Glacial-interglacial Climate Change Research Articles

Nitrogen isotope homogenization of dissolved ammonium through depth and 15N enrichment of ammonium during the incorporation into expandable layer silicates occurred in organic-rich marine sediment from Guaymas Basin, Gulf of California

Sedimentary nitrogen isotopic ratios are used as a proxy for ancient biogeochemical cycles on Earth's surface. It is generally accepted that sediment core tops record primary signatures because organic nitrogen (ON) is predominant in this part of the core. In contrast to such early to middle diagenetic stages, it is well known that heavier nitrogen isotope 15N tends to enrich the sedimentary and metamorphic rocks during latter diagenetic and metamorphic stages. However, there are some critical gaps in our understanding of nitrogen isotopic alteration associated with abiotic processes during early-middle diagenesis. In this study, we examined the isotope ratios of ammonium nitrogen in interstitial water (IW) and total nitrogen (TN), including exchangeable ammonium and mineral nitrogen, in the solid-phase of those associated organic-rich-sediment recovered by International Ocean Discovery Program (IODP) Expedition 385 cores drilled in the Guaymas Basin, Gulf of California, that contained ammonium-rich IW. The isotopic ratios (δ15N value) of TN were the most variable with depth compared to any other type of nitrogen. This variation can be interpreted as reflecting changes in the water mass environment in the basin caused by glacial–interglacial climate changes, which modifies the δ15N values of the marine primary producers. Thus, the δ15N value of TN is a proxy for environmental change in the basin, while each component of TN shows different trends. The δ15N values of IW and exchangeable ammonium did not exhibit significant changes with depth, but the latter values were about 3 ‰ enriched in 15N. This may be due to advective transport of solute into adjacent layers followed by the formation of an isotopic equilibrium between IW and exchangeable ammonium in the case of fast accumulation rate. The δ15N value of exchangeable ammonium was the highest among the other types of nitrogen with one exception, where the δ15N value of TN was the highest. The calculated δ15N values of ON based on mass balance were almost the same to those of associated TN in the shallow sediment layers (< 150 m below seafloor), but the difference in the δ15N values of TN and ON were significant in the deeper layers, where proportions of ON contents were <50%. In particular, in the layer where the δ15N value of TN was the highest, that of ON showed an even higher value and the difference reaches 3.5 ‰. The δ15N values of mineral nitrogen were similar to that of IW ammonium except the surface layers. Under such conditions, when δ15N value of TN is intermediate between those of mineral nitrogen and exchangeable ammonium, calculated δ15N value of ON is close to that of TN. On the other hand, if δ15N value of TN is out of the range between mineral nitrogen and exchangeable ammonium, it causes further difference in δ15N value of ON. It means that the fluctuation of δ15N values of TN is reduced relative to those of ON through depth. It has been considered that δ15N value of TN in sediment is similar to that of ON, and changes in the δ15N value of TN due to diagenesis are limited, but in such environment ON fluctuations over depth may be slightly underestimated.

Orbital global change drove fluvial aggradation and incision in Tibetan upper Mekong river: Chronological perspectives

The Tibetan Plateau (TP), often known as the “Asia Water Tower”, is the source region of several continental-scale rivers. However, due to the extremely difficult access and harsh living conditions in the interior plateau, fluvial processes in the headwaters of these large rivers and their connections to global climate changes remain unknown. In this study, the luminescence (using both quartz and K-feldspar) and AMS 14C dating techniques were employed to date the four terraces of the Zado Basin in order to elucidate the aggradation and incision history of the initial intermontane basin in the headwater of the Mekong River. One sample from the upper part of T4 terrace (which features a 12 m thick gravel layer, the base of which is unexposed) provides a K-feldspar pIR50IR225 age of 125 ± 10 ka, indicating that the initial deposition of this terrace could predate marine isotope stage (MIS) 5. Considering the margin of error, this age also suggests that the onset of incision on T4 terrace during the climate transition from MIS 6 (glacial) to early MIS 5 (interglacial). This incision likely occurred due to increased meltwater and precipitation, causing the Mekong carving into the bedrock for more than 50 m. Eight luminescence samples are collected from T3 terrace (26.5 m in thickness) with ages ranging from 83 ± 7.6 ka to 22.3 ± 1 0.2 ka, indicating T3 formation/aggradation from late MIS 5 to the Last Glacial Maximum (LGM), possibly owing to reduced precipitation and enhanced sediment supply from intensive glacial activities. At around 22 ka, the Mekong once again shifted towards incision, crafting the T3 terrace, situated roughly 28 m above the current floodplain. This incision event was recorded by two luminescence samples from a sandy lens located at the top of gravel layer of T3, with OSL ages of about 22 ka. Floodplain samples from T2 and T1, dated at 16 ka and 2.8 ka respectively, demonstrate that from the last deglaciation to the Holocene, the Mekong continued its downward incision. This erosion developed two cut and fill terraces at elevations of 22 m and 11 m above the present floodplain, likely due to increased precipitation and enhanced vegetation at that time. Overall, the glacial–interglacial climate changes were the most likely driving force behind fluvial processes in the upper Mekong basin since the Late Pleistocene, with aggradation occurring during the glacial period while incision in deglacial and interglacial periods, suggesting a close link between the fluvial geomorphic evolution and orbital-scale climate changes.

