Global Climate Cycles Research Articles

Persistent Habitat Instability and Patchiness, Sexual Attraction, Founder Events, Drift and Selection: A Recipe for Rapid Diversification of Orchids.

Orchidaceae is one of the most species-rich families of flowering plants, with most current diversity having evolved within the last 5 My. Patterns associated with species richness and rapid diversification have been identified but have not often been associated with evolutionary processes. We review the most frequently identified correlates of diversity and suggest that the processes and rate by which they occur vary geographically and are largely dependent on persistent pulses of habitat instabilities, especially for epiphytes. Aggressive orogenesis creates fragmented habitats while global climatic cycles exacerbate the ecological instabilities. The need for repeated cycles of dispersal results in frequent founder events, which sets the stage for allopatric diversification via bouts of genetic drift and natural selection. The allopatry requirement can be bypassed by pollination systems involving flowers attracting pollinators through the production of sex signaling semiochemicals. The drift-selection model of diversification, coupled with persistent habitat instability throughout ecological and geological time scales, and sex signaling are the likely components of a multifactorial process leading to the rapid, recent diversification in this family.

Natural Drivers of Global Warming: Ocean Cycles, Anthropogenic Greenhouse Gases and the Question of Percentages

There is a widespread policy assumption that anthropogenic greenhouse gases are the main driver of the observed 1 °C rise in global surface air temperatures since ‘pre-industrial’ times. This paper demonstrates that the onset of the current warming trend began in the mid-19th century and is consistent with the rising phase of variable global warming and cooling cycles in both the Northern and Southern Hemispheres. Hemispheres. The last trough of the millennial cycle, the Little Ice Age, coincides approximately with the baseline of pre-industrial times used to calculate the impact of Anthropogenic Global Warming. Yet, half of the observed 20th century temperature rise occurred before 1950 when carbon dioxide levels remained low, with the remaining half happening at a similar rate of warming despite the much higher concentrations of greenhouse gases in the atmosphere. This study shows that when the amplitudes and rates of change of the long-term global cycles are considered, the anthropogenic component of warming can be reduced to 38% (using factors derived from the latest IPCC Working Group reports) to as little as 25% (using observational flux data of dominant Short Wave Absorbed Surface Radiation). These global climate cycles can be extrapolated into the future and the implications for policy of a large natural component to climate change are explored—in particular, the potential for mitigation strategies to have minimal impact and for the climate to cool consequent upon a cyclic down-phase.

Response of atmospheric CO2 changes to the Abyssal Pacific overturning during the last glacial cycle

Response of atmospheric CO2 changes to the Abyssal Pacific overturning during the last glacial cycle

Modeling freezing and BioGeoChemical processes in Antarctic sea ice

AbstractThe Antarctic sea ice, which undergoes annual freezing and melting, plays a significant role in the global climate cycle. Since satellite observations in the Antarctic region began, 2023 saw a historically unprecedented decrease in the extent of sea ice. Further ocean warming and future environmental conditions in the Southern Ocean will influence the extent and amount of ice in the Marginal Ice Zones (MIZ), the BioGeoChemical (BGC) cycles, and their interconnected relationships. The so‐called pancake floes are a composition of a porous sea ice matrix with interstitial brine, nutrients, and biological communities inside the pores. The ice formation and salinity are both dependent on the ambient temperature. To realistically model these multiphasic and multicomponent coupled processes, the extended Theory of Porous Media (eTPM) is used to develop Partial Differential Equations (PDEs) based high‐fidelity models capable of simulating the different seasonal variations in the region. All critical variables like salinity, ice volume fraction, and temperature, among others, are considered and have their equations of state. The phase transition phenomenon is approached through a micro‐macro linking scheme. In this paper, a phase‐field solidification model [4] coupled with salinity is used to model the microscale freezing processes and up‐scaled to the macroscale eTPM model. The evolution equations for the phase field model are derived following Landau‐Ginzburg order parameter gradient dynamics and mass conservation of salt allowing to model the salt trapped inside the pores. A BGC flux model for sea ice is set up to simulate the algal species present in the sea ice matrix. Ordinary differential equations (ODE) are employed to represent the diverse environmental factors involved in the growth and loss of distinct BGC components. Processes like photosynthesis are dependent on temperature and salinity, which are derived through an ODE‐PDE coupling with the eTPM model. Academic simulations and results are presented as validation for the mathematical model. These high‐fidelity models eventually lead to their incorporation into large‐scale global climate models.

