Glacier contributions to streamflow moderate summer water temperatures and help keep rivers cool during periods of hot, dry weather. As glaciers retreat, the length of channel exposed to solar ...radiation above a given point of interest would increase, which should ultimately result in higher water temperatures. However, formation of proglacial lakes may complicate river temperature response to glacier retreat. This study examined river and lake temperature response to the retreat of lake‐terminating Bridge Glacier, British Columbia, using a combination of manual spot and continuous river temperatures at a stream gauge, lake surface temperatures derived from Landsat imagery, and in situ lake temperatures made during a field campaign during summer 2013. Temperature data spanned the period from 1984 to 2022. Lake and river temperatures were relatively constant prior to and during a period of rapid retreat, but exhibited an upward trend following 2012, when iceberg density declined due to an apparent decrease in calving rate, resulting in an increase in lake surface area and river temperature of about 5°C even though the glacier remained lake terminating. In addition to providing the first longitudinal study of water temperature response to the retreat of a lake‐terminating glacier, this study adds to a body of literature that demonstrates that routine spot river temperatures, if collected in a consistent manner over a number of years, can provide valid information about river and stream temperature trends.
Lake surface and downstream river temperatures did not initially exhibit a significant warming trend during a period of rapid glacial retreat. However, changes in glacier flow dynamics associated with thinning and a reduced area of floating ice resulted in a decline in iceberg density even though the glacier remained lake terminating. This decrease in iceberg density was associated with increases in lake and river temperatures of approximately 5°C over a decade.
Western North American (WNA) glaciers outside of Alaska cover 14,384 km2 of mountainous terrain. No comprehensive analysis of recent mass change exists for this region. We generated over 15,000 ...multisensor digital elevation models from spaceborne optical imagery to provide an assessment of mass change for WNA over the period 2000–2018. These glaciers lost 117 ± 42 gigatons (Gt) of mass, which accounts for up to 0.32 ± 0.11 mm of sea level rise over the full period of study. We observe a fourfold increase in mass loss rates between 2000–2009 −2.9 ± 3.1 Gt yr−1 and 2009–2018 −12.3 ± 4.6 Gt yr−1, and we attribute this change to a shift in regional meteorological conditions driven by the location and strength of upper level zonal wind. Our results document decadal‐scale climate variability over WNA that will likely modulate glacier mass change in the future.
Plain Language Summary
Glaciers in western North America provide important thermal and flow buffering to streams when seasonal snowpack is depleted. We used spaceborne optical satellite imagery to produce thousands of digital elevation models to assess recent mass loss for glaciers in western North America outside of Alaska. Our analysis shows that glacier loss over the period 2009–2018 increased fourfold relative to the period 2000–2009. This mass change over the last 18 years is partly explained by changes in atmospheric circulation. Our results can be used for future modeling studies to understand the fate of glaciers under future climate change scenarios.
Key Points
We provide a comprehensive assessment of mass change for western North American (WNA) glaciers excluding those in Alaska
WNA glaciers lost 117 +/‐ 42 gigatons (Gt) of mass over the period 2000‐2018 and could account for 0.32 +/‐ 0.11 mm of sea level rise
Regional changes in glacier mass are partly explained by decadal scale changes in atmospheric circulation
► A cross-check of two inhibitors shows both inhibit a β-lactamase and a proteasome. ► Similar inhibition mechanisms and similar products. ► Active site homology but enantiotopic. ► Convergent ...evolution?
O-Aryloxycarbonyl hydroxamates and 1,3,4-oxathiazol-2-ones have been identified as covalent inhibitors of β-lactamases and proteasomes, respectively. The products of these inhibition reactions are remarkably similar, involving carbonyl cross-linking of the active sites. We have cross-checked these inhibitors, showing that the former inhibit proteasomes and the latter β-lactamases, to form the same inactive carbonyl adducts. These results are discussed in terms of similarities of the active site structures and catalytic mechanisms. It is likely that a mechanistic imperative has led to convergent evolution of these enzyme active sites, of a β-lactam-recognizing enzyme and a N-terminal protease belonging to different amidohydrolase superfamilies.
