Mangroves are coastal environments that provide resources for adjacent ecosystems due to their high productivity, organic matter decomposition, and carbon cycling by microbial communities in sediments. Since the industrial revolution, the increase of Greenhouse Gases (GHG) released due to fossil fuel burning led to many environmental abnormalities such as an increase in average temperature and ocean acidification. Based on the hypothesis that climate change modifies the microbial diversity associated with decaying organic matter in mangrove sediments, this study aimed to evaluate the microbial diversity under simulated climate change conditions during the litter decomposition process and the emission of GHG. Thus, microcosms containing organic matter from the three main plant species found in mangroves throughout the State of São Paulo, Brazil (Rhizophora mangle, Laguncularia racemosa, and Avicennia schaueriana) were incubated simulating climate changes (increase in temperature and pH). The decay rate was higher in the first seven days of incubation, but the differences between the simulated treatments were minor. GHG fluxes were higher in the first ten days and higher in samples under increased temperature. The variation in time resulted in substantial impacts on α-diversity and community composition, initially with a greater abundance of Gammaproteobacteria for all plant species despite the climate conditions variations. The PCoA analysis reveals the chronological sequence in β-diversity, indicating the increase of Deltaproteobacteria at the end of the process. The GHG emission varied in function of the organic matter source with an increase due to the elevated temperature, concurrent with the rise in the Deltaproteobacteria population. Thus, these results indicate that under the expected climate change scenario for the end of the century, the decomposition rate and GHG emissions will be potentially higher, leading to a harmful feedback loop of GHG production. This process can happen independently of an impact on the bacterial community structure due to these changes.
Continue reading ‘Organic matter decay and bacterial community succession in mangroves under simulated climate change scenarios’Posts Tagged 'sediment'
Organic matter decay and bacterial community succession in mangroves under simulated climate change scenarios
Published 24 July 2024 Science ClosedTags: abundance, biological response, BRcommunity, chemistry, community composition, laboratory, molecular biology, morphology, otherprocess, physiology, prokaryotes, sediment, South Atlantic
Ocean warming and acidification adjust inter- and intra-specific variability in the functional trait expression of polar invertebrates
Published 3 July 2024 Science ClosedTags: abundance, biological response, BRcommunity, chemistry, community composition, echinoderms, mollusks, otherprocess, performance, sediment
Climate change is known to affect the distribution and composition of species, but concomitant alterations to functionally important aspects of behaviour and species-environment relations are poorly constrained. Here, we examine the ecosystem ramifications of changes in sediment-dwelling invertebrate bioturbation behaviour—a key process mediating nutrient cycling—associated with near-future environmental conditions (+ 1.5 °C, 550 ppm [pCO2]) for species from polar regions experiencing rapid rates of climate change. We find that responses to warming and acidification vary between species and lead to a reduction in intra-specific variability in behavioural trait expression that adjusts the magnitude and direction of nutrient concentrations. Our analyses also indicate that species behaviour is not predetermined, but can be dependent on local variations in environmental history that set population capacities for phenotypic plasticity. We provide evidence that certain, but subtle, aspects of inter- and intra-specific variation in behavioural trait expression, rather than the presence or proportional representation of species per se, is an important and under-appreciated determinant of benthic biogeochemical responses to climate change. Such changes in species behaviour may act as an early warning for impending ecological transitions associated with progressive climate forcing.
Continue reading ‘Ocean warming and acidification adjust inter- and intra-specific variability in the functional trait expression of polar invertebrates’Shell size variation of pteropod Heliconoides inflatus: inferences on Indian Ocean carbonate chemistry during late Quaternary
Published 30 May 2024 Science ClosedTags: biological response, chemistry, Indian, laboratory, mollusks, morphology, sediment
The current study is an effort to understand the relationship between the average shell size and Limacina Dissolution Index (LDX) of pteropod species, Heliconoides inflatus as a metric for shell calcification using several cores, ranging in age from recent to 1.2 Myr. The current study is based on the variability of H. inflatus average shell size, LDX, and fragmentation ratio (FR) and their correlation among different spatial and temporal sediment core records from the Northern Indian Ocean. Results suggest that in the cores collected above the Aragonite lysocline (Aly) and the Aragonite Compensation Depth (ACD) (SPC 05, 06, 09, 11, 12, 13, 14, and NGHP-17), the average shell size values exhibited larger shells during the stadials/glacial periods (Little Ice Age (LIA), Marine Isotope Stages (MIS) 3, 6, 10 − 9 transition etc.) which corresponds to lower LDX values. However, the cores beyond the ACD (SK168, AAS11, and RVS2) show larger shell size values during the warm interstadials (e.g., Bølling–Allerød) with higher FR. The variability in shell size and LDX shows an indication of the carbonate ion saturation in the water column over glacial/interglacial time scales and the impact of changing atmospheric CO2 in the atmosphere. However, the factors adding to the carbonate ion saturation within the water column could be varied physiographically. The calcification proxy complements the dissolution proxies and reveals that the most intense aragonite dissolution occurred during the Holocene and interstadials/interglacials.
