Climatic Transition Zone Research Articles

Effects of Tourism Trampling on Soil Nitrogen Mineralization in Quercus variabilis Blume Forests Varies with Altitudes in the Climate Transition Zone

Tourism trampling is one of the critical disturbance factors affecting forest structure and function apart from forest management activities. However, how tourism trampling affects soil nitrogen (N) mineralization rate at different altitudes in scenic forest spots is still unclear. To determine whether the responses of soil net N mineralization rate to tourism trampling varies with altitudes, we incubated soils using a field buried pipe method and analyzed soil ammonium N (NH4+-N) and nitrate N (NO3−-N) content at three altitudes (810 m, 1030 m, and 1240 m) at the Baotianman forest scenic spot in Henan Province. The results showed that tourism trampling significantly increased the soil bulk density and soil pH value but substantially reduced soil organic carbon (C) and total N content at all altitudes. Tourism trampling also resulted in a significant decrease in NO3−-N in the soil before and after incubation at all altitudes. The effects of tourism trampling on soil net N mineralization varied with latitudes, showing positive effects at 1030 m altitude (+51.4%), but negative effects at 1240 m altitude (−43.5%). For the soil net N nitrification rate, however, tourism trampling resulted in an increased rate (+141.1%) only at the 810 m altitude. Across all altitudes, soil microbial biomass C is primarily responsible for the variation in the soil net N mineralization rate. This study indicates that the effect of tourism trampling on soil net N mineralization rate varies with altitudes, which is related to the intensity of tourist disturbance and the synthetic effects of vegetation and soil microbes.

Disentangling the effects of species interactions and environmental factors on the spatial pattern and coexistence of two congeneric Pinus species in a transitional climatic zone.

Congeneric species are critical for understanding the underlying ecological mechanisms of biodiversity maintenance. Ecological mechanisms such as conspecific negative density dependence, species differences in life‐history stages related to habitat preference, and limiting similarity are known to influence plant fitness, thereby influencing species coexistence and biodiversity. However, our understanding of these phenomena as they apply to coexistence among coniferous species is limited. We studied two congeneric Pinus species, Pinus armandii (PA) and Pinus tabulaeformis (PT), both of which are common pioneer species typically succeeded by oaks (Quercus), in a 25‐ha warm temperate deciduous broad‐leaved forest. Here, we addressed the following questions: (1) How do population structures and distributions patterns of these two Pinus species vary with respect to different life‐history stages? (2) Does intra‐ and interspecific competition vary with respect to three life‐history stages? And (3) What are the relative contributions of topographic and soil variables to the spatial distributions of the species across the three life‐history stages? In addressing these questions, we utilized the pair‐correlation function g(r), redundancy analysis (RDA), variance partitioning (VP), and hierarchical partitioning (HP) to identify habitat preferences and conspecific negative density dependence at different life‐history stages from small to large trees. The results revealed that in both Pinus species, individuals in different life‐history stages were subject to significant habitat heterogeneity, with a tendency for small trees to be distributed at higher latitudes that may be represents climate‐change‐driven migration in both species. In addition, the effects of conspecific negative density dependence on PT were stronger than those on PA due to limited dispersal in PT. Furthermore, we found that interspecific competition was weak due to the species differences in resource utilization and preference for key habitats. Our study shows that congeneric Pinus species avoids competition by exploiting distinct habitats and provides insight into forest community structure.

Persistence in a tropical transition zone? Sargassum forests alternate seasonal growth forms to maintain productivity in warming waters at the expense of annual biomass production

Macroalgal forests provide productivity and biomass that underpins the function of many coastal ecosystems globally. The phenology of forests is seasonally driven by environmental conditions, with the environment-productivity relationship understood for most coastlines of the world. Climatic transition zones, however, have characteristics of temperate and tropical regions, creating large fluctuations in environmental conditions, and potentially limiting productivity and the persistence of macroalgal forests. The response of a forest-forming, dimorphic seaweed (Sargassum hemiphyllum) to seasonal temperature and light conditions in a rapidly warming tropical-temperate transitional zone (Hong Kong) was quantified by measuring in situ growth, net primary productivity (NPP), respiration, and photosynthetic potential. These physiological responses of S. hemiphyllum were then experimentally tested in response to changing temperatures (16.5–27 °C) and irradiances (20, 110, and 300 μmol m−2 s−1) in laboratory mesocosms. In contrast to predictions, S. hemiphyllum demonstrated asynchronous NPP and growth patterns, with growth maximized in cooler conditions but, counter-intuitively, highest photosynthetic rates in summer after annual senescence and dormancy were established. This discrepancy between peak photosynthetic rates and growth may provide regional populations of S. hemiphyllum the ability to survive higher temperatures in the near future, resisting the predicted range shifts under ocean warming. In contrast, warming is likely to drive a shorter growth season, longer dormancy, and reduced annual biomass production in bi-phasic seaweeds inhabiting climatic transition zones, potentially reducing system-wide productivity of these algal forests.

