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Geology topics

Julio L. Betancourt

Publications and source records attributed to Julio L. Betancourt.

At least 37 records · Page 2Linked to original sources
USGS2017

Northern hemisphere jet stream positions indices as diagnostic tools for climate and ecosystem dynamics

The latitudinal position of the Northern Hemisphere jet stream (NHJ) modulates the occurrence and frequency of extreme weather events. Precipitation anomalies in particular are associated with NHJ variability; the resulting floods and droughts can have considerable societal and economic impacts. This study develops a new climatology of the 300-hPa NHJ using a bottom-up approach based on seasonally explicit latitudinal NHJ positions. Four seasons with coherent NHJ patterns were identified (January–February, April–May, July–August, and October–November), along with 32 longitudinal sectors where the seasonal NHJ shows strong spatial coherence. These 32 longitudinal sectors were then used as NHJ position indices to examine the influence of seasonal NHJ position on the geographical distribution of NH precipitation and temperature variability and their link to atmospheric circulation pattern. The analyses show that the NHJ indices are related to broad-scale patterns in temperature and precipitation variability, in terrestrial vegetation productivity and spring phenology, and can be used as diagnostic/prognostic tools to link ecosystem and socioeconomic dynamics to upper-level atmospheric patterns.

Earth Interactions↗
USGS2017

Grand challenges for integrated USGS science — A workshop report

Executive Summary The U.S. Geological Survey (USGS) has a long history of advancing the traditional Earth science disciplines and identifying opportunities to integrate USGS science across disciplines to address complex societal problems. The USGS science strategy for 2007–2017 laid out key challenges in disciplinary and interdisciplinary arenas, culminating in a call for increased focus on a number of crosscutting science directions. Ten years on, to further the goal of integrated science and at the request of the Executive Leadership Team (ELT), a workshop with three dozen invited scientists spanning different disciplines and career stages in the Bureau convened on February 7–10, 2017, at the USGS John Wesley Powell Center for Analysis and Synthesis in Fort Collins, Colorado. The workshop focused on identifying “grand challenges” for integrated USGS science. Individual participants identified nearly 70 potential grand challenges before the workshop and through workshop discussions. After discussion, four overarching grand challenges emerged: Natural resource security, Societal risk from existing and emerging threats, Smart infrastructure development, and Anticipatory science for changing landscapes. Participants also identified a “comprehensive science challenge” that highlights the development of integrative science, data, models, and tools—all interacting in a modular framework—that can be used to address these and other future grand challenges: Earth Monitoring, Analyses, and Projections (EarthMAP) EarthMAP is our long-term vision for an integrated scientific framework that spans traditional scientific boundaries and disciplines, and integrates the full portfolio of USGS science: research, monitoring, assessment, analysis, and information delivery. The Department of Interior, and the Nation in general, have a vast array of information needs. The USGS meets these needs by having a broadly trained and agile scientific workforce. Encouraging and supporting cross-discipline engagement would position the USGS to tackle complex and multifaceted scientific and societal challenges in the 21st Century.

Open-File Report↗
USGS2017

Late Quaternary vegetation and climate history of a perennial river canyon in the Rīo Salado basin (22°S) of Northern Chile

Plant macrofossils from 33 rodent middens sampled at three sites between 2910 and 3150 m elevation in the main canyon of the Rīo Salado, northern Chile, yield a unique record of vegetation and climate over the past 22,000 cal yr BP. Presence of low-elevation Prepuna taxa throughout the record suggests that mean annual temperature never cooled by more than 5°C and may have been near-modern at 16,270 cal yr BP. Displacements in the lower limits of Andean steppe and Puna taxa indicate that mean annual rainfall was twice modern at 17,520-16,270 cal yr BP. This pluvial event coincides with infilling of paleolake Tauca on the Bolivian Altiplano, increased ENSO activity inferred from a marine core near Lima, abrupt deglaciation in southern Chile, and Heinrich Event 1. Moderate to large increases in precipitation also occurred at 11,770-9550 (Central Atacama Pluvial Event), 7330-6720, 3490-2320 and at 800 cal yr BP. Desiccation occurred at 14,180, 8910-8640, and 4865 cal yr BP. Compared to other midden sites in the region, early Holocene desiccation seems to have happened progressively earlier farther south. Emerging trends from the cumulative midden record in the central Atacama agree at millennial timescales with improved paleolake chronologies for the Bolivian Altiplano, implying common forcing through changes in equatorial Pacific sea-surface temperature gradients.

