Posts Tagged 'paleo'

« Previous Entries
Next Entries »

From holocene to anthropogenic impact: surpassing coral’s pH up-regulation capacity under ocean acidification

Published 1 January 2025 Science Closed
Tags: , , , , ,

Highlights

  • Coral calcifying fluid chemistry during the past ∼5500 years.
  • No clear responses of coral CF chemistry to pre-industrial climate shifts.
  • Declines in coral pHcf and [CO32−]cf during the CWP.
  • A pantropical compilation of δ11B-pHcf matches atmospheric CO2 since Mid-Holocene.
  • Limits of corals’ pHcf up-regulation to counteract ocean acidification.

Abstract

Corals’ regulation of internal calcifying fluid (CF or cf) chemistry is crucial for their extraordinary calcification capacity, endowing them with a certain ability to cope with environmental changes such as anthropogenic ocean acidification (OA) and warming. However, it remains unclear whether the impacts of these changes on corals have substantially surpassed their regulation capacity, particularly in comparison to the CF chemistry responses to natural climate variability with minor or no human perturbation. In this study, we reconstructed the pH, dissolved inorganic carbon, and carbonate ion concentrations in coral CF (pHcf, DICcf, and [CO32−]cf) during the Mid- to Late-Holocene, by analyzing the skeletal δ11B and B/Ca of 80 Porites spp. from eastern Hainan Island in the South China Sea (SCS). Our records indicate considerable inter-colony variations in CF chemistry, with maximum disparities reaching 0.18 units for pHcf and 1664 μmol/kg for DICcf. With this in mind, we found no clear responses of coral DICcf to the climate fluctuations during the past ∼5500 years, nor evident differences in pHcf and [CO32−]cf across pre-industrial natural epochs. However, pHcf and [CO32−]cf of modern corals have significantly declined compared to fossil corals. Further analyzes compiling global data on Porites spp. also confirm this pronounced pHcf decrease in modern corals, suggesting the limitations of pantropical corals to counteract OA by up-regulating pHcf. Importantly, these fossil and modern corals reveal a clear long-term pHcf descending trend parallel to atmospheric CO2 changes, supporting the reliability of coral δ11B in recording long-term changes in seawater pH (pHsw).

Continue reading ‘From holocene to anthropogenic impact: surpassing coral’s pH up-regulation capacity under ocean acidification’

Marine biological responses to abrupt climate change in deep time

Published 24 December 2024 Science Closed
Tags: , ,

Non-technical Summary
Paleobiology can offer diverse insights into how climate change has affected past species and ecosystems. Timely and important areas of research focus on the potential of paleobiology to contribute to solutions for climate impacts on natural ecosystems. But how far can past responses to abrupt climate change be generalized to derive predictions for the modern and future worlds? The long timescales over which biological responses are observed in the deep time past hamper the applicability of paleontological observations, but by how much? To address these questions, we review paleontological evidence for the impacts of geologically rapid climatic change. Fruitful avenues for future research lie in (1) characterizing the relationship between the magnitude of warming and extinction toll, (2) using physiology to bridge timescales, and (3) assessing the role of long-term climate history to predict the impact of short-term climate change. Identifying how consistent and robust paleontological signals are across timescales will help to make deep-time observations more useful for the modern world.

Abstract
Ancient changes in the biosphere, from organismic traits to wholesale ecosystem changes, can be aligned with climate forcing across the Phanerozoic. Clear examples of abrupt climate warming causing biodiversity crises are primarily found between the Permian and Paleogene periods. During these times, catastrophic events occurred, resembling the extreme climate scenarios projected for the near future. The paleobiologic literature around these events generally supports the hypothesis that abrupt climate change was a dominant trigger of extinction and/or ecological crisis. When climate change and climate history are considered, virtually all post-Paleozoic global biotic events can be confidently attributed to climatic change, with abrupt warming (hyperthermal events) leaving the most consistent fingerprint. The combined stress of deoxygenation and warming are sufficient to explain marine extinction patterns across most hyperthermal events. Although ocean acidification may have contributed, the direct role of pH on the extinction toll of organisms is not consistently demonstrated. Future research can enhance the correspondence between the magnitudes of climatic changes and their biological impacts, even though observed rates of change cannot currently be compared across different timescales. Mimicking multi-scale approaches in modern ecology, paleontological approaches to climate impact research will benefit from specifically targeting scaling relationships

Continue reading ‘Marine biological responses to abrupt climate change in deep time’

Rhodolith beds in a shifting world: a palaeontological perspective

Published 16 December 2024 Science Closed
Tags: , , ,

The occurrence of rhodolith beds in the stratigraphic record from the Cretaceous to the Pleistocene was analysed from published papers. Most data refer to low-mid latitude records of rhodolith beds described in the Tethyan-Paratethyan-Mediterranean domain. The first putative rhodolith beds are from Albian (uppermost Lower Cretaceous) deposits. These rhodolith beds are made up mostly of unattached loose branching corallines as well as of nodular structures. From the Coniacian (Upper Cretaceous) to the Langhian (Middle Miocene), abundance of rhodolith beds shows a generally increasing fluctuating trend with two significant expansions in the Priabonian (late Eocene) and during the Aquitanian-Langhian (Early-Middle Miocene). After the Langhian maximum, rhodolith beds sharply declined to a minimum in the Zanclean (Early Pliocene). During the Pleistocene, they recovered to values similar to those reached in the Langhian. The general increase in rhodolith beds up the Langhian maximum correlates well with global temperature and pCO2 declines and with an ocean pH increase. The tectonic activity leading to important palaeogeographic changes in the Tethyan-Parathetyan-Mediterranean realm might account for the Serravallian-Zanclean downfall of rhodolith-dominated deposits. The Cretaceous-Pleistocene record of rhodolith beds shows that these ecosystems withstood successfully a highly changing world. The rapid acclimation of particular taxa to environmental changes and the variable reaction of taxa distributed at different water depths can be crucial to understand their success. In this regard, it would be interesting to analyse how different taxa in modern deep rhodolith beds respond to changing oceanic conditions.

