Contrasting Climate Regimes Research Articles

Comparison of macroalgae meadows in warm Atlantic versus cold Arctic regimes in the high-Arctic Svalbard

A warmer Arctic with less sea ice will likely improve macroalgae growth conditions, but observational data to support this hypothesis are scarce. In this study, we combined hydroacoustic and video inspections to compare the depth of growth, density and thickness of macroalgae (>10 cm) meadows in two contrasting climate regimes in Svalbard 1) the warm, ice free, Atlantic influenced West Spitsbergen and 2) the cold, Arctic and seasonal ice covered East Spitsbergen. Both places had similar insolation and comparable turbidity levels. Macroalgae communities at both places were similar and were formed mainly by common north Atlantic kelp species: Saccharina latissima, Alaria esculenta, Laminaria digitata and L. hyperborea. However, the density of the bottom coverage and thalli condition were strikingly different between the two sites. Algae at the warmer site were intact and fully developed and occupied most of the available hard substrate. At the colder site, only patchy macroalgae canopies were found and most thallies were physically damaged and trimmed at a uniform height due to physical ice scouring. These differences in macroalgal density and thalli condition were only found at depths down to 5 m. Deeper, no distinct differences were observed between the warm and cold sites. Sea urchins were only observed at the warm site, but in few numbers with no visible negative top-down control on macroalgae growth.

Recent changes in high-mountain plant community functional composition in contrasting climate regimes

High-mountain plant communities are strongly determined by abiotic conditions, especially low temperature, and are therefore susceptible to effects of climate warming. Rising temperatures, however, also lead to increased evapotranspiration, which, together with projected shifts in seasonal precipitation patterns, could lead to prolonged, detrimental water deficiencies.The current study aims at comparing alpine plant communities along elevation and water availability gradients from humid conditions (north-eastern Alps) to a moderate (Central Apennines) and a pronounced dry period during summer (Lefka Ori, Crete) in the Mediterranean area.We do this in order to (1) detect relationships between community-based indices (plant functional leaf and growth traits, thermic vegetation indicator, plant life forms, vegetation cover and diversity) and soil temperature and snow duration and (2) assess if climatic changes have already affected the vegetation, by determining directional changes over time (14-year period; 2001–2015) in these indices in the three regions.Plant community indices responded to decreasing temperatures along the elevation gradient in the NE-Alps and the Apennines, but this elevation effect almost disappeared in the summer-dry mountains of Crete. This suggests a shift from low-temperature to drought-dominated ecological filters. Leaf trait (Leaf Dry Matter Content and Specific Leaf Area) responses changed in direction from the Alps to the Apennines, indicating that drought effects already become discernible at the northern margin of the Mediterranean. Over time, a slight increase in vegetation cover was found in all regions, but thermophilisation occurred only in the NE-Alps and Apennines, accompanied by a decline of cold-adapted cushion plants in the Alps. On Crete, xeromorphic shrubs were increasing in abundance.Although critical biodiversity losses have not yet been observed, an intensified monitoring of combined warming-drought impacts will be required in view of threatened alpine plants that are either locally restricted in the south or weakly adapted to drought in the north.

Interactive effects of temperature and redox on soil carbon and iron cycling

Shifts in temperature and rainfall regimes with climate change can feed back on redox dynamics and associated biogeochemical cycling in humid environments. This has global implications for greenhouse gas emissions and ecosystem carbon (C) storage and loss. Though aerobic carbon dioxide (CO2) production is generally understood to follow an Arrhenius-type temperature dependence, the temperature sensitivity of anaerobic metabolisms such as iron (Fe) reduction and methane (CH4) fluxes, both processes affecting C cycling in soils, remains unclear in upland soils. We used a fully factorial incubation experiment to examine the interactive effects of temperature (8, 26, and 35 °C) and redox (oxic and anoxic) conditions on CO2 production, CH4 fluxes, Fe reduction, microbial biomass C, and the microbial metabolic quotient (MMQ) in upland soils from two contrasting climate regimes and redox environments: a tropical forest in Puerto Rico (PR) and a temperate peatland in California (CA). Under oxic conditions, we found that CO2 production increased across both temperature gradients (8–26 °C and 26–35 °C). In contrast, under anoxic conditions, net CH4 fluxes and Fe reduction exhibited a greater temperature sensitivity between 26 and 35 °C than 8–26 °C in both PR and CA soils. We also observed coupling between Fe reduction and net CH4 fluxes in PR and CA soils consistent with competition for acetate. The anoxic MMQ increased in PR soils at high temperature, but not in CA soils, suggesting that the native PR environment may favor the development of more efficient microbial communities better able to tolerate warmer, wetter conditions. Together, our results suggest that anaerobic microbial metabolisms may be much more sensitive to higher temperature than aerobic ones, possibly due to proportionally greater anaerobic microbial activity at high temperature. Our results suggest that increased global temperatures combined with higher rainfall regimes may significantly increase anaerobic greenhouse gas production in humid environments.

