Ammonium in coastal Antarctic aerosol and snow: Role of polar ocean and penguin emissions

first_imgYear-round aerosol samples collected in the boundary layer at coastal Antarctic sites (Dumont D’Urville, Neumayer, and Halley) indicate a seasonal cycle of ammonium concentrations with a minimum in winter (April–September). A large intersite difference appears in the summer (November–February) maxima values, from ∼12.5 ng m−3 at Neumayer to 140–230 ng m−3 at Dumont D’Urville. At Dumont D’Urville, ammonium concentrations are the largest ever reported from Antarctic sites, and the large summer maxima are associated with large enrichments with respect to sea salt for potassium and calcium. In addition, seasonal ammonium variations at Dumont D’Urville are in phase with a well-marked seasonal cycle of oxalate concentrations which exhibit maxima of 5–10 ng m−3 in spring and summer and minima of less than 0.5 ng m−3 in winter. Such a composition of aerosols present in the boundary layer at Dumont D’Urville in summer is linked to the presence of a large Adélie penguin population from the end of October to March at the site. Ornithogenic soils (defined as guano-enriched soils), together with the bacterial decomposition of uric acid, are a source of ammonium, oxalate, and cation (such as potassium and calcium) aerosol, in addition to a subsequent large ammonia loss from ornithogenic soils to the atmosphere. The total breeding population of 5 million Adélie penguins widely distributed around the Antarctic continent may emit, at most, some 2.5 × 10−4 Mt of NH3-N during the summer months. In contrast, Halley and Neumayer Stations are far less exposed to penguin colony emissions. At Neumayer, ammonium concentrations peak from January to March and are in phase with the increase of biogenic sulfur species. Here the NH4+/(MSA + nss SO4−) molar ratio is close to 13% in summer aerosol and to 40% in winter aerosol. Using this summer ratio, which may be related to ammonia and sulfur oceanic emissions occurring south of 50°S in summer and estimated DMS emissions in these regions at this time, we derive an upper limit of 0.064 Mt NH3-N emitted per year by the high-latitude Southern Ocean in summer. This study indicates a very limited ammonia neutralization of acidic sulfate aerosols at high southern latitudes, except in the vicinity of ornithogenic soils occupied by large penguin colonies.last_img read more

Continue reading »

An examination of the precipitation regime at Thurston Island, Antarctica, from ECMWF re-analysis data

first_imgIn this study numerical weather prediction model data are utilized to examine the precipitation regime at Thurston Island (TI) (∼72°S, 99°W) in West Antarctica. This region was chosen because the precipitation may well reflect the high variability of cyclones in the Amundsen Sea, which in some years appears related to the El Niño–Southern Oscillation (ENSO) phenomenon. The data used are derived from the European Centre for Medium-range Weather Forecasts (ECMWF) Re-Analysis (ERA) project, encompassing the 15-year period from 1979 to 1993. A comparison of monthly TI precipitation derived from both ERA and ECMWF operational data for a 101-month overlap period demonstrates that the known ERA problems associated with moisture fluxes over Antarctica are not significant at TI. The annual precipitation cycle at TI (mean of 713 mm water equivalent) is related directly to the frequency of cyclones in the Amundsen Sea, which, in turn, reflects the semi-annual oscillation. The majority of these systems develop in the circumpolar trough although ∼4% undergo cyclogenesis east of New Zealand. No trends in precipitation at TI can be discerned in the model data. Significant precipitation at TI occurs when the longwaves over the Pacific are amplified such that an intense low (blocking high) pressure is located west (east) of the island. Correlations between TI precipitation and mean sea level pressure in these two regions suggest that they are of equal importance in determining the precipitation that falls at TI. There is a small but significant anticorrelation between TI precipitation and the Southern Oscillation Index (SOI) from 1990 onwards. It is postulated that an increase in cyclone intensity during the El Niño years of the early 1990s is at least partially responsible because cyclone numbers are well correlated to the SOI during this period. No consistent relationship between TI precipitation and SOI is observed prior to 1990 in the ERA data. Copyright © 2000 Royal Meteorological Societylast_img read more

Continue reading »

Strontium isotope stratigraphy and age model for CRP-2/2A, Victoria Land basin, Antarctica

first_imgStrontium isotope stratigraphy was used to date 16 discrete horizons within the CRP-2/2A drillhole. Reworked Quaternary (<1.7 Ma) and possible Pliocene (31 Ma) deposits below this boundary were cut by multiple erosion surfaces of uncertain duration. Strontium isotope ages are combined with 40Ar/39Ar dates,diatom and calcareous nannofossil datums and a palaeomagnetic polarity zonation, to produce an age model for the core.last_img

