Sea Ice Formation, Glacial Melt and the Solubility Pump Boundary Conditions in the Ross Sea.

Seasonal formation of Dense Shelf Water (DSW) in the Ross Sea is a direct precursor to Antarctic Bottom Water, which fills the deep ocean with atmospheric gases in what composes the southern limb of the solubility pump. Measurements of seawater noble gas concentrations during katabatic wind events in two Ross Sea polynyas reveal the physical processes that determine the boundary value properties for DSW. This decomposition reveals 5–6 g kg−1 of glacial meltwater in DSW and sea‐ice production rates of up to 14 m yr−1 within the Terra Nova Bay polynya. Despite winds upwards of 35 m s−1 during the observations, air bubble injection had a minimal contribution to gas exchange, accounting for less than 0.01 μmols kg−1 of argon in seawater. This suggests the slurry of frazil ice and seawater at the polynya surface inhibits air‐sea exchange. Most noteworthy is the revelation that sea‐ice formation and glacial melt contribute significantly to the ventilation of DSW, restoring 10% of the gas deficit for krypton, 24% for argon, and 131% for neon, while diffusive gas exchange contributes the remainder. These measurements reveal a cryogenic component to the solubility pump and demonstrate that while sea ice blocks air‐sea exchange, sea ice formation and glacial melt partially offset this effect via addition of gases. While polynyas are a small surface area, they represent an important ventilation site within the southern‐overturning cell, suggesting that ice processes both enhance and hinder the solubility pump. Plain Language Summary: Previous scientific studies have demonstrated that the water which fills the deep sea is created in isolated regions of the surface ocean where wind, evaporation, heat loss, and sea ice formation can work in concert to make very cold salty seawater at the ocean surface. As this water leaves the surface it can carry oxygen and carbon dioxide, as well as heat away from the atmosphere for nearly a millennium, suggesting the sequestration mechanism may impact earth's climate and human climate change. This study sought to reveal how different types of sea ice and glacier ice might influence the gases that are dissolved in seawater and sequestered in the ocean. We made measurements of the noble gases (helium, neon, argon, krypton, and xenon) in the Ross Sea in late fall of 2017, when the conditions are cold and windy, leading to lots of dense water production. The results reveal that sea ice interrupts the process of air‐sea exchange of gases, which can slow down the uptake of human‐generated carbon dioxide by dense water. But our results also revealed that sea ice formation and glacial ice melt can both add gas to dense water during its creation. Key Points: Noble gas tracers can infer the rate of sea ice production in polynyasFrazil ice in polynyas appears to block air‐sea gas exchange mechanismsThe solubility pump is influenced by glacial ice melt and sea ice formation [ABSTRACT FROM AUTHOR]

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