Organic carbon burial in Mediterranean sapropels intensified during Green Sahara Periods since 3.2 Myr ago

AbstractDark organic-rich layers (sapropels) have accumulated in Mediterranean sediments since the Miocene due to deep-sea dysoxia and enhanced carbon burial at times of intensified North African run-off during Green Sahara Periods (GSPs). The existence of orbital precession-dominated Saharan aridity/humidity cycles is well known, but lack of long-term, high-resolution records hinders understanding of their relationship with environmental evolution. Here we present continuous, high-resolution geochemical and environmental magnetic records for the Eastern Mediterranean spanning the past 5.2 million years, which reveal that organic burial intensified 3.2 Myr ago. We deduce that fluvial terrigenous sediment inputs during GSPs doubled abruptly at this time, whereas monsoon run-off intensity remained relatively constant. We hypothesize that increased sediment mobilization resulted from an abrupt non-linear North African landscape response associated with a major increase in arid:humid contrasts between GSPs and intervening dry periods. The timing strongly suggests a link to the onset of intensified northern hemisphere glaciation.

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Abrupt change in North African hydroclimate and landscape evolution 3.2 million years ago

10.21203/rs.3.rs-579142/v1 ◽

2021 ◽

Author(s):

Katharine Grant ◽

Udara Amarathunga ◽

Jessica Amies ◽

Pengxiang Hu ◽

Yao Qian ◽

...

Keyword(s):

High Resolution ◽

Eastern Mediterranean ◽

North African ◽

Hominin Evolution ◽

Carbon Burial ◽

Run Off ◽

Landscape Response ◽

Major Increase ◽

And Migration

Abstract Dark organic-rich layers (sapropels) have accumulated in Mediterranean sediments since the Miocene due to deep-sea dysoxia and enhanced carbon burial at times of intensified North African run-off during ‘Green’ Sahara Periods (GSPs). The existence of orbital precession-dominated Saharan aridity/humidity cycles is well known, but lack of long-term, high-resolution records hinders understanding of their precise relationships with environmental and hominin evolution. Here we present continuous, high-resolution geochemical and environmental magnetic records for the Eastern Mediterranean that span the past 5.2 million years, which reveal that organic burial in sapropels intensified 3.2 Myr ago. We deduce that fluvial terrigenous sediment inputs during GSPs doubled abruptly at this time, whereas monsoon run-off intensity remained relatively constant. We attribute the increase in sediment mobilisation to an abrupt non-linear North African landscape response associated with a major increase in arid:humid contrasts between GSPs and intervening dry periods. This likely limited hominin (and other animal) inhabitation of, and migration through, the Sahara region to GSPs only.

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Long-term Aptian marine osmium isotopic record of Ontong Java Nui activity

Geology ◽

10.1130/g48863.1 ◽

2021 ◽

Author(s):

Hironao Matsumoto ◽

Rodolfo Coccioni ◽

Fabrizio Frontalini ◽

Kotaro Shirai ◽

Luigi Jovane ◽

...

Keyword(s):

Organic Carbon ◽

Volcanic Eruptions ◽

Hydrothermal Activity ◽

Published Data ◽

Isotopic Data ◽

Oceanic Plateaus ◽

Carbon Burial ◽

Organic Carbon Burial ◽

Isotopic Records

The early to mid-Aptian was punctuated by episodic phases of organic-carbon burial in various oceanographic settings, which are possibly related to massive volcanism associated with the emplacement of the Ontong Java, Manihiki, and Hikurangi oceanic plateaus in the southwestern Pacific Ocean, inferred to have formed a single plateau called Ontong Java Nui. Sedimentary osmium (Os) isotopic compositions are one of the best proxies for determining the timing of voluminous submarine volcanic episodes. However, available Os isotopic records during the age are limited to a narrow interval in the earliest Aptian, which is insufficient for the reconstruction of long-term hydrothermal activity. We document the early to mid-Aptian Os isotopic record using pelagic Tethyan sediments deposited in the Poggio le Guaine (Umbria-Marche Basin, Italy) to precisely constrain the timing of massive volcanic episodes and to assess their impact on the marine environment. Our new Os isotopic data reveal three shifts to unradiogenic values, two of which correspond to black shale horizons in the lower to mid-Aptian, namely the Wezel (herein named) and Fallot Levels. These Os isotopic excursions are ascribed to massive inputs of unradiogenic Os to the ocean through hydrothermal activity. Combining the new Os isotopic record with published data from the lowermost Aptian organic-rich interval in the Gorgo a Cerbara section of the Umbria-Marche Basin, it can be inferred that Ontong Java Nui volcanic eruptions persisted for ~5 m.y. during the early to mid-Aptian.

