1,500 year quantitative reconstruction of winter precipitation in the Pacific Northwest

Multiple paleoclimate proxies are required for robust assessment of past hydroclimatic conditions. Currently, estimates of drought variability over the past several thousand years are based largely on tree-ring records. We produced a 1,500-y record of winter precipitation in the Pacific Northwest using a physical model-based analysis of lake sediment oxygen isotope data. Our results indicate that during the Medieval Climate Anomaly (MCA) (900–1300 AD) the Pacific Northwest experienced exceptional wetness in winter and that during the Little Ice Age (LIA) (1450–1850 AD) conditions were drier, contrasting with hydroclimatic anomalies in the desert Southwest and consistent with climate dynamics related to the El Niño Southern Oscillation (ENSO) and the Pacific Decadal Oscillation (PDO). These findings are somewhat discordant with drought records from tree rings, suggesting that differences in seasonal sensitivity between the two proxies allow a more compete understanding of the climate system and likely explain disparities in inferred climate trends over centennial timescales.     

Community clusters of tsunami vulnerability in the US Pacific Northwest

Many coastal communities throughout the world are threatened by local (or near-field) tsunamis that could inundate low-lying areas in a matter of minutes after generation. Although the hazard and sustainability literature often frames vulnerability conceptually as a multidimensional issue involving exposure, sensitivity, and resilience to a hazard, assessments often focus on one element or do not recognize the hazard context. We introduce an analytical framework for describing variations in population vulnerability to tsunami hazards that integrates (i) geospatial approaches to identify the number and characteristics of people in hazard zones, (ii) anisotropic path distance models to estimate evacuation travel times to safety, and (iii) cluster analysis to classify communities with similar vulnerability. We demonstrate this approach by classifying 49 incorporated cities, 7 tribal reservations, and 17 counties from northern California to northern Washington that are directly threatened by tsunami waves associated with a Cascadia subduction zone earthquake. Results suggest three primary community groups: (i) relatively low numbers of exposed populations with varied demographic sensitivities, (ii) high numbers of exposed populations but sufficient time to evacuate before wave arrival, and (iii) moderate numbers of exposed populations but insufficient time to evacuate. Results can be used to enhance general hazard-awareness efforts with targeted interventions, such as education and outreach tailored to local demographics, evacuation training, and/or vertical evacuation refuges.During the last decade, tsunamis have killed hundreds of thousands of people and destroyed coastal communities throughout the world (1). Geologic evidence of past events and geophysical models of potential sources suggest that many communities face substantial tsunami hazards. Although tsunami scenarios are often regional, local vulnerability varies because of how communities choose to use tsunami-prone areas, the types of people in hazard zones, the local conditions that enable or hinder evacuations, and the ability and willingness to mitigate threats.The sustainability and hazards literature includes multiple efforts to conceptualize vulnerability, yet they share a common perspective that it is influenced by the exposure, sensitivity, and resilience of a system to a threat (2–5). Efforts to measure population vulnerability to tsunamis primarily have relied on indices that summarize population exposure (6), potential building damage (7), or institutional aspects of resilience (8). Indices also have been developed based on characteristics of people that make them more sensitive to hazards in general but are detached from a specific hazard context (9). These approaches are of limited utility to practitioners because they focus on individual components of vulnerability and inadequately capture the complex interactions between natural events and at-risk populations. For example, exposure to tsunamis should not be interpreted as a loss estimate given the potential for evacuations. Age as a vulnerability indicator for reasons related to mobility (2, 9) will likely have greater relevance for tsunamis requiring self-evacuations within minutes than they do for events with hours of warning.To address these shortcomings, we developed an analytical approach for hazard-specific vulnerability assessment that considers population exposure, demographic sensitivity, and short-term resilience. This approach is an advance over traditional vulnerability measures because it relates compositional aspects of the population and landscape to the hazard. We focus on the tsunami threat posed by earthquakes associated with the Cascadia subduction zone (CSZ) in the US Pacific Northwest, where regional impacts could be analogous to those in Japan during the 2011 Tohoku disaster. Of all tsunami-prone areas in the United States, CSZ-related tsunamis represent one of the greatest threats to human safety (10) based on the regional extent of the source (∼1,000 km from northern California to Washington), the limited amount of time available for evacuations (15–-30 min for many communities), and the thousands of people that would need to self-evacuate (6, 11, 12).The policy-relevant questions that drive this research are determining where loss of life is possible, what types of interventions could best serve at-risk populations, and what knowledge networks can be established to connect communities with similar issues. The work addresses the lack of pedestrian-evacuation studies to guide US tsunami risk-reduction efforts (10) by integrating geospatial and statistical methods, specifically demographic overlays to gauge exposure, anisotropic path distance models to estimate potential travel times to safety (13), and clustering algorithms (14) to segment coastal settlements into distinctive types. It deviates from current practices of developing indicators to rank geographic areas and instead focuses on the similarities and differences in community vulnerability. Community classification provides policymakers and practitioners with a framework for understanding vulnerability drivers and actionable information, as well as helps to minimize the reductionism and oversimplification involved in translating the multidimensional construct of vulnerability into a single index score.     