Chronology and paleoclimatic context of hominin occupations in the Fenhe River Basin of northern China during the middle to Late Pleistocene

The relationship between climate change and hominin evolution over the Pleistocene in East Asia is still poorly understood, in particular due to the limited number of archaeological finds and fossils with reliable chronologies. Paleolithic sites preserved in loess-paleosol sequences in eastern Chinese Loess Plateau provide prospective evidence for understanding hominin evolution and dispersion across the Middle to Late Pleistocene in northern China. The Fenhe River Basin has been known as a key area for paleolithic sites and fossil hominins. Here, quartz Optically stimulated luminescence (OSL) and K-feldspar post-infrared infrared stimulated luminescence (pIRIR) dating was employed on 61 samples from 13 paleolithic sites in the Fenhe River Basin. The reliability of the ages are checked by analysis of luminescence characteristics and comparison between quartz OSL and K-feldspar pIRIR ages. Paleoclimatic records were established using alternating loess-paleosol sequences, and multi-proxy indices of grain size, magnetic susceptibility, CaCO3 and color from the dated sites. These results provide the reliable chronology for hominin presence in the Fenhe River Basin spanning the past three glacial-interglacial cycles. Our results show that this region experienced predominantly dusty, dry and cold conditions during glacials and comparatively moist and warm interglacial conditions, that are sensitive to variations in East Asian Summer and Winter Monsoon (EASM and EAWM respectively) intensities over glacial-interglacial timescales. The Fenhe River Basin is a key geographic refuge for hominins during glacial-interglacial climatic changes in northern China. It was occupied over glacial and interglacial periods spanning at least the last 370 ky, and the evidence for hominin presence is especially clear from ∼250 to 60 ka and since ∼35 ka. The frequency of hominin activity, as indicated by the number of archaeological sites and density of stone artifacts, increased during warm and humid periods of MIS 7 and MIS 5, in contrast to the cold, windy, and dry period of MIS 6. Site numbers increased in MIS 3 and the Last Glacial Maximum, in association with microblade technology. The dating results indicate that hominins with ‘modern’ features may have occurred in the Fenhe River Basin ∼140 ka ago, however, the exact timing of modern human occupation in the region needs a more combined approach consisting of morphological, ancient DNA and geochronological studies.

Vertical biome shifts and climate changes since the last glacial maximum in the southeastern margin of the Tibetan plateau, Southwest China

Since the last glacial maximum (LGM), global warming has significantly influenced the intricate dynamics of vegetation on the southeastern margin of the Tibetan Plateau in southwest (SW) China. However, the responses of montane vegetation to glacial-interglacial climate changes have received less attention than those of modern alpine vegetation belts. Here, we present a continuous pollen record from the lake Caohai area of Guizhou Province and a quantitative reconstruction of the region's biome and climate changes over the past 21 ka. Our findings demonstrate that the study area was encompassed by evergreen sclerophyll Quercus forest during the LGM, which subsequently transitioned to deciduous broadleaved forest around 15.8 ka, shortly after the termination of the last glacial period. During the early Holocene, the deciduous forest underwent a transformation and gave way to evergreen broadleaved forest around 10.3 ka. The abundance of evergreen subtropical elements peaked between 9 and 5 ka, coinciding with the Holocene thermal maximum (HTM). This was followed by the return of deciduous taxa after the 4 ka in the late Holocene. However, anthropogenic impacts on local vegetation became apparent only from about 2 ka. The pollen-based biome reconstruction features clear vertical shifts that correspond to the modern vegetation belts at different elevations, with a maximum vertical movement of about 1000 m between the last glacial and the Holocene. Statistical analysis of pollen data reveals that principal components can serve as reliable climate indicators, consistent with climate simulations using the TraCE model. Both proxy and model results demonstrate that forest ecosystems undergo transformation when thermal and moisture conditions exceed bioclimatic thresholds, emphasizing the crucial role of climate boundaries in driving biome succession. Our findings unveil an extended cold and dry period during the LGM, with the lowest precipitation observed during the last glacial termination due to intense North Atlantic cooling and weak overturning circulation. The strong agreement between the transition from sclerophyll to deciduous forests and increasing temperatures suggests that deglacial warming primarily drove vertical biome shifts after the LGM in the southeastern margin of the Tibetan Plateau. Conversely, forest succession during the Holocene, which align with variations in fire intensity, were predominantly triggered by summer monsoon changes. The quantitative reconstructions of both biomes and climates presented in this study provide novel insights into temporal relationships between climate dynamics and ecosystem changes in SW China.

