Michael M. Joachimski

Lethally Hot Temperatures During the Early Triassic Greenhouse

Too-Hot Times Climate warming has been invoked as a factor contributing to widespread extinction events, acting as a trigger or amplifier for more proximal causes, such as marine anoxia. Sun et al. (p. 366; see the Perspective by Bottjer) present evidence that exceptionally high temperatures themselves may have caused some extinctions during the end-Permian. A rapid temperature rise coincided with a general absence of ichthyofauna in equatorial regions, as well as an absence of many species of marine mammals and calcareous algae, consistent with thermal influences on the marine low latitudes. Sea surface temperatures approached 40°C, which suggests that land temperatures likely fluctuated to even higher values that suppressed terrestrial equatorial plant and animal abundance during most of the Early Triassic. Global warming in the Early Triassic was so severe that equatorial latitudes were uninhabitable for many plants and animals. Global warming is widely regarded to have played a contributing role in numerous past biotic crises. Here, we show that the end-Permian mass extinction coincided with a rapid temperature rise to exceptionally high values in the Early Triassic that were inimical to life in equatorial latitudes and suppressed ecosystem recovery. This was manifested in the loss of calcareous algae, the near-absence of fish in equatorial Tethys, and the dominance of small taxa of invertebrates during the thermal maxima. High temperatures drove most Early Triassic plants and animals out of equatorial terrestrial ecosystems and probably were a major cause of the end-Smithian crisis.

Anoxic events in the late Frasnian—Causes of the Frasnian-Famennian faunal crisis?

Carbon isotope data collected from five Frasnian-Famennian boundary sections in central Europe show two positive δ 13 C excursions in the late Frasnian (∼367 Ma). Both anomalies coincided with the deposition of the bituminous lower and upper Kellwasser horizons. The carbon isotope patterns indicate two phases of enhanced burial and subsequent recycling of organic carbon. A maximum formation of warm saline waters on the subtropical to tropical epicontinental shelves during late Frasnian transgressive episodes may have induced oceanic oxygen deficits. Variations in the C org burial rates may have resulted in changes in the CO 2 concentrations in the oceans and in the atmosphere, culminating in global climatic changes. We propose that the repeated co-occurrences of sea-level fluctuations, anoxic conditions, and global climatic changes during the late Frasnian would affect especially the subtropical to tropical shallow-water communities and reef ecosystems, which were severely affected during the Frasnian-Famennian faunal crisis.

Climate warming in the latest Permian and the Permian-Triassic mass extinction

High-resolution oxygen isotope records document the timing and magnitude of global warming across the Permian-Triassic (P-Tr) boundary. Oxygen isotope ratios measured on phosphate-bound oxygen in conodont apatite from the Meishan and Shangsi sections (South China) decrease by 2‰ in the latest Permian, translating into low-latitude surface water warming of 8 °C. The oxygen isotope shift coincides with the negative shift in carbon isotope ratios of carbonates, suggesting that the addition of isotopically light carbon to the ocean-atmosphere system by Siberian Traps volcanism and related processes resulted in higher greenhouse gas levels and global warming. The major temperature rise started immediately before the main extinction phase, with maximum and harmful temperatures documented in the latest Permian (Meishan: bed 27). The coincidence of climate warming and the main pulse of extinction suggest that global warming was one of the causes of the collapse of the marine and terrestrial ecosystems. In addition, very warm climate conditions in the Early Triassic may have played a major role in the delayed recovery in the aftermath of the Permian-Triassic crisis.

Oxygen isotope fractionation in marine aragonite of coralline sponges

Oxygen isotope values of the extant Caribbean coralline sponge Ceratoporella nicholsoni are compared with published temperatures and δ18O of water calculated from salinities. The measured values from aragonitic sponge skeletons have a mean offset of 1.0 ± 0.1‰ from calculated calcite equilibrium values (αaragonite-calcite = 1.0010). This is in good agreement with published values from synthetic aragonite. They further agree with published near-equilibrium oxygen isotope values of temperate and cold water molluscs and foraminifera extrapolated to the temperature range of the coralline sponges. These results and the mode of skeleton formation of Ceratoporella nicholsoni suggest that these sponges precipitate aragonite close to isotopic equilibrium. The temperature dependence of oxygen isotopic fractionation between the aragonite of Ceratoporella nicholsoni and water is only roughly constrained by the available data, due to the narrow temperature range of the Caribbean reef sites. However, as the data suggest oxygen isotopic equilibrium, we can calculate a well constrained temperature equation combining temperate and cold water equilibrium values from molluscs and foraminifera with our sponge data: Full-size image (<1 K) and Full-size image (<1 K).

