Ice nucleating abilities of deep waters from the Mexican Pacific ocean

Marine aerosol particles from biogenic origin are able to act as ice nucleating particles (INPs) and can play an important role in mixed-phase cloud formation. Although several field campaigns have been performed in the Atlantic, Arctic, and Southern oceans to evaluate the ice nucleating abilities of marine aerosol particles, this is not the case for the eastern Pacific Ocean, especially at the coasts of Mexico. The ice nucleating abilities via immersion freezing, of water samples collected during two oceanographic cruises in the Gulf of California (GoC) and off the west coast of the Baja California Peninsula (WBCP) at three different depths (i.e., 3–7 m, 10–72 m, and 500 m) were evaluated. The onset freezing temperature of the water samples from the GoC ranged between −10 °C and −22 °C, while it varied between −14.5 °C and −23 °C for the WBCP samples. The median freezing temperatures (i.e., the temperature at which 50% of the droplets freeze, T50) from both sets of samples was found to decrease with depth, indicating that superficial waters contain more ice active material. Although some meteorological variables (i.e., temperature, salinity, and chlorophyll-a), nutrients concentration, and primary production showed differences between the sampling points and depth, the obtained correlations with T50 were not statistically significant. The INP concentration of the GoC and the WBCP samples varied between 2 × 102 L−1 and 9 × 104 L−1 at a freezing temperature range from −10 °C to −36 °C. These concentrations are in agreement with those measured in the Gulf of Mexico; however, they are two orders of magnitude lower than those reported at higher latitudes. Even though it is clear that the ocean-atmosphere exchange takes place at the sea surface microlayer, it was found that deep waters also contain ice active material. Although the present results suggest that the Mexican Pacific Ocean is not a great source of INPs, in the absence of efficient INPs such as mineral dust or terrestrial bioparticles, the locally emitted marine aerosol particles can likely impact mixed-phase cloud formation.