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Terrestrial biome distribution in the Late Neogene inferred from a black carbon record in the northeastern equatorial Pacific

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ABSTRACT

The appearance and expansion of C4 plants in the Late Cenozoic was a dramatic example of terrestrial ecological change. The fire hypothesis, which suggests fire as a major cause of C4 grassland is gaining support, yet a more detailed relationship between fire and vegetation-type change remains unresolved. We report the content and stable carbon isotope record of black carbon (BC) in a sediment core retrieved from the northeastern equatorial Pacific that covers the past 14.3 million years. The content record of BC suggests the development process of a flammable ecosystem. The stable carbon isotope record of BC reveals the existence of the Late Miocene C4 expansion, the ‘C4 maximum period of burned biomass’ during the Pliocene to Early Pleistocene, and the collapse of the C4 in the Late Pleistocene. Records showing the initial expansion of C4 plants after large fire support the role of fire as a destructive agent of C3-dominated forest, yet the weak relationships between fire and vegetation after initial expansion suggest that environmental advantages for C4 plants were necessary to maintain the development of C4 plants during the late Neogene. Among the various environmental factors, aridity is likely most influential in C4 expansion.

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(A) BC content from deep-sea core sediment obtained from the northeastern equatorial Pacific. (B) Goethite/(goethite + hematite), G/(G + H) value at ODP Site 926 to represent aridity of Amazon and proto-Amazon lowland source areas. Lower G/(G + H) value suggests more arid condition (modified from Harris and Mix33). (C) Mass accumulation rate of eolian dust at ODP Site 885/886 (modified from Rea et al.39). (D) BC mass accumulation rate (MAR), (E) BC δ13C value, and (F) calculated proportion of C4 plants from deep-sea core sediment obtained from the northeastern equatorial Pacific. Black bold line across the center represents the time interval when the source area changed from Southern Hemisphere to Northern Hemisphere. Grey areas represent arid time intervals. Blue area represents error range assuming extreme environmental condition(closed-forest to steppe). Dotted lines in (E) and (F) define five time intervals (1–5) showing noticeable characteristics in δ13C value (see text for details).
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f2: (A) BC content from deep-sea core sediment obtained from the northeastern equatorial Pacific. (B) Goethite/(goethite + hematite), G/(G + H) value at ODP Site 926 to represent aridity of Amazon and proto-Amazon lowland source areas. Lower G/(G + H) value suggests more arid condition (modified from Harris and Mix33). (C) Mass accumulation rate of eolian dust at ODP Site 885/886 (modified from Rea et al.39). (D) BC mass accumulation rate (MAR), (E) BC δ13C value, and (F) calculated proportion of C4 plants from deep-sea core sediment obtained from the northeastern equatorial Pacific. Black bold line across the center represents the time interval when the source area changed from Southern Hemisphere to Northern Hemisphere. Grey areas represent arid time intervals. Blue area represents error range assuming extreme environmental condition(closed-forest to steppe). Dotted lines in (E) and (F) define five time intervals (1–5) showing noticeable characteristics in δ13C value (see text for details).

Mentions: Down-core BC content ranges from 0.00% to 0.23%, with an average of 0.05% (Dataset 1; Fig. 2A). Prior to 7.6 Ma, when the sediment was mainly delivered from Southern Hemisphere continents, Central and South America232432, the BC content averages 0.04% (range of 0.00–0.12%). Two periods with high BC content occurring at 14.3–12.7 Ma and 11.1–10.2 Ma are noticeable, and the BC content decreases gradually with time from the high values. These two periods coincide with arid periods in tropical South America33 (Fig. 2B), which indicates a potential relationship between tropical South American aridity and an increase in the quantity of burned biomass, because the arid climate results in low fuel moisture content and easy spread of fire. The gradual decrease of BC content following a peak can be explained by shortage of fuel due to frequent fires.