Soil biodiversity is essential for building environmental resilience

Soil biodiversity is essential for building environmental resilience The School of Agriculture and Environment and Institute of Agriculture at the University of Western Australia recognise the importance of soil biodiversity in managing soil conditions and building resilience against environmental changes. Soil is a biodiversity ‘hotspot.’ The diversity of organisms in soil is even greater than that found in above-ground ecosystems. Soil biodiversity is dictated by its surroundings, and the communities present comprise groups of organisms that are interdependent. Indeed, soil organisms are represented in all six Kingdoms (Monera, Archaea, Protista, Fungi, Animalia, and Plantae) and fulfill key roles in important processes relevant to soil health, including those that regulate global nutrient and climate cycles.

Loess formation and chronology at the Palaeolithic key site Rheindahlen, Lower Rhine Embayment, Germany

Abstract. The loess–palaeosol sequence and intercalated Palaeolithic find layers at the former brickyard of Rheindahlen are matters of ongoing scientific dispute. The age of different palaeosols and loess layers, hence their correlation with the global climate cycles, and the timing of repeated Neanderthal occupations have been hotly debated. These disagreements should be solved because the exceptional sedimentary and Palaeolithic sequences at Rheindahlen provide a unique opportunity to study diachronic changes in Neanderthal behaviour within the context of past climate change. We thus revisited one of the key loess sections of the Rheindahlen site to improve our understanding of loess formation processes and provide a more reliable chronostratigraphic framework for the sequence. High-resolution grain size analyses and micromorphology show that the Erkelenz Soil and the Rheindahlen Soil are characterized by more strongly developed Bt horizons than the modern soil. While these soils represent interglacial phases, the lowermost palaeosol likely formed during an interstadial and has been overprinted by weak clay illuviation during the formation of the Rheindahlen Soil. Sedimentary features of prolonged frost characterize loess and palaeosols below the modern soil and give indirect evidence for a Holocene age of the uppermost part of the sequence. Our luminescence dating approach corroborates this correlation and adds several Last Glacial deposition ages for the upper metres of the sequence. Previous correlation of this part of the sedimentary sequence with the penultimate glacial is thus rejected, whereas placing the Middle Palaeolithic inventories A3, B1, and B2 into the Last Glacial is confirmed. Luminescence measurements for the parental loess of the Erkelenz Soil and for loess layers below did not provide reliable ages probably related to signal saturation. The age of this part of the sequence thus remains open, hence the timing of human occupation testified by Palaeolithic inventories B3, B4/5, C1, and D1. The new findings provide an improved base for stratigraphic correlation of the Rheindahlen loess sequence and for investigating diachronic change in Neanderthal behaviour against the background of past climate change.

The Indonesian Throughflow circulation under solar geoengineering

Abstract. The Indonesia Throughflow (ITF) is the only low-latitude channel between the Pacific and Indian oceans, and its variability has important effects on global climate and biogeochemical cycles. Climate models consistently predict a decline in ITF transport under global warming, but it has not yet been examined under solar geoengineering scenarios. We use standard parameterized methods for estimating the ITF – the Amended Island Rule and buoyancy forcing – to investigate the ITF under the SSP2-4.5 and SSP5-8.5 greenhouse gas scenarios and the geoengineering experiments G6solar and G6sulfur, which reduce net global mean radiative forcing from SSP5-8.5 levels to SSP2-4.5 levels using solar dimming and sulfate aerosol injection strategies, respectively. Six-model ensemble-mean projections for 2080–2100 show reductions of 19 % under the G6solar scenario and 28 % under the G6sulfur scenario relative to the historical (1980–2014) ITF, which should be compared with reductions of 23 % and 27 % under SSP2-4.5 and SSP5-8.5. Despite standard deviations amounting to 5 %–8 % for each scenario, all scenarios are significantly different from each other (p<0.05) when the whole 2020–2100 simulation period is considered. Thus, significant weakening of the ITF occurs under all scenarios, but G6solar more closely approximates SSP2-4.5 than G6sulfur does. In contrast with the other three scenarios, which show only reductions in forcing due to ocean upwelling, the G6sulfur experiment shows a large reduction in ocean surface wind stress forcing accounting for 47 % (38 %–65 % across the model range) of the decline in wind + upwelling-driven ITF transport. There are also reductions in deep-sea upwelling in extratropical western boundary currents.