Continue reading ‘Shell size variation of pteropod Heliconoides inflatus: inferences on Indian Ocean carbonate chemistry during late Quaternary’Century‐Long records of sedimentary input on a caribbean reef from coral Ba/Ca ratios
Published 14 May 2024 Science ClosedTags: biological response, BRcommunity, corals, laboratory, modeling, North Atlantic, regionalmodeling, sediment
Abstract
Coral reef ecosystems are delicately balanced and are thus prone to disruption by stressors such as storms, disease, climate variability and natural disasters. Most tropical coral populations worldwide are now in rapid decline owing to additional anthropogenic pressures, such as global warming, ocean acidification and a variety of local stressors. One such problem is the addition of excess sediment and nutrients flux to reefs from increased soil erosion from land use changes. Here we present century-long Ba/Ca records from two Siderastrea siderea colonies as a proxy for local riverine discharge and sediment flux to the southern Mesoamerican Barrier Reef System (MBRS). The coral colonies have linear extension trends, which can be seen as a first-order indicator for coral health and response. The coral colony that exhibits a decline in linear extension rate from the forereef of the MBRS, mainly receives riverine input from Honduras, whilst the coral from the backreef, which does not exhibit a decline in extension rate, primarily receives riverine input from more sparsely populated regions of Belize. Coral Ba/Ca increased (>70%) through time in the forereef colony, while the backreef colony showed little long-term increase in Ba/Ca over the last century. Our results suggest that increasing sediment supply may have played a role in the decline of forereef skeletal extension in the southernmost MBRS region, likely stemming from increasing land-use changes in Honduras.
Key Points
- Coral skeletal Ba/Ca measured by LA-ICP-MS is a proxy for river discharge and sediment flux to the reefs in this study
- Skeletal Ba/Ca has increased in forereef corals that mainly receive riverine flux from Honduras
- Results suggest that changing land-use around the Mesoamerican Barrier Reef System could be influencing long-term coral growth trends
Sea surface acidification events in the Andaman Sea associated with the last Toba volcanic activity
Published 7 May 2024 Science ClosedTags: chemistry, laboratory, paleo, sediment
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’Decline of a distinct coral reef holobiont community under ocean acidification
Published 22 April 2024 Science ClosedTags: algae, annelids, biological response, BRcommunity, bryozoa, chemistry, cnidaria, corals, laboratory, molecular biology, physiology, porifera, prokaryotes, sediment, South Pacific
Background
Microbes play vital roles across coral reefs both in the environment and inside and upon macrobes (holobionts), where they support critical functions such as nutrition and immune system modulation. These roles highlight the potential ecosystem-level importance of microbes, yet most knowledge of microbial functions on reefs is derived from a small set of holobionts such as corals and sponges. Declining seawater pH — an important global coral reef stressor — can cause ecosystem-level change on coral reefs, providing an opportunity to study the role of microbes at this scale. We use an in situ experimental approach to test the hypothesis that under such ocean acidification (OA), known shifts among macrobe trophic and functional groups may drive a general ecosystem-level response extending across macrobes and microbes, leading to reduced distinctness between the benthic holobiont community microbiome and the environmental microbiome.
Results
We test this hypothesis using genetic and chemical data from benthic coral reef community holobionts sampled across a pH gradient from CO2 seeps in Papua New Guinea. We find support for our hypothesis; under OA, the microbiome and metabolome of the benthic holobiont community become less compositionally distinct from the sediment microbiome and metabolome, suggesting that benthic macrobe communities are colonised by environmental microbes to a higher degree under OA conditions. We also find a simplification and homogenisation of the benthic photosynthetic community, and an increased abundance of fleshy macroalgae, consistent with previously observed reef microbialisation.
Conclusions
We demonstrate a novel structural shift in coral reefs involving macrobes and microbes: that the microbiome of the benthic holobiont community becomes less distinct from the sediment microbiome under OA. Our findings suggest that microbialisation and the disruption of macrobe trophic networks are interwoven general responses to environmental stress, pointing towards a universal, undesirable, and measurable form of ecosystem change.
