Southern Hemisphere Continents Research Articles

Fossil marine vertebrates (Chondrichthyes, Actinopterygii, Reptilia) from the Upper Cretaceous of Akkermanovka (Orenburg Oblast, Southern Urals, Russia)

Upper Cretaceous coastal marine deposits are widespread in the Southern Urals with a number of marine vertebrates previously reported from this region. However, previous studies on the vertebrate faunas in this region often lack detailed taxonomic descriptions and illustrations, rendering comparisons to other faunal assemblages difficult. A new diverse vertebrate assemblage comprising cartilaginous and bony fishes, as well as marine reptiles, is described here from the Orenburg region near Akkermanovka (Southern Urals, Russia). Thirty five taxa are identified, including three holocephalans (Elasmodus sp., Ischyodus yanschini, Chimaeroid indet.), two hybodontiform sharks (Meristodonoides sp., cf. Polyacrodus sp.), 17 neoselachians (Paraorthacodus cf. andersoni, Paraorthacodus sp., Synechodus sp., Cederstroemia nilsi, Acrolamna acuminata, Archaeolamna ex gr. kopingensis, Cretalamna sarcoportheta, Cretoxyrhina mantelli, Eostriatolamia segedini, E. venusta, Hispidaspis horridus, H. cf. gigas, Pseudocorax laevis, Pseudoscapanorhynchus compressidens, Scapanorhynchus rhaphiodon, Squalicorax kaupi, Ptychodus rugosus), a holostean (Lepisosteidae indet.), nine teleosts (Protosphyraena sp., Saurodontidae indet., cf. Pachyrhizodus sp., Pachyrhizodontidae indet., Enchodus petrosus, E. ferox, E. cf. gladiolus, E. spp., Alepisauroidei indet.), two plesiosaurs (Polycotylidae indet., Plesiosauria indet.), and one mosasaurid (Tylosaurinae indet.). Based on the faunal assemblage, a Santonian–?early Campanian age is proposed. Lamniform sharks are the best represented group in terms of taxic diversity and relative abundance, probably reflecting the peak in diversity this group experienced following the Cenomanian radiation in the Late Cretaceous. The faunal assemblage of Akkermanovka exhibits significant taxonomic overlaps with assemblages reported from Asia and North America, but not from Southern Hemisphere continents, indicating east–west dispersal of several marine taxa during the Late Cretaceous.

Monsoon Seasonality Advanced by Opposite‐Hemisphere Continental Drift

AbstractCharacteristics of regional monsoons are largely determined by continental configuration. Motivated by the impacts of Australia on the East Asian monsoon, we investigate the modulation of the monsoon by opposite‐hemisphere continent using aquaplanet simulations with idealized continents. Simulation results show that the monsoon seasonality is advanced significantly by a near‐equator continent in the opposite‐hemisphere. In the early boreal summer, the rapid cooling of the Southern Hemisphere continents forms a high pressure on it, leading to enhanced cross‐equatorial flow and premoistening of the Northern Hemisphere monsoon, thus promoting the monsoon onset. This mechanism requires the opposite‐hemispheric continent to be within a 25° tropical belt to activate this mechanism. The results imply that the continental drift of Australia over the past 40 Ma might have shaped the seasonality of the East Asian monsoon over the geological timescale.

