Abstract
Small mountain glaciers are an important part of the cryosphere and tend to respond rapidly to climate warming. Historically, mapping very small glaciers (generally considered to be <0.5 km
...2
) using satellite imagery has often been subjective due to the difficulty in differentiating them from perennial snowpatches. For this reason, most scientists implement minimum size-thresholds (typically 0.01–0.05 km
2
). Here, we compare the ability of different remote-sensing approaches to identify and map very small glaciers on imagery of varying spatial resolutions (30–0.25 m) and investigate how operator subjectivity influences the results. Based on this analysis, we support the use of a minimum size-threshold of 0.01 km
2
for imagery with coarse to medium spatial resolution (30–10 m). However, when mapping on high-resolution imagery (<1 m) with minimal seasonal snow cover, glaciers <0.05 km
2
and even <0.01 km
2
are readily identifiable and using a minimum threshold may be inappropriate. For these cases, we develop a set of criteria to enable the identification of very small glaciers and classify them as
certain
,
probable
or
possible.
This should facilitate a more consistent approach to identifying and mapping very small glaciers on high-resolution imagery, helping to produce more comprehensive and accurate glacier inventories.
Brothers volcano, of the Kermadec intraoceanic arc, is host to a hydrothermal system unique among seafloor hydrothermal systems known anywhere in the world. It has two distinct vent fields, known as ...the NW Caldera and Cone sites, whose geology, permeability, vent fluid compositions, mineralogy, and ore-forming conditions are in stark contrast to each other. The NW Caldera site strikes for ∼600 m in a SW–NE direction with chimneys occurring over a ∼145-m depth interval, between ∼1,690 and 1,545 m. At least 100 dead and active sulfide chimney spires occur in this field and are typically 2–3 m in height, with some reaching 6–7 m. Their ages (at time of sampling) fall broadly into three groups: <4, 23, and 35 years old. The chimneys typically occur near the base of individual fault-controlled benches on the caldera wall, striking in lines orthogonal to the slopes. Rarer are massive sulfide crusts 2–3 m thick. Two main types of chimney predominate: Cu-rich (up to 28.5 wt.% Cu) and, more commonly, Zn-rich (up to 43.8 wt.% Zn). Geochemical results show that Mo, Bi, Co, Se, Sn, and Au (up to 91 ppm) are correlated with the Cu mineralization, whereas Cd, Hg, Sb, Ag, and As are associated with the dominant Zn-rich mineralization. The Cone site comprises the Upper Cone site atop the summit of the recent (main) dacite cone and the Lower Cone site that straddles the summit of an older, smaller, more degraded dacite cone on the NE flank of the main cone. Huge volumes of diffuse venting are seen at the Lower Cone site, in contrast to venting at both the Upper Cone and NW Caldera sites. Individual vents are marked by low-relief (≤0.5 m) mounds comprising predominately native sulfur with bacterial mats. Vent fluids of the NW Caldera field are focused, hot (≤300°C), acidic (pH ≥ 2.8), metal-rich, and gas-poor. Calculated end-member fluids from NW Caldera vents indicate that phase separation has occurred, with Cl values ranging from 93% to 137% of seawater values. By contrast, vent fluids at the Cone site are diffuse, noticeably cooler (≤122°C), more acidic (pH 1.9), metal-poor, and gas-rich. Higher-than-seawater values of SO
4
and Mg in the Cone vent fluids show that these ions are being added to the hydrothermal fluid and are not being depleted via normal water/rock interactions. Iron oxide crusts 3 years in age cover the main cone summit and appear to have formed from Fe-rich brines. Evidence for magmatic contributions to the hydrothermal system at Brothers includes: high concentrations of dissolved CO
2
(e.g., 206 mM/kg at the Cone site); high CO
2
/
3
He; negative δD and δ
18
O
H2O
for vent fluids; negative δ
34
S for sulfides (to −4.6‰), sulfur (to −10.2‰), and δ
15
N
2
(to −3.5‰); vent fluid pH values to 1.9; and mineral assemblages common to high-sulfidation systems. Changing physicochemical conditions at the Brothers hydrothermal system, and especially the Cone site, occur over periods of months to hundreds of years, as shown by interlayered Cu + Au- and Zn-rich zones in chimneys, variable fluid and isotopic compositions, similar shifts in
3
He/
4
He values for both Cone and NW Caldera sites, and overprinting of “magmatic” mineral assemblages by water/rock-dominated assemblages. Metals, especially Cu and possibly Au, may be entering the hydrothermal system via the dissolution of metal-rich glasses. They are then transported rapidly up into the system via magmatic volatiles utilizing vertical (∼2.5 km long), narrow (∼300-m diameter) “pipes,” consistent with evidence of vent fluids forming at relatively shallow depths. The NW Caldera and Cone sites are considered to represent stages along a continuum between water/rock- and magmatic/hydrothermal-dominated end-members.
