The success of today’s calcifying organisms in tomorrow’s oceans depends, in part, on the resilience of their skeletons to ocean acidification. To the extent this statement is true there is reason to have hope. Many marine calcifiers demonstrate resilience when exposed to environments that mimic near-term ocean acidification. The fossil record similarly suggests that resilience in skeletons has increased dramatically over geologic time. This “deep resilience” is seen in the long-term stability of skeletal chemistry, as well as a decreasing correlation between skeletal mineralogy and extinction risk over time. Such resilience over geologic timescales is often attributed to genetic canalization—the hardening of genetic pathways due to the evolution of increasingly complex regulatory systems. But paradoxically, our current knowledge on biomineralization genetics suggests an opposing trend, where genes are co-opted and shuffled at an evolutionarily rapid pace. In this paper we consider two possible mechanisms driving deep resilience in skeletons that fall outside of genetic canalization: microbial co-regulation and macroevolutionary trends in skeleton structure. The mechanisms driving deep resilience should be considered when creating risk assessments for marine organisms facing ocean acidification and provide a wealth of research avenues to explore.
Continue reading ‘Deep resilience: an evolutionary perspective on calcification in an age of ocean acidification’Posts Tagged 'paleo'
Deep resilience: an evolutionary perspective on calcification in an age of ocean acidification
Published 16 March 2023 Science Leave a CommentTags: biological response, calcification, paleo, review
Assessing the impact of different carbonate system parameters on benthic foraminifera from controlled growth experiments
Published 14 March 2023 Science Leave a CommentTags: biological response, foraminifera, growth, laboratory, methods, morphology, mortality, paleo
Insights into past marine carbon cycling and water mass properties can be obtained by means of geochemical proxies calibrated through controlled laboratory experiments with accurate seawater carbonate system (C-system) manipulations. Here, we explored the use of strontium/calcium ratio (Sr/Ca) of the calcite shells of benthic foraminifera as a potential seawater C-system proxy through a controlled growth experiment with two deep-sea species (Bulimina marginata and Cassidulina laevigata) and one intertidal species (Ammonia T6). To this aim, we used two experimental set-ups to decouple as much as possible the individual components of the carbonate system, i.e., changing pH at constant dissolved inorganic carbon (DIC) and changing DIC at constant pH. Four climatic chambers were used with different controlled concentrations of atmospheric pCO2 (180 ppm, 410 ppm, 1000 ppm, 1500 ppm). Our results demonstrated that pH did not influence the survival and growth of the three species. However, low DIC conditions (879 μmol kg−1) negatively affected B. marginata and C. laevigata through reduced growth, whereas no effect was observed for Ammonia T6. Our results also showed that Sr/Ca was positively correlated with total Alkalinity (TA), DIC and bicarbonate ion concentration ([HCO3−]) for Ammonia T6 and B. marginata; i.e., DIC and/or [HCO3−] were the main controlling factors. For these two species, the regression models were coherent with published data (existing so far only for Ammonia T6) and showed overall similar slopes but different intercepts, implying species-specific effects. Furthermore, the Sr/Ca – C-system relationship was not impacted by ontogenetic trends between chamber stages, which is a considerable advantage for paleo-applications. This applied particularly to Ammonia T6 that calcified many chambers compared to the two other species. However, no correlation with any of the C-system parameters was observed for Sr/Ca in C. laevigata. This might imply either a strong species-specific effect and/or a low tolerance to laboratory conditions leading to a physiological stress, thereby impacting the Sr incorporation into the calcite lattice of C. laevigata.
Continue reading ‘Assessing the impact of different carbonate system parameters on benthic foraminifera from controlled growth experiments’Multiple proxies demonstrate the mechanism of dolomitization variations during global warming periods
Published 23 February 2023 Science ClosedTags: chemistry, field, paleo
The genesis of the sedimentary dolomite has been an unexplained mystery for more than two centuries, known as the ‘dolomite problem’. There may be some coupling relationship between the Phanerozoic variations in dolomite abundance and major geological events (i.e., mass extinction, oceanic anoxia, global warming, and ocean acidification); but its cause is still not adequately understood, which impedes our understanding of global geochemical cycles and long-term climate change. Understanding the controlling factors of dolomitization variations during global warming periods is the key to resolving this issue. Multiple factors controlling the dolomitization of the Middle Eocene Bohai Bay Basin, Holocene Lake Van, and Permian-Triassic dolomitization event were (re)evaluated in this study using astronomical tuning, correlation coefficient analysis, and multiple regression analysis. We demonstrate that dolomitization is more intense during global warming periods, and that its variation is more affected by temperature and pH cycling resulting from astronomical forcing. These phenomena may be caused by the Cannikin Law or the strengthening of temperature and pH cycling during global warming periods. The elevated atmospheric pCO2 and associated ocean acidification strengthen the temperature and pH cycling, thereby promoting the dolomitization of metastable carbonates by a non-equilibrium cyclic growth and replacement mechanism. This process is an important overlooked reason for the higher dolomite abundance during global warming. This study offers a novel perspective on the ‘dolomite problem’, ocean acidification and their relationship.