Coupled impacts of sea ice variability and North Pacific atmospheric circulation on Holocene hydroclimate in Arctic Alaska

Arctic Alaska lies at a climatological crossroads between the Arctic and North Pacific Oceans. The modern hydroclimate of the region is responding to rapidly diminishing sea ice, driven in part by changes in heat flux from the North Pacific. Paleoclimate reconstructions have improved our knowledge of Alaska’s hydroclimate, but no studies have examined Holocene sea ice, moisture, and ocean−atmosphere circulation in Arctic Alaska, limiting our understanding of the relationship between these phenomena in the past. Here we present a sedimentary diatom assemblage and diatom isotope dataset from Schrader Pond, located ∼80 km from the Arctic Ocean, which we interpret alongside synthesized regional records of Holocene hydroclimate and sea ice reduction scenarios modeled by the Hadley Centre Coupled Model Version 3 (HadCM3). The paleodata synthesis and model simulations suggest the Early and Middle Holocene in Arctic Alaska were characterized by less sea ice, a greater contribution of isotopically heavy Arctic-derived moisture, and wetter climate. In the Late Holocene, sea ice expanded and regional climate became drier. This climatic transition is coincident with a documented shift in North Pacific circulation involving the Aleutian Low at ∼4 ka, suggesting a Holocene teleconnection between the North Pacific and Arctic. The HadCM3 simulations reveal that reduced sea ice leads to a strengthened Aleutian Low shifted west, potentially increasing transport of warm North Pacific water to the Arctic through the Bering Strait. Our findings demonstrate the interconnectedness of the Arctic and North Pacific on multimillennial timescales, and are consistent with future projections of less sea ice and more precipitation in Arctic Alaska.

Rapidly rising Arctic air and sea surface temperatures have resulted in the reduced annual duration and extent of Arctic sea ice (1), which in turn drives the ice−albedo feedback leading to amplified warming in the Arctic (2). These reductions in sea ice are projected to continue in future decades (3) and have important implications for Arctic terrestrial hydroclimate, as sea ice extent and duration impact the seasonality, type, and amount of precipitation in this region (4). Recent studies have also suggested teleconnections between the extent and duration of Arctic sea ice and midlatitudinal storm tracks (5, 6), as well as synoptic-scale processes involving the Aleutian Low atmospheric pressure cell (AL) (7, 8) and ocean−atmosphere circulation in the Bering Strait (9–11), which might link North Pacific hydroclimate directly to changes in Arctic sea ice. While recent observations show the influence of North Pacific climate on Arctic sea ice, little is known about their long-term dynamics or their coupled influence on hydroclimate in the western Arctic.Our understanding of past hydroclimate in Arctic Alaska is based in part on stable isotope reconstructions that reflect changes in the oxygen (δ¹⁸O) and hydrogen (δD) isotope composition of water. δ¹⁸O has proven particularly useful for studying both current (12, 13) and past (14–20) hydroclimate in the region, because it is sensitive to climate and environmental variables. As a result, δ¹⁸O has been used as a paleoclimate proxy for precipitation source (16), effective moisture (14), and temperature (20) in Arctic Alaska. Interpretations of these paleoclimate datasets have considered the impact of Holocene changes in AL variability (15, 16, 18), but they have not been used to examine the influence of Holocene Arctic sea ice variability on western Arctic climate, despite well-established sea ice conditions for this time period (e.g., ref. 21). The influence of sea ice extent on δ¹⁸O in various climate archives has been demonstrated in Arctic Alaska during the Pleistocene−Holocene transition (19), as well as in Greenland during the Holocene (22) and the Last Interglacial period (LIG) (23), suggesting that sites adjacent to seasonally ice-free Arctic waters can be sensitive recorders of sea ice conditions.In light of increasing evidence from both data and models for a modern connection between North Pacific circulation and Arctic sea ice (5–8), as well as the demonstrated influence of North Pacific (15, 16, 18) and Arctic (13, 19) ocean−atmosphere systems on past and present terrestrial hydroclimate conditions, it appears that northern Alaska lies at a climatological crossroads within the western Arctic. This means that paleoclimate records from Arctic Alaska are especially well situated for studying the effects of both changing Arctic sea ice and North Pacific circulation. However, existing paleoclimate datasets from this region have not been interpreted in the context of such a coupled system, and little has been done to synthesize possible multimillennial patterns among these and other datasets. Potential teleconnections during the Holocene must be explored, because this paleoclimate context is important for understanding the coevolution of Arctic and Pacific hydroclimate systems on longer timescales, which could help clarify predictions of their continued coevolution in the future.Here we present Holocene diatom assemblage and oxygen isotope (δ¹⁸O_diatom) datasets from Arctic Alaska, which we interpret in terms of past hydroclimatic change. Our results show that Holocene variability in δ¹⁸O_diatom at Schrader Pond (SP) in the northeastern Brooks Range was driven by changes in moisture source associated with fluctuating Arctic sea ice extent. We also present a data−model comparison, featuring a synthesis of Holocene hydroclimate and sea ice reconstructions from regional terrestrial and marine sites, together with coupled atmosphere−ocean model simulations, which supports our interpretation of δ¹⁸O_diatom variability. Our data highlight a prominent shift in terrestrial hydroclimate and sea ice in the region, concomitant with a well-documented shift in North Pacific hydroclimate at ∼4 ka (24). The timing of these near-synchronous shifts suggests an Arctic−Pacific teleconnection has been present over the Middle to Late Holocene, emphasizing the important role of both sea ice and lower-latitude ocean−atmosphere dynamics in the past and future of the Arctic.     

A 2,300-year-long annually resolved record of the South American summer monsoon from the Peruvian Andes

Decadal and centennial mean state changes in South American summer monsoon (SASM) precipitation during the last 2,300 years are detailed using an annually resolved authigenic calcite record of precipitation δ¹⁸O from a varved lake in the Central Peruvian Andes. This unique sediment record shows that δ¹⁸O peaked during the Medieval Climate Anomaly (MCA) from A.D. 900 to 1100, providing evidence that the SASM weakened considerably during this period. Minimum δ¹⁸O values occurred during the Little Ice Age (LIA) between A.D. 1400 and 1820, reflecting a prolonged intensification of the SASM that was regionally synchronous. After the LIA, δ¹⁸O increased rapidly, particularly during the current warm period (CWP; A.D. 1900 to present), indicating a return to reduced SASM precipitation that was more abrupt and sustained than the onset of the MCA. Diminished SASM precipitation during the MCA and CWP tracks reconstructed Northern Hemisphere and North Atlantic warming and a northward displacement of the Intertropical Convergence Zone (ITCZ) over the Atlantic, and likely the Pacific. Intensified SASM precipitation during the LIA follows reconstructed Northern Hemisphere and North Atlantic cooling, El Niño-like warming in the Pacific, and a southward displacement of the ITCZ over both oceans. These results suggest that SASM mean state changes are sensitive to ITCZ variability as mediated by Western Hemisphere tropical sea surface temperatures, particularly in the Atlantic. Continued Northern Hemisphere and North Atlantic warming may therefore help perpetuate the recent reductions in SASM precipitation that characterize the last 100 years, which would negatively impact Andean water resources.     