Quantifying Intra-Catchment Streamflow Processes and Response to Climate Change within a Climatic Transitional Zone: A Case Study of Buffalo Catchment, Eastern Cape, South Africa

The complexity of streamflow processes inhibits significant information about catchment performance and its sensitivity to climate change. Little is known about the severity of climate change within the coastal area of the monsoon–subtropical zone of climatic transition. This study advances a quasi-local scale analysis to simplify daily streamflow dynamics and their relationship with monthly hydro-climatic series (1981–2020) using six gauging stations on the Buffalo River due to its socio-economic significance. An integrated framework based on continuous wavelet transform (CWT), wavelet coherence (WC), innovative trend analysis (ITA), Mann–Kendall (MK), Sequential Mann–Kendall, and Pettitt tests were employed. CWT showed huge declivity in daily streamflow intensity (7676 to 719), >100 mm/day streamflow frequency (15 to 0), and wetness spell time-gap. WC obtained significant streamflow–rainfall co-movement of 8–196-month periodicities, which characterized Buffalo as anti-phase (1–4-month), lag-lead (8–32-month), and in-phase (64–196-month) in processes. The Buffalo River’s sensitivity to significantly decreasing rainfall trends and increasing temperature trends depicts Streamflow–ENSO teleconnection. Contrarily, ITA and MK exhibited significantly increasing trends of tributaries’ low flow and inferred the perennial status of the catchment. The Pettitt test corroborates the deductions and asserts 1990 (temperature), 1996 (streamflow), and 2004/2013 (rainfall) as the abrupt change points, while SMK captured a critical streamflow slump in 2015–2020. Overall, the study proved the reductionist approach and model framework to achieve the hydrological process simplification and resolution of hotspots of hydrologic extremes within a bimodal climate with complex topography. This study remarks on the management policy of the BR and provides a reference for managing water resources and catchment hydro-climatic extremes.

Investigating and predicting spatiotemporal variations in vegetation cover in transitional climate zone: a case study of Gansu (China)

Vegetation ecosystems are sensitive to large-scale climate variability in climate transition zones. As a representative transitional climate zone in Northwest China, Gansu is characterized by a sharp climate and vegetation gradient. In this study, the spatiotemporal variations of vegetation over Gansu are characterized using the satellite-based normalized difference vegetation index (NDVI) observations during 2000–2020. Results demonstrate that a significant greening trend in vegetation over Gansu is positively linked with large-scale climate factors through modulating the water and energy dynamics. As a climate transition zone, the northern water-limited and southern energy-limited regions of Gansu are affected by water and energy dynamics, differently. In the water-limited region, a weakening Asian monsoon along with colder Central Pacific (CP) and warmer North Pacific (NP) Oceans enhances prevailing westerlies which bring more atmospheric moisture. The enhanced atmospheric moisture and rising temperature promote the local vegetation growth. In contrast, large-scale climate variations suppress the southwest monsoon moisture fluxes and reduce precipitation in southern energy-limited regions. In these energy-limited regions, temperature has more effects on vegetation growth than precipitation. Therefore, the greenness of vegetation is because of more available energy from higher temperatures despite overall drying conditions in the region. Based on the above mechanism, future scenarios for climate impacts on vegetation cover over Gansu region are developed based on the two latest generation from coupled climate models (Coupled Model Intercomparison Project Phase 5 and Phase 6; CMIP5 and CMIP6). In the near-term future (2021–2039), the vegetation is likely to increase due to rising temperature. However, the vegetation is expected to decrease in a long-term future (2080–2099) when the energy-limited regions become water-limited due to increasing regional temperatures and lowering atmospheric moisture flux. This study reveals an increasing desertification risk over Gansu. Similar investigations will be valuable in climate transition regions worldwide to explore how large-scale climate variability affects local ecological services under different future climate scenarios.