Continue reading ‘Rhodolith beds in a shifting world: a palaeontological perspective’

Paleo-atmospheric CO2 reconstructions from deep-ocean sediments

Published 22 November 2024 Science Closed
Tags: ,

Biological remains in ocean sediments document the remarkable history of atmospheric CO2 and its fundamental control on Earth’s climate. Higher resolution studies are needed to better understand the short-term processes that inform imminent anthropogenic climate changes.

Human activities have increased the concentration of carbon dioxide in our atmosphere from 280 ppm before industrialization to 424 parts per millin (ppm) in 2024. Without reductions in emissions, CO2 is projected to rise to >800 ppm by the end of this century, driving warming well in excess of the 1°C already recorded (IPCC 2021). How warm it will get can be projected by complex numerical climate models whose skills are validated using the detailed relationship between atmospheric CO2 and global climate in Earth’s history. Instrumental measurements of CO2 have been collected since 1958 (Lan et al. 2024), and ancient air trapped in Antarctic ice documents Earth’s atmospheric composition over hundreds of thousands of years prior (Bereiter et al. 2015; Yan et al. 2019). However, CO2 during this geologically recent past was generally lower than today, and global temperatures colder. Much warmer intervals occurred in the distant past, but because the atmosphere of that time cannot be sampled directly, paleo-CO2 reconstructions rely on indirect proxies preserved in the sedimentary record.

Reconstructing CO2 from ocean sediments

Deep-sea sediments are key to paleoreconstructions; they are globally distributed and gradually accumulate biogenic and inorganic proxy materials over tens of millions of years, thereby providing excellent age stratigraphy. Uniquely useful in documenting past surface-ocean temperatures and the partial pressure of CO2 (PCO2) are the mineralized and organic remains left behind by organisms that once inhabited the ancient surface ocean. This is because gas exchange at the air-sea interface drives PCO2 in seawater towards equilibrium with PCO2 in the atmosphere. Once absorbed in seawater, CO2 reacts with water (H2O) and forms a suite of carbon species whose abundances are controlled by well-understood chemical equilibrium reactions that also determine seawater acidity (i.e. pH).

Not all oceanic regions are appropriate for paleo-CO2 studies because vigorous photosynthesis can diminish sea-surface CO2 while upwelling of deeper waters delivers respired CO2 to the surface, disturbing the air–sea equilibrium. Therefore, paleo-CO2 studies focus on off-shore regions such as subtropical gyres, where photosynthesis is weak and downwelling of surface waters allows air–sea equilibrium to be established.

There are two main frameworks for marine-based CO2 reconstructions: the stable carbon isotopic composition of organic phytoplankton (δ13Cphytoplankton) remains and the boron isotopic composition (δ11B) of fossilized CaCO3 shells. Briefly, the δ13Cphytoplankton proxy assumes CO2 passively diffuses into an algae cell, and the CO2-fixing enzyme RuBisCo preferentially takes up 12C over 13C during oxygenic photosynthesis. When CO2 is abundant, 12C is preferentially incorporated into organic matter (resulting in relatively lower δ13Cphytoplankton). The opposite occurs at low CO2 (Fig. 1). Although first applied to bulk organic matter (Popp et al. 1989), selective preservation and mixed organic sources imposed problems. These challenges have been resolved by using: (1) specific compounds produced by select algae (e.g. alkenones from Haptophytes); (2) specific compounds produced by the broader phytoplankton community (e.g. chlorophyll), enabling greater spatial and temporal diversity of reconstructions; and (3) organic carbon bound to mineral or organic exteriors of e.g. coccolithophores, diatoms or dinoflagellates. The detailed systematics of these approaches are reviewed in Hollis et al. (2019).

Figure 1: Basic systematics of the two marine CO2 proxies. Fossil organic compounds and CaCO3 shells are preserved in layered ocean sediments that can be extracted by deep-ocean drilling

…

Continue reading ‘Paleo-atmospheric CO2 reconstructions from deep-ocean sediments’

Coupled decline in ocean pH and carbonate saturation during the Palaeocene–Eocene Thermal Maximum

Published 20 November 2024 Science Closed
Tags: , , , ,

The Palaeocene–Eocene Thermal Maximum, a climate event 56 million years ago, was characterized by rapid carbon release and extensive ocean acidification. However, our understanding of acidification and the evolution of ocean saturation states continues to be hindered by considerable uncertainties, primarily stemming from the limited availability of proxy data. Under such conditions, data assimilation allows for an internally consistent assessment of atmospheric CO2 changes, ocean acidification and carbonate saturation state during this period. Here, we present a reconstruction of the Palaeocene–Eocene Thermal Maximum carbon cycle perturbation by assimilating seafloor sediment CaCO3 and sea surface temperature proxy data with simulations from an Earth system model, which includes a comprehensive carbonate system. Our reconstructions indicate a substantial increase in atmospheric CO2 from 890 ppm (95% credible interval: 680–1,170 ppm) to 1,980 ppm (1,680–2,280 ppm), coupled with a notable decline in pH (0.46 units, ranging from 0.31 to 0.63 units) and surface-water calcite saturation state, decreasing from 10.2 (7.5–12.8) in the pre-event period to 3.8 (2.8–5.1) during the thermal maximum. Carbonate undersaturation intensified substantially in high-latitude surface waters during the Palaeocene–Eocene Thermal Maximum, paralleling the current decline in Arctic aragonite saturation driven by anthropogenic CO2 emissions.