Microbial productivity at hydrothermal vents is among the highest found anywhere in the deep ocean, but constraints on microbial growth and metabolism at vents are lacking. We used a combination of ...cultivation, molecular, and geochemical tools to verify pure culture H ₂ threshold measurements for hyperthermophilic methanogenesis in low-temperature hydrothermal fluids from Axial Volcano and Endeavour Segment in the northeastern Pacific Ocean. Two Methanocaldococcus strains from Axial and Methanocaldococcus jannaschii showed similar Monod growth kinetics when grown in a bioreactor at varying H ₂ concentrations. Their H ₂ half-saturation value was 66 μM, and growth ceased below 17–23 μM H ₂, 10-fold lower than previously predicted. By comparison, measured H ₂ and CH ₄ concentrations in fluids suggest that there was generally sufficient H ₂ for Methanocaldococcus growth at Axial but not at Endeavour. Fluids from one vent at Axial (Marker 113) had anomalously high CH ₄ concentrations and contained various thermal classes of methanogens based on cultivation and mcrA / mrtA analyses. At Endeavour, methanogens were largely undetectable in fluid samples based on cultivation and molecular screens, although abundances of hyperthermophilic heterotrophs were relatively high. Where present, Methanocaldococcus genes were the predominant mcrA / mrtA sequences recovered and comprised ∼0.2–6% of the total archaeal community. Field and coculture data suggest that H ₂ limitation may be partly ameliorated by H ₂ syntrophy with hyperthermophilic heterotrophs. These data support our estimated H ₂ threshold for hyperthermophilic methanogenesis at vents and highlight the need for coupled laboratory and field measurements to constrain microbial distribution and biogeochemical impacts in the deep sea.
Here we present a glacial and periglacial geomorphological map of a ∼6800 km
2
region of central Troms and Finnmark county, Arctic Norway. The map is presented at a 1:115,000 scale with the aim of ...characterising the spatial distribution of glacial and periglacial landforms and facilitating the reconstruction of the glacial history of the region during the latter stages of deglaciation from the Last Glacial Maximum and into the Holocene. Mapping was conducted predominantly by manual digitisation of landforms using a combination of Sentinel-2A/2B satellite imagery (10 m pixel resolution), vertical aerial photographs (<1 m pixel resolution), and Digital Elevation Models (10 and 2 m pixel resolution). Over 20,000 individual features have been mapped and include moraines (subdivided into major and minor moraines), ridges within areas of discrete debris accumulations (DDAs), flutings, eskers, irregular mounded terrain, lineations, glacially streamlined bedrock, possible glacially streamlined terrain, pronival ramparts, rock glaciers (subdivided into valley wall and valley floor, and rock glacierised moraines), lithalsas, contemporary glaciers and lakes. The map records several noteworthy large moraine assemblages within individual valleys, forming inset sequences from pre-Younger Dryas limits up to the 2018/19 ice margins and represents a valuable dataset for reconstructing Holocene glacial and periglacial activity.
Glaciers are important indicators of climate change, and recent observations worldwide document increasing rates of mountain glacier recession. Here we present approximately 200 years of change in ...mountain glacier extent in northern Troms and western Finnmark, northern Norway. This was achieved through (1) mapping and lichenometric dating of major moraine systems within a subset of the main study area (the Rotsund Valley) and (2) mapping recent (post-1980s) changes in ice extent from remotely sensed data. Lichenometric dating reveals that the Little Ice Age (LIA) maximum occurred approximately 1814 (±41 years), which is before the early twentieth-century LIA maximum proposed on the nearby Lyngen Peninsula but younger than LIA maximum limits in southern and central Norway (mid-eighteenth century). Between LIA maximum and 1989, a small sample of measured glaciers (n = 15) shrank a total of 3.9 km
2
(39 percent), and those that shrank by more than 50 percent are fronted by proglacial lakes. Between 1989 and 2018, the total area of glaciers within the study area (n = 219 in 1989) shrank by approximately 35 km
2
. Very small glaciers (<0.5 km
2
) show the highest relative rates of shrinkage, and 90 percent of mapped glaciers within the study area were less than 0.5 km
2
in 2018.
