scholarly journals The recovery of the biological pump across the K/Pg boundary in the GSSP of El Kef, Tunisia

2021 ◽  
Author(s):  
Joep van Dijk ◽  
Julio Sepúlveda ◽  
Laia Alegret ◽  
Heather Birch ◽  
Timothy Bralower ◽  
...  
Keyword(s):  
Isotopic Composition ◽  
Carbon Fixation ◽  
Open Ocean ◽  
Marine Phytoplankton ◽  
Outer Shelf ◽  
Biological Pump ◽  
Mass Extinctions ◽  
Physiological Models ◽  
El Kef ◽  
The Impact

<p>The study of Earth’s Big Five mass extinctions provides insight into the resilience of ecosystems to environmental perturbations. Earth’s most recent mass extinction at the Cretaceous/Paleogene boundary (K/Pg) was caused by the impact of an asteroid in the Yucatan peninsula rather than by intense volcanism. Mass extinctions among marine calcareous nannoplankton heavily disrupted the marine food web resulting in a severe weakening of the ocean’s biological pump. The timing and heterogeneous nature of the recovery of the biological pump remain poorly resolved in the neritic zone in the aftermath of the impact. Here, we address the evolution of the biological pump across the K/Pg at the Global Boundary Stratotype Section (GSSP) at El Kef, Tunisia using high-resolution compound-specific carbon isotope records (<em>δ</em><sup>13</sup>C<sub>biomarker</sub>) of non-calcareous marine phototrophs from an outer shelf to upper bathyal setting of the southwestern Tethys Ocean. We use <em>δ</em><sup>13</sup>C<sub>biomarker</sub> to reconstruct ε<sub>p</sub>, which is a function of the community structure of marine phototrophs, their rate of carbon fixation, and the concentration and isotopic composition of aqueous CO<sub>2</sub>. We then use our <em>ε</em><sub>p</sub> record to constrain the recovery of the biological pump in this region while considering the composition of marine phytoplankton, the assemblage and isotopic composition of benthic foraminifera, state-of-the-art physiological models for <em>ε</em><sub>p</sub>, and carbon cycle simulations using cGENIE. Our results indicate that the recovery of the biological pump in the outer shelf-upper bathyal zone likely outpaced the recovery in the open ocean. This is in agreement with the selective extinctions among phytoplankton at the K/Pg, with most survivors that would later repopulate open-ocean sites being adapted to neritic environments.</p>

scholarly journals Marine Phytoplankton Stoichiometry Mediates Nonlinear Interactions Between Nutrient Supply, Temperature, and Atmospheric CO<sub>2</sub>

2017 ◽  
Author(s):  
Allison R. Moreno ◽  
George I. Hagstrom ◽  
Francois W. Primeau ◽  
Simon A. Levin ◽  
Adam C. Martiny
Keyword(s):  
Carbon Cycling ◽  
Ocean Circulation ◽  
Negative Relationship ◽  
Nutrient Supply ◽  
Marine Phytoplankton ◽  
Phosphorus Concentration ◽  
Biological Pump ◽  
Carbon Export ◽  
Environmental Model ◽  
The Impact

Abstract. Marine phytoplankton stoichiometry links nutrient supply to marine carbon export. Deviations of phytoplankton stoichiometry from Redfield proportions (106C : 1P) could therefore have a significant impact on carbon cycling, and understanding which environmental factors drive these deviations may reveal new mechanisms that regulate the carbon cycle. To explore the links between environmental conditions, stoichiometry, and carbon cycling, we compared four different models for variations in phytoplankton C : P: a fixed Redfield model, a model with C : P given as a function of surface phosphorus concentration ([P]), a model with C : P given as a function of temperature, and a new multi-environmental model that predicts C : P as a function of light, temperature, and [P]. These stoichiometric models were embedded into a box model of the ocean circulation, which resolves the three major ocean biomes (high-latitude, subtropical gyres, and iron-limited tropical upwelling regions). Contrary to the expectation of a monotonic relationship between surface nutrient drawdown and carbon export, we found that lateral nutrient transport from lower C : P tropical waters to high C : P subtropical waters could cause carbon-export to decrease with increased tropical nutrient utilization. Temperature is thought to be one of the primary drivers of changes in atmospheric pCO2 (pCO2,atm) across glacial/interglacial periods, and it has been hypothesized that a positive feedback between temperature and pCO2,atm will play an important role in anthropogenic climate change, with changes in the biological pump playing at most a secondary role. Here we show that environmentally driven shifts in stoichiometry make the biological pump more influential, and may reverse the expected negative relationship between temperature and pCO2,atm. In the temperature-only model changes in tropical temperature have more impact on the Δ pCO2,atm (~ 41 ppm) compared to subtropical temperature (~ 4.5 ppm). Our multi-environmental model produced a decline in pCO2,atm of ~ 46 when temperature spanned a change of 10 °C. Thus, we find that variation in marine phytoplankton stoichiometry and its environmental controlling factor can lead to counterintuitive controls on pCO2,atm, suggesting the need for further studies of ocean C : P and the impact on ocean carbon cycling.