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Earliest land plants created modern levels of atmospheric oxygen

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1604787113 ◽

2016 ◽

Vol 113 (35) ◽

pp. 9704-9709 ◽

Cited By ~ 99

Author(s):

Timothy M. Lenton ◽

Tais W. Dahl ◽

Stuart J. Daines ◽

Benjamin J. W. Mills ◽

Kazumi Ozaki ◽

...

Keyword(s):

Organic Carbon ◽

Land Surface ◽

Atmospheric Oxygen ◽

Geochemical Data ◽

Regulatory Regime ◽

Carbon Burial ◽

C:P Ratio ◽

Marine Biomass ◽

Organic Carbon Burial

The progressive oxygenation of the Earth’s atmosphere was pivotal to the evolution of life, but the puzzle of when and how atmospheric oxygen (O2) first approached modern levels (∼21%) remains unresolved. Redox proxy data indicate the deep oceans were oxygenated during 435–392 Ma, and the appearance of fossil charcoal indicates O2 >15–17% by 420–400 Ma. However, existing models have failed to predict oxygenation at this time. Here we show that the earliest plants, which colonized the land surface from ∼470 Ma onward, were responsible for this mid-Paleozoic oxygenation event, through greatly increasing global organic carbon burial—the net long-term source of O2. We use a trait-based ecophysiological model to predict that cryptogamic vegetation cover could have achieved ∼30% of today’s global terrestrial net primary productivity by ∼445 Ma. Data from modern bryophytes suggests this plentiful early plant material had a much higher molar C:P ratio (∼2,000) than marine biomass (∼100), such that a given weathering flux of phosphorus could support more organic carbon burial. Furthermore, recent experiments suggest that early plants selectively increased the flux of phosphorus (relative to alkalinity) weathered from rocks. Combining these effects in a model of long-term biogeochemical cycling, we reproduce a sustained +2‰ increase in the carbonate carbon isotope (δ13C) record by ∼445 Ma, and predict a corresponding rise in O2 to present levels by 420–400 Ma, consistent with geochemical data. This oxygen rise represents a permanent shift in regulatory regime to one where fire-mediated negative feedbacks stabilize high O2 levels.

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Exploring the Growing Role of Terrestrial Carbon Across North Atlantic Fjords

10.5194/egusphere-egu2020-9393 ◽

2020 ◽

Author(s):

Craig Smeaton ◽

William Austin

Keyword(s):

Organic Carbon ◽

Marine Environment ◽

North Atlantic ◽

Planetary Science ◽

Terrestrial Environment ◽

Carbon Burial ◽

Organic Carbon Burial ◽

Fjord Sediments

Fjords are recognized as globally significant hotspots for the burial (Smith et al., 2015) and long-term storage (Smeaton et al., 2017) of marine and terrestrially derived organic carbon (OC). By trapping and locking away OC over geological timescales, fjord sediments provide a potentially important yet largely overlooked climate regulation service. The proximity of fjords to the terrestrial environment in combination with their geomorphology and hydrography results in the fjordic sediments being subsidized with organic carbon (OC) from the terrestrial environment. This terrestrial OC (OCterr) transferred to the marine environment has traditionally be considered lost to the atmosphere in the form of CO2 in most carbon (C) accounting schemes yet globally it is estimated that 55% of OC trapped in fjord sediments is derived from terrestrial sources (Cui et al., 2016). So is this terrestrial OC truly lost? Here, we estimate the quantity of OCterr held within North Atlantic fjords with the aim of better understanding the recent and long-term role of the terrestrial environment in the evolution of these globally significant sedimentary OC stores. By understanding this subsidy of OC from the terrestrial to the marine environment we can take the first steps in quantifying the terrestrial OC stored in fjords and the wider coastal marine environment.Cui, X., Bianchi, T.S., Savage, C. and Smith, R.W., 2016. Organic carbon burial in fjords: Terrestrial versus marine inputs.&#160;Earth and Planetary Science Letters,&#160;451, pp.41-50.Smeaton, C., Austin, W.E., Davies, A., Baltzer, A., Howe, J.A. and Baxter, J.M., 2017. Scotland's forgotten carbon: a national assessment of mid-latitude fjord sedimentary stocks.&#160;Biogeosciences.Smith, R.W., Bianchi, T.S., Allison, M., Savage, C. and Galy, V., 2015. High rates of organic carbon burial in fjord sediments globally.&#160;Nature Geoscience,&#160;8(6), p.450.&#160;