Comparison of the carbon cycle and climate response to artificial ocean alkalinization and solar radiation modification

Comparison of the carbon cycle and climate response to artificial ocean alkalinization and solar radiation modification

A kitchen experiment for replicating lava-ice interaction on stratovolcanoes

Many Quaternary stratovolcanoes host (or hosted) glacial ice with volumes that have fluctuated in response to long-term global climate cycles. The repeated advance and retreat of ice in valleys on the flanks of volcanoes throughout their eruptive histories has impacted how and where lava flows are emplaced and preserved. Understanding the dynamics of lava-ice interaction is a vital part of reconstructing the growth histories of many stratovolcanoes and can provide valuable clues about the evolution of Earth’s climate. We have constructed a basic experiment, using common kitchen ingredients and utensils, to replicate the interaction between lava flows and glaciers on stratovolcanoes. This article outlines the ingredients and recipes for soda bread (stratovolcano analogy), ice cream (glacier analogies), and sauce (lava flow analogies), and describes exercises that provide qualitative lessons about the morphology of volcanoes, natural hazards, and paleoclimate. As such, the experiment can be used in geoscience outreach demonstrations for students and will assist non-specialist scientists with undertaking field identification of ice-bounded lava flows.

Global distribution and climate sensitivity of the tropical montane forest nitrogen cycle

Tropical forests are pivotal to global climate and biogeochemical cycles, yet the geographic distribution of nutrient limitation to plants and microbes across the biome is unresolved. One long-standing generalization is that tropical montane forests are nitrogen (N)-limited whereas lowland forests tend to be N-rich. However, empirical tests of this hypothesis have yielded equivocal results. Here we evaluate the topographic signature of the ecosystem-level tropical N cycle by examining climatic and geophysical controls of surface soil N content and stable isotopes (δ15N) from elevational gradients distributed across tropical mountains globally. We document steep increases in soil N concentration and declining δ15N with increasing elevation, consistent with decreased microbial N processing and lower gaseous N losses. Temperature explained much of the change in N, with an apparent temperature sensitivity (Q10) of ~1.9. Although montane forests make up 11% of forested tropical land area, we estimate they account for >17% of the global tropical forest soil N pool. Our findings support the existence of widespread microbial N limitation across tropical montane forest ecosystems and high sensitivity to climate warming.

A 1.8 million year history of Amazon vegetation

A 1.8 million year history of Amazon vegetation

Revegetation affects the response of land surface phenology to climate in Loess Plateau, China

Revegetation affects the response of land surface phenology to climate in Loess Plateau, China

Early Cretaceous climate in North Africa: Insights from the calcareous nannofossils in the atlantic passive margin of Morocco

Early Cretaceous climate in North Africa: Insights from the calcareous nannofossils in the atlantic passive margin of Morocco

Cruise observation of the marine atmosphere and ship emissions in South China Sea: Aerosol composition, sources, and the aging process

Cruise observation of the marine atmosphere and ship emissions in South China Sea: Aerosol composition, sources, and the aging process

Insights from Fossil-Bound Nitrogen Isotopes in Diatoms, Foraminifera, and Corals.

Nitrogen is a major limiting element for biological productivity, and thus understanding past variations in nitrogen cycling is central to understanding past and future ocean biogeochemical cycling, global climate cycles, and biodiversity. Organic nitrogen encapsulated in fossil biominerals is generally protected from alteration, making it an important archive of the marine nitrogen cycle on seasonal to million-year timescales. The isotopic composition of fossil-bound nitrogen reflects variations in the large-scale nitrogen inventory, local sources and processing, and ecological and physiological traits of organisms. The ability to measure trace amounts of fossil-bound nitrogen has expanded with recent method developments. In this article, we review the foundations and ground truthing for three important fossil-bound proxy types: diatoms, foraminifera, and corals. We highlight their utility with examples of high-resolution evidence for anthropogenic inputs of nitrogen to the oceans, glacial-interglacial-scale assessments of nitrogen inventory change, and evidence for enhanced CO2 drawdown in the high-latitude ocean. Future directions include expanded method development, characterization of ecological and physiological variation, and exploration of extended timescales to push reconstructions further back in Earth's history.