Long-term effects of a trophic cascade in a large lake ecosystem

Introductions or invasions of nonnative organisms can mediate major changes in the trophic structure of aquatic ecosystems. Here we document multitrophic level impacts in a spatially extensive system that played out over more than a century. Positive interactions among exotic vertebrate and invertebrate predators caused a substantial and abrupt shift in community composition resulting in a trophic cascade that extended to primary producers and to a nonaquatic species, the bald eagle. The opossum shrimp, Mysis diluviana, invaded Flathead Lake, Montana, the largest freshwater lake in the western United States. Lake trout had been introduced 80 y prior but remained at low densities until nonnative Mysis became established. The bottom-dwelling mysids eliminated a recruitment bottleneck for lake trout by providing a deep water source of food where little was available previously. Lake trout subsequently flourished on mysids and this voracious piscivore now dominates the lake fishery; formerly abundant kokanee were extirpated, and native bull and westslope cutthroat trout are imperiled. Predation by Mysis shifted zooplankton and phytoplankton community size structure. Bayesian change point analysis of primary productivity (27-y time series) showed a significant step increase of 55 mg C m(-2) d(-1) (i.e., 21% rise) concurrent with the mysid invasion, but little trend before or after despite increasing nutrient loading. Mysis facilitated predation by lake trout and indirectly caused the collapse of kokanee, redirecting energy flow through the ecosystem that would otherwise have been available to other top predators (bald eagles).     

Long-term relationships among pesticide applications,mobility, and soil erosion in a vineyard watershed

Agricultural pesticide use has increased worldwide during the last several decades, but the long-term fate, storage, and transfer dynamics of pesticides in a changing environment are poorly understood. Many pesticides have been progressively banned, but in numerous cases, these molecules are stable and may persist in soils, sediments, and ice. Many studies have addressed the question of their possible remobilization as a result of global change. In this article, we present a retro-observation approach based on lake sediment records to monitor micropollutants and to evaluate the long-term succession and diffuse transfer of herbicides, fungicides, and insecticide treatments in a vineyard catchment in France. The sediment allows for a reliable reconstruction of past pesticide use through time, validated by the historical introduction, use, and banning of these organic and inorganic pesticides in local vineyards. Our results also revealed how changes in these practices affect storage conditions and, consequently, the pesticides'' transfer dynamics. For example, the use of postemergence herbicides (glyphosate), which induce an increase in soil erosion, led to a release of a banned remnant pesticide (dichlorodiphenyltrichloroethane, DDT), which had been previously stored in vineyard soil, back into the environment. Management strategies of ecotoxicological risk would be well served by recognition of the diversity of compounds stored in various environmental sinks, such as agriculture soil, and their capability to become sources when environmental conditions change.Viticulture is an important type of agricultural land use in many countries, including France. During the last several decades, the use of many chemical substances to control disease, insect damage, and weed competition in vineyards, which was practiced with few studies examining the behavior of these substances in various environmental compartments, has become a primary focus of interest for the European Union (1, 2). France accounts for ∼30% of European consumption of pesticides and remains the region’s leading consumer, with 20% of the nation’s pesticides used in viticulture despite the fact that this sector represents only 3% of agricultural land (3).It is now widely accepted that the routine use of pesticides (herbicides, fungicides, and insecticides) has adverse effects on the health of ecosystems and humans. Many of these substances are highly toxic and have been progressively banned as their toxicity has been proven. Many substances also are now subject to European regulation (4). Unfortunately, in many cases, these pesticides and/or their degradation products are stable molecules that may persist for several years, or even decades, in soils and sediments (5, 6), from which they can propagate into the environment through various dynamic processes (7, 8). In many vineyards, soil erosion, which is often intense as a result of both practices in sloping vineyards (e.g., tillage, herbicide applications) and the climate, has an important effect on the dispersion of pollutants into other environmental compartments (rivers, sediments, groundwater), where they may persist (9–12). Thus, there is a potentially complex interplay between pesticide dissemination, which, among other processes, increases soil erodibility, and soil erosion, which is influenced by pesticides but is also involved in the dynamics of pollutant dissemination. The long-term environmental fate of pesticides has rarely been studied (13), despite the chronology of the products and their direct and indirect interactions. With the aim of understanding these complex relationships, we used a retrospective approach based on well-constrained lake sediment stratigraphy to reconstruct the histories of both pesticide dynamics and soil erosion in a small-scale vineyard watershed that contains a small lake as a final sink for the erosion products.Lake sediment cores have been used extensively to evaluate and reconstruct historical contaminant trends in aquatic environments in relation to human practices in watersheds (14–18). Vertical profiles of particular contaminants in sediment cores associated with high- resolution sedimentologic and geochemical proxies provide a precise chronology of the long-term evolution of contaminant dynamics in watersheds. In this study, we were able to reconstruct the complex, long-term succession of pesticide applications (herbicides, fungicides, and insecticides) in a watershed. Independently, we reconstructed erosion patterns in the same watershed, using geochemical proxies to investigate the potential relationships.Our study focused on Lake Saint André, which is located in eastern France (45° 29′ 37″ N, 5° 59′ 10″ E) at an elevation of 295 m above sea level. Lake Saint André is a 350-m long by 250-m wide low-altitude lake located in the French Alps 10 km south of the city of Chambéry (Fig. 1). This lake was formed in A.D. 1248 after the Mount Granier landslide caused a 3.5 × 10⁸ m³ limestone cliff collapse and a gravity slide involving the Valanginian marls in the lower part of the cliff (19, 20). The Lake Saint André watershed is relatively small, with a surface area of 48.5 ha, including 17.4 ha of vineyard in 2009. The vineyards make up 36% of the watershed and drain only this landslide deposit (Fig. 1). This land use has been relatively constant since the beginning of World War II (WWII), although it has slowly and constantly decreased in size until the present day. The area of vineyard land use measured 21.5 ha in 1939, 19.3 ha in 1956, 18.8 ha in 1970, and 18.9 ha in 1990. Lake Saint André is deeper in its northern part, where the maximum water depth is 12 m and from which sediment cores were retrieved (Fig. 1).Open in a separate windowFig. 1.The Lake Saint André watershed and the vineyards in 2009 (interpreted from aerial photographs), as well as the bathymetric map with the location of core SAN11P2 retrieved from the deeper part of the lake.     