Palaeoclimatic variability during last eight millennia from a morainal lake in Zanskar, northwest Himalaya, India

Centennial–scale palaeoenvironmental variability has been deduced during past eight millennia using multi–proxy study (textural analysis, environmental magnetic parameters, stable carbon isotopes, palynofacies and elemental concentration), from Khangok–Padam in Zanskar Valley, northwest Himalaya. The multi–proxy record from this morainal lake spanning last ~8200 cal years BP has revealed four hydroclimatic phases. The overall progressively improving hydroclimatic trend is indicated by multi proxy study: sediment size/texture (as a proxy for the energy condition and depositional environment), mineral magnetism (proxy for sediment flux or lithogenic input and lithologic variation), carbon isotope signature (δ13Corg) preserved in organic constituents of sediments (a proxy for palaeovegetation and climate change), elemental geochemistry (proxy for weathering and erosion) and selected samples for palynofacies data (a proxy for changes in biological organic matter). This improving hydroclimatic trend is however punctuated by an abrupt wet spell at ~6200–5200 cal years BP and relatively drier climate during the Little Ice Age between 1400 and 1900 CE. The main driving force implicated for the changes are seen to be the solar output variations. The area lying in a transitional climatic zone of NW Himalaya shows no emphatic record of the events like the 4200 cal. years BP, 2600 cal. years BP and Holocene Climatic Optima. Contrary to the earlier studies in the region (e.g., Tsokar and TsoMorari), our results show an improving hydroclimatic condition in this transition climatic zone between the Indian Summer Monsoon dominated Higher and westerly dominated Trans Himalaya.

Perception of climate change from the Himalayan ‘cold desert’ Ladakh, India

Climate change perception survey is a method designed to gain insights on people’s perspectives of the changing climate and recognizing important factors, complexities, and limitations towards a climate-conscious conduct. Such surveys are particularly important in ecologically sensitive transitional climatic zones but logistically difficult terrains, where meteorological data is scarce and minor changes in climatic parameters can have unanticipated consequences for the local ecosystem. The current research is focused on one of such climate-sensitive areas, in the northwestern Himalaya. A binary question-based survey (interview) was conducted in the high-altitude, cold desert region – Ladakh, which covered all the five subdivisions of the union territory. According to the climate perception data, the majority of respondents are aware of climate change or global warming regardless of age, gender, and background. The exponential growth in tourist inflow over the last two decades (attributed to ‘war tourism’) equates with the increasing number of vehicles and is well perceived by the locals. Approximately 86 percent of respondents believe that humans have had a negative impact on the environment. They appear to be quite optimistic about curbing the effects of climate change, with approximately 91 percent willing to participate in mitigation efforts. The results of this study show an overall agreement between people’s perceptions of climate change and the scientific evidence of these changes. These findings are eventually intended to serve as an important parameter in developing adaptation and mitigation strategies in this ecologically sensitive and vulnerable region.

Spatial heterogeneity effects on land surface modeling of water and energy partitioning

Abstract. Understanding the influence of land surface heterogeneity on surface water and energy fluxes is crucial for modeling earth system variability and change. This study investigates the effects of four dominant heterogeneity sources on land surface modeling, including atmospheric forcing (ATM), soil properties (SOIL), land use and land cover (LULC), and topography (TOPO). Our analysis focused on their impacts on the partitioning of precipitation (P) into evapotranspiration (ET) and runoff (R), partitioning of net radiation into sensible heat and latent heat, and corresponding water and energy fluxes. An initial set of 16 experiments were performed over the continental US (CONUS) using the E3SM land model (ELMv1) with different combinations of heterogeneous and homogeneous datasets. The Sobol' total and first-order sensitivity indices were utilized to quantify the relative importance of the four heterogeneity sources. Sobol' total sensitivity index measures the total heterogeneity effects induced by a given heterogeneity source, consisting of the contribution from its own heterogeneity (i.e., the first-order index) and its interactions with other heterogeneity sources. ATM and LULC are the most dominant heterogeneity sources in determining spatial variability of water and energy partitioning, mainly contributed by their own heterogeneity and slightly contributed by their interactions with other heterogeneity sources. Their heterogeneity effects are complementary, both spatially and temporally. The overall impacts of SOIL and TOPO are negligible, except TOPO dominates the spatial variability of R/P across the transitional climate zone between the arid western and humid eastern CONUS. Accounting for more heterogeneity sources improves the simulated spatial variability of water and energy fluxes when compared with ERA5-Land reanalysis dataset. An additional set of 13 experiments identified the most critical components within each heterogeneity source, which are precipitation, temperature, and longwave radiation for ATM, soil texture, and soil color for SOIL and maximum fractional saturated area parameter for TOPO.

