ALBERT

Description: Bottom-simulating reflectors (BSR) are observed commonly at a depth of several hundred meters below the seafloor in continental margin sedimentary sections that have undergone recent tectonic consolidation or rapid accumulation. They are believed to correspond to the deepest level at which methane hydrate (clathrate) is stable. We present a model in which BSR hydrate layers are formed through the removal of methane from upward moving pore fluids as they pass into the hydrate stability field. In this model, most of the methane is generated below the level of hydrate stability, but not at depths sufficient for significant thermogenic production; the methane is primarily biogenic in origin. The model requires either a mechanism to remove dissolved methane from the pore fluids or disseminated free gas carried upward with the pore fluid. The model accounts for the evidence that the hydrate is concentrated in a layer at the base of the stability field, for the source of the large amount of methane contained in the hydrate, and for BSRs being common only in special environments. Strong upward fluid expulsion into the hydrate stability field does not occur in normal sediment depositional regimes, so BSRs are uncommon. Upward fluid expulsion does occur as a result of tectonic thickening and loading in subduction zone accretionary wedges and in areas where rapid deposition results in initial undercconsolidation. In these areas hydrate BSRs are common. The most poorly quantified aspect of the model is the efficiency with which methane is removed and hydrate is formed as pore fluids pass into the hydrate stability field. The critical boundary in the phase diagram between the fluid-plus-hydrate and fluid-only fields is not well constrained. However, the amount of methane required to form the hydrate and limited data on methane concentrations in pore fluids from deep-sea boreholes suggest very efficient removal of methane from rising fluid that may contain less than the amount required for free gas production. In most fluid expulsion regimes, the quantity of fluid moved upward to the seafloor is great enough to continually remove the excess chloride and the residue of isotope fractionation resulting from hydrate formation. Thus, as observed in borehole data, there are no large chloride or isotope anomalies remaining in the local pore fluids. The differences in the concentration of methane and probably of CO2 in the pore fluid above and below the base of the stability field may have a significant influence on early sediment diagenetic reactions.

Description: The sediment-buried eastern flank of the Juan de Fuca Ridge provides a unique environment for studying the thermal nature and geochemical consequences of hydrothermal circulation in young ocean crust. Just 18 km east of the spreading axis, where the sea-floor age is 0.62 Ma, sediments lap onto the ridge flank and create a sharp boundary between sediment-free and sediment-covered igneous crust. Farther east, beneath the nearly continuous turbidite sediment cover of Cascadia Basin, the buried basement topography is extremely smooth in some areas and rough in others. At a few isolated locations, small volcanic edifices penetrate the sediment surface. An initial cruise in 1978 and two subsequent cruises in 1988 and 1990 on this sedimented ridge flank have produced extensive single-channel seismic coverage, detailed heat flow surveys co-located with seismic lines, and pore-fluid geochemical profiles of piston and gravity cores taken over heat flow anomalies. Complementary multichannel seismic reflection data were collected across the ridge crest and eastern flank in 1985 and 1989. Preliminary results of these studies provide important new information about hydrothermal circulation in ridge flank environments. Near areas of extensive basement outcrop, ventilated hydrothermal circulation in the upper igneous crust maintains temperatures of less than 10–20 °C; geochemically, basement fluids are virtually identical to seawater. Turbidite sediment forms an effective hydrologic and geochemical seal that restricts greatly any local exchange of fluid between the igneous crust and the ocean. Once sediment thickness reaches a few tens of metres, local vertical fluid flux through the sea floor is limited to rates of less than a few millimetres per year. Fluids and heat are transported over great distances laterally in the igneous crust beneath sediment however. Heat flow, basement temperatures, and basement fluid compositions are unaffected by ventilated circulation only where continuous sediment cover extends more than 15–20 km away from areas of extensive outcrop. Where small basement edifices penetrate the sediment cover in areas that are otherwise fully sealed, fluids discharge at rates sufficient to cause large heat flow and pore-fluid geochemical anomalies in the immediate vicinity of the outcrops. After complete sediment burial, hydrothermal circulation continues in basement. Estimated basement temperatures and, to the limited degree observed, fluid compositions are uniform over large areas despite large local variations in sediment thickness. Because of the resulting strong relationship between heat flow and sediment thickness, it is not possible, in most areas, to detect any systematic pattern of heat flow that might be associated with cellular hydrothermal circulation in basement. However, an exception to this occurs at one location where the sediment thickness is sufficiently uniform to allow detection of a systematic variation in heat flow that can probably be ascribed to cellular circulation. At that location, temperatures at the sediment–basement interface vary smoothly between about 40 and 50 °C, with a half-wavelength of about 700 m. A permeable-layer thickness of similar dimension is inferred by assuming that circulation is cellular with an aspect ratio of roughly one. This thickness is commensurate with the subbasement depth to a strong seismic reflector observed commonly in the region. Seismic velocities in the igneous crustal layer above this reflector have been observed to be low near the ridge crest and to increase significantly where the transition from ventilated to sealed hydrothermal conditions occurs, although no associated reduction in permeability can be ascertained from the thermal data.