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Changes in northeast African hydrology and vegetation associated with Pliocene–Pleistocene sapropel cycles

Philosophical Transactions of the Royal Society B Biological Sciences ◽

10.1098/rstb.2015.0243 ◽

2016 ◽

Vol 371 (1698) ◽

pp. 20150243 ◽

Cited By ~ 11

Author(s):

Cassaundra Rose ◽

Pratigya J. Polissar ◽

Jessica E. Tierney ◽

Timothy Filley ◽

Peter B. deMenocal

Keyword(s):

Climate Change ◽

Eastern Mediterranean ◽

East African ◽

Major Transitions ◽

Tropical Oceans ◽

Lignin Phenols ◽

Run Off ◽

Isotopic Analyses ◽

Phenol Composition

East African climate change since the Late Miocene consisted of persistent shorter-term, orbital-scale wet–dry cycles superimposed upon a long-term trend towards more open, grassy landscapes. Either or both of these modes of palaeoclimate variability may have influenced East African mammalian evolution, yet the interrelationship between these secular and orbital palaeoclimate signals remains poorly understood. Here, we explore whether the long-term secular climate change was also accompanied by significant changes at the orbital-scale. We develop northeast African hydroclimate and vegetation proxy data for two 100 kyr-duration windows near 3.05 and 1.75 Ma at ODP Site 967 in the eastern Mediterranean basin, where sedimentation is dominated by eastern Sahara dust input and Nile River run-off. These two windows were selected because they have comparable orbital configurations and bracket an important increase in East African C 4 grasslands. We conducted high-resolution (2.5 kyr sampling) multiproxy biomarker, H- and C-isotopic analyses of plant waxes and lignin phenols to document orbital-scale changes in hydrology, vegetation and woody cover for these two intervals. Both intervals are dominated by large-amplitude, precession-scale (approx. 20 kyr) changes in northeast African vegetation and rainfall/run-off. The δ 13 C wax values and lignin phenol composition record a variable but consistently C 4 grass-dominated ecosystem for both intervals (50–80% C 4 ). Precessional δD wax cycles were approximately 20–30‰ in peak-to-peak amplitude, comparable with other δD wax records of the Early Holocene African Humid Period. There were no significant differences in the means or variances of the δD wax or δ 13 C wax data for the 3.05 and 1.75 Ma intervals studied, suggesting that the palaeohydrology and palaeovegetation responses to precessional forcing were similar for these two periods. Data for these two windows suggest that the eastern Sahara did not experience the significant increase in C 4 vegetation that has been observed in East Africa over this time period. This observation would be consistent with a proposed mechanism whereby East African precipitation is reduced, and drier conditions established, in response to the emergence of modern zonal sea surface temperature gradients in the tropical oceans between 3 and 2 Ma. This article is part of the themed issue ‘Major transitions in human evolution’.

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Continental erosion and the Cenozoic rise of marine diatoms

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1412883112 ◽

2015 ◽

Vol 112 (14) ◽

pp. 4239-4244 ◽

Cited By ~ 39

Author(s):

Pedro Cermeño ◽

Paul G. Falkowski ◽

Oscar E. Romero ◽

Morgan F. Schaller ◽

Sergio M. Vallina

Keyword(s):

Silicic Acid ◽

Lithium Isotope ◽

Marine Diatoms ◽

Carbon Burial ◽

Input Flux ◽

Organic Carbon Burial ◽

Isotope Record ◽

Cenozoic Era ◽

Global Carbon

Marine diatoms are silica-precipitating microalgae that account for over half of organic carbon burial in marine sediments and thus they play a key role in the global carbon cycle. Their evolutionary expansion during the Cenozoic era (66 Ma to present) has been associated with a superior competitive ability for silicic acid relative to other siliceous plankton such as radiolarians, which evolved by reducing the weight of their silica test. Here we use a mathematical model in which diatoms and radiolarians compete for silicic acid to show that the observed reduction in the weight of radiolarian tests is insufficient to explain the rise of diatoms. Using the lithium isotope record of seawater as a proxy of silicate rock weathering and erosion, we calculate changes in the input flux of silicic acid to the oceans. Our results indicate that the long-term massive erosion of continental silicates was critical to the subsequent success of diatoms in marine ecosystems over the last 40 My and suggest an increase in the strength and efficiency of the oceanic biological pump over this period.

