Late Ordovician mass extinction caused by volcanism, warming, and anoxia, not cooling and glaciation

The Ordovician saw major diversification in marine life abruptly terminated by the Late Ordovician mass extinction (LOME). Around 85% of species were eliminated in two pulses 1 m.y. apart. The first pulse, in the basal Hirnantian, has been linked to cooling and Gondwanan glaciation. The second pulse, later in the Hirnantian, is attributed to warming and anoxia. Previously reported mercury (Hg) spikes in Nevada (USA), South China, and Poland implicate an unknown large igneous province (LIP) in the crisis, but the timing of Hg loading has led to different interpretations of the LIP-extinction scenario in which volcanism causes cooling, warming, or both. We report close correspondence between Hg, Mo, and U anomalies, declines in enrichment factors of productivity proxies, and the two LOME pulses at the Ordovician-Silurian boundary stratotype (Dob's Linn, Scotland). These support an extinction scenario in which volcanogenic greenhouse gases caused warming around the Katian-Hirnantian boundary that led to expansion of a preexisting deepwater oxygen minimum zone, productivity collapse, and the first LOME pulse. Renewed volcanism in the Hirnantian stimulated further warming and anoxia and the second LOME pulse. Rather than being the odd-one-out of the "Big Five" extinctions with origins in cooling, the LOME is similar to the others in being caused by volcanism, warming, and anoxia

On the causes of mass extinctions

The temporal link between large igneous province (LIP) eruptions and at least half of the major extinctions of the Phanerozoic implies that large scale volcanism is the main driver of mass extinction. Here we review almost twenty biotic crises between the early Cambrian and end Cretaceous and explore potential causal mechanisms. Most extinctions are associated with global warming and proximal killers such as marine anoxia (including the Early/Middle Cambrian, the Late Ordovician, the intra-Silurian, intra-Devonian, end-Permian, and Early Jurassic crises). Many, but not all of these are accompanied by large negative carbon isotope excursions, supporting a volcanogenic origin. Most post-Silurian biocrises affected both terrestrial and marine biospheres, suggesting that atmospheric processes were crucial in driving global extinctions. Volcanogenic-atmospheric kill mechanisms include ocean acidification, toxic metal poisoning, acid rain, and ozone damage and consequent increased UV-B radiation, volcanic darkness, cooling and photosynthetic shutdown, each of which has been implicated in numerous events. Intriguingly, some of the most voluminous LIPs such as the oceanic plateaus of the Cretaceous were emplaced with minimal faunal losses and so volume of magma is not the only factor governing LIP lethality. The missing link might be continental configuration because the best examples of the LIP/extinction relationship occurred during the time of Pangaea. Many of the proximal kill mechanisms in LIP/extinction scenarios are also potential effects of bolide impact, including cooling, warming, acidification and ozone destruction. However, the absence of convincing temporal links between impacts and extinctions other than the Chicxulub-Cretaceous example, suggests that impacts are not the main driver of extinctions. With numerous competing extinction scenarios, and the realisation that some of the purported environmental stresses may once again be driving mass extinction, we explore how experimental biology might inform our understanding of ancient extinctions as well as future crises

How Large Igneous Provinces Have Killed Most Life on Earth—Numerous Times

Evolution has not been a simple path. Since the first appearance of complex life, there have been several mass extinctions on Earth. This was exemplified by the most severe event during the Phanerozoic, the end-Permian mass extinction that occurred 252 million years ago and saw a loss of 90% and 70% of all marine and terrestrial species, respectively. Such mass extinctions have entirely reset ecosystems. Increasing evidence points to the massive eruption and crustal emplacement of magmas associated with large igneous provinces (LIPs) as key drivers of these events. Understanding how LIP events disrupted global biogeochemical cycles is of prime importance, especially as humans alter the atmosphere and biosphere today. We explore the cascading impacts of LIP events on global climate, oceans, and land—including runaway greenhouses, the release of toxic metals to the environment, the destruction of the ozone layer, and how global oceans are driven to anoxic and acidic states—all of which have parallels in the consequences of modern industrialisation