Water column anoxia, enhanced productivity and concomitant changes in δ13C and δ34S across the Frasnian–Famennian boundary (Kowala — Holy Cross Mountains/Poland)

The investigation of the trace element and organic geochemistry of the Frasnian–Famennian boundary section at Kowala (Holy Cross Mountains/Poland) shows that the lower water column was oxygen-deficient during late Frasnian and early Famennian times. The abundance and carbon isotopic composition of diaryl isoprenoids, biomarkers indicative for green sulfur bacteria, prove that euxinic waters reached into the photic zone, at least episodically. Total organic carbon (TOC) contents show two maxima that are time-equivalent to the Kellwasser horizons deposited in shallower water settings. Enhanced TOC concentrations are explained by a higher primary productivity, presumably as a consequence of an enhanced nutrient supply from the continent. The increase in the abundance of hopanes and bituminite suggests that the bacterial contribution to TOC increased at the Frasnian–Famennian transition. The sulfur isotopic composition of pyritic- and organically bound sulfur shows a +27‰ excursion across the boundary. The observation that the δ34S values of organic-bound sulfur closely resemble that of pyrite sulfur indicates a common sulfur source, likely early diagenetic sulfide. A change in the δ13C of total dissolved inorganic carbon as a consequence of an enhanced burial of 12C-enriched organic carbon is indicated by a +3‰ excursion measured for TOC as well as for individual n-alkanes and isoprenoids. The burial of large amounts of organic carbon is expected to result in a decrease in pCO2 and should affect the photosynthetic carbon isotope fractionation (ep). The fact that we observe no change in ep can be explained by the circumstance that ep was most probably at maximum values, as a consequence of high atmospheric and oceanic-dissolved CO2 concentrations during the Devonian.

Conodont apatite δ18O signatures indicate climatic cooling as a trigger of the Late Devonian mass extinction

The oxygen isotopic composition of conodont apatite from two Frasnian-Famennian boundary sections was measured in order to reconstruct variations in marine paleotemperatures during the late Frasnian mass-extinction event. The measured conodont apatite δ18O values reveal two positive excursions with maximum amplitudes of +1‰ to +1.5‰ that parallel positive excursions in the carbonate carbon isotopic composition. The +3‰ excursions in carbonate δ13C have been interpreted as consequences of enhanced organic carbon burial rate resulting in a decrease in atmospheric CO2 concentration. Climatic cooling as a potential consequence of lower atmospheric CO2 concentration is confirmed by the conodont apatite δ18O records, which translate into cooling of low-latitude surface waters by 5–7 °C. Repeated cooling of the low latitudes during the late Frasnian had a severe impact on the tropical shallow-water faunas that were probably adapted to warm surface-water temperatures and severely affected during the late Frasnian crisis. These prominent variations in ocean-water temperature were stressful to the tropical shallow-water fauna and potentially culminated in low origination rates of new species, one of the major factors of the decline in diversity during the latest Frasnian.

Carbon isotope geochemistry of the Frasnian^Famennian transition

Abstract Carbon isotope records for inorganic and total organic carbon (TOC) as well as for individual organic biomarkers show two positive excursions in the Late Frasnian with comparable shape and amplitude in δ13C. The positive shifts in δ13C can be correlated with the deposition of the Kellwasser horizons. The inorganic carbon isotope excursions are explained by an enhanced organic carbon burial that is expected to lower the concentration of oceanic dissolved CO2. TOC δ13C values do not exhibit a larger shift than that recorded by inorganic carbon δ13C values; this is unexpected since a decrease in the dissolved CO2 concentration should result in lower carbon isotope fractionation during photosynthesis (ep). δ13C values of presumed algal biomarkers (low-molecular-weight n-alkanes, pristane, phytane), although offset by ∼2.5‰, exhibit essentially identical records as TOC, and confirm this unexpected result. It is proposed that high atmospheric and oceanic CO2 concentrations during the Devonian resulted in maximum photosynthetic fractionation. Any change in the CO2 concentration would thus not affect ep. As such, δ13C of primary organic carbon and δ13Ccarb will exhibit parallel excursions. The data imply that carbon isotopes and the relationship between ep and [CO2] will not be effective to study changes in pCO2 levels during the Devonian since CO2 concentrations were too high.

