Month: May 2021

Feeding rates and diel vertical migration of copepods near South Georgia: a comparison of shelf and oceanic sites

first_imgSeventeen Longhurst Hardy Plankton Recorder profiles were taken over a diel cycle in January 1990 to study the feeding of four major copepods over the South Georgia shelf. Ontogenetic changes in vertical migration were followed and feeding cycles determined by gut fluorometry for Calanoides acutus Stage CV, Calanus sinillimus CV and CVI♀, C. propinquus CV and Rhincalanus gigas CV and CVI♀. In common with a neighbouring oceanic site visited two weeks later and reported elsewhere, all four species had a diel cycle of feeding and migration. The vertical distributions of C. simillimus (all stages), R. gigas (nauplii) and Euphausia frigida (postlarvae) were similar at both sites, the night being spent within the chlorophyll maximum at 15 to 30 m. However, the biomass dominants, C. acutus and R. gigas, dwelt below the chlorophyll maximum, about 30 m deeper than their oceanic counterparts. Unlike the oceanic site, feeding at the shelf site was not restricted to darkness, but increased 6 to 10 h before nightfall and finished at dawn; the intervening period coincided with sinking and digestion. Daylight feeding may have been induced by the shorter night, lower light levels or greater food requirements at the shelf site, despite planktonic predators being over three times more abundant. Daily ration estimates for R. gigas at both sites were only ∼2% body carbon per day. These low values contrast with its smaller competirors, whose rations were in the range 5.6 to 27%.last_img read more

Improvements to the accuracy of measurements of NO2 by zenith-sky visible spectrometers. II: Errors in zero using a more complete chemical model

first_imgUsing a flexible chemical box model with full heterogeneous chemistry, intercepts of chemically modified Langley plots have been computed for the 5 years of zenith-sky NO2 data from Faraday in Antarctica (65°S). By using these intercepts as the effective amount in the reference spectrum, drifts in zero of total vertical NO2 were much reduced. The error in zero of total NO2 is plus/minus 0.03 x 10 15 from one year to another. This error is small enough to determine trends in midsummer and any variability in denoxification between midwinters. The technique also suggests a more sensitive method for determining N2O5 from zenith-sky NO2 data.last_img read more

Statistical characteristics of the spatial distribution of Pc3-4 geomagnetic pulsations at high latitudes in the Antarctic regions

first_imgThe diumal variations in the parameters of Pc3 (20–60 mHz) and Pc4 (10–19 mHz) pulsations at latitudes of the dayside cusp and polar cap have been studied using data of the magnetic stations of the trans-Antarctic meridional profile for the time interval from January to March 1997 (local summer) under weakly disturbed geomagnetic conditions (AE ≤ 250 nT). The technique for estimating pulsation parameters is based on the separation of the wave packets and noise. The diumal variations in the hourly average parameters of the wave packets in the Pc3 and Pc4 bands and noise in the Pc3-4 band (10–60 mHz)—the average number of wave packets, energy of wave packets and noise, and energy of a single wave packet—turned out to be different for the stations located deep in the polar cap (Φ ∼ 87°) and at the latitudes of the dayside polar cusp (Φ ∼ 70°) and auroral oval (Φ ∼ 66°). Several sources of pulsations caused by different channels of wave energy penetration into the magnetosphere through the dayside cusp, dayside magnetopause, and dawn flank of the magnetotail apparently exist at high latitudes.last_img read more