Continue reading ‘Multiple proxies demonstrate the mechanism of dolomitization variations during global warming periods’High-resolution marine osmium and carbon isotopic record across the Aptian–Albian boundary in the southern South Atlantic: evidence for enhanced continental weathering and ocean acidification
Published 22 February 2023 Science ClosedTags: field, paleo, South Atlantic
The Early Cretaceous Aptian–Albian boundary (AAB) interval (∼113 Ma) was marked by severe environmental perturbations, including Oceanic Anoxic Event (OAE) 1b, global warming, and a major species turnover of planktonic foraminifera. Most paleoenvironmental studies across the AAB have focused on Tethyan sedimentary sequences deposited at low latitudes, but, because of the scarcity of well-dated sedimentary sequences across the AAB at high latitudes, the global extent of these environmental perturbations remains uncertain. Deep Sea Drilling Project (DSDP) Site 511 was drilled on the Falkland Plateau, southern South Atlantic, and is one of the few sedimentary sequences at southern high latitudes to record an almost continuous AAB interval. Previous studies documented the planktonic foraminiferal changes across the AAB at DSDP Site 511, but chemostratigraphic information has been limited. We reconstructed an osmium and carbon isotopic stratigraphy to further constrain the position of the AAB. We also inferred the paleo-marine redox conditions at southern high latitudes by combining chemical and lithological information. We found an abrupt negative δ13Ccarb shift coincident with the first occurrence of Microhedbergella renilaevis, an event that marks the base of the Albian Stage. This negative δ13Ccarb shift has also been observed across the AAB interval in the Tethyan and Atlantic regions. The fact that the osmium isotopic ratios show a pronounced radiogenic shift after the AAB is consistent with osmium isotopic variations detected in the Tethys and Pacific regions. Because the Os shift corresponded to a warming event during OAE1b in the low-latitude Atlantic and Tethyan regions, we interpret this radiogenic osmium isotopic shift as a response to increased continental weathering caused by global warming. A large marcasite crystal in the AAB interval at DSDP Site 511 suggests that the southern Atlantic Ocean may have been oxygen-depleted with a low pH caused by contemporaneous global environmental perturbations.
Continue reading ‘High-resolution marine osmium and carbon isotopic record across the Aptian–Albian boundary in the southern South Atlantic: evidence for enhanced continental weathering and ocean acidification’Abrupt episode of mid-Cretaceous ocean acidification triggered by massive volcanism
Published 17 February 2023 Science ClosedTags: field, paleo, South Pacific
Large-igneous-province volcanic activity during the mid-Cretaceous triggered a global-scale episode of reduced marine oxygen levels known as Oceanic Anoxic Event 2 approximately 94.5 million years ago. It has been hypothesized that this geologically rapid degassing of volcanic carbon dioxide altered seawater carbonate chemistry, affecting marine ecosystems, geochemical cycles and sedimentation. Here we report on two sites drilled by the International Ocean Discovery Program offshore of southwest Australia that exhibit clear evidence for suppressed pelagic carbonate sedimentation in the form of a stratigraphic interval barren of carbonate minerals, recording ocean acidification during the event. We then use the osmium isotopic composition of bulk sediments to directly link this protracted ~600 kyr shoaling of the marine calcite compensation depth to the onset of volcanic activity. This decrease in marine pH was prolonged by biogeochemical feedbacks in highly productive regions where elevated heterotrophic respiration added carbon dioxide to the water column. A compilation of mid-Cretaceous marine stratigraphic records reveals a contemporaneous decrease of sedimentary carbonate content at continental slope sites globally. Thus, we contend that changes in marine carbonate chemistry are a primary ecological stress and important consequence of rapid emission of carbon dioxide during many large-igneous-province eruptions in the geologic past.
Continue reading ‘Abrupt episode of mid-Cretaceous ocean acidification triggered by massive volcanism’Calcareous nannoplankton response to a high CO2 world: evidence from sediment traps (Aegean and Ionian Seas) and Pliocene paleofluxes
Published 20 December 2022 Science ClosedTags: abundance, biological response, BRcommunity, community composition, field, Mediterranean, otherprocess, paleo, phytoplankton, sediment
One of the most enigmatic features of long-term Cenozoic climatic evolution, with some analogue potential for present/ future global climate change, is the last sustained warm and high-atmospheric CO2 interval in Earth’s history. The Pliocene is the most recent period in Earth’s history when average global temperature, atmospheric CO2 concentrations, and sea level were higher than today. This time period offers an appropriate interval to understand the climatic processes of a warm, high CO2 world, similar to the ongoing climatic conditions. Also, due to the high absorption capacity of the Eastern Mediterranean to anthropogenic CO2, the study area (Aegean and Ionian seas) is an ideal location to assess the impact of anthropogenic ocean acidification on calcifying organisms. The main objective of the present study is to investigate calcareous nannoplankton fluxes in the NE Mediterranean Sea as recorded by sediment traps and paleoceanographic records. The study material is collected from sediment traps in the Aegean and Ionian Seas and from the sedimentary record of the Eastern Mediterranean Deep Sea Drilling Project (DSDP Leg42A, Site 378). In the present study, coccolith fluxes from sediment traps were examined and compared in different sites of the Aegean and Ionian Seas. Data were compared in order to define the spatial and seasonal variability in assemblage composition and coccolithophore fluxes. The present study reflects in the coccolithophore export productivity the context of biogenic sedimentation in the water column. Furthermore, a water and sediment trap samples (N.Aegean Sea) analysis was carried out and through the comparison with data derived from surface sediment of the same site, valuable information were provided on the alterations observed in coccolithophore assemblage composition during their export from the euphotic zone to the seafloor. In addition, the morphometric analysis of coccoliths contributed to the investigation of water masses in the water column of the North Aegean Sea. In the DSDP core data we focus on the “warm Pliocene” interval, after the Zanclean “flooding” phenomenon in the Aegean after the Messinian Mediterranean Salinity Crisis (Zanclean reflooding). According to the detailed biostratigraphy and the derived age model, this study presents a composite dataset of the two boreholes of DSDP-Leg42A-Site 378 for the interval 3.8-5.08Ma. Subsequently, we studied how coccolithophores adapted to the Pliocene environment by quantifying their abundance through paleofluxes, species composition and correlation with geochemical paleo-indices analyses performed on the core material. In addition, the DSDP sedimentary record provided evidence on the Zanclean reflooding mechanism in the Cretan Basin. This study aims to improve our understanding of long-term adaptation strategies of calcareous nannoplankton in warm, high-CO2 climates by combining present-day evidence with Lower Pliocene fossil time series.