Continue reading ‘Decline of a distinct coral reef holobiont community under ocean acidification’Meiobenthos and ocean acidification: effects on meiobenthic communities inhabiting Mediterranean cold shallow CO2-vents
Published 5 April 2024 Science ClosedTags: biological response, BRcommunity, chemistry, community composition, field, Mediterranean, nematodes, otherprocess, sediment, vents
Highlights
- Ocean acidification modify the composition of marine communities.
- Meiobenthos around Castello Aragonese is influenced by CO2 emissions.
- Nematofauna inhabiting CO2 vents is adapted to pH variability.
- Acidification influences nematode diversity and functional diversity.
- Sediment type and O2 are major factors affecting the nematofauna.
Abstract
Ocean acidification is causing major changes in marine ecosystems, with varying levels of impact, depending both on the habitat and the studied organisms. Here, we investigated for the first time the meiobenthos and nematode fauna inhabiting the sediments around Castello Aragonese (Ischia, Italy), characterized by variable pH values due to coastal volcanic CO2 venting. In this scenario, nematode functional diversity changed according to different pH levels and grain size: maturity index was higher at most acidic stations and trophic composition spanned from the dominance of predators in the acidic stations, to the high abundance of non-selective deposit feeders and epistrate feeders in the ambient-pH stations. Overall, the present study revealed a relatively high tolerance of meiobenthos and nematodes to lower pH conditions. However, an in-depth analysis of nematode fauna showed differences in their assemblages at different pH levels with few nematode genera rather adapted to the extreme environmental conditions at the acidic stations.
Continue reading ‘Meiobenthos and ocean acidification: effects on meiobenthic communities inhabiting Mediterranean cold shallow CO2-vents’Countering the effect of ocean acidification in coastal sediments through carbonate mineral additions
Published 4 April 2024 Science ClosedTags: biogeochemistry, chemistry, dissolution, mitigation, modeling, mollusks, regionalmodeling, sediment
Along with its impact on calcifying plankton, ocean acidification also affects benthic biogeochemistry and organisms. Compared to the overlying water, fluid composition in sediments is altered through the effect of the mineralization of organic matter, which can further lower both pH and the carbonate saturation state. This can potentially be counteracted by the addition of carbonate minerals to the sediment surface. To explore the biogeochemical effects of mineral additions to coastal sediments, we experimentally quantified carbonate mineral dissolution kinetics, and then integrated this data into a reactive transport model that represents early diagenetic cycling of C, O, N, S and Fe, and traces total alkalinity, pH and saturation state of CaCO3. Model simulations were carried out to delineate the impact of mineral type and amount added, porewater mixing and organic matter mineralization rates on sediment alkalinity and its flux to the overlying water. Model results showed that the added minerals undergo initial rapid dissolution and generate saturated conditions. Aragonite dissolution led to higher alkalinity concentrations than calcite. Simulations of carbonate mineral additions to sediment environments with low rates of organic matter mineralization exhibited a significant increase in mineral saturation state compared to sediments with high CO2 production rates, highlighting the environment-specific extent of the buffering effect. Our work indicates that carbonate additions have the potential to effectively buffer surficial sediments over multiple years, yielding biogeochemical conditions that counteract the detrimental effect of OA conditions on larval recruitment, and potentially increase benthic alkalinity fluxes to support marine carbon dioxide removal (mCDR) in the overlying water.
Continue reading ‘Countering the effect of ocean acidification in coastal sediments through carbonate mineral additions’Acidification offset warming-induced increase in N2O production in estuarine and coastal sediments
Published 22 March 2024 Science ClosedTags: biological response, BRcommunity, chemistry, community composition, field, laboratory, molecular biology, North Pacific, otherprocess, prokaryotes, sediment
Global warming and acidification, induced by a substantial increase in anthropogenic CO2 emissions, are expected to have profound impacts on biogeochemical cycles. However, underlying mechanisms of nitrous oxide (N2O) production in estuarine and coastal sediments remain rarely constrained under warming and acidification. Here, the responses of sediment N2O production pathways to warming and acidification were examined using a series of anoxic incubation experiments. Denitrification and N2O production were largely stimulated by the warming, while N2O production decreased under the acidification as well as the denitrification rate and electron transfer efficiency. Compared to warming alone, the combination of warming and acidification decreased N2O production by 26 ± 4%, which was mainly attributed to the decline of the N2O yield by fungal denitrification. Fungal denitrification was mainly responsible for N2O production under the warming condition, while bacterial denitrification predominated N2O production under the acidification condition. The reduced site preference of N2O under acidification reflects that the dominant pathways of N2O production were likely shifted from fungal to bacterial denitrification. In addition, acidification decreased the diversity and abundance of nirS-type denitrifiers, which were the keystone taxa mediating the low N2O production. Collectively, acidification can decrease sediment N2O yield through shifting the responsible production pathways, partly counteracting the warming-induced increase in N2O emissions, further reducing the positive climate warming feedback loop.