Carbonate formation events in ALH 84001 trace the evolution of the Martian atmosphere

Carbonate minerals provide critical information for defining atmosphere–hydrosphere interactions. Carbonate minerals in the Martian meteorite ALH 84001 have been dated to ∼3.9 Ga, and both C and O-triple isotopes can be used to decipher the planet’s climate history. Here we report Δ¹⁷O, δ¹⁸O, and δ¹³C data of ALH 84001 of at least two varieties of carbonates, using a stepped acid dissolution technique paired with ion microprobe analyses to specifically target carbonates from distinct formation events and constrain the Martian atmosphere–hydrosphere–geosphere interactions and surficial aqueous alterations. These results indicate the presence of a Ca-rich carbonate phase enriched in ¹⁸O that formed sometime after the primary aqueous event at 3.9 Ga. The phases showed excess ¹⁷O (0.7‰) that captured the atmosphere–regolith chemical reservoir transfer, as well as CO₂, O₃, and H₂O isotopic interactions at the time of formation of each specific carbonate. The carbon isotopes preserved in the Ca-rich carbonate phase indicate that the Noachian atmosphere of Mars was substantially depleted in ¹³C compared with the modern atmosphere.Geological evidence suggests that early Mars was sufficiently warm for liquid water to flow on the surface for at least brief periods, if not longer (1). Identifying the nature and duration of warmer conditions on the Martian surface is one of the key pieces of information for understanding atmosphere–hydrosphere–geosphere interactions, the evolution of the atmosphere, and potential past habitability. A better understanding of the evolution of the Martian atmosphere and, in particular, the behavior of its primary component, CO₂, provides a means for characterizing the nature of the ancient Martian environment. The amount of CO₂ present in the atmosphere should provide critical insight into the characteristics of the Martian climate, with a denser atmosphere being more likely to be able to support prolonged warmer temperatures (2, 3).The Martian meteorite ALH 84001 is a critical source for understanding the history of the Martian atmosphere, as it is the oldest known rock (crystallographic age ∼4.09 ± 0.03 Ga) (4), and its carbonate fractions (<1% wt/wt) are considered to have preserved the carbon isotope signature of the ancient atmosphere ∼3.9 Ga ago (5). These carbonates are chemically (Mg-, Ca-, and Fe-Mn rich) and isotopically (δ¹³C_VPDB = 27–64, where VPDB stands for Vienna Pee Dee Belemnite, and δ¹⁸O_SMOW = −10–27‰, where SMOW stands for Standard Mean Ocean Water) heterogeneous on micrometer scales; carbon and oxygen isotopes show a covariant relationship that is correlated with Mg content of the mineral (6–8). The exact process responsible for their formation is not clear, although low-temperature aqueous precipitation, biogenic production, evaporation, and high-temperature reactions are all candidate processes (9–13). Decoding the fingerprints of various oxygen-carrying reservoirs on Mars (atmosphere–hydrosphere–geosphere) and how they interact from δ¹⁸O alone is nearly impossible because of the lack of direct information on the isotopic composition of the primary O-carrying reservoirs in the carbonate system (CO₂–H₂O) and the extreme variability observed in chemical and isotopic composition of carbonate minerals in ALH 84001. The O-isotopic anomaly (∆¹⁷O = δ¹⁷O − 0.52 × δ¹⁸O) observed in O₃, SO₄, NO₃, CO₃, and H₂O₂ has been successfully used to investigate physicochemical and photochemical processes in terrestrial and extraterrestrial materials (14–18). In this study, we used five stable isotopes of carbonates (¹²C, ¹³C, ¹⁶O, ¹⁷O, and ¹⁸O) on Ca- and Fe-rich phases to decipher atmosphere–hydrosphere interactions and Martian CO₂/CO₃ geochemical cycling. This high-precision multi-O-isotope analysis of secondary minerals was coordinated with detailed petrographic and ion microprobe analyses.The primary goal of this study was to specifically identify carbonate phases from distinct formation events to provide better understanding of oxygen and carbon reservoirs on Mars. There have been no previous measurements of both carbon isotope and O-triple isotope compositions of the same CO₂ sample from ALH 84001, and previous measurements of O-triple isotopes did not attempt to use stepped extraction to separate different carbonate phases (19). To accomplish this goal, a stepped acid dissolution technique was performed to extract CO₂ from several portions of ALH 84001. The O-isotope values (Δ¹⁷O, δ¹⁸O) are reported with respect to SMOW, and δ¹³C of the CO₂ gas evolved with respect to V-PDB standard. We also report oxygen isotope SIMS (secondary ion mass spectrometer or ion microprobe) analyses coupled with SEM images of petrographically unusual carbonate phases in the meteorite, which provide a link between ion microprobe data, petrographic relationships, and the multiisotopic high-precision bulk analyses, allowing placement of further constraints on the alteration history of the meteorite.     