scholarly journals Marine phytoplankton stoichiometry mediates nonlinear interactions between nutrient supply, temperature, and atmospheric CO<sub>2</sub>

2018 ◽  
Vol 15 (9) ◽  
pp. 2761-2779 ◽  
Author(s):  
Allison R. Moreno ◽  
George I. Hagstrom ◽  
Francois W. Primeau ◽  
Simon A. Levin ◽  
Adam C. Martiny
Keyword(s):  
Carbon Cycling ◽  
Ocean Circulation ◽  
Circulation Model ◽  
Nutrient Supply ◽  
Marine Phytoplankton ◽  
Phosphorus Concentration ◽  
Biological Pump ◽  
Carbon Export ◽  
Environmental Model ◽  
The Impact

Abstract. Marine phytoplankton stoichiometry links nutrient supply to marine carbon export. Deviations of phytoplankton stoichiometry from Redfield proportions (106C : 1P) could therefore have a significant impact on carbon cycling, and understanding which environmental factors drive these deviations may reveal new mechanisms regulating the carbon cycle. To explore the links between environmental conditions, stoichiometry, and carbon cycling, we compared four different models of phytoplankton C : P: a fixed Redfield model, a model with C : P given as a function of surface phosphorus concentration (P), a model with C   P given as a function of temperature, and a new multi-environmental model that predicts C : P as a function of light, temperature, and P. These stoichiometric models were embedded into a five-box ocean circulation model, which resolves the three major ocean biomes (high-latitude, subtropical gyres, and tropical upwelling regions). Contrary to the expectation of a monotonic relationship between surface nutrient drawdown and carbon export, we found that lateral nutrient transport from lower C : P tropical waters to high C : P subtropical waters could cause carbon export to decrease with increased tropical nutrient utilization. It has been hypothesized that a positive feedback between temperature and pCO2, atm will play an important role in anthropogenic climate change, with changes in the biological pump playing at most a secondary role. Here we show that environmentally driven shifts in stoichiometry make the biological pump more influential, and may reverse the expected positive relationship between temperature and pCO2, atm. In the temperature-only model, changes in tropical temperature have more impact on the Δ pCO2, atm (∼ 41 ppm) compared to subtropical temperature changes (∼ 4.5 ppm). Our multi-environmental model predicted a decline in pCO2, atm of ∼ 46 ppm when temperature spanned a change of 10 °C. Thus, we find that variation in marine phytoplankton stoichiometry and its environmental controlling factors can lead to nonlinear controls on pCO2, atm, suggesting the need for further studies of ocean C : P and the impact on ocean carbon cycling.

