Posts Tagged 'paleo'

Evolution of paleo-climate and seawater pH from the late Permian to postindustrial periods recorded by boron isotopes and B/Ca in biogenic carbonates

Highlights

• The fundamentals and advances in δ11B-pH and B/Ca proxies have been demonstrated.

• The evolution of atmospheric CO2 over million-year scale and millennium scale is reviewed.

• The significant ocean acidifications and the associated driving forces were clarified.

Abstracts

Cycling of CO2 between the oceans and the atmosphere has significant impacts on the global climate change. The accurate reconstructions of paleo-pH and atmospheric-oceanic carbon cycling using geochemical tracers (e.g., δ11B, B/Ca) in marine carbonates are reviewed in this work, including the fundamental mechanisms and the remaining challenges in these proxies and the progresses in understanding of evolution of paleo-climate and seawater pH from the late Permian to postindustrial periods. The proxies provide new insight into the evolution of atmospheric CO2 concentrations at time scales from tens of millions to thousands of years, and the direct evidence to the significant ocean acidification during the mass extinction events, and the CO2 cycling in ocean-atmosphere system during the Last Deglaciation and post-industrial periods. On the basis of extensive investigation, it could be concluded that: (i) the carbon dioxide levels and their impacts on Earth surface temperature during the Cenozoic cooling, the Pliocene warmth, and the mid-Pleistocene transition have been evaluated by the combination of multiple proxies; (ii) the benthic/planktonic foraminiferal B/Ca and δ11B data provided consistent implications for global climate variations during the Late Pleistocene, the Late Glacial, Last Glacial Maximum, and the Younger Dryas event; (iii) perturbations of surface ocean pH at the Permo-Triassic (P-T) boundary, the Pliensbachian-Toarcian (Pl-To) boundary, the Cretaceous-Paleogene (K/Pg) boundary and the Palaeocene-Eocene Thermal Maximum (PETM) global warming event were triggered by the large injection of carbon, the short episodic pulses of volcanogenic CO2, the Chicxulub impact, and the volcanism activities of the North Atlantic Igneous Province, respectively; (iv) the ocean acidification in the equatorial and polar Pacific during the Last Deglaciation implied an expanded zone of equatorial upwelling and resultant CO2 emission from higher subsurface dissolved inorganic carbon concentration. The acceleration of modern acidification in post-industrial time was not only driven by anthropogenic CO2 but also varied synchronously with inter-decadal changes in Asian Winter Monsoon Intensity.

Continue reading ‘Evolution of paleo-climate and seawater pH from the late Permian to postindustrial periods recorded by boron isotopes and B/Ca in biogenic carbonates’

Shell mineralogy of a foundational marine species, Mytilus californianus, over half a century in a changing ocean

Anthropogenic warming and ocean acidification are predicted to negatively affect marine calcifiers. While negative effects of these stressors on physiology and shell calcification have been documented in many species, their effects on shell mineralogical composition remains poorly known, especially over longer time periods. Here, we quantify changes in the shell mineralogy of a foundation species, Mytilus californianus, under 60 y of ocean warming and acidification. Using historical data as a baseline and a resampling of present-day populations, we document a substantial increase in shell calcite and decrease in aragonite. These results indicate that ocean pH and saturation state, not temperature or salinity, play a strong role in mediating the shell mineralogy of this species and reveal long-term changes in this trait under ocean acidification.

Continue reading ‘Shell mineralogy of a foundational marine species, Mytilus californianus, over half a century in a changing ocean’

Stable Ca and Sr isotopes support volcanically triggered biocalcification crisis during Oceanic Anoxic Event 1a

