The amount of ice present in clouds can affect cloud lifetime, precipitation and radiative properties 1,2 . The formation of ice in clouds is facilitated by the presence of airborne ice nucleating particles 1,2 . Sea spray is one of the major global sources of atmospheric particles, but it is unclear to what extent these particles are capable of nucleating ice 3-11 . Sea spray aerosol contains large amounts of organic material that is ejected into the atmosphere during bubble bursting at the organically enriched sea-air interface or sea surface microlayer [12][13][14][15][16][17][18][19] . Here we show that organic material in the sea surface microlayer nucleates ice under conditions relevant for mixed-phase cloud and high-altitude ice cloud formation. The ice nucleating material is likely biogenic and less than ~0.2 μm in size. We find that exudates separated from cells of the marine diatom T. Pseudonana nucleate ice and propose that organic material associated with phytoplankton cell exudates is a likely candidate for the observed ice nucleating ability of the microlayer samples. Global model simulations of marine organic aerosol in combination with our measurements suggest that marine organic material may be an important source of ice nucleating particles in remote marine environments such as the Southern Ocean, North Pacific and North Atlantic.Atmospheric ice nucleating particles (INPs) allow ice to nucleate heterogeneously at higher temperatures or lower relative humidity than is typical for homogeneous ice nucleation. Heterogeneous ice nucleation proceeds via different pathways depending on temperature and humidity. In low altitude mixed-phase clouds, INPs are commonly immersed in supercooled liquid droplets and freezing can occur on them at temperatures between -36 and 0°C 2 . At higher altitudes and lower temperatures (<-36°C) where cirrus clouds form, nucleation occurs below water saturation, proceeding by homogeneous, deposition or immersion-in-solution nucleation 1 . Understanding the sources of atmospheric INPs is important because they affect cloud lifetime, cloud albedo and precipitation 1,2 . Recent modelling work has shown that the ocean is potentially an important source of biogenic atmospheric INPs particularly in remote, high latitude regions 9,10 . However, it has never been directly shown that there is a source of atmospheric INPs associated with organic material found in marine waters or sea-spray aerosol.Organic material makes up a substantial fraction of sub-micron sea-spray aerosol and it is estimated that 10±5 Tg yr -1 of primary organic sub-micron aerosol is emitted from marine sources globally 12 . Rising bubbles scavenge surface active organic material from the water column at their interfaces and this process facilitates the formation of the organic enriched sea-air interface known as the sea surface microlayer (SML). This organic material is ejected into the atmosphere during bubble bursting resulting in sea spray aerosol containing similar organic material to that of the microlaye...

No abstract

Scottish Rock Ptarmigan (Lagopus mutus) showed unstable population dynamics, with density-dependent features differing between areas on rich and poor soils. The study was conducted on arctic-alpine land on four submassifs, three of nutrient-poor granite and one of richer schist. Ptarmigan numbers cycled with a period usually of ϳ10 yr, but sometimes 6 yr. Delayed density dependence was detected in populations on granite submassifs, but not on schist, despite significant cyclicity there. Spring densities and the number of young reared per brood were higher on schist than on granite. Population change from one spring to the next was related to intervening breeding success on both granite and schist, but to summer loss only on granite. The same factors that determined variations in clutch size among years also largely affected breeding success. Population change, breeding success, summer loss, and clutch size showed delayed density dependence on granite, but not on schist, where numbers fluctuated more erratically. On granite, but not schist, early plant growth was followed by larger clutches, breeding success was related to June air temperature, and June temperature tended to peak 1-2 yr before ptarmigan peaks. Cyclic June temperature may have entrained the timing of ptarmigan cycles on granite. Results on both schist and granite were inconsistent with expectations from predator-prey hypotheses for cycles. In years of rising numbers, hens laid more eggs and reared more chicks per extra egg laid than in years of decline, and the proportion of surviving young recruited into the spring population was probably greater. Our hypothesis is that Scottish Rock Ptarmigan show unstable dynamics, driven by intrinsic positive feedback between recruitment in one year and the next, regulated by negative feedback between recruitment and density, and modified by the physical factors of weather and soil fertility that affect female nutrition and breeding success.

No abstract

Body mass loss is frequently observed in breeding birds: whether this is an adaptive response to a change in the relative value of body stores and locomotion performance or a consequence of energetic constraint is still in debate. The male alone cares for most nests of the Eurasian dotterel Charadrius morinellus, although females assist at a proportion of nests. Energetic costs are probably high in the dotterel's arctic‐alpine environment and uniparental care restricts the foraging time available to meet these costs, so that incubating dotterel may have to fuel themselves partly using body stores. Nesting male dotterel lost 7.8% of their mass through the incubation period but were 6.8% heavier during periods of high food abundance. Males that were assisted in incubation by a female were 6.7% heavier than uniparental males. We conclude that, since dotterel were heavier when energetic constraints were lifted, mass loss through incubation was principally a consequence of energetic constraint, rather than adaptive mass optimisation.