The α-hydroxydepsipeptide 3-carboxyphenyl N-(phenylacetyl)-α-hydroxyglycinate (5) is a quite effective substrate of serine β-lactamases and low molecular mass DD-peptidases. The class C P99 and ampC ...β-lactamases catalyze the hydrolysis of both enantiomers of 5, although they show a strong preference for one of them. The class A TEM-2 and class D OXA-1 β-lactamases and the Streptomyces R61 and Actinomadura R39 DD-peptidases catalyze hydrolysis of only one enantiomer of at any significant rate. Experiments show that all of the above enzymes strongly prefer the same enantiomer, a surprising result since β-lactamases usually prefer L(S) enantiomers and DD-peptidases D(R). Product analysis, employing peptidylglycine α-amidating lyase, showed that the preferred enantiomer is D(R). Thus, it is the β-lactamases that have switched preference rather than the DD-peptidases. Molecular modeling of the P99 β-lactamase active site suggests that the α-hydroxyl 5 of may interact with conserved Asn and Lys residues. Both α-hydroxy and α-amido substituents on a glycine ester substrate can therefore enhance its productive interaction with the β-lactamase active site, although their effects are not additive; this may also be true for inhibitors.
The class C serine β-lactamase of Enterobacter cloacae P99 is irreversibly inhibited by O-aryloxycarbonyl hydroxamates. A series of these new inhibitors has been prepared to investigate the kinetics ...and mechanism of the inactivation reaction. A pH−rate profile for the reaction indicated that the reactive form of the inhibitor is neutral rather than anionic. The reaction rate is enhanced by electron-withdrawing aryloxy substituents and by hydrophobic substitution on both aryloxy and hydroxamate groups. Kinetics studies show that the rates of loss of the two possible leaving groups, aryloxide and hydroxamate, are essentially the same as the rate of enzyme inactivation. Nucleophilic trapping experiments prove, however, that the aryl oxide is the first to leave. It is likely, therefore, that the rate-determining step of inactivation is the initial acylation reaction, most likely of the active site serine, yielding a hydroxamoyl-enzyme intermediate. This then partitions between hydrolysis and aminolysis by Lys 315, the latter to form an inactive, cross-linked active site. A previously described crystal structure of the inactivated enzyme shows a carbamate cross-link of Ser 64 and Lys 315. Structure−activity studies of the reported compounds suggest that they do not react at the enzyme active site in the same way as normal substrates. In particular, it appears that the initial acylation by these compounds does not involve the oxyanion hole, an unprecedented departure from known and presumed reactivity. Molecular modeling suggests that an alternative oxyanion hole may have been recruited, consisting of the side chain functional groups of Tyr 150 and Lys 315. Such an alternative mode of reaction may lead to the design of novel inhibitors.
Seasonal measurements of glacier mass balance provide
insight into the relation between climate forcing and glacier change. To
evaluate the feasibility of using remotely sensed methods to assess ...seasonal
balance, we completed tandem airborne laser scanning (ALS) surveys and
field-based glaciological measurements over a 4-year period for six
alpine glaciers that lie in the Columbia and Rocky Mountains, near the
headwaters of the Columbia River, British Columbia, Canada. We calculated
annual geodetic balance using coregistered late summer digital elevation
models (DEMs) and distributed estimates of density based on surface
classification of ice, snow, and firn surfaces. Winter balance was derived
using coregistered late summer and spring DEMs, as well as density measurements
from regional snow survey observations and our glaciological measurements.
Geodetic summer balance was calculated as the difference between winter and
annual balance. Winter mass balance from our glaciological observations
averaged 1.95±0.09 m w.e. (meter water equivalent), 4 % larger than those derived from
geodetic surveys. Average glaciological summer and annual balance were 3 %
smaller and 3 % larger, respectively, than our geodetic estimates. We find
that distributing snow, firn, and ice density based on surface classification
has a greater influence on geodetic annual mass change than the density
values themselves. Our results demonstrate that accurate assessments of
seasonal mass change can be produced using ALS over a series of glaciers
spanning several mountain ranges. Such agreement over multiple seasons,
years, and glaciers demonstrates the ability of high-resolution geodetic
methods to increase the number of glaciers where seasonal mass balance can
be reliably estimated.