Continue reading ‘Coupled decline in ocean pH and carbonate saturation during the Palaeocene–Eocene Thermal Maximum’

Correlation of sub-centennial-scale pulses of initial Central Atlantic Magmatic Province lavas and the end-Triassic extinctions

Published 30 October 2024 Science Closed
Tags:

Significance

During the initial phase of eruptions, Central Atlantic Magmatic Province (CAMP) basalts spewed more than 500 times the amount of sulfur released during the Laki historic eruption in Iceland. The repeated injections of sulfate aerosols, constrained by paleosecular variation data, occurred in rapid succession. The resulting severe [albedo-induced] volcanic winters may have been the proximal cause for the well-resolved end-Triassic mass extinction in the continental realm. However, in the less temporally constrained marine realm, longer-term cumulative release of carbon dioxide from CAMP eruptive and intrusive activity may have played an important albeit somewhat diachronous role in the extinctions through ocean acidification and longer-term warming.

Abstract

The end-Triassic extinction (ETE) on land was synchronous with the initial lavas of the Central Atlantic Magmatic Province (CAMP) and occurred just after the brief 26 thousand year (kyr) reverse geomagnetic polarity Chron E23r that can be used for global correlation. Lava-by-lava paleomagnetic secular variation data, previously reported from Morocco and northeastern United States combined with our data for the North Mountain Basalt from the Fundy Basin of Canada show that the initial phase of CAMP volcanism occurred in only five directional groups or pulses each occupying less than a century. The first four directional groups occur during a ~40 kyr period based on available astrochronology and U-Pb geochronology. The coincidence of the initial major pulse of CAMP volcanism with the ETE points to short-lived volcanic winters albedo-induced by sulfate aerosols as a plausible key agent of the extinctions in the tropical continental realm, whereas looser correlations allow prolonged CO2 emissions to contribute to more long-ranging effects in the marine realm via ocean acidification and longer-term warming.

Continue reading ‘Correlation of sub-centennial-scale pulses of initial Central Atlantic Magmatic Province lavas and the end-Triassic extinctions’

Low sensitivity of a heavily-calcified coccolithophore under increasing CO2: the case study of Helicosphaera carteri

Published 17 October 2024 Science Closed
Tags: , , , , , , , ,

Studies on CO2 effects on coccolithophores, unicellular calcifying phytoplankton, show species-specific responses, although only less than 5 % of the ~280 living species have been tested so far. Helicosphaera carteri significantly contributes to carbon fluxes and CaCO3 storage due to its size and high calcite production. Despite its importance, few studies have examined H. carteri under experimental conditions, and only one has addressed the effects of rising CO2/decreasing pH. Being H. carteri a large-sized, obligated calcifier species, an important aspect to understand is how changes in seawater carbonate chemistry may affect its morphology. It has already been suggested for other coccolithophores species, that the presence of malformed coccoliths may represent a disadvantage for these organisms. Moreover, an alteration in coccolith morphology may affect their contribution to CaCO3 sedimentation and ballasting. As for H. carteri, it has also been suggested that due to its high PIC:POC ratio, the species could show a high-sensitivity to CO2 rise. In this study, we investigate for the first time whether high pCO2/low pH does affect the morphology of H. carteri coccoliths, by culturing this species under pre-industrial CO2 levels (~295 µatm) and ~600 µatm, i.e., the SSP 2-4.5 scenario for 2100 (IPCC, 2021). We also analyzed cellular PIC and POC quotas using morphometric data, roundness, and protoplast and coccosphere size to observe the pCO2 influence on the calcification and photosynthesis ratio.

Our results indicate that H. carteri morphology is only slightly affected by increasing CO2, in contrast to other heavily calcified species. Helicosphaera carteri protoplast and coccosphere shapes did not vary with changes in CO2, indicating unaltered general health. The low PIC:POC ratio found in this work for H. carteri compared to ratios previously measured in the same strain under different experimental conditions, and compared to other highly-calcified species, could explain the observed low sensitivity of H. carteri to CO2. Moreover, the observation of a stable ratio between calcification and photosynthesis in H. carteri under increasing CO2 might suggest a constant contribution to the rain ratio under climate change. However, further studies comparing experimental and field data from past ocean acidification events will be required to confirm the conclusions drawn here.

Continue reading ‘Low sensitivity of a heavily-calcified coccolithophore under increasing CO2: the case study of Helicosphaera carteri’

Impact of the Jenkyns Event on shallow-marine carbonates and coeval emerged paleoenvironments (the Plitvice Lakes region, Croatia)

Published 1 October 2024 Science Closed
Tags:

Highlights

  • Peritidal record of the Jenkyns Event.
  • Jenkyns Event confirmed with palyno-, chemo and microbiofacies stratigraphy.
  • Evidence for subaerial exposure within the NCIE interval.
  • Peritidal carbonate factory of the AdCP remained resilient in the Jenkyns Event.
  • Local synsedimentary tectonics and eustatic changes superimposed on global trends.