Quaternary Research↗
USGS2017

Annual precipitation in the Yellowstone National Park region since AD 1173

Cores and cross sections from 133 limber pine (Pinus flexilis James) and Douglas fir (Pseudotsuga menziesii (Mirbel) Franco) at four sites were used to estimate annual (July to June) precipitation in the Yellowstone National Park region for the period from AD 1173 to 1998. Examination of the long-term record shows that the early 20th century was markedly wet compared to the previous 700 yr. Extreme wet and dry years within the instrumental period fall within the range of past variability, and the magnitude of the worst-case droughts of the 20th century (AD 1930s and 1950s) was likely equaled or exceeded on numerous occasions before AD 1900. Spectral analysis showed significant decadal to multidecadal precipitation variability. At times this lower frequency variability produces strong regime-like behavior in regional precipitation, with the potential for rapid, high-amplitude switching between predominately wet and predominately dry conditions. Over multiple time scales, strong Yellowstone region precipitation anomalies were almost always associated with spatially extensive events spanning various combinations of the central and southern U.S. Rockies, the northern U.S.-Southern Canadian Rockies and the Pacific Northwest.

Yellowstone National Park↗
USGS2017

Paleowetlands and regional climate change in the central Atacama Desert, northern Chile

Widespread, organic-rich diatomaceous deposits are evidence for formerly wetter times along the margins of the central Atacama Desert, one of the driest places on Earth today. We mapped and dated these paleowetland deposits at three presently waterless locations near Salar de Punta Negra (24.5°S) on the western slope of the Andes. Elevated groundwater levels supported phreatic discharge into wetlands during two periods: 15,900 to ~ 13,800 and 12,700 to ~ 9700 cal yr BP. Dense concentrations of lithic artifacts testify to the presence of paleoindians around the wetlands late in the second wet phase (11,000?–9700 cal yr BP). Water tables dropped below the surface before 15,900 and since 8100 cal yr BP, and briefly between ~ 13,800 and 12,700 cal yr BP. This temporal pattern is repeated, with some slight differences, in rodent middens from the study area, in both paleowetland and rodent midden deposits north and south of the study area, and in lake level fluctuations on the adjacent Bolivian Altiplano. The regional synchroneity of these changes points to a strengthening of the South American Monsoon — which we term the "Central Andean Pluvial Event" — in two distinct intervals (15,900–13,800 and 12,700–9700 cal yr BP), probably induced by steepened SST gradients across the tropical Pacific (i.e., La Niña-like conditions).

Atacama Desert;Andes Mountains↗
USGS2017

Vegetation history along the eastern, desert escarpment of the Sierra San Pedro Mártir, Baja California, Mexico

Plant macrofossils from 38 packrat middens spanning the last ~ 33,000 cal yr BP record vegetation between ~ 650 and 900 m elevation along the eastern escarpment of the Sierra San Pedro Mártir, northern Baja California. The middens span most of the Holocene, with a gap between ~ 4600 and 1800 cal yr BP, but coverage in the Pleistocene is uneven with a larger hiatus between 23,100 and 14,400 cal yr BP. The midden flora is relatively stable from the Pleistocene to Holocene. Exceptions include Pinus californiarum , Juniperus californica and other chaparral elements that were most abundant > 23,100 cal yr BP and declined after 14,400 cal yr BP. Despite being near the chaparral/woodland-desertscrub ecotone during glacial times, the midden assemblages reflect none of the climatic reversals evident in the glacial or marine record, and this is corroborated by a nearby semi-continuous pollen stratigraphy from lake sediments. Regular appearance of C 4 grasses and summer-flowering annuals since 13,600 cal yr BP indicates occurrence of summer rainfall equivalent to modern (JAS average of ~ 80–90 mm). This casts doubt on the claim, based on temperature proxies from marine sediments in the Guaymas Basin, that monsoonal development in the northern Gulf and Arizona was delayed until after 6200 cal yr BP.