Climate oscillations and erosional processes in the Ordos tectonic block and implications for sediment supply to the Yellow River

Climate variations in both space and time can impact mountain topography and drainage-basin morphology through a variety of surface processes. This is illustrated dramatically in the Ordos Block of northern China, which encompasses the main body of the Loess Plateau in the southeast and the Mu Us Desert in the northwest. The plateau is known for severe soil erosion by fluvial processes; whereas the desert is dominated by aeolian processes. Here we characterize the spatial transition in landscape relief and drainage network integration of the middle Ordos Block, corresponding to a precipitation gradient across the region, that is otherwise homogeneous in terms of its tectonics and bedrock. Differences in landscape relief and drainage network integration occur over a short range in precipitation rate, and outside this transition zone, landscape morphologic metrics appear to be relatively insensitive to precipitation. Where precipitation rates are greater than ∼420 mm/yr, landscapes are characterized by integrated drainage networks with relief over 100 m within a 1 km radius. With precipitation rates lower than ∼380 mm/yr, the landscapes tend to have lower relief, discontinuous channels and hundreds of playa lakes indicating inefficient runoff. Combined with stratigraphic records, we posit that continuous drainage networks in the semi-arid to arid transition zone expand in wetter periods, and shrink and fragment when precipitation falls below a threshold. Today the Ordos Block is experiencing the transition from a drier (glacial) stage to a wetter (interglacial) stage, with higher precipitation rates over the past ∼12 thousand years. It follows that fluvial processes likely have increased in efficiency and are currently advancing into regions to the northwest formerly dominated by aeolian processes. Our findings suggest that a component of the severe sediment erosion of the Loess Plateau is a transient feature locally associated with glacial-interglacial climate change and the transition from aeolian- to fluvial-dominated surface processes.

Sedimentary records and implications for the evolution of sedimentary environments inferred from BH1302 during the late Quaternary in the Bohai Sea, China

Under the influence of glacial-interglacial climate change and regional tectonic activities in the Quaternary, the sedimentary environments of the Bohai Sea changed greatly, providing significant information on transgression-regression events, East Asian monsoon changes and regional tectonic activities. This study analyzed the sedimentological characteristics of the BH1302 core (water depth of 12.3 m, length of 70.2 m) in the southern Bohai Sea based on grain size, foraminiferal assemblages, carbon and oxygen isotopes in foraminiferal shells and element geochemistry, and established a chronological framework based on AMS 14C, optically stimulated luminescence dating and Oxcal age-depth model using Bayesian modeling. The results showed that three interglacial transgressions and one interstadial transgression were revealed in BH1302 since the late Quaternary, corresponding to marine isotope stages (MIS) 7, 5, 3 and 1, and three subinterglacial transgressions were further identified during MIS 7. The sedimentary environments of Laizhou Bay transitioned from an estuary environment dominated by rivers to a neritic environment dominated by marine conditions because of subsidence of the Miaodao uplift in late MIS 7.1. Three subinterglacial transgressions occurred in MIS5 and two subinterstadial transgressions in MIS 3, and the highstand sea level of MIS 3 reached approximately −18 ∼ −21 m. Under the influence of sea level fluctuations and the East Asian monsoon, the sedimentary environments of MIS 1 can be divided into a low salinity tidal-flat environment (12.0–7.0 kyr BP), a low salinity neritic environment (7.0–4.5 kyr BP) and a modern neritic environment (∼4.5 kyr BP).