Early Summer Temperature Variation Recorded by Earlywood Width in the Northern Boundary of Pinus taiwanensis Hayata in Central China and Its Linkages to the Indian and Pacific Oceans.

Simple SummaryThis paper analyzed the different relationships between earlywood and latewood as well as total tree-ring growth and the climate factors and reconstructed 106 years of May–June mean temperature (TMJ) in the Tongbai Mountains based on the earlywood width chronology of Pinus taiwanensis Hayata. It also analyzed the linkages to the Indian and Pacific Oceans. This paper found that earlywood width chronology has better response to the climate factors than latewood width and total tree-ring width. This study also found that the main limiting factors that restrained radial growth of Pinus taiwanensis Hayata in the Tongbai Mountains were May–June mean temperature and mean maximum temperature. The reconstructed TMJ series have a better reliability and are significantly negatively correlated with sea surface temperature (SST) over the tropical Western Pacific Ocean and Indian Ocean and are significantly positively correlated with SST over the subtropical Pacific Ocean. Finally, the periodic fluctuations of TMJ in the Tongbai Mountains might be related to the quasi-biennial interannual oscillation of SST over the Indo-Pacific equatorial region (QBO). The results of this study are significant for further understanding and exploring forest growth and climate change in the climatic transition zone.The Tongbai Mountains are an ecologically sensitive region to climate change, where there lies a climatic transitional zone from a subtropical to a warm–temperate monsoon climate. The northern boundary of Pinus taiwanensis Hayata is here; thus, climate information is well recorded in its tree rings. Based on developed earlywood width (EWW), latewood width (LWW) and total ring width (RW) chronologies (time period: 1887–2014 year) of Pinus taiwanensis Hayata in the Tongbai Mountains in central China, this paper analyzed characteristics of these chronologies and correlations between these chronologies and climate factors. The correlation results showed that earlywood width chronology contains more climate information than latewood width chronology and total ring width chronology, and mean temperature and mean maximum temperature in May–June were the main limiting factors for radial growth of Pinus taiwanensis Hayata. The highest significant value in all correlation analyses is −0.669 (p < 0.05) between earlywood width chronology and May–June mean temperature (TMJ) in the pre-mutation period (1958–2005) based on mutating in 2006. Thus, this paper reconstructed May–June mean temperature using earlywood width chronology from 1901 to 2005 (reliable period of earlywood width chronology is 1901–2014). The reconstructed May–June mean temperature experienced eight warmer periods and eight colder periods and also showed 2–3a cycle change over the past 105 years. The spatial correlation showed that the reconstructed series was representative of the May–June mean temperature variation in central and eastern China and significant positive/negative correlation with the sea surface temperature (SST) of the subtropical Pacific Ocean and the tropical Western Pacific Ocean and Indian Ocean from the previous October to the current June. This also indicated that May–June mean temperature periodic fluctuations might be related to the quasi-biennial oscillation (QBO) in the tropical Western Pacific Ocean and Indian Ocean. The results of this study have extended and supplemented the meteorological records of the Tongbai Mountains and have a guiding significance for forest tending and management in this area.

Mechanism of the summer rainfall variation in Transitional Climate Zone in East Asia from the perspective of moisture supply during 1979–2010 based on the Lagrangian method

Transitional Climate Zone (TCZ) over East Asia, characterized by semi-arid climate, is ecologically fragile environment with limited water resources, making atmospheric moisture supply being the key influential factor. This study investigates the moisture sources of summer (JJA) rainfall in the TCZ over East Asia and associated impact during 1979–2010 with the Lagrangian particle dispersion model. Seven moisture source regions and associated contribution are quantified: Eurasia continent to northwest of the TCZ (EC, 32.14%), central-eastern China (CEC, 16.62%), western Pacific Ocean (WPO, 8.58%), South China Sea and Indonesia (SCSI, 2.99%), Bay of Bengal (BOB, 1.4%), Arabian Sea (AS, 0.71%) and local evaporation (TCZ, 32.58%). The direct moisture contribution from ocean (13.67%) is much less than those from the continent (81.34%), due to the great loss en-route. In particular, the local evaporation not only contributes the most moisture among 7 selected source regions, but also exerts the greatest influence in summer precipitation variability in TCZ. Furthermore, the moisture related to summer rainfall over TCZ conveyed by westerlies and monsoon are discriminated according to the dominant system of moisture source regions. It is found that moisture contributions from summer monsoon system (30.3%) and the mid-latitude westerlies (32.14%) dominant areas are quite close. However, further analysis shows that summer monsoon system takes more responsibility for inter-annual fluctuation of summer precipitation in TCZ from the perspective of moisture supply, followed by local evaporation and mid-latitude westerlies.