Persistence of temperature and precipitation: From local to global anomalies

ract: Using detrended fluctuation analysis (DFA) we find that the all continents are persistent in temperature. The scaling exponents of the southern hemisphere (SH) continents, i.e., South America (α=0.78) and Oceania (0.75) are somewhat higher than scaling exponents of Europe (0.70), Asia (0.69) and North America (0.65), but the scaling of Africa is by far the highest (0.89). The scaling exponents of the precipitation are much smaller, i.e., between 0.54 (Europe) and 0.67 (North America). The scaling exponent of Europe is near the exponent of random Brownian noise, which is 0.5. The other continents are slightly persistent in precipitation. The slopes of the logarithmic power spectra of the continents are in line with the scaling exponents confirming the DFA analysis results. We also show that the persistence is real and not the intrinsic property of the data itself. We find that scaling exponent α, i.e., persistence of the monthly temperature increases when going from local to larger area averages, at least in the case where climate type does not change much. The situation is not so obvious for the monthly precipitation. We also show that the three southernmost climate regions of USA, Ohio Valley, South and Southeast, have smaller scaling exponents for temperature anomalies, and are thus less persistent in temperature than other six climate regions. On the other hand they are slightly more persistent in precipitation that the other regions. The scaling exponents of the monthly temperature anomalies of the latitude zones of land area are 0.71 and 0.68 for the southern zones S44-S24, and S64-S44, respectively. For the northern zones N24-N44, N44-N64 and N64-N90, the scaling exponents are between 0.67-0.70. Interestingly the scaling exponents are extremely high for the equatorial zones S24-EQ and EQ-N24, i. e., 1.02 and 0.95, respectively. The corresponding exponents of the monthly precipitation anomalies are between 0.55-0.61 for other zones than S24-EQ and EQ-N24, which have exponents 0.72 and 0.77, respectively.

Introduction to volcanism in Antarctica: 200 million years of subduction, rifting and continental break-up

Antarctica has undergone several important phases of volcanism throughout its long history. It was formerly at the heart of Gondwana but, from early Jurassic time ( c. 200 Ma), it commenced the prolonged process of disintegration, which resulted in the dispersal and final disposition of the southern hemisphere continents that we are familiar with today (Veevers 2012; Storey and Granot 2021 ). As a consequence, volcanism has been particularly important in its construction and it is geographically widespread, although mainly located within West Antarctica (Fig. 1). Its effects have frequently been felt far outside of the continent. For example, it has been a driver of global mass extinctions (Burgess et al. 2015; Ernst and Youbi 2017) and it has potentially driven Antarctica climatically, and by implication the world, both into and out of glacials (Bay et al. 2006; McConnell et al. 2017). Conversely, Antarctica's volcanoes may have played a pivotal role in helping Life not only to survive multiple glacial episodes during the past few tens of millions of years but to undergo species diversification on the continent in spite of the dramatic climate variations (Fraser et al. 2014). Eruptions from Mount Erebus also represent a significant point source of gases and aerosols to the Austral polar troposphere, including affecting the ozone layer (Boichu et al. 2011; Zuev et al. 2015). Some of Antarctica's active volcanoes also have the potential to have a significant impact on southern hemisphere aviation (Geyer et al. 2017). Finally, Antarctica contains the world's largest and longest-lived glaciovolcanic province. The glaciovolcanic sequences contain a detailed record of the terrestrial Antarctic ice sheet going back to nearly 30 Ma and that record is now beginning to be tapped (e.g. Smellie et al. 2009; Smellie and Edwards 2016; Wilch et al. 2021 ). Despite these …

The Noongar of south-western Australia: a case study of long-term biodiversity conservation in a matrix of old and young landscapes

AbstractOccurring across all southern hemisphere continents except Antarctica, old, climatically buffered, infertile landscapes (OCBILs) are centres of biological richness, often in biodiversity hotspots. Among a matrix of young, often disturbed, fertile landscapes (YODFELs), OCBILs are centres of endemism and diversity in the exceptionally rich flora of the south-west Australian global biodiversity hotspot, home to Noongar peoples for ≥ 48 000 years. We analysed contemporary traditional Noongar knowledge of adjacent OCBILs (e.g. granite outcrops) and YODFELs (e.g. creekline fringes) both at a single site and in two larger areas to test whether patterns of disturbance dictated by Noongar custom align with OCBIL theory. We found that Noongar traditional knowledge reflects a regime of concentrated YODFEL rather than OCBIL disturbance—a pattern which aligns with maximal biodiversity preservation. SIMPER testing found traditional Noongar OCBIL and YODFEL activities are 64–75% dissimilar, whereas Pearson’s chi-square tests revealed camping, burning, travelling through country and hunting as primarily YODFEL rather than OCBIL activities. We found that Noongar activities usually avoid OCBIL disturbance. This combined with high floristic diversity following enduring First Peoples’ presence, suggests that traditional Noongar knowledge is valuable and necessary for south-west Australian biodiversity conservation. Similar cultural investigations in other OCBIL-dominated global biodiversity hotspots may prove profitable.