Increased terrigenous input from North America to the northern Mendeleev Ridge (western Arctic Ocean) since the mid-Brunhes Event

Mid-Brunhes Event (MBE) occurred at approximately 420 ka between Marine Isotope Stage 11 and 12, and is considered the most pronounced climatic shift during the last ~ 800 kyrs. On the other hand, it is unclear if the MBE was global, despite being observed in the high-latitude Northern Hemispheric cryosphere in terms of climate systems. A 5.35-m long gravity core ARC5-MA01 was obtained from the northern Mendeleev Ridge in the western Arctic Ocean to track the paleoenvironmental changes in terms of the terrigenous sedimentation in response to the glacial-interglacial climate changes across the MBE. Geochemical proxies (biogenic opal, total organic carbon, C/N ratio, carbon isotope of organic matter, and calcium carbonate) of MA01 suggest that the terrigenous input was generally higher during the interglacial periods. Based on a mineralogical examination, most of the terrigenous input was attributed to the abundance of dolomite and the increased kaolinite content from North America. In particular, most paleoceanographic proxies showed that the terrigenous input from North America was enhanced distinctly during the post-MBE interglacial periods. These results suggest that the MBE in the western Arctic Ocean was a global climatic shift closely linked to cryospheric development in North America during the middle Pleistocene.

Geometry of the Meridional Overturning Circulation at the Last Glacial Maximum

Abstract Understanding the contribution of ocean circulation to glacial–interglacial climate change is a major focus of paleoceanography. Specifically, many have tried to determine whether the volumes and depths of Antarctic- and North Atlantic–sourced waters in the deep ocean changed at the Last Glacial Maximum (LGM; ∼22–18 kyr BP) when atmospheric pCO2 concentrations were 100 ppm lower than the preindustrial. Measurements of sedimentary geochemical proxies are the primary way that these deep ocean structural changes have been reconstructed. However, the main proxies used to reconstruct LGM Atlantic water mass geometry provide conflicting results as to whether North Atlantic–sourced waters shoaled during the LGM. Despite this, a number of idealized modeling studies have been advanced to describe the physical processes resulting in shoaled North Atlantic waters. This paper aims to critically assess the approaches used to determine LGM Atlantic circulation geometry and lay out best practices for future work. We first compile existing proxy data and paleoclimate model output to deduce the processes responsible for setting the ocean distributions of geochemical proxies in the LGM Atlantic Ocean. We highlight how small-scale mixing processes in the ocean interior can decouple tracer distributions from the large-scale circulation, complicating the straightforward interpretation of geochemical tracers as proxies for water mass structure. Finally, we outline promising paths toward ascertaining the LGM circulation structure more clearly and deeply.

Stable persistence of relict populations involved evolutionary shifts of reproductive characters in the genusTanakaea(Saxifragaceae)

AbstractTertiary relicts often show evolutionary stasis in morphology and ecology and have been hypothesized to retain stable population sizes in refugia. However, recent studies have reported that some relicts evolutionarily shifted their physiology, ecology, and morphology and experienced various patterns of demography. To understand the historical survival of relict plants, a multidimensional study investigating the evolution of ecological and morphological traits as well as population demographic history is needed. The genusTanakaea(Saxifragaceae) comprises two species in China and Japan. These species share most vegetative characteristics and are sometimes treated as a single species. The distribution pattern is relictual, as the populations are confined to small areas in mesic warm temperate forests less influenced by Quaternary glacial climates. Focusing on the relictual plant group, this study tested the hypotheses of evolutionary stasis and population stability in long‐term refugia. Genetic analyses using plastome sequences and genome‐wide single‐nucleotide polymorphisms revealed divergence of the two species approximately 6.8 million years ago and strong genetic differentiation of the regional populations. Demographic analysis revealed that almost all populations retained stable population sizes during glacial–interglacial climate changes, supporting the traditional view. However, morphological assessments revealed a simultaneous shift in breeding systems (from hermaphrodite to dioecy/non‐clonal to clonal reproduction) in Japanese species and intraspecific differentiation of leaf traits. Therefore, the relict species do not show evolutionary stasis in every aspect. Changes in reproductive characteristics may have contributed to their long‐termin situsurvival.