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Herbivory and its effect on Phanerozoic oxygen concentrations

Geology ◽

10.1130/g47085.1 ◽

2020 ◽

Vol 48 (4) ◽

pp. 410-414

Author(s):

T.A. Laakso ◽

J.V. Strauss ◽

K.J. Peterson

Keyword(s):

Organic Compounds ◽

Atmospheric Oxygen ◽

Deep Ocean ◽

Land Plant ◽

Plant Colonization ◽

Terrestrial Plants ◽

Oxygen Levels ◽

Carbon Burial ◽

Organic Carbon Burial

Abstract The appearance of terrestrial land plants is thought to have accompanied an increase in atmospheric oxygen levels, producing the highest O2 concentrations estimated from the geological record, and marking the transition to a permanently oxygenated deep ocean. This Paleozoic oxygenation event, which likely peaked in the Carboniferous Period, was at least partially mediated by the development of recalcitrant, carbon-rich organic compounds in terrestrial plants. A number of studies have argued that shifts in coal formation and paleogeography led to declining preservation of these compounds on land, depressing oxygen levels in the terminal Paleozoic and early Mesozoic. In contrast, we propose that the evolution and diversification of terrestrial herbivores may have limited transport and long-term burial of terrestrial organic compounds in marine sediments, resulting in less organic carbon burial and attendant declines in atmospheric oxygen. This mechanism suggests that interactions among a triad of biological processes—marine photosynthesis, land plant colonization, and the advent of herbivory—may have dictated the long-term redox state of Earth’s surface environments over the Phanerozoic Eon.

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Ancient genomes from North Africa evidence prehistoric migrations to the Maghreb from both the Levant and Europe

10.1101/191569 ◽

2017 ◽

Cited By ~ 6

Author(s):

Rosa Fregel ◽

Fernando L. Méndez ◽

Youssef Bokbot ◽

Dimas Martín-Socas ◽

María D. Camalich-Massieu ◽

...

Keyword(s):

North Africa ◽

Eastern Mediterranean ◽

North African ◽

Early Neolithic ◽

Late Neolithic ◽

Neolithic Culture ◽

Early Arrival ◽

Genetic Pool ◽

Demic Diffusion

ABSTRACTThe extent to which prehistoric migrations of farmers influenced the genetic pool of western North Africans remains unclear. Archaeological evidence suggests the Neolithization process may have happened through the adoption of innovations by local Epipaleolithic communities, or by demic diffusion from the Eastern Mediterranean shores or Iberia. Here, we present the first analysis of individuals’ genome sequences from early and late Neolithic sites in Morocco, as well as Early Neolithic individuals from southern Iberia. We show that Early Neolithic Moroccans are distinct from any other reported ancient individuals and possess an endemic element retained in present-day Maghrebi populations, confirming a long-term genetic continuity in the region. Among ancient populations, Early Neolithic Moroccans are distantly related to Levantine Natufian hunter-gatherers (∼9,000 BCE) and Pre-Pottery Neolithic farmers (∼6,500 BCE). Although an expansion in Early Neolithic times is also plausible, the high divergence observed in Early Neolithic Moroccans suggests a long-term isolation and an early arrival in North Africa for this population. This scenario is consistent with early Neolithic traditions in North Africa deriving from Epipaleolithic communities who adopted certain innovations from neighbouring populations. Late Neolithic (∼3,000 BCE) Moroccans, in contrast, share an Iberian component, supporting theories of trans-Gibraltar gene flow. Finally, the southern Iberian Early Neolithic samples share the same genetic composition as the Cardial Mediterranean Neolithic culture that reached Iberia ∼5,500 BCE. The cultural and genetic similarities of the Iberian Neolithic cultures with that of North African Neolithic sites further reinforce the model of an Iberian migration into the Maghreb.SIGNIFICANCE STATEMENTThe acquisition of agricultural techniques during the so-called Neolithic revolution has been one of the major steps forward in human history. Using next-generation sequencing and ancient DNA techniques, we directly test if Neolithization in North Africa occurred through the transmission of ideas or by demic diffusion. We show that Early Neolithic Moroccans are composed of an endemic Maghrebi element still retained in present-day North African populations and distantly related to Epipaleolithic communities from the Levant. However, late Neolithic individuals from North Africa are admixed, with a North African and a European component. Our results support the idea that the Neolithization of North Africa might have involved both the development of Epipaleolithic communities and the migration of people from Europe.

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A tentative attempt to better trace the late Pleistocene oxygen cycle

10.5194/egusphere-egu21-12623 ◽

2021 ◽

Author(s):

Ji-Woong Yang ◽

Thomas Extier ◽

Martin Kölling ◽

Amaëlle Landais ◽

Gaëlle Leloup ◽

...

