Terrestrial or marine? – Indications towards the origin of Ice Nucleating Particles during melt season in the European Arctic up to 83.7° N

Abstract

Abstract. Ice nucleating particles (INPs) initiate the primary ice formation in clouds at temperatures above ca. −38° C and have an impact on precipitation formation, cloud optical properties and cloud persistence. Despite their roles in both weather and climate, INPs are not well characterized, especially in remote regions such as the Arctic. We present results from a ship-based campaign to the European Arctic in May to July 2017. We deployed a filter sampler and a continuous flow diffusion chamber for off- and online INP analysis, respectively. We also investigated the ice nucleation properties of samples from different environmental compartments, i.e., the sea surface microlayer (SML), the bulk seawater (BSW), and fog water. Concentrations of INP (NINP) in the air vary between two to three orders of magnitudes at any particular temperature and are, except for the temperatures above −10° C and below −32° C, lower than in mid-latitudes. In these temperature ranges INP concentrations are the same or even higher than in the mid-latitudes. Heating of the filter samples to 95° C for 1 hour we found a significant reduction in ice nucleation activity, i.e., indications that the INPs active at warmer temperatures are biogenic. At colder temperatures the INP population was likely dominated by mineral dust. The SML was found to be enriched in INP compared to the BSW in almost all samples. The enrichment factor (EF) varied mostly between 1 and 10, but EFs as high as 94.97 were also observed. Filtration of the seawater samples with 0.2 µm syringe filters lead to a significant reduction in ice activity, indicating the INPs are larger, and/or are associated with particles larger than 0.2 µm. A closure study showed that aerosolization of SML and/or seawater alone cannot explain the observed air-borne NINP unless significant enrichment of INP by a factor of 105 takes place during the transfer from the ocean surface to the atmosphere. In the fog water samples with −3.47° C we observed the highest freezing onset of any sample. A closure study connecting NINP in fog water and the ambient NINP derived from the filter samples shows good agreement of the concentrations in both compartments, which indicates that INPs in the air are likely all activated into fog droplets during fog events. In a case study we considered a situation during which the ship was located in the marginal sea ice zone and NINP in air and the SML were highest in the temperature range above −10° C. Chlorophyll-a measurements by satellite remote sensing point towards the waters in the investigated region being biologically active. Heat induced reduction of ice nucleating ability indicated the biogenic nature of the air-borne INPs. Similar slopes in the temperature spectra suggested a connection between the INP populations in the SML and the air. Air mass history had no influence on the observed air-borne INP population. Therefore, we conclude that during the case study collected air-borne INPs originated from a local biogenic probably marine source.

Ice nucleating particles in the Canadian High Arctic during the fall of 2018

“…[56][57][58][59][60] As a result, heating tests have been used in previous studies as a tool to identify possible biological INPs. [27][28][29]33,34,41,56,61,62 Consistent with previous studies, we assume that a decrease in the INP concentrations of the samples after heating indicates the presence of biological INPs, similar to previous studies in the Arctic. [27][28][29] For the heating assay, an aliquot of each suspension generated from the filter samples was located in polypropylene tubes capped with lids and heated at 100 °C 41,42 for one hour in a heating block (Accublock, Labnet).…”

“…[27][28][29]33,34,41,56,61,62 Consistent with previous studies, we assume that a decrease in the INP concentrations of the samples after heating indicates the presence of biological INPs, similar to previous studies in the Arctic. [27][28][29] For the heating assay, an aliquot of each suspension generated from the filter samples was located in polypropylene tubes capped with lids and heated at 100 °C 41,42 for one hour in a heating block (Accublock, Labnet). The freezing temperatures and INP concentrations of the heated samples were then determined as described in Section 2.2.…”

“…The findings based on the heat assay are consistent with previous studies that have shown biological particles as an important component of the INP population for certain times of the year at freezing temperatures ≥ -15 °C in the Arctic based on a similar heat treatment assay. [27][28][29] Overall, our results provide additional evidence that biological INPs likely make up a significant fraction of the INP population in the Arctic at freezing temperatures ≥ -15 °C and even lower temperatures for certain times of the year.…”

“…Several studies have measured the concentrations of INPs in the Arctic. [16][17][18][19][20][21][22][23][24][25][26][27][28][29][30] In most cases, these measurements were carried out for relatively short periods of time during intensive field campaigns. A few studies have quantified INP concentrations over longer periods of time.…”

“…Using a heat treatment assay, Šantl-Temkiv et al 27 showed that 82% to 100% of the INPs at T ≥ -15 °C over Greenland during the summer were likely biological. Also using a heat treatment assay, Hartmann and Adachi et al 28 and Hartmann and Gong et al 29 showed that for some of their samples collected over the Arctic Ocean during the spring and early summer, 100% of the INPs at T ≥ -15 °C were likely biological. In addition, other researchers have speculated that biological particles were an important source of INPs in the Arctic based on the warm freezing temperatures (T > -15 °C) of their samples.…”