Abstract

Early Jurassic (late Pliensbachian–early Toarcian) Large Igneous Province (LIP) magmatism affected the entire ocean-atmosphere system culminating in a cascade of paleoenvironmental perturbations known as the Jenkyns Event which globally impacted marine, transitional and terrestrial paleoenvironments. Carbonate platforms at low latitudes in the Western Tethys realm drowned or shifted to non-skeletal production during the early Toarcian due to sea level rise, global warming, and ocean acidification. Unlike deep-marine deposits, shallow-marine carbonates present a challenge in defining global geochemical signals due to common diagenetic modifications. An integrated dataset including δ13Ccarb and δ18Ocarb, TOC, biomicrofacies, SEM, XRD, and palynological study of two stratigraphic successions in the Plitvice Lake region, Bjelopolje (BJ) and Plitvice Spring (PS), in Croatia, provides an overview of the paleoenvironmental evolution and lateral facies changes in a peritidal setting during the Early Jurassic on the Adriatic Carbonate Platform (AdCP). The investigated stratigraphic succession starts with upper Pliensbachian, peloid-ooid-bioclastic grainstones alternating with fenestral and massive mudstones overlain by lower Toarcian, lagoonal, bioturbated, “spotted” limestones with horizons indicative of short-lived subaerial emergence during the early Toarcian. A negative excursion in δ13Ccarb, foraminifer assemblages, and the predominance of Classopollis pollen within the “spotted” limestones marks the stratigraphic position of the Jenkyns Event. Global-scale events (sea level variation, climate change, C-cycle perturbation, anoxia) operated simultaneously with local to regional synsedimentary tectonics and eustatic movements that preserved the AdCP carbonate factory from collapse or drowning but resulted in pronounced facies differentiation on the shallow-marine carbonate platforms.

Continue reading ‘Impact of the Jenkyns Event on shallow-marine carbonates and coeval emerged paleoenvironments (the Plitvice Lakes region, Croatia)’

Boron isotopic compositions of middle Miocene to recent shallow-water carbonates from the South China Sea: assessing diagenetic effects and implications for paleoclimate changes

Published 23 August 2024 Science Closed
Tags: , , ,

Highlights

  • A high-resolution δ11B dataset for carbonates from the South China Sea.
  • Limestone without strong recrystallization can record ambient seawater pH.
  • Diagenetic processes do not affect δ11B records of marine limestone.
  • Dolomites should be excluded as archives for seawater δ11B.

Abstract

The partial pressure of atmospheric CO2 (pCO2) significantly influences global climate change and biological evolution through geological history. Boron isotopic composition (δ11B) in carbonates has been used to reconstruct the paleo-pH of seawater, providing insight into atmospheric pCO2 levels. However, the fidelity of δ11B records in marine carbonates due to diagenesis remains uncertain. Here, to understand how diagenetic processes influence B isotopic records in marine carbonates, we examined B concentrations and δ11B values of modern corals (from Hainan Island), unconsolidated shallow pushcores (Jiuzhang A and Jiuzhang B from Nansha Islands, South China Sea), and a long drillcore (XK-1 from Xisha Islands, South China Sea) covering the Late Miocene to Holocene periods. Our coral samples show a uniform δ11B range (20.16 ± 0.85%), consistent with previously published values for modern corals in other open oceans. The δ11B values of the unlithified carbonate sediments from Jiuzhang A and B pushcores vary within a narrow range (18.70 ± 0.84%), yielding pH and CO2 concentrations consistent with the range between modern and pre-industrial values. Since we did not observe any statistically significant covariations between traditionally established diagenetic proxies (such as δ13C, δ18O, Mn/Sr, and Al/Ca) and δ11B values for non-dolomitized samples in the XK-1 drillcore, we suggest that δ11B values of bulk limestones are not significantly affected by typical diagenesis (meteoric, mixed-diagenetic, and marine diagenetic processes), likely due to limited post-depositional recrystallization of our study carbonates. In contrast, dolomitization significantly decreases δ11B values of bulk carbonates, rendering dolomites unsuitable as archives for reconstructing seawater δ11Bborate values. Our study supports that marine limestone with limited recrystallization or dolomitization have the potential to record ambient seawater pH values with high resolution. The established secular seawater pH variations based on XK-1 δ11B records provide information about ocean acidification over the past 5.1 million years.

Continue reading ‘Boron isotopic compositions of middle Miocene to recent shallow-water carbonates from the South China Sea: assessing diagenetic effects and implications for paleoclimate changes’

Decadal timescale evolution of coral islands: insights from Lakshadweep Archipelago