Continue reading ‘Calcareous nannoplankton response to a high CO2 world: evidence from sediment traps (Aegean and Ionian Seas) and Pliocene paleofluxes’Calcium isotope ratios of malformed foraminifera reveal biocalcification stress preceded Oceanic Anoxic Event 2
Published 16 December 2022 Science ClosedTags: biological response, calcification, field, laboratory, Mediterranean, morphology, paleo, protists
Ocean acidification causes biocalcification stress. The calcium isotope composition of carbonate producers can archive such stress because calcium isotope fractionation is sensitive to precipitation rate. Here, we synthesize morphometric observations of planktic foraminifera with multi-archive calcium isotope records from Gubbio, Italy and the Western Interior Seaway spanning Cretaceous Ocean Anoxic Event 2 (~94 million years ago). Calcium isotope ratios increase ~60 thousand years prior to the event. The increase coincides with foraminiferal abnormalities and correlates with existing proxy records for carbon dioxide release during large igneous province volcanism. The results highlight Ocean Anoxic Event 2 as a geologic ocean acidification analog. Moreover, decreasing calcium isotope ratios during the event provide evidence for ocean alkalinization, which could have shifted air-sea carbon dioxide partitioning. These data offer an explanation for the Plenus Cold Event and further have implications for refining ocean alkalinity enhancement, a leading anthropogenic carbon dioxide removal strategy.
Continue reading ‘Calcium isotope ratios of malformed foraminifera reveal biocalcification stress preceded Oceanic Anoxic Event 2’Characteristics of calcium isotopes at different water depths and their palaeoenvironmental significance for carbonate rocks of the Permian-Triassic boundary in Chibi, southern China
Published 24 November 2022 Science ClosedTags: biogeochemistry, field, North Pacific, paleo, vents
Calcium isotopes of carbonate rocks can trace calcium cycles and record changes in the marine environment. As published calcium isotope profiles of carbonate rocks at the Permian-Triassic boundary are rare, comparative studies on deep-water profiles were lacking for the major extinction event that occurred during this time. We present sections of different water depths in the Chibi area of southern China that we have selected for a comparative study. We analyzed carbon isotopes, calcium isotopes, as well as major and trace elements of carbonates from two sections (Chibi North and Chibi West) to obtain information on the volcanic activity, ocean acidification, as well as sea level rise and fall in the Chibi area during the mass extinction period. All carbon and calcium isotopes of carbonates from both sections are all negative after the mass extinction boundary. Carbonates from the Chibi North section have higher δ44/40Ca values and lower Sr/Ca ratios than the rocks from the Chibi West section. We propose that the negative bias of the calcium isotopes in the two sections result from diagenesis. Diagenesis transforms primary aragonite into calcite, showing the characteristics of high δ44/40Ca value and low Sr/Ca. By comparing our data with three published profiles of shallow-water carbonate rock, we recognize that calcium isotopes record gradients at different water depths. In the slope environment, the enhancement of pore fluid action near the coast caused an increase of the fluid buffer alteration, and we propose that a regression event occurred in the Chibi region during the Late Permian.