A state-of-the-art parameterization of atmospheric nutrient deposition fluxes in the global ocean

2020 ◽  
Author(s):  
Stelios Myriokefalitakis ◽  
Matthias Gröger ◽  
Jenny Hieronymus ◽  
Ralf Döscher
Keyword(s):  
Atmospheric Deposition ◽  
State Of The Art ◽  
Marine Ecosystem ◽  
Open Ocean ◽  
Marine Phytoplankton ◽  
Global Ocean ◽  
Model Calculations ◽  
Deposition Fluxes ◽  
Atmospheric Processing ◽  
The Impact

&lt;p&gt;Atmospheric deposition of trace constituents of natural and anthropogenic origin act as a nutrient source into the open ocean, affecting the marine ecosystem functioning and subsequently the exchange of CO&lt;sub&gt;2&lt;/sub&gt; between the atmosphere and the global ocean. Among other species that are deposited into the open ocean, nitrogen (N), iron (Fe), and phosphorus (P) are considered as highly significant nutrients that can limit marine phytoplankton growth and thus directly impact on ocean carbon fluxes in the ocean, particularly where the nutrient availability is the limiting factor for productivity. For this work, we take into account the up-to-date understanding of the effects of air quality on the atmospheric aerosol cycles to investigate the potential ocean biogeochemistry perturbations via the atmospheric input with the European Community Earth System Model EC-Earth (http://www.ec-earth.org/), which is jointly developed by several European institutes. In more detail, state-of-the-art N, Fe, and P atmospheric deposition fields are coupled to the embedded marine biogeochemistry model and the response of oceanic biogeochemistry to natural and anthropogenic atmospheric aerosols deposition changes is demonstrated and quantified. Model calculations show that compared to the present day, the preindustrial atmospheric deposition fluxes are calculated lower (~1.7, ~1.5, and ~1.4 times for N, Fe, and P, respectively) corresponding to a respective lower marine primary production. On the other hand, future changes in air pollutants under the RCP8.5 scenario result in a modest decrease of the bioaccessible nutrients input into the global ocean (~ -15%, ~ -16% and ~ -22% for N, Fe and P, respectively) and overall to a slightly lower projected export production compared to present day. Although the impact of atmospheric processing on atmospheric inputs to the ocean results in a relatively weak response in total global-scale simulated marine productivity estimates, strong regional changes up to 40-60% are calculated in the subtropical gyres. Overall, this study indicates that both the atmospheric processing and the speciation of the atmospheric nutrients deposited in the ocean should be considered in detail in carbon-cycling studies, since they may significantly affect the marine ecosystems and thus the current estimates of the carbon cycle feedbacks to climate.&lt;/p&gt;&lt;p&gt;This work has been financed by the National Observatory of Athens internal grant (number 5065), the &amp;#8220;Atmospheric deposition impacts on the ocean system&amp;#8221;, and the European Commission's Horizon 2020 Framework Programme, under Grant Agreement number 641816, the &quot;Coordinated Research in Earth Systems and Climate: Experiments, kNowledge, Dissemination, and Outreach (CRESCENDO)&quot;.&lt;/p&gt;

scholarly journals Pb isotopes in the impact melt breccia 66095: Association with the Imbrium basin and the isotopic composition of lithologies at the Apollo 16 landing site

2017 ◽  
Vol 466 ◽  
pp. 608-616 ◽  
Author(s):  
Joshua F. Snape ◽  
Alexander A. Nemchin ◽  
Jeremy J. Bellucci ◽  
Martin J. Whitehouse
Keyword(s):  
Isotopic Composition ◽  
Landing Site ◽  
Pb Isotopes ◽  
Impact Melt ◽  
The Impact

scholarly journals Investigation of post-depositional processing of nitrate in East Antarctic snow: isotopic constraints on photolytic loss, re-oxidation, and source inputs

2015 ◽  
Vol 15 (16) ◽  
pp. 9435-9453 ◽  
Author(s):  
G. Shi ◽  
A. M. Buffen ◽  
M. G. Hastings ◽  
C. Li ◽  
H. Ma ◽  
...  
Keyword(s):  
Isotopic Composition ◽  
Mass Fraction ◽  
Stratospheric Ozone ◽  
Warm Season ◽  
Cold Season ◽  
Depth Interval ◽  
Depositional Processes ◽  
Antarctic Snow ◽  
Exponential Change ◽  
The Impact