Climate influence on zinc isotope variations in a loess–paleosol sequence of the Chinese Loess Plateau

Zinc (Zn) is an essential micronutrient, and its isotopes are increasingly applied to understand trace metal biogeochemical cycling. Atmospheric deposition from anthropogenic or natural origins can perturbate the nutrient supply globally. However, our understanding on Zn isotope variations in natural mineral dust and during dust–climate interaction is still rare. This study presents Zn isotope data and leaching experiments with ammonium acetate buffering solution (pH = 5) on a loess–paleosol profile (S0–L3) from the Yimaguan section in the central Chinese Loess Plateau. The loess–paleosol sequence records the contributions from Asian mineral dust accumulation and chemical weathering, and the response to glacial–interglacial climate changes. Bulk loess–paleosol samples display limited Zn/Al (3.5 × 10-4 – 4.5 × 10-4) and δ66Zn variations (0.17–0.30‰). The mean δ66Zn of paleosol (0.19 ± 0.01‰, 2SD/√n, n = 11) is slightly lower than that of loess (0.24 ± 0.01‰, 2SD/√n, n = 13). Correlations with magnetic susceptibility and grain size distribution suggest that bulk δ66Zn variations between loess and paleosol are not sensitive to glacial–interglacial source fluctuations or wind sorting, but could result from loess pedogenesis.The leachable Zn fractions have high δ66Zn values (0.80–1.29‰) and display good positive correlations with Ca, Sr, Mg, Fe and Mn (r > 0.7), suggesting that carbonates are enriched in heavy Zn isotopes. Although Zn contents in carbonates are low (<3%) and dissolution of carbonates alone cannot explain the bulk Zn/Al variations (∼7% of Zn loss), significant carbonate weathering and biotic activities during loess pedogenesis could modify soil conditions (pH) and provide dissolved bicarbonate ions and organic ligands, which may facilitate the transport of heavy Zn isotopes by soil liquids. Conversely, the bulk δ66Zn of loess developed during glacial times were not modified by the low degree of chemical weathering, and thus the mean value of 0.24‰ for loess can be regarded as the average composition of the upper continental crust.

A simulation-based method for selecting calibration areas for ecological niche models and species distribution models

Ecological niche models and species distribution models (ENM and SDM, respectively) are tools that have seen massive use and considerable improvement during the last twenty years. The choice of calibration areas for such models has strong effects on model outcomes and model interpretation, as well as on model transfer to distinct environmental settings. However, approaches to selecting these areas remain simple and/or unlinked to biological concepts. Such models should be calibrated within areas that the species of interest has explored throughout its recent history, the accessible area (M). In this paper, we provide a simulation approach for estimating a species’ M considering processes of dispersal, colonization, and extinction in constant current climate or glacial-interglacial climate change frameworks, implemented within a new R package we developed called grinnell. Using the avian genus Aphelocoma, we explored different parameterizations of our simulation, and compared them to current approaches for M selection, in terms of model performance and risk of extrapolation using the algorithm Maxent and mobility-oriented parity analyses. Model calibration exercises from all approaches resulted in at least one model meeting optimal performance criteria for each species; however, we noted high variability among taxa and M selection methods. More importantly, M hypotheses derived directly from simulations of key biological processes, rather than being based on simple proxies of those processes, and as such are better suited to erecting biologically appropriate contrasts in model calibration, and to characterizing the potential for model extrapolation more rigorously. Major factors in our simulations were environmental layer resolution, dispersal kernel characteristics, and the inclusion of a changing framework of climatic conditions. This contribution represents the first simulation-based method for selecting calibration areas for ENM and SDM, offering a quantitative approach to estimate the accessible area of a species while considering its dispersal ability, along with patterns of change in environmental suitability across space and time.

Patterns and drivers of taxonomic, phylogenetic and functional diversity of understory bird communities in Chinese forests captured by camera traps

Birds are important in regulating and maintaining forest ecosystem functioning and services, which are threatened by human activities in the Anthropocene. Camera traps are now widely used to monitor forest bird diversity. But few studies have tested forest bird diversity distribution patterns based on camera traps, especially from the phylogenetic and functional perspectives. Here, we linked the taxonomic, phylogenetic and functional diversity of Chinese forest bird communities captured by camera traps with contemporary climate, glacial-interglacial climate change, and elevational range. Our results showed that 2701 cameras in 58 forest sites captured 290 bird species, most of which were ground-dwelling species and the species number was 21% of all Chinese bird species. Notably, the phylogenetic and functional diversity of these understory birds was 28% and 51% of all Chinese birds, respectively. There were also eight endangered species, 13 vulnerable species, and 37 near threatened species among the 290 species. In addition, forest sites with relatively stable glacial-interglacial climate had relatively higher species richness, but lower phylogenetic and functional diversity. Phylogenetic diversity was also negatively associated with elevational range, while functional diversity was negatively associated with contemporary temperature and precipitation. These findings suggest that camera traps could be an effective technology for forest bird monitoring and conservation, especially for the understory species. In addition, forest in regions with relatively stable paleoclimate, warm and wet contemporary climate, and large elevational range may harbor more bird species through recent rapid in situ diversification.

