Short-term Climate Change Research Articles

Identification of root-colonizing AM fungal communities and their responses to short-term climate change and grazing on Tibetan plateau

The molecular diversity of arbuscular mycorrhizal (AM) fungi remains largely unexplored in sedge-dominated ecosystems, much less their responses to global climate change and grazing. To determine the molecular diversity of AM fungi and how they are affected by climate change and grazing, we examined AM fungal communities inside roots in a sedge meadow ecosystem (4875 m a.s.l.) undergoing 4 yr. of fully factorial manipulations of experimental warming, snow addition and grazing on the Tibetan Plateau. A total of 21 AM fungal virtual taxa (VTs) were identified, including one new genus-like clade and one new VT unrecorded in the MaarjAM database. However, we did not observe significant effects of climate change and/or grazing on AM fungal abundance, diversity and community composition. These results indicate that diverse AM fungal taxa inhabit in the sedge-dominated meadows on the Tibetan Plateau, but the AM fungal communities were not sensitive to short-term climate change and grazing.

Experimental and observational studies find contrasting responses of soil nutrients to climate change.

Manipulative experiments and observations along environmental gradients, the two most common approaches to evaluate the impacts of climate change on nutrient cycling, are generally assumed to produce similar results, but this assumption has rarely been tested. We did so by conducting a meta-analysis and found that soil nutrients responded differentially to drivers of climate change depending on the approach considered. Soil carbon, nitrogen, and phosphorus concentrations generally decreased with water addition in manipulative experiments but increased with annual precipitation along environmental gradients. Different patterns were also observed between warming experiments and temperature gradients. Our findings provide evidence of inconsistent results and suggest that manipulative experiments may be better predictors of the causal impacts of short-term (months to years) climate change on soil nutrients but environmental gradients may provide better information for long-term correlations (centuries to millennia) between these nutrients and climatic features. Ecosystem models should consequently incorporate both experimental and observational data to properly assess the impacts of climate change on nutrient cycling.

The contrasting effects of short-term climate change on the early recruitment of tree species.

Predictions of plant responses to climate change are frequently based on organisms' presence in warmer locations, which are then assumed to reflect future performance in cooler areas. However, as plant life stages may be affected differently by environmental changes, there is little empirical evidence that this approach provides reliable estimates of short-term responses to global warming. Under this premise, we analyzed 8years of early recruitment data, seed production and seedling establishment and survival, collected for two tree species at two latitudes. We quantified recruitment to a wide range of environmental conditions, temperature, soil moisture and light, and simulated recruitment under two forecasted climatic scenarios. Annual demographic transitions were affected by the particular conditions taking place during their onset, but the effects of similar environmental shifts differed among the recruitment stages; seed production was higher in warmer years, while seedling establishment and survival peaked during cold years. Within a species, these effects also varied between latitudes; increasing temperatures at the southern location will have stronger detrimental effects on recruitment than similar changes at the northern locations. Our simulations illustrate that warmer temperatures may increase seed production, but they will have a negative effect on establishment and survival. When the three early recruitment processes were simultaneously considered, simulations showed little change in recruitment dynamics at the northern site and a slight decrease at the southern site. It is only when we considered these three stages that we were able to assess likely changes in early recruitment under the predicted conditions.

Short-term growth and biomechanical responses of the temperate seagrass Cymodocea nodosa to CO2 enrichment

Seagrasses are often regarded as climate change ‘winners’ because they exhibit higher rates of photosynthesis, carbon fixation and growth when exposed to increasing levels of ocean acidification. However, questions remain whether such growth enhancement compromises the biomechanical properties of the plants, altering their vulnerability to structural damage and leaf loss. Here, we investigated the short-term (6 wk) effects of decreasing pH by CO2 enrichment on the growth, morphology and leaf-breaking force of the temperate seagrass Cymodocea nodosa. We found that the plant biomass balance under levels of acidification representative of short-term climate change projections (pH 8.04) was positive and led to an increase in leaf abundance in the shoots. However, we also found that plant biomass balance was negative under levels of acidification experienced presently (pH 8.29) and those projected over the long-term (pH 7.82). Leaf morphology (mean leaf length, thickness and width) was invariant across our imposed acidification gradient, although leaves were slightly stronger under [CO2] representative of short-term climate change. Taken together, these findings indicate that a subtle increase in growth and mechanical resistance of C. nodosa is likely to occur following short- to medium-term changes in ocean chemistry, but that these positive effects are unlikely to be maintained over the longer term. Our study emphasises the need to account for the interdependencies between environmental conditions and variations in multiple aspects of the structure and functioning of seagrass communities when considering the likely consequences of climate change.