Forests are the dominant source of volatile organic compounds into the atmosphere, with isoprene being the most significant species. The oxidation chemistry of these compounds is a significant driver ...of local, regional and global atmospheric composition. Observations made over Borneo during the OP3 project in 2008, together with an observationally constrained box model are used to assess our understanding of this oxidation chemistry. In line with previous work in tropical forests, we find that the standard model based on MCM chemistry significantly underestimates the observed OH concentrations. Geometric mean observed to modelled ratios of OH and HO2 in airmasses impacted with isoprene are 5.32-4.43+3.68 and 1.18-0.30+0.30 respectively, with 68 % of the observations being within the specified variation. We implement a variety of mechanistic changes into the model, including epoxide formation and unimolecular decomposition of isoprene peroxy radicals, and assess their impact on the model success. We conclude that none of the current suggestions can simultaneously remove the bias from both OH and HO2 simulations and believe that detailed laboratory studies are now needed to resolve this issue.
K. K. McCully, R. A. Fielding, W. J. Evans, J. S. Leigh Jr and J. D. Posner
Department of Medicine, Medical College of Pennsylvania, Philadelphia 19129.
This study compared in vivo measurements of ...muscle metabolism in humans
with magnetic resonance spectroscopy (MRS) and in vitro analysis of
biopsies. Healthy subjects 4 young males, 28.2 +/- 6.8 (SD) yr, and 6
older subjects (5 males, 1 female), 66 +/- 6.0 yr performed a maximal
cycle ergometer test, and MRS measurements of the calf muscles and needle
biopsies of the lateral gastrocnemius were performed. Biopsies were
analyzed for fiber type and citrate synthase (CS) activity. MRS
measurements of inorganic phosphate (Pi), phosphocreatine (PCr), ATP, and
pH were made using a 1.8-T 78-cm clear-bore magnet-and-spectrometer system.
Two or three 5-min bouts of plantar flexion were performed against variable
resistance to deplete PCr levels to 50% of resting values (mean end pH
6.99). PCr values during recovery were fit to an exponential curve, and the
rate constant (PCrrate) was calculated. PCrrate was used as an index of
oxidative metabolism. Older subjects had lower peak O2 uptake (VO2 peak)
values (19.2 +/- 5.6 vs. 49.5 +/- 8.1 ml O2.min-1 x kg-1), CS activities
(16 +/- 2.8 vs. 25 +/- 2.6 mmol.kg wet wt-1 x min-1), and PCrrate values
(25.3 +/- 8. vs. 37.5 +/- 5.3 mmol PCr.kg wet wt-1.min-1) than young
subjects. PCrrate correlated with CS activity, and both PCrrate and CS
activity correlated with VO2 peak (P < 0.05). No correlations were found
between percent fiber type and PCrrate, CS activity, and VO2 peak. These
results support studies that showed decreases in muscle metabolism with age
in healthy humans and show a good correlation between in vivo and in vitro
measurements of oxidative metabolism.
Antiangiogenic therapy based on blocking the actions of vascular endothelial growth factor‐A (VEGF) can lead to “normalization” of blood vessels in both animal and human tumors. Differential ...expression of VEGF isoforms affects tumor vascular maturity, which could influence the normalization process and response to subsequent treatment. Fibrosarcoma cells expressing only VEGF120 or VEGF188 isoforms were implanted either subcutaneously (s.c.) or in dorsal skin‐fold “window” chambers in SCID mice. VEGF120 was associated with vascular fragility and hemorrhage. Tumor‐bearing mice were treated with repeat doses of SU5416, an indolinone receptor tyrosine kinase inhibitor with activity against VEGFR‐2 and proven preclinical ability to induce tumor vascular normalization. SU5416 reduced vascularization in s.c. implants of both VEGF120 and VEGF188 tumors. However, in the window chamber, SU5416 treatment increased red cell velocity in VEGF120 (representing vascular normalization) but not VEGF188 tumors. SU5416 treatment had no effect on growth or necrosis levels in either tumor type but tended to counteract the increase in interstitial fluid pressure seen with growth of VEGF120 tumors. SU5416 pretreatment resulted in the normally fragile blood vessels in VEGF120‐expressing tumors becoming resistant to the vascular damaging effects of the tubulin‐binding vascular disrupting agent (VDA), combretastatin A4 3‐O‐phosphate (CA4P). Thus, vascular normalization induced by antiangiogenic treatment can reduce the efficacy of subsequent VDA treatment. Expression of VEGF120 made tumors particularly susceptible to vascular normalization by SU5416, which in turn made them resistant to CA4P. Therefore, VEGF isoform expression may be useful for predicting response to both antiangiogenic and vascular‐disrupting therapy.
What's new?
