Elevated atmospheric CO2 drove an increase in tropical cyclone intensity during the early Toarcian hyperthermal

The occurrence of sedimentary storm deposits around the Tethys Ocean during the early Toarcian hyperthermal (~183 Ma) suggests that intensified tropical cyclone (TC) activity occurred in response to CO2 rise and marked warming. However, this hypothesized linkage between extreme warmth and storm activity remains untested, and the spatial pattern of any changes in TCs is unclear. Here, model results show that there were two potential storm genesis centers over Tethys during the early Toarcian hyperthermal located around the northwestern and southeastern Tethys. The empirically determined doubling of CO2 concentration that accompanied the early Toarcian hyperthermal (~500 to ~1,000 ppmv) leads to increased probability of stronger storms over Tethys, in tandem with more favorable conditions for coastal erosion. These results match well with the geological occurrence of storm deposits during the early Toarcian hyperthermal and confirm that increased TC intensity would have accompanied global warming.

Plio-Pleistocene deep-sea ventilation in the eastern Pacific and potential linkages with Northern Hemisphere glaciation

Antarctic bottom water (AABW) production is a key factor governing global ocean circulation, and the present disintegration of the Antarctic Ice Sheet slows it. However, its long-term variability has not been well documented. On the basis of high-resolution chemical scanning of a well-dated marine ferromanganese nodule from the eastern Pacific, we derive a record of abyssal ventilation spanning the past 4.7 million years and evaluate its linkage to AABW formation over this period. We find that abyssal ventilation was relatively weak in the early Pliocene and persistently intensified from 3.4 million years ago onward. Seven episodes of markedly reduced ocean ventilation indicative of AABW formation collapse are identified since the late Pliocene, which were accompanied by key stages of Northern Hemisphere glaciation. We suggest that the interpolar climate synchronization within these inferred seven collapse events may have intensified global glaciation by inducing poleward moisture transport in the Northern Hemisphere.

Thresholds of temperature change for mass extinctions

Climate change is a critical factor affecting biodiversity. However, the quantitative relationship between temperature change and extinction is unclear. Here, we analyze magnitudes and rates of temperature change and extinction rates of marine fossils through the past 450 million years (Myr). The results show that both the rate and magnitude of temperature change are significantly positively correlated with the extinction rate of marine animals. Major mass extinctions in the Phanerozoic can be linked to thresholds in climate change (warming or cooling) that equate to magnitudes >5.2 °C and rates >10 °C/Myr. The significant relationship between temperature change and extinction still exists when we exclude the five largest mass extinctions of the Phanerozoic. Our findings predict that a temperature increase of 5.2 °C above the pre-industrial level at present rates of increase would likely result in mass extinction comparable to that of the major Phanerozoic events, even without other, non-climatic anthropogenic impacts.

Cyclostratigraphy and astrochronology: Case studies from China

A high-precision geologic time scale is the essential key for understanding the Earth's evolutionary history and geologic processes. Astronomical tuning of orbitally forced stratigraphic records to construct high-resolution Astronomical Time Scales (ATS) has led to a progressive refinement of the geologic time scale over the past two decades. In turn, these studies provide new insights regarding the durations and rates of major Earth events, evolutionary processes, and climate changes, all of which provide a scientific basis for contextualizing and predicting future global change trends. South China hosts some of the best-exposed and well-dated Neoproterozoic through Mesozoic stratigraphic sections in the world; many of which are suitable for cyclostratigraphy and calibrating the geologic time scale. In North China, several Cenozoic oil-bearing basins have deep boreholes with continuous sampling and/or well logging that enable derivation of astronomically tuned time scales for an improved understanding of basin evolution and hydrocarbon generation. This Special Issue focuses on case studies of astrochronology and applied cyclostratigraphy research using reference sections within China. In this introductory overview, we: (1) summarize all existing astrochronology studies of the Neoproterozoic through Cenozoic sections within China that have been used to enhance the international geologic time scale, (2) examine briefly the astronomically forced paleoclimate information recorded in various depositional systems and the modern techniques employed to analyze the periodicity of these signals encoded within the sedimentary record, and (3) summarize the 20 contributions to this Special Issue of Palaeogeography, Palaeoclimatology, Palaeoecology on 'Cyclostratigraphy and Astrochronology: Case studies from China'.