Influence of Monsoon Climate on Chemical Weathering of Granitic Regoliths

AbstractChemical weathering of silicates is a key process regulating global climate and biogeochemical cycles. However, little consensus has emerged on whether and how climate controls the chemical weathering of regolith. We present data on climate, geochemistry, and denudation rates of six low‐gradient granitic regoliths in the summer monsoon region. We used the time‐integrated Na loss rate (QNa) and chemical depletion fraction (CDF) to indicate plagioclase weathering and total weathering, respectively. Most profiles are primarily influenced by supply‐limited weathering (i.e., tectonic control on weathering), while the weak insignificant correlations between CDF or QNa and erosion rates or slopes suggest that tectonics and topography did not have the major control on weathering. In contrast, annual mean temperature (MAT) and annual mean water availability (MAP‐MAPET) strongly regulate weathering (QNa and CDF) exponentially, likely because of the approximately synergistic effects of temperature and water availability in the monsoon climate. The total sufficient monthly mean temperature (MMT) and monthly mean water availability (MMP‐MMPET) are utilized to further evaluate the relative influence of climate on CDF and QNa. The results suggest that total MMT and MMP‐MMPET both strongly influence CDF exponentially and linearly, respectively. However, total MMT and MMP‐MMPET show significant exponential correlations with QNa. The different effects of water availability imply that total weathering responding to variations in water availability is probably less sensitive than plagioclase weathering. The influence of climate on weathering on a large scale through MAT and MAP needs to be interpreted with caution due to the seasonal discrepancy of temperature and water availability.

Community dynamics of estuarine forage fishes are associated with a latitudinal basal resource regime

AbstractForage fishes are an important component of marine, estuarine, and aquatic food webs that facilitate the transfer of energy and nutrients from primary producers to upper trophic levels. Previous studies of forage fishes have focused primarily on pelagic planktivorous species in pelagic environments. However, benthically associated taxa can be just as important as planktivorous species, particularly in highly productive estuarine environments that provide critical habitat for many predators. In this study, we analyzed a 20‐year forage fish community composition and abundance dataset across four eastern Gulf of Mexico estuaries spanning a broad latitudinal gradient to investigate spatiotemporal variability in community structure and quantify associations with habitat. Our analyses revealed significant regional structuring of forage fish communities, coupled with a strong association with habitat characteristics related to latitudinal effects and basal resource regime. Communities in the two northern estuaries and two southern estuaries were associated primarily with planktonically reliant and benthically reliant taxa, respectively. Despite regional differences, we uncovered a coherent annual cycle in forage fish communities across all estuaries related to seasonal shifts in abundances of several abundant and ubiquitous species. We additionally revealed significant subdecadal periodicity potentially associated with bottom‐up effects of global climatic cycles. The significant association of forage fish communities with habitat regime shown in this study underlies the importance of continued monitoring of these communities. This study represents a novel approach to assess this critical ecosystem component in diverse estuarine systems globally.

Cyclic evolution of phytoplankton forced by changes in tropical seasonality.

Although the role of Earth's orbital variations in driving global climate cycles has long been recognized, their effect on evolution is hitherto unknown. The fossil remains of coccolithophores, a key calcifying phytoplankton group, enable a detailed assessment of the effect of cyclic orbital-scale climate changes on evolution because of their abundance in marine sediments and the preservation of their morphological adaptation to the changing environment1,2. Evolutionary genetic analyses have linked broad changes in Pleistocene fossil coccolith morphology to species radiation events3. Here, using high-resolution coccolith data, we show that during the last 2.8 million years the morphological evolution of coccolithophores was forced by Earth's orbital eccentricity with rhythms of around 100,000 years and 405,000 years-a distinct spectral signature to that of coeval global climate cycles4. Simulations with an Earth System Model5 coupled with an ocean biogeochemical model6 show a strong eccentricity modulation of the seasonal cycle, which we suggest directly affects the diversity of ecological niches that occur over the annual cycle in the tropical ocean. Reduced seasonality in surface ocean conditions favours species with mid-size coccoliths, increasing coccolith carbonate export and burial; whereas enhanced seasonality favours a larger range of coccolith sizes and reduced carbonate export. We posit that eccentricity pacing of phytoplankton evolution contributed to the strong 405,000-year cyclicity that is seen in global carbon cycle records.