Keyword(s):

Organic Carbon ◽

Late Pleistocene ◽

Global Ocean ◽

Geological Time Scale ◽

Sources And Sinks ◽

The Earth ◽

Carbon Burial ◽

Organic Carbon Burial ◽

Burial Flux

Atmospheric abundance of oxygen (O2) has been co-evolved with different aspects of the Earth system since appearance of oxygenic photosynthesis by cyanobacteria around 2.4 109 years before present (Ga). Therefore, much attention has been paid to understand the changes in O2 and the underlying mechanisms over the Earth&#8217;s history. The pioneering work by Stolper et al. (2016) revealed the long-term decreasing trend of O2 mixing ratios over the last 800,000 years using the ice-core composite record of molar ratios of O2 and nitrogen (&#948;(O2/N2)), implying a slight imbalance between sources and sinks. Over geological time scale, O2 is mainly controlled by burial and oxidation of organic carbon and pyrite, but also by oxidation of volcanic gases and sedimentary rocks. Nevertheless, the O2 cycle of the late Pleistocene has not been well understood, partly due to the lack of knowledge about the individual sources and sinks. Since then, K&#246;lling et al. (2019) proposed a simple model to estimate the O2 release/uptake fluxes due to the pyrite burial/oxidation that predicts up to ~70% of the O2 decrease of the last 800,000 years could be explained by pyrite burial/oxidation.Building on this, we present here our preliminary, tentative attempt for reconstruction of the net organic carbon burial flux over the last 800,000 years by combining available information (including new &#948;(O2/N2) data) and assuming constant O2 fluxes associated with volcanic outgassing and rock weathering. The long-term organic carbon burial flux trend obtained with our new calculations is similar to the global ocean &#948;13C records but also to simulations using a conceptual carbon cycle model (Paillard, 2017). These results partly support the geomorphological hypothesis that the major sea-level drops during the earlier period of the last 800,000 years lead to enhanced organic carbon burial, and that significant changes in the net organic carbon happen around Marine Isotopic Stage (MIS) 13. In addition, we present the long-term decreasing trend of the global biosphere productivity, or gross photosynthetic O2 flux, reconstructed from new measurements of triple-isotope composition of atmospheric O2 trapped in ice cores. As the largest O2 flux, the observed decrease in gross photosynthesis requires to be compensated by parallel reduction of global ecosystem respiration.

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Calcification-driven CO2 emissions exceed “Blue Carbon” sequestration in a carbonate seagrass meadow

10.21203/rs.3.rs-120551/v1 ◽

2021 ◽

Author(s):

Bryce Van Dam ◽

Mary Zeller ◽

Christian Lopes ◽

Ashley Smyth ◽

Michael Böttcher ◽

...

Keyword(s):

Carbon Dioxide ◽

Carbon Sequestration ◽

Organic Carbon ◽

Seagrass Meadow ◽

Blue Carbon ◽

Carbonate Sediments ◽

Seagrass Meadows ◽

Carbon Burial ◽

Organic Carbon Burial

Abstract Long-term “blue carbon” burial in seagrass meadows is complicated by other carbon and alkalinity exchanges that shape net carbon sequestration. We measured a suite of such processes, including denitrification, sulfur, and inorganic carbon cycling, and assessed their impact on air-water carbon dioxide exchange in a typical seagrass meadow underlain by carbonate sediments. Contrary to the prevailing concept of seagrass meadows acting as carbon sinks, eddy covariance measurements reveal this ecosystem as a consistent source of carbon dioxide to the atmosphere, at an average rate of 610 ± 990 µmol m-2 hr-1 during our study and 700 ± 660 µmol m-2 hr-1 over an annual cycle. A robust mass-balance shows that net alkalinity consumption by ecosystem calcification explains >95% of the observed carbon dioxide emissions, far exceeding alkalinity generated by net reduced sulfur, iron and organic carbon burial. Isotope geochemistry of porewaters suggests substantial dissolution and re-crystallization of more stable carbonates mediated by sulfide oxidation-induced acidification, enhancing long-term carbonate burial and ultimate carbon dioxide production. We show that the “blue carbon” sequestration potential of calcifying seagrass meadows has been over-estimated, and that in-situ organic carbon burial only offsets a small fraction (<5%) of calcification-induced CO2 emissions. Ocean-based climate change mitigation activities in such calcifying regions should be approached with caution and an understanding that net carbon sequestration may not be possible.

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