Thermal niches of planktonic foraminifera are static throughout glacial–interglacial climate change

Abiotic niche lability reduces extinction risk by allowing species to adapt to changing environmental conditions in situ. In contrast, species with static niches must keep pace with the velocity of climate change as they track suitable habitat. The rate and frequency of niche lability have been studied on human timescales (months to decades) and geological timescales (millions of years), but lability on intermediate timescales (millennia) remains largely uninvestigated. Here, we quantified abiotic niche lability at 8-ka resolution across the last 700 ka of glacial-interglacial climate fluctuations, using the exceptionally well-known fossil record of planktonic foraminifera coupled with Atmosphere-Ocean Global Climate Model reconstructions of paleoclimate. We tracked foraminiferal niches through time along the univariate axis of mean annual temperature, measured both at the sea surface and at species' depth habitats. Species' temperature preferences were uncoupled from the global temperature regime, undermining a hypothesis of local adaptation to changing environmental conditions. Furthermore, intraspecific niches were equally similar through time, regardless of climate change magnitude on short timescales (8 ka) and across contrasts of glacial and interglacial extremes. Evolutionary trait models fitted to time series of occupied temperature values supported widespread niche stasis above randomly wandering or directional change. Ecotype explained little variation in species-level differences in niche lability after accounting for evolutionary relatedness. Together, these results suggest that warming and ocean acidification over the next hundreds to thousands of years could redistribute and reduce populations of foraminifera and other calcifying plankton, which are primary components of marine food webs and biogeochemical cycles.

The Effects of Multi-Scale Climate Variability on Biodiversity Patterns of Chinese Evergreen Broad-Leaved Woody Plants: Growth Form Matters

Large-scale patterns of species diversity are thought to be linked to contemporary climate variability and Quaternary glacial–interglacial climate change. For plants, growth forms integrate traits related to competition or migration capacity, which determine their abilities to deal with the climate variability they face. Evergreen broad-leaved woody plants (EBWPs) are major components of numerous biomes in the subtropical and tropical regions. Hence, incorporating phylogenetic (temporal) and biogeographic (spatial) approaches, we assessed the relative importance of short- and long-term climate variability for biodiversity patterns of different growth forms (i.e., tree, shrub, liana, and bamboo) in EBWPs. We used a dated phylogeny and the distribution records for 6,265 EBWP species which are naturally occurred in China, and computed the corrected weighted endemism, standardized phylogenetic diversity and net relatedness index for the four growth forms, respectively. Ordinary least squares linear regressions, spatial error simultaneous autoregressive models, partial regression and hierarchical variation partitioning were employed to estimate the explanatory power of contemporary climate variability and climate-change velocity from the Last Glacial Maximum to the present. Our results showed that short- and long-term climate variability play complementary role in the biogeographic patterns of Chinese EBWPs. The former had larger effects, but the legacy effects of past climate changes were also remarkable. There were also differences in the effects of historical and current climate among the four growth forms, which support growth forms as a critical plant trait in predicting vegetation response to climate change. Compared to the glacial-interglacial climate fluctuation, seasonality as a unique feature of mid-latitude monsoon climate played a dominant role in the diversification and distribution of EBWP species at the macroscale. The results indicated that the relative importance of climate variability at different temporal scales may relate to distinct mechanisms. To understand effects of future climate change on species distribution more thoroughly, climate conditions in different time scales should be incorporated.

Climate, vegetation, and weathering across space and time in Lake Tanganyika (tropical eastern Africa)

Climate and vegetation influence weathering rates and processes; however, evaluating the effects of each and feedbacks between systems, has yet to be accomplished for many types of landscapes. A detailed understanding of how these processes interact to shape landscapes is particularly crucial for reconciling future scenarios of changing climate, where profound alterations to both the biosphere and geosphere are anticipated. In the tropics, ecosystem services, such as soil and water quality, are linked to both vegetation and weathering processes that form a strong control on natural resources that are the foundation of many communities’ daily subsistence. This understanding is further complicated by intensifying land-use within tropical watersheds, which decouples vegetation change from climate; it is yet unclear what the direct effects of vegetation change may be on erosion and weathering when operating independent of climate. Long term observational records tracking changes to the critical zone do not exist in tropical Africa, however, sedimentary paleo-records from lakes are often of sufficient length and resolution to record the impact of bioclimatic variability on surface processes. Here, we use a novel approach combining long (60ka) and intermediate-length (400yrs) lake sediment records along with historical repeat photography from Lake Tanganyika (Tanzania) to document changes and relationships among climate, vegetation, and weathering at multiple scales. These records illustrate that glacial-interglacial climate change did not significantly alter weathering intensity. Instead, we observe chemical and physical weathering responses only when the vegetation becomes more open beginning at the transition to the Holocene. Also, the largest change in chemical weathering intensity occurs only within the last ∼3ka. This is consistent with a major reorganization of vegetation and is directly attributable to Iron Age human activity, rather than climate. Furthermore, anthropogenic landscape alteration as early as ∼2.5ka, in addition to well-documented comparisons of historical land-use, suggest widespread responses of both chemical weathering intensity and enhanced soil erosion to human activity. This shows that changes in vegetation structure induced by anthropogenic activity, decoupled from climate change, generate a disproportionately large weathering response.