Large igneous province (LIP) eruptions are hypothesized to trigger biocalcification crises. The Aptian nannoconid crisis, which correlates with emplacement of the Ontong Java Plateau and Oceanic Anoxic Event 1a (OAE 1a, ca. 120 Ma), represents one such example. The Ca isotope (δ44/40Ca) system offers potential to detect biocalcification fluctuations in the rock record because Ca isotope fractionation is sensitive to precipitation rate. However, other primary and secondary processes, such as input-output flux perturbations and early diagenesis, can produce similar signals. Here, we exploit emergent properties of the stable Sr isotope (δ88/86Sr) system to resolve the origin of δ44/40Ca variability during OAE 1a. This study reports high-precision thermal ionization mass spectrometry (TIMS) δ44/40Ca, δ88/86Sr, and 87Sr/86Sr records for Hole 866A of Ocean Drilling Program Leg 143 drilled in Resolution Guyot, mid-Pacific Ocean. The samples span ~27 m.y. from the Barremian (ca. 127 Ma) to the Albian (ca. 100 Ma). The δ44/40Ca and δ88/86Sr secular trends differ from the 87Sr/86Sr record but mimic each other. δ44/40Ca and [Sr], as well as δ44/40Ca and δ88/86Sr, strongly correlate and yield slopes predicted for kinetic control, which demonstrates that variable mass-dependent fractionation rather than end-member mixing dominated the isotopic relationship between carbonates and seawater. Positive δ44/40Ca and δ88/86Sr shifts that begin before OAE 1a and peak within the interval are consistent with reduced precipitation rates. All results combined point to a cascade of effects on rate-dependent Ca and Sr isotope fractionation, which derive from the dynamic interplay between LIP eruptions and biocalcification feedbacks.

Continue reading ‘Stable Ca and Sr isotopes support volcanically triggered biocalcification crisis during Oceanic Anoxic Event 1a’

Conodont calcium isotopic evidence for multiple shelf acidification events during the early Triassic

Highlights

  • Conodont δ44/40Ca curve is established for the latest Permian to Middle Triassic.
  • Three episodes of decreasing δ44/40Ca (0.16–0.23‰) occurred in the Early Triassic.
  • Negative δ44/40Ca shift in the PTB suggests a CO2-driven ocean acidification event.
  • Negative δ44/40Ca shifts in SSB & OAB suggest upwelling-driven shelf acidification.

Abstract

The marine calcium (Ca) cycle is controlled by rates of continental weathering, seawater pH, and carbonate deposition on the seafloor and is linked to atmospheric CO2, climate change, and marine biotic evolution. Here, we provide the first continuous seawater Ca isotope profile from conodont apatite in South China for the latest Permian to early Middle Triassic, revealing major fluctuations in the Early Triassic calcium cycle. Three episodes of decreasing conodont δ44/40Ca (by 0.16–0.23‰) occurred around the Permian-Triassic, Smithian-Spathian, and Olenekian-Anisian boundaries. The first episode, coincident with a negative excursion of carbonate carbon isotopes, global warming, oceanic anoxia, enhanced weathering, and sea-level fall, was likely caused by a combination of volcanic CO2 release, ocean acidification, a reduced skeletal carbonate sink, and enhanced weathering of shelf carbonates. The latter two episodes, coincident with positive excursions of carbon isotopes, global cooling, and oceanic anoxia, possibly resulted from upwelling-driven shelf acidification and reduced skeletal carbonate burial. All three events were associated with marine biotic diversity losses, demonstrating a link between the calcium cycle and mass extinctions.

Continue reading ‘Conodont calcium isotopic evidence for multiple shelf acidification events during the early Triassic’

Chapter: Volcanic past cycles indicators: paleoclimatology and extinctions using benthic and planktonic forams community dynamics