Contrasting diversity patterns of breeding Anatidae in the Northern and Southern Hemispheres.

For sustaining ecosystem functions and services, environmental conservation strategies increasingly target to maintain the multiple facets of biodiversity, such as functional diversity (FD) and phylogenetic diversity (PD), not just taxonomic diversity (TD). However, spatial mismatches among these components of biodiversity can impose challenges for conservation decisions. Hence, understanding the drivers of biodiversity is critical. Here, we investigated the global distribution patterns of TD, FD, and PD of breeding Anatidae. Using null models, we clarified the relative importance of mechanisms that influence Anatidae community. We also developed random forest models to evaluate the effects of environmental variables on the Anatidae TD, FD, and PD. Our results showed that geographical variation in Anatidae diversity is hemispheric rather than latitudinal. In the species‐rich Northern Hemisphere (NH), the three diversity indices decreased with latitude within the tropical zone of the NH, but increased in the temperate zone reaching a peak at 44.5–70.0°N, where functional and phylogenetic clustering was a predominant feature. In the Southern Hemisphere (SH), Anatidae diversity increased poleward and a tendency to overdispersion was common. In NH, productivity seasonality and temperature in the coldest quarter were the most important variables. Productivity seasonality was also the most influential predictor of SH Anatidae diversity, along with peak productivity. These findings suggested that seasonality and productivity, both consistent with the energy‐diversity hypothesis, interact with the varying histories to shape the contrasting hemispheric patterns of Anatidae diversity. Phylogenetic diversity (PD) and FD underdispersion, widespread across the species‐rich, seasonally productive mid‐to‐high latitudes of the NH, reflects a rapid evolutionary radiation and resorting associated with Pleistocene cycles of glaciation. The SH continents (and southern Asia) are characterized by a widespread tendency toward PD and FD overdispersion, with their generally species‐poor communities comprising proportionately more older lineages in thermally more stable but less predictably productive environments.

Mid-Holocene drylands: A multi-model analysis using Paleoclimate Modelling Intercomparison Project Phase III (PMIP3) simulations

This study examines changes in aridity levels during the mid-Holocene (approximately 6000 cal. yr ago) using multi-model simulations from the Paleoclimate Modelling Intercomparison Project Phase III. Overall, there is little difference in the total area of drylands from the preindustrial period; global drylands are 8% wetter than during the preindustrial period as measured by an aridity index; and 16% of preindustrial drylands convert to a wetter climate subtype, double the sum of zones that are replaced by a drier category. Considerable variations are present among regions with major contractions of each dryland subtype from northern Africa to South Asia and the main expansions of arid, semiarid, and dry subhumid climates in southern hemisphere continents. The difference in precipitation is the leading factor of the aforementioned changes. The second factor is the altered potential evapotranspiration as mainly induced by relative humidity, which contributes to additional aridity changes in a same direction as precipitation does. The collective effects of precipitation and relative humidity account for more than 80% of the dryland variations. In comparison, the simulated aridity change is in reasonable agreement with reconstructions, while there are model–data discrepancies for Australia and uncertainties across proxies for southern Africa.

