Perturbation to the nitrogen cycle during rapid Early Eocene global warming

Junium, Christopher K.; Dickson, Alexander J.; Uveges, Benjamin T.

doi:10.1038/s41467-018-05486-w

Cited by 33 publications

(20 citation statements)

References 67 publications

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“…If the marine N cycle of OAE 2 can maintain a fundamentally different structure from the modern version, one might expect comparably different N cycle states to occur at other times in Earth history. For example, Late Devonian black shales (31) as well as PETM black shales (16) are characterized by depleted δ 15 N bulk values similar to those reported for OAE 2. The climate state and paleogeography, which determine the specific sensitivity of the marine N cycle to changes in oxygenation state, were different during those events compared to OAE 2.…”

Section: −supporting

confidence: 63%

“…This makes the strength and state of the biological pump in the ocean highly susceptible to disruption, with potential past and future implications. basins of the Tethys Ocean during the Paleocene Eocene Thermal Maximum (PETM) (16), suggesting an important role for ammonium assimilation during this transient global warming event. Together, these observations suggest that ammonium assimilation might be inherent to deoxygenation events during the Phanerozoic and may reflect the changing balance in redox speciation of the major components of dissolved inorganic nitrogen (DIN), namely: NO 3 − and NH 4 + (together: the fixed-nitrogen pool).…”

Section: Significancementioning

confidence: 99%

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Fundamentally different global marine nitrogen cycling in response to severe ocean deoxygenation

Naafs

Monteiro

Pearson

et al. 2019

Proc. Natl. Acad. Sci. U.S.A.

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The present-day marine nitrogen (N) cycle is strongly regulated by biology. Deficiencies in the availability of fixed and readily bioavailable nitrogen relative to phosphate (P) in the surface ocean are largely corrected by the activity of diazotrophs. This feedback system, termed the “nitrostat,” is thought to have provided close regulation of fixed-N speciation and inventory relative to P since the Proterozoic. In contrast, during intervals of intense deoxygenation such as Cretaceous ocean anoxic event (OAE) 2, a few regional sedimentary δ15N records hint at the existence of a different mode of marine N cycling in which ammonium plays a major role in regulating export production. However, the global-scale dynamics during this time remain unknown. Here, using an Earth System model and taking the example of OAE 2, we provide insights into the global marine nitrogen cycle under severe ocean deoxygenation. Specifically, we find that the ocean can exhibit fundamental transitions in the species of nitrogen dominating the fixed-N inventory––from nitrate (NO3−) to ammonium (NH4+)––and that as this transition occurs, the inventory can partially collapse relative to P due to progressive spatial decoupling between the loci of NH4+ oxidation, NO3− reduction, and nitrogen fixation. This finding is relatively independent of the specific state of ocean circulation and is consistent with nitrogen isotope and redox proxy data. The substantive reduction in the ocean fixed-N inventory at an intermediate state of deoxygenation may represent a biogeochemical vulnerability with potential implications for past and future (warmer) oceans.

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Section: −supporting

confidence: 63%

Section: Significancementioning

confidence: 99%

Fundamentally different global marine nitrogen cycling in response to severe ocean deoxygenation

Naafs

Monteiro

Pearson

et al. 2019

Proc. Natl. Acad. Sci. U.S.A.

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“…Clay mineral assemblages were identified by X-ray diffraction on oriented mounts of noncalcareous clay-sized particles (< 2 µm). SSTs based on isoprenoidal glyceroldialkylglyceroltetraethers (isoGDGTs) (Schouten et al, 2002) were reconstructed using the TEX H 86 calibration of Kim et al (2010). Palynological sampling resolution is approximately 5 cm, and δ 15 N and δ 13 C TOC sampling resolution approximately 0.5 cm, in the body of the PETM section.…”

Section: Methodsmentioning

confidence: 99%

Life and death in the Chicxulub impact crater: a record of the Paleocene–Eocene Thermal Maximum

et al. 2020

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Abstract. Thermal stress on the biosphere during the extreme warmth of the Paleocene–Eocene Thermal Maximum (PETM) was most severe at low latitudes, with sea surface temperatures at some localities exceeding the 35 ∘C at which marine organisms experience heat stress. Relatively few equivalent terrestrial sections have been identified, and the response of land plants to this extreme heat is still poorly understood. Here, we present a new record of the PETM from the peak ring of the Chicxulub impact crater that has been identified based on nannofossil biostratigraphy, an acme of the dinoflagellate genus Apectodinium, and a negative carbon isotope excursion. Geochemical and microfossil proxies show that the PETM is marked by elevated TEX86H-based sea surface temperatures (SSTs) averaging ∼37.8 ∘C, an increase in terrestrial input and surface productivity, salinity stratification, and bottom water anoxia, with biomarkers for green and purple sulfur bacteria indicative of photic zone euxinia in the early part of the event. Pollen and plants spores in this core provide the first PETM floral assemblage described from Mexico, Central America, and the northern Caribbean. The source area was a diverse coastal shrubby tropical forest with a remarkably high abundance of fungal spores, indicating humid conditions. Thus, while seafloor anoxia devastated the benthic marine biota and dinoflagellate assemblages were heat-stressed, the terrestrial plant ecosystem thrived.

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“…The standard UVic ESCM version 2.9 includes a NPZD (nutrients-phytoplankton-zooplankton-detritus) submodel with "mixed phytoplankton" and "diazotroph" phytoplankton functional types and one "zooplankton" functional type (Schmittner et al, 2008). The MIXED model configuration is the standard UVic ESCM NPZD submodel, updated with the changes made by Keller et al (2012). The CAL model configuration builds upon MIXED and additionally includes a "small and calcifying phytoplankton" functional type (simplified to "calcifiers" throughout this paper) and a prognostic CaCO 3 tracer (Kvale et al, 2015a).…”

Section: Methodsmentioning

confidence: 99%

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Kvale¹

2019

Preprint

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Phytoplankton calcifiers contribute to global carbon cycling through their dual formation of calcium carbonate and particulate organic carbon (POC). The carbonate might provide an efficient export pathway for the associated POC to the deep ocean, reducing the particles' exposure to biological degradation in the upper ocean and increasing the particle settling rate. Previous work has suggested ballasting of POC by carbonate might increase in a warming climate, in spite of increasing carbonate dissolution rates, because calcifiers benefit from the widespread nutrient limitation arising from stratification. We compare the biogeochemical responses of three models containing (1) a single mixed phytoplankton class, (2) additional explicit small phytoplankton and calcifiers, and (3) additional explicit small phytoplankton and calcifiers with a prognostic carbonate ballast model, to two rapid changes in atmospheric CO 2 . The first CO 2 scenario represents a rapid (151-year) transition from a stable icehouse climate (283.9 ppm) into a greenhouse climate (1263 ppm); the second represents a symmetric rapid transition from a stable greenhouse climate into an icehouse climate. We identify a slope change in the global net primary production response with a transition point at about 3.5 • C global mean sea surface temperature change in all models, driven by a combination of physical and biological changes. We also find that in both warming and cooling scenarios, the application of a prognostic carbonate ballast model moderates changes in carbon export production, suboxic volume, and nitrate sources and sinks, reducing the long-term model response to about one-third that of the cal-

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Perturbation to the nitrogen cycle during rapid Early Eocene global warming

Cited by 33 publications

References 67 publications

Fundamentally different global marine nitrogen cycling in response to severe ocean deoxygenation

Fundamentally different global marine nitrogen cycling in response to severe ocean deoxygenation

Life and death in the Chicxulub impact crater: a record of the Paleocene–Eocene Thermal Maximum

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