4.6 Article

Could atmospheric carbon be driving sedimentation?

Journal

JOURNAL OF SOILS AND SEDIMENTS
Volume 22, Issue 11, Pages 2912-2928

Publisher

SPRINGER HEIDELBERG
DOI: 10.1007/s11368-022-03282-0

Keywords

Climate change; Pb-210 and Cs-137 dating; Carbon; Particle size distribution; X-ray powder diffraction; The Adriatic Sea; The Black Sea; Sediment; Sedimentation rate

Funding

  1. Croatian Science Foundation-Youth Careers Development Project [ESF-DOK-1-2018]
  2. Croatian Science Foundation [IP-01-2018]

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This study provides insights into the recent responses of sediments to climate change and their ability to sequester atmospheric carbon. The results show that the accumulation rates of organic and inorganic carbon in sediments have increased over time, mainly due to the increase in atmospheric carbon dioxide. Additionally, CO2 fertilization and increasing sea temperatures have also influenced the accumulation of carbon in sediments.
Purpose The objective of this study was to provide insights into the most recent responses of sediments to climate change and their capability to sequester atmospheric carbon (C). Methods Three sediment cores were collected, one from the western Black Sea, and two from the southern Adriatic Sea. Cores were extruded and sectioned into 1 cm or 0.5 cm intervals. Sections were frozen, weighed, freeze-dried, and then weighed again to obtain dry weights. Freeze-dried samples were dated by using lead 210 (Pb-210) and cesium 137/ americium 241 (Cs-137/Am-241). Organic and inorganic C were determined by combustion. Particle size distribution was determined using a Beckman Coulter particle size analyzer (LS 13,320; Beckman Coulter Inc.). Mineralogical analyses were carried out by a Philips X'Pert powder diffractometer. Results Sedimentation and organic and inorganic C accumulation rates increased with time in both the Black Sea and the Adriatic Sea. The increase in accumulation rates continued after the global introduction in the early 1970s of controls on the release of phosphorus (P) into the environment and despite the reduced sediment yield of major rivers (Po and Danube). Therefore, the increased accumulation of organic and inorganic C in the sediments cannot be assigned only to nutrient availability. Instead, we suggest that the increase in organic C is the consequence of the increase in atmospheric C, which has made more carbon dioxide (CO2) available to phytoplankton, thus enabling more efficient photosynthesis. This process known as CO2 fertilization may increase the organic C accumulation in sediments. Simultaneously, the increase of sea temperatures decreases the calcite solubility resulting in increases of the inorganic C accumulation. Conclusion Our results suggest that long-term, general increases in accumulation rates of organic and inorganic C in sediments are the consequence of increases in atmospheric C. This shows that coastal sediments play an important role in C uptake and thus in regulating the Earth's climate.

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