ALBERT

Description: We analyzed the resonance characteristics of a prominent natural arch in Canyonlands National Park, Mesa Arch, as measured from ambient seismic data. Evaluating spectral and polarization attributes, we distinguished the first four resonant frequencies of the arch: 2.9, 6.0, 6.9, and 8.5 Hz, as well as basic properties of the associated mode shapes. We then affirmed experimental data using 3D numerical modal analysis, providing estimates of material properties and clarifying vibrational mode shapes. Monitoring resonant frequencies over time, we searched for shifts associated with changing environmental conditions and long-term progressive damage. We measured ~3% direct daily variation in resonant frequency associated with changing rock temperature, thermal stress and stiffening of the rock matrix. Independent tilt data showed similar diurnal cycles associated with thermo-elastic stresses and deformation of the arch. We observed no permanent resonant frequency shifts related to irreversible damage of Mesa arch during our study period.

Description: Biological aerosols represent a diverse subset of particulate matter that is emitted directly to the atmosphere in the form of (but not limited to) bacteria, fungal spores, pollens, viruses, and plant debris. These particles can have local air quality implications, but potentially play a larger climate role by acting as efficient ice nucleating particles (INPs) and cloud condensation nuclei. We have deployed a Wideband Integrated Bioaerosol Sensor (WIBS-4A) on the NASA DC-8 aircraft to 1) quantify boundary layer (BL) variability of fluorescent biological aerosol particle (FBAP) concentrations in the Southeast United States (SEUS), 2) link this variability explicitly to land-cover heterogeneity in the region, and 3) examine the vertical profile of bioaerosols in the context of convective vertical redistribution. Flight-averaged FBAP concentrations ranged between 0.1-0.43 scm −3 (cm −3 at standard temperature and pressure) with relatively homogeneous concentrations throughout the region; croplands showed the highest concentrations in the BL (0.37 scm −3 ) and lowest concentrations were associated with evergreen forests (0.24 scm −3 ). Observed FBAP concentrations are in generally good agreement with model parameterized emission rates for bacteria and discrepancies are likely the result of fungal spore contributions. Shallow convection in the region is shown to be a relatively efficient lofting mechanism as the vertical transport efficiency of FBAP is at least equal to black-carbon aerosol, suggesting that ground-level FBAP survive transport into the free troposphere to be available for INP activation. Comparison of the fraction of coarse-mode particles that were biological ( f FBAP ) suggested that the SEUS ( f FBAP  = 8.5%) was a much stronger source of bioaerosols than long-range transport during a Saharan Air Layer (SAL) dust event ( f FBAP  = 0.17%) or summertime marine emissions in the Gulf of Mexico ( f FBAP  = 0.73%).

Description: The northwestern Indian Ocean harbors a number of larger marine vertebrate taxa that warrant the investigation of genetic population structure given remarkable spatial heterogeneity in biological characteristics such as distribution, behavior, and morphology. Here, we investigate the genetic population structure of four commercially exploited shark species with different biological characteristics ( Carcharhinus limbatus , Carcharhinus sorrah , Rhizoprionodon acutus , and Sphyrna lewini ) between the Red Sea and all other water bodies surrounding the Arabian Peninsula. To assess intraspecific patterns of connectivity, we constructed statistical parsimony networks among haplotypes and estimated (1) population structure; and (2) time of most recent population expansion, based on mitochondrial control region DNA and a total of 20 microsatellites. Our analysis indicates that, even in smaller, less vagile shark species, there are no contemporary barriers to gene flow across the study region, while historical events, for example, Pleistocene glacial cycles, may have affected connectivity in C. sorrah and R. acutus . A parsimony network analysis provided evidence that Arabian S. lewini may represent a population segment that is distinct from other known stocks in the Indian Ocean, raising a new layer of conservation concern. Our results call for urgent regional cooperation to ensure the sustainable exploitation of sharks in the Arabian region. Here we investigate the genetic population structure of four commercially exploited shark species with different biological characteristics between the Red Sea and all other water bodies surrounding the Arabian Peninsula. To assess intra-specific patterns of connectivity, we constructed statistical parsimony networks among haplotypes and estimated (1) population structure; and (2) time of most recent population expansion, based on mitochondrial control region DNA (mtDNA) and a total of 20 microsatellites. Our analysis indicates that, even in smaller, less vagile shark species, there are no contemporary barriers to gene flow across the region, while historical events, e.g. Pleistocene glacial cycles, may have affected connectivity in C. sorrah and R. acutus .