Evolution of the Southern Annular Mode during the past millennium

first_imgThe Southern Annular Mode (SAM) is the primary pattern of climate variability in the Southern Hemisphere1, 2, influencing latitudinal rainfall distribution and temperatures from the subtropics to Antarctica. The positive summer trend in the SAM over recent decades is widely attributed to stratospheric ozone depletion2; however, the brevity of observational records from Antarctica1—one of the core zones that defines SAM variability—limits our understanding of long-term SAM behaviour. Here we reconstruct annual mean changes in the SAM since AD 1000 using, for the first time, proxy records that encompass the full mid-latitude to polar domain across the Drake Passage sector. We find that the SAM has undergone a progressive shift towards its positive phase since the fifteenth century, causing cooling of the main Antarctic continent at the same time that the Antarctic Peninsula has warmed. The positive trend in the SAM since ~AD 1940 is reproduced by multimodel climate simulations forced with rising greenhouse gas levels and later ozone depletion, and the long-term average SAM index is now at its highest level for at least the past 1,000 years. Reconstructed SAM trends before the twentieth century are more prominent than those in radiative-forcing climate experiments and may be associated with a teleconnected response to tropical Pacific climate. Our findings imply that predictions of further greenhouse-driven increases in the SAM over the coming century3 also need to account for the possibility of opposing effects from tropical Pacific climate changes.last_img read more

Decadal Ocean Forcing and Antarctic Ice Sheet Response: Lessons from the Amundsen Sea

first_imgMass loss from the Antarctic Ice Sheet is driven by changes at the marine margins. In the Amundsen Sea, thinning of the ice shelves has allowed the outlet glaciers to accelerate and thin, resulting in inland migration of their grounding lines. The ultimate driver is often assumed to be ocean warming, but the recent record of ocean temperature is dominated by decadal variability rather than a trend. The distribution of water masses on the Amundsen Sea continental shelf is particularly sensitive to atmospheric forcing, while the regional atmospheric circulation is highly variable, at least in part because of the impact of tropical variability. Changes in atmospheric circulation force changes in ice shelf melting, which drive step-wise movement of the grounding line between localized high points on the bed. When the grounding line is located on a high point, outlet glacier flow is sensitive to atmosphere-ocean variability, but once retreat or advance to the next high point has been triggered, ocean circulation and melt rate changes associated with the evolution in geometry of the sub-ice-shelf cavity dominate, and the sensitivity to atmospheric forcing is greatly reduced.last_img read more

Evidence of marine ice-cliff instability in Pine Island Bay from iceberg-keel plough marks

first_imgMarine ice-cliff instability (MICI) processes could accelerate future retreat of the Antarctic Ice Sheet if ice shelves that buttress grounding lines more than 800 metres below sea level are lost1, 2. The present-day grounding zones of the Pine Island and Thwaites glaciers in West Antarctica need to retreat only short distances before they reach extensive retrograde slopes3, 4. When grounding zones of glaciers retreat onto such slopes, theoretical considerations and modelling results indicate that the retreat becomes unstable (marine ice-sheet instability) and thus accelerates5. It is thought1, 2 that MICI is triggered when this retreat produces ice cliffs above the water line with heights approaching about 90 metres. However, observational evidence confirming the action of MICI has not previously been reported. Here we present observational evidence that rapid deglacial ice-sheet retreat into Pine Island Bay proceeded in a similar manner to that simulated in a recent modelling study1, driven by MICI. Iceberg-keel plough marks on the sea-floor provide geological evidence of past and present iceberg morphology, keel depth6 and drift direction7. From the planform shape and cross-sectional morphologies of iceberg-keel plough marks, we find that iceberg calving during the most recent deglaciation was not characterized by small numbers of large, tabular icebergs as is observed today8, 9, which would produce wide, flat-based plough marks10 or toothcomb-like multi-keeled plough marks11, 12. Instead, it was characterized by large numbers of smaller icebergs with V-shaped keels. Geological evidence of the form and water-depth distribution of the plough marks indicates calving-margin thicknesses equivalent to the threshold that is predicted to trigger ice-cliff structural collapse as a result of MICI13. We infer rapid and sustained ice-sheet retreat driven by MICI, commencing around 12,300 years ago and terminating before about 11,200 years ago, which produced large numbers of icebergs smaller than the typical tabular icebergs produced today. Our findings demonstrate the effective operation of MICI in the past, and highlight its potential contribution to accelerated future retreat of the Antarctic Ice Sheet.last_img read more