Description: We present the result of the third Marine Ice Sheet Intercomparison project, MISMIP+. MISMIP+ is intended to be a test of ice flow models which include fast sliding marine ice streams and floating ice shelves and in particular a treatment of viscous stress that is sufficient for buttressing, where upstream ice flow is restrained by a downstream ice shelf. A set of idealized experiments test the models in circumstances where buttressing contributes to a stable steady state, and where a reduction in that buttressing causes ice stream acceleration, thinning, and grounding line retreat. We find that the most important distinction between models in this particular type of simulation is in the treatment of sliding at the bed, with other distinctions – notably the difference between the simpler and more complete treatments of englacial stress, but also the differences between numerical methods – taking a secondary role.

Description: Ice flow models of the Antarctic ice sheet are commonly used to simulate its future evolution in response to different climate scenarios and inform on the mass loss that would contribute to future sea level rise. However, there is currently no consensus on estimated the future mass balance of the ice sheet, primarily because of differences in the representation of physical processes and the forcings employed. This study presents results from 18 simulations from 15 international groups focusing on the evolution of the Antarctic ice sheet during the period 2015–2100, forced with different scenarios from the Coupled Model Intercomparison Project Phase 5 (CMIP5) representative of the spread in climate model results. The contribution of the Antarctic ice sheet in response to increased warming during this period varies between −7.8 and 30.0 cm of Sea Level Equivalent (SLE). The evolution of the West Antarctic Ice Sheet varies widely among models, with an overall mass loss up to 21.0 cm SLE in response to changes in oceanic conditions. East Antarctica mass change varies between −6.5 and 16.5 cm SLE, with a significant increase in surface mass balance outweighing the increased ice discharge under most RCP 8.5 scenario forcings. The inclusion of ice shelf collapse, here assumed to be caused by large amounts of liquid water ponding at the surface of ice shelves, yields an additional mass loss of 8 mm compared to simulations without ice shelf collapse. The largest sources of uncertainty come from the ocean-induced melt rates, the calibration of these melt rates based on oceanic conditions taken outside of ice shelf cavities and the ice sheet dynamic response to these oceanic changes. Results under RCP 2.6 scenario based on two CMIP5 AOGCMs show an overall mass loss of 10 mm SLE compared to simulations done under present-day conditions, with limited mass gain in East Antarctica.