Published 29 July 2024 Science Closed
Tags: , , ,

Low–lying coral islands are susceptible to rising sea levels and climate change, posing risks to island habitability over the next century. The decadal timescale evolution of the islands can provide an understanding of the governing controls of change and island response. This study investigates variations in the shoreline morphology of the Lakshadweep coral islands (Northern Indian Ocean/Arabian Sea) using satellite datasets (2003–2022; CNES/Airbus;0.3m – 0.7m resolution) and sedimentological data. Of the thirty islands (ten inhabited), six islands (Bangaram, Thinnakara, Suheli, Minicoy, Androth and Bitra) have been studied. Most of these islands are less than 1 km2 in size except Androth and Minicoy (>4 km2). While the data is discontinuous for the islands due to cloud obscuring, the shoreline morphology depicts variations for all the islands’ studied, irrespective of habitation and size. Larger islands have undergone consistent erosion since 2007 (total land loss is approximately 3 – 5% cumulatively). Smaller islands have undergone lateral migration, with sediment erosion usually along the southern edge and sediment migration and accumulation northwards, however, overall, their size remains consistently stable. The migration of sediments is observed only from 2007–2017, which coincides with severe El–Nino Southern Oscillation (ENSO) and low amplitude positive Indian Ocean Dipole (IOD) events. Furthermore, sedimentological analysis along Bangaram’s (small island) accreting margin reveals unconsolidated bio-detrital grainstones with predominant sand-sized fractions (2 – 0.25mm). Corals (43%), molluscs (33%), forams (13%), and algae (8%) are the major sediment producers (with 3% unidentified bioclasts). The ongoing climate warming and ocean acidification will influence the carbonate sediment budget in addition to the changing hydrodynamics owing to monsoons, cyclones, and coupled ocean-atmospheric regional phenomenon, altering the sediment production, transport and accumulation on these islands. Furthermore, rising sea levels and consequent erosion by wave action might lead to rapid drowning in the next few centuries. Our study identifies the current status of the island size variability in the Lakshadweep Archipelago and how site-specific and global factors influence them, thus providing insights into assessing the habitability within these low-lying coral islands.

Continue reading ‘Decadal timescale evolution of coral islands: insights from Lakshadweep Archipelago’

Non-traditional stable metal and metalloid isotopes and their potential applications in earth, ocean, and environmental sciences

Published 26 July 2024 Science Closed
Tags: , ,

Highlights

  • Recent advancement has revolutionized the field of “Non-Traditional” isotopes.
  • Non-traditional isotopes provide useful tool in diverse fields.
  • Highlight challenges and perspectives of non-traditional isotopes.

Abstract

Recent technological advancement has revolutionized the field of non-traditional stable metal and metalloid isotopes for their wide applications for the study of earth surface processes, reconstructing past oceanic environments, tracing contaminants, and biomedical investigations. Beyond the conventional stable isotopes (H, C, O, N, S), this field has led to a wide exploration of stable isotopes (e.g., Li, B, Mg, Si, Ca, K, V, Cr, Ni, Fe, Cu, Zn, Sr, Mo, Cd, Ba, Hg, U) and their potential applications. This review delves into the applications of stable metal and metalloid isotopes as an important tool for tracing sources and elucidating various processes within the realm of earth, ocean, and environmental studies. The fundamental concept of mass-dependent and -independent isotope fractionations are introduced firstly; the selected “emerging” stable isotopes like Li isotopes (δ7Li), B isotopes (δ11B), and Mo isotopes (δ98Mo) are discussed; their applications as a proxy for earth surface processes, paleo-ocean pH, and paleo-redox conditions in oceans are highlighted respectively; various measurement techniques and their advantages/disadvantages are presented, including chemical extractions of elements and their isotope measurements using a Multi-Collector Inductively Coupled Plasma Mass Spectrometer (MC-ICPMS). Finally, this article highlights the caveats and limitations, challenges, and scopes for future research of the stable isotopes.

Continue reading ‘Non-traditional stable metal and metalloid isotopes and their potential applications in earth, ocean, and environmental sciences’

Carbonate uranium isotopes record global expansion of marine anoxia during the Toarcian Oceanic Anoxic Event

Published 22 July 2024 Science Closed
Tags: , ,

Significance

A significant negative δ238U excursion (~0.4‰) starting just prior to the onset of the negative carbon isotope excursion within the Toarcian Oceanic Anoxic Event (T-OAE) has been recorded, followed by a long-lived recovery of δ238U values. This excursion represents a global expansion of marine anoxia of ~6 to 8% of the global seafloor during the peak of the T-OAE, which represents 28 to 38 times the extent of anoxia in the modern ocean. When compared with estimates of seafloor anoxic area for other CO2-driven global anoxic events, the T-OAE was the second-largest anoxic event of at least the last 300 My. As such, the T-OAE represents a powerful analog for future anthropogenic ocean deoxygenation.

Abstract

The Toarcian Oceanic Anoxic Event (T-OAE; ~183 Mya) was a globally significant carbon-cycle perturbation linked to widespread deposition of organic-rich sediments, massive volcanic CO2 release, marine faunal extinction, sea-level rise, a crisis in carbonate production related to ocean acidification, and elevated seawater temperatures. Despite recognition of the T-OAE as a potential analog for future ocean deoxygenation, current knowledge on the severity of global ocean anoxia is limited largely to studies of the trace element and isotopic composition of black shales, which are commonly affected by local processes. Here, we present the first carbonate-based uranium isotope (δ238U) record of the T-OAE from open marine platform limestones of the southeastern Tethys Ocean as a proxy for global seawater redox conditions. A significant negative δ238U excursion (~0.4‰) is recorded just prior to the onset of the negative carbon isotope excursion comprised within the T-OAE, followed by a long-lived recovery of δ238U values, thus confirming that the T-OAE represents a global expansion of marine anoxia. Using a Bayesian inverse isotopic mass balance model, we estimate that anoxic waters covered ~6 to 8% of the global seafloor during the peak of the T-OAE, which represents 28 to 38 times the extent of anoxia in the modern ocean. These data, combined with δ238U-based estimates of seafloor anoxic area for other CO2-driven Phanerozoic OAEs, suggest a common response of ocean anoxia to carbon release, thus improving prediction of future anthropogenically induced ocean deoxygenation.