Legacy effects of simulated short-term climate change on ammonia oxidisers, denitrifiers, and nitrous oxide emissions in an acid soil.

Although the effect of simulated climate change on nitrous oxide (N2O) emissions and on associated microbial communities has been reported, it is not well understood if these effects are short-lived or long-lasting. Here, we conducted a field study to determine the interactive effects of simulated warmer and drier conditions on nitrifier and denitrifier communities and N2O emissions in an acidic soil and the longevity of the effects. A warmer (+2.3°C) and drier climate (-7.4% soil moisture content) was created with greenhouses. The variation of microbial population abundance and community structure of ammonia-oxidizing archaea (AOA), bacteria (AOB), and denitrifiers (nirK/S, nosZ) were determined using real-time PCR and high-throughput sequencing. The results showed that the simulated warmer and drier conditions under the greenhouse following urea application significantly increased N2O emissions. There was also a moderate legacy effect on the N2O emissions when the greenhouses were removed in the urea treatment, although this effect only lasted a short period of time (about 60days). The simulated climate change conditions changed the composition of AOA with the species affiliated to marine group 1.1a-associated lineage increasing significantly. The abundance of all the functional denitrifier genes decreased significantly under the simulated climate change conditions and the legacy effect, after the removal of greenhouses, significantly increased the abundance of AOB, AOA (mainly the species affiliated to marine group 1.1a-associated lineage), and nirK and nosZ genes in the urea-treated soil. In general, the effect of the simulated climate change was short-lived, with the denitrifier communities being able to return to ambient levels after a period of adaptation to ambient conditions. Therefore, the legacy effect of simulated short-time climate change conditions on the ammonia oxidizer and denitrifier communities and N2O emissions were temporary and once the conditions were removed, the microbial communities were able to adapt to the ambient conditions.

Improvement of grapevine physiology and yield under summer stress by kaolin-foliar application: water relations, photosynthesis and oxidative damage

Knowledge about short-term climate change adaptation strategies for Mediterranean vineyards is needed in order to improve grapevine physiology and yield-quality attributes. We investigated effects of kaolin-particle film suspension on water relations, photosynthesis and oxidative stress of field-grown grapevines in the Douro region (northern Portugal) in 2012 and 2013. Kaolin suspension decreased leaf temperature by 18% and increased leaf water potential (up to 40.7% in 2013). Maximum photochemical quantum efficiency of PSII was higher and the minimal chlorophyll fluorescence was lower in the plants sprayed by kaolin. Two months after application, net photosynthesis and stomatal conductance at midday increased by 58.7 and 28.4%, respectively, in treated plants. In the same period, kaolin treatment increased photochemical reflectance, photosynthetic pigments, soluble proteins, soluble sugars, and starch concentrations, while decreased total phenols and thiobarbituric acid-reactive substances. Kaolin application can be an operational tool to alleviate summer stresses, which ameliorates grapevine physiology and consequently leads to a higher yield.