Drought,agricultural adaptation,and sociopolitical collapse in the Maya Lowlands

Paleoclimate records indicate a series of severe droughts was associated with societal collapse of the Classic Maya during the Terminal Classic period (∼800–950 C.E.). Evidence for drought largely derives from the drier, less populated northern Maya Lowlands but does not explain more pronounced and earlier societal disruption in the relatively humid southern Maya Lowlands. Here we apply hydrogen and carbon isotope compositions of plant wax lipids in two lake sediment cores to assess changes in water availability and land use in both the northern and southern Maya lowlands. We show that relatively more intense drying occurred in the southern lowlands than in the northern lowlands during the Terminal Classic period, consistent with earlier and more persistent societal decline in the south. Our results also indicate a period of substantial drying in the southern Maya Lowlands from ∼200 C.E. to 500 C.E., during the Terminal Preclassic and Early Classic periods. Plant wax carbon isotope records indicate a decline in C₄ plants in both lake catchments during the Early Classic period, interpreted to reflect a shift from extensive agriculture to intensive, water-conservative maize cultivation that was motivated by a drying climate. Our results imply that agricultural adaptations developed in response to earlier droughts were initially successful, but failed under the more severe droughts of the Terminal Classic period.The decline of the lowland Classic Maya during the Terminal Classic period (800–900/1000 C.E.) is a preeminent example of societal collapse (1), but its causes have been vigorously debated (2–5). Paleoclimate inferences from lake sediment and cave deposits (6–11) indicate that the Terminal Classic was marked by a series of major droughts, suggesting that climate change destabilized lowland Maya society. Most evidence for drought during the Terminal Classic comes from the northern Maya Lowlands (Fig. 1) (6–8, 10), where societal disruption was less severe than in the southern Maya Lowlands (12, 13). There are fewer paleoclimate records from the southern Maya Lowlands, and they are equivocal with respect to the relative magnitude of drought impacts during the Terminal Classic (9, 11, 14). Further, the supposition that hydrological impacts were a primary cause for societal change is often challenged by archaeologists, who stress spatial variability in societal disruption across the region and the complexity of human responses to environmental change (2, 3, 12). The available paleoclimate data, however, do not constrain possible spatial variability in drought impacts (6–11). Arguments for drought as a principal cause for societal collapse have also not considered the potential resilience of the ancient Maya during earlier intervals of climate change (15).Open in a separate windowFig. 1.Map of the Maya Lowlands indicating the distribution of annual precipitation (64) and the location of paleoclimate archives discussed in the text. The locations of modern lake sediment and soil samples (Fig. 2) are indicated by diamonds.For this study, we analyzed coupled proxy records of climate change and ancient land use derived from stable hydrogen and carbon isotope analyses of higher-plant leaf wax lipids (long-chain n-alkanoic acids) in sediment cores from Lakes Chichancanab and Salpeten, in the northern and southern Maya Lowlands, respectively (Fig. 1). Hydrogen isotope compositions of n-alkanoic acids (δD_wax) are primarily influenced by the isotopic composition of precipitation and isotopic fractionation associated with evapotranspiration (16). In the modern Maya Lowlands, δD_wax is well correlated with precipitation amount and varies by 60‰ across an annual precipitation gradient of 2,500 mm (Fig. 2). This modern variability in δD_wax is strongly influenced by soil water evaporation (17), and it is possible that changes in potential evapotranspiration could also impact paleo records. Accordingly, we interpret δD_wax values as qualitative records of water availability influenced by both precipitation amount and potential evapotranspiration. These two effects are complementary, since less rainfall and increased evapotranspiration would lead to both increased δD_wax values and reduced water resources, and vice versa.Open in a separate windowFig. 2.Scatter plot showing the negative relationship between annual precipitation and δD_wax-corr measured in modern lake sediment and soil samples (Fig. 1). Results from Lake Chichancanab (CH) and Salpeten (SP) are indicated. The black line indicates a linear regression fit to these data, with regression statistics reported at the bottom of the plot. Large squares indicate mean values for each sampling region, with error bars indicating SEM in both δD_wax-corr and annual precipitation. The black error bar indicates the 1σ error for δD_wax-corr values (SI Text). Original δD_wax data from ref. 17. VSMOW, Vienna Standard Mean Ocean Water.Plant wax carbon isotope signatures (δ¹³C_wax) in sediments from low-elevation tropical environments, including the Maya lowlands, are primarily controlled by the relative abundance of C₃ and C₄ plants (18–20). Ancient Maya land use was the dominant influence on the relative abundance of C₃ and C₄ plants during the late Holocene, because Maya farmers cleared C₃ plant-dominated forests and promoted C₄ grasses, in particular, maize (21–24). Thus, we apply δ¹³C_wax records as an indicator of the relative abundance of C₄ and C₃ plants that reflects past land use change (SI Text). Physiological differences between plant groups also result in differing δD_wax values between C₃ trees and shrubs and C₄ grasses (16), and we use δ¹³C_wax records to correct for the influence of vegetation change on δD_wax values (25) (δD_wax-corr, SI Text and Fig. S1).Plant waxes have been shown to have long residence times in soils in the Maya Lowlands (26). Therefore, age−depth models for our plant wax isotope records are based on compound-specific radiocarbon ages (Fig. 3), which align our δD_wax records temporally with nearby hydroclimate records derived from other methodologies (26) (SI Text and Fig. S2). The mean 95% confidence range for the compound-specific age−depth models is 230 y at Lake Chichancanab and 250 y at Lake Salpeten. Given these age uncertainties, we focus our interpretation on centennial-scale variability (26). The temporal resolution of our plant wax isotope records is lower than speleothem-derived climate records (8, 9), but combining plant wax records from multiple sites allows comparisons of climate change and land use in the northern and southern Maya Lowlands, which would otherwise not be possible. In addition, plant wax isotope records extend to the Early Preclassic/Late Archaic period (1500–2000 B.C.E.), providing a longer perspective on climate change in the Maya Lowlands than most other regional records (6, 8–11).Open in a separate windowFig. 3.Plant wax (green; left) and terrigenous macrofossil (red; right) age−depth models for (A) Lake Chichancanab and (B) Lake Salpeten. The age probability density of individual radiocarbon analyses is shown. The black lines indicate the best age model based on the weighted mean of 1,000 age model iterations (62). Colored envelopes indicate 95% confidence intervals. Cal, calendar.     