The Benthic and planktonic foraminiferal communities’ dynamics as volcanic past cycles indicators are very well placed within the Paleoclimatology and extinctions studies. We have showed a bit, of what is available to explain how communities have evolved in the past. The past volcanic activity has released as much carbon dioxide into the atmosphere as anthropogenic as predicted emissions projections for the twenty-first century and they are linked to increases in carbon dioxide emissions and with faunal patterns, with marine extinctions observed sediment cores after volcanic episodes, and this increase in carbon dioxide and other volcanic gaseous influences on global warming and ocean acidification is responsible for the extinction of three quarters of species on Earth on the past. For example, dinosaurs were pretty much extinct because of “The Deccan Traps”, an igneous province, one of the largest volcanic features on Earth, located on the west-central India, and the Siberian Traps have influenced the end-Permian extinction, in which more than 90% of life on Earth disappeared. Many patterns should be first understood to be able to forecast future climate change scenarios. We can however explain that the modern ongoing carbon dioxide emissions are similar to those that led to the end-Triassic mass extinction. The importance of understanding Earth’s deep water past is predicated on predicting how it will respond to future climate change. The mass extinction and high-stress conditions were explained by the intense Deccan volcanism leading to rapid global warming and cooling, with enhanced weathering, continental runoff, and ocean acidification, resulting in a carbonate crisis in the marine environment. The chronic explosive volcanic activity generated unstable benthic habitat colonized by only a few species. The increase in atmospheric CO2 concentrations lead to decreased pH and carbonate availability in the ocean, known as Ocean Acidification, and the ability of marine invertebrates to tolerate acidity are the ‘windows into the future’ to study. Cores with ashes and tephra in Papua New Guinea (PNG) during Expedition 363 sampled by the IODP show that total foraminiferal diversity was low when volcanic activity was in place detected by the presence of tephra and volcanic ashes. Foraminiferal density and diversity in PNG were high and similar to those observed on the Great Barrier Reef or other sites, however diversity decreases, and show inverse correlation by benthic foraminifera to high presence of ashes and tephra in the past. However, ecological studies from shallow reef environments observed increased foraminiferal dominance of opportunists when corals became rare from chronic or acute anthropogenic influences, for example with sewage and oil spills. Agglutinate taxa that do not rely on calcification will replace calcifying species, and we call it a fauna replacement by invasive species. Density and diversity of agglutinated taxa is also in decline, but are less marked than calcifying taxa in an environment where pH is low. Dissolution of foraminifera seen in marine sediment under elevated pCO2 unravels other direct ecological impacts. Impacts such as dissolution and loss of biogenesis of carbonate by other organisms that are under near-future pCO2 conditions, which will reach a problematic real-time scenario. None of the previous extinctions were as severe as the ecological or even taxonomic extinction in shallow carbonate areas which we are predicting. Because of the rate of increasing pCO2, and unfortunately, we expect that the increase in the temperature in the Holocene and the tendency until 2100 will take us to the warmest Pliocene climate with the unfortunate consequences of living in a warmer than optimum world. The variability based on the frequency and intensity of some events are one of the warmest our world has ever seen, reflecting changes in temperature derived from data from deep sea sediment core samples, and of course shells of benthic and planktonic Forams and other organisms like pollen act as proxies in drilled marine sediment cores reflecting historic climate. A unique fauna of foraminiferal species from these highly opposed environments created by differences in temperature in the past are recorded paleo cycles, of which responds to the amount of ice in the world, due to their high sensitivity to the environmental changes in the modern and past sediments. Here we show that tephra and ashes of IODP Hole U1485A (Exp. 363 WPWP) record a periodicity of explosive volcanism within the last 0.8 Myr. Possible triggering mechanisms for these mass flow deposits include earthquakes and associated tsunamis and shelf/slope sediment instabilities during times of rapid deposition such as can occur during river flood events. Over longer timescales, it is also possible that sea level played a role in the storage and release of sediment from the PNG shelf (although the shelf itself is very narrow) and from the paleo-valley of the Sepik River, which is a relatively large area presently few meters above sea level. Changes in diversity shows balance of alternating deep (cold) and shallow (warm) benthic foraminifera fauna along time in the past. The “at least” five decreases in diversity peaks in the past show that the response of the benthic community to adverse climate is a change in their ecological pattern. These changes can take a whole community and an entire ecosystem to extinctions, and we have already seen five extinctions along Earth’s history. And if history teaches us anything, it is how to react to and prepare for crisis rather than repeat mistakes. Research suggests we are fast approaching disastrous effects of this sixth Anthropocene extinction. However, we can successfully surmount the challenges of biodiversity loss and climate change and dramatically alter the trajectory if we can pinpoint and remediate problems within a near future. With our planet “in crisis”, evidence demonstrates widespread ecological collapse and biodiversity loss. We know that as average temperatures rise and the frequency of extremely warm years increases, the impacts of habitat loss and fragmentation become even more increasingly apparent. We are with without a doubt entering a sixth mass extinction event because of the rapid decline in biodiversity. The majority of these species inhabit environmentally delicate tropical and subtropical areas susceptible to human impacts. This refers to a situation where the extinction of one species affects other species that rely on it for survival, thereby also placing them at a ‘domino effect’ risk of extinction as part of a destructive chain reaction. Stop cutting and burn forests, stop global trade of wild species, study and protect, preserve, and conserve our planet’s biodiversity.