Baja California, Sierra San Pedro Mártir↗
USGS2017

Holocene fire occurrence and alluvial responses at the leading edge of pinyon–juniper migration in the Northern Great Basin, USA

Fire and vegetation records at the City of Rocks National Reserve (CIRO), south-central Idaho, display the interaction of changing climate, fire and vegetation along the migrating front of single-leaf pinyon ( Pinus monophylla ) and Utah juniper ( Juniperus osteosperma ). Radiocarbon dating of alluvial charcoal reconstructed local fire occurrence and geomorphic response, and fossil woodrat ( Neotoma ) middens revealed pinyon and juniper arrivals. Fire peaks occurred ~ 10,700–9500, 7200–6700, 2400–2000, 850–700, and 550–400 cal yr BP, whereas ~ 9500–7200, 6700–4700 and ~ 1500–1000 cal yr BP are fire-free. Wetter climates and denser vegetation fueled episodic fires and debris flows during the early and late Holocene, whereas drier climates and reduced vegetation caused frequent sheetflooding during the mid-Holocene. Increased fires during the wetter and more variable late Holocene suggest variable climate and adequate fuels augment fires at CIRO. Utah juniper and single-leaf pinyon colonized CIRO by 3800 and 2800 cal yr BP, respectively, though pinyon did not expand broadly until ~ 700 cal yr BP. Increased fire-related deposition coincided with regional droughts and pinyon infilling ~ 850–700 and 550–400 cal yr BP. Early and late Holocene vegetation change probably played a major role in accelerated fire activity, which may be sustained into the future due to pinyon–juniper densification and cheatgrass invasion.

Idaho↗
USGS2017

Phylogeny, diet, and habitat of an extinct ground sloth from Cuchillo Curá, Neuquén Province, southwest Argentina

Advancements in ancient DNA analyses now permit comparative molecular and morphological studies of extinct animal dung commonly preserved in caves of semiarid regions. These new techniques are showcased using a unique dung deposit preserved in a late glacial vizcacha ( Lagidium sp.) midden from a limestone cave in southwestern Argentina (38.5° S). Phylogenetic analyses of the mitochondrial DNA show that the dung originated from a small ground sloth species not yet represented by skeletal material in the region, and not closely related to any of the four previously sequenced extinct and extant sloth species. Analyses of pollen and plant cuticles, as well as analyses of the chloroplast DNA, show that the Cuchillo Curá ground sloth browsed on many of the same herb, grass, and shrub genera common at the site today, and that its habitat was treeless Patagonian scrub-steppe. We envision a day when molecular analyses are used routinely to supplement morphological identifications and possibly to provide a time-lapse view of molecular diversification.

Quaternary Research↗
USGS2017

Using state-and-transition modeling to account for imperfect detection in invasive species management

Buffelgrass, a highly competitive and flammable African bunchgrass, is spreading rapidly across both urban and natural areas in the Sonoran Desert of southern and central Arizona. Damages include increased fire risk, losses in biodiversity, and diminished revenues and quality of life. Feasibility of sustained and successful mitigation will depend heavily on rates of spread, treatment capacity, and cost–benefit analysis. We created a decision support model for the wildland–urban interface north of Tucson, AZ, using a spatial state-and-transition simulation modeling framework, the Tool for Exploratory Landscape Scenario Analyses. We addressed the issues of undetected invasions, identifying potentially suitable habitat and calibrating spread rates, while answering questions about how to allocate resources among inventory, treatment, and maintenance. Inputs to the model include a state-and-transition simulation model to describe the succession and control of buffelgrass, a habitat suitability model, management planning zones, spread vectors, estimated dispersal kernels for buffelgrass, and maps of current distribution. Our spatial simulations showed that without treatment, buffelgrass infestations that started with as little as 80 ha (198 ac) could grow to more than 6,000 ha by the year 2060. In contrast, applying unlimited management resources could limit 2060 infestation levels to approximately 50 ha. The application of sufficient resources toward inventory is important because undetected patches of buffelgrass will tend to grow exponentially. In our simulations, areas affected by buffelgrass may increase substantially over the next 50 yr, but a large, upfront investment in buffelgrass control could reduce the infested area and overall management costs.