A million year vegetation history and palaeoenvironmental record from the Lake Magadi Basin, Kenya Rift Valley

This study examines a one-million-year pollen record from a 194-m-long Lake Magadi core (HSPDP-MAG14-2A) in the south Kenya Rift Valley. The pollen indicate a general trend through the last 740 kyr from wetter conditions to generally drier environments. Grassland dominated with less common Podocarpus and Cyperaceae in a sparse flora between 1000 and 740 ka. Poaceae, woodland and herbaceous plants are common through the remaining core and abundant between 740 and 528 ka and after 200 ka. Pollen diversity increased after 200 ka. Podocarpus and Cyperaceae reached a peak abundance at ~575 ka with a subsequent decline that suggests a progressive increase in aridity, interrupted by wetter intervals.Podocarpus-dominated forests expanded and contracted many times during the Quaternary and document an anti-phased relationship with data from Lake Malawi. Similar anti-phased correlations are noted for herbaceous plants, suggesting that the two basins responded differently to the same climate or were influenced by contrasting climate regimes. Increases in macrocharcoal correlate with increasing pollen abundance and suggest wetter conditions.Data from the Magadi, Koora and Olorgesailie basins indicate similar trends and a dominant climate control on vegetation and habitats. Large lakes characterised all three basins at 740–528 ka with climate subsequently becoming drier, but with many wetter intervals. At various times the lakes expanded, contracted and dried out, except at Lake Magadi where spring inflows maintained lacustrine conditions through the late Quaternary. Faulting also contributed to fragmentation of the landscape and formation of a mosaic of habitats.An especially intense period of aridity at ~528–392 ka coincided with extinction of many large-bodied mammals and may have helped to drive a change from the use of Acheulean hand axes to the production of Middle Stone Age tools by 320 ka. After 200 ka pollen diversity increased substantially with a mix of montane, riparian and dry forest associations that were present in varying amounts through to ~4.2 ka at the core top.

Field and acclimated metabolomes of a resurrection plant suggest strong environmental regulation in the extreme end of the species’ range

Plant secondary metabolites are significant mediators of the interactions of plants with their environment. The desiccation tolerant “resurrection plant” Myrothamnus flabellifolia Welw. is distributed throughout southern Africa and is vicariantly separated between arid Namibia and the comparatively mesic South Africa where it is subjected to contrasting climate regimes. Our earlier study indicated that these populations were metabolomically and phylogenetically distinct, leading us to hypothesise that the metabolic signature of the arid-adapted plants from Namibia was environmentally determined. To test this, we profiled the metabolomes of plants from both regions that had been sampled directly in the field (non-acclimated) with those of plants from the same regions that had been long-term acclimated in a greenhouse (acclimated). Long-term acclimation resulted in a convergence of the metabolic profiles of the plants collected from the different regions. However, while the South African plants demonstrated little difference between their acclimated and non-acclimated metabolomes, the metabolomes of the acclimated Namibian samples were distinct from those of the plants sampled in the field in Namibia. Further scrutiny of the metabolite differences between the acclimated and non-acclimated Namibian samples revealed several metabolites that were significantly more abundant in the field samples, and we propose that these might contribute to survival in this region. To further test the metabolomic response from a temporal perspective, we subjected the acclimated plants to short-term high-temperature treatment in climate chambers. However, this treatment had no significant impact on the metabolomes of the plants. Our findings suggest that long-term, rather than short-term, environmental conditions warrant large-scale reprogramming of the metabolome in M. flabellifolia, and that the climate conditions in the more arid region of the species’ range necessitate the production of particular phenolic metabolites.