Biomarker signatures of the iconic Glossopteris plant

Glossopteris is the quintessential marker plant that dominated the forests of the Southern Hemisphere continents during the Permian before their abrupt extinction at the close of the Palaeozoic. Fossilized leaf and stem remains of Glossopteris plants, collected from the Permian succession of eastern India, were analysed to recognize the molecular signatures of solvent-extractable and non-extractable organic matter. Lipid-derived aliphatic and aromatic biomarkers were studied using GC–MS and GC×GC-TOFMS, while tetramethylammonium hydroxide (TMAH) thermochemolysis with GC–MS and GC×GC-TOFMS was used to reveal lignin precursors. The thermal maturity indices indicate low thermal rank for both samples. The presence of aromatic diterpanes in the leaf extract suggests that the Glossopteris plant was able to biosynthesize abietic acid and related plant terpenoids. The thermochemolysis products (thermochemolysates) of the samples contain monomethoxy-, and dimethoxybenzene derivatives produced from p‑hydroxyphenyl and guaiacyl units of lignin, respectively, which are the main constituents of extant gymnosperm lignin. The thermochemolysates indicate that lignin biosynthesis had evolved in Glossopteris.

Reassessment of historical sections from the Paleogene marine margin of the Congo Basin reveals an almost complete absence of Danian deposits

The early Paleogene is critical for understanding global biodiversity patterns in modern ecosystems. During this interval, Southern Hemisphere continents were largely characterized by isolation and faunal endemism following the breakup of Gondwana. Africa has been proposed as an important source area for the origin of several marine vertebrate groups but its Paleogene record is poorly sampled, especially from sub-Saharan Africa. To document the early Paleogene marine ecosystems of Central Africa, we revised the stratigraphic context of sedimentary deposits from three fossil-rich vertebrate localities: the Landana section in the Cabinda exclave (Angola), and the Manzadi and Bololo localities in western Democratic Republic of Congo. We provide more refined age constraints for these three localities based on invertebrate and vertebrate faunas, foraminiferal and dinoflagellate cyst assemblages, and carbon isotope records. We find an almost complete absence of Danian-aged rocks in the Landana section, contrary to prevailing interpretations over the last half a century (only the layer 1, at the base of the section, seems to be Danian). Refining the age of these Paleocene layers is crucial for analyzing fish evolution in a global framework, with implications for the early appearance of Scombridae (tunas and mackerels) and Tetraodontiformes (puffer fishes). The combination of vertebrate fossil records from Manzadi and Landana sections suggests important environmental changes around the K/Pg transition characterized by an important modification of the ichthyofauna. A small faunal shift may have occurred during the Selandian. More dramatic is the distinct decrease in overall richness that lasts from the Selandian to the Ypresian. The Lutetian of West Central Africa is characterized by the first appearance of numerous cartilaginous and bony fishes. Our analysis of the ichthyofauna moreover indicates two periods of faunal exchanges: one during the Paleocene, where Central Africa appears to have been a source for the European marine fauna, and another during the Eocene when Europe was the source of the Central Africa fauna. These data indicate that Central Africa has had connections with the Tethyian realm.