Continue reading ‘Characteristics of calcium isotopes at different water depths and their palaeoenvironmental significance for carbonate rocks of the Permian-Triassic boundary in Chibi, southern China’Gastropods underwent a major taxonomic turnover during the end-Triassic marine mass extinction event
Published 7 November 2022 Science ClosedTags: biological response, field, mollusks, multiple factors, paleo, temperature
Based on an exhaustive database of gastropod genera and subgenera during the Triassic–Jurassic transition, origination and extinction percentages and resulting diversity changes are calculated, with a particular focus on the end-Triassic mass extinction event. We show that gastropods suffered a loss of 56% of genera and subgenera during this event, which was higher than the average of marine life (46.8%). Among molluscs, gastropods were more strongly affected than bivalves (43.4%) but less than ammonoids, which were nearly annihilated. However, there were also pronounced differences among gastropod subclasses. The most strongly affected subclass was the Neritimorphia, which lost 72.7% of their Rhaetian genera; on the other extreme, the Heterobranchia remained nearly unaffected (11% loss). We analysed this extinction pattern with respect to larval development, palaeobiogeography, shell size, and anatomy and found that putative feeding of the pelagic larval stage, adaptation to tropical-temperate water temperatures, and flexibility of the mantle attachment were among the factors that might explain extinction resilience of heterobranchs during the end-Triassic crisis. Among molluscs, extinction magnitude roughly correlates with locomotion activity and thus metabolic rates. We suggest three potential kill mechanisms that could account for these observations: global warming, ocean acidification, and extinction of marine plankton. The end-Triassic extinction of gastropods therefore fits to proposed extinction scenarios for this event, which invoke the magmatic activity of the Central Atlantic Magmatic Province as the ultimate cause of death. With respect to gastropods, the effect of the end-Triassic mass extinction was comparable to that of the end-Permian mass extinction. Notably, Heterobranchia was relatively little affected by both events; the extinction resilience of this subclass during times of global environmental changes was therefore possibly a key aspect of their subsequent evolutionary success.
Continue reading ‘Gastropods underwent a major taxonomic turnover during the end-Triassic marine mass extinction event’An experimental study on post-mortem dissolution and overgrowth processes affecting coccolith assemblages: a rapid and complex process
Published 25 October 2022 Science ClosedTags: biological response, dissolution, paleo, phytoplankton, sediment
Coccolith dissolution together with post-mortem morphological features are immensely important phenomena that can affect assemblage compositions, complicate taxonomic identification as well as provide valuable palaeoenvironmental insights. This study summarizes the effects of pH oscillations on post-mortem coccolith morphologies and the abundances and compositions of calcareous nannoplankton assemblages in three distinct types of material—(i) Cretaceous chalk, (ii) Miocene marls, and (iii) late Holocene calcareous ooze. Two independent experimental runs within a semi-enclosed system setting were realized to observe assemblage alterations. One experiment was realized with the presence of bacteria and, in contrast, the second one inhibited their potential effect on the studied system. The pH was gradually decreased within the range of 8.3–6.4 using a reaction of CO2 with H2O forming weak carbonic acid (H2CO3), thereby affecting CO32-. Further, a subsequent overgrowth study was carried out during spontaneous degassing accompanied by a gradual pH rise. The experiment revealed that the process and intensity of coccolith corrosion and subsequent overgrowth build-ups are influenced by a plethora of different factors such as (i) pH and associated seawater chemistry, (ii) mineral composition of the sediment, (iii) the presence of coccoliths within a protective substrate (faecal pellets, pores, pits), and (iv) the presence/absence of bacteria. Nannoplankton assemblages with corroded coccoliths or with coccoliths with overgrowth build-ups showed that the observed relative abundances of taxa experienced alteration from the original compositions. Additionally, extreme pH oscillations may result in enhanced morphological changes that make coccoliths unidentifiable structures, and might even evoke the absence of coccoliths in the fossil record.
Continue reading ‘An experimental study on post-mortem dissolution and overgrowth processes affecting coccolith assemblages: a rapid and complex process’Investigating the effect of ocean acidification (natural and anthropogenic) on the size of Emiliania huxleyi from late Holocene sediments of the north Aegean sea (NE Mediterranean)
Published 19 October 2022 Science ClosedTags: biological response, field, Mediterranean, morphology, paleo, phytoplankton, sediment
The impact of ocean acidification on calcareous nannoplankton has been debated among researchers. This study focused to enrich the available data on coccolith size and calcification for the cosmopolitan species Emiliania huxleyi and assess their connection to natural and anthropogenic environmental changes. The analysis was based on the M2 core from Athos basin (North Aegean Sea, Greece). In total, 80 samples were selected and processed in laboratory to prepare for Scanning Electron Microscope (SEM) imaging. About 4000 E. huxleyi coccoliths were inspected under the SEM and their morphometric values were calculated. Morphometric values displayed fluctuations across the core depths, which were compared to the age model and multiproxy analyses of previous studies in the same area (Gogou et al., 2016; Skampa et al., 2019; Dimiza et al., 2020). Evident changes were based mainly to the Relative Tube Width (RTW), with a tendency towards slightly increased calcified coccoliths within the Little Ice Age (c. 1200-1850 AD). Afterwards, during the Instrumental Period (c. 1850-present) values show a decreasing pattern. It is possible that human activities, especially in the last century, have affected the marine equilibrium with higher atmospheric CO2 absorption, environmental parameters changes and depletion of bioavailable carbonate ions. Although naturally induced environmental changes in the Northern Aegean could mask the clear effect of ocean acidification on E. huxleyi, these data may contribute to a potential tool for environmental monitoring in the context of tackling future climate change.
