shelf. The radiocarbon content of DOC in the surface water of the ASP reflected higher primary production than in the region covered by sea ice. The radiocarbon measurements of DOC, taken two years apart in the ASP, were different, suggesting rapid cycling of DOC. The increase in DOC concentration was less than expected from the observed increase in radiocarbon content from those at the greatest depths. Based on a radiocarbon mass balance, we show that deep-DOC is consumed along with fresh-DOC in the ASP. Our observations imply that water circulation through the surface layer, where fresh-DOC is produced, may play an important role in global DOC cycling.

Farnsworth, K.K., Chevrier, V.F., Steckloff, J.K., Laxton, D., Singh, S., Soto, A., Soderblom, J.M., 2019. Nitrogen exsolution and bubble formation in Titan's lakes. Geophysical Research Letters 46, 13658-13667.

https://doi.org/10.1029/2019GL084792 Abstract: Titan's surface liquids are composed primarily of methane, ethane, and dissolved atmospheric nitrogen. The nitrogen content depends on the alkane composition and temperature, and exsolves as bubbles when these parameters are sufficiently perturbed. Herein, we present an experimental study of nitrogen bubbles in methane - ethane liquids, and propose that both methane and ethane are required for bubbles to form under Titan conditions. Bubbles occur when methane composes 40 - 95 mol% of the alkanes within the liquid. We identify two mechanisms that produce bubbles: ethane mediated titration and temperature-induced stratification. Both of these mechanisms produce a metastable nitrogen supersaturation within the liquid; equilibration triggers rapid nitrogen exsolution in the form of bubbles. Such equilibration could cause bubble events in Titan's lakes, possibly explaining the transient 'Magic Island' features seen by Cassini RADAR (bubbles within the liquid column), and the presence of deltas in Ontario Lacus. Plain Language Summary: Saturn's largest moon, Titan, has stable lakes on its surface composed of liquid methane, ethane, and dissolved atmospheric nitrogen. While nitrogen can dissolve into the liquid (dissolution), it can also be forced out of the liquid (exsolution). Nitrogen bubbles in Titan's lakes have been hypothesized, but not experimentally measured under Titan surface conditions. Here we create bubbles in a laboratory under Titan conditions using two methods: ethane slowly added to methane (titrat ion) and temperature-induced methane-ethane liquid layering (cooling then warming). Both mechanisms create a metastable supersaturation of nitrogen. Once the metastable limit is reached, bubble nucleation occurs, triggering rapid bubble formation. Transien t bright structures observed in Titan's lakes by the Cassini RADAR, known as 'Magic Islands,' may in fact be bubbles within the liquid column. Bubbles can also form in rivers as they flow into lakes and seas, potentially influencing geologic structures, such as the delta seen in one of Titan's largest lakes, Ontario Lacus.

Fayet, A.L., Hansen, E.S., Biro, D., 2020. Evidence of tool use in a seabird. Proceedings of the National Academy of Sciences 117, 1277-1279.

https://doi.org/10.1073/pnas.1918060117 Documenting novel cases of tool use in wild animals can inform our understanding of the evolutionary drivers of the behavior's emergence in the natural world. We describe a previously unknown tool -use behavior for wild birds, so far only documented in the wild in primates and elephants. We observed 2 Atlantic puffins at their breeding colonies, one in Wales and the other in Iceland (the latter captured on camera), spontaneously using a small wooden stick to scratch their bodies. The importance of these observations is 3-fold. First, while to date only a single form of body-care-related tool use has been recorded in wild birds (anting), our finding shows that the wild avian tool-use repertoire is wider than previously thought and extends to contexts other than food extraction. Second, we expand the taxonomic breadth of tool use to include another group of birds, seabirds, and a different suborder (Lari). Third, our independent observations span a distance of more than 1,700 km, suggesting that occasional tool use may be widespread in this group, and that seabirds' physical cognition may have been underestimated.

Ferguson, A., Solo-Gabriele, H., Mena, K., 2020. Assessment for oil spill chemicals: Current knowledge, data gaps, and uncertainties addressing human physical health risk. Marine Pollution Bulletin 150, 110746.