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The relationship between leaf longevity and growth ring markedness in modern conifer woods and its implications for palaeoclimatic studies

first_imgGrowth rings in modern conifer woods were quantitatively analysed to investigate the relationship between leaflongevity and the markedness of the growth ring boundary. Five conifer species exhibiting a wide range of Leaf Retention Times (LRTs) were examined in anatomical sections stored in the Jodrell Laboratory, Royal Botanic Gardens, Kew, Surrey, UK. The species studied were Larix decidua Mill. (deciduous), Pinus sylvestris L. (LRT=1–3 years), Picea abies (L.) H. Karst. (LRT=3–5 years), Cedrus libani A. Rich. (LRT=3–6 years), and Araucaria araucana (Molina) K. Koch (LRT=3–15 years). Two aspects of ringmarkedness were quantified: (1) the percentage of latewood in each growthring increment and (2) the difference between the maximum and minimum radial cell diameters in the growthring increment expressed as a percentage of the maximum cell diameter (percentage diminution). The product of these two parameters was calculated to give a RingMarkedness Index (RMI). Five growthring increments were measured for each species from poorly provenanced specimens grown in southern England. Statistical analysis of these data shows that there is a significant inverse linear relationship between median LRT and percentage latewood (R2=0.86), percentage diminution (R2=0.77), and RMI (R2=0.91), at P<0.001. These data suggest that leaflongevity exerts an important control on growthringmarkedness, in addition to the influence exerted by the growing environment (climatic and edaphic conditions). The significance of these results for the palaeoclimatic analysis of growthrings in fossil woods is discussed with reference to two case-studies: (1) the Early Carboniferous tropical climate of the British Isles and (2) the Early Cretaceous polar climate of the Antarctic Peninsula.last_img read more

Centurial‐millenial ice‐rafted debris pulses from ablating marine ice sheets

first_imgWe use an ice‐sheet model to show that (i) margins of marine ice‐sheets can be expected to be frozen to the bed, except where ice‐streams discharge; (ii) 20–50km retreats induced by ablation rates of 2 m/yr provide sufficient debris flux through the grounding line to produce large sedimentation events. Such ablation would reduce ice‐shelf extent markedly, permitting debris to reach the calving front and be transported by icebergs leading to ice‐rafted debris (IRD) events. Ice shelf break‐up takes around a century (start of IRD pulse), while the creation of warm‐based conditions (end of IRD pulse) due to upwards motion of warm ice takes a few more centuries. Such IRD pulses are unlikely to explain Heinrich events, which are associated with relatively cold periods within glaciations. Surges are not necessary conditions for the production of large IRD events.last_img read more

Against the flow: evidence of multiple recent invasions of warmer continental shelf waters by a Southern Ocean brittle star

first_imgThe Southern Ocean is anomalously rich in benthos. This biodiversity is native, mostly endemic and perceived to be uniquely threatened from climate- and anthropogenically- mediated invasions. Major international scientific effort throughout the last decade has revealed more connectivity than expected between fauna north and south of the worlds strongest marine barrier – the Polar Front (the strongest jet of the Antarctic Circumpolar Current). To date though, no research has demonstrated any radiations of marine taxa out from the Southern Ocean, except at abyssal depths (where conditions differ much less). Our phylogeographic investigation of one of the most ubiquitous and abundant clades at high southern latitudes, the ophiuroids (brittlestars), shows that one of them, Ophiura lymani, has gone against the flow. Remarkably our genetic data suggest that O. lymani has successfully invaded the South American shelf from Antarctica at least three times, in recent (Pleistocene) radiation. Many previous studies have demonstrated links within clades across the PF this is the first in which northwards directional movement of a shelf-restricted species is the only convincing explanation. Rapid, recent, regional warming is likely to facilitate multiple range shift invasions into the Southern Ocean, whereas movement of cold adapted fauna (considered highly stenothermal) out of the Antarctic to warmer shelves has, until now, seemed highly unlikely.last_img read more

Temporal variations in the flow of a large Antarctic ice stream controlled by tidally induced changes in the subglacial water system

first_imgObservations show that the flow of Rutford Ice Stream (RIS) is strongly modulated by the ocean tides, with the strongest tidal response at the 14.77 day tidal period (Msf). This is striking because this period is absent in the tidal forcing. A number of mechanisms have been proposed to account for this effect, yet previous modeling studies have struggled to match the observed large amplitude and decay length scale. We use a nonlinear 3-D viscoelastic full-Stokes model of ice-stream flow to investigate this open issue. We find that the long period Msf modulation of ice-stream velocity observed in data cannot be reproduced quantitatively without including a coupling between basal sliding and tidal subglacial water pressure variations. Furthermore, the subglacial water system must be highly conductive and at low effective pressure, and the relationship between sliding velocity and effective pressure highly nonlinear in order for the model results to match GPS measurements. Hydrological and basal sliding model parameters that produced a best fit to observations were a mean effective pressure N of 105 kPa, subglacial drainage system conductivity K of 7 × 109 m2d-1, with sliding law exponents m = 3 and q =10. Coupled model results show the presence of tides result in a ~ 12% increase in mean surface velocity. Observations of tidally-induced variations in flow of ice-streams provide stronger constraints on basal sliding processes than provided by any other set of measurements.last_img read more

