Evaluation of Ice Nucleating Particles and their Sources in the Central Arctic During MOSAiC

Abstract

The accelerated rate of warming in the Arctic is of great concern due to potential impacts that include the release of greenhouse gases from permafrost, melting glacial ice contributing to sea level rise, and declining sea ice cover exposing the darker ocean surface. These processes induce positive feedbacks and contribute to further warming that affects climate globally. Clouds play a crucial role in regulating the energy reaching the sea ice and snow surfaces, but the magnitude of their effects on surface temperature is not well constrained in the Arctic. Aerosols are also an important contributor by serving as seeds for cloud particle formation, but even less is known about their overall impact and origin. In particular, aerosols that serve as ice nucleating particles (INPs) are vastly understudied, especially above the central Arctic Ocean. However, INPs likely play a significant role in Arctic mixed-phase cloud (AMPC) microphysics and the resulting impacts of such clouds on the surface energy budget.

To date, a full year’s worth of INP measurements have not been conducted anywhere in the Arctic, and no INP data exist from the central Arctic in the winter or spring, creating a significant gap in understanding AMPC microphysical processes. The year-long transpolar drift experiment, Multidisciplinary drifting Observatory for Study of Arctic Climate (MOSAiC), will start in fall 2019 and provide the unique opportunity to execute these novel INP measurements.

The overarching goal of this project is to achieve unprecedented characterization of INP abundance and sources (including biological vs. mineral) to evaluate their capacity to modulate cloud ice formation over the central Arctic. Under the context of this overarching goal, our project targets three main scientific objectives:

Objective 1: Process size-resolved and total aerosol samples collected during MOSAiC for quantitative INP measurements and aerosol microbiological characterization to produce a high-quality dataset to be made available to the scientific community.

Objective 2: Coordinate collection of seawater, surface microlayer (SML), snow, and ice samples for assessment of local INP sources to leverage ARM and ASR aerosol INP measurements.

Objective 3: Address a set of targeted scientific research questions based on current gaps in the understanding of INPs in the central Arctic:

• • How do seasonal changes in sea ice and air mass transport influence INP abundance and sources in the central Arctic?
  • Are marine and sea ice biological processes a significant source of atmospheric INPs as compared to terrestrial sources?
  • Are open water environments such as leads and melt ponds viable sources of INPs over the sea ice, and do such environments exchange INPs with the atmosphere?

Currently, the DOE Atmospheric Radiation Measurement (ARM) program has funded collection of a continuous time series of size-resolved and total aerosol samples during MOSAiC. These measurement efforts will be conducted over an entire year to capture trends and variability spanning a full sea ice cycle and involves deployment of two aerosol collectors with the second ARM Mobile Facility (AMF2) on the Polarstern icebreaker. The project described here will support the processing of these samples toward the aforementioned objectives and to use this information to address our stated research questions.

The information afforded from the proposed INP and biological analyses are currently a critical gap in DOE and MOSAiC science. Collaboration with several of the MOSAiC teams, including the Atmosphere, Ecosystems, Biogeochemistry, and Sea-ice teams, will provide synergistic opportunities to evaluating aerosol-cloud interactions through coordination of sample collection and collaboration using holistic and multidisciplinary datasets. Results from the proposed work will leverage ARM and ASR resources and inform models of all scales through improvement of understanding Arctic aerosol-cloud interactions from detailed observations at the atmosphere-ocean-sea ice interface.