Groundwater storage dynamics in the world's large aquifer systems from GRACE: uncertainty and role of extreme precipitation

Abstract. Under variable and changing climates groundwater storage sustains vital ecosystems and enables freshwater withdrawals globally for agriculture, drinking water, and industry. Here, we assess recent changes in groundwater storage (ΔGWS) from 2002 to 2016 in 37 of the world's large aquifer systems using an ensemble of datasets from the Gravity Recovery and Climate Experiment (GRACE) and land surface models (LSMs). Ensemble GRACE-derived ΔGWS is well reconciled to in situ observations (r=0.62–0.86, p value <0.001) for two tropical basins with regional piezometric networks and contrasting climate regimes. Trends in GRACE-derived ΔGWS are overwhelmingly non-linear; indeed, linear declining trends adequately (R2>0.5, p value <0.001) explain variability in only two aquifer systems. Non-linearity in ΔGWS derives, in part, from the episodic nature of groundwater replenishment associated with extreme annual (>90th percentile, 1901–2016) precipitation and is inconsistent with prevailing narratives of global-scale groundwater depletion at the scale of the GRACE footprint (∼200 000 km2). Substantial uncertainty remains in estimates of GRACE-derived ΔGWS, evident from 20 realisations presented here, but these data provide a regional context to changes in groundwater storage observed more locally through piezometry.

Exploring genomic variation associated with drought stress in Picea mariana populations.

Predicted increases in drought and heat stress will likely induce shifts in species bioclimatic envelopes. Genetic variants adapted to water limitation may prove pivotal for species response under scenarios of increasing drought. In this study, we aimed to explore this hypothesis by investigating genetic variation in 16 populations of black spruce (Picea mariana) in relation to climate variables in Alaska. A total of 520 single nucleotide polymorphisms (SNPs) were genotyped for 158 trees sampled from areas of contrasting climate regimes. We used multivariate and univariate genotype‐by‐environment approaches along with available gene annotations to investigate the relationship between climate and genetic variation among sampled populations. Nine SNPs were identified as having a significant association with climate, of which five were related to drought stress response. Outlier SNPs with respect to the overall environment were significantly overrepresented for several biological functions relevant for coping with variable hydric regimes, including osmotic stress response. This genomic imprint is consistent with local adaptation of black spruce to drought stress. These results suggest that natural selection acting on standing variation prompts local adaptation in forest stands facing water limitation. Improved understanding of possible adaptive responses could inform our projections about future forest dynamics and help prioritize populations that harbor valuable genetic diversity for conservation.

Influence of the dry event induced hydraulic redistribution on water and carbon cycles at five AsiaFlux forest sites: A site study combining measurements and modeling

Recent studies have incorporated hydraulic redistribution (HR) schemes into Earth system models to explore its effects on the hydrological, biogeochemical, and ecological processes of terrestrial ecosystems. However, the influence of HR on ecosystems during increasingly frequent extreme drought events, and the performance of different HR schemes at sites with contrasting ecosystem types and climate regimes, remains unclear, especially among ecologically fragile forest ecosystems in Asia. In this study, we incorporated two different HR schemes into Community Land Model version 4.5 (CLM4.5). The model generally improved predictions of soil moisture, evapotranspiration (ET), and carbon (C) fluxes at five AsiaFlux sites with contrasting climate regimes. Upward HR stimulated surface soil moisture, and increased ET by 0.29–0.68 mm H2O day−1, and net ecosystem C uptake by 1.03 × 10–6 to 1.64 × 10–5 g C m−2 s−1, at the five forest sites during dry events. Remarkable downward HR was found only in a semi-arid ecosystem located at the northeastern margin of the Qinghai–Tibet Plateau. Incorporating of a simple empirical HR scheme into CLM4.5 yielded better performance than incorporating a physically based scheme into the model for ecosystems with seasonal frozen soil layers. Combined with previous studies at AmeriFlux sites, it can be concluded that climate zones with overlapped dry season and growing season showed clear hydraulic lift during dry season; climate zones with overlapped wet season and growing season showed clear hydraulic descent if precipitation was limited (e.g. ≤ 400 mm a−1), and did not showed clear influences of HR if the precipitation was unlimited (e.g. ≥ 800 mm a−1).