Mercury anomalies associated with three extinction events (Capitanian Crisis, Latest Permian Extinction and the Smithian/Spathian Extinction) in NW Pangea

Copyright © Cambridge University Press 2015. Strata of Permian - Early Triassic age that include a record of three major extinction events (Capitanian Crisis, Latest Permian Extinction and the Smithian/Spathian Extinction) were examined at the Festningen section, Spitsbergen. Over the c. 12 Ma record examined, mercury in the sediments shows relatively constant background values of 0.005-0.010 μg g -1 . However, there are notable spikes in Hg concentration over an order of magnitude above background associated with the three extinctions. The Hg/total organic carbon (TOC) ratio shows similar large spikes, indicating that they represent a true increase in Hg loading to the environment. We argue that these represent Hg loading events associated with enhanced Hg emissions from large igneous province (LIP) events that are synchronous with the extinctions. The Hg anomalies are consistent across the NW margin of Pangea, indicating that widespread mercury loading occurred. While this provides utility as a chemostratigraphic marker the Hg spikes may also indicate loading of toxic metals to the environment, a contributing cause to the mass extinction events

Identification of a Marine Green Alga Percursaria percursa from Hypersaline Springs in the Middle of the North American Continent

The chlorophycean alga Percursaria percursa (Ulvaceae, Ulvales, Chlorophyceae), typical of marine inter-tidal zones, is reported for the first time from hypersaline springs located along the north-western shore of Lake Winnipegosis in Manitoba. Although not usually found inland, P. percursa is the dominant member of microbial mat communities that thrive in shallow pools at the outlets of hypersaline springs

Life Beneath Glacial Ice - Earth(!) Mars(?) Europa(?)

We are investigating a set of cold springs that deposit sulfur and carbonate minerals on the surface of a Canadian arctic glacier. The spring waters and mineral deposits contain microorganisms, as well as clear evidence that biological processes mediate subglacial chemistry, mineralogy, and isotope fractionation . The formation of native sulphur and associated deposits are related to bacterially mediated reduction and oxidation of sulphur below the glacier. A non-volcanic, topography driven geothermal system, harboring a microbiological community, operates in an extremely cold environment and discharges through solid ice. Microbial life can thus exist in isolated geothermal refuges despite long-term subfreezing surface conditions. Earth history includes several periods of essentially total glaciation. lee in the near subsurface of Mars may have discharged liquid water in the recent past Cracks in the ice crust of Europa have apparently allowed the release of water to the surface. Chemolithotrophic bacteria, such as those in the Canadian springs, could have survived beneath the ice of "Snowball Earth", and life forms with similar characteristics might exist beneath the ice of Mars or Europa. Discharges of water from such refuges may have brought to the surface living microbes, as well as longlasting chemical, mineralogical, and isotopic indications of subsurface life

An abrupt extinction in the Middle Permian (Capitanian) of the Boreal Realm (Spitsbergen) and its link to anoxia and acidification

The controversial Capitanian (Middle Permian, 262 Ma) extinction event is only known from equatorial latitudes, and consequently its global extent is poorly resolved. We demonstrate that there were two, severe extinctions amongst brachiopods in northern Boreal latitudes (Spitsbergen) in the Middle to Late Permian, separated by a recovery phase. New age dating of the Spitsbergen strata (belonging to the Kapp Starostin Formation), using strontium isotopes and d13C trends and comparison with better-dated sections in Greenland, suggests that the first crisis occurred in the Capitanian. This age assignment indicates that this Middle Permian extinction is manifested at higher latitudes. Redox proxies (pyrite framboids and trace metals) show that the Boreal crisis coincided with an intensification of oxygen depletion, implicating anoxia in the extinction scenario. The widespread and near-total loss of carbonates across the Boreal Realm also suggests a role for acidification in the crisis. The recovery interval saw the appearance of new brachiopod and bivalve taxa alongside survivors, and an increased mollusk dominance, resulting in an assemblage reminiscent of younger Mesozoic assemblages. The subsequent end-Permian mass extinction terminated this Late Permian radiation