High-resolution record of the Matuyama-Brunhes transition constrains the age of Javanese Homo erectus in the Sangiran dome, Indonesia

A detailed paleomagnetic study conducted in the Sangiran area, Java, has provided a reliable age constraint on hominid fossil-bearing formations. A reverse-to-normal polarity transition marks a 7-m thick section across the Upper Tuff in the Bapang Formation. The transition has three short reversal episodes and is overlain by a thick normal polarity magnetozone that was fission-track dated to the Brunhes chron. This pattern closely resembles another high-resolution Matuyama-Brunhes (MB) transition record in an Osaka Bay marine core. In the Sangiran sediments, four successive transitional polarity fields lie just below the presumed main MB boundary. Their virtual geomagnetic poles cluster in the western South Pacific, partly overlapping the transitional virtual geomagnetic poles from Hawaiian and Canary Islands' lavas, which have a mean (40)Ar/(39)Ar age of 776 ± 2 ka. Thus, the polarity transition is unambiguously the MB boundary. A revised correlation of tuff layers in the Bapang Formation reveals that the hominid last occurrence and the tektite level in the Sangiran area are nearly coincident, just below the Upper Middle Tuff, which underlies the MB transition. The stratigraphic relationship of the tektite level to the MB transition in the Sangiran area is consistent with deep-sea core data that show that the meteorite impact preceded the MB reversal by about 12 ka. The MB boundary currently defines the uppermost horizon yielding Homo erectus fossils in the Sangiran area.     

湖沼地区湖北钉螺小尺度分布的空间自相关分析

目的研究湖沼地区湖北钉螺小尺度分布的空间自相关性。方法从安徽省池州市贵池区的秋浦河沿岸随机选择一个滩地的中间层和河边层作为研究现场，采用交叉复核随机抽检的查螺方法于滩地水淹前后各普查钉螺100框，判别死活，并分辨成螺和幼螺。在两层内各随机取10份土壤样本，测量土壤湿度。先计算并比较水淹前后两层的土壤湿度和钉螺密度，然后计算Moran'sI和Geary's C两个空间自相关指标，探讨钉螺的小尺度分布情况及是否存在空间自相关。结果钉螺的小尺度分布始终存在正空间自相关，其变化与钉螺密度的高低一致。Moran,s I均>0. 22，Geary，s C均<0. 76，P相似文献   

湖沼地区钉螺分布动态性的初步证据

目的研究湖沼地区钉螺分布的规律,为正确认识钉螺的生态学提供依据。方法从安徽省贵池区秋浦河沿岸随机抽取4块滩地作为研究现场,按《血吸虫病防治手册》推荐的查螺方法调查钉螺,并记录线框号。所有钉螺带回实验室用水测法判别死活,并记录活螺数。计算4块滩地的中位数、95%可信区间(95%CI)等描述性统计指标,并分别用负二项分布、对数正态分布、指数分布和Weibull分布拟合钉螺数据以分析钉螺的分布规律。结果4块滩地钉螺的分布均为正偏态分布,钉螺密度(只/0.1m2)的中位数分别为9.0、15.0、41.5和22.0,95%CI分别为(0,41)、(0,68)、(0,170)和(4,73),聚集性指数分别为1.12、1.25、1.37和2.31。谷潭湖滩既符合负二项分布,又近似指数分布,秋浦河外滩近似指数分布,菜籽湖滩可能近似指数分布,欧阳湖滩近似Weibull分布。结论湖沼地区钉螺的分布不是简单的负二项分布,可能是动态变化的过程。     

Cerebral lipiodol embolism related to a vascular lake during chemoembolization in hepatocellular carcinoma: A case report and review of the literature

A male patient underwent conventional transcatheter chemoembolization for advanced recurrent hepatocellular carcinoma(HCC). Even after the injection of 7 m L of lipiodol followed by gelatin sponge particles, the flow of feeding arteries did not slow down. A repeat angiography revealed a newly developed vascular lake draining into systemic veins; however, embolization was continued without taking noticing of the vascular lake. The patient's level of consciousness deteriorated immediately after the procedure, and non-contrast computed tomography revealed pulmonary and cerebral lipiodol embolisms. The patient's level of consciousness gradually improved after 8 wk in intensive care. In this case, a vascular lake emerged during chemoembolization and drained into systemic veins, offering a pathway carrying lipiodol to pulmonary vessels, the most likely cause of this serious complication. We should be aware that vascular lakes in HCC may drain into systemic veins and can cause intratumoral arteriovenous shunts.     

