Sea ice coverage and water depth influence dissolved organic matter composition in Arctic waters and generated aerosols

Arctic warming has resulted in record sea ice reduction, increasing the length and extent of photosynthetic microorganism blooms, which impact water chemistry through the production and cycling of organic carbon. Chemical species in surface waters can become aerosolized, affecting atmospheric chemistry, cloud dynamics, and ultimately, radiative budgets. A greater understanding of how Arctic water and aerosol chemistry change with sea ice coverage is pivotal in modeling ocean-atmosphere dynamics in a changing climate. As such, water samples were collected from the marginal ice zone (MIZ) to pack ice conditions in the high Arctic Ocean and added to a marine aerosol reference tank to generate and collect aerosols for further characterization. Water and aerosol dissolved organic matter (DOM) was isolated using PPL solid phase extraction resin and characterized using high-resolution Fourier transform ion cyclotron resonance mass spectrometry. Analysis of seawater samples revealed that greater heteroatom (N, S, P) abundance was characteristic of the MIZ seawater DOM relative to pack ice seawater DOM. Greater phytoplankton and bacterial cell counts found in MIZ seawater suggests that greater microbial activity results in greater heteroatom assimilation into their biomass, as measured in the marine DOM characterized here. Surface water samples collected at approximately 100 µm and 1 m were chemically similar, containing DOM with more surface-active lipid- and protein-like compounds and devoid of more photo-labile, lignin-like/carboxylic-rich alicyclic material, which was abundant in deeper waters (3–8 m), indicating the strong influence of photochemical and biological processes on DOM chemistry. Aerosol DOM did not mirror water DOM chemistry, but rather certain compounds appeared to be preferentially aerosolized. Aerosol DOM was more aliphatic in character, less oxidized, with greater heteroatom content, proteins, carbohydrates, and unsaturated hydrocarbons relative to the source water.