The effect of partial dissolution on sea-ice chemical transport: a combined model–observational study using poly- and perfluoroalkyl substances (PFAS)
Abstract. We investigate the effect of partial dissolution on the transport of chemicals in sea ice. Physically plausible mechanisms are added to a brine convection model that decouple chemicals from convecting brine. The model is evaluated against a recent observational dataset where a suite of qualitatively similar chemicals (poly- and perfluoroalkyl substances, PFAS) with quantitatively different physico-chemical properties were frozen into growing sea ice. With no decoupling the model performs poorly – failing to reproduce the measured concentrations of high chain-length PFAS. A decoupling scheme where PFAS are decoupled from salinity as a constant fraction, and a scheme where decoupling is proportional to the brine salinity, give better performance and bring the model into reasonable agreement with observations. A scheme where the decoupling is proportional to the internal sea-ice surface area performs poorly. All decoupling schemes capture a general enrichment of longer chained PFAS and can produce concentrations in the uppermost sea-ice layers above that of the underlying water concentration, as observed. Our results show that decoupling from convecting brine can enrich chemical concentrations in growing sea ice and can lead to bulk chemical concentrations greater than that of the liquid from which the sea ice is growing. Brine convection modelling is useful for predicting the dynamics of chemicals with more complex behaviour than sea salt, highlighting the potential of these modelling tools for a range of biogeochemical research.
Max Thomas et al.
Status: final response (author comments only)
RC1: 'Comment on tc-2023-37', Anonymous Referee #1, 13 Mar 2023
- AC1: 'Reply on RC1', Max Thomas, 25 May 2023
RC2: 'Comment on tc-2023-37', Anonymous Referee #2, 04 May 2023
- AC2: 'Reply on RC2', Max Thomas, 25 May 2023
Max Thomas et al.
Reproduction capsule for The effect of partial dissolution on sea-ice chemical transport: a combined model--observational study using poly- and perfluoroalkylated substances (PFAS) https://doi.org/10.24433/CO.6237417.v1
Max Thomas et al.
Viewed (geographical distribution)
Max Thomas et al. determine if and how a 1D parametrization of brine convection can be expanded to reproduce the laboratory PFA measurements of a previous study (Garnett et al. 2021). The paper consists of roughly four parts. In part one, the authors propose four different methods (A,B,C,D). In part two, they tune the free parameters of methods B, C, and D to minimize the absolute bias. In part three, they compare the model against the observed PFA profiles. Finally, in part four, they discuss if their results would apply to longer sea-ice simulations and other chemicals of interest.
The paper's text is clear and the method is clearly formulated (with one small exception) and applied thoroughly. The main conclusions are clearly stated, relevant to the field, and well supported by the results. The plots are mostly legible and not misleading, and the code has been made fully available. The topic of the submitted manuscript fits The Cryosphere. Based on my experience, the quality of the draft is well above average.
However, I found the structure of the paper's second half confusing, and the paper is somewhat ambiguous about its scope. Moreover, the figures could be improved upon, and there are a few minor other issues to address. Accordingly, I recommend accepting the submitted paper, but with minor revisions.
Minor comments in roughly descending importance
I am trying to understand why the authors chose the name method A instead of reference or control. It is not a flaw and does not need to change, but I did find it strange that the first "method of decoupling" is "none". Accordingly, there is alpha_B, alpha_C, and alpha_D, but no alpha_A, and so on.