Keeping track of time under ice and snow in a sub-arctic lake: plasma melatonin rhythms in Arctic charr overwintering under natural conditions

Abstract:  Although photoperiod is considered as a major environmental cue for timing of seasonal events in fish, little is known about the photic information perceived by fish in different aquatic environments. The strongly seasonal Arctic charr, Salvelinus alpinus , reside in lakes covered by thick ice and snow throughout the dark winter in the north. In the present study, we have measured diel changes in their plasma melatonin concentrations from September to June in Lake Storvatnet (70°N), northern Norway. In addition, we have measured the in vitro melatonin production of Arctic charr pineal glands held at experimental light conditions. From September to April a diel profile in plasma melatonin was seen in the charr in Lake Storvatn, with highest concentrations at night. This profile reflected the prevailing above-surface photoperiod, even in February when there were minimal changes in sub-surface irradiance between day and night. In June, plasma melatonin was low throughout the 24-hr cycle, despite there being a marked sub-surface difference in irradiance between night and day. At this time the irradiance in night probably remained above the threshold for suppression of melatonin production. The in vitro experiments revealed no endogenous rhythm in the pineal melatonin secretion, supporting the conclusion that the diel profile seen in the Arctic charr in their natural habitat was driven by ambient photoperiod. In conclusion, the Arctic charr appear to keep track of time even under the extreme conditions of high latitudes during winter, when lakes have thick ice and snow cover.     

Coupled CH4 production and oxidation support CO2 supersaturation in a tropical flood pulse lake (Tonle Sap Lake,Cambodia)

Carbon dioxide (CO₂) supersaturation in lakes and rivers worldwide is commonly attributed to terrestrial–aquatic transfers of organic and inorganic carbon (C) and subsequent, in situ aerobic respiration. Methane (CH₄) production and oxidation also contribute CO₂ to freshwaters, yet this remains largely unquantified. Flood pulse lakes and rivers in the tropics are hypothesized to receive large inputs of dissolved CO₂ and CH₄ from floodplains characterized by hypoxia and reducing conditions. We measured stable C isotopes of CO₂ and CH₄, aerobic respiration, and CH₄ production and oxidation during two flood stages in Tonle Sap Lake (Cambodia) to determine whether dissolved CO₂ in this tropical flood pulse ecosystem has a methanogenic origin. Mean CO₂ supersaturation of 11,000 ± 9,000 μatm could not be explained by aerobic respiration alone. ¹³C depletion of dissolved CO₂ relative to other sources of organic and inorganic C, together with corresponding ¹³C enrichment of CH₄, suggested extensive CH₄ oxidation. A stable isotope-mixing model shows that the oxidation of ¹³C depleted CH₄ to CO₂ contributes between 47 and 67% of dissolved CO₂ in Tonle Sap Lake. ¹³C depletion of dissolved CO₂ was correlated to independently measured rates of CH₄ production and oxidation within the water column and underlying lake sediments. However, mass balance indicates that most of this CH₄ production and oxidation occurs elsewhere, within inundated soils and other floodplain habitats. Seasonal inundation of floodplains is a common feature of tropical freshwaters, where high reported CO₂ supersaturation and atmospheric emissions may be explained in part by coupled CH₄ production and oxidation.

Globally, most lakes and rivers are supersaturated with dissolved carbon dioxide (CO₂) relative to the atmosphere, highlighting their outsized role in transferring and transforming terrestrial carbon (C) (1–3). Terrestrial–aquatic transfers of C can include CO₂ dissolved in terrestrial ground and surface waters (3–6), dissolved inorganic carbon (DIC) from carbonate weathering (7, 8), or organic C from various sources that is subsequently respired in lakes and rivers (9, 10). Initially, oceanic export was thought to be the only fate for terrestrial–aquatic transfers of C, but a growing body of research on sediment burial of organic C and CO₂ emissions from freshwaters prompted the “active pipe” revision to this initial set of assumptions (11). Although freshwaters are now recognized as focal points for transferring and transforming C on the landscape, most of this research has been conducted within temperate freshwaters (2, 11, 12). Few studies focus on the mechanisms of CO₂ supersaturation in tropical lakes and rivers, with most conducted in just one watershed, the Amazon (4, 13–15).CO₂ supersaturation within tropical freshwaters is likely influenced by their unique flood pulse hydrology. The canonical flood pulse concept hypothesizes that annual flooding of riparian land will lead to organic C mobilization and respiration (16). Partial pressures of CO₂ (pCO₂) have been measured in excess of 44,000 μatm in the Amazon River (13), 16,000 μatm in the Congo River (17), and 12,000 μatm in the Lukulu River (17). Richey et al. (13), Borges et al. (18), and Zuidgeest et al. (17) have each shown that that riverine pCO₂ scales with the amount of land flooded in these watersheds. Yet it was only recently that Abril and Borges (19) proposed the importance of flooded land to the “active pipe.” These authors differentiate uplands that unidirectionally drain water downhill (via ground and surface water) from floodplains that bidirectionally exchange water with lakes and rivers (19). They conceptualize how floodplains combine high hydrologic connectivity, high rates of primary production, and high rates of respiration to transfer relatively large amounts of C to tropical freshwaters (19).Methanogenesis inevitably results on floodplains after dissolved oxygen (O₂) and other electron acceptors for anaerobic respiration such as iron and sulfate are consumed (16, 19). Horizontal gradients in dissolved O₂ and reducing conditions have been observed extending from the center of lakes and rivers through their floodplains in the Mekong (20, 21), Congo (22), Pantanal (23), and Amazon watersheds (4). CH₄ production and oxidation occur along such redox gradients (4, 16, 19, 23). CH₄ is produced by acetate fermentation (Eq. 1) and carbonate reduction (Eq. 2) within freshwaters (24, 25). CH₄ production coupled with aerobic oxidation results in CO₂ (Eq. 3 and ref. 25), yet no studies have quantified the relative contribution of coupled CH₄ production and oxidation to CO₂ supersaturation within tropical freshwaters.CH3COOH→CO2+CH4,[1]CO2+8H++8e−→CH4+2H2O,[2]CH4+2O2→CO2+2H2O.[3]The relative contribution of coupled CH₄ production and oxidation to CO₂ supersaturation within tropical freshwaters can be traced with stable C isotopes of CO₂ and CH₄. Methanogenesis results in CH₄ that is depleted in ¹³C (δ¹³C = −65 to −50‰ from acetate fermentation and −110 to −60‰ from carbonate reduction) compared to other potential sources of organic and inorganic C (δ¹³C = −37 to −7.7‰; see Materials and Methods) (24–26). The oxidation of this ¹³C-depleted CH₄ results in ¹³C-depleted CO₂ (24–26). At the same time, CH₄ oxidation enriches the ¹³C/¹²C of residual CH₄ as bacteria and archaea preferentially oxidize ¹²C-CH₄ (25). This means that the ¹³C/¹²C of CO₂ and CH₄ can serve as powerful tools to determine the source of CO₂ supersaturation within freshwaters.Tonle Sap Lake (TSL) is Southeast Asia’s largest lake and an understudied flood pulse ecosystem that supports a regionally important fishery (21, 22, 27). Each May through October, monsoonal rains and Himalayan snowmelt increase discharge in the Mekong River and cause one of its tributaries, the Tonle Sap River, to reverse course from southeast to northwest (21). During this course reversal, the Tonle Sap River floods TSL. The TSL flood pulse increases lake volume from 1.6 to 60 km³ and inundates 12,000 km² of floodplain for 3 to 6 mo per year (21, 27). Holtgrieve et al. (22) have shown that aerobic respiration is consistently greater than primary production in TSL (i.e., net heterotrophy), with the expectation of consistent CO₂ supersaturation. But, the partial pressures, C isotopic compositions, and ultimately the source of dissolved CO₂ in TSL remain unquantified.To quantify CO₂ supersaturation and its origins in TSL, we measured the partial pressures of CO₂ and CH₄ and compared their C isotopic composition to other potential sources of organic and inorganic C. We carried out these measurements in distinct lake environments during the high-water and falling-water stages of the flood pulse, hypothesizing that CH₄ production and oxidation on the TSL floodplain would support CO₂ supersaturation during the high-water stage. We found that coupled CH₄ production and oxidation account for a nontrivial proportion of the total dissolved CO₂ in all TSL environments and during both flood stages, showing that anaerobic degradation of organic C at aquatic–terrestrial transitions can support CO₂ supersaturation within tropical freshwaters.     