Modern Climate and Soil Properties Explain Functional Structure Better Than Phylogenetic Structure of Plant Communities in Northern China

Mechanisms of plant community assembly at geographical scale are an interesting topic in ecology and biogeography, which are of great significance for the understanding of species coexistence and biodiversity conservation. But so far, only a few studies have simultaneously assessed the relative roles of multiple-scale factors in shaping phylogenetic and functional structure of plant communities at a macroecological scale. In this study, we linked modern climate, glacial-interglacial climate change and soil properties with phylogenetic and functional structure of shrub and herbaceous plant communities in Inner Mongolia, China, an arid and semi-arid region. Our results showed that functional structure of plant communities was more associated with modern climate and soil properties than phylogenetic structure, especially for the soil properties. Modern precipitation was found in all the combinations of variables that were most closely related to the community structure in this arid and semi-arid region. These findings suggest that phylogenetic and functional structure of biotic communities may be affected by processes at divergent spatial-temporal scales. That is, functional structure is better linked with modern and local factors, while phylogenetic structure is more associated with historical and 2 regional processes. This study highlights the importance of the associations between different biodiversity dimensions and divergent drivers.

Precipitation is the dominant driver for bird species richness, phylogenetic and functional structure in university campuses in northern China

BackgroundAlthough urbanization is threatening biodiversity worldwide, the increasing green urban spaces could harbor relatively high biodiversity. Therefore, how to maintain the biodiversity in urban ecosystem is crucial for sustainable urban planning and management, especially in arid and semiarid regions with relatively fragile environment and low biodiversity. Here, for the first time we linked species richness, phylogenetic and functional structure of bird assemblages in university campuses in northern China with plant species richness, glacial-interglacial climate change, contemporary climate, and anthropogenic factors to compare their relative roles in shaping urban bird diversity.MethodsBird surveys were conducted in 20 university campuses across Inner Mongolia, China. Ordinary least squares models and simultaneous autoregressive models were used to assess the relationships between bird species richness, phylogenetic and functional structure with environmental factors. Structural equation models were used to capture the direct and indirect effects of these factors on the three components of bird diversity.ResultsSingle-variable simultaneous autoregressive models showed that mean annual precipitation was consistently a significant driver for bird species richness, phylogenetic and functional structure. Meanwhile, mean annual temperature and plant species richness were also significant predictors for bird species richness.ConclusionsThis study suggests that campuses with warmer and wetter climate as well as more woody plant species could harbor more bird species. In addition, wetter campuses tended to sustain over-dispersed phylogenetic and functional structure. Our findings emphasize the dominant effect of precipitation on bird diversity distribution in this arid and semiarid region, even in the urban ecosystem.

Reconstruction of monsoon evolution in southernmost Sumatra over the past 35 kyr and its response to northern hemisphere climate changes