The global hydroclimate response during the Younger Dryas event

To analyze the global hydroclimate response during the Younger Dryas cold event, we evaluate climate model results that have been constrained with proxy-based temperatures from the North Atlantic region. We find that both the temperature and the hydroclimate response have a clear global signature. A marked cooling is simulated over the North Atlantic Ocean (more than 5 °C) and the downwind continents (2–4 °C). This response is related to the weakening of the Atlantic meridional overturning circulation under influence of meltwater discharges. The hydroclimate response is most expressed over Eurasia in a belt between 40 and 60°N, and over Northern Africa in the Sahel region. In both areas, a strong decrease in soil moisture is simulated (up to 20% reduction). In contrast, a striking increase in moisture is found over southeastern North America (15% increase), where southerly atmospheric flow brings moist air to the continent. Outside these areas that are clearly affected by the cold North Atlantic Ocean, the responses of temperature and moisture are decoupled, with different causes for these temperature and hydroclimate responses. In the tropics, the hydroclimate response is governed by the southward shift of the intertropical convergence zone (ITCZ) due to the cooling of the North Atlantic Ocean. This causes drier conditions north of the equator and wetter conditions in the Southern Hemisphere tropics. The associated changes in soil moisture are relatively gradual here, taking up to two centuries to complete, suggesting that the impact of the ITCZ shift on the tropical hydroclimate is building up. Our experiment indicates that Southern Hemisphere continents experienced a small cooling (less than 0.5 °C) during the Younger Dryas, caused by the negative radiative forcing associated with reduced atmospheric methane concentrations and enhanced dust levels. In our simulation, the bi-polar seesaw mechanism is relatively weak, so that the associated warming of the South Atlantic Ocean is not overwhelming the reduction in radiative forcing. Our results thus indicate that in the tropics and/or Southern Hemisphere, the cooling is a response to the negative radiative forcing, while the hydroclimatic changes are predominantly resulting from ITCZ variations. Consequently, when interpreting hydroclimatic proxy records from these regions, data should not be compared directly to key records from high latitudes, such as Greenland ice core stable isotope records.

Reactivation of the Venezuelan vertical deflection data set from classical astrogeodetic observations

Astrogeodetic vertical deflections (VDs) are gravity field functionals which are independent from any other field observation such as gravity accelerations from gravimetry or geoid undulations from GPS and geometric levelling. They may be useful for the validation of global geopotential models or height transfer via GPS and astronomical levelling. VDs are sensitive to the local mass-distribution, so can be used in geophysical studies, too. Over Southern Hemisphere continents in general and South America in particular, VDs are exceptionally rare. This paper describes the reactivation of a unique VD data set that extends over parts of the Andes Mountains in Venezuela. The VD data was acquired 1983 and 1985 with classical astrogeodetic instrumentation at 24 field stations along a ∼80 km traverse crossing the Cordillera de Mérida with observation site elevations as high as ∼4500 m. To be compatible with modern geocentric gravity field products, the geodetic coordinates of the VD sites were transformed from the historic (non-geocentric) Venezuelan reference system to the geocentric ITRF2014, with residuals smaller than ∼1 m. In the ITRF, the measured VDs have RMS signal strengths of ∼20 arc-seconds (North-South) and ∼14 arc-seconds (East-West), with magnitudes exceeding 60 arc-seconds at one benchmark. The observed VDs were compared against VDs from GRACE, GOCE and EGM2008 data and from the ultra-high resolution GGMplus gravity maps. The GGMplus model was found to capture ∼85 to 90% (in terms of root-mean-square signals) of the measured VD signals. Both VD components are in ∼2 arc-sec agreement with GGMplus. Overall, the agreement between observed VDs and modelled VDs is considered satisfactory, given the VDs were measured in a topographically rugged region, where residual signals may be large and global models are not well supported through regional terrestrial gravity data. The VDs may be useful, e.g., for the assessment of high-frequency constituents of present and future high-degree gravitational models (e.g., EGM2020) and calibration of model commission errors. The Venezuelan VD data is freely available.

Investigating Local and Remote Terrestrial Influence on Air Masses at Contrasting Antarctic Sites Using Radon‐222 and Back Trajectories