Climate, cryosphere and carbon cycle controls on Southeast Atlantic orbital-scale carbonate deposition since the Oligocene (30–0 Ma)

Abstract. The evolution of the Cenozoic cryosphere from unipolar to bipolar over the past 30 million years (Myr) is broadly known. Highly resolved records of carbonate (CaCO3) content provide insight into the evolution of regional and global climate, cryosphere, and carbon cycle dynamics. Here, we generate the first Southeast Atlantic CaCO3 content record spanning the last 30 Myr, derived from X-ray fluorescence (XRF) ln(Ca / Fe) data collected at Ocean Drilling Program Site 1264 (Walvis Ridge, SE Atlantic Ocean). We present a comprehensive and continuous depth and age model for the entirety of Site 1264 (∼ 316 m; 30 Myr). This constitutes a key reference framework for future palaeoclimatic and palaeoceanographic studies at this location. We identify three phases with distinctly different orbital controls on Southeast Atlantic CaCO3 deposition, corresponding to major developments in climate, the cryosphere and the carbon cycle: (1) strong ∼ 110 kyr eccentricity pacing prevails during Oligocene–Miocene global warmth (∼ 30–13 Ma), (2) increased eccentricity-modulated precession pacing appears after the middle Miocene Climate Transition (mMCT) (∼ 14–8 Ma), and (3) pervasive obliquity pacing appears in the late Miocene (∼ 7.7–3.3 Ma) following greater importance of high-latitude processes, such as increased glacial activity and high-latitude cooling. The lowest CaCO3 content (92 %–94 %) occurs between 18.5 and 14.5 Ma, potentially reflecting dissolution caused by widespread early Miocene warmth and preceding Antarctic deglaciation across the Miocene Climatic Optimum (∼ 17–14.5 Ma) by 1.5 Myr. The emergence of precession pacing of CaCO3 deposition at Site 1264 after ∼ 14 Ma could signal a reorganisation of surface and/or deep-water circulation in this region following Antarctic reglaciation at the mMCT. The increased sensitivity to precession at Site 1264 between 14 and 13 Ma is associated with an increase in mass accumulation rates (MARs) and reflects increased regional CaCO3 productivity and/or recurrent influxes of cooler, less corrosive deep waters. The highest carbonate content (%CaCO3) and MARs indicate that the late Miocene–early Pliocene Biogenic Bloom (LMBB) occurs between ∼ 7.8 and 3.3 Ma at Site 1264; broadly contemporaneous with the LMBB in the equatorial Pacific Ocean. At Site 1264, the onset of the LMBB roughly coincides with appearance of strong obliquity pacing of %CaCO3, reflecting increased high-latitude forcing. The global expression of the LMBB may reflect increased nutrient input into the global ocean resulting from enhanced aeolian dust and/or glacial/chemical weathering fluxes, due to enhanced glacial activity and increased meridional temperature gradients. Regional variability in the timing and amplitude of the LMBB may be driven by regional differences in cooling, continental aridification and/or changes in ocean circulation in the late Miocene.

Identifying Metocean Drivers of Turbidity Using 18 Years of MODIS Satellite Data: Implications for Marine Ecosystems under Climate Change

Turbidity impacts the growth and productivity of marine benthic habitats due to light limitation. Daily/monthly synoptic and tidal influences often drive turbidity fluctuations, however, our understanding of what drives turbidity across seasonal/interannual timescales is often limited, thus impeding our ability to forecast climate change impacts to ecologically significant habitats. Here, we analysed long term (18-year) MODIS-aqua data to derive turbidity and the associated meteorological and oceanographic (metocean) processes in an arid tropical embayment (Exmouth Gulf in Western Australia) within the eastern Indian Ocean. We found turbidity was associated with El Niño Southern Oscillation (ENSO) cycles as well as Indian Ocean Dipole (IOD) events. Winds from the adjacent terrestrial region were also associated with turbidity and an upward trend in turbidity was evident in the body of the gulf over the 18 years. Our results identify hydrological processes that could be affected by global climate cycles undergoing change and reveal opportunities for managers to reduce impacts to ecologically important ecosystems.