Continue reading ‘Acidification offset warming-induced increase in N2O production in estuarine and coastal sediments’Morphometric changes in Watznaueria barnesiae across the mid Cretaceous: Paleoecological implications
Published 5 March 2024 Science ClosedTags: biological response, field, Mediterranean, morphology, paleo, phytoplankton, sediment
Highligthts
- W. barnesiae evidenced moderate size variations in the mid Cretaceous (western Tethys).
- Size variations in W. barnesiae differed from those of B. constans.
- During OAE1a and OAE1b both species showed size reduction and ellipticity increase.
- The effects of fertility were opposite on the two species size variations.
Abstract
This study reveals moderate yet important variations in Watznaueria barnesiae coccolith and central unit size throughout the Aptian–late Cenomanian (27 my) time interval in western Tethys. A new statistical approach was applied to determine whether non-random size trends apply to these metrics and to identify possible links between their variation and fertility or temperature. During OAE 1a, W. barnesiae coccoliths were the smallest and the most elliptical, with reduced central unit size. A further minor size decrease occurs during OAE 1b but not during OAE 1d. From the middle Albian to the middle Cenomanian, larger and less elliptical coccoliths are observed, with unchanged central unit dimensions. These results, together with concomitantly larger size changes in Biscutum constans confirm that W. barnesiae is a tolerant taxon. High-frequency, high-amplitude paleoenvironmental changes during the Aptian–early Albian indicate that temperature and fertility – either individually or in combination – had no direct impact on the mean coccolith size and potentially other factors affected coccolith size. Instead, lower nutrients with lower temperatures probably played a role in promoting larger W. barnesiae but smaller B. constans coccoliths during the middle Albian–Cenomanian. The size and ellipticity changes during OAE 1a and 1b were the strongest, likely resulting from ocean acidification and trace metal inputs, in addition to (or independently of) fertility and temperature variations.
Continue reading ‘Morphometric changes in Watznaueria barnesiae across the mid Cretaceous: Paleoecological implications’Nannofossil imprints across the Paleocene-Eocene thermal maximum
Published 29 February 2024 Science ClosedTags: BRcommunity, chemistry, field, morphology, North Atlantic, paleo, phytoplankton, protists, sediment
The Paleocene–Eocene thermal maximum (PETM; ca. 56 Ma) geological interval records a marked decline in calcium carbonate (CaCO3) in seafloor sediments, potentially reflecting an episode of deep- and possibly shallow-water ocean acidification. However, because CaCO3 is susceptible to postburial dissolution, the extent to which this process has influenced the PETM geological record remains uncertain. Here, we tested for evidence of postburial dissolution by searching for imprint fossils of nannoplankton preserved on organic matter. We studied a PETM succession from the South Dover Bridge (SDB) core, Maryland, eastern United States, and compared our imprint record with previously published data from traditionally sampled CaCO3-preserved nannoplankton body fossils. Abundant imprints through intervals devoid of CaCO3 would signify that postburial dissolution removed much of the CaCO3 from the rock record. Imprints were recorded from most samples but were rare and of low diversity. Body fossils were substantially more numerous and diverse, capturing a more complete record of the living nannoplankton communities through the PETM. The SDB succession records a dissolution zone/low-carbonate interval at the onset of the PETM, through which nannoplankton body fossils are rare. No nannoplankton imprints were found from this interval, suggesting that the rarity of body fossils is unlikely to have been the result of postburial dissolution. Instead, our findings suggest that declines in CaCO3 through the PETM at the SDB location were the result of: (1) biotic responses to changes that were happening during this event, and/or (2) CaCO3 dissolution that occurred before lithification (i.e., in the water column or at the seafloor).