The human impact on North American erosion, sediment transfer, and storage in a geologic context

Humans are primary agents of geomorphic change, and rates of anthropogenic landscape change likely far exceed the pace of change expected from natural geologic processes. Nevertheless, our understanding of the impact of humans on the natural landscape is limited by difficulties in accurately comparing past and present rates of change across wide spatial and temporal scales. Here, we present a compilation of  >4000 rates of alluvial sediment accumulation that provide an indirect record of North American erosion, mass transfer and sediment storage from the late Pleistocene to the present day. Continent-wide rates of alluvium accumulation were broadly stable for ~40,000 years, but increased 10-fold during the rapid expansion of agriculture and river system modification associated with European colonization. Interpreted in terms of mass transfer, humans have moved as much sediment in North America in the past century as natural processes can transfer in 700–3000 years.

Human activities have accelerated soil erosion and landscape change in many areas. Here the authors show how rates of erosion, sediment transfer and alluvial sedimentation have increased by an order of magnitude across North America since European colonization, far exceeding the rates expected of natural processes.

Astronomical time scale for the lower Doushantuo Formation of early Ediacaran, South China

Nearly 90% of the Ediacaran Period (635-541 Ma) of the Neoproterozoic is represented by the Doushantuo Formation (DST Fm) in South China. Its lowest Member I is a 3.7 m-thick cap carbonate deposited at the termination of the Cryogenian Marinoan glaciation. The DST Fm consists of alternating organic-rich black shale and thinly bedded dolostone, and it contains some of the oldest records of multi-cellular life and three pronounced negative carbon isotope excursions. The Jiulongwan (JLW) section is a well-studied reference section for these Ediacaran events. Spectral analysis of geochemical data through the lower DST Fm (22.3 m) shows 27 predominant ∼90 cm sedimentary cycles that correspond to 405-ka long eccentricity cycles. The power spectra of the 405-ka tuned Ca and Fe/Ti series show significant peaks at ∼1.2-Ma, 405-ka, 133-ka, 128-ka, 100-ka, 82-ka, ∼31-ka and 29-ka periods, respectively. A 11.16 Ma-long astronomical time scale has been constructed for the lower DST Fm and provide a duration of 1.6 Ma for the cap carbonate (Member I) based on the 405-ka long eccentricity cycle tuning. Using the U-Pb age of 635.2 ± 0.6 Ma for the volcanic ash bed at the Member I/II boundary, we proposed a 636.8 Ma age for the base of the DST Fm. These ages and astronomical timescale provide important new constraints on the subdivision of Ediacaran strata, and have implications for understanding the character of the first negative δ¹³C excursion (EN1). Orbital forcing may have been played an important role for the climate changes and the evolution of Ediacaran multi-cellular life and the carbon cycle variations.

Maximum rates of climate change are systematically underestimated in the geological record

Recently observed rates of environmental change are typically much higher than those inferred for the geological past. At the same time, the magnitudes of ancient changes were often substantially greater than those established in recent history. The most pertinent disparity, however, between recent and geological rates is the timespan over which the rates are measured, which typically differ by several orders of magnitude. Here we show that rates of marked temperature changes inferred from proxy data in Earth history scale with measurement timespan as an approximate power law across nearly six orders of magnitude (10² to >10⁷ years). This scaling reveals how climate signals measured in the geological record alias transient variability, even during the most pronounced climatic perturbations of the Phanerozoic. Our findings indicate that the true attainable pace of climate change on timescales of greatest societal relevance is underestimated in geological archives.