Global warming leads to Early Triassic nutrient stress across northern Pangea

The largest extinction in Earth history, in the latest Permian, was followed throughout most of the Early Triassic by a prolonged period of ecologic recovery. What factors delayed biotic recovery are still under debate and partly revolve around impacts of global warming on primary marine productivity. We examined N isotope records from the Festningen section on Spitsbergen, Arctic Norway, to examine changes in nutrient availability through the Early to Middle Triassic along the northern margin of Pangea. Our results show progressive decline in N availability throughout the Griesbachian, leading to severe nutrient limitations through the remainder of the Early Triassic, until returning to a highly productive continental margin in Middle Triassic time. These results are consistent with other studies from northern and western Pangea and thus show regional nutrient limitations occurred in what should have been the main zone of marine primary productivity. Such nutrient limitation likely stressed primary production and consequently contributed to prolonged marine recovery. We suggest this was driven by high ocean temperatures depressing the marine nutricline

Tellurium in Late Permian-Early Triassic Sediments as a Proxy for Siberian Flood Basalt Volcanism

We measured the concentrations of trace elements in Late Permian to Early Triassic sediments from Spitsbergen. High mercury concentrations in sediments from the level of the Permo-Triassic Mass Extinction (PTME) at this location were previously attributed to the emplacement of the Siberian Traps Large Igneous Province and used to link the timing of volcanism with the record of environmental change and extinction in these sediments. We investigated the use of the moderately to highly volatile, siderophile elements Ni, Zn, Cd, Sb, Te, Re, and Tl as proxies for the intensity of Siberian volcanism. These trace elements, like Hg, have high concentrations in volcanic gas compared to crustal rocks. Tellurium is highly enriched at the PTME, and Te/Th ratios increase by a factor of ∼20 across the PTME, similar to the variation in Hg/total organic carbon (TOC) in the same samples. Te/Th and Hg/TOC values imply that Siberian volcanism initiated at the onset of the PTME, coincident with the start of the δ13Corganic excursion and abrupt warming. Based on Te and Hg, most Siberian volcanism occurred between the two phases of the PTME boundary (a period of less than 100 ky), but also continued into the Early Triassic. The duration of Siberian volcanism inferred from Te/Th and Hg/TOC is shorter than that indicated by recent high-precision U-Pb ages of Siberian intrusive and extrusive rocks. Te concentrations and Te/Th ratios in sediments represent a useful new proxy for volcanism, which can be used to link the marine sedimentary record with large volcanic events on land

Ultra-shallow-marine anoxia in an Early Triassic shallow-marine clastic ramp (Spitsbergen) and the suppression of benthic radiation

Lower Triassic marine strata in Spitsbergen accumulated on a mid-to-high latitude ramp in which high-energy foreshore and shoreface facies passed offshore into sheet sandstones of probable hyperpycnite origin. More distal facies include siltstones, shales and dolomitic limestones. Carbon isotope chemostratigraphy comparison allows improved age dating of the Boreal sections and shows a significant hiatus in the upper Spathian. Two major deepening events, in earliest Griesbachian and late Smithian time, are separated by shallowing-upwards trends that culminated in the Dienerian and Spathian substages. The redox record, revealed by changes in bioturbation, palaeoecology, pyrite framboid content and trace metal concentrations, shows anoxic phases alternating with intervals of better ventilation. Only Dienerian–early Smithian time witnessed persistent oxygenation that was sufficient to support a diverse benthic community. The most intensely anoxic, usually euxinic, conditions are best developed in offshore settings, but at times euxinia also developed in upper offshore settings where it is even recorded in hyperpycnite and storm-origin sandstone beds: an extraordinary facet of Spitsbergen's record. The euxinic phases do not track relative water depth changes. For example, the continuous shallowing upwards from the Griesbachian to lower Dienerian was witness to several euxinic phases separated by intervals of more oxic, bioturbated sediments. It is likely that the euxinia was controlled by climatic oscillations rather than intra-basinal factors. It remains to be seen if all the anoxic phases found in Spitsbergen are seen elsewhere, although the wide spread of anoxic facies in the Smithian/Spathian boundary interval is clearly a global event