Continue reading ‘Nannofossil imprints across the Paleocene-Eocene thermal maximum’Archival records of the Antarctic clam shells from Marian Cove, King George Island suggest a protective mechanism against ocean acidification
Published 21 February 2024 Science ClosedTags: Antarctic, biological response, dissolution, field, mollusks, morphology, paleo, physiology, sediment
Abstract
Continuous emissions of anthropogenic CO2 are changing the atmospheric and oceanic environment. Although some species may have compensatory mechanisms to acclimatize or adapt to the changing environment, most marine organisms are negatively influenced by climate change. In this study, we aimed to understand the compensatory mechanisms of the Antarctic clam, Laternula elliptica, to climate-related stressors by using archived shells from 1995 to 2018. Principal component analysis revealed that seawater pCO2 and salinity in the Antarctic Ocean, which have increased since the 2000’s, are the most influential factors on the characteristics of the shell. The periostracum thickness ratio and nitrogen on the outermost surface have increased, and the dissolution area (%) has decreased. Furthermore, the calcium content and mechanical properties of the shells have not changed. The results suggest that L. elliptica retains the mechanism of protecting the shell from high pCO2 by thickening the periostracum as a phenotype plasticity.
Highlights
- We analyzed archival shells of the Antarctic clams in response to climate change.
- Seawater pCO2 and salinity in the Antarctic Ocean have increased since the 2000’s.
- Shell dissolution decreased over time while total shell thickness remained constant.
- The calcium content and mechanical properties of the shell remained unchanged.
- Shell integrity was retained by thickening the organic layer enriched with nitrogen.
Effects of acidification on the biogeochemistry of unvegetated and seagrass marine sediments
Published 14 February 2024 Science ClosedTags: chemistry, field, Mediterranean, sediment
Highlights
- A −0.3 pH units difference causes minor effects on unvegetated sediments organic matter
- Acidification slows down organic C degradation in unvegetated sediments
- Acidification stimulates organic C in seagrass sediments
- Acidification will affect benthic trophic webs under worsening ocean scenarios
Abstract
Many studies addressed ocean acidification (OA) effects on marine life, whereas its effects on sedimentary organic matter (OM) have received less attention. We investigated differences in OM features in sediments from unvegetated and seagrass (Posidonia oceanica) beds in a shallow hydrothermal area (Aeolian Archipelago, Mediterranean Sea), under natural (8.1–8.0) and acidified (7.8–7.9) conditions. We show that a pH difference of −0.3 units have minor effects on OM features in unvegetated sediments, but relevant consequences within acidified seagrass meadows, where OM quantity and nutritional quality are lower than those under natural pH conditions. Effects of acidified conditions on OM biogeochemistry vary between unvegetated and seagrass sediments, with lower C degradation rates and longer C turnover time in the former than in the latter. We conclude that OA, although with effects not consistent between unvegetated and vegetated sediments, can affect OM quantity, composition, and degradation, thus having possible far-reaching consequences for benthic trophic webs.
Continue reading ‘Effects of acidification on the biogeochemistry of unvegetated and seagrass marine sediments’Acidification and hypoxia in seawater, and pollutant enrichment in the sediments of Qi’ao Island mangrove wetlands, Pearl River Estuary, China
Published 9 February 2024 Science ClosedTags: chemistry, field, North Pacific, sediment
Highlights
- Nutrient absorption and consumption in the mangrove forest exhibited a significantly higher nitrogen-to-phosphorus ratio compared to utilized nutrients.
- The mangrove forest demonstrated a concerning trend of hypoxia and acidification, with dissolved oxygen saturation reaching a mere 57.0% and pH measuring 7.58 during ebb tides.
- The enrichment factors of oils, organic carbon, and sulfide were 4.37, 2.04, and 2.06, respectively, fostering the accumulation of total Hg, Zn, and Cu in the sediments of the mangrove forest.