Combined measurement and modeling of the hydrological impact of hydraulic redistribution using CLM4.5 at eight AmeriFlux sites

Abstract. Effects of hydraulic redistribution (HR) on hydrological, biogeochemical, and ecological processes have been demonstrated in the field, but the current generation of standard earth system models does not include a representation of HR. Though recent studies have examined the effect of incorporating HR into land surface models, few (if any) have done cross-site comparisons for contrasting climate regimes and multiple vegetation types via the integration of measurement and modeling. Here, we incorporated the HR scheme of Ryel et al. (2002) into the NCAR Community Land Model Version 4.5 (CLM4.5), and examined the ability of the resulting hybrid model to capture the magnitude of HR flux and/or soil moisture dynamics from which HR can be directly inferred, to assess the impact of HR on land surface water and energy budgets, and to explore how the impact may depend on climate regimes and vegetation conditions. Eight AmeriFlux sites with contrasting climate regimes and multiple vegetation types were studied, including the Wind River Crane site in Washington State, the Santa Rita Mesquite savanna site in southern Arizona, and six sites along the Southern California Climate Gradient. HR flux, evapotranspiration (ET), and soil moisture were properly simulated in the present study, even in the face of various uncertainties. Our cross-ecosystem comparison showed that the timing, magnitude, and direction (upward or downward) of HR vary across ecosystems, and incorporation of HR into CLM4.5 improved the model-measurement matches of evapotranspiration, Bowen ratio, and soil moisture particularly during dry seasons. Our results also reveal that HR has important hydrological impact in ecosystems that have a pronounced dry season but are not overall so dry that sparse vegetation and very low soil moisture limit HR.

Linking Surface Temperature Based Approaches for Estimating Soil Heat Flux with Error Propagation

Soil heat flux is an inseparable component of the surface energy balance. Accurate estimation of regional soil heat flux is valuable to studies of meteorology and hydrology. Conventional measurement of using soil heat flux plates at the site scale is impractical to estimate large-scale flux. Other approaches generally require soil temperature to be measured in at least two soil layers, which is also difficult to implement at the regional scale. In the last decade, single-layer based approaches were developed to fulfill the regional requirement. This study used a simple but more general approach for estimating soil heat flux solely with surface temperature. The generalized approach can be conditionally linked to two existing single-layer based approaches but has fewer restrictions or assumptions. Error analysis revealed that measurement error in surface temperature would have limited effects on soil heat flux estimated from the new approach. Model simulations showed that soil heat flux estimated from the approach agreed with those simulated from the heat transfer equation. Furthermore, case examinations at two sites with contrasting climate regimes demonstrated that the generalized approach had better performance than the existing single-layer approaches. It achieved the highest correlation of determination and the lowest mean, standard deviation, and root mean squared error of the differences between the estimates and the field measures at either site. The generalized approach can estimate soil heat flux at a depth but it requires only surface temperature data as input, which is an advantage to remote sensing applications.

Multi-step streamflow forecasting using data-driven non-linear methods in contrasting climate regimes

Considering the popularity of using data-driven non-linear methods for forecasting streamflow, there has been no exploration of how well such models perform in climate regimes with differing hydrological characteristics, nor has the performance of these models, coupled with wavelet transforms, been compared for lead times of less than 1 month. This study compares the use of four different models, namely artificial neural networks (ANNs), support vector regression (SVR), wavelet-ANN, and wavelet-SVR in a Mediterranean, Oceanic, and Hemiboreal watershed. Model performance was tested for 1, 2 and 3 day forecasting lead times, measured by fractional standard error, the coefficient of determination, Nash–Sutcliffe model efficiency, multiplicative bias, probability of detection and false alarm rate. SVR based models performed best overall, but no one model outperformed the others in more than one watershed, suggesting that some models may be more suitable for certain types of data. Overall model performance varied greatly between climate regimes, suggesting that higher persistence and slower hydrological processes (i.e. snowmelt, glacial runoff, and subsurface flow) support reliable forecasting using daily and multi-day lead times.

