Nature and origin of variations in pelagic carbonate production in the tropical ocean since the mid-Miocene (ODP Site 927)
<p>Marine plankton is an important component of the global carbon cycle. Whereas the production and seafloor export of organic carbon produced by the plankton, the biological pump, has received much attention, the long-term variability in plankton calcification, controlling the carbonate count...
| Main Authors: | , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2023-02-01
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| Series: | Biogeosciences |
| Online Access: | https://bg.copernicus.org/articles/20/597/2023/bg-20-597-2023.pdf |
| Summary: | <p>Marine plankton is an important component of the global carbon cycle.
Whereas the production and seafloor export of organic carbon produced by the
plankton, the biological pump, has received much attention, the long-term
variability in plankton calcification, controlling the carbonate counter
pump, remains less well understood. However, it has been shown that changes in pelagic calcification (biological
compensation) could affect the ocean's buffering capacity and thus regulate
global carbon budget on
geological timescales. Here we use Neogene pelagic sediments deposited on the
Ceara Rise in the tropical Atlantic to characterize the variability in
pelagic carbonate production with a focus on warm climates. A re-evaluation of
published records of carbonate accumulation at the Ceara Rise reveals a
systematic increase in sedimentation rates since the late Miocene, but the
carbonate accumulation rate does not show a clear trend. Instead, we observe
substantial orbital timescale variability in carbonate accumulation,
combined with a trend towards less carbonate on average at sites located
below 4 km, likely due to the effect of carbonate dissolution. To evaluate
long-term changes against possible orbital-scale variability, we generated
new high-resolution records of carbonate accumulation rate at Ocean Drilling Program (ODP) Site 927
across two Quaternary interglacials (MIS 5 and MIS 9), the Pliocene warm
period (MIS KM5) and the Miocene Climatic Optimum (MCO). We observe that the
highest carbonate accumulation rates occurred during the Pliocene but that
each of the studied intervals was characterized by large-magnitude orbital
variability. Prominent variations in carbonate accumulation prior to the
Quaternary preservation cycles appear to follow Earth obliquity and
eccentricity. These results imply that pelagic carbonate accumulation in the
tropical ocean, buffered from large temperature changes, varied on orbital
timescales. The magnitude of the orbital-scale variability was similar or
even higher than the long-term mean differences among the studied intervals.
Since preservation can be excluded as a driver of these changes prior to the
Quaternary, the observed variations must reflect changes in the export flux
of pelagic biogenic carbonate. We conclude that the overall carbonate
production by pelagic calcifiers responded to local changes in light,
temperature, and nutrients delivered by upwelling, which followed long
orbital cycles, as well as to long-term shifts in climate and/or ocean
chemistry. The inferred changes on both timescales were sufficiently large
such that when extrapolated on a global scale, they could have played a role
in the regulation of the carbon cycle and global climate evolution during
the transition from the Miocene warm climates into the Quaternary icehouse.</p> |
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| ISSN: | 1726-4170 1726-4189 |