Out of Antarctica: quaternary colonization of sub-Antarctic Marion Island by the limpet genus Nacella (Patellogastropoda: Nacellidae)

first_imgThe distribution of the Southern Ocean nearshore marine benthic fauna is the consequence of major geologic, oceanographic, and climatic changes during the last 50 Ma. As a result, a main biogeographic principle in the Southern Ocean is the clear distinction of the Antarctic biota. The Antarctic Polar Front (APF) represents an important barrier between Antarctica and other sub-Antarctic provinces. However, the high degree of genetic affinity between populations of the Antarctic limpet Nacella concinna and its sub-Antarctic relative Nacella delesserti from Marion Island stands against this tenet. Here, we performed new phylogenetic reconstructions in Nacella with special emphasis on the relationship between N. concinna and N. delesserti. Similarly, we performed population-based analyses in N. concinna and N. delesserti to further understand the genetic legacy of the Quaternary glacial cycles. Phylogenetic reconstructions recognized N. concinna and N. delesserti as two closely but distinct monophyletic entities and therefore as valid evolutionary units. The cladogenetic process separating them occurred ~0.35 Ma and is consistent with the origin of Marion Island (~0.45 Ma). Exceptional long-distance dispersal between provinces located inside and outside the APF, rather than revealing the permeability of the Antarctic Polar Front, seems to be related to latitudinal shift in the position of the APF during coldest periods of the Quaternary. Diversity indices, neutrality tests, haplotype networks, and demographic inference analysis showed that the demography of both species exhibits a clear signal of postglacial expansion.last_img read more

Oxygen isotope mass balance of atmospheric nitrate at Dome C, East Antarctica, during the OPALE campaign

first_imgVariations in the stable oxygen isotope composition of atmospheric nitrate act as novel tools for studying oxidative processes taking place in the troposphere. They provide both qualitative and quantitative constraints on the pathways determining the fate of atmospheric nitrogen oxides (NO + NO2 = NOx). The unique and distinctive 17O-excess (Δ17O = δ17O − 0.52 × δ18O) of ozone, which is transferred to NOx via oxidation, is a particularly useful isotopic fingerprint in studies of NOx transformations. Constraining the propagation of 17O-excess within the NOx cycle is critical in polar areas where there exists the possibility of extending atmospheric investigations to the glacial/interglacial time scale using deep ice core records of nitrate. Here we present measurements of the comprehensive isotopic composition of atmospheric nitrate collected at Dome C (East Antarctic plateau) during the austral summer of 2011/12. Nitrate isotope analysis has been here combined for the first time with key precursors involved in nitrate production (NOx, O3, OH, HO2, RO2, etc.) and direct observations of the transferrable Δ17O of surface ozone, which was measured at Dome C throughout 2012 using our recently developed analytical approach. Assuming that nitrate is mainly produced in Antarctica in summer through the OH + NO2 pathway and using concurrent measurements of OH and NO2, we calculated a Δ17O signature for nitrate in the order of (21–22 ± 3) ‰. These values are lower than the measured values that ranged between 27 and 31 ‰. This discrepancy between expected and observed Δ17O(NO3−) values suggests the existence of an unknown process that contributes significantly to the atmospheric nitrate budget over this east Antarctic region.last_img read more

A global cline in a colour polymorphism suggests a limited contribution of gene flow towards the recovery of a heavily exploited marine mammal

first_imgEvaluating how populations are connected by migration is important for understanding species resilience because gene flow can facilitate recovery from demographic declines. We therefore investigated the extent to which migration may have contributed to the global recovery of the Antarctic fur seal (Arctocephalus gazella), a circumpolar distributed marine mammal that was brought to the brink of extinction by the sealing industry in the eighteenth and nineteenth centuries. It is widely believed that animals emigrating from South Georgia, where a relict population escaped sealing, contributed to the re-establishment of formerly occupied breeding colonies across the geographical range of the species. To investigate this, we interrogated a genetic polymorphism (S291F) in the melanocortin 1 receptor gene, which is responsible for a cream-coloured phenotype that is relatively abundant at South Georgia and which appears to have recently spread to localities as far afield as Marion Island in the sub-Antarctic Indian Ocean. By sequencing a short region of this gene in 1492 pups from eight breeding colonies, we showed that S291F frequency rapidly declines with increasing geographical distance from South Georgia, consistent with locally restricted gene flow from South Georgia mainly to the South Shetland Islands and Bouvetøya. The S291F allele was not detected farther afield, suggesting that although emigrants from South Georgia may have been locally important, they are unlikely to have played a major role in the recovery of geographically more distant populations.last_img read more