Recently observed rates of climatic change are typically much higher than those inferred for the geological past. Here, the authors show that maximum rates of climate change inferred from geological data are likely erroneously underestimated.

Astronomical pacing of methane release in the Early Jurassic period

A pronounced negative carbon-isotope (delta13C) excursion of approximately 5-7 per thousand (refs 1-7) indicates the occurrence of a significant perturbation to the global carbon cycle during the Early Jurassic period (early Toarcian age, approximately 183 million years ago). The rapid release of 12C-enriched biogenic methane as a result of continental-shelf methane hydrate dissociation has been put forward as a possible explanation for this observation. Here we report high-resolution organic carbon-isotope data from well-preserved mudrocks in Yorkshire, UK, which demonstrate that the carbon-isotope excursion occurred in three abrupt stages, each showing a shift of -2 per thousand to -3 per thousand. Spectral analysis of these carbon-isotope measurements and of high-resolution carbonate abundance data reveals a regular cyclicity. We interpret these results as providing strong evidence that methane release proceeded in three rapid pulses and that these pulses were controlled by astronomically forced changes in climate, superimposed upon longer-term global warming. We also find that the first two pulses of methane release each coincided with the extinction of a large proportion of marine species.

Cerebrospinal fluid levels of magnesium in patients with preeclampsia after treatment with intravenous magnesium sulfate: a preliminary report

The purpose of this study is twofold: (1) to correlate magnesium levels of serum with those of cerebrospinal fluid in patients with preeclampsia receiving intravenous magnesium sulfate, and (2) to determine whether the magnesium ion crosses the blood-brain barrier in significant amounts after intravenous magnesium sulfate therapy. Of the 21 patients in whom spinal anesthesia was used for delivery, ten patients with preeclampsia with therapeutic serum magnesium levels made up the study group and 11 term nontreated normotensive gravid women served as controls. At the time of spinal anesthesia, a 1 ml aliquot of cerebrospinal fluid was obtained from each patient. The mean cerebrospinal fluid magnesium level for the control group was 2.56 +/- 0.19 mg/dl (range 2.2 to 2.8 mg/dl). For the preeclamptic group who received intravenous magnesium sulfate, the mean cerebrospinal fluid magnesium level was 3.04 +/- 0.12 mg/dl (range 2.9 to 3.2 mg/dl). Although only a small amount of magnesium crosses the blood-brain barrier after intravenous magnesium sulfate treatment, this increment is highly significant (p less than 0.001).

Properties of adenylate cyclase in the cardiovascular tissues of renal hypertensive rats

Adenylate cyclase activity in the myocardium and aorta of Grollman one-kidney renal hypertensive rats (RHR) and sham-operated control rats was compared. The experimental rats revealed significantly higher blood pressure and cardiac hypertrophy 6-8 weeks postoperation as compared to controls. Basal, guanine nucleotide-, fluoride-, and isoproterenol-stimulated adenylate cyclase activities were consistently decreased in the myocardium of RHR as compared to control rats. Similar changes were observed in aorta of RHR; however, the magnitude of difference was greater in aorta as compared to myocardium. The kinetic properties of enzyme with regard to the Ka (quantity of agonist required for half-maximal stimulation of adenylate cyclase) values for GTP, Gpp (NH)p, and GTP-gamma-S in the absence and presence of isoproterenol and the Ka values for isoproterenol in the presence of GTP, Gpp(NH)p, or GTP-gamma-S were comparable in RHR and control rats. However, Vmax of adenylate cyclase stimulation by guanine nucleotides, isoproterenol, and fluoride was reduced in RHR as compared to control rats. No differences between RHR and control rat myocardial membranes were observed in the affinity of [3H]DHA binding. However, the number of binding sites was reduced 20-25% in RHR as compared to control rats. These data would suggest that the number of receptor--cyclase complexes may be reduced in the RHR.