封洲禁牧防制湖区血吸虫病效果的现场观察

目的观察封洲禁牧对控制湖区血吸虫病的效果。方法在鄱阳湖区选择4个重疫区,从每年的3月1日起至10月31日止,实施封洲禁牧措施或以封洲禁牧为主的综合防治措施,监测各试点人、畜、螺血吸虫的感染率,连续2-3年。结果经过2-3年后,4个试点人、畜、螺血吸虫的感染率大幅度下降或达到0,无急感病人,人、畜、螺无血吸虫新感染。结论封洲禁牧措施或以封洲禁牧为主的综合防治措施能有效的控制湖沼地区血吸虫病的传播。     

2012-2014年海宁市水网型血吸虫病监测点疫情分析

目的 目的 了解海宁市省级血吸虫病监测点疫情动态和流行现状。方法 方法 根据 《浙江省血吸虫病监测点监测方 案》, 2012-2014年对海宁市海昌街道勤民村省级监测点螺情、 常住居民、 流动人口病情等进行监测。结果 结果 2012-2014 年监测点共调查常住居民600人, 血检阳性率为3.17% （19/600）, 粪检均为阴性; 3年血检阳性率分别为2.50% （5/200）、 0 （0/200）、 7.00% （14/200）, 2014年血检阳性率显著高于2013年 （χ2 = 14.508, P < 0.01）。3年共监测流动人口1 591人, 血 检阳性率为0.94% （15/1 591）, 粪检均为阴性; 其中主动监测和被动监测血检阳性率分别为0.92% （14/1 521） 和1.43% （1/ 70）, 差异无统计学意义 （χ2 = 1.659, P > 0.05）; 各年血检阳性率分别为1.50% （8/534）、 0.56% （3/531）、 0.76% （4/526）, 差异 无统计学意义 （χ2 = 2.752, P > 0.05）。螺情监测显示未发现阳性钉螺环境和钉螺输入。结论 结论 海宁市存在血吸虫病传 染源, 需警惕局部流行的可能。今后仍需加强螺情监测和外来流动人员病情监测。     

HIV discrimination: integrating the results from a six-country situational analysis in the Asia Pacific

The findings of the six independent studies on institutional forms of HIV discrimination in the Asia Pacific presented in this Special Issue of AIDS Care are integrated. At first glance, the general pattern of the results across the study sites suggests that discrimination is most pertinent in the domain of 'practice' rather than in the domains of law or institutional policy. On closer analysis, however, utilising the qualitative data, this conclusion does not take sufficient account of the cultural context within which the interpersonal interaction (practice) between the health carers and people living with HIV/AIDS occurs. Limitations on the use of anti-discrimination legislations and protective written policies for reducing discrimination in these contexts are discussed. The need for alternative approaches to thinking about discrimination intervention is raised and this is done through a consideration of the strategy of universal precautions.     

First palaeoparasitological record of a dioctophymatid egg in an archaeological sample from Patagonia

The collection of parasitological information from ancient material requires an exhaustive study of samples. In 2005, cestode and nematode eggs were found in a coprolite sample tentatively assigned to a canid. The sample was obtained from the layer of the archaeological site located in Cerro Casa de Piedra, Santa Cruz Province, Argentina, and dated from 6540 ± 110 years before present. The aim of the present work was to reexamine this fixed sample in order to confirm the presence of these parasites. The palaeoparasitological results support our previous findings. Interestingly, another parasite was also confirmed: a dioctophymatid nematode. Dioctophyma renale has been reported in several modern carnivores in the Southern Hemisphere but in ancient materials, it has only been reported in human coprolites from Switzerland. This report constitutes the first evidence of the presence of a dioctophymatid nematode parasite dioctophymatid nematode in American pre-Columbian times. The results obtained in this work show the importance of revising earlier palaeoparasitological results.