Abstract. Snowpits along a traverse from coastal East Antarctica to the summit of the ice sheet (Dome Argus) are used to investigate the post-depositional processing of nitrate (NO3−) in snow. Seven snowpits from sites with accumulation rates between 24 and 172 kg m−2 a−1 were sampled to depths of 150 to 300 cm. At sites from the continental interior (low accumulation, < 55 kg m−2 a−1), nitrate mass fraction is generally > 200 ng g−1 in surface snow and decreases quickly with depth to < 50 ng g−1. Considerably increasing values of δ15N of nitrate are also observed (16–461 ‰ vs. air N2), particularly in the top 20 cm, which is consistent with predicted fractionation constants for the photolysis of nitrate. The δ18O of nitrate (17–84 ‰ vs. VSMOW (Vienna Standard Mean Ocean Water)), on the other hand, decreases with increasing δ15N, suggestive of secondary formation of nitrate in situ (following photolysis) with a low δ18O source. Previous studies have suggested that δ15N and δ18O of nitrate at deeper snow depths should be predictable based upon an exponential change derived near the surface. At deeper depths sampled in this study, however, the relationship between nitrate mass fraction and δ18O changes, with increasing δ18O of nitrate observed between 100 and 200 cm. Predicting the impact of post-depositional loss, and therefore changes in the isotopes with depth, is highly sensitive to the depth interval over which an exponential change is assumed. In the snowpits collected closer to the coast (accumulation > 91 kg m−2 a−1), there are no obvious trends detected with depth and instead seasonality in nitrate mass fraction and isotopic composition is found. In comparison to the interior sites, the coastal pits are lower in δ15N (−15–71 ‰ vs. air N2) and higher in δ18O of nitrate (53–111 ‰ vs. VSMOW). The relationships found amongst mass fraction, δ15N, δ18O and Δ17O (Δ17O = δ17O–0.52 × δ18O) of nitrate cannot be explained by local post-depositional processes alone, and are instead interpreted in the context of a primary atmospheric signal. Consistent with other Antarctic observational and modeling studies, the isotopic results are suggestive of an important influence of stratospheric ozone chemistry on nitrate formation during the cold season and a mix of tropospheric sources and chemistry during the warm season. Overall, the findings in this study speak to the sensitivity of nitrate isotopic composition to post-depositional processing and highlight the strength of combined use of the nitrogen and oxygen isotopes for a mechanistic understanding of this processing.

scholarly journals Resolving ecological feedbacks on the ocean carbon sink in Earth system models

2020 ◽  
Author(s):  
David I. Armstrong McKay ◽  
Sarah E. Cornell ◽  
Katherine Richardson ◽  
Johan Rockström
Keyword(s):  
Climate Change ◽  
Carbon Sink ◽  
Biological Pump ◽  
Earth System ◽  
Temperature Dependent ◽  
System Models ◽  
Plankton Ecology ◽  
Ocean Carbon ◽  
The Impact ◽  
Earth System Models

Abstract. The Earth’s oceans are one of the largest sinks in the Earth system for anthropogenic CO2 emissions, acting as a negative feedback on climate change. Earth system models predict, though, that climate change will lead to a weakening ocean carbon uptake rate as warm water holds less dissolved CO2 and biological productivity declines. However, most Earth system models do not incorporate the impact of warming on bacterial remineralisation and rely on simplified representations of plankton ecology that do not resolve the potential impact of climate change on ecosystem structure or elemental stoichiometry. Here we use a recently-developed extension of the cGEnIE Earth system model (ecoGEnIE) featuring a trait-based scheme for plankton ecology (ECOGEM), and also incorporate cGEnIE's temperature-dependent remineralisation (TDR) scheme. This enables evaluation of the impact of both ecological dynamics and temperature-dependent remineralisation on the soft-tissue biological pump in response to climate change. We find that including TDR strengthens the biological pump relative to default runs due to increased nutrient recycling, while ECOGEM weakens the biological pump by enabling a shift to smaller plankton classes. However, interactions with concurrent ocean acidification cause opposite sign responses for the carbon sink in both cases: TDR leads to a smaller sink relative to default runs whereas ECOGEM leads to a larger sink. Combining TDR and ECOGEM results in a net strengthening of the biological pump and a small net reduction in carbon sink relative to default. These results clearly illustrate the substantial degree to which ecological dynamics and biodiversity modulate the strength of climate-biosphere feedbacks, and demonstrate that Earth system models need to incorporate more ecological complexity in order to resolve carbon sink weakening.