Terrestrial biome distribution in the Late Neogene inferred from a black carbon record in the northeastern equatorial Pacific
(A) BC content from deep-sea core sediment obtained from the northeastern equatorial Pacific. (B) Goethite/(goethite + hematite), G/(G + H) value at ODP Site 926 to represent aridity of Amazon and proto-Amazon lowland source areas. Lower G/(G + H) value suggests more arid condition (modified from Harris and Mix33). (C) Mass accumulation rate of eolian dust at ODP Site 885/886 (modified from Rea et al.39). (D) BC mass accumulation rate (MAR), (E) BC δ13C value, and (F) calculated proportion of C4 plants from deep-sea core sediment obtained from the northeastern equatorial Pacific. Black bold line across the center represents the time interval when the source area changed from Southern Hemisphere to Northern Hemisphere. Grey areas represent arid time intervals. Blue area represents error range assuming extreme environmental condition(closed-forest to steppe). Dotted lines in (E) and (F) define five time intervals (1–5) showing noticeable characteristics in δ13C value (see text for details).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5015089&req=5

f2: (A) BC content from deep-sea core sediment obtained from the northeastern equatorial Pacific. (B) Goethite/(goethite + hematite), G/(G + H) value at ODP Site 926 to represent aridity of Amazon and proto-Amazon lowland source areas. Lower G/(G + H) value suggests more arid condition (modified from Harris and Mix33). (C) Mass accumulation rate of eolian dust at ODP Site 885/886 (modified from Rea et al.39). (D) BC mass accumulation rate (MAR), (E) BC δ13C value, and (F) calculated proportion of C4 plants from deep-sea core sediment obtained from the northeastern equatorial Pacific. Black bold line across the center represents the time interval when the source area changed from Southern Hemisphere to Northern Hemisphere. Grey areas represent arid time intervals. Blue area represents error range assuming extreme environmental condition(closed-forest to steppe). Dotted lines in (E) and (F) define five time intervals (1–5) showing noticeable characteristics in δ13C value (see text for details).
Mentions: Down-core BC content ranges from 0.00% to 0.23%, with an average of 0.05% (Dataset 1; Fig. 2A). Prior to 7.6 Ma, when the sediment was mainly delivered from Southern Hemisphere continents, Central and South America232432, the BC content averages 0.04% (range of 0.00–0.12%). Two periods with high BC content occurring at 14.3–12.7 Ma and 11.1–10.2 Ma are noticeable, and the BC content decreases gradually with time from the high values. These two periods coincide with arid periods in tropical South America33 (Fig. 2B), which indicates a potential relationship between tropical South American aridity and an increase in the quantity of burned biomass, because the arid climate results in low fuel moisture content and easy spread of fire. The gradual decrease of BC content following a peak can be explained by shortage of fuel due to frequent fires.

View Article: PubMed Central - PubMed

ABSTRACT

The appearance and expansion of C4 plants in the Late Cenozoic was a dramatic example of terrestrial ecological change. The fire hypothesis, which suggests fire as a major cause of C4 grassland is gaining support, yet a more detailed relationship between fire and vegetation-type change remains unresolved. We report the content and stable carbon isotope record of black carbon (BC) in a sediment core retrieved from the northeastern equatorial Pacific that covers the past 14.3 million years. The content record of BC suggests the development process of a flammable ecosystem. The stable carbon isotope record of BC reveals the existence of the Late Miocene C4 expansion, the ‘C4 maximum period of burned biomass’ during the Pliocene to Early Pleistocene, and the collapse of the C4 in the Late Pleistocene. Records showing the initial expansion of C4 plants after large fire support the role of fire as a destructive agent of C3-dominated forest, yet the weak relationships between fire and vegetation after initial expansion suggest that environmental advantages for C4 plants were necessary to maintain the development of C4 plants during the late Neogene. Among the various environmental factors, aridity is likely most influential in C4 expansion.

No MeSH data available.


Related in: MedlinePlus