Movements and diving behaviour of white-chinned petrels: diurnal variation and implications for bycatch mitigation

first_img1. Many seabirds dive to forage, and the ability to use this hunting technique varies according to such factors as morphology, physiology, prey availability, and ambient light levels. Proficient divers are more able to seize sinking baits deployed by longline fishing vessels and may return them to the surface, increasing exposure of other species. Hence, diving ability has major implications for mitigating incidental mortality (bycatch) in fisheries.2. Here, the diving behaviour and activity patterns of the most bycaught seabird species worldwide, the white‐chinned petrel (Procellaria aequinoctialis), tracked from Bird Island (South Georgia), are analysed. Three data sources (dives, spatial movements, and immersion events) are combined to examine diverse aspects of at‐sea foraging behaviour, and their implications for alternative approaches to bycatch mitigation are considered.3. The tracked white‐chinned petrels (n = 14) mostly performed shallow dives (<3 m deep) of very short duration (<5 s), predominantly during darkness, but only 7 and 10% of landings in daylight and darkness, respectively, involved diving, suggesting that surface‐seizing is the preferred foraging technique. Nonetheless, individuals were able to dive to considerable depth (max = 14.5 m) and at speed (max = 2.0 m·s−1), underlining the importance of using heavy line‐weighting to maximize hook sink rates, and bird‐scaring lines (Tori lines) that extend for long distances behind vessels to protect hooks until beyond diving depths.last_img read more

ESPN: New York Knicks trade Kristaps Porzingis to Dallas Mavericks

first_imgJanuary 31, 2019 /Sports News – National ESPN: New York Knicks trade Kristaps Porzingis to Dallas Mavericks FacebookTwitterLinkedInEmailMoses Kinnah/iStock(NEW YORK) — The New York Knicks and Dallas Mavericks have completed a trade that sends Kristaps Porzingis to Dallas and sets the Knicks up for a major run at two star free agents this offseason.The Knicks are also sending Tim Hardaway Jr. and Courtney Lee to Dallas, freeing up salary cap room for this offseason. The Mavericks would send back Dennis Smith Jr., DeAndre Jordan and Wesley Matthews.Dallas will also send two future first-round draft picks in the trade. They owe their own first-rounder this year to the Atlanta Hawks as part of the draft-night trade to acquire Luka Doncic.Sources told ESPN earlier on Thursday that Porzingis met with Knicks management to discuss concerns about the state of the franchise and his future. ESPN says Knicks officials were left with the impression that the 23-year-old would prefer to be traded.Porzingis tore his ACL last January and hasn’t played since. The fourth overall draft pick in 2015, Porzingis was averaging a career-high 22.7 points per game before the knee injury. The 10-40 Knicks are angling for one of the top picks in this summer’s draft. They decided against signing Porzingis to a rookie extension before this season, resulting in more salary cap room. That move, however, gave Porzingis the chance to be a restricted free agent this offseason.Copyright © 2019, ABC Radio. All rights reserved. Written bycenter_img Beau Lundlast_img read more

BYU Football Hosts Washington Saturday

first_imgSeptember 16, 2019 /Sports News – Local BYU Football Hosts Washington Saturday FacebookTwitterLinkedInEmailPROVO, Utah-Saturday, BYU football (2-1) hosts No. 21/22 Washington (2-1) in hopes of continuing their winning streak against Power 5 conference squads as they have knocked off Tennessee from the SEC and USC from the Pac-12 in subsequent weeks.The Huskies lead the Cougars 6-4 all-time, but BYU has a 3-1 advantage in the series at Provo.The Cougars come into Saturday’s game scoring 23.7 points per game, which is tied for 92nd in NCAA FBS Division I with West Virginia. They are 83rd in scoring defense by surrendering 27.7 points per contest.BYU is led by rising star signal-caller, sophomore Zach Wilson who has completed 63.2 percent of his passes (60-95) for 720 yards, two touchdowns and two interceptions. Wilson also added his first rushing touchdown of the season against USC.The Cougars’ leading tailback is graduate transfer Ty’Son Williams (48 touches, 266 scrimmage yards, 3 rush TD’s) and senior receiver Micah Simon (13 rec, 210 yards, 16.2 yards per catch) is their leading receiver.Defensively, freshman linebacker Payton Wilgar, junior linebacker Kavika Fonua, senior defensive back Dayan Ghanwoloku and junior linebacker Isaiah Kaufusi all have an interception.The Huskies, who are making their first road trip of the season, bounced back from a disappointing 20-19 loss to California in their Pac-12 opener September 7 by routing Hawaii 52-20 September 14.Washington ranks 27th in the FBS in scoring offense (39.3 points a game) and is 38th in scoring defense (18 points per game).The Huskies are led by junior quarterback Jacob Eason who has completed 69.2 percent of his passes (63-91) for 773 yards, 7 touchdowns and only one interception on the season thus far.Junior tailback Salvon Ahmed (49 touches, 293 scrimmage yards, 2 rushing touchdowns) is Washington’s leading rusher.Junior tight end Hunter Bryant (15 rec, 236 yards, rec TD) and senior receiver Aaron Fuller (13 rec, 168 yards, 3 rec TD’s) are Washington’s leading receivers.Senior defensive lineman Benning Potoa’e (2 sacks) and senior defensive back Myles Bryant (2 interceptions) are the Huskies’ defensive leaders. Written by Tags: BYU Football/Washington Football Brad Jameslast_img read more