scholarly journals Microbial dark carbon fixation fueled by nitrate enrichment

2021 ◽  
Author(s):  
Joseph H. Vineis ◽  
Ashley N. Bulseco ◽  
Jennifer L. Bowen
Keyword(s):  
Microbial Communities ◽  
Marine Sediments ◽  
Salt Marshes ◽  
Carbon Fixation ◽  
Niche Partitioning ◽  
Coastal Marine Sediments ◽  
Functional Relationships ◽  
Coastal Marine ◽  
Dark Carbon Fixation ◽  
The Impact

Anthropogenic nitrate amendment to coastal marine sediments can increase rates of heterotrophic mineralization and autotrophic dark carbon fixation (DCF). DCF may be favored in sediments where organic matter is biologically unavailable, leading to a microbial community supported by chemoautotrophy. Niche partitioning among DCF communities and adaptations for nitrate metabolism in coastal marine sediments remain poorly characterized, especially within salt marshes. We used genome-resolved metagenomics, phylogenetics, and comparative genomics to characterize the potential niche space, phylogenetic relationships, and adaptations important to microbial communities within nitrate enriched sediment. We found that nitrate enrichment of sediment from discrete depths between 0-25 cm supported both heterotrophs and chemoautotrophs that use sulfur oxidizing denitrification to drive the Calvin-Benson-Bassham (CBB) or reductive TCA (rTCA) DCF pathways. Phylogenetic reconstruction indicated that the nitrate enriched community represented a small fraction of the phylogenetic diversity contained in coastal marine environmental genomes, while pangenomics revealed close evolutionary and functional relationships with DCF microbes in other oligotrophic environments. These results indicate that DCF can support coastal marine microbial communities and should be carefully considered when estimating the impact of nitrate on carbon cycling in these critical habitats.

scholarly journals Desiccation-crack-induced salinization in deep clay sediment

2012 ◽  
Vol 9 (11) ◽  
pp. 13155-13189
Author(s):  
S. Baram ◽  
Z. Ronen ◽  
D. Kurtzman ◽  
C. Küells ◽  
O. Dahan
Keyword(s):  
Isotopic Composition ◽  
Conceptual Model ◽  
Pore Water ◽  
Vadose Zone ◽  
Land Surface ◽  
Water Infiltration ◽  
Arid Environments ◽  
Desiccation Cracks ◽  
The Impact ◽  
Desiccation Crack

Abstract. A study on water infiltration and solute transport in a clayey vadose zone underlying a dairy farm waste source was conducted to assess the impact of desiccation cracks on subsurface evaporation and salinization. The study is based on five years of continuous measurements of the temporal variation in the vadose zone water-content and on the chemical and isotopic composition of the sediment and pore-water in it. The isotopic composition of water stable isotopes (δ18O and δ2H) in water and sediment samples, from the area where desiccation crack networks prevail, indicated subsurface evaporation down to ∼3.5 m below land surface, and vertical and lateral preferential transport of water, following erratic preferential infiltration events. Chloride (Cl-) concentrations in the vadose zone pore water substantially increased with depth, evidence of deep subsurface evaporation and down flushing of concentrated solutions from the evaporation zones during preferential infiltration events. These observations led to development of a Desiccation-Crack-Induced Salinization (DCIS) conceptual model. DCIS suggests that thermally driven convective air flow in the desiccation cracks induces evaporation and salinization in relatively deep sections of the subsurface. This conceptual model supports previous conceptual models on vadose zone and groundwater salinization in fractured rock in arid environments and extends its validity to clayey soils in semi-arid environments.

scholarly journals How marine emissions of bromoform impact the remote atmosphere

2019 ◽  
Vol 19 (17) ◽  
pp. 11089-11103 ◽  
Author(s):  
Yue Jia ◽  
Susann Tegtmeier ◽  
Elliot Atlas ◽  
Birgit Quack
Keyword(s):  
Dispersion Model ◽  
Hot Spot ◽  
Open Ocean ◽  
Advective Transport ◽  
Localized Source ◽  
Mixing Ratios ◽  
Low Wind Speed ◽  
Uniform Background ◽  
Lagrangian Dispersion ◽  
The Impact