Seasonal patterns of macroalgal and sessile invertebrate communities in a monsoonal marine ecosystem

Climatic transition zones are characterized by large annual variation in environmental conditions which heavily influence seasonal abundance of organisms and their assemblage patterns. With climate change altering phenology and distribution of species globally, establishing baseline biological patterns allows us to understand trends and challenges local communities might face in adverse conditions. We surveyed the seasonal biomass and cover of subtidal macroalgal and sessile invertebrate communities at 12 rocky subtidal habitats in Hong Kong to establish the first baseline for these communities. Overall productivity and composition of shallow (∼1 m depth) assemblages were prone to dynamic influences from environmental drivers and exhibited seasonal patterns, while those of deeper (∼5 m) communities had less biomass but were more stable across seasons. Abundance of fleshy macroalgae was greatest during winter, dominated by canopy forming Sargassum hemiphyllum, low-laying turfs, and encrusting algae. S. hemiphyllum had the greatest seasonal productivity on shallow substrate, reaching up to 33.8 kg m−2 in winter. In contrast, macroalgae were almost absent in the hot and rainy season, with encrusting algae defining benthic communities. Sessile invertebrate communities were generally dominated by oysters, barnacles, and live corals at both depths, characterized by a shift towards oyster-dominant during summer in the shallow. With the temperature of coastal waters increasing under climate change and winter algal growing seasons shortening, this study forms a baseline from which to assess any changes in algal productivity and community composition in the future.

Fine-Grained Climate Classification for the Qaidam Basin

The Qaidam Basin is a sensitive climate transition zone revealing a wide spectrum of local climates and their variability. In order to obtain an objective and quantitative expression of local climate regions as well as avoid the challenge to pre-define the number of heterogeneous local climates, the ISODATA cluster method is employed to achieve the fine-grained climate divisions of the Qaidam Basin, which can heuristically alter the number of clusters based on the input of monthly temperature and precipitation data. The fine-grained climate classification extends the traditional Köppen climate classification and represents the complex climate transformation processes in terms of fine-grained climate clusters. The following results are observed: (i) The Qaidam Basin is divided into an arid desert basin area and the surrounding alpine mountainous areas. The climate distribution is affected by both the altitude and the dryness ratio, which, employing the Budyko framework, largely characterizes the local energy–water fluxes at the surface and the related vegetation regimes (biomes). The fine-grained climate classification successfully captures their causal relationships and represents them well by the local climates: the climatic spatial differentiation in the mountainous areas is highly consistent with the topography and reveals an elevation-dependent circular distribution from the edges to the center of the basin; the climate heterogeneity within the basin presents a west-to-east meridional distribution due to the combined effect of the mid-latitude westerlies and the Indian monsoon. (ii) The climate gradients are spatially different over the Qaidam Basin. The surrounding mountainous areas have a large climate gradient compared to the inner basin; the southern mountain edge is governed by a more severe climate change than the north-eastern one; and the climate gradient is larger in the eastern than in the western basin. (iii) The lake regions within the basin show an obvious lake effect and reveal a local lake climate. Spatially, a common structure emerges with a dryer-climate zone or watershed embedding a wetter lake-affected area, which appears to migrate eastward becoming stepwise wetter from the very dry center to the wet eastern boundary of the Qaidam basin. This provides a topographically induced insight of the wet climate expansion of initially arid climates and is crucial to improve the Qaidam Basin’s ecological environment. Finally, although this work mainly focuses on the local-scale climates and their variability in the Qaidam Basin, the data-driven cluster methodology for climate refinement is transferable to regional- even global-scale climate studies, which offers broad application prospects.

Climate-Growth Relationships of Chinese Pine (Pinus tabulaeformis Carr.) at Mt. Shiren in Climatic Transition Zone, Central China.