AbstractWe report on the first summer of high‐sensitivity radon measurements from a two‐filter detector at Jang Bogo Station (Terra Nova Bay) and contrast them with simultaneous observations at King Sejong Station (King George Island). King Sejong radon concentrations were characteristic of a marine baseline station (0.02–0.3 Bq m−3), whereas Jang Bogo values were highly variable (0.06–5.2 Bq m−3), mainly due to emissions from exposed coastal ground (estimated mean flux 0.09–0.11 atoms cm−2 s−1) and shallow atmospheric mixing depths. For wind speeds of ≤3.5 m s−1 the influence of local radon emissions became increasingly more prominent at both sites. A cluster analysis of back trajectories from King Sejong (62°S) revealed a fairly even distribution between air masses that had passed recently over South America, the Southern Ocean, and Antarctica, whereas at Jang Bogo (75°S) 80% of events had recently passed over the Ross Ice Shelf and West Antarctica, 12% were synoptically forced over Cape Adare, and 8% were associated with subsidence over the Antarctic interior and katabatic flow to the station. When cross‐checked against radon concentrations, only half of the back trajectories ending at Jang Bogo that had indicated distant contact with nonpolar southern hemisphere continents within the past 10 days showed actual signs of terrestrial influence. A simple‐to‐implement technique based on high‐pass filtered absolute humidity is developed to distinguish between predominantly katabatic, oceanic, and near‐coastal air masses for characterization of trace gas and aerosol measurements at coastal East Antarctic sites.

First record of flower visitation by a rodent in Neotropical Proteaceae, Oreocallis grandiflora

Abstract:There is still much to learn about pollination ecology in areas of high species diversity, such as the Neotropical region. For example, the role of non-flying mammals in pollination is largely unknown in the Neotropical areas, despite the importance of this group in the pollination of plants in other regions. Here we report evidence for flower visitation by a rodent to Oreocallis grandiflora (Proteaceae) in our study site in the southern Andes of Ecuador. For a period of 241 h, camcorders equipped with infrared lights revealed 22 occurrences of floral visitation by Microryzomys altissimus (Cricetidae) to inflorescences of O. grandiflora. Pollen samples taken from the fur of captured individuals showed that M. altissimus carries pollen of O. grandiflora, indicating a potential pollinator role for the rodent. This is the first record of flower visitation by a rodent in the Neotropical Andes. Pollination interactions between non-flying mammals and Proteaceae have been reported in other southern hemisphere continents. This study underscores the need for more research on pollination interactions in the Neotropics, especially in critical Andean biodiversity hotspots.

Around the World in Eight Million Years: Historical Biogeography and Evolution of the Spray Zone Spider Amaurobioides (Araneae: Anyphaenidae).

Closely related organisms with transoceanic distributions have long been the focus of historical biogeography, prompting the question of whether long-distance dispersal, or tectonic-driven vicariance shaped their current distribution. Regarding the Southern Hemisphere continents, this question deals with the break-up of the Gondwanan landmass, which has also affected global wind and oceanic current patterns since the Miocene. With the advent of phylogenetic node age estimation and parametric bioinformatic advances, researchers have been able to disentangle historical evolutionary processes of taxa with greater accuracy. In this study, we used the coastal spider genus Amaurobioides to investigate the historical biogeographical and evolutionary processes that shaped the modern-day distribution of species of this exceptional genus of spiders. As the only genus of the subfamily Amaurobioidinae found on three Southern Hemisphere continents, its distribution is well-suited to study in the context of Gondwanic vicariance versus long-distance, transoceanic dispersal. Ancestral species of the genus Amaurobioides appear to have undergone several long-distance dispersal events followed by successful establishments and speciation, starting from the mid-Miocene through to the Pleistocene. The most recent common ancestor of all present-day Amaurobioides species is estimated to have originated in Africa after arriving from South America during the Miocene. From Africa the subsequent dispersals are likely to have taken place predominantly in an eastward direction. The long-distance dispersal events by Amaurobioides mostly involved transoceanic crossings, which we propose occurred by rafting, aided by the Antarctic Circumpolar Current and the West Wind Drift.