O-Aryloxycarbonyl hydroxamates represent a new class of β-lactamase inhibitors. N-Benzyloxycarbonyl-O-(phenoxycarbonyl) hydroxylamine, for example, inactivates the class C Enterobacter cloacae P99 ...β-lactamase with a rate constant of 6.1 × 103 s-1 M-1; approximately two turnover events accompany the inhibition. N-Benzyloxycarbonyl-O-(3-carboxyphenoxy)carbonyl hydroxylamine is comparably effective. These compounds also inactivate the class A TEM β-lactamase. A crystal structure of the inactivated AmpC enzyme, another class C β-lactamase, reveals that the active site has become cross-linked by a carbamate bridge spanning Ser64, the active site nucleophile, and Lys315, a conserved active site residue.
Over the last century, northwestern Canada experienced some of the highest rates of tropospheric warming globally, which caused glaciers in the region to rapidly retreat. Our study seeks to extend ...the record of glacier fluctuations and assess climate drivers prior to the instrumental record in the Mackenzie and Selwyn mountains of northwestern Canada. We collected 27 10Be surface exposure ages across nine cirque and valley glacier moraines to constrain the timing of their emplacement. Cirque and valley glaciers in this region reached their greatest Holocene extents in the latter half of the Little Ice Age (1600–1850 CE). Four erratic boulders, 10–250 m distal from late Holocene moraines, yielded 10Be exposure ages of 10.9–11.6 ka, demonstrating that by ca. 11 ka, alpine glaciers were no more extensive than during the last several hundred years. Estimated temperature change obtained through reconstruction of equilibrium line altitudes shows that since ca. 1850 CE, mean annual temperatures have risen 0.2–2.3 ∘C. We use our glacier chronology and the Open Global Glacier Model (OGGM) to estimate that from 1000 CE, glaciers in this region reached a maximum total volume of 34–38 km3 between 1765 and 1855 CE and had lost nearly half their ice volume by 2019 CE. OGGM was unable to produce modeled glacier lengths that match the timing or magnitude of the maximum glacier extent indicated by the 10Be chronology. However, when applied to the entire Mackenzie and Selwyn mountain region, past millennium OGGM simulations using the Max Planck Institute Earth System Model (MPI-ESM) and the Community Climate System Model 4 (CCSM4) yield late Holocene glacier volume change temporally consistent with our moraine and remote sensing record, while the Meteorological Research Institute Earth System Model 2 (MRI-ESM2) and the Model for Interdisciplinary Research on Climate (MIROC) fail to produce modeled glacier change consistent with our glacier chronology. Finally, OGGM forced by future climate projections under varying greenhouse gas emission scenarios predicts 85 % to over 97 % glacier volume loss by the end of the 21st century. The loss of glaciers from this region will have profound impacts on local ecosystems and communities that rely on meltwater from glacierized catchments.
The -hydroxydepsipeptide 3-carboxyphenyl
N
-(phenylacetyl)--hydroxyglycinate (
5
) is a quite effective substrate of serine -lactamases and low molecular mass
dd
-peptidases. The class C P99 and ampC ...-lactamases catalyze the hydrolysis of both enantiomers of
5
, although they show a strong preference for one of them. The class A TEM-2 and class D OXA-1 -lactamases and the
Streptomyces
R61 and
Actinomadura
R39
dd
-peptidases catalyze hydrolysis of only one enantiomer of
5
at any significant rate. Experiments show that all of the above enzymes strongly prefer the same enantiomer, a surprising result since -lactamases usually prefer
l
(
S
) enantiomers and
dd
-peptidases
d
(
R
). Product analysis, employing peptidylglycine -amidating lyase, showed that the preferred enantiomer is
d
(
R
). Thus, it is the -lactamases that have switched preference rather than the
dd
-peptidases. Molecular modeling of the P99 -lactamase active site suggests that the -hydroxyl of
5
may interact with conserved Asn and Lys residues. Both -hydroxy and -amido substituents on a glycine ester substrate can therefore enhance its productive interaction with the -lactamase active site, although their effects are not additive; this may also be true for inhibitors.
-Lactam-recognizing enzymes make a choice between an
R
and an
S
-hydroxyl group.
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