Warming alters routing of labile and slower-turnover carbon through distinct microbial groups in boreal forest organic soils

Our understanding of the mechanisms driving the response of soil organic carbon (SOC) pools to warming, though critical for predicting climate feedbacks, remains limited. Here we report results from a warming experiment using O-horizon soils from two mesic, boreal forest sites with contrasting climate regimes. We replaced extant Oi soil horizons, or litterfall C, with another coniferous Oi possessing a distinct δ13C signature, and tracked the net incorporation of the replaced Oi and, by difference, Oea-C into soil microbial phospholipid fatty acids (PLFA) following 120-day incubations at 15 °C and 20 °C. We demonstrate how regional climate (site effects) and experimental warming (temperature effects) influence microbial incorporation of Oi versus slower-turnover Oea SOC pools. Microbial biomass, estimated from total PLFA, increased by 32–60% with temperature and was 20–42% higher within soils from the warmer versus cooler site, congruent with increased mineralization in those soils. The proportion of Gram-positive bacterial PLFA-C derived from Oi-C more than doubled and coincided with a reduction in the incorporation of Oi-C into fungal relative to bacterial PLFA with warming and in soils from the warmer site. Mirroring the relative decrease in fungal incorporation of Oi-C, warming led to an increase of 22–31% in the proportion of fungal PLFA-C derived from the Oea-C, consistent with the increased incorporation of this slower-turnover SOC pool in soils from the warmer site. The increase in microbial biomass and shift in routing of Oi and Oea pools through PLFA indicate that warming preferentially increases fungal mineralization of more slow-turnover C pools in these boreal organic soils. Shifts in microbial substrate routing and biomass increases with warming observed here underscore the potential importance of changing proportions of microbial biomass remnant contributions to SOC pools with climate warming.

Quantifying uncertainty in the impacts of climate change on river discharge in sub-catchments of the Yangtze and Yellow River Basins, China

Abstract. Quantitative evaluations of the impacts of climate change on water resources are primarily constrained by uncertainty in climate projections from GCMs. In this study we assess uncertainty in the impacts of climate change on river discharge in two catchments of the Yangtze and Yellow River Basins that feature contrasting climate regimes (humid and semi-arid). Specifically we quantify uncertainty associated with GCM structure from a subset of CMIP3 AR4 GCMs (HadCM3, HadGEM1, CCSM3.0, IPSL, ECHAM5, CSIRO, CGCM3.1), SRES emissions scenarios (A1B, A2, B1, B2) and prescribed increases in global mean air temperature (1 °C to 6 °C). Climate projections, applied to semi-distributed hydrological models (SWAT 2005) in both catchments, indicate trends toward warmer and wetter conditions. For prescribed warming scenarios of 1 °C to 6 °C, linear increases in mean annual river discharge, relative to baseline (1961–1990), for the River Xiangxi and River Huangfuchuan are +9% and 11% per +1 °C respectively. Intra-annual changes include increases in flood (Q05) discharges for both rivers as well as a shift in the timing of flood discharges from summer to autumn and a rise (24 to 93%) in dry season (Q95) discharge for the River Xiangxi. Differences in projections of mean annual river discharge between SRES emission scenarios using HadCM3 are comparatively minor for the River Xiangxi (13 to 17% rise from baseline) but substantial (73 to 121%) for the River Huangfuchuan. With one minor exception of a slight (−2%) decrease in river discharge projected using HadGEM1 for the River Xiangxi, mean annual river discharge is projected to increase in both catchments under both the SRES A1B emission scenario and 2° rise in global mean air temperature using all AR4 GCMs on the CMIP3 subset. For the River Xiangxi, there is substantial uncertainty associated with GCM structure in the magnitude of the rise in flood (Q05) discharges (−1 to 41% under SRES A1B and −3 to 41% under 2° global warming) and dry season (Q95) discharges (2 to 55% under SRES A1B and 2 to 39% under 2° global warming). For the River Huangfuchuan, all GCMs project a rise in the Q05 flow but there is substantial uncertainty in the magnitude of this rise (7 to 70% under SRES A1B and 2 to 57% under 2° global warming). Differences in the projected hydrological changes are associated with GCM structure in both catchments exceed uncertainty in emission scenarios. Critically, estimated uncertainty in projections of mean annual flows is less than that calculated for extreme (Q05, Q95) flows. The common approach of reporting of climate change impacts on river in terms of mean annual flows masks the magnitude of uncertainty in flows that are of most importance to water management.