Description: Opportunities to include Cetancodontamorpha in the study of the evolution of the immune system in the clades of Artiodactylamorpha, Ruminantiamorpha, Suinamorpha, and Camelidamorpha have increased with the use of the bottlenose dolphin, Tursiops truncatus, as a sentinel species to study the effects of environmental pollutants on the health of marine mammals. Efforts are currently underway to increase the number reagents needed for detailed studies. Thus far, screening of monoclonal antibodies (mAbs) made to leukocyte differentiation molecules (LDM) and the major histocompatibility (MHC) class I and class II molecules in Ruminantiamorpha have yielded some mAbs that recognize conserved epitopes expressed on orthologues in the bottlenose dolphin. More direct approaches are in progress to identify additional mAbs to bottlenose LDM and cytokines. As reported here, both direct and indirect approaches were used to identify mAbs specific for cytokines useful in monitoring the effects of environmental pollutants on the immune system. Immunization of mice with expressed bottlenose dolphin cytokines yielded mAbs specific for IFN-γ, TNF-α, IL-6, IL-8, IL-10, and IL-17A. Screening of previously developed mAbs used in livestock immunology research revealed mAbs developed against ovine IFN-γ and bovine IL-17 and IL-1β recognize conserved epitopes in bottlenose dolphin orthologues. The mAbs identified in the present study expand the reagents available to study the function of the immune system in bottlenose dolphins and cattle.

Description: A comprehensive database of paleoclimate records is needed to place recent warming into the longer-term context of natural climate variability. We present a global compilation of quality-controlled, published, temperature-sensitive proxy records extending back 12,000 years through the Holocene. Data were compiled from 679 sites where time series cover at least 4000 years, are resolved at sub-millennial scale (median spacing of 400 years or finer) and have at least one age control point every 3000 years, with cut-off values slackened in data-sparse regions. The data derive from lake sediment (51%), marine sediment (31%), peat (11%), glacier ice (3%), and other natural archives. The database contains 1319 records, including 157 from the Southern Hemisphere. The multi-proxy database comprises paleotemperature time series based on ecological assemblages, as well as biophysical and geochemical indicators that reflect mean annual or seasonal temperatures, as encoded in the database. This database can be used to reconstruct the spatiotemporal evolution of Holocene temperature at global to regional scales, and is publicly available in Linked Paleo Data (LiPD) format.

Description: Since 2016, the European Union (EU) has required Member States to prevent, control and eradicate selected invasive alien species (IAS) designated as Species of Union Concern. To improve these conservation efforts, online information systems are used to convey IAS information to the wider public, often as a means to bolster community-based environmental monitoring. Despite this, both the conformity and quality of information presented amongst online databases remain poorly understood. Here, we assess the harmonisation and educational potential of four major IAS databases (i.e., conformity of information and information quality, respectively): CABI, EASIN, GISD and NOBANIS. All databases were interrogated for information concerning 49 IAS of Union Concern. For each species, information presented within the evaluated databases was scored in relation to several key topics: morphological identification; EU distribution; detrimental impacts; control options; and the use of source material citations. Overall, scores differed significantly among databases and thus lacked harmonisation, whereby CABI ranked significantly highest based on the combined scores for all topics. In addition, CABI ranked highest for the individual topics of species identification, impacts, control options, and for the use of citations. EASIN ranked highest for species distribution data. NOBANIS consistently ranked as the lowest scoring database across all topics. For each topic, the highest scoring databases achieved scores indicative of detailed or highly detailed information, which suggests a high educational potential for the information portrayed. Nevertheless, the extent of harmonisation and quality of information presented amongst online databases should be improved. This is especially pertinent if online databases are to contribute to public participatory monitoring initiatives for IAS detection.

Description: The quasi‐biennial oscillation (QBO) of the equatorial zonal wind leads to zonally symmetric temperature variations in the stratosphere that descend downward. Here we investigate the QBO‐induced temperature anomalies in the tropical tropopause layer (TTL) and detect pronounced longitudinal variations of the signal. In addition, the QBO temperature anomalies show a strong seasonal variability. The magnitude of these seasonal and longitudinal QBO variations is comparable to the magnitude of the well‐known zonal mean QBO signal in the TTL. At the cold point tropopause, the strongest QBO variations of around ±1.6 K are found over regions of active convection such as the West Pacific and Africa during boreal winter. The weakest QBO variations of ±0.25 K are detected over the East Pacific during boreal summer, while the zonal mean signal ranges around ±0.7 K. The longitudinal variations are associated with enhanced convective activity that occurs during QBO cold phases and locally enhances the cold anomalies.