Continue reading »

Laser-derived, particle size data from CRP-2/2A: implications for sequence and seismic stratigraphy

first_imgGravel-free, high-resolution (1-metre spacing, 32 channel) particle size data from theCRP-2/2A drill core indicate that many of the diamictites were likely deposited from floatingice. Textural dislocations occur at most sequence boundaries and provide independentcorroboration of the sequence stratigraphic interpretation. Likewise the data largely support thecorrelation drawn (Fielding et al., this volume) between the sequence stratigraphic cycles andthe regional seismic stratigraphy (an alternative correlation to Reflector ‘f’ is also suggested).The gravel-free data appear to be reflecting predominantly regional (global?) forcing with somepossible local effects, and long-term trends persisting through gravelly textural dislocations.last_img read more

Continue reading »

Pigmentation as a survival strategy for ancient and modern photosynthetic microbes under high ultraviolet stress on planetary surfaces

first_imgSolar radiation is the primary energy source for surface planetary life, so that pigments are fundamental components of any surface-dwelling organism. They may therefore have evolved in some form on Mars as they did on Earth. Photosynthetic microbes are major primary producers on Earth, but are concurrently vulnerable to ultraviolet (UV) damage. Using non-intrusive laser Raman spectroscopy to recognize the component parts of biomolecules, we have shown not only the abundance of microbial photosynthetic and photoprotective pigments in situ, but also their spatial distribution within their microhabitat. This essential aspect of their screening or avoidance survival strategies is lost on extraction with solvents. This precise approach is eminently suited to analysis of epilithic (surface) and endolithic (within rocks) communities in Antarctic desert habitats, which are putative analogues of early Mars. Raman spectra for key biomolecules (e.g. the UV screen parietin and the antioxidant β-carotene in epilithic lichens) enable not only the detection of organics in light-stratified habitats, but also the characterization of unknown pigments. Typical biomarkers of astrobiological relevance in our Raman spectral database include scytonemin (a UV screen), chlorophyll (primary photosynthetic pigment), phycocyanin (accessory pigment for shade adaptation) and a hopanoid extracted from 2·5 Gya microbial stromatolite from Australia. This compound dates from the same time period when a wetter Mars could have had a potentially flourishing surface microbial community of its own. Analyses with a laboratory Raman instrument have been extended to a novel miniature Raman spectrometer, operating at the same optimal excitation wavelength (1064 nm) via an In-Ga-As detector. After evaluation in Antarctica, this instrument will be space-qualified for a proposed Mars rover mission to detect biomolecules in the near-surface sediment profile of palaeolakes, using experience with Antarctic biomarkers to interpret alien spectra of fundamental components, without the need for prior knowledge of the identity of the target compounds.last_img read more

Continue reading »

Frequency response of ice streams

first_imgChanges at the grounding line of ice streams have consequences for inland ice dynamics and hence sea level. Despite substantial evidence documenting upstream propagation of frontal change, the mechanisms by which these changes are transmitted inland are not well understood. In this vein, the frequency response of an idealized ice stream to periodic forcing in the downstream strain rate is examined for basally and laterally resisted ice streams using a one-dimensional, linearized membrane stress approximation. This reveals two distinct behavioural branches, which we find to correspond to different mechanisms of upstream velocity and thickness propagation, depending on the forcing frequency. At low frequencies (centennial to millennial periods), slope and thickness covary hundreds of kilometres inland, and the shallow-ice approximation is sufficient to explain upstream propagation, which occurs through changes in grounding-line flow and geometry. At high frequencies (decadal to sub-decadal periods), penetration distances are tens of kilometres; while velocity adjusts rapidly to such forcing, thickness varies little and upstream propagation occurs through the direct transmission of membrane stresses. Propagation properties vary significantly between 29 Antarctic ice streams considered. A square-wave function in frontal stress is explored by summing frequency solutions, simulating some aspects of the dynamical response to sudden ice-shelf change.last_img read more

Continue reading »