Simple SummaryTree rings are widely used in global change research based on the accurate dating capabilities, climate sensitivity and wide distribution of samples. In the context of global warming, the response of tree growths in north–south transition zones to climate change is one of the hot issues in Dendroecology. The research results found that trees’ growth had different responses to May–June temperature and precipitation on the north and south of the mountain. Therefore, we analyzed the relationship between tree ring and a regional hydrothermal composite factor and reconstructed its variation. The variations agree with other drought series and represent the drought variation in central and eastern monsoon regions, and may provide better understanding of drought variation and service for agricultural production.Tree ring data from the southern boundary of Chinese Pine (Pinus tabulaeformis Carr.) distribution where is the southern warm temperate margin, the paper analyzes the response of climate factors along north–south direction to tree growth. The results show that temperature and precipitation in May–June and relative moisture from March to June are main limiting factors on trees growth; however, the temperature in the south of the mountains and the moisture in the north of the mountains have relatively greater influence on trees’ growth. Additionally, we also found that the regional scPDSIMJ (that is scPDSI in May–June) was the most significant and stable factor limiting tree growth to be used for reconstruction. The reconstructed scPDSIMJ revealed that there were 29 extremely dry years and 30 extremely wet years during 1801–2016, and it could represent the drought variation in central and eastern monsoon region. The variation exists in good agreement with the reconstructed PDSI for Mt. Shennong and the drought/wetness series in Zhengzhou. Further research found that the droughts of May–June in central China were mainly impacted by local temperature and moisture (including precipitation, soil moisture, potential evaporation and water pressure), and then by the northern Pacific Ocean and the northern Atlantic Ocean. These results may provide better understanding of May–June drought variation and service for agricultural production in central China.

Environmental factors driving evapotranspiration over a grassland in a transitional climate zone in China

AbstractThe surface evapotranspiration (ET) process is the key link in the interaction between land and atmosphere. However, the influence of different environmental factors on ET over transitional climate zones and the physical pattern of the interaction between multiple factors remain unclear. Therefore, based on the continuous observation data during the vegetation growing season of a typical grassland in the Semi‐Arid Climate and Environment Observation of Lanzhou University (SACOL) station from 2007 to 2012, the influence pattern of multiple environmental factors on ET over China's transitional climate zone was analysed. Each environmental factor exhibited significant seasonal and interannual variations. The mean value of ET was 1.67 mm day−1. Although the maximum values of sensible heat flux and vapour pressure deficit occurred in April and June, respectively, the maximum values of other environmental factors appeared from July to August. Net radiation, soil moisture, and normalized difference vegetation index (NDVI) were the main controlling factors of ET over the grassland, with correlation coefficients of 0.54, 0.52, and 0.46, respectively. The analysis of multiple environmental factors showed that when soil moisture, wind speed, net radiation, and NDVI reached 0.2 m3 m−3, 2 m s−1, 100 W m−2, and 0.2, respectively, ET varied in contrast with vapour pressure, vapour pressure deficit, and air temperature under the influences of weather processes, land–atmosphere coupling, and drought stress. These findings deepen our understanding of the role of ET in the land–atmosphere coupling process over the transitional climate zone in China.

Late Glacial and Holocene Palaeolake History of the Última Esperanza Region of Southern Patagonia

We undertook multi-proxy analyses on two sediment cores from Lago Pato, a small lake basin at 51°S topographically separated from Lago del Toro in Torres del Paine (TdP), to provide insights into glacier dynamics and lake-level change in the TdP and Última Esperanza region over the last ∼30,000 cal a BP (30 ka). Lago Pato is situated in a region overridden by the Southern Patagonian Ice Field during the Last Glacial and in a transitional climatic zone of Southern Patagonia sensitive to seasonal- to millennial-scale changes in the Southern Hemisphere Westerly Winds (SWW). Results show that a deep ice-dammed and enlarged palaeolake encompassed Lago del Toro and Lago Pato c. 30–20 ka after the ice had retreated from local-Last Glacial Maximum (l-LGM) limits at c. 48–34 ka and during the build-up to the global-Last Glacial Maximum (g-LGM), c. 26–19 ka. Gaps in both sediment records between c. 20–13.4 ka and c. 20–10 ka suggest hiatuses in sediment accumulation during the g-LGM and Antarctic Cold Reversal (ACR) readvances and/or removal by lake lowering or flushing during the Late Glacial–early Holocene. The palaeolake level dropped from &amp;gt;100 m a.s.l. to ∼40–50 m a.s.l. towards the end of the ACR c. 13.4–13.0 ka, creating a shallower glaciolacustrine environment dammed by an ice tongue in the Estancia Puerto Consuelo–Última Esperanza fjord. Further lowering of the enlarged palaeolake level occurred when the ice thinned to &amp;lt;40 m a.s.l., eventually isolating Lago Pato from Lago del Toro and glaciogenic sediment input at c. 11.7 ka. After isolation, the ecology and water levels in Lago Pato became sensitive to regional climate shifts. The shallow, stable, and highly anoxic environment that developed after c. 11.7 ka is associated with weaker (or poleward shifted) SWW at 51°S and was replaced at c. 10 ka by an increasingly productive shallow-littoral lake with a variable lake-level and periodic shifts in anoxic-oxic bottom water conditions and ratios of benthic-planktonic diatoms. A more open Nothofagus forest, established at c. 8.6–7.5 ka, and more arid conditions c. 7.5–5.7 cal ka BP are linked to another phase of weaker (or poleward shifted) SWW at 51°S. More persistently wet conditions from c. 5.7 ka, with extensive closed Nothofagus forests and planktonic diatoms dominant, are associated with stronger (or equatorward shifted) SWW over 51°S. The abrupt return of benthic-to-tychoplanktonic diatoms after c. 3 ka reflects enhanced SWW at 51°S. Increasingly stable lacustrine and littoral wetland conditions established in the last ∼500 years reflect weaker SWW and lasted until recent decades.