Continue reading ‘Carbonate uranium isotopes record global expansion of marine anoxia during the Toarcian Oceanic Anoxic Event’

Geochemistry of cherts from the northern Jiangxi region, South China: implication for paleoenvironment

Published 12 July 2024 Science Closed
Tags: ,

Highlights

  • Mineral composition, trace and REEs of the PYC and HT cherts were investigated.
  • The PYC and HT cherts primarily originated from direct seawater precipitation, with the PYC siliceous rocks exhibiting some weak hydrothermal evidence.
  • There are significant shifts in redox conditions in the E-C transition.

Abstract

The extensive bedded cherts deposited during the Ediacaran–Cambrian (E–C) transition period play a crucial role in understanding the geological evolution of this period, yet the origin of these cherts remains disputed. Here, we present new geochemical data for cherts of the Piyuancun (PYC) Formation deposited during the Late Ediacaran and the Hetang (HT) Formation deposited during the Early Cambrian in northern Jiangxi region, Lower Yangtze region, South China. The PYC cherts contain a small amount of monaxons sponge spicules and radiolarian fragments, while the HT cherts lack siliceous organism evidence. Major and trace element analysis, coupled with discriminant diagrams, indicate a possible shift in redox conditions of seawater during the E–C transition in the northern Jiangxi region. The shift suggests a change from weakly–moderately restricted euxinic conditions to strongly restricted euxinic conditions. Furthermore, the location of both cherts are distant from the source area of siliceous organisms. Fossil evidence, as well as the values of Fe/Ti and Fe/(Mn+Ti), Eu anomalies, Post-Archean Australian Shale (PAAS) normalized REE+Y patterns, and various discriminant diagrams, support the conclusion that the PYC and HT cherts originated primarily from direct seawater precipitation, with the PYC cherts exhibiting weak hydrothermal evidence. Upwelling contributes to the formation of HT cherts and organic matter (OM) accumulation. Ocean acidification, triggered by OM degradation and biodegradation processes during the E–C transition period, leads to the extensive silica precipitation and preservation. These results enhance our understanding of the geological processes during the E–C transition.

Continue reading ‘Geochemistry of cherts from the northern Jiangxi region, South China: implication for paleoenvironment’

A novel multi-scale μCT characterization method to quantify biogenic carbonate production

Published 5 July 2024 Science Closed
Tags: , , , ,

Highlights

  • Multi-scale µCT and SEM analysis used to characterize biogenic calcareous nodules.
  • µCT and machine learning based image analysis coupled to compute volume fractions.
  • Taxa-specific volumetric quantification obtained for biogenic carbonate nodule.
  • CCA and Encrusting Foraminifers are key contributors to Red Sea carbonate budget.

Abstract

Biogenic carbonate structures such as rhodoliths and for-algal nodules are a significant part of marine carbonate production and are being increasingly used as paleoenvironmental indicators for predictive modeling of the global carbon cycle and ocean acidification research. However, traditional methods to characterize and quantify the carbonate production of biogenic nodules are typically limited to two-dimensional analysis using optical and electron microscopy. While micro-computed tomography (µCT) is an excellent tool for 3D analysis of inner structures of geomaterials, the trade-off between sample size and image resolution is often a limiting factor. In this study, we address these challenges by using a novel multi-scale µCT image analysis methodology combined with electron microscopy, to visualize and quantify the carbonate volumes in a biogenic calcareous nodule. We applied our methodology to a foraminiferal algal nodule collected from the Red Sea along the coast of NEOM, Saudi Arabia. Integrated µCT and SEM image analyses revealed the main biogenic carbonate components of this nodule to be encrusting foraminifera (EF) and crustose coralline algae (CCA). We developed a multi-scale µCT analysis approach for this study, involving a hybrid thresholding and machine-learning based image segmentation. We utilized a high resolution µCT scan from the sample as a ground-truth to improve the segmentation of the lower resolution full volume µCT scan which provided reliable volumetric quantification of the EF and CCA layers. Together, the EF and CCA layers contribute to approximately 65.5 % of the studied FAN volume, corresponding to 69.01 cm3 and 73.32 cm3 respectively, and the rest is comprised of sediment infill, voids and other minor components. Moreover, volumetric quantification results in conjunction with CT density values, indicate that the CCA layers are associated with the highest amount of carbonate production within this for-algal nodule. The methodology developed for this study is suitable for analyzing biogenic carbonate structures for a wide array of applications including quantification of carbonate production and studying the impact of ocean acidification on skeletal structures of marine calcifying organisms. In particular, the hybrid µCT image analysis we adopted in this study proved to be advantageous for the analysis of biogenic structures in which the textures and components of the internal layers are distinctly visible despite having an overlap in the range of CT density values.

Continue reading ‘A novel multi-scale μCT characterization method to quantify biogenic carbonate production’

Ocean acidification in the tropical Indian Ocean over the past 37 years: insights from 𝛿11B and B/Ca records in a Maldives coral

Published 1 July 2024 Science Closed
Tags: , , , , , , , ,

Highlights

  • This is the first coral’s carbonate chemistry record in the tropical Indian Ocean.
  • Porites calcification pH is sensitive to ocean acidification, but the transfer function to seawater pH needs re-evaluation.
  • A different internal energy/dissolved inorganic carbon (DIC) supply might explain the lower [DIC] CF observed in Maldives corals.
  • Data from a wider geographic range is required to constrain the impacts of ocean acidification on corals.