Abstract
Mangrove forests are crucial in absorbing, storing, and purifying pollutants while maintaining ecological balance. A study was conducted in 2020 to investigate the biogeochemical processes of seawater and sedimentary environmental factors in the Qi’ao Island mangrove wetland. The study comprised two survey sections and ten survey stations within the mangrove forest and 16 large-scale survey stations in the adjacent sea area. During ebb tides, the mean concentrations of inorganic nitrogen and phosphate in Section D1 of the mangrove forest were 0.63 mg/L and 0.003 mg/L, respectively. These levels were significantly lower than the results observed in the adjacent sea area and Section D2 of the mangrove forest during flood tides. The mangrove forest efficiently absorbed and consumed nutrients, with the nitrogen-to-phosphorus ratio of consumed nutrients being notably higher than that typically utilized by plants during growth. We identified various biogeochemical processes, including nitrogen fixation, mineralization, nitrification, and denitrification, occurring within the mangrove forest. Seawater measurements in Section D1 during ebb tides showed the mean pH of 7.58 and dissolved oxygen levels of 4.52 mg/L, resulting in a dissolved oxygen saturation level of only 57.0 %. The low dissolved oxygen levels were attributed to organic matter degradation in the forest. Consequently, the longer the water retention time, the more obvious the trend of hypoxia and acidification was observed. In the adjacent sea area, the sedimentary environment was deemed healthy, with pollutants primarily originating from runoff and ship discharge from waterways and ports. However, within the mangrove forest, the sediments exhibited higher enrichment factors for organic carbon and sulfide, indicating significant pollution compared to the adjacent sea area. The sediments were conducive to the accumulation and burial of total Hg, Zn, and Cu, while other heavy metals did not show prominent deposition and enrichment. Notably, the enrichment factor of oils was as high as 4.37, leading to the formation of an oil pollution zone at the forest edge, and the enrichment of pollutants in sediment may inhibit the growth and expansion of mangroves. Overall, this study shed light on the occurrence of seawater acidification, hypoxia, and the behavior of sediment pollutants within the mangrove forest. The findings provide valuable insights to support efforts aimed at promoting and maintaining the ecosystem health of mangrove forests.
Continue reading ‘Acidification and hypoxia in seawater, and pollutant enrichment in the sediments of Qi’ao Island mangrove wetlands, Pearl River Estuary, China’Atmospheric CO2 estimates for the Late Oligocene and Early Miocene using multi-species cross-calibrations of boron isotopes
Published 31 January 2024 Science ClosedTags: biological response, BRcommunity, chemistry, methods, paleo, protists, sediment
Abstract
The boron isotope (δ11B) proxy for seawater pH is a tried and tested means to reconstruct atmospheric CO2 in the geologic past, but uncertainty remains over how to treat species-specific calibrations that link foraminiferal δ11B to pH estimates prior to 22 My. In addition, no δ11B-based reconstructions of atmospheric CO2 exist for wide swaths of the Oligocene (33–23 Ma), and large variability in CO2 reconstructions during this epoch based on other proxy evidence leaves climate evolution during this period relatively unconstrained. To add to our understanding of Oligocene and early Miocene climate, we generated new atmospheric CO2 estimates from new δ11B data from fossil shells of surface-dwelling planktic foraminifera from the mid-Oligocene to early Miocene (∼28–18 Ma). We estimate atmospheric CO2 of ∼680 ppm for the mid-Oligocene, which then evolves to fluctuate between ∼500–570 ppm during the late Oligocene and between ∼420–700 ppm in the early Miocene. These estimates tend to trend higher than Oligo-Miocene CO2 estimates from other proxies, although we observe good proxy agreement in the late Oligocene. Reconstructions of CO2 fall lower than estimates from paleoclimate model simulations in the early Miocene and mid Oligocene, which indicates that more proxy and/or model refinement is needed for these periods. Our species cross-calibrations, assessing δ11B, Mg/Ca, δ18O, and δ13C, are able to pinpoint and evaluate small differences in the geochemistry of surface-dwelling planktic foraminifera, lending confidence to paleoceanographers applying this approach even further back in time.
Key points:
- We measure δ11B on multiple species of planktic foraminifera to generate new CO2 reconstructions for the late Oligocene and early Miocene
- Using a novel cross-calibration approach, we reconstruct CO2 of 500–680 ppm for the mid-late Oligocene and 420–700 ppm for the early Miocene
- Mean CO2 values tend to trend higher than other proxy estimates, but generally lower than paleoclimate model simulations
Paleoceanographic importance of tri- and di-unsaturated alkenones through the early phase of Cretaceous Oceanic Anoxic Event 2 from southern high latitudes of the proto-Indian Ocean
Published 17 January 2024 Science ClosedTags: algae, biological response, field, Indian, paleo, physiology, sediment
Alkenones are biomarkers derived exclusively from species of haptophyte algae. The relative abundance of di- to tri-unsaturated C37 alkenones expressed as UK’37 is widely applied as a sea surface paleotemperature proxy for Cenozoic marine sediments. However, the absence of alkatrienones prior to the Eocene has precluded application of the UK’37 proxy for assessment of Cretaceous paleoclimates. Herein, we report a C40 alkatrienone (tetraconta-9E, 16E, 23E-trien-3-one; C40:3 Et) in deep-sea sediments from southern high latitudes (International Ocean Discovery Program: IODP site U1516). This discovery extends the geologic record of alkatrienones to the late Cenomanian, ∼70 million years earlier than previous reports. The parallel occurrence of higher abundances of a C40 alkadienone (tetraconta-16E, 23E-dien-3-one; C40:2 Et) allowed calculation of the UK’40 unsaturation index, comparable to UK’37. Stratigraphic variations in the δ13C of C40:2 Et revealed an elevated (∼1.5 ‰) positive carbon isotope excursion (CIE) relative to those observed in carbonate from other OAE2 sequences likely reflecting a decrease in global pCO2. The UK’40 profile suggests a concurrent drop in sea surface temperature associated with the decline in pCO2 during the early phase of OAE2. The timing of these environmental perturbations in the southern high latitude of the proto-Indian Ocean suggests they were triggered by volcanism associated with large igneous province (LIP) formation.