Arizona↗
USGS2017

Isotopic characterization of late Neogene travertine deposits at Barrancas Blancas in the eastern Atacama Desert, Chile

Here we explore the potential of spring-related, surface and subsurface carbonates as an archive of paleoenvironmental change at Barrancas Blancas, located in the broadest and driest sector of the Atacama Desert at 24.5°S. From these deposits we present a new stable isotopic record of paleoenvironmental conditions over portions of the past ~ 11.5 Ma. U-Pb dates from the carbonates, both surface and subsurface, demonstrate that springs have discharged at this location over much of the last 11.5 Ma, attesting to the exceptional geomorphic stability of the central Atacama. Many of the sampled vein systems line vertical fissures, and formed within the aquifer before groundwater discharged at the surface. Carbonates in such circumstances should not undergo off-gassing and kinetic fractionation prior to formation, simplifying the interpretation of their isotopic composition. Oxygen isotopic compositions of carbonates are generally high (>− 5‰VPDB), and using paleospring water temperatures of 3–13 °C reconstructed from clumped isotopes, point to strongly (up to 50%) evaporated water isotope values, like those associated with the hyperarid core of the Atacama Desert today. Carbon isotopic compositions are also high (≥+3‰ PDB), reflecting a recharge area essentially devoid of plants and dominated by volcanic CO 2 , as is the case today. Our isotopic results are very similar to those from the Calama Basin to the north, suggesting that the western face of the Andes between 21 and 25°S has been highly evaporative and nearly plantless when these springs discharged over the last 11.5 Ma. The spring carbonates at Barrancas Blancas strongly resemble those found at Devils Hole and Furnace Creek in Death Valley, USA, and as such warrant further exploration as potential archives of climate change.

Atacama Desert↗
USGS2016

A dynamic leaf gas-exchange strategy is conserved in woody plants under changing ambient CO 2 : evidence from carbon isotope discrimination in paleo and CO 2 enrichment studies

Rising atmospheric [CO 2 ], c a , is expected to affect stomatal regulation of leaf gas-exchange of woody plants, thus influencing energy fluxes as well as carbon (C), water, and nutrient cycling of forests. Researchers have proposed various strategies for stomatal regulation of leaf gas-exchange that include maintaining a constant leaf internal [CO 2 ], c i , a constant drawdown in CO 2 ( c a − c i ), and a constant c i / c a . These strategies can result in drastically different consequences for leaf gas-exchange. The accuracy of Earth systems models depends in part on assumptions about generalizable patterns in leaf gas-exchange responses to varying c a . The concept of optimal stomatal behavior, exemplified by woody plants shifting along a continuum of these strategies, provides a unifying framework for understanding leaf gas-exchange responses to c a . To assess leaf gas-exchange regulation strategies, we analyzed patterns in c i inferred from studies reporting C stable isotope ratios (δ 13 C) or photosynthetic discrimination (∆) in woody angiosperms and gymnosperms that grew across a range of c a spanning at least 100 ppm. Our results suggest that much of the c a -induced changes in c i / c a occurred across c a spanning 200 to 400 ppm. These patterns imply that c a − c i will eventually approach a constant level at high c a because assimilation rates will reach a maximum and stomatal conductance of each species should be constrained to some minimum level. These analyses are not consistent with canalization toward any single strategy, particularly maintaining a constant c i . Rather, the results are consistent with the existence of a broadly conserved pattern of stomatal optimization in woody angiosperms and gymnosperms. This results in trees being profligate water users at low c a , when additional water loss is small for each unit of C gain, and increasingly water-conservative at high c a , when photosystems are saturated and water loss is large for each unit C gain.

Global Change Biology↗
USGS2016

Teleconnected ocean forcing of Western North American droughts and pluvials during the last millennium

Western North America (WNA) is rich in hydroclimate reconstructions, yet questions remain about the causes of decadal-to-multidecadal hydroclimate variability. Teleconnection patterns preserved in annually-resolved tree-ring reconstructed drought maps, and anomalies in a global network of proxy sea surface temperature (SST) reconstructions, were used to reassess the evidence linking ocean forcing to WNA hydroclimate variability over the past millennium. Potential forcing mechanisms of the Medieval Climate Anomaly (MCA) and individual drought and pluvial events—including two multidecadal-length MCA pluvials—were evaluated. We show strong teleconnection patterns occurred during the driest (wettest) years within persistent droughts (pluvials), implicating SSTs as a potent hydroclimate forcing mechanism. The role of the SSTs on longer timescales is more complex. Pacific teleconnection patterns show little long-term change, whereas low-resolution SST reconstructions vary over decades to centuries. While weaker than the tropical Pacific teleconnections, North Atlantic teleconnection patterns and SST reconstructions also show links to WNA droughts and pluvials, and may in part account for longer-term WNA hydroclimate changes. Nonetheless, evidence linking WNA hydroclimate to SSTs still remains sparse and nuanced—especially over long-timescales with a broader range of hydroclimatic variability than characterized during the 20th century.