A 2018 Horizon Scan of Emerging Issues for Global Conservation and Biological Diversity

first_imgThis is our ninth annual horizon scan to identify emerging issues that we believe could affect global biological diversity, natural capital and ecosystem services, and conservation efforts. Our diverse and international team, with expertise in horizon scanning, science communication, as well as conservation science, practice, and policy, reviewed 117 potential issues. We identified the 15 that may have the greatest positive or negative effects but are not yet well recognised by the global conservation community. Themes among these topics include new mechanisms driving the emergence and geographic expansion of diseases, innovative biotechnologies, reassessments of global change, and the development of strategic infrastructure to facilitate global economic priorities.last_img read more

Pan-Arctic surface ozone: modelling vs. measurements

first_imgWithin the framework of the International Arctic Systems for Observing the Atmosphere (IASOA), we report a modelling-based study on surface ozone across the Arctic. We use surface ozone from six sites – Summit (Greenland), Pallas (Finland), Barrow (USA), Alert (Canada), Tiksi (Russia), and Villum Research Station (VRS) at Station Nord (North Greenland, Danish realm) – and ozone-sonde data from three Canadian sites: Resolute, Eureka, and Alert. Two global chemistry models – a global chemistry transport model (parallelised-Tropospheric Offline Model of Chemistry and Transport, p-TOMCAT) and a global chemistry climate model (United Kingdom Chemistry and Aerosol, UKCA) – are used for model data comparisons. Remotely sensed data of BrO from the GOME-2 satellite instrument and ground-based multi-axis differential optical absorption spectroscopy (MAX-DOAS) at Eureka, Canada, are used for model validation. The observed climatology data show that spring surface ozone at coastal sites is heavily depleted, making ozone seasonality at Arctic coastal sites distinctly different from that at inland sites. Model simulations show that surface ozone can be greatly reduced by bromine chemistry. In April, bromine chemistry can cause a net ozone loss (monthly mean) of 10–20 ppbv, with almost half attributable to open-ocean-sourced bromine and the rest to sea-ice-sourced bromine. However, the open-ocean-sourced bromine, via sea spray bromide depletion, cannot by itself produce ozone depletion events (ODEs; defined as ozone volume mixing ratios, VMRs, < 10 ppbv). In contrast, sea-ice-sourced bromine, via sea salt aerosol (SSA) production from blowing snow, can produce ODEs even without bromine from sea spray, highlighting the importance of sea ice surface in polar boundary layer chemistry. Modelled total inorganic bromine (BrY) over the Arctic sea ice is sensitive to model configuration; e.g. under the same bromine loading, BrY in the Arctic spring boundary layer in the p-TOMCAT control run (i.e. with all bromine emissions) can be 2 times that in the UKCA control run. Despite the model differences, both model control runs can successfully reproduce large bromine explosion events (BEEs) and ODEs in polar spring. Model-integrated tropospheric-column BrO generally matches GOME-2 tropospheric columns within ∼ 50 % in UKCA and a factor of 2 in p-TOMCAT. The success of the models in reproducing both ODEs and BEEs in the Arctic indicates that the relevant parameterizations implemented in the models work reasonably well, which supports the proposed mechanism of SSA production and bromide release on sea ice. Given that sea ice is a large source of SSA and halogens, changes in sea ice type and extent in a warming climate will influence Arctic boundary layer chemistry, including the oxidation of atmospheric elemental mercury. Note that this work dose not necessary rule out other possibilities that may act as a source of reactive bromine from the sea ice zone.last_img read more