Incidence of the early Toarcian global change on Dasycladales (Chlorophyta) and the subsequent recovery: comparison with end-Triassic Mass Extinction
Published 17 January 2024 Science ClosedTags: community composition, otherprocess, paleo, phytoplankton, review, sediment
The early Toarcian biotic crisis (∼ 183 Ma), characterized in marine environments by abrupt temperature fluctuations, included a hyperthermal event (Jenkyns Event) with sea-level fluctuations, a carbon cycle perturbation, a crisis of carbonate productivity, and oxygen depleted conditions in some basins, resulting in a second order mass extinction. We suggest that the early Toarcian biotic crisis was key in the evolution of primary producers, including chlorophycean Dasycladales. The effect of the Jenkyns Event on Dasycladales has not been studied previously despite the fact that the impact on many groups of organisms have been the subject of many articles. In this work the stratigraphic distribution of Dasycladalean species from Upper Triassic to end of Jurassic is presented, discussed and compared with climatic fluctuations and sea-level changes.
The end-Triassic Mass Extinction constitutes a main biotic crisis for Dasycladales. All Triassic species became extinct at the Rhaetian-Hettangian boundary, and Dasycladales are not recorded in the lower Hettangian. The diversity of Dasycladales increased after the end-Triassic Mass Extinction and reached a maximum in the Sinemurian. Abrupt climatic changes related to the Pliensbachian/Toarcian boundary and the Jenkyns Event strongly affected the diversity of Dasycladales, very sensitive to sea-level and temperature fluctuations, as sessile benthic organisms inhabiting very shallow marine environments. Dasycladales are not recorded during the Toarcian. Sea-water acidification, enhanced weathering and increased terrigenous input from emerged lands —as well as potentially increased turbidity related to eutrophic conditions in some basins— were additional unfavorable conditions for Dasycladales, augmenting their ecological stress during the early Toarcian. The fragmentation of carbonate platforms in many Tethys paleomargins limited the shallower-water carbonate areas available for Dasycladales.
Warm conditions persisted during the middle and late Toarcian, less severe than during the Jenkyns Event according to oxygen isotopic data, and Dasycladales did not recover until the Bajocian and Bathonian. This biotic crisis for Dasycladales was longer than that of the end-Triassic Mass Extinction. The Callovian-Oxfordian transition was characterized by a cooling episode and a sea-level fall that produced a new biotic crisis affecting Dasycladales. From the middle Oxfordian, the increased temperature and sea-level rise, along with the development of large epeiric platforms, favored the carbonate productivity and diversity of primary producers, including Dasycladales, calcareous nannoplankton, dinoflagellate, calcareous Udoteaceae, and charophyte Clavatoraceae.
Continue reading ‘Incidence of the early Toarcian global change on Dasycladales (Chlorophyta) and the subsequent recovery: comparison with end-Triassic Mass Extinction’Shallow-water carbonate facies herald the onset of the Palaeocene eocene thermal maximum (Hazara basin, Northern Pakistan)
Published 27 December 2023 Science ClosedTags: abundance, biological response, community composition, corals, otherprocess, paleo, protists, sediment
Highlights
- Pre-PETM-onset neritic carbonates show early signs of what will occur during PETM.
- Corals declined over the study period, whereas foraminifera and red algae increased.
- Similar patterns can be observed in most of the Neotethys.
- Quantitative data are crucial to better understanding palaeo-environmental changes.
