Evidence and Mass Quantification of Atmospheric Microplastics in a Coastal New Zealand City.

This study investigated the atmospheric deposition of microplastics (MPs) in Auckland, New Zealand, from two sampling sites over a 9-week period. The sizes, morphologies, number counts, and mass concentrations of specific polymers were determined for airborne MPs using a combination of a Nile Red-assisted automated fluorescence microscopy technique in series with pyrolysis-gas chromatography-mass spectrometry (Pyr-GC/MS). This enabled a larger number of MPs to be analyzed from each sample compared to traditional spectroscopic techniques. Microplastic number concentrations increased exponentially with decreasing size. The results show the importance of using consistent methodologies and size cutoffs when comparing microplastic data between studies. Eight polymers were quantified in the atmospheric deposition samples, with polyethylene (PE), polycarbonate (PC), and poly(ethylene terephthalate) (PET) being the most commonly observed. The largest MP deposition rates at an urban rooftop correlated with winds originating from the marine environment with speeds between 15 and 20 m s-1, indicating that airborne MPs in coastal regions may originate from wave-breaking mechanisms. This study represents the first report of using Pyr-GC/MS to determine the chemical compositions and mass concentrations of atmospheric microplastics, along with corresponding data on their sizes, morphologies, and number counts.

Group 2i Isochrysidales produce characteristic alkenones reflecting sea ice distribution.

Alkenones are biomarkers produced solely by algae in the order Isochrysidales that have been used to reconstruct sea surface temperature (SST) since the 1980s. However, alkenone-based SST reconstructions in the northern high latitude oceans show significant bias towards warmer temperatures in core-tops, diverge from other SST proxies in down core records, and are often accompanied by anomalously high relative abundance of the C37 tetra-unsaturated methyl alkenone (%C37:4). Elevated %C37:4 is widely interpreted as an indicator of low sea surface salinity from polar water masses, but its biological source has thus far remained elusive. Here we identify a lineage of Isochrysidales that is responsible for elevated C37:4 methyl alkenone in the northern high latitude oceans through next-generation sequencing and lab-culture experiments. This Isochrysidales lineage co-occurs widely with sea ice in marine environments and is distinct from other known marine alkenone-producers, namely Emiliania huxleyi and Gephyrocapsa oceanica. More importantly, the %C37:4 in seawater filtered particulate organic matter and surface sediments is significantly correlated with annual mean sea ice concentrations. In sediment cores from the Svalbard region, the %C37:4 concentration aligns with the Greenland temperature record and other qualitative regional sea ice records spanning the past 14 kyrs, reflecting sea ice concentrations quantitatively. Our findings imply that %C37:4 is a powerful proxy for reconstructing sea ice conditions in the high latitude oceans on thousand- and, potentially, on million-year timescales.

The emergence of modern sea ice cover in the Arctic Ocean.

Arctic sea ice coverage is shrinking in response to global climate change and summer ice-free conditions in the Arctic Ocean are predicted by the end of the century. The validity of this prediction could potentially be tested through the reconstruction of the climate of the Pliocene epoch (5.33-2.58 million years ago), an analogue of a future warmer Earth. Here we show that, in the Eurasian sector of the Arctic Ocean, ice-free conditions prevailed in the early Pliocene until sea ice expanded from the central Arctic Ocean for the first time ca. 4 million years ago. Amplified by a rise in topography in several regions of the Arctic and enhanced freshening of the Arctic Ocean, sea ice expanded progressively in response to positive ice-albedo feedback mechanisms. Sea ice reached its modern winter maximum extension for the first time during the culmination of the Northern Hemisphere glaciation, ca. 2.6 million years ago.