Continue reading ‘Investigating the effect of ocean acidification (natural and anthropogenic) on the size of Emiliania huxleyi from late Holocene sediments of the north Aegean sea (NE Mediterranean)’Biotic and paleoceanographic changes across the Late Cretaceous Oceanic Anoxic Event 2 in the southern high latitudes (IODP sites U1513 and U1516, SE Indian Ocean)
Published 29 September 2022 Science ClosedTags: field, Indian, paleo, protists, sediment
Abstract
Oceanic Anoxic Event 2, spanning the Cenomanian/Turonian boundary (93.9 Ma), was an episode of major perturbations in the global carbon cycle. To investigate the response of biota and the paleoceanographic conditions across this event, we present data from International Ocean Discovery Program sites U1513 and U1516 in the Mentelle Basin (offshore SW Australia; paleolatitude 59°–60°S in the mid-Cretaceous) that register the first complete records of OAE 2 at southern high latitudes. Calcareous nannofossils provide a reliable bio-chronostratigraphic framework. The distribution and abundance patterns of planktonic and benthic foraminifera, radiolaria, and calcispheres permit interpretation of the dynamics of the water mass stratification and provide support for the paleobathymetric reconstruction of the two sites, with Site U1513 located northwest of the Mentelle Basin depocenter and at a deeper depth than Site U1516. The lower OAE 2 interval is characterized by reduced water mass stratification with alternating episodes of enhanced surface water productivity and variations of the thickness of the mixed layer as indicated by the fluctuations in abundance of the intermediate dwelling planktonic foraminifera. The middle OAE 2 interval contains lithologies composed almost entirely of radiolaria reflecting extremely high marine productivity; the low CaCO3 content is consistent with marked shoaling of the Carbonate Compensation Depth and ocean acidification because of CaCO3 undersaturation. Conditions moderated after deposition of the silica-rich, CaCO3-poor rocks as reflected by the microfossil changes indicating a relatively stable water column although episodes of enhanced eutrophy did continue into the lower Turonian at Site U1516.
Key Points
- Documentation of first complete record of the Late Cretaceous Oceanic Anoxic Event 2 (OAE 2) at southern high latitudes (60°S) in the Indian Ocean
- Dynamics of the water mass stratification inferred from distribution patterns of foraminifera, radiolaria, calcispheres
- OAE 2 is characterized by alternating episodes of enhanced surface water productivity and variations of the thickness of the mixed layer
Response of calcareous nannoplankton to the Paleocene–Eocene Thermal Maximum in the Paratethys seaway (Tarim Basin, West China)
Published 15 September 2022 Science ClosedTags: North Pacific, paleo, phytoplankton
Highlights
- A new, shallow marine Paleocene–Eocene Thermal Maximum (PETM) record was discovered in the eastern Tethys.
- High-resolution calcareous nannofossil biostratigraphy across the PETM was established.
- The PETM “excursion taxa” are marker species for identifying PETM record in the eastern Tethys.
- Low pre- and syn-PETM carbonate contents were attributed to ocean acidification and terrestrial dilution.
- Marine productivity increased during the PETM due to elevated nutrient input from continental weathering.
Abstract
The Paleocene-Eocene Thermal Maximum (PETM) was a rapid global warming occurred 56 million years ago and has been widely viewed as an ancient analogue to the ongoing warming driven by anthropogenic CO2 emissions. The complete and continuous Paleogene shallow marine strata well preserved and outcropped in the Tarim Basin, northwestern China are ideal to study the paleoenvironmental change of the Paratethys Seaway during the PETM. To date, no high-resolution calcareous nannofossil biostratigraphy has been performed for the PETM interval in the Tarim Basin. Outcrop samples taken from the Qimugen Formation in the Kuzigongsu section contain abundant, moderately well preserved calcareous nannofossils allows for the establishment of a high-resolution biostratigraphic framework. Overall, 73 species of calcareous nannofossils from 33 genera were observed, with the dominant species including Coccolithus pelagicus, various Toweius species, Pontosphaera exilis, and Micrantholithus flos. The five calcareous nannofossil datums allow for the recognization of nannofossil Zone NP6 through Zone NP10. The common occurrence of shallow-water taxa (Micrantholithus) throughout the section suggests a middle to outer neritic setting for depositional environment of the Kuzigongsu section. The stratigraphic distribution of “excursion taxa” (Coccolithus bownii, Discoaster araneus, D. acutus, Rhomboaster spp.) is consistent with the range of negative excursion in δ13Ccarb and δ18Ocarb, indicating that these excursion taxa are micropaleontological means for identifying the presence of the PETM in the Paratethys Seaway. During the PETM, the deteriorated preservation and extremely low abundance of nannofossils and near-zero wt% CaCO3 values suggest that ocean acidification occurred in the shallow water of the Paratethys Seaway. In addition, a significant increase in the species Neochiastozygus junctus, which is a high productivity indicator indicates increased surface ocean productivity. Higher primary productivity may be triggered by enhanced continental weathering delivering increased nutrient through river runoff.