Abstract

Boron isotopes (𝛿11B) in coral skeletons of Porites have been widely applied to reconstruct past seawater pH (pHSW) on decadal to centennial timescales. However, due to biological regulation within corals, an additional transfer function is required to estimate ambient seawater chemistry during the skeleton growth under the calcification site fluid pH. Temperature may also interfere with coral calcification fluid pH (pHCF) due to changes in kinetics of coral aragonite precipitation, or buffering capacity in coral calcification fluid. To decipher how coral Porites adjusts pHCF in response to pHSW from complex environmental controls, long-term records from sites with least fluctuations in environmental conditions other than pHSW are essential. Here we present a 37-year record of coral 𝛿11B and B/Ca ratios derived from a coral core collected from southern Maldives, the tropical Indian Ocean. Our results show no clear seasonality in the coral 𝛿11B and B/Ca ratios between monsoons, but a long-term decline in coral pHCF is evident across the entire record. When applying different existing transfer functions, we also observe discrepancies among the calculated pHCF values, model results and short-term instrumental data. Calculated calcification fluid dissolved inorganic carbon concentration ([DIC]CF) values are relatively low compared to literature, suggesting that coral calcification fluid carbonate chemistry may be under different levels of control, even within the same coral taxa. Thus, coral records from a wider geographic range are required to better quantify coral response to ocean acidification, and our results can serve as a baseline for future comparisons.

Continue reading ‘Ocean acidification in the tropical Indian Ocean over the past 37 years: insights from 𝛿11B and B/Ca records in a Maldives coral’

Taphonomy and aleoecology of lycoptera: a case study from the lower jehol group in Western Liaoning, Northeastern China

Published 27 June 2024 Science Closed
Tags: , , , , , ,

Taphonomy and paleoecology (biological behavior) of the Early Cretaceous fish fossils are poorly described. This study reports for the first time a detailed taphonomical and paleoecological study on Lycoptera in the Mesozoic strata of western Liaoning Province, NE China. The XRD analysis shows that gismondine is the dominant clay minerals that could have contributed to the preservation of Lycoptera fossils and microbial mat fragments in the fossil-bearing horizon. Gismondine may have formed under volcanism-related hydrothermal regime that was transformed from crystal and lithic fragments. The μ-XRF imaging analysis shows a dominant chemical composition of Al, Si, P, S, Rh, K, Ca, Ti, C, Cr, Mn, Fe, Ni, among which P, Ca, C and S are enriched in the fish skeleton in comparison to the matrix. This suggests a dominant apatite composition for the fish skeleton. Hydrothermal influence did not smear off these organic signals probably because of protection of gismondine. The coexistance of C and S with Ni is assumed to represent recovered primary productivity following volcanic explosions and toxic gas emissions. The head of juvenile fish stays close to the body of adult fish. Pending further discoveries, such phenomenon is interpreted to suggest that adult fish actively protected juvenile fish in the presence of environmental pressures such as anoxia and deterioration of water quality induced by volcanism. Ocean acidification and hypoxia in association with volcanism created a harmful environment causing mass extinction of fish. The adult Lycoptera protected their juveniles by its body at the moment before death. Such biological behavior will be increasingly reported given the wide occurrence of Lycoptera in Mesozoic strata.

Continue reading ‘Taphonomy and aleoecology of lycoptera: a case study from the lower jehol group in Western Liaoning, Northeastern China’

Patterns of extinction and recovery across the Triassic–Jurassic Boundary interval in three resilient Southern Tethyan carbonate platforms

Published 26 June 2024 Science Closed
Tags: ,

Highlights

  • Facies, biostratigraphy and δ13C of three TJB carbonate platform sections.
  • No evidence of drowning or gaps across the TJB in S-Tethys carbonate platforms.
  • The extinction of Rhaetian taxa postdates the initial CIE.
  • Pre-ETE assemblages are diverse and dominated by aragonitic biocalcifiers.
  • Microbially-mediated CaCO3 precipitation dominates in the post-ETE interval.

Abstract

During the end-Triassic extinction (ETE), carbonate platform biocalcifiers suffered high extinction rates that have been linked to volcanically-induced global changes in climate and carbon cycle. Most studies have been focused on the classical sections of the Northern Calcareous Alps (NCA, Austria) and Lombardy Basin (Italy), where the extinction of the aragonitic Dachstein-type biota (involutinid foraminifera and megalodontid bivalves) coincides with the demise of the carbonate platform and with the initial negative carbon isotope excursion (CIE) of the reference sections for the Triassic/Jurassic Boundary (TJB).

In this study, we present a detailed facies analysis, bio- and carbon-isotope stratigraphy of three Southern Tethyan carbonate platform sections, Mt. Messapion (Greece), Valle Agricola and Mt. Sparagio (southern Italy) that instead show persisting carbonate productivity across the TJB and potentially preserve the most detailed record of timing and patterns of the ETE in these ecosystems.

In the studied sections, the disappearance of the Dachstein-type biota is observed within a positive δ13Ccarb excursion that, according to our study, correlates with that documented in the Schattwald beds (NCA) and Malanotte Fm (Lombardy Basin) above the initial CIE. This level represents the true extinction of the Dachstein-type biota, while the disappearance in Northern Tethyan represents a pseudoextinction coinciding with the carbonate platform demise. Above the ETE, most Tethyan carbonate platform sections are characterized either by microbial laminites or ooid and oncoid limestones and low-diversity associations.