Incorporating rainfall data to better plan eucalyptus clones deployment in eastern Brazil

The goals of this study were to identify and group three eucalyptus clones, each under coppice and clear-cut management regimes, into two or more groups based on similar growth rates; and fit a site index equation as a function of rainfall variables for each group to evaluate how different groups were impacted by climatic variation. The database came from the Continuous Forest Inventory (CFI) and weather stations. The CFI was conducted between 1994 and 2012, with climatic data also being gathered for the same period. The study area was managed by clear-cut and coppice regimes, with 126 and 72 CFI plots, respectively. The relationship between clones, management regimes and stand age with annual dominant height growth was assessed by linear mixed effects modeling. Ridge regression was applied for fitting each group as a function of the rainfall variables. Finally, ordinary Kriging was applied for each of the rainfall variables in the study area. Then, site index equations were applied to the generated maps enabling the observation of their pattern throughout the study area as well as their evaluation under a pessimistic climatic scenario. Three groups were defined, since each clone exhibited similar growth behavior under either management regimes; however, the 3 clones differ among each other. A significant reduction in the annual dominant height growth over time was observed for all 3 clones. Ridge regressions afforded good accuracy and equations with sound biological behavior. Applying the fitted site index equations to the maps of precipitation and rainy days enabled the definition of the most appropriate clone to be planted throughout the area. Site quality as a function of rainfall variables could be an important tool to better enable silvicultural planning, since it provides estimates of the site index and also enables the incorporation of short-term climate change.

Local soil type variability controls the water budget and stand productivity in a beech forest

Climate change and particularly increasing frequency of drought events during the vegetation period may threaten tree vitality and forest biomass productivity in many temperate regions in the future. In that context, the identification of critical environmental factors and a better understanding of their impact on forests are decisive. The water balance is recognized as one of the most important soil factors for stand productivity in temperate forests. Hence, the consequences of short or long term climate change might vary considerably spatially in function of soil type within a given forest. Our study objective was to assess the impact of contrasting soil types on the water balance and stand growth of a beech (Fagus sylvatica) forest ecosystem of similar age and management during four climatically contrasting years. The experimental forest site of Montiers presents different soils with contrasting physicochemical properties (Dystric Cambisol, Eutric Cambisol and Rendzic Leptosol) monitored to quantify water fluxes and stand biomass increment. Using data collected over the period 2012–2015, including a particularly dry year (−24% precipitations in 2015), we also quantified the impact of water shortage on stand productivity at the annual scale as a function of soil type. We evidenced important differences in soil water holding capacities (SWHC) along the studied soil sequence, ranging between 57mm for the Rendzic Leptosol downhill over limestone and 205mm for the Dystric Cambisol uphill over detrital sediments. The results show that the canopy intercepted the same amount of incident rainfall in the three plots and that there were no significant differences in annual soil moisture dynamics among the studied soils. We evidenced different rooting patterns depending on soil type. Under a same climate and with stand, site exposition and solar radiation equivalency, trees transpiration was the evident primary driver of the stand potential to produce aboveground biomass. Soil water holding capacity, annual trees transpiration and aboveground biomass production increased in that order: Rendzic Leptosol<Eutric Cambisol<Dystric Cambisol. During the drier year 2015, the decrease in aboveground biomass productivity was of similar amplitude on the three soil types.

Seeing through the haze to learn how clouds shape climate

Scientists’ uncertainty as to how air pollution affects clouds greatly complicates our understanding of short-term climate change. Scientists’ uncertainty as to how air pollution affects clouds greatly complicates our understanding of short-term climate change.

Estimating the Impact of Drought on Groundwater Resources of the Marshall Islands

Groundwater resources of small coral islands are threatened due to short-term and long-term changes in climate. A significant short-term threat is El Niño events, which typically induce a severe months-long drought for many atoll nations in the western and central Pacific regions that exhausts rainwater supply and necessitates the use of groundwater. This study quantifies fresh groundwater resources under both average rainfall and drought conditions for the Republic of Marshall Islands (RMI), a nation composed solely of atolls and which is severely impacted by El Niño droughts. The atoll island algebraic model is used to estimate the thickness of the freshwater lens for 680 inhabited and uninhabited islands of the RMI, with a focus on the severe 1998 drought. The model accounts for precipitation, island width, hydraulic conductivity of the upper Holocene-age sand aquifer, the depth to the contact between the Holocene aquifer and the lower Pleistocene-age limestone aquifer, and the presence of a reef flat plate underlying the ocean side of the island. Model results are tested for islands that have fresh groundwater data. Results highlight the fragility of groundwater resources for the nation. Average lens thickness during typical seasonal rainfall is approximately 4 m, with only 30% of the islands maintaining a lens thicker than 4.5% and 55% of the islands with a lens less than 2.5 m thick. Thicker lenses typically occur for larger islands, islands located on the leeward side of an atoll due to lower hydraulic conductivity, and islands located in the southern region of the RMI due to higher rainfall rates. During drought, groundwater on small islands (&lt;300 m in width) is completely depleted. Over half (54%) of the islands are classified as “Highly Vulnerable” to drought. Results provide valuable information for RMI water resources planners, particularly during the current 2016 El Niño drought, and similar methods can be used to quantify groundwater availability for other atoll island nations, including the Federated State of Micronesia, Republic of Maldives, and Republic of Kiribati.