Continue reading ‘Chapter: Volcanic past cycles indicators: paleoclimatology and extinctions using benthic and planktonic forams community dynamics’

Chapter: Amplifying factors leading to the collapse of primary producers during the Chicxulub impact and Deccan Traps eruptions

The latest Cretaceous (Maastrichtian) through earliest Paleogene (Danian) interval was a time marked by one of the five major mass extinctions in Earth’s history. The synthesis of published data permits the temporal correlation of the Cretaceous-Paleogene boundary crisis with two major geological events: (1) the Chicxulub impact, discovered in the Yucatan Peninsula (Mexico), and (2) eruption of the Deccan Traps large igneous province, located on the west-central Indian plateau. In this study, environmental and biological consequences from the Chicxulub impact and emplacement of the Deccan continental flood basalts were explored using a climate-carbon-biodiversity coupled model called the ECO-GEOCLIM model. The novelty of this study was investigation into the ways in which abiotic factors (temperature, pH, and calcite saturation state) acted on various marine organisms to determine the primary productivity and biodiversity changes in response to a drastic environmental change. Results showed that the combination of Deccan volcanism with a 10-km-diameter impactor would lead to global warming (3.5 degrees C) caused by rising carbon dioxide (CO 2) concentration (+470 ppmv), interrupted by a succession of short-term cooling events, provided by a “shielding effect” due to the formation of sulfate aerosols. The consequences related to these climate changes were the decrease of the surface ocean pH by 0.2 (from 8.0 to 7.8), while the deep ocean pH dropped by 0.4 (from 7.8 to 7.4). Without requiring any additional perturbations, these environmental disturbances led to a drastic decrease of the biomass of calcifying species and their biodiversity by similar to 80%, while the biodiversity of noncalcifying species was reduced by similar to 60%. We also suggest that the short-lived acidification caused by the Chicxulub impact, when combined with eruption of the Deccan Traps, may explain the severity of the extinction among pelagic calcifying species.

Continue reading ‘Chapter: Amplifying factors leading to the collapse of primary producers during the Chicxulub impact and Deccan Traps eruptions’

Boron isotope records from Pacific microatolls: modifications in Porites lutea calcifying fluid composition under anthropogenic ocean acidification and natural pH variability

Anthropogenic ocean acidification (OA) has compromised the ability of marine organisms to calcify. However, many coastal environments naturally exhibit high variability in seawater pH (pHsw) and the impact of OA on these environments is unclear. For instance, sub-tropical corals can modify the pH of the calcifying fluid (pHcf) from which they precipitate their skeleton. This study examines the influence of OA on pHcf upregulation of Porites lutea microatolls inhabiting reef flat environments. Environmental measurements including pHsw and temperature were performed on reef flats and adjacent fore-reefs on Kiritimati Island (Kiribati), Arno Atoll (Marshall Islands), and Rarotonga (Cook Islands) to quantify the temporal and spatial variability of these parameters. Slabs were removed from microatolls to construct multi-decadal (1938 – 2018) records of their boron isotopic (δ11B) and geochemical composition. The sensitivity of microatoll pHcf upregulation to ambient pHsw was evaluated by comparing annual band δ11B with synchronously recorded pHsw and temperature, and microatoll records were compared to a fore-reef record of similar age. Although daily means in pHsw on reef flats and fore-reefs were relatively similar, large diurnal cycles in pHsw (ΔpHsw = 0.28) and temperature (ΔT = 2.0°C) were found on reef flats exceeding that on fore-reefs by far (ΔpHsw = 0.07, ΔT = 0.7°C). Furthermore, spatial variations in pHsw and temperature were observed that were linked to reef flat hydrodynamics. Microatoll pHcf revealed a higher correlation to ambient seawater temperatures than to pHsw and only the fore-reef core showed a long-term trend in pHcf (-0.0003±0.0009 year-1) that is indicative of OA, while microatoll records revealed variable long-term trends unlikely reflecting ocean conditions (-0.0030±0.0005 to +0.0007±0.0003 year-1). Corals from the three sites revealed similar mean pHcf ≈ 8.44 although the difference in pHsw between the locations (ΔpHsw = 0.17) noticeably exceeded the decline in pHsw due to OA (ΔpHsw = 0.10). In conclusion, Porites lutea microatoll pHcf appeared to be relatively insensitive to OA. This is likely a result of the large variability in seawater conditions on reef flats that supersede OA, and the strong modification of coral pHcf by physiological processes.

