Stable Isotope Clues to the Formation and Evolution of Refrozen Melt Ponds on Arctic Sea Ice

Abstract

Sea ice is one of the determining parameters of the climate system. The presence of melt ponds on the surface of Arctic sea ice plays a critical role in the mass balance of sea ice. A total of nine cores was collected from multiyear ice refrozen melt ponds and adjacent hummocks during the 2015 Arctic Sea State research cruise. The depth profiles of water isotopes, salinity, and ice texture for these sea ice cores were examined to provide information about the development of refrozen melt ponds and water balance generation processes, which are otherwise difficult to acquire. The presence of meteoric water with low oxygen isotope values as relatively thin layers indicates melt pond water stability and little mixing during formation and refreezing. The hydrochemical characteristics of refrozen melt pond and seawater depth profiles indicate little snowmelt enters the upper ocean during melt pond refreezing. Due to the seasonal characters of deuterium excess for Arctic precipitation, water balance calculations utilizing two isotopic tracers (oxygen isotope and deuterium excess) suggest that besides the melt of snow cover, the precipitation input in the melt season may also play a role in the evolution of melt ponds. The dual‐isotope mixing model developed here may become more valuable in a future scenario of increasing Arctic precipitation. The layers of meteoric origin were found at different depths in the refrozen melt pond ice cores. Surface topography information collected at several core sites was examined for possible explanations of different structures of refrozen melt ponds.

Overview of the Arctic Sea State and Boundary Layer Physics Program

“…The program also observed multiyear floes, including the study by Tian et al () which uses isotopes to understand the relative importance of snow melt and seawater, especially in melt ponds. An example of multiyear ice is shown in Figure .…”

Contribution of Snow to Arctic First‐Year and Multi‐Year Sea Ice Mass Balance Within the Last Ice Area

“…Tian et al (2018) calculated a mean total snow fraction contribution to ice mass for MYI in the Beaufort and Chukchi seas (2015) of 19% (range: 5%-30%), a slightly higher value than our average of 10% (4%-24%) but within a similar range (Table 1). The thinner MYI sampled during the Tian et al (2018) summer study (0.23-1.58 m) may be related to the higher bottom ice-melt rates in the Beaufort Sea, relative to other regions of the Arctic (Perovich & Richter-Menge, 2015), causing the upper portions of the sea ice to have more snow-melt water input (e.g., melt ponds, superimposed/interposed ice). The thinner MYI and increased bottom ice melt rates can explain the observed higher percentages in the Beaufort Sea compared to our thicker MYI samples.…”

“…This is evident by the higher snow fraction contribution, f s,mid values at or near the surface of the cores with the smallest freeboard (cores: 10-4, 11-1, 11-5, 12-1; Figures 2 and 3; Table 1). Tian et al (2018) also observed higher snow-melt fraction in the depressed regions owing to the formation of melt ponds in these regions. Peaks or higher f s,mid values in the upper portion of the ice, other than near the surface (e.g., 10-2, 10-5, 11-6, 12-1; Figures 2 and 3; Table 1), most likely represent interposed ice layers.…”

“…This is a conservative estimate given that not all snow melt would be integrated and refrozen within the sea ice as some of the snow-melt water percolates through the ice or drains over the floe edge (Polashenski et al, 2012). Tian et al (2018) calculated a mean total snow fraction contribution to ice mass for MYI in the Beaufort and Chukchi seas (2015) of 19% (range: 5%-30%), a slightly higher value than our average of 10% (4%-24%) but within a similar range (Table 1). The thinner MYI sampled during the Tian et al (2018) summer study (0.23-1.58 m) may be related to the higher bottom ice-melt rates in the Beaufort Sea, relative to other regions of the Arctic (Perovich & Richter-Menge, 2015), causing the upper portions of the sea ice to have more snow-melt water input (e.g., melt ponds, superimposed/interposed ice).…”

Snow-ice contribution to the structure of sea ice in the Amundsen Sea, Antarctica

“…The ice sections are not a closed system for water isotopes due to brine drainage or convective transport during the snow-ice formation and freezing (Golden and others, 1998). While in an Arctic study (Tian and others, 2018), the hydrochemical characteristics of sea-ice core and seawater depth profiles indicated little snowmelt enters the upper ocean during sea-ice evolution. Since it is not known how much of the meteoric signature in the slush drains into the ocean during freezing in this study, we instead assume that the meteoric signal is 'diffused' through the ice column but not lost to the ocean.…”