Multiproxy records of vegetation and monsoon variability from the lacustrine sediments of eastern Ganga Plain since 1350 A.D.

The lacustrine sediments of 90 cm thick profile of Nikahari Tal (lake), Deoria district in the Ganga Plain were analyzed for multiproxy study using pollen analysis, sedimentology and AMS radiocarbon date to deduce short term climate and vegetational changes since about 1350 A.D. (600 BP). The presence of arboreal and dominance of herbaceous vegetation along with aquatic elements and fresh water alga Botryococcus from the basal part suggests the prior existence of lake and open grass land vegetation in the region. However, the scantiness of tree and shrubby taxa along with higher percentage of clay in the beginning indicates relatively warm and less humid climate than today. The presence of Cerealia with other culture pollen taxa indicates prevalence of agrarian practice in the region. Substantial increase in the tree taxa of Holoptelea integrifolia, Madhuca indica, Acacia, Emblica officinalis, Syzygium cumini and Myrtaceae along with the increase in shrubs, marshy and aquatic elements suggest the expansion of forest grove within the grassland as a consequence of enhanced precipitation during ∼1420–1620 A.D. Similar trends are observed by higher percentage of silt content owing to increased surface runoff in response to enhanced precipitation and high water budget under strong Indian Summer Monsoon (ISM) during above period. A highly variable vegetation scenario existed during 1620–1900 A.D. as a consequence of fluctuating climatic conditions. The variable percentages of silt and clay indicate the increase and decrease in the surface runoff so as the water column and energy in the lake, in direct response to enhanced and weak ISM respectively. During 1620–1700 A.D., the arboreals became less diversified and a decline in the diversity of terrestrial herbs is also witnessed, which is also corroborated by exceptionally high percentages of clay elucidating stagnant low-energy ponding condition under weak ISM during the Little Ice Age (LIA). During the time interval of 1700–1800 A.D., considerable improvement in the floristics has been noticed due to climate amelioration. From 1800 A.D. onwards, the increasing frequency trends of arboreal and aquatic taxa along with relatively increased silt content suggests moderately warm and humid climate. The well-sorted sediment explains the consistency in the water level and energy of the lake.Pollen analysis coupled with sediment grain parameters indicate intense ISM from 1400 to 1600 A.D. and 1850 A.D. onwards and weak monsoon around 1600–1750 A.D. The signals of weak monsoon around 1650, 1770 and 1850 A.D. are synchronous with the Little Ice Age.

Effects of Short-Term Warming and Altered Precipitation on Soil Microbial Communities in Alpine Grassland of the Tibetan Plateau.

Soil microbial communities are influenced by climate change drivers such as warming and altered precipitation. These changes create abiotic stresses, including desiccation and nutrient limitation, which act on microbes. However, our understanding of the responses of microbial communities to co-occurring climate change drivers is limited. We surveyed soil bacterial and fungal diversity and composition after a 1-year warming and altered precipitation manipulation in the Tibetan plateau alpine grassland. In isolation, warming and decreased precipitation treatments each had no significant effects on soil bacterial community structure; however, in combination of both treatments altered bacterial community structure (p = 0.03). The main effect of altered precipitation specifically impacted the relative abundances of Bacteroidetes and Gammaproteobacteria compared to the control, while the main effect of warming impacted the relative abundance of Betaproteobacteria. In contrast, the fungal community had no significant response to the treatments after 1-year. Using structural equation modeling (SEM), we found bacterial community composition was positively related to soil moisture. Our results indicate that short-term climate change could cause changes in soil bacterial community through taxonomic shifts. Our work provides new insights into immediate soil microbial responses to short-term stressors acting on an ecosystem that is particularly sensitive to global climate change.