Description: Control strategies for established populations of invasive alien species can be costly and complex endeavours, which are frequently unsuccessful. Therefore, rapid-reaction techniques that are capable of maximising efficacy whilst minimising environmental damage are urgently required. The Asian clam (Corbicula fluminea Müller, 1774), and the zebra mussel (Dreissena polymorpha Pallas, 1771), are invaders capable of adversely affecting the functioning and biodiversity of freshwater ecosystems. Despite efforts to implement substantial population-control measures, both species continue to spread and persist within freshwater environments. As bivalve beds often become exposed during low-water conditions, this study examined the efficacy of steam-spray (≥100 °C, 350 kPa) and open-flame burn treatments (~1000 °C) to kill exposed individuals. Direct steam exposure lasting for 5 min caused 100% mortality of C. fluminea buried at a depth of 3 cm. Further, combined rake and thermal shock treatments, whereby the substrate is disturbed between each application of either a steam or open flame, caused 100% mortality of C. fluminea specimens residing within a 4-cm deep substrate patch, following three consecutive treatment applications. However, deeper 8-cm patches and water-saturated substrate reduced maximum bivalve species mortality rates to 77% and 70%, respectively. Finally, 100% of D. polymorpha specimens were killed following exposure to steam and open-flame treatments lasting for 30 s and 5 s, respectively. Overall, our results confirm the efficacy of thermal shock treatments as a potential tool for substantial control of low-water-exposed bivalves. Although promising, our results require validation through upscaling to field application, with consideration of other substrate types, increased substrate depth, greater bivalve densities, non-target and long-term treatment effects.

Description: The tropical tropopause layer (TTL) is the transition region between the well-mixed convective troposphere and the radiatively controlled stratosphere with air masses showing chemical and dynamical properties of both regions. The representation of the TTL in meteorological reanalysis data sets is important for studying the complex interactions of circulation, convection, trace gases, clouds, and radiation. In this paper, we present the evaluation of climatological and long-term TTL temperature and tropopause characteristics in the reanalysis data sets ERA-Interim, ERA5, JRA-25, JRA-55, MERRA, MERRA-2, NCEP-NCAR (R1), and CFSR. The evaluation has been performed as part of the SPARC (Stratosphere–troposphere Processes and their Role in Climate) Reanalysis Intercomparison Project (S-RIP). The most recent atmospheric reanalysis data sets (ERA-Interim, ERA5, JRA-55, MERRA-2, and CFSR) all provide realistic representations of the major characteristics of the temperature structure within the TTL. There is good agreement between reanalysis estimates of tropical mean temperatures and radio occultation data, with relatively small cold biases for most data sets. Temperatures at the cold point and lapse rate tropopause levels, on the other hand, show warm biases in reanalyses when compared to observations. This tropopause-level warm bias is related to the vertical resolution of the reanalysis data, with the smallest bias found for data sets with the highest vertical resolution around the tropopause. Differences in the cold point temperature maximize over equatorial Africa, related to Kelvin wave activity and associated disturbances in TTL temperatures. Interannual variability in reanalysis temperatures is best constrained in the upper TTL, with larger differences at levels below the cold point. The reanalyses reproduce the temperature responses to major dynamical and radiative signals such as volcanic eruptions and the quasi-biennial oscillation (QBO). Long-term reanalysis trends in temperature in the upper TTL show good agreement with trends derived from adjusted radiosonde data sets indicating significant stratospheric cooling of around −0.5 to −1 K per decade. At 100 hPa and the cold point, most of the reanalyses suggest small but significant cooling trends of −0.3 to −0.6 K per decade that are statistically consistent with trends based on the adjusted radiosonde data sets. Advances of the reanalysis and observational systems over the last decades have led to a clear improvement in the TTL reanalysis products over time. Biases of the temperature profiles and differences in interannual variability clearly decreased in 2006, when densely sampled radio occultation data started being assimilated by the reanalyses. While there is an overall good agreement, different reanalyses offer different advantages in the TTL such as realistic profile and cold point temperature, continuous time series, or a realistic representation of signals of interannual variability. Their use in model simulations and in comparisons with climate model output should be tailored to their specific strengths and weaknesses.