Quaternary Science Reviews↗
USGS2016

Iterative ecological forecasting: Needs, opportunities, and challenges

A fundamental environmental challenge facing humanity in the 21st century and beyond is predicting the impacts of global environmental change. This challenge is complicated by the fact that we live on a non-stationary, unreplicated planet that is rapidly moving outside the envelope of natural variability into an historical non-analog world. In other words, while the past helps inform us about how the world has worked, it may no longer be the relevant frame of reference for management, conservation, and sustainability. In this future world the two questions at the foundation of sustainability are “How are ecosystems and the services they provide going to change in the future?” and “How do human decisions affect this trajectory?” These are, at their heart, questions about ecological forecasting.

Conference Paper↗
USGS2015

Late Holocene expansion of Ponderosa pine (Pinus ponderosa) in the Central Rocky Mountains, USA

"Aim: Ponderosa pine (Pinus ponderosa) experienced one of the most extensive and rapid post-glacial plant migrations in western North America. We used plant macrofossils from woodrat (Neotoma) middens to reconstruct its spread in the Central Rocky Mountains, identify other vegetation changes coinciding with P. ponderosa expansion at the same sites, and relate P. ponderosa migrational history to both its modern phylogeography and to a parallel expansion by Utah juniper (Juniperus osteosperma). Location: Central Rocky Mountains, Wyoming and Montana, and Black Hills, Wyoming and South Dakota, USA. Methods: Plant macrofossils were analyzed in 90 middens collected at 14 widely separated sites in the northern part of the range of P. ponderosa var. scopulorum. Middens with and without P. ponderosa were 14C dated to pinpoint time of appearance at each site. Sensitivity experiments using a bioclimatic model were used to evaluate potential climatic drivers of late Holocene expansion. Results: P. ponderosa colonized the Black Hills region by at least 3850 yr BP (all ages given in calendar years before present). It expanded into the eastern Bighorn Mountains of northern Wyoming by 2630 yr BP, quickly spreading north in the western Bighorns from 1400 to 1000 yr BP. Concurrent with the latter expansion, P. ponderosa spread c. ~350 km to the Little Belt and Big Belt Mountains in western Montana, establishing its northern limit and the modern introgression zone between var. scopulorum and var. ponderosa. Expansion in the Central Rockies of P. ponderosa involved two known haplotypes. Main conclusions: P. ponderosa expanded its range across large parts of northern Wyoming and central Montana during the late Holocene, probably in response to both northward and westward increases in summer temperature and rainfall. The underlying climatic driver may be the same as for the contemporaneous expansion of J. osteosperma, but will remain undetermined without focused development and integration of independent palaeoclimate records in the region."

Arizona, California, Colorado, Idaho, Montana, Nev↗
USGS2015

Trends and natural variability of North American spring onset as evaluated by a new gridded dataset of spring indices

Climate change is expected to modify the timing of seasonal transitions this century, impacting wildlife migrations, ecosystem function, and agricultural activity. Tracking seasonal transitions in a consistent manner across space and through time requires indices that can be used for monitoring and managing biophysical and ecological systems during the coming decades. Here a new gridded dataset of spring indices is described and used to understand interannual, decadal, and secular trends across the coterminous United States. This dataset is derived from daily interpolated meteorological data, and the results are compared with historical station data to ensure the trends and variations are robust. Regional trends in the first leaf index range from 20.8 to 21.6 days decade21, while first bloom index trends are between20.4 and 21.2 for most regions. However, these trends are modulated by interannual to multidecadal variations, which are substantial throughout the regions considered here. These findings emphasize the important role large-scale climate modes of variability play in modulating spring onset on interannual to multidecadal time scales. Finally, there is some potential for successful subseasonal forecasts of spring onset, as indices from most regions are significantly correlated with antecedent large-scale modes of variability.

Journal of Climate↗
USGS2015

On critiques of “Stationarity is dead: Whither water management?”

We review and comment upon some themes in the recent stream of critical commentary on the assertion that “stationarity is dead,” attempting to clear up some misunderstandings; to note points of agreement; to elaborate on matters in dispute; and to share further relevant thoughts.

Water Resources Research↗