View in EDS

Limited Organic Carbon Burial by the Rusty Carbon Sink in Swedish Fjord Sediments.

Saved in:
Bibliographic Details
Title: Limited Organic Carbon Burial by the Rusty Carbon Sink in Swedish Fjord Sediments.
Authors: Placitu, S.1 (AUTHOR) silvia.placitu@ulb.be, van de Velde, S. J.2 (AUTHOR), Hylén, A.2,3 (AUTHOR), Hall, P. O. J.3 (AUTHOR), Robertson, E. K.3 (AUTHOR), Eriksson, M.4 (AUTHOR), Leermakers, M.5 (AUTHOR), Mehta, N.1 (AUTHOR), Bonneville, S.1 (AUTHOR)
Source: Journal of Geophysical Research. Biogeosciences. Nov2024, Vol. 129 Issue 11, p1-16. 16p.
Subject Terms: *Oxygen in water, *Marine sediments, *Sedimentation & deposition, *Fjords, Sediment sampling
Abstract: Marine sediments bury ∼160 Tg of organic carbon (OC) annually and represent an essential component of the global carbon cycle. OC burial is inherently multifactorial; however, in the past decade, the role of iron in regulating OC burial via the formation of organo‐mineral associations, known as "rusty carbon sink," has been extensively studied. Despite widespread recognition, the origin of the OC preserved within these associations and the effect of the bottom‐water oxygenation on their stability are still debated. Here, we investigate the rusty carbon sink in sediments collected across transects from the head to mouth of three Swedish fjords presenting contrasting bottom‐water oxygenation regimes (the oxic Hake fjord, seasonally hypoxic Gullmar fjord, and anoxic By fjord). We found that the oxygenation regimes, the intensity of benthic iron cycling or the OC origin have little to no influence on the amount of OC bound to Fe (OC – Fe). The lack of correlation with any of the parameters studied, in combination with an increase in the OC – Fe in the fjords with riverine input suggest, at least partially, an allochthonous origin of these organo‐mineral associations. Our results also show that the rusty carbon sink plays a modest role in the OC burial in these fjords (∼6% OC is bound to Fe). While these fjords still represent important OC burial hotspots with an average of ∼35 g C m−2 buried annually, the OC burial is controlled by other sedimentary processes, such as the high mass accumulation rates found in these fjord systems. Plain Language Summary: Marine sediments are critical reservoirs of organic carbon playing a significant role regulating the Earth's climate. Numerous studies have examined how iron influences carbon storage through the formation of organo‐mineral associations, often referred to as the "rusty carbon sink." Ongoing debates still persist regarding the organic carbon source and the impact of the oxygen levels in bottom waters on the stability of these organo‐mineral associations. We investigate sediment samples from three distinct Swedish fjords, each characterized by different bottom waters oxygen concentrations. Surprisingly, our findings indicate that neither oxygen levels nor iron content significantly affected the carbon storage associated with iron. Additionally, the origin of the carbon did not play a major role in this process. Although only a small fraction of the total carbon content in these sediments is preserved by iron, the fjords remain crucial for carbon storage. Our results suggest that other factors, beyond oxygen and iron levels, may play a more significant role in the preservation and stability of organic carbon in these environments. Key Points: Low organic carbon‐iron (OC – Fe) associations in fjord sedimentsNo clear relation with the sedimentary dynamics, pre‐formed OC – Fe associations likely transported by rivers (at least partially)Fjords represent organic carbon hotspot, despite low rusty carbon sink [ABSTRACT FROM AUTHOR]
Copyright of Journal of Geophysical Research. Biogeosciences is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)
Database: GreenFILE
Description
Abstract:Marine sediments bury ∼160 Tg of organic carbon (OC) annually and represent an essential component of the global carbon cycle. OC burial is inherently multifactorial; however, in the past decade, the role of iron in regulating OC burial via the formation of organo‐mineral associations, known as "rusty carbon sink," has been extensively studied. Despite widespread recognition, the origin of the OC preserved within these associations and the effect of the bottom‐water oxygenation on their stability are still debated. Here, we investigate the rusty carbon sink in sediments collected across transects from the head to mouth of three Swedish fjords presenting contrasting bottom‐water oxygenation regimes (the oxic Hake fjord, seasonally hypoxic Gullmar fjord, and anoxic By fjord). We found that the oxygenation regimes, the intensity of benthic iron cycling or the OC origin have little to no influence on the amount of OC bound to Fe (OC – Fe). The lack of correlation with any of the parameters studied, in combination with an increase in the OC – Fe in the fjords with riverine input suggest, at least partially, an allochthonous origin of these organo‐mineral associations. Our results also show that the rusty carbon sink plays a modest role in the OC burial in these fjords (∼6% OC is bound to Fe). While these fjords still represent important OC burial hotspots with an average of ∼35 g C m−2 buried annually, the OC burial is controlled by other sedimentary processes, such as the high mass accumulation rates found in these fjord systems. Plain Language Summary: Marine sediments are critical reservoirs of organic carbon playing a significant role regulating the Earth's climate. Numerous studies have examined how iron influences carbon storage through the formation of organo‐mineral associations, often referred to as the "rusty carbon sink." Ongoing debates still persist regarding the organic carbon source and the impact of the oxygen levels in bottom waters on the stability of these organo‐mineral associations. We investigate sediment samples from three distinct Swedish fjords, each characterized by different bottom waters oxygen concentrations. Surprisingly, our findings indicate that neither oxygen levels nor iron content significantly affected the carbon storage associated with iron. Additionally, the origin of the carbon did not play a major role in this process. Although only a small fraction of the total carbon content in these sediments is preserved by iron, the fjords remain crucial for carbon storage. Our results suggest that other factors, beyond oxygen and iron levels, may play a more significant role in the preservation and stability of organic carbon in these environments. Key Points: Low organic carbon‐iron (OC – Fe) associations in fjord sedimentsNo clear relation with the sedimentary dynamics, pre‐formed OC – Fe associations likely transported by rivers (at least partially)Fjords represent organic carbon hotspot, despite low rusty carbon sink [ABSTRACT FROM AUTHOR]
ISSN:21698953
DOI:10.1029/2024JG008277