Continue reading ‘Response of calcareous nannoplankton to the Paleocene–Eocene Thermal Maximum in the Paratethys seaway (Tarim Basin, West China)’The cold-water coral Solenosmilia variabilis as a paleoceanographic archive for the reconstruction of intermediate water mass temperature variability on the Brazilian continental margin
Published 9 September 2022 Science ClosedTags: corals, methods, paleo, South Atlantic
Recent oceanographic observations have identified significant changes of intermediate water masses characterized by increased temperatures, lowered pH and deoxygenation. In order to improve our understanding as to how these changes may impact deep-sea ecosystems one important strategy is to reconstruct past oceanic conditions. Here we examine the applicability of the scleractinian cold-water coral Solenosmilia variabilis as a marine archive for the reconstructions of past intermediate water mass temperatures by using Lithium (Li)/Magnesium (Mg) ratios. In particular, our study addresses 1) the calibration of Li/Mg ratios against in-situ temperature data, 2) the reconstruction of past intermediate water mass temperatures using scleractinian coral fossil samples from the Brazilian continental margin and 3) the identification of intraspecies variability within the coral microstructure. Results showed that Li/Mg ratios measured in the skeletons of S. variabilis fit into existing Li/Mg-T calibrations of other cold-water scleractinian. Furthermore, the coral microstructure exhibits interspecies variability of Li/Ca and Mg/Ca ratios were also similar to what has been observed in other cold-water scleractinian corals, suggesting a similar biomineralization control on the incorporation of Li and Mg into the skeleton. However, the Li/Mg based temperature reconstruction using fossil samples resulted in unexpectedly high variations >10°C, which might not be solely related to temperature variations of the intermediate water mass over the last 160 ka on the Brazilian continental margin. We speculate that such temperature variability may be caused by vertical movements of the aragonite saturation horizon and the associated seawater pH changes, which in turn influence the incorporation of Li and Mg into the coral skeleton. Based on these results it is recommended that future studies investigating past oceanic conditions need to consider the carbonate system parameters and how they might impact the mechanisms of Li and Mg being incorporated into skeletons of cold-water coral species such as S. variabilis.
Continue reading ‘The cold-water coral Solenosmilia variabilis as a paleoceanographic archive for the reconstruction of intermediate water mass temperature variability on the Brazilian continental margin’Geochemical significance of Acropora death assemblages in the northern South China Sea: implications for environmental reconstruction using branching corals
Published 30 August 2022 Science ClosedTags: biological response, chemistry, corals, North Pacific, paleo
Highlights
- Acropora-derived SST reconstruction using Sr/Ca has registered SST shifts around 4–5 ka BP and the modern warming.
- The universal Li/Mg-SST calibration tends to underestimate the SST reconstruction.
- Reduced pHcf is found for the post-industrial corals compared to the ancient corals.
- Coral DICcf exhibits a progressive decrease since the mid-Holocene.
- Skeletal δ13C is intrinsically linked to the coral CF carbonate chemistry.
Abstract
The geochemistry preserved in coral skeletons provides access to pre-instrumental records of environmental changes. While a variety of proxies have been established for coral paleoclimatology, their applications to the use of Acropora to generate longer-term reconstructions have been studied less. Here, we examine the geochemical proxies (i.e., Sr/Ca, Li/Mg, δ18O, δ13C, δ11B, and B/Ca) of dead Acropora assemblages collected from a fringing reef off Hainan Island in the northern South China Sea. These samples have been precisely dated using U
Th isotopes and record reef development episodes since the mid-Holocene, allowing us to assess their potential as paleoclimate archives. The sea surface temperature (SST) trend reconstructed by Sr/Ca and Li/Mg exhibits better consistency with each other, and they have recorded the SST shifts around 5–4 ka BP and the subdued variability during the Medieval Climate Anomaly (MCA), whereas the δ18O-SST record exhibits less clear variations over the past 7000 years. However, the universal Li/Mg-SST calibration tends to underestimate the SST reconstruction from tropical corals, highlighting the importance of using a site- and species-specific calibration of the Li/Mg-SST. Boron systematics are used to reconstruct the carbonate chemistry of coral calcifying fluid (CF), which reveals significant differences between the ancient and modern corals. The pH of the coral CF (pHcf) is significantly lower in the modern Acropora compared to the ancient corals, with a mean difference of ~0.08 pH, corroborating the pronounced influence of ocean acidification on the coral CF chemistry. The dissolved inorganic carbon of the coral CF (DICcf) is also lower for modern Acropora, and this decreasing trend seems to have persisted over the past 7000 years. In addition, the skeletal δ13C is closely related to the CF carbonate chemistry, highlighting the intrinsic relationship between the coral internal carbon pool used for calcification and the up-regulation of the pHcf.
Shallow water records of the PETM: novel insights From NE India (eastern Tethys)
Published 4 August 2022 Science ClosedTags: biological response, BRcommunity, community composition, corals, Indian, modeling, multiple factors, otherprocess, paleo, protists, regionalmodeling, temperature
Abstract
The Paleocene-Eocene Thermal Maximum (PETM) is associated with major extinctions in the deep ocean, and significant paleogeographic and ecological changes in surface ocean and terrestrial environments. However, the impact of the associated environmental change on shelf biota is less well understood. Here, we present a new PETM record of a low paleolatitude shallow-marine carbonate platform from Meghalaya, NE India (eastern Tethys). The biotic assemblage was distinctly different to other Tethyan PETM records dominated by larger benthic foraminifera and calcareous algae both in the Paleocene and Eocene. A change in taxa and forms indicating deeper waters with a concurrent decrease in abundance of shallow water algae suggests a sea-level rise during the onset of the PETM. The record is lacking the ecological change from corals to larger foraminiferal assemblages and the Lockhartia dominance, characteristic of several other sections in the Tethys. Comparison with a global circulation model (GCM) indicates high regional temperatures in the Thanetian which may have excluded corals from the region. Furthermore, the regional circulation pattern is isolating the site from the wider Paratethys. Our study highlights the need for a diverse global perspective on shallow-marine response to the PETM and the strength of coupling data to global climate models for interpretation.
