matching the depth at which MSA disappears to the climate conditions likely to be responsible for the loss of MSA at 6.48 m depth. While a variety of factors can lead to MSA mobility in ice cores (Osman et al, 2017), the movement of liquid water is the most likely cause of MSA loss in this case (Moore et al, 2005; Supplementary material). The presence of liquid water in the snow pack is most likely during snow pack melt during warm temperatures.…”