Abstract
We investigate the Palaeocene succession of the Hazara Basin (Northern Pakistan) to better understand the impact of climate change on marine carbonate-producing organisms. These shallow-water carbonates, deposited during the Late Palaeocene, before the onset of the Palaeocene-Eocene Thermal Maximum, were studied using a quantitative approach to highlight changes in the skeletal assemblage. We recognise a decrease in the abundance of colonial corals and green calcareous algae and an increase in larger benthic foraminifera and red calcareous algae from the early Thanetian to the late Thanetian. Increasing temperatures may represent a plausible cause for the decline of the more sensitive colonial corals in favor of the more tolerant larger benthic foraminifera. A similar pattern is observed in most successions deposited along the margins of the Neotethys Ocean, suggesting a connection with the Late Palaeocene environmental changes that heralded the PETM hyperthermal event. Our stratigraphic analysis of the Hazara Basin strata suggests that the biotic turnovers occurred during the Palaeocene – Eocene transition started already before the onset of the Palaeocene Eocene Thermal Maximum as recorded by the geochemical proxies.
Continue reading ‘Shallow-water carbonate facies herald the onset of the Palaeocene eocene thermal maximum (Hazara basin, Northern Pakistan)’Tidal, geological, and biological impacts to Humboldt Bay’s pH
Published 19 December 2023 Science ClosedTags: chemistry, field, North Pacific, sediment
This research examines factors that control pH in Humboldt Bay – a shallow, tidally-driven estuary in northern California (USA) that supports shellfisheries which are economically important to the state. Time-series data from hydrographic sensors at two Central and Northern California Ocean Observing System (CenCOOS) stations, as well as multiple 2021 undergraduate cruises, were used to understand the role of tides, biological productivity and carbonate dissolution in controlling pH on various timescales. Differences in pH, dissolved oxygen, chlorophyll, and temperature between an in-bay sensor and a coastal sensor indicate that the tidal flux exerts a long term, seasonal control on pH, but biological productivity substantially modifies carbon and oxygen thereby controlling pH on daily and weekly timescales. Sediment samples were also collected from the bay in 2021 to study carbonate dissolution. Sediments were incubated for three days in both stirred and unstirred conditions (to mimic tidal mixing and no tidal mixing respectively) and DO, pH and alkalinity were monitored. For all stirred incubations, large increases in pH and alkalinity suggested considerable carbonate sediment dissolution. When scaled to the bay’s in-situ suspended sediment concentrations, carbonate dissolution may exert a supplementary control on pH at similar time scales as biological productivity, but the magnitude of its effect is less.
Continue reading ‘Tidal, geological, and biological impacts to Humboldt Bay’s pH’Multi-proxy record of the mid-Maastrichtian event in the European Chalk Sea: paleoceanographic implications
Published 13 December 2023 Science ClosedTags: Baltic, chemistry, field, paleo, sediment
The Cretaceous provides us with an excellent case history of ocean-climate-biota system perturbations. Such perturbations occurred several times during the Cretaceous, such as oceanic anoxic events and the end-Cretaceous mass extinction, which have been the subject of an abundant literature. Other perturbations, such as the mid-Maastrichtian Event (MME) remain poorly understood. The MME was associated with global sea-level rise, changes in climate and deep-water circulation that were accompanied by biotic extinctions including “true” inoceramids and the demise of the Caribbean-Tethyan rudist reef ecosystems. So far, the context and causes behind the MME remain poorly studied. We conducted high-resolution integrated biotic, petrological and geochemical studies in order to fill this knowledge gap. We studied, in particular, carbonate Nd and Os isotopes, whole-rock Hg, C and N content, C and N isotopes in organic matter, SCAS isotopes, along with C and O isotopes from foraminifera from the European Chalk Sea: the Polanówka UW-1 core from Poland and the Stevns-1 core from Denmark. Our data showed that sea-level rise of ∼50-100 m lasted around ∼2 Ma and co-occurred with anomalously high mercury concentration. Along with previously published data, our results strongly suggest that the MME was driven by intense volcanic–tectonic activity, likely related to the production of vast oceanic plateaus (LIP, Large Igneous Province). The collapse of reef ecosystems could have been the consequence of LIP-related environmental stress factors, including climate warming, presumably caused by emission of greenhouse gases, modification of the oceanic circulation, oceanic acidification and/or toxic metal input. The disappearance of the foraminifer Stensioeina lineage on the European shelf was likely caused by the collapse of primary production triggered by sea-level rise and limited amount of nutrient input. Nd isotopes and foraminiferal assemblages attest for changes in sea-water circulation in the European Shelf and the increasing contribution of North Atlantic water masses.
Continue reading ‘Multi-proxy record of the mid-Maastrichtian event in the European Chalk Sea: paleoceanographic implications’