Description: Wind is the major abiotic disturbance in New Zealand's planted forests, but little is known about how the risk of wind damage may be affected by future climate change. We linked a mechanistic wind damage model (ForestGALES) to an empirical growth model for radiata pine ( Pinus radiata D. Don) and a process-based growth model (CenW) to predict the risk of wind damage under different future emissions scenarios and assumptions about the future wind climate. The CenW model was used to estimate site productivity for constant CO 2 concentration at 1990 values and for assumed increases in CO 2 concentration from current values to those expected during 2040 and 2090 under the B1 (low), A1B (mid-range) and A2 (high) emission scenarios. Stand development was modelled for different levels of site productivity, contrasting silvicultural regimes and sites across New Zealand. The risk of wind damage was predicted for each regime and emission scenario combination using the ForestGALES model. The sensitivity to changes in the intensity of the future wind climate was also examined. Results showed that increased tree growth rates under the different emissions scenarios had the greatest impact on the risk of wind damage. The increase in risk was greatest for stands growing at high stand density under the A2 emissions scenario with increased CO 2 concentration. The increased productivity under this scenario resulted in increased tree height, without a corresponding increase in diameter, leading to more slender trees that were predicted to be at greater risk from wind damage. The risk of wind damage was further increased by the modest increases in the extreme wind climate that are predicted to occur. These results have implications for the development of silvicultural regimes that are resilient to climate change and also indicate that future productivity gains may be offset by greater losses from disturbances. This article is protected by copyright. All rights reserved.

Description: The temporal and spatial evolution of a seismogenic megasplay fault in the Kumano area, Nankai Trough (southwest Japan), is revealed by detailed investigation of the three-dimensional structure of the shallow portions of the fault, combined with the results of drilling and dating of cores from Integrated Ocean Drilling Program (IODP) Expedition 316. The ENE striking eastern portion of the splay fault has remained active since the inception of faulting at ∼1.95 Ma. The recent shortening rate is ∼1 m/kyr, which represents ∼1.5%–2.5% of the total plate convergence rate of ∼40–65 m/kyr. The NE striking western portion of the splay fault exhibits a different mode of activity. Early stage activity (before 1.55 Ma) was similar to the eastern portion, but the fault was inactive between 1.55 and 1.24 Ma. The fault was reactivated for a short time at ∼1.24 Ma but again ceased activity after formation of the secondary branch and has been inactive since 1.24 Ma. Cessation of splay fault activity in the western domain after 1.55 Ma may be due to collision with a seamount and resulting bending of the accretionary prism in the splay fault footwall. Continuous activity of the eastern domain of the splay fault after 1.24 Ma may be related to geometrical favorability due to reorientation of the fault after the seamount passed beneath the imbricate thrust zone, leading to initiation of slightly oblique subduction.

Description: We use continuous and discrete measurements of the dissolved O2/Ar ratio in the mixed layer to investigate the dynamics of biological productivity during the Southern Ocean Gas Exchange Experiment in March and April 2008. Injections of SF6 defined two water masses (patches) that were followed for up to 2 weeks. In the first patch, dissolved O2/Ar was supersaturated, indicating net biological production of organic carbon. In the second patch, rapidly decreasing O2/Ar could only be reasonably explained if the mixed layer was experiencing a period of net heterotrophy. The observations rule out dominant contributions from vertical mixing, lateral dilution, or respiration in the ship's underway seawater supply lines. We also compare nine different estimates of net community, new, primary, or gross production made during the experiment. Net community and new production estimates agreed well in the first patch but disagreed in the second patch, both during an initial net heterotrophic period but also during the apparently autotrophic period at the end of the observations. Rapidly changing productivity during the second patch complicated the comparison of methods that integrate over daily and several week timescales. Primary productivity values from on-deck 24 h 14C incubations and gross carbon production values from photosynthesis-irradiance experiments were nearly identical even during highly dynamic periods of net heterotrophy, while gross oxygen production measurements were 3.5–4.2 times higher but with uncertainties in that ratio near ±2. These comparisons show that the photosynthesis-irradiance experiments based on 1–2 h 14C incubations underestimated gross carbon production.