Hydrothermal Factors Influence on Spatial-Temporal Variation of Evapotranspiration-Precipitation Coupling over Climate Transition Zone of North China

As a land–atmosphere coupling “hot spot”, the northern China climate transition zone has a sharp spatial gradient of hydrothermal conditions, which plays an essential role in shaping the spatial and temporal pattern of evapotranspiration-precipitation coupling, but whose mechanisms still remain unclear. This study analyzes the spatial and temporal variation in land–atmosphere coupling strength (CS) in the climate transitional zone of northern China and its relationship with soil moisture and air temperature. Results show that CS gradually transitions from strong positive in the northwest to negative in the southeast and northeast corners. The spatial distribution of CS is closely related to climatic hydrothermal conditions, where soil moisture plays a more dominant role: CS increases first, and then decreases with increasing soil moisture, with the threshold of soil moisture at 0.2; CS gradually transitions from positive to negative at soil moisture between 0.25 and 0.35; CS shows an exponential decreasing trend with increasing temperature. In terms of temporal variation, CS is strongest in spring and weakens sequentially in summer, autumn, and winter, and has significant interdecadal fluctuations. The trend in CS shifts gradually from significantly negative in the west to a non-significant positive in the east. Soil moisture variability dominates the intra-annual variability of CS in the study regions, and determines the interannual variation of CS in arid and semi-arid areas. Moreover, the main reason for the positive and negative spatial differences in CS in the study area is the different driving regime of evapotranspiration (ET). ET is energy-limited in the southern part of the study area, leading to a positive correlation between ET and lifting condensation level (LCL), while in most of the northern part, ET is water-limited and is negatively correlated with LCL; LCL has a negative correlation with P across the study area, thus leading to a negative ET-P coupling in the south and a positive coupling in the north.

EVALUATION OF SEISMIC IMPACTS OF STRONG EARTHQUAKES IN VARIOUS PERMAFROST AND SEISMIC ZONES OF THE MONGOLIAN-SIBERIAN REGION

Based on the study of the features of seismicity within the limits of continuous permafrost and in transitional climatic zones, the influence of natural and climatic factors on the magnitude of seismic impacts is revealed. The results of studies carried out to develop a regional methodology for predicting the parameters of seismic effects of strong earthquakes in the Mongolian-Siberian region during permafrost degradation are summarized. These results are based on the data of complex geophysical measurements. They are aimed at developing methods and techniques for assessing the seismic impacts of strong earthquakes on critical engineering structures located within the permafrost zone and at developing recommendations for conducting seismic micro zoning in various seismic-climatic zones of Siberia and Mongolia, taking into account potential earthquake sources.The main goal of this study is to use the data obtained in planning and construction in seismically active permafrost areas. The developed methods and approaches are presented at the current level of requirements for the design of earthquake-resistant structures in the permafrost zone in specific areas: at the Uyanga site sum, located in Northern Mongolia, and at the Tupik site (using the example of the construction of a tailings dam), located in Russia in the Zabaykalsky Krai (Transbaikal Territory). The first section is located in the zone of insular permafrost with a probability of earthquakes of VIII-degree intensity. The second is in the area of continuous permafrost with a likelihood of VII-degree earthquakes.The proposed and implemented integrated methodological approach makes it possible to obtain at the present level of research for the natural and predicted state of soils in the foundations of designed structures a set of seismic characteristics (accelerograms, spectra, frequency characteristics) and the main parameters of seismic effects for predicted strong earthquakes (maximum accelerations, prevailing frequencies, maxima spectra and resonant frequencies). The noted set of characteristics and parameters of seismic effects meets the modern requirements of designers. It should be accounted for earthquake-resistant structures located in various seismic-climatic zones of the Mongolian-Siberian region.