Key Points
- Shallow-marine Paleocene-Eocene Thermal Maximum (PETM) successions are rare; here, we presented from the low paleolatitude NE India (eastern Tethys)
- The absence of coral reefs in NE India, in contrast to other Tethyan records, was driven by very high temperatures
- Linking biotic records of this section with climate modeling allow to interpret the biotic differences across the Tethyan region
The changing ocean carbon sink in the earth system
Published 3 August 2022 Science ClosedTags: biogeochemistry, chemistry, globalmodeling, mitigation, modeling, paleo
Eunice Foote, who was the first to measure the solar heating of CO2 in her early experiments already in the 1850s noted: “An atmosphere of that gas would give to our Earth a high temperature“ (Foote, 1856). Indeed, our planet is warming unprecedently fast due to rising anthropogenic CO2 emissions (Masson-Delmotte et al., 2021). Next to catastrophic floodings, wildfires and droughts on land, with tragic consequences for people, the ocean silently suffers from the ongoing heating, acidification, and deoxygenation with tragic impacts for marine systems.
The ocean plays an essential role in regulating Earth’s climate; it is also essential for regulating the Earth’s carbon cycle. The ocean contains around 38,000 Gt of carbon. This is 16 times more than the terrestrial biosphere (plant and the underlying soils), and about 60 times more than the pre-industrial atmosphere (Canadell et al., 2021). Therefore, even a small perturbation to the ocean carbon content by changing its capacity to store carbon would impact atmospheric CO2 concentrations (Fig.1.1), making the ocean carbon sink a major regulator of the Earth’s climate on a time scale of hundreds to thousands of years. As the ocean currently continuously absorbs anthropogenic carbon from the atmosphere, it thereby has a key role in moderating ongoing climate change.
Based on the Global Carbon Budget (GCB) estimates (Friedlingstein et al., 2020), the global ocean has already taken up about one third of the cumulative anthropogenic CO2 emissions (Fig.1.2). The strength of the ocean carbon sink is determined by chemical reactions in seawater (carbonate system), biological processes (photosynthesis, export flux, and remineralization by aerobic and anaerobic respiration), and physical processes (including ocean circulation and vertical mixing). But even though these key mechanisms are identified (Landschutzer et al., 2021), there are considerable uncertainties regarding their interannual and decadal variations, as well as their susceptibility to ongoing climate change. Here, a major uncertainty arises from the lack of knowledge regarding the contribution of the natural variability of the climate system (Ilyina, 2016).
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In this essay, I present my research contributions based on my papers explicitly mentioned in the text. My research was guided by the following questions:
- How do ocean biogeochemical cycles accommodate perturbations brought about by anthropogenic activities or natural forcings?
- What are the predictability horizons of variations in the ocean carbon sink?
- What is the potential of the ocean carbon sink, artificially enhanced by ocean alkalinity additions, to mitigate climate change?
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Continue reading ‘The changing ocean carbon sink in the earth system’Coralline algae at the Paleocene/Eocene thermal maximum in the southern Pyrenees (N Spain)
Published 7 July 2022 Science ClosedTags: abundance, biological response, BRcommunity, corals, otherprocess, paleo
During the Paleocene/Eocene Thermal Maximum, ~55.6 Ma, the Earth experienced the warmest event of the last 66 Ma due to a massive release of CO2. This event lasted for ~100 thousands of years with the consequent ocean acidification (estimated pH = 7.8-7.6). In this paper, we analyze the effects of this global environmental shift on coralline algal assemblages in the Campo and Serraduy sections, in the south-central Pyrenees (Huesca, N Spain), where the PETM is recorded within coastal-to-shallow marine carbonate and siliciclastic deposits. In both sections, coralline algae occur mostly as fragments, although rhodoliths and crusts coating other organisms are also frequent. Rhodoliths occur either dispersed or locally forming dense concentrations (rhodolith beds). Distichoplax biserialis and geniculate forms (mostly Jania nummulitica) of the order Corallinales dominated the algal assemblages followed by Sporolithales and Hapalidiales. Other representatives of Corallinales, namely Spongites, Lithoporella as well as Neogoniolithon, Karpathia, and Hydrolithon, are less abundant. Species composition does not change throughout the Paleocene/Eocene boundary but the relative abundance of coralline algae as components of the carbonate sediments underwent a reduction. They were abundant during the late Thanetian but became rare during the early Ypresian. This abundance decrease is due to a drastic change in the local paleoenvironmental conditions immediately after the boundary. A hardground at the top of the Thanetian carbonates was followed by continental sedimentation. After that, marine sedimentation resumed in shallow, very restricted lagoon and peritidal settings, where muddy carbonates rich in benthic foraminifera, e.g., milioliids (with abundant Alveolina) and soritids, and eventually stromatolites were deposited. These initial restricted conditions were unfavorable for coralline algae. Adverse conditions continued to the end of the study sections although coralline algae reappeared and were locally frequent in some beds, where they occurred associated with corals. In Serraduy, the marine reflooding was also accompanied by significant terrigenous supply, precluding algal development. Therefore, the observed changes in coralline algal assemblages during the PETM in the Pyrenees were most likely related to local paleoenvironmental shifts rather than to global oceanic or atmospheric alterations.