Description: Savanna ecosystems comprise 22% of the global terrestrial surface and 25% of Australia (almost 1.9 million km 2 ) and provide significant ecosystem services through carbon and water cycles and the maintenance of biodiversity. The current structure, composition and distribution of Australian savannas have co-evolved with fire, yet remain driven by the dynamic constraints of their bioclimatic niche. Fire in Australian savannas influences both the biophysical and biogeochemical processes at multiple scales from leaf to landscape. Here we present the latest emission estimates from Australian savanna biomass burning and their contribution to global greenhouse gas budgets. We then review our understanding of the impacts of fire on ecosystem function and local surface water and heat balances, which in turn influence regional climate. We show how savanna fires are coupled to the global climate through the carbon cycle and fire regimes. We present new research that climate change is likely to alter the structure and function of savannas through shifts in moisture availability and increases in atmospheric carbon dioxide (CO 2 ), in turn altering fire regimes with further feedbacks to climate. We explore opportunities to reduce net greenhouse gas emissions from savanna ecosystems through changes in savanna fire management. This article is protected by copyright. All rights reserved.

Description: Drought struck California during 7 of the 9 years from 2007 through 2015, reducing the state's available water resources. Pumping of Central Valley groundwater has produced spectacular land subsidence. Uplift of the adjacent Sierra Nevada mountains has been proposed to be either tectonic uplift or solid Earth's elastic response to unloading of Central Valley groundwater. We find that, of the 24 mm of uplift of the Sierra Nevada from October 2011 to October 2015, just 5 mm is produced by Central Valley groundwater loss, less than 2 mm is tectonic uplift, and 17 mm is solid Earth's elastic response to water loss in the Sierra Nevada. We invert GPS vertical displacements recording solid Earth's elastic response to infer changes in water storage across the western U.S. from January 2006 to October 2017. We find water changes to be sustained over periods of drought or heavy precipitation: the Sierra Nevada lost 15 ±19 km 3 of water during drought from October 2006 to October 2009, gained 18 ±14 km 3 of water during heavy precipitation from October 2009 to October 2011, and lost 45 ±21 km 3 of water during severe drought from October 2011 to October 2015 (95% confidence limits). Such large changes are not in hydrology models: snow accumulation in October is negligible and long-term soil moisture change is small. We infer there must be large loss of either deep soil moisture or groundwater in river alluvium and in crystalline basement in the Sierra Nevada. The results suggest there to be parching of water in the ground during the summer of years of drought and seeping of melting snow into the Sierra Nevada in the spring of years of heavy precipitation.

Description: The natural modes of vibration of bedrock landforms, as well as the sources and effects of stimulated resonance remain poorly understood. Here we show that seismic energy created by an induced earthquake and an artificial reservoir has spectral content coincident with the natural modes of vibration of a prominent rock bridge. We measured the resonant frequencies of Rainbow Bridge, Utah using data from two broadband seismometers placed on the span, and identified eight distinct vibrational modes between 1 and 6 Hz. A distant, induced earthquake produced local ground motion rich in 1 Hz energy, stimulating a 20 dB increase in measured power at the bridge's fundamental mode. Moreover, we establish that wave action on Lake Powell, an artificial reservoir, generates microseismic energy with peak power ~1 Hz, also exciting resonance of Rainbow Bridge. These anthropogenic sources represent relatively new energy input for the bridge with unknown consequences for structural fatigue.

Description: Data from 279 dropsonde profiles collected during the Deep Propagating Gravity Wave Experiment (DEEPWAVE) over New Zealand between 4 June and 20 July 2014 were used to verify the relative humidity (RH) fields simulated by regional configurations of the UK Met Office Unified Model (MetUM) in the troposphere. Significant RH biases (predictions up to 28% too high) were found in the middle and upper troposphere during this period. This RH bias was found to be mainly caused by the errors in the simulated-specific humidity. It is demonstrated here that evaporation from the lower boundary (mainly sea surface) is not a factor leading to the moist bias. A similar magnitude of moist bias was also found in the Global UM (the global configuration of the MetUM) and from a preliminary inspection is also very likely to occur in ERA-interim and NCEP-GFS reanalyses. This study suggests that the moist bias is very likely not a regional or a model specific issue.