Environmental determination of spring wheat yield in a climatic transition zone under global warming.

Understanding environmental determination of crop yield plays a critical role in agricultural. management in resource-limited areas. The climatic transition zone was a naturally ideal place to study. the relations between environmental factors and crop yield, due to its large annual variability of climatic factors and high speed of temperature increase under global warming. Our objectives were to identify the most critical environmental factor in determining spring wheat yield and analyze the convergence and divergence of water-yield relations for spring wheat in a typical climatic transition zone (semi-arid area). The study was conducted at two locations, Dingxi and Pengyang in Northwest China, with a long-term experiment (1987-2018) and two short-term irrigation experiments. Meanwhile, data of water use and spring wheat yield was collected from a series of previously published literature in the study area. The highest spring wheat yield was obtained under year pattern with higher soil water content at sowing (SWCS) and lower atmospheric dryness condition (ADC, the difference between reference evapotranspiration and precipitation during spring wheat growing season). SWCS was more important than precipitation during the growing season (PGS) in determining spring wheat yield in the study area. The relations between available water supply, water use, and spring wheat yield were convergence. However, SWCS had an impact on the relationship between yield and PGS and SWCS-yield relation was affected by ADC. We concluded that precipitation in 7months before sowing was the dominant factor determining spring wheat yield in the climatic transition zone under global warming whereas the impact of high atmospheric evaporative demand resulted from the increasing temperature on crop yields and SWCS-yield relation must be taken into account for the analysis of environmental determination of spring wheat yield.

Intergrading reef communities across discrete seaweed habitats in a temperate-tropical transition zone: Lessons for species reshuffling in a warming ocean.

Temperate reefs are increasingly affected by the direct and indirect effects of climate change. At many of their warm range edges, cool‐water kelps are decreasing, while seaweeds with warm‐water affinities are increasing. These habitat‐forming species provide different ecological functions, and shifts to warm‐affinity seaweeds are expected to modify the structure of associated communities. Predicting the nature of such shifts at the ecosystem level is, however, challenging, as they often occur gradually over large geographical areas. Here, we take advantage of a climatic transition zone, where cool‐affinity (kelp) and warm‐affinity (Sargassum) seaweed forests occur adjacently under similar environmental conditions, to test whether these seaweed habitats support different associated seaweed, invertebrate, coral, and fish assemblages. We found clear differences in associated seaweed assemblages between habitats characterized by kelp and Sargassum abundance, with kelp having higher biomass and seaweed diversity and more cool‐affinity species than Sargassum habitats. The multivariate invertebrate and fish assemblages were not different between habitats, despite a higher diversity of fish species in the Sargassum habitat. No pattern in temperature affinity of the invertebrate or fish assemblages in each habitat was found, and few fish species were exclusive to one habitat or the other. These findings suggest that, as ocean warming continues to replace kelps with Sargassum, the abundance and diversity of associated seaweeds could decrease, whereas fish could increase. Nevertheless, the more tropicalized seaweed habitats may provide a degree of functional redundancy to associated fauna in temperate seaweed habitats.

Super droughts over East Asia since 1960 under the impacts of global warming and decadal variability

AbstractIn the last decade, a sequence of once‐in‐50 year or even once‐in‐100 year high‐impact drought events have hit East Asia. By defining a super drought with the Standardized Precipitation Evaporation Index for the time scales of 3, 6, 12 and 24 months all below −1.5, this study aims to examine the changes in super droughts and the underlying mechanism over East Asia in the past 60 years, putting the recent high‐impact droughts in the context. Super droughts in the last 10 years over East Asia have been the most expansive, with two hotspots located in the Transitional Climate Zone (TCZ) and the Southeast Asian region (SEA) regions, together accounting for 2/3 of the total. The seasonal distribution characterizes the largest contribution from summer followed by autumn and then spring and winter. Super droughts over TCZ peak in the recent two decades, which are primarily driven by the increase in potential evaporation (PET) contributing 41 and 80% in the first and second 10 years, respectively. It turns out that global warming signal can explain more than 90% of this PET increase. Over SEA, the recent decade and the period around 1990 saw the most widespread super droughts that were not spatially uniformly distributed but clustered in three subregions. Different from TCZ, the precipitation rather than PET is the most influential in governing super droughts over SEA. Out of the total variability in precipitation, about half of the super droughts in the recent decade is caused by decadal variability, while the trend mode has negligible influence.