Climate change causing phase transitions of walleye pollock ( Theragra chalcogramma ) recruitment dynamics

In 1976 the North Pacific climate shifted, resulting in an average increase of the water temperature. In the Gulf of Alaska the climate shift was followed (i.e. early 1980s) by a gradual but dramatic increase in the abundance of groundfish species that typically prey on pre-recruitment stages of walleye pollock. In the present study we used a previously parameterized model to investigate the effect of these climate and biological changes on the recruitment dynamics of walleye pollock in the Gulf of Alaska. Simulations covered the 1970-2000 time frame and emphasized the medium-to-long temporal scale (i.e. about 5-10 years) of environmental variability. Results showed that during periods characterized by high sea surface temperature and high predation on juvenile pollock stages, recruitment variability and magnitude were below average, and recruitment control was delayed to stages older than the 0-group. Opposite dynamics (i.e. high abundance and variability, and early recruitment control) occurred during periods characterized by low temperature and predation. These results are in general agreement with empirical observations, and allowed us to formulate causal explanations for their occurrence. We interpreted the delay of recruitment control and the reduction of variability as an effect of increased constraint on the abundance of post age-0 stages, in turn imposed by high density dependence and predation mortality. On the other hand, low density-dependence and predation favoured post age-0 survival, and allowed for an unconstrained link between larval and recruitment abundance. Our findings demonstrate that the dominant mechanisms of pollock survival change over contrasting climate regimes. Such changes may in turn cause a phase transition of recruitment dynamics with profound implications for the management of the entire stock.

Hemipelagic record of orbitally-induced dilution cycles in Lower Cretaceous sediments of the Neuquén Basin

Abstract The lower Valanginian-lower Barremian Agrio Formation in the Mendoza region of the Neuquén Basin (Argentina) accumulated in a hemipelagic outer ramp/basin setting. The formation records the alternation of periods of fine-grained carbonate accumulation and periods of fine-grained clastic deposition, which resulted in a strongly rhythmic succession in which dark clastic hemicycles alternate with light carbonate hemicycles. Clastic and carbonate hemicycles show distinct geochemical signatures that reflect cyclic fluctuations in terrigenous influx to the basin. Clastic hemicycles have relatively high percentages of Fe, Al and K, and less than 60% CaCO 3 , whereas carbonate hemicycles contain relatively low quantities of detrital elements (Fe, Al and K), and more than 60% CaCO 3 . Fluctuations in terrigenous supply to the basin occurred in response to the alternation between two contrasting climate regimes and resulted in the formation of dilution cycles. Warm temperate (winter-wet) climate conditions led to the accumulation of clastic hemicycles, whereas arid conditions promoted the deposition of carbonate hemicycles. The ultimate mechanism that controlled the alternation of the dark and light intervals was orbital forcing, as the latitudinal shifting of climate zones was driven by the c . 21 000 years precessional cycle.

Stability of Holocene Climate Regimes in the Yellowstone Region

A 12,500-yr pollen record from Loon Lake, Wyoming provides information on the climate history of the southwestern margin of Yellowstone National Park. The environmental reconstruction was used to evaluate hypotheses that address spatial variations in the Holocene climate of mountainous regions. Loon Lake lies within the summer-dry/winter-wet climate regime. An increase in xerophytic pollen taxa suggests drier-than-present conditions between ca. 9500 and 5500 14 C yr B.P. This response is consistent with the hypothesis that increased summer radiation and the expansion of the east Pacific subtropical high-pressure system in the early Holocene intensified summer drought at locations within the summer-dry/winter-wet regime. This climate history contrasts with that of nearby sites in the summer-wet/winter-dry region, which were under the influence of stronger summer monsoonal circulation in the early Holocene. The Loon Lake record implies that the location of contrasting climate regimes did not change in the Yellowstone region during the Holocene. The amplitude of the regimes, however, was determined by the intensity of circulation features and these varied with temporal changes in the seasonal distribution of solar radiation.