Continue reading ‘Boron isotope records from Pacific microatolls: modifications in Porites lutea calcifying fluid composition under anthropogenic ocean acidification and natural pH variability’

The seawater carbon inventory at the Paleocene–Eocene Thermal Maximum

The Paleocene–Eocene Thermal Maximum (PETM) (55.6 Mya) was a geologically rapid carbon-release event that is considered the closest natural analog to anthropogenic CO2 emissions. Recent work has used boron-based proxies in planktic foraminifera to characterize the extent of surface-ocean acidification that occurred during the event. However, seawater acidity alone provides an incomplete constraint on the nature and source of carbon release. Here, we apply previously undescribed culture calibrations for the B/Ca proxy in planktic foraminifera and use them to calculate relative changes in seawater-dissolved inorganic carbon (DIC) concentration, surmising that Pacific surface-ocean DIC increased by + 1,010+1,415−646+1,010−646+1,415 µmol/kg during the peak-PETM. Making reasonable assumptions for the pre-PETM oceanic DIC inventory, we provide a fully data-driven estimate of the PETM carbon source. Our reconstruction yields a mean source carbon δ13C of −10‰ and a mean increase in the oceanic C inventory of +14,900 petagrams of carbon (PgC), pointing to volcanic CO2 emissions as the main carbon source responsible for PETM warming.

Continue reading ‘The seawater carbon inventory at the Paleocene–Eocene Thermal Maximum’

Rapid shifts in circulation and biogeochemistry of the Southern Ocean during deglacial carbon cycle events

The Southern Ocean plays a crucial role in regulating atmospheric CO2 on centennial to millennial time scales. However, observations of sufficient resolution to explore this have been lacking. Here, we report high-resolution, multiproxy records based on precisely dated deep-sea corals from the Southern Ocean. Paired deep (∆14C and δ11B) and surface (δ15N) proxy data point to enhanced upwelling coupled with reduced efficiency of the biological pump at 14.6 and 11.7 thousand years (ka) ago, which would have facilitated rapid carbon release to the atmosphere. Transient periods of unusually well-ventilated waters in the deep Southern Ocean occurred at 16.3 and 12.8 ka ago. Contemporaneous atmospheric carbon records indicate that these Southern Ocean ventilation events are also important in releasing respired carbon from the deep ocean to the atmosphere. Our results thus highlight two distinct modes of Southern Ocean circulation and biogeochemistry associated with centennial-scale atmospheric CO2 jumps during the last deglaciation.

Continue reading ‘Rapid shifts in circulation and biogeochemistry of the Southern Ocean during deglacial carbon cycle events’

Evolution of deep-sea sediments across the Paleocene-Eocene and Eocene-Oligocene boundaries

The composition and distribution of deep-sea sediments is the result of a multitude of climatic, biotic and oceanic conditions relating to biogeochemical cycles and environmental change. Here we utilize the extensive sediment archives of the International Ocean Discovery Program (IODP) and its predecessors to construct maps of deep-sea sediment type across two critical but contrasting boundaries in the Paleogene, one characterised by an interval of extreme warmth (Paleocene/Eocene) and the other by global cooling (Eocene/Oligocene). Ocean sediment distribution shows significant divergence both between the latest Paleocene and Paleocene Eocene Thermal Maximum (PETM), across the Eocene-Oligocene Transition (EOT), and in comparison to modern sediment distributions. Carbonate sedimentation in the latest Paleocene extends to high southern latitudes. Disappearance of carbonate sediments at the PETM is well documented and can be attributed to dissolution caused by significant ocean acidification as a result of carbon-cycle perturbation. Biosiliceous sediments are rare and it is posited that the reduced biogenic silica deposition at the equator is commensurate with an overall lack of equatorial upwelling in the early Paleogene ocean. In the Southern Ocean, we attribute the low in biosiliceous burial, to the warm deep water temperatures which would have impacted biogenic silica preservation. In the late Eocene, our sediment depositional maps record a tongue of radiolarian ooze in the eastern equatorial Pacific. Enhanced biosiliceous deposits in the late Eocene equatorial Pacific and Southern Ocean are due to increased productivity and the spin-up of the oceans. Our compilation documents the enhanced global carbonate sedimentation in the early Oligocene, confirming that the drop in the carbonate compensation depth was global.

Continue reading ‘Evolution of deep-sea sediments across the Paleocene-Eocene and Eocene-Oligocene boundaries’


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