Super-cooled glacial deep waters

Sea-ice formation in the Southern Ocean can generate supercooled waters, which can even remain below the in-situ freezing point at depths below 1,000 m. These water masses can play an important role in carbon transport to the abyssal ocean and may have therefore also played an important role in glacial-interglacial CO2 cycles.

To address this question, we examined model outputs from the transient 3 Ma simulation conducted with the CESM1.2 model (Community Earth System Model version 1.2, ~3.75 horizontal resolution. This simulation was driven by time-varying orbital forcing and estimates of atmospheric greenhouse gas concentrations and northern hemispheric ice-sheet orography and albedo. Our analysis shows the presence of large swaths of supercooled glacial deep waters mainly in the northern Pacific. This water is originally formed in the seasonal sea-ice formation regions in the subarctic North Pacific during periods of brine release and rapid mixed layer deepening. During interglacial periods, the volume of supercooled water decreases, which may hint towards a possible positive climate-carbon cycle feedback.

In climate models the freezing condition is usually only applied at the surface. Hence, they are incapable of simulating brinicles – vertical sea-ice structures that can extend from the surface to shallower depths, sometimes even reaching the ocean floor. In my presentation, I will address whether such structures may have played a more prominent role during glacial periods, and whether localized deep ocean freezing may have been a possibility.