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The presence of ice in clouds can influence cloud lifetime, precipitation and radiative properties; here, organic material at the sea-air interface, possibly associated with phytoplankton cell exudates, is shown to nucleate ice under conditions relevant for ice cloud formation in the atmospheric environment. Ice-forming 'biological' particles in the marine atmosphere The presence of ice in clouds can have an influence on cloud lifetime and radiative properties. It remains uncertain to what extent sea spray may act as ice nucleating particles that facilitate the formation of ice in clouds. This study finds that organic material at the sea-air interface, probably derived from phytoplankton cell exudates, nucleates ice under conditions relevant for ice cloud formation in the atmospheric environment. Model simulations suggest that marine organic material may be an important source of ice nucleating particles in remote marine environments such as the Southern Ocean. The amount of ice present in clouds can affect cloud lifetime, precipitation and radiative properties.sup.1,2. The formation of ice in clouds is facilitated by the presence of airborne ice-nucleating particles.sup.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.sup.3,4,5,6,7,8,9,10,11. 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.sup.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 probably biogenic and less than approximately 0.2 micrometres in size. We find that exudates separated from cells of the marine diatom Thalassiosira 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 Ocean and North Atlantic Ocean., Author(s): Theodore W. Wilson [sup.1] , Luis A. Ladino [sup.2] , Peter A. Alpert [sup.3] , Mark N. Breckels [sup.4] , Ian M. Brooks [sup.1] , Jo Browse [sup.1] , [...]

A synthesis of new and existing data allows Heinrich Stadial 11 (HS11), a prominent Northern Hemisphere cold event, to be linked to the timing of peak sea-level rise during glacial termination T-II, whereas rapid sea-level rise in T-I is shown to clearly post-date Heinrich Stadial 1, so fundamentally different mechanisms seem to be at work during glacial terminations. Anatomy of a glacial termination A central goal of palaeoclimate research is that of deciphering the mechanisms responsible for major state shifts in the Earth system, such as between glacial and interglacial conditions. This has proven difficult enough even for the last glacial termination (T-I), much less termination II (T-II), which ended glacial conditions about 130,000 years ago. Gianluca Marino et al. use new and existing data to demonstrate a link, within uncertainties, between Heinrich Stadial 11 (HS11) -- a prominent Northern Hemisphere cold event -- and the timing of peak sea level rise during T-II. A strong Southern Hemisphere warming also occurred during HS11, consistent with the idea of a bipolar seesaw that would probably have promoted Antarctic ice sheet melting. In contrast, rapid sea level rise in T-1 clearly postdated Heinrich Stadial 1. Possibly in response to differing CO.sub.2 and insolation conditions during T-I and T-II, fundamentally different mechanisms seem to be at work in triggering glacial terminations. Our current understanding of ocean-atmosphere-cryosphere interactions at ice-age terminations relies largely on assessments of the most recent (last) glacial-interglacial transition.sup.1,2,3, Termination I (T-I). But the extent to which T-I is representative of previous terminations remains unclear. Testing the consistency of termination processes requires comparison of time series of critical climate parameters with detailed absolute and relative age control. However, such age control has been lacking for even the penultimate glacial termination (T-II), which culminated in a sea-level highstand during the last interglacial period that was several metres above present.sup.4. Here we show that Heinrich Stadial 11 (HS11), a prominent North Atlantic cold episode.sup.5,6, occurred between 135 [plus or minus] 1 and 130 [plus or minus] 2 thousand years ago and was linked with rapid sea-level rise during T-II. Our conclusions are based on new and existing.sup.6,7,8,9 data for T-II and the last interglacial that we collate onto a single, radiometrically constrained chronology. The HS11 cold episode.sup.5,6 punctuated T-II and coincided directly with a major deglacial meltwater pulse, which predominantly entered the North Atlantic Ocean and accounted for about 70 per cent of the glacial-interglacial sea-level rise.sup.8,9. We conclude that, possibly in response to stronger insolation and CO.sub.2 forcing earlier in T-II, the relationship between climate and ice-volume changes differed fundamentally from that of T-I. In T-I, the major sea-level rise clearly post-dates.sup.3,10,11 Heinrich Stadial 1. We also find that HS11 coincided with sustained Antarctic warming, probably through a bipolar seesaw temperature response.sup.12, and propose that this heat gain at high southern latitudes promoted Antarctic ice-sheet melting that fuelled the last interglacial sea-level peak., Author(s): G. Marino [sup.1] , E. J. Rohling [sup.1] [sup.2] , L. Rodríguez-Sanz [sup.1] , K. M. Grant [sup.1] , D. Heslop [sup.1] , A. P. Roberts [sup.1] , J. [...]

Ice clouds in marine regions at high latitudes might form in warmer and drier air than was previously believed because of freezing induced by airborne particles that contain organic materials from ocean surface waters. See Letter p.234 Ice-forming 'biological' particles in the marine atmosphere The presence of ice in clouds can have an influence on cloud lifetime and radiative properties. It remains uncertain to what extent sea spray may act as ice nucleating particles that facilitate the formation of ice in clouds. This study finds that organic material at the sea-air interface, probably derived from phytoplankton cell exudates, nucleates ice under conditions relevant for ice cloud formation in the atmospheric environment. Model simulations suggest that marine organic material may be an important source of ice nucleating particles in remote marine environments such as the Southern Ocean., Author(s): Lynn M. Russell [sup.1] Author Affiliations: (1) Lynn M. Russell is at the Scripps Institution of Oceanography, University of California, San Diego, La Jolla, California 92093-0221, USA., The oceans [...]

A record of boron isotopes in fossils of microscopic plankton provides fresh evidence that some ocean regions were a source of carbon dioxide to the atmosphere when Earth warmed at the end of the last ice age. See Letter p.219 Oceanic CO.sub.2 loss during the last deglaciation It is thought that ventilation of a deep ocean carbon reservoir in the Southern Ocean played an important role in the deglacial atmospheric CO.sub.2 rise, but there has been no direct documentation of changes in surface ocean carbon content during deglaciations. Boron isotope pH proxy data, a more direct tracer of oceanic CO.sub.2 outgassing, now show that surface waters -- partly derived from deep water upwelled in the Southern Ocean -- became a significant source of carbon to the atmosphere during the last deglaciation., Author(s): Katherine A. Allen [sup.1] Author Affiliations: (1) Katherine A. Allen is in the Department of Marine and Coastal Sciences, Rutgers University, New Brunswick, New Jersey 08901, USA., During the [...]