This study reveals a possible paleogeographic and/or latitudinal control on the response of biocalcifiers and carbonate platform ecosystems during the ETE. The Dachstein-type biota was initially more resilient in Southern Tethys, but probably failed to survive prolonged stress. Despite extinctions, Southern Tethyan carbonate platforms adapted to environmental disturbances through a shift from the dominant carbonate production style from aragonitic biocalcification to chemical and microbially-mediated CaCO3 precipitation. The ecosystem recovery was slow and aragonitic biocalcifiers (dasycladacean algae) reappeared during the early Sinemurian.

Continue reading ‘Patterns of extinction and recovery across the Triassic–Jurassic Boundary interval in three resilient Southern Tethyan carbonate platforms’

Thermal and nutrient stress drove Permian-Triassic shallow marine extinctions

Published 17 May 2024 Science Closed
Tags: , , ,

Impact Statement: What are the biggest consequences of climate change for marine ecosystems? Is it deoxygenation, thermal stress, ocean acidification, or any combination thereof? The Permian-Triassic climate crisis was an episode of severe and rapid climate warming with similarities to the worst-case projected scenarios for the near future. To better understand which consequences of this climate event led to one of the most severe biodiversity crisis ever, we implemented a novel approach of statistically integrating high-resolution fossil data with high-resolution geochemical data. Our results demonstrate that for equatorial, marine ecosystems, oxygen isotope (temperature proxy) and cadmium isotope (primary productivity proxy) dynamics best explain the marine extinction. This suggests that the biggest threats to past and modern biodiversity in these settings are the impacts of thermal and nutrient stress, as well as associated trophic knock-on effects.

Abstract: The Permian-Triassic climate crisis can provide key insights into the potential impact of horizon threats to modern-day biodiversity. This crisis coincides with the same extensive environmental changes that threaten modern marine ecosystems (i.e., thermal stress, deoxygenation and ocean acidification), but the primary drivers of extinction are currently unknown. To understand which factors caused extinctions, we conducted a data analysis to quantify the relationship (anomalies, state-shifts and trends) between geochemical proxies and the fossil record at the most intensively studied locality for this event, the Meishan section, China. We found that δ18O apatite (paleotemperature proxy) and δ 32 114/110Cd (primary productivity proxy) best explain changes in species diversity and species composition in Meishan’s paleoequatorial setting. These findings suggest that the physiological stresses induced by ocean warming and nutrient availability played a predominant role in driving equatorial marine extinctions during the Permian-Triassic event. This research enhances our understanding of the interplay between environmental changes and extinction dynamics during a past climate crisis, presenting an outlook for extinction threats in the worst-case “Shared Socioeconomic Pathways (SSP5-8.5) scenario.

Continue reading ‘Thermal and nutrient stress drove Permian-Triassic shallow marine extinctions’

Ideas and perspectives: human impacts alter the marine fossil record

Published 9 May 2024 Science Closed
Tags: ,

The youngest fossil record is a crucial source of data documenting the recent history of marine ecosystems and their long-term alteration by humans. However, human activities that reshape communities and habitats also alter sedimentary and biological processes that control the formation of the sedimentary archives recording those impacts. These diverse physical, geochemical, and biological disturbances include changes in sediment fluxes due to the alteration of alluvial and coastal landscapes, seabed disturbance by bottom trawling and ship traffic, ocean acidification and deoxygenation, removal of native species, and introduction of invasive ecosystem engineers. These novel processes modify sedimentation rates, the depth and intensity of sediment mixing, the pore-water saturation state, and the preservation potential of skeletal remains – the parameters controlling the completeness and spatiotemporal resolution of the fossil record. We argue that humans have become a major force transforming the nature of the marine fossil record in ways that can both impede and improve our ability to reconstruct past ecological and climate dynamics. A better understanding of the feedback between human impacts on ecosystem processes and their preservation in the marine fossil record offers new research opportunities and novel tools for interpreting geohistorical archives of the ongoing anthropogenic transformation of the coastal ocean.

Continue reading ‘Ideas and perspectives: human impacts alter the marine fossil record’

Sea surface acidification events in the Andaman Sea associated with the last Toba volcanic activity

Published 7 May 2024 Science Closed
Tags: , , ,

Highlights

  • High resolution reconstruction of surface seawater pH using boron isotopes.
  • Toba volcano impacted the surface seawater chemistry of the Andaman Sea.
  • Episodes of surface seawater acidification were observed in the Andaman Sea during volcanic avtivity of Toba volcano.
  • Following the volcanic eruption, an increase of surface seawater pH happened due to alkalinisation.

Abstract

To date, little is known about the impact of super-eruptions on ocean biogeochemistry. Using boron isotopes ratios measured on planktonic foraminifera in the marine sediment core BAR94–25, we provide a high-resolution pH record in the Andaman Sea (North of Sumatra), spanning Marine Isotopic Stage 5 to 3. This transition encompasses the super-eruption of the Toba volcano, 74,000 years ago, making it possible to decipher the potential impact of the super-eruption emissions on the ocean pH for the first time. Our results show that inferred foraminiferal pH values generally follow those predicted by glacial-interglacial CO2 variations. However, several abrupt pH drops coincide with Toba ash deposition. This suggests the occurrence of acidification events possibly related to Toba volcanic sulphur emission episodes. These pH drops are followed by anomalous pH increases, possibly relating to localised increases in seawater alkalinity following the alteration of large ash deposits on land.

Continue reading ‘Sea surface acidification events in the Andaman Sea associated with the last Toba volcanic activity’

Subscribe

Search

  • Reset

OA-ICC Highlights

Resources