The Cenozoic history of New Zealand temperate rainforests: comparisons with southern Australia and South America

ABSTRACTThe temperate rainforests of southern hemisphere continents share Gondwanan antecedents, but subsequent trajectories exhibit divergent patterns. We review the Cenozoic history of major forest elements (c. 30 genera/families) of the temperate rainforests of New Zealand and compare these with South America and southeast Australia. From macro- and microfossil evidence, the major structural components of temperate rainforests in New Zealand have lineages dating back almost continuously to the Eocene or earlier. These include the tree ferns (Cyathea and Dicksonia), Agathis, all but one of the podocarps, Nothofagaceae and other broadleaved genera such as Lauraceae and Cunoniaceae. Collectively these taxa contribute approximately 50% of current biomass in New Zealand temperate forests. However, several previously important groups in the Cenozoic such as Araucaria, the Brassospora-type beeches, and Casuarinaceae became extinct in New Zealand in the Miocene to Pleistocene. Patterns of extinction are broadly similar in New Zealand and South America (mostly late Miocene to Pleistocene) in response to climate cooling along steepened environmental gradients whereas in southern Australia taxa became extinct later (Pleistocene) reflecting limited suitable habitat during glacials. The deep-time continuity evident in the composition of New Zealand temperate rainforests was not influenced by the decrease in land area during the maximum marine transgression in the late Oligocene (c. 25–24 million years ago). Forest canopy dominants and emergents appear to have remained remarkably stable, perhaps reflecting community resilience. However, new subcanopy and open habitat lineages arrived as forest taxa were extirpated and climates cooled, reducing potential forest habitats.

A long distance dispersal hypothesis for the Pandanaceae and the origins of the Pandanus tectorius complex

Pandanaceae (screwpines) is a monocot family composed of c. 750 species widely distributed in the Paleotropics. It has been proposed that the family may have a Gondwanan origin with an extant Paleotropical distribution resulting from the breakup of that supercontinent. However, fossils supporting that hypothesis have been recently reassigned to other families while new fossil discoveries suggest an alternate hypothesis. In the present study, nuclear and chloroplast sequences were used to resolve relationships among Pandanaceae genera. Two well-supported fossils were used to produce a chronogram to infer whether the age of major intra-familial lineages corresponds with the breakup of Gondwana. The Pandanaceae has a Late Cretaceous origin, and genera on former Gondwanan landmasses began to diverge in the Late Eocene, well after many of the southern hemisphere continents became isolated. The results suggest an extant distribution influenced by long-distance-dispersal. The most widespread group within the family, the Pandanus tectorius species complex, originated in Eastern Queensland within the past six million years and has spread to encompass nearly the entire geographic extent of the family from Africa through Polynesia. The spread of that group is likely due to dispersal via hydrochory as well as a combination of traits such as agamospermy, anemophily, and multi-seeded propagules which can facilitate the establishment of new populations in remote locations.

Atmospheric mercury observations from Antarctica: seasonal variation and source and sink region calculations

Abstract. Long term atmospheric mercury measurements in the Southern Hemisphere are scarce and in Antarctica completely absent. Recent studies have shown that the Antarctic continent plays an important role in the global mercury cycle. Therefore, long term measurements of gaseous elemental mercury (GEM) were initiated at the Norwegian Antarctic Research Station, Troll (TRS) in order to improve our understanding of atmospheric transport, transformation and removal processes of GEM. GEM measurements started in February 2007 and are still ongoing, and this paper presents results from the first four years. The mean annual GEM concentration of 0.93 ± 0.19 ng m−3 is in good agreement with other recent southern-hemispheric measurements. Measurements of GEM were combined with the output of the Lagrangian particle dispersion model FLEXPART, for a statistical analysis of GEM source and sink regions. It was found that the ocean is a source of GEM to TRS year round, especially in summer and fall. On time scales of up to 20 days, there is little direct transport of GEM to TRS from Southern Hemisphere continents, but sources there are important for determining the overall GEM load in the Southern Hemisphere and for the mean GEM concentration at TRS. Further, the sea ice and marginal ice zones are GEM sinks in spring as also seen in the Arctic, but the Antarctic oceanic sink seems weaker. Contrary to the Arctic, a strong summer time GEM sink was found, when air originates from the Antarctic plateau, which shows that the summertime removal mechanism of GEM is completely different and is caused by other chemical processes than the springtime atmospheric mercury depletion events. The results were corroborated by an analysis of ozone source and sink regions.