The ancestral Mississippi drainage archived in the late Wisconsin Mississippi deep-sea fan

The response of continental-scale drainage systems to short-term (i.e., millennial-scale) climate change is unknown but has wide implications for understanding climate feedbacks and terrestrial-marine fluxes. The late Wisconsin Mississippi River to deep-sea fan of North America was one of Earth’s largest sediment-routing networks during the most recent glacio-eustatic cycle. To understand late Pleistocene sediment production and dispersal related to the partly glaciated, ancestral Mississippi system, we sampled late Wisconsin deep-sea fan channel-fill and lobe deposits for detrital zircon U-Pb and (U-Th)/He double-dating analyses, from Deep Sea Drilling Project (Leg 96) cores and U.S. Geological Survey piston cores. Our results suggest a late Pleistocene glacial Mississippi system that forced a larger transfer of sediment from Cordilleran magmatic provinces and the Canadian Shield when compared to the modern drainage. This indicates a potentially more expansive and/or erosive ancestral Mississippi catchment, and the efficient dispersal of terrigenous sediment, nutrients, and solutes into the deep-sea via high-discharge meltwater and glacial-lake outbursts during ice retreat.

A Bayesian Belief Network for Murray Valley encephalitis virus risk assessment in Western Australia.

BackgroundMurray Valley encephalitis virus (MVEV) is a clinically important virus in Australia responsible for a number of epidemics over the past century. Since there is no vaccine for MVEV, other preventive health measures to curtail its spread must be considered, including the development of predictive risk models and maps to help direct public health interventions. This article aims to support these approaches by presenting a model for assessing MVEV risk in Western Australia (WA).MethodsA Bayesian Belief Network (BBN) for assessing MVEV risk was developed and used to quantify and map disease risks in WA. The model combined various abiotic, biotic, and anthropogenic factors that might affect the risk of MVEV into a predictive framework, based on the ecology of the major mosquito vector and waterbird hosts of MVEV. It was further refined and tested using retrospective climate data from 4 years (2000, 2003, 2009, and 2011).ResultsImplementing the model across WA demonstrated that it could predict locations of human MVEV infection and sentinel animal seroconversion in the 4 years tested with some degree of accuracy. In general, risks are highest in the State’s north and lower in the south. The model predicted that short-term climate change, based on the Intergovernmental Panel on Climate Change’s A1B emissions scenario, would decrease MVEV risks in summer and autumn, largely due to higher temperatures decreasing vector survival.ConclusionsTo our knowledge, this is the first model to use a BBN to quantify MVEV risks in WA. The models and maps developed here may assist public health agencies in preparing for and managing Murray Valley encephalitis in the future. In its current form, the model is knowledge-driven and based on the analysis of potential risk factors that affect the dynamics of MVEV using retrospective data. Further work and additional testing should be carried out to test its validity in future years.Electronic supplementary materialThe online version of this article (doi:10.1186/s12942-016-0036-x) contains supplementary material, which is available to authorized users.

Climate changes and solar cycles recorded at the Holocene Paraná Delta, and their impact on human population.

The Paraná delta, growing at a rate of c. 2 km2 yr−1 since 6,000 yrs, is one of the most complete records of the Late Holocene in southern South America. The evolution of this 17,400 km2 delta enclosed in Plata estuary, can be tracked by a series of 343 successive coastal-ridges showing a c.11 years period, in coincidence with sunspot cycle, also found in some North Hemisphere coastal-ridge successions. The Paraná delta shifted from fluvial, to wave-dominated, and back to the present fluvial-dominated delta, in response to climate changes associated with wind activity correlating with South American glacial cycles. The wave-dominated windy period coincides with the activation of the Pampean Sand Sea, suggesting desert conditions prevailed on the Pampas between 5,300 and 1,700 yrs, in coincidence with scarce or absent pre-historic aborigine remains (“archeological silence”). Further warmer and less windy conditions allowed human repopulation. Results suggest that aside the solar forcing, both short and medium term climate changes controlled delta evolution. An important learning is that a slight cooling would turn the highly productive pampas, into that unproductive desert and, given the lack of artificial irrigation systems, changing present-day warmhouse into a cooling cycle might be economically catastrophic for the region.

