Highly Active Ice‐Nucleating Particles at the Summer North Pole

Abstract

The amount of ice versus supercooled water in clouds is important for their radiative properties and role in climate feedbacks. Hence, knowledge of the concentration of ice‐nucleating particles (INPs) is needed. Generally, the concentrations of INPs are found to be very low in remote marine locations allowing cloud water to persist in a supercooled state. We had expected the concentrations of INPs at the North Pole to be very low given the distance from open ocean and terrestrial sources coupled with effective wet scavenging processes. Here we show that during summer 2018 (August and September) high concentrations of biological INPs (active at >−20°C) were sporadically present at the North Pole. In fact, INP concentrations were sometimes as high as those recorded at mid‐latitude locations strongly impacted by highly active biological INPs, in strong contrast to the Southern Ocean. Furthermore, using a balloon borne sampler we demonstrated that INP concentrations were often different at the surface versus higher in the boundary layer where clouds form. Back trajectory analysis suggests strong sources of INPs near the Russian coast, possibly associated with wind‐driven sea spray production, whereas the pack ice, open leads, and the marginal ice zone were not sources of highly active INPs. These findings suggest that primary ice production, and therefore Arctic climate, is sensitive to transport from locations such as the Russian coast that are already experiencing marked climate change.

Using Novel Molecular-Level Chemical Composition Observations of High Arctic Organic Aerosol for Predictions of Cloud Condensation Nuclei

“…However, clouds in the summertime Arctic are normally mixed-phase 89 (consisting of both water droplets and ice), which was also the case during most of our expedition. 45 Measured INP 48 concentrations between September 11 and September 19 were however relatively low and exhibited a low ice-nucleating ability (freezing temperature at 0.1 INP L –1 was around −25 to −30 °C). This indicates that the clouds were largely composed of liquid droplets and that κ -Köhler theory can be used to predict the cloud activation, which simplifies the description of the aerosol–cloud interactions.…”

“…The geographical locations for the scientific activities ranged from the marginal ice zone (MIZ, ∼82° N) north of Svalbard to close to the North Pole (89° N), where the icebreaker was moored and drifting for nearly 5 weeks. The general goal of MOCCHA was to investigate potential links between marine microbiology, local aerosol emissions, and cloud formation in the central Arctic Ocean. ,,− …”

“…The general goal of MOCCHA was to investigate potential links between marine microbiology, local aerosol emissions, and cloud formation in the central Arctic Ocean. 29 , 38 , 42 − 48 …”

Physical and Chemical Properties of Cloud Droplet Residuals and Aerosol Particles During the Arctic Ocean 2018 Expedition

“…However, recently Porter et al. ( 2022 ) found that the most active INP in the central Arctic could be traced back to the waters and coasts of Siberia, while local sources in the pack ice and marginal ice zone were less important.…”

“…In the summertime high Arctic, the limited influence of long-range transport means more local sources may also be important Leck & Svensson, 2015). However, recently Porter et al (2022) found that the most active INP in the central Arctic could be traced back to the waters and coasts of Siberia, while local sources in the pack ice and marginal ice zone were less important.…”