Wind-driven export of Weddell Sea slope water

first_imgThe export of waters from the Weddell Gyre to lower latitudes is an integral component of the southern subpolar contribution to the three-dimensional oceanic circulation. Here we use more than 20 years of repeat hydrographic data on the continental slope on the northern tip of the Antarctic Peninsula and 5 years of bottom lander data on the slope at 1000 m to show the intermittent presence of a relatively cold, fresh, westward flowing current. This is often bottom-intensified between 600 and 2000 dbar with velocities of over 20 cm s−1, transporting an average of 1.5 ± 1.5 Sv. By comparison with hydrography on the continental slope within the Weddell Sea and modeled tracer release experiments we show that this slope current is an extension of the Antarctic Slope Current that has crossed the South Scotia Ridge west of Orkney Plateau. On monthly to interannual time scales the density of the slope current is negatively correlated (r > 0.6 with a significance of over 95%) with eastward wind stress over the northern Weddell Sea, but lagging it by 6–13 months. This relationship holds in both the high temporal resolution bottom lander time series and the 20+ year annual hydrographic occupations and agrees with Weddell Sea export variability observed further east. We compare several alternative hypotheses for this wind stress/export relationship and find that it is most consistent with wind-driven acceleration of the gyre boundary current, possibly modulated by eddy dynamics, and represents a mechanism by which climatic perturbations can be rapidly transmitted as fluctuations in the supply of intermediate-level waters to lower latitudes.last_img read more

Continue reading »

Subglacial geology and geomorphology of the Pensacola‐Pole Basin, East Antarctica

first_imgThe East Antarctic Ice Sheet (EAIS) is underlain by a series of low‐lying subglacial sedimentary basins. The extent, geology and basal topography of these sedimentary basins are important boundary conditions governing the dynamics of the overlying ice sheet. This is particularly pertinent for basins close to the grounding line wherein the EAIS is grounded below sea level, and therefore potentially vulnerable to rapid retreat. Here, we analyze newly acquired airborne geophysical data over the Pensacola‐Pole Basin (PPB), a previously unexplored sector of the EAIS. Using a combination of gravity, magnetic and ice‐penetrating radar data, we present the first detailed subglacial sedimentary basin model for the PPB. Radar data reveal that the PPB is defined by a topographic depression situated ~500 m below sea level. Gravity and magnetic depth‐to‐source modeling indicate that the southern part of the basin is underlain by a sedimentary succession 2–3 km thick. This is interpreted as an equivalent of the Beacon Supergroup and associated Ferrar dolerites that are exposed along the margin of East Antarctica. However, we find that similar rocks appear to be largely absent from the northern part of the basin, close to the present‐day grounding line. In addition, the eastern margin of the basin is characterized by a major geological boundary and a system of overdeepened subglacial troughs. We suggest that these characteristics of the basin may reflect the behavior of past ice sheets and/or exert an influence on the present‐day dynamics of the overlying EAIS.last_img read more

Continue reading »

Real Salt Lake beats 10-man DC United 3-2

first_img Robert Lovell Tags: Baseball/PCL/Real Salt Lake Written by FacebookTwitterLinkedInEmailSANDY, Utah (AP) — Jefferson Savarino and Albert Rusnak each had a goal and an assist in Real Salt Lake’s 3-2 victory over 10-man D.C. United on Saturday night.D.C. United went down a man in the 22nd minute when Joseph Mora was initially shown a yellow card for a violent tackle, but was then sent off after video review.Corey Baird’s header tied it at 1 a minute earlier for RSL (4-5-1), and Rusnak made it 2-1 in the 26th with a right-footed shot that split through several United defenders. Jefferson Savarino added a third for Salt Lake, slotting a well-timed chip past goalkeeper Steve Clark in the 56th.Paul Arriola opened the scoring in the ninth minute for D.C. United (1-5-2).Steve Birnbaum’s header brought United within one with in the 83rd minute. May 12, 2018 /Sports News – Local Real Salt Lake beats 10-man DC United 3-2last_img read more

Continue reading »

Star South Sevier High Alum Makes All-Nebraska Honorable Mention

first_imgJune 26, 2018 /Sports News – Local Star South Sevier High Alum Makes All-Nebraska Honorable Mention Tags: Kenlee Wanlass/North Platte CC Knights/Omaha World-Herald FacebookTwitterLinkedInEmailNORTH PLATTE, Neb.-Per an announcement from the Omaha World-Herald, a former South Sevier High star softball player has made the all-Nebraska two-year college softball team.Kenlee Wanlas, an Elsinore native who starred for the Rams, batted .293 with three doubles for the North Platte C.C. Knights. Additionally, she posted a slugging percentage of .345 and was tied for the team lead with five steals on the season.Wanlass’ magnificence also extended to defense as she broke the all-time program record for fewest errors in a season.Despite being part of a team that went 5-34 on the season, Wanlass was clearly one of the bright spots in 2018 for the Knights. Written by Brad Jameslast_img read more

Continue reading »