Isotopic composition of sheep wool records seasonality of climate and diet.

Hair keratin is a very important material in ecological and archaeological studies because it grows continuously, can be obtained non-invasively, does not require extensive processing prior to analysis and can be found in archaeological sites. Only a few studies have examined seasonal variations in hair isotope values, and there is no published dataset examining the isotope variability recorded in the keratinous tissues of stationary (i.e., non-migrating) domestic mammals. Thirty-six Irish sheep were sampled in eight farms every three months between September 2006 and June 2007. A shearing strategy was adopted to sample only the most recently grown wool in order to represent an average of the summer, autumn, winter and spring conditions. The stable isotope ratios of the ground samples were measured using two different stable isotope mass spectrometers operated in dual-inlet (C, N) and continuous-flow (O, H) mode. Wool O isotope ratios are a good proxy for seasonal variability in climate and can be used to anchor a chronology independently of other isotope records (C, N) that are influenced by diet or physiology. By contrast, interpretation of seasonal variations in hair H isotope composition in terms of climate is more complex probably due to the influence of dietary H. The C and N isotope values of grass-fed animals varied seasonally, probably reflecting the annual cycle of seasonal variation in grass isotope values. The highest δ(13) C values were measured in summer-grown wool, while the highest δ(15) N values were measured in winter-grown wool. Supplementation of the sheep diet with concentrates was detected easily and was marked by an increase in δ(13) C values and a decrease in δ(15) N values in winter-grown wool. The present study demonstrates that time-resolved sampling and stable isotope ratio analysis of sheep wool can be used to identify short-term changes in diet and climate and therefore offer a tool to examine a wide variety of present and past husbandry practices.

Management opportunities for boosting productivity of cool-temperate dairy farms under climate change

Improved knowledge of the effects of climate change on farming systems can help increase long-term production, economic performance, and mitigate risk. Here we assessed the effects of stocking rate and seasonal calving times on pasture and milk production under short and long term climate changes on dairy farms in Tasmania, Australia. Annual and monthly perennial ryegrass pasture production was simulated from 1971 to 2065 to examine trends in pasture productivity, forage requirements, and impacts on milk production in 2015 and 2050. The projected future climate for the study region indicates a mean warming of up to 1.4°C, with moderate declines in rainfall of up to 5%. Despite lower rainfall, climate change will likely have a positive impact on pasture yields, with annual production increasing by 13–16%, even though summer growth is reduced and inter-annual variability is increased. We found that greater pasture production is conducive to greater forage conservation, and together these factors allow intensification of stocking rates. These effects increase milk yields by 3–16% per annum and reduce reliance on purchased feeds, which together implies greater profitability of cool-temperate Australian dairy systems under future climates. We also found that total milk production in a spring calving system allows greater stocking rates and pasture utilisation compared with an autumn calving system, and whilst milk produced per animal declines under higher stocking rates, milk yield per hectare increases. Overall, our results suggest that global warming and climate change will positively affect pasture growth rates in Tasmania, and that greater production and conservation of home-grown feeds will be conducive to increased farm milk yields, provided that stocking rates are intensified sustainably.

Climate security and economic security: The limits to climate change action in Australia?

In 2007, Kevin Rudd was elected Prime Minister of Australia with the promise of pursuing strong action on global climate change. Less than 3 years later, he was deposed as leader of his party after walking away from proposed climate legislation. One important part of this puzzle concerns the nature of political debate in Australia about climate action, with this debate orienting around the economic costs of climate action. This can be read as a competition between discourses of security: one focused on securing Australia and vulnerable others from the long-term threat posed by climate change, the other on securing Australia and Australians from the short-term threat climate change action posed to continued economic growth. Over time, the latter came to dominate contestation over climate change. This article maps these competing discourses, reflecting on what this case tells us about the politics of climate change in Australia and beyond.