Molecular phylogenetics, historical biogeography, and chromosome number evolution of Portulaca (Portulacaceae)

Portulaca is the only genus in Portulacaceae and has ca. 100 species distributed worldwide, mainly in the tropics and subtropics. Molecular data place the genus as one of the closest relatives of Cactaceae, but phylogenetic relationships within Portulaca are barely known. This study samples 59 species of Portulaca, 10 infraspecific taxa, and three cultivars, including multiple samples of widespread species. The sampled taxa represent all subgenera in the classifications of von Poellnitz (1934), Legrand (1958), and Geesink (1969) and come from around the world. Nuclear ITS and chloroplast ndhF, trnT-psbD intergenic spacer, and ndhA intron DNA sequences were analyzed using maximum likelihood and Bayesian methods to produce a hypothesis of relationships within Portulaca. Divergence times were estimated using Hawaiian endemics for calibration, and biogeographical patterns were examined using a Bayes–DIVA approach. In addition, the evolution of chromosome numbers in the genus was investigated using probabilistic models. The analyses strongly support the monophyly of Portulaca, with an age of the most recent common ancestor (MRCA) of 23Myr. Within Portulaca are two major lineages: the OL clade (comprising opposite-leaved species) distributed in Africa, Asia, and Australia, and the AL clade (comprising alternate to subopposite-leaved species), which is more widespread and originated in the New World. Sedopsis, a genus sometimes recognized as distinct from Portulaca based on a long corolla tube, is nested within the OL clade and does not merit taxonomic recognition. Samples of Portulaca grandiflora, Portulaca halimoides, and Portulaca oleracea were found to be non-monophyletic. It is hypothesized that the ancestral distribution area of Portulaca included southern hemisphere continents and Asia. The OL clade remained restricted to the Old World (except Portulaca quadrifida, a pantropical weed), while the AL clade, with a South American origin, was able to disperse multiple times to other continents. The base chromosome number for Portulaca is inferred to be x=9, although the analysis was primarily based on the available data for the AL clade. A number of chromosome number change events (polyploidization, demi-polyploidization, gain, and loss) were shown to have occurred in the genus, especially within the Oleracea clade.

Have the Southern Westerlies changed in a zonally symmetric manner over the last 14,000 years? A hemisphere-wide take on a controversial problem

The prevailing view in the palaeoclimate literature of the last 20 years is that the Southern Westerly Winds (SWW) were intensified over southern Australia and Tasmania during the warmer-than-present early Holocene (11–8ka). At similar latitudes on the opposite side of the southern mid-latitudes, palaeoclimate studies have suggested a poleward shift of the northern edge of the westerlies and focusing at 49°S in southern South America. This zonal asymmetry contrasts with the modern day zonal symmetry displayed by the SWW and poses a formidable challenge to an understanding of the modes of climatic variability of the southern extra-tropics. This paper presents an updated synthesis of continuous, radiocarbon-dated palaeoenvironmental data from the westerlies zone of influence in all Southern Hemisphere continents. Synchronous multi-millennial trends in moisture, vegetation, fire, and hydrologic balance are remarkably consistent with the way the SWW changes impact upon the climate in Southern Hemisphere landmasses in the modern climate. Considering the modern relationships between local precipitation and zonal wind speeds, it is suggested that the SWW changed in a zonally symmetric manner at multi-millennial scale between 14 and 5ka. Regional asymmetry develops after 5ka across the Southern Hemisphere, with a pattern of precipitation anomalies akin to the modern functioning of El Niño – Southern Oscillation, which started ∼6200 years ago.

Climate change: a cause for new biodiversity conservation objectives but let’s not throw the baby out with the bathwater

Climate change: a cause for new biodiversity conservation objectives but let’s not throw the baby out with the bathwater