The amount of ice versus supercooled water in clouds defines their
radiative properties and role in climate feedbacks. Hence, knowledge of
the concentration of ice-nucleating particles (INPs) is needed.
Generally, the concentrations of INP is found to be very low in remote
marine locations allowing clouds to persist in a supercooled state.
However, little is known about the INP population in clouds at and
around the summertime North Pole. We had expected that concentrations of
INPs at the North Pole would have been 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 present at the North Pole. In fact, INP concentrations were
sometimes as high as those recorded in 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 that there were 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.