Reconstruction of monsoon evolution in the tropical Indian Ocean and evaluation of its influence on large-scale ocean circulation and sea-air interaction processes can help us understand climate driving mechanisms. Herein, we used a gravity core SO184-10043 to present the marine sedimentary record from the southernmost Sumatra, spanning the past 35 kyr. The age model is well constrained by 12 accelerator mass spectrometry (AMS) radiocarbon dates determined in mixed planktic foraminifera. We also measured sediment grain size and major and trace elements to reconstruct the variations in hydrodynamic conditions and chemical weathering intensity. These data were then used to reveal the evolution of the northwest (Indonesian) monsoon system over the past 35 kyr. The results showed that both monsoon current and chemical weathering coincided with summer insolation in the Northern Hemisphere and responded to glacial-interglacial climate changes in the northern Atlantic. Higher grain-size values of sensitive components, increased chemical index of alteration (CIA), and Ba/Sr ratios, together with lower CaO/MgO ratios, reflect a stronger monsoon current and chemical weathering during the late marine isotope stage 3 and Holocene. Higher intensity of chemical weathering might be attributed to a stronger northwest monsoon carrying warm and moist air from the Asian continent to Indonesian waters. Lower values of sensitive components, CIA, and Ba/Sr, along with higher CaO/MgO values, reveal a weaker monsoon current and lower intensity of chemical weathering during the last glaciation-deglaciation phase, which was controlled by a weaker monsoon system. At a millennial timescale, cold events occurred during the following intervals: 30–26 ka BP, Heinrich Stadial 1 (HS1; 18–15 ka BP), Last Glacial Maximum (LGM; 23–18 ka BP), Younger Dryas (YD; 11–10 ka BP), and 8.2 ka BP. The same cold events were identified from core SO184-10043, indicating a perfect match with climatic cooling in the Northern Hemisphere. We also observed periodicities of ~ 7.9 ka, 3.0–3.1 ka, 2.2–2.3 ka, and ~ 1.0 ka in our core records. These periodicities are coincident with solar-induced climate changes and support the hypothesis that monsoon evolution in the tropical Indian Ocean during the late Pleistocene coincided with the climate change in the Northern Hemisphere.

More endemic birds occur in regions with stable climate, more plant species and high altitudinal range in China

BackgroundGeographical distribution of endemic species and its multiple scale drivers are an important topic in biodiversity conservation, because these species are especially vulnerable to climate change and habitat degradation, and therefore have high conservation priority. Here, for the first time, we simultaneously linked glacial-interglacial climate change, contemporary climate, plant species richness and altitudinal range with endemic bird distribution in China.MethodsOrdinary least squares models and simultaneous autoregressive models were used to assess the associations between endemic bird richness, endemic bird ratio and each explanatory variable. Structural Equation Models were also performed to test the direct and indirect effects of these variables on endemic bird richness and endemic bird ratio.ResultsHigher endemic bird richness and endemic bird ratio occurred in regions with stable glacial-interglacial temperature, i.e., southwest China. Plant species richness and altitudinal range were also positively correlated with endemic bird richness and endemic bird ratio. Glacial-interglacial temperature change, contemporary precipitation, plant species richness and altitudinal range were all included in the best combination of variables for endemic bird richness. Importantly, glacial-interglacial temperature change had strong direct effects on both endemic bird richness and endemic bird ratio, while plant species richness only had a direct effect on endemic bird richness.ConclusionsOur results indicate that endemic birds in China concentrate in southwest regions where there are stable glacial-interglacial temperature, more plant species and larger altitudinal range. Notably, while stable climate has strong direct effects on both endemic bird richness and endemic bird ratio, plant species may affect endemic bird richness through its effect on overall bird species richness. Importantly, the recent anthropogenic activities have also significantly intensified in this region, which would pose huge challenge for biodiversity conservation in China.

Assessing the potential capability of reconstructing glacial Atlantic water masses and AMOC using multiple proxies in CESM

Reconstructing the Atlantic Meridional Overturning Circulation (AMOC) during the Last Glacial Maximum (LGM) is essential for understanding glacial-interglacial climate change and the carbon cycle. However, despite many previous studies, uncertainties remain regarding the glacial water mass distributions in the Atlantic and the AMOC intensity. Here we use an isotope enabled ocean model with multiple geotracers (δ13C, εNd, 231Pa/230Th, δ18O and Δ14C) and idealized water tracers to study the potential constraints on LGM ocean circulation from multiple proxies. Our model suggests that the glacial Atlantic water mass distribution can be accurately constrained by the air-sea gas exchange signature of water masses (δ13CAS), but εNd might overestimate the North Atlantic Deep Water (NADW) percentage in the deep Atlantic probably because of the boundary source of Nd. A sensitivity experiment with an AMOC of similar geometry but much weaker strength suggests that the correct AMOC geometry is more important than the AMOC strength for simulating the observed glacial δ13C and εNd distributions. The kinematic tracer 231Pa/230Th is sensitive to AMOC intensity, but the interpretation might be complicated by the AMOC geometry and AABW transport changes during the LGM. δ18O in the benthic foraminifera (δ18Oc) from the Florida Straits provides a consistent measure of the upper ocean boundary current in the model, which potentially provides an unambiguous method to reconstruct glacial AMOC intensity. Finally, we propose that the moderate difference between AMOC intensity at LGM and PD, if any, is caused by the competition of the responses to CO2 forcing and continental ice sheet forcing.