Meta-analysis of Holocene fluvial sedimentary archives: A methodological primer

This paper describes developments in the analysis and interpretation of Holocene fluvial chronologies over the past 25years. Particular consideration is given to meta-analysis approaches pioneered by Macklin and Lewin (2003), using radiocarbon-dated fluvial deposits in Britain, which have transformed fluvial geochronologies and correlations with climate and land-use records worldwide. During the last decade methodological developments have addressed issues such as correction for the shape of the radiocarbon calibration curve in the probability analysis of dated fluvial units and for variable alluvial unit preservation. The number of regional database analyses of fluvial sedimentary archives has also expanded significantly during the past decade, with studies now available for Africa, the Mediterranean region, India, Ireland, New Zealand, Poland, the Rhine catchment and the UK. Methods for incorporating optically stimulated luminescence ages in the probability analysis have also been developed and are illustrated using the database of Eastern Mediterranean dated fluvial deposits. There is considerable potential for meta-analysis research to inform long-term flood risk assessment, to evaluate short-term climate and land-use change impacts on flooding and river behaviour, and to test landscape evolution models.

Early Mississippian Orbital-Scale Glacio-Eustasy Detected From High-Resolution Oxygen Isotopes of Marine Apatite (Conodonts)

Abstract Stratigraphic and geochemical studies from tropical through polar latitude records now recognize that the late Paleozoic ice age (LPIA) began earlier and ended later than traditionally thought and was characterized by discrete, My-scale intervals of increased glacial ice volumes that were separated by My-scale intervals of diminished ice volumes. Whereas the onset of LPIA glaciation now is recognized to have started as early as the Late Devonian, the continuity and patterns of glaciation in the > 15 My interval between this onset date and the well-documented mid-Carboniferous portion of the LPIA are less well understood. This study utilizes detailed cyclostratigraphic and δ18O records from Lower Mississippian (mid Tournaisian) tropical marine deposits and conodont apatite to argue that in addition to evidence for a discrete, My-scale early LPIA glaciation, there is compelling evidence for superimposed high-frequency (orbital-scale) glacial–interglacial climate oscillations driving glacio-eustasy and changes in sea-surface temperature (SST). Cyclostratigraphic evidence includes the development of asymmetric (progressive shallowing) and symmetric (deepening followed by shallowing) subtidal cycles in the Tournaisian Woodhurst Member of Lodgepole Formation which record repeated high-frequency water-depth changes from below storm wave base to above fairweather wave base. δ18O values from samples originating from six cycles range from 17.8‰ to 21.6‰, and intracycle trends record progressive increases in isotopic values from the deepest-water facies (at cycle base for asymmetric cycles or mid cycle for symmetric cycles) into the shallower-water cycle caps. Four of the cycles record average intracycle isotopic shifts of 1.4‰, and two cycles record shifts of ≥ 2.5‰. These co-varying trends between interpreted water-depth and δ18O changes are consistent with the hypothesis that the water-depth changes were controlled by orbital-scale glacio-eustasy. Assuming that the observed intracycle δ18O shifts represent the combined effects of ice-volume and SST changes, calculated glacio-eustatic magnitudes were < 50 m with tropical SST changes of < 4°C. Cycles recording ≥ 2.5‰ shifts may reflect additional SST cooling related to intensification of coastal upwelling during the onset of glacial stages. Orbital-scale glacio-eustatic interpretations imply that in addition to overall long-term Early Mississippian cooling and glaciation, the mid Tournaisian was characterized by superimposed high-frequency orbital-scale climate changes which controlled marked changes in glacial ice volumes, eustatic sea levels, coastal-upwelling intensities, and tropical SSTs. These long-term and superimposed short-term climate changes highlight the dynamic nature of the early LPIA and are reminiscent of climate patterns observed for Cenozoic and Late Ordovician greenhouse-to-icehouse climatic transitions.