Abstract. It is an open question how localized elevated emissions of bromoform (CHBr3) and other very short-lived halocarbons (VSLHs), found in coastal and upwelling regions, and low background emissions, typically found over the open ocean, impact the atmospheric VSLH distribution. In this study, we use the Lagrangian dispersion model FLEXPART to simulate atmospheric CHBr3 resulting from assumed uniform background emissions, and from elevated emissions consistent with those derived during three tropical cruise campaigns. The simulations demonstrate that the atmospheric CHBr3 distributions in the uniform background emissions scenario are highly variable with high mixing ratios appearing in regions of convergence or low wind speed. This relation holds on regional and global scales. The impact of localized elevated emissions on the atmospheric CHBr3 distribution varies significantly from campaign to campaign. The estimated impact depends on the strength of the emissions and the meteorological conditions. In the open waters of the western Pacific and Indian oceans, localized elevated emissions only slightly increase the background concentrations of atmospheric CHBr3, even when 1∘ wide source regions along the cruise tracks are assumed. Near the coast, elevated emissions, including hot spots up to 100 times larger than the uniform background emissions, can be strong enough to be distinguished from the atmospheric background. However, it is not necessarily the highest hot spot emission that produces the largest enhancement, since the tug-of-war between fast advective transport and local accumulation at the time of emission is also important. Our results demonstrate that transport variations in the atmosphere itself are sufficient to produce highly variable VSLH distributions, and elevated VSLHs in the atmosphere do not always reflect a strong localized source. Localized elevated emissions can be obliterated by the highly variable atmospheric background, even if they are orders of magnitude larger than the average open ocean emissions.

Reefs as the Centralizing Theme in an Undergraduate Invertebrate Paleontology Course

2012 ◽  
Vol 12 ◽  
pp. 21-42
Author(s):  
Constance M. Soja
Keyword(s):  
Fossil Record ◽  
Evolutionary History ◽  
Marine Invertebrate ◽  
Scientific Information ◽  
Field Trip ◽  
Mass Extinctions ◽  
Paleontological Data ◽  
San Salvador ◽  
Invertebrate Paleontology ◽  
The Impact

This course is designed so that topics in invertebrate paleontology are discussed in the context of reefs and their change through time. The goal is to help undergraduate students connect modern conservation issues with an enlightened appreciation of the fossil record. Using reefs as the centralizing theme of the course allows key concepts (invertebrate taxonomy and systematics, form and function, evolution, etc.) to be emphasized while exploring the importance of biogenic buildups—and communities that inhabited ecosystems adjacent to those “engines of evolution”—from the past to the present. Students who satisfactorily complete the course achieve seven main learning objectives: They 1) are intimately familiar with the fossil record of marine invertebrate life; 2) understand the evolutionary history of reefs and the ecological roles played by key reef-building invertebrates through time; 3) are able to engage in discussions about paleontological data published in the primary literature; 4) are knowledgeable about the value of paleontological evidence for shedding insights into the decline of ancient and living reefs; 5) gain experience working collaboratively and thinking outside-of-the-box to explore solutions to societal problems linked with the degradation of modern coral reefs; 6) improve scientific writing; and 7) develop a personal style for communicating scientific information to the general public. During classroom discussions, laboratories, a field trip, and museum visit, students explore the anatomy, ecology, evolutionary history, and life-sustaining ecosystem services of shelly animals and associated marine organisms that coexisted in reefs and adjacent habitats past and present. Evolutionary events, including the Cambrian “explosion,” mass extinctions, and gaps in reef existence, are linked to dramatic physical (tectonic) and climatic changes that occurred in Earth's past. Emphasizing evidence for the impact of global change on ancient reef communities alerts students to the value of paleontological data for predicting how modern reefs—and invertebrates living in interconnected marine ecosystems—will respond as the Sixth Extinction gains traction. That topic is the focus of an optional extended study (nine-day field trip offered in alternate years during spring break) of modern and Pleistocene reefs on San Salvador Island, Bahamas.

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