Targeting the blood supply of tumors remains an important therapeutic strategy in the fight against cancer. Strategic approaches are aimed at vascular “normalization” primarily using compounds that interfere with the vascular endothelial growth factor (VEGF) pathway or vascular “disruption” using so‐called vascular disrupting agents (VDAs) agents. Using mice carrying tumors expressing specific isoforms of VEGF the authors show that the soluble 120 amino acids VEGF isoform is associated with susceptibility to vascular normalization induced by VEGFR‐2‐targeting treatment. Furthermore, normalization rendered tumor blood vessels resistant to subsequent treatment with an archetypal vascular disrupting agent, CA4P. These results suggest typing VEGF isoform expression in tumors may be useful to predict the response to vascular‐targeted therapy in patients.
Observations of the tropical atmosphere are fundamental to the understanding of global changes in air quality, atmospheric oxidation capacity and climate, yet the tropics are under-populated with ...long-term measurements. The first three years (October 2006–September 2009) of meteorological, trace gas and particulate data from the global WMO/Global Atmospheric Watch (GAW) Cape Verde Atmospheric Observatory Humberto Duarte Fonseca (CVAO; 16° 51′ N, 24° 52′ W) are presented, along with a characterisation of the origin and pathways of air masses arriving at the station using the NAME dispersion model and simulations of dust deposition using the COSMO-MUSCAT dust model. The observations show a strong influence from Saharan dust in winter with a maximum in super-micron aerosol and particulate iron and aluminium. The dust model results match the magnitude and daily variations of dust events, but in the region of the CVAO underestimate the measured aerosol optical thickness (AOT) because of contributions from other aerosol. The NAME model also captured the dust events, giving confidence in its ability to correctly identify air mass origins and pathways in this region. Dissolution experiments on collected dust samples showed a strong correlation between soluble Fe and Al and measured solubilities were lower at high atmospheric dust concentrations. Fine mode aerosol at the CVAO contains a significant fraction of non-sea salt components including dicarboxylic acids, methanesulfonic acid and aliphatic amines, all believed to be of oceanic origin. A marine influence is also apparent in the year-round presence of iodine and bromine monoxide (IO and BrO), with IO suggested to be confined mainly to the surface few hundred metres but BrO well mixed in the boundary layer. Enhanced CO
2
and CH
4
and depleted oxygen concentrations are markers for air-sea exchange over the nearby northwest African coastal upwelling area. Long-range transport results in generally higher levels of O
3
and anthropogenic non-methane hydrocarbons (NMHC) in air originating from North America. Ozone/CO ratios were highest (up to 0.42) in relatively fresh European air masses. In air heavily influenced by Saharan dust the O
3
/CO ratio was as low as 0.13, possibly indicating O
3
uptake to dust. Nitrogen oxides (NO
x
and NO
y
) show generally higher concentrations in winter when air mass origins are predominantly from Africa. High photochemical activity at the site is shown by maximum spring/summer concentrations of OH and HO
2
of 9 × 10
6
molecule cm
−3
and 6 × 10
8
molecule cm
−3
, respectively. After the primary photolysis source, the most important controls on the HO
x
budget in this region are IO and BrO chemistry, the abundance of HCHO, and uptake of HO
x
to aerosol.
Departments of 1 Medicine and 2 Obstetrics and
Gynecology, Christchurch School of Medicine, Christchurch 8001, New
Zealand; and 3 Baker Medical Research Institute, Prahran,
Victoria ...8008, Australia
Levels of expression of adrenomedullin (AM) in the
uterus have been reported to vary with the reproductive cycle. This
study examines the relationships among uterine AM mRNA, the stage of the estrous cycle, and circulating estradiol and progesterone in
cycling rats and in ovariectomized (OVX) rats without or with estrogen
replacement (ER). Strong AM mRNA, AM immunoreactivity, and pro-AM
NH 2 -terminal 20 peptide (PAMP) immunoreactivity were observed in endometrial stroma by use of in situ hybridization and
immunocytochemistry. Endometrial expression was particularly intense at
proestrus and estrus, with weaker expression in the myometrium. By
RNase protection assay, significant differences in AM mRNA between the
stages of the estrous cycle could not be established. However, levels
of AM mRNA were positively correlated with plasma estradiol in cycling
rats ( r = 0.56, P < 0.005) and in OVX and
ER rats ( r = 0.92, P < 0.001) and were not
correlated with plasma progesterone. Levels of AM mRNA were
significantly reduced after OVX compared with cycling rats, and ER
restored AM mRNA to levels equivalent to those seen at the peak of the cycle (proestrus). In conclusion, although AM expression in the uterus
varies throughout the estrous cycle, it is more closely correlated with
circulating estradiol levels than with the stage of the cycle itself.
adrenomedullin; proadrenomedullin NH 2 -terminal 20 peptide; estradiol; uterus; estrous cycle
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