Deciphering kinetic, metabolic and environmental controls on stable isotope fractionations between seawater and the shell of Terebratalia transversa (Brachiopoda)

This study presents carbon and oxygen stable isotope data obtained from high-resolution sampling (<500 μm) of the brachiopod Terebratalia transversa from the San Juan Islands (Washington State, USA). The aim of this study is to unravel the respective effects of physiological and environmental controls on the stable isotopic composition of brachiopod shell calcite. Based on an SEM study of the shell, a three-dimensional sampling was performed in order to investigate carbon and oxygen isotope variations along isochrons and ontogenetic transects. The primary as well as the outer part of the secondary shell layer display large and variable isotopic offsets as high as −7‰ for δ13C and −6‰ for δ18O relative to expected equilibrium values. The significant positive correlations between δ18O and δ13C values indicate that the isotopic compositions of these shell domains are mainly controlled by kinetic isotope fractionation effects. The ontogenetic δ13C and δ18O variations can be used to establish a growth curve of the studied specimen whose age is estimated close to 8 years. The extent of apparent O-18 disequilibrium observed in this study is about as large as any yet measured in any organism, which makes this brachiopod an interesting and important case. The carbon and oxygen isotope compositions increase from the outer towards the inner part of the secondary layer, where they reach values of 0–0.8‰ and −0.8‰ to −0.2‰, respectively. Corresponding calculated temperatures are between 12 and 13.8 °C and fall in the range of seawater temperatures recorded off the San Juan Islands (7–13 °C). These results suggest that the calcite fibres were secreted more and more slowly during the thickening of the shell throughout the animals life, finally approximating isotopic equilibrium. This study illustrates that the stable isotopic composition of the modern brachiopod T. transversa is predominantly influenced by kinetic fractionation and, to a minor degree, by metabolic effects. Except for the innermost part of the shell, the measured isotope ratios do not reflect environmental conditions during shell precipitation. It remains to be tested by comparable studies whether other modern brachiopod species or even fossil brachiopods reflect comparable fractionation effects. These results point out the need for re-examination of Paleozoic oceanographic conditions.

Constraints on Pennsylvanian glacioeustatic sea-level changes using oxygen isotopes of conodont apatite

Conodonts from U.S. Midcontinent cyclothems were studied for oxygen isotopes in order to constrain Pennsylvanian glacioeustatic sea-level fluctuations. Pennsylvanian deposits of the Midcontinent United States are composed of cyclic alternations of thin transgressive limestones, offshore gray to black phosphatic shales, and thick regressive limestones, a sequence that is underlain and overlain by nearshore to terrestrial shales with paleosols and coal beds. Glacioeustatic sea-level fluctuations are considered the primary cause for the formation of these cyclothems. Oxygen isotope analyses of conodont apatite from the black (20.1 ± 0.5‰, Vienna standard mean ocean water [VSMOW]) and gray shale units (20.5 ± 0.5‰, VSMOW) show lowest average δ 18 O values, whereas conodont elements from the regressive (21.0 ± 0.3‰, VSMOW) and transgressive limestone units (21.1 ± 0.6‰, VSMOW) are enriched in 18 O. The maximum change in δ 18 O of conodonts from the black shale and carbonate units from individual cyclothems is 1.7‰. The 1.7%c difference in δ 18 O compares relatively well to Pleistocene interglacial-glacial changes in δ 18 O of equatorial surface-dwelling foraminifers and suggests that Pennsylvanian glacioeustatic sea-level changes may have been of comparable amplitude. However, since the Pennsylvanian glacial maxima are represented by terrestrial sediments and are not documented in the conodont oxygen isotope record, Pennsylvanian glacioeustatic sea-level changes were probably larger than the 120 m fluctuations recorded for the Pleistocene glaciations.

Carbon isotope records from extant Caribbean and South Pacific sponges: Evolution of δ13C in surface water DIC

Stable isotope records of demosponges from the Caribbean and Coral Sea are described for the purpose of studying the influence of fossil fuel CO2 on the carbon isotopic composition of dissolved inorganic carbon (DIC) in surface water. The slow-growing sponges precipitate calcium carbonate in isotopic equilibrium with ambient sea water and are used to detect changes in δ13CDIC from pre-industrial times (early 19th century) to the present. We observed similar shapes and ranges in δ13C curves measured on Caribbean specimens collected from water depths of 25, 84 and 91 m as well as a specimen collected in shallow waters off New Caledonia. The records reveal a highly significant correlation with atmospheric δ13CCO2. δ13CDIC values for Caribbean and Coral Sea surface waters were calculated using the δ13C sponge records. While δ13C of atmospheric CO2 decreased by about 1.4‰ from the early 19th century to 1990, δ13CDIC of Caribbean and Coral Sea surface waters decreased by 0.9±0.2‰ and 0.7±0.3‰, respectively. No isotopic equilibrium between surface water DIC and atmospheric CO2 was observed, either during the pre-industrial steady state or during the last 100 years. The lower amount of depletion in the surface water δ13CDIC with respect to the atmospheric anthropogenic signal is explained by the dilution of the surface waters by biologically altered subsurface water DIC. The lower δ13C decrease in the Coral Sea points to a stronger influence of the subsurface water source compared to the Caribbean.