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Abstract Climate conditions and instantaneous depositional events can influence the relative contribution of sediments from terrestrial and marine environments and ultimately the quantity and composition of carbon buried in the sediment record. Here, we analyze the elemental, isotopic, and organic geochemical composition of marine sediments to identify terrestrial and marine sources in sediment horizons associated with droughts, turbidites, and floods in the Santa Barbara Basin (SBB), California, during the last 2,000 years. Stable isotopes (δ13C and δ15N) indicate that more terrestrial organic carbon (OC) was deposited during floods relative to background sediment, while bulk C to nitrogen (C/N) ratios remained relatively constant (~10). Long‐chainn‐alkanes (C27, C29, C31, and C33), characteristic of terrestrial OC, dominated all types of sediment deposition but were 4 times more abundant in flood layers. Marine algae (C15, C17, and C19) and macrophytes (C21and C23) were also 2 times higher in flood versus background sediments. Turbidites contained twice the terrestrialn‐alkanes relative to background sediment. Conversely, drought intervals were only distinguishable from background sediment by their higher proportion of marine algaln‐alkanes. Combined, our data indicate that 15% of the total OC buried in SBB over the past 2,000 years was deposited during 11 flood events where the sediment was mostly terrestrially derived, and another 12% of deep sediment OC burial was derived from shelf remobilization during six turbidite events. Relative to twentieth century river runoff, our data suggest that floods result in considerable terrestrial OC burial on the continental margins of California.
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Synchronous Marine and Terrestrial Carbon Cycle Perturbation in the High Arctic During the PETM
Abstract The Paleocene‐Eocene Thermal Maximum (PETM; 56 Ma) is considered to be one of the best analogs for future climate change. The carbon isotope composition (δ13C) ofn‐alkanes derived from leaf waxes of terrestrial plants and marine algae can provide important insights into the carbon cycle perturbation during the PETM. Here, we present new organic geochemical data and compound‐specific δ13C data from sediments recovered from an early Cenozoic basin‐margin succession from Spitsbergen. These samples represent one of the most expanded PETM sites and provide new insights into the high Arctic response to the PETM. Our results reveal a synchronous ∼−6.5‰ carbon isotope excursion (CIE) in short‐chainn‐alkanes (nC19; marine algae/bacteria) with a ∼−5‰ CIE in long‐chainn‐alkanes (nC29andnC31; plant waxes) during the peak of the PETM. Although δ13Cn‐alkanesvalues were potentially affected via a modest thermal effect (1‰–2‰), the relative changes in the δ13Cn‐alkanesremain robust. A simple carbon cycle modeling suggests peak carbon emission rate could be ∼3 times faster than previously suggested using δ13CTOCrecords. The CIE magnitude of both δ13Cn‐C19and δ13Cn‐C29can be explained by the elevated influence of13C‐depleted respired CO2in the water column and increased water availability on land, elevatedpCO2in the atmosphere, and changes in vegetation type during the PETM. The synchronous decline in δ13C of both leaf waxes and marine algae/bacteria argues against a significant contribution to the sedimentary organic carbon pool from the weathering delivery of fossiln‐alkanes in the Arctic region.
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- Award ID(s):
- 2002370
- PAR ID:
- 10386992
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Paleoceanography and Paleoclimatology
- Volume:
- 36
- Issue:
- 4
- ISSN:
- 2572-4517
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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