Resilience in Greenland intertidal Mytilus: The hidden stress defense

first_imgThe Arctic is experiencing particularly rapid rates of warming, consequently invasive boreal species are now able to survive the less extreme Arctic winter temperatures. Whilst persistence of intertidal and terrestrial species in the Arctic is primarily determined by their ability to tolerate the freezing winters, air temperatures in the Arctic summer can reach 36 °C in the intertidal, which is beyond the upper thermal limits of many marine species. This is normally lethal for the conspicuous ecosystem engineer Mytilus edulis. Transcriptomic analyses were undertaken on both in situ collected and experimentally warmed animals to understand whether M. edulis is able to tolerate these very high summer temperatures. Surprisingly there was no significant enrichment for Gene Ontology terms (GO) when comparing the inner and outer fjord intertidal animals with outer fjord subtidal (control) animals, representing animals collected at 27 °C, 19 °C and 3 °C respectively. This lack of differentiation indicated a wide acclimation ability in this species. Conversely, significant enrichment for processes such as signal transduction, cytoskeleton and cellular protein modification was identified in the expression profiles of the 22 °C and 32 °C experimentally heated animals. This difference in gene expression between in situ collected and experimentally warmed animals was almost certainly due to the former being acclimated to a fluctuating, but predictable, temperature regime, which has increased their thermal tolerances. Interestingly, there was no evidence for enrichment of the classical cellular stress response in any of the animals sampled. Identification of a massive expansion of the HSPA12 heat shock protein 70 kDa gene family presented the possibility of these genes acting as intertidal regulators underpinning thermal resilience. This expansion has resulted in a modified cellular stress response, as an evolutionary adaptation to the rigour of the invasive intertidal life style. Thus, M. edulis appear to have considerable capacity to withstand the current rates of Arctic warming, and the very large attendant thermal variation.last_img read more

US women’s soccer team honors Stoneman Douglas victim

first_img FacebookTwitterLinkedInEmailABC News(ORLANDO, Fla.) — By everyone’s account, Alyssa Alhadeff, a 14-year-old student and member of the Marjory Stoneman Douglas High girls soccer team, was bound for great things in life, on and off the field.“Alyssa took every second of her life and did something with it,” her mother, Lori Alhadeff, said. “She had the fire to fight. She had the spirit.”Alyssa Alhadeff was one of 17 students and teachers gunned down Feb. 14 at the Parkland, Florida, school. A former student was indicted this week on 34 counts in the massacre, including first-degree premeditated murder.According to Lori Alhadeff, a soccer player herself, Alyssa Alhadeff started playing soccer at the age of 3 and by age 8, was playing competitively.She said her daughter, who played center mid, was on track to play soccer in college and had dreamed of one day being on the U.S. women’s national soccer team.“She loved the sport. … I always thought someday that she would be on the women’s national soccer team,” Lori Alhadeff said. “She aspired for that greatness. … She was probably one of the smallest on the team but the fiestiest.”She said Alyssa Alhadeff was also a huge fan of Alex Morgan, a forward on the U.S. women’s national soccer team. The two had even met six years ago, Lori Alhadeff said, and Morgan had signed not only Alyssa Alhadeff’s book but also her cellphone.Her father, Ilan Alhadeff, said that after her death, her friend Jamie Morris tweeted Morgan to let her know how much Alyssa Alhadeff had loved her and the women’s soccer team. Morgan reached out to the friend, Ilan Alhadeff said, and invited the family and the school’s team to a game.On Wednesday, the Alhadeffs and the Stoneman Douglas girls soccer team traveled to Orlando to watch the U.S. women’s national soccer team play against England. Before the game, a moment of silence was held for Alyssa Alhadeff and her picture was posted on the Jumbotron. Her teammates stood in the stands, holding posters bearing her pictures and messages of friendship.The family and team were also each presented with a national team jersey, complete with Alyssa Alhadeff’s name on it and her number: 8. After the game, members of the U.S. soccer team signed the jerseys for the girls.Laurie Thomas, the girls’ soccer team coach, said that after the shootings, the team had gotten together for days, focused on keeping the memory of their friend and team captain alive.“She was the voice of our team,” Thomas said of Alyssa Alhadeff. “She was a leader, not just by what she said, but also by the character. She lead the team on and off the field.”Lori Alhadeff said the school team as well as her sons had felt the love, compassion and strength from the U.S. women’s team.“It has literally taken my breath away,” she said of the day and experience. “Alyssa would be ecstatic. She would’ve been just jumping for joy, crying and laughing.”Ilan Alhadeff said his daughter would have loved to share the moment with her family, friends and teammates.“It would have been the best day ever,” he said. “It’s just amazing, the overwhelming support. … Helping not just us, but our entire city heal.”Copyright © 2018, ABC Radio. All rights reserved. Beau Lund Written bycenter_img March 9, 2018 /Sports News – National US women’s soccer team honors Stoneman Douglas victimlast_img read more