Continue reading ‘Coralline algae at the Paleocene/Eocene thermal maximum in the southern Pyrenees (N Spain)’Environmental change and carbon-cycle dynamics during the onset of Cretaceous oceanic anoxic event 1a from a carbonate-ramp depositional system, Abu Dhabi, U.A.E.
Published 30 June 2022 Science ClosedTags: chemistry, Indian, paleo, sediment
Highlights
- Negative δ13C excursion at onset of OAE1a recorded in carbonate-ramp deposits.
- Time-series analysis shows relative complete record of C3 segment of OAE1a.
- Evidence for short-lived carbonate dissolution event at the negative δ13C peak of C3.
- Discussion of effects of seawater temperature, pH, and diagenesis on δ18O record.
Abstract
We report the first high-resolution sedimentological and geochemical record of the negative carbon-isotope excursion (CIE) at the onset of the early Aptian oceanic anoxic event (OAE) 1a from a carbonate-ramp depositional environment, analysed from a well core from c. 2500 m depth, 100 km offshore Abu Dhabi, United Arab Emirates. Time-series analysis of stable oxygen isotope values and concentrations of Si, Al, and Ti resulted in durations of the C3 and C4 segments of the CIE that support relative completeness of the C3 segment and high sediment preservation rates of c. 13 cm/kyr of the studied sedimentary sequence. Stable oxygen-isotope ratios of bulk carbonates are interpreted to indicate two episodes of cooling, separated by rapid warming during the peak of the negative CIE. The contributions of diagenesis and seawater pH on the bulk oxygen-isotope record will have affected the palaeoclimatic signal and are critically discussed. A major shift in oxygen isotope values at the peak of the negative CIE in the C3 segment coincides with relatively carbonate-poor, marly deposits, time-equivalent with other, global evidence for a reduction of carbonate saturation of sea-surface water. According to our chemo- and cyclostratigraphic calibration, this episode of low carbonate saturation of seawater reflects a pulse of major volcanic CO2 release from the Ontong-Java large igneous province that was sufficiently short to have escaped internal buffering by the dynamics of the ocean lysocline.
Continue reading ‘Environmental change and carbon-cycle dynamics during the onset of Cretaceous oceanic anoxic event 1a from a carbonate-ramp depositional system, Abu Dhabi, U.A.E.’Environmental change and carbon-cycle dynamics during the onset of Cretaceous oceanic anoxic event 1a from a carbonate-ramp depositional system, Abu Dhabi, U.A.E.
Published 10 June 2022 Science ClosedTags: chemistry, Indian, paleo, sediment
Highlights
- Negative δ13C excursion at onset of OAE1a recorded in carbonate-ramp deposits.
- Time-series analysis shows relative complete record of C3 segment of OAE1a.
- Evidence for short-lived carbonate dissolution event at the negative δ13C peak of C3.
- Discussion of effects of seawater temperature, pH, and diagenesis on δ18O record.
Abstract
We report the first high-resolution sedimentological and geochemical record of the negative carbon-isotope excursion (CIE) at the onset of the early Aptian oceanic anoxic event (OAE) 1a from a carbonate-ramp depositional environment, analysed from a well core from c. 2500 m depth, 100 km offshore Abu Dhabi, United Arab Emirates. Time-series analysis of stable oxygen isotope values and concentrations of Si, Al, and Ti resulted in durations of the C3 and C4 segments of the CIE that support relative completeness of the C3 segment and high sediment preservation rates of c. 13 cm/kyr of the studied sedimentary sequence. Stable oxygen-isotope ratios of bulk carbonates are interpreted to indicate two episodes of cooling, separated by rapid warming during the peak of the negative CIE. The contributions of diagenesis and seawater pH on the bulk oxygen-isotope record will have affected the palaeoclimatic signal and are critically discussed. A major shift in oxygen isotope values at the peak of the negative CIE in the C3 segment coincides with relatively carbonate-poor, marly deposits, time-equivalent with other, global evidence for a reduction of carbonate saturation of sea-surface water. According to our chemo- and cyclostratigraphic calibration, this episode of low carbonate saturation of seawater reflects a pulse of major volcanic CO2 release from the Ontong-Java large igneous province that was sufficiently short to have escaped internal buffering by the dynamics of the ocean lysocline.
Continue reading ‘Environmental change and carbon-cycle dynamics during the onset of Cretaceous oceanic anoxic event 1a from a carbonate-ramp depositional system, Abu Dhabi, U.A.E.’
