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Abstract Carbon isotope minima were a ubiquitous feature in the mid-depth (1.5–2.5 km) Atlantic during Heinrich Stadial 1 (HS1, 14.5–17.5 kyr BP) and the Younger Dryas (YD, 11.6–12.9 kyr BP), with the most likely driver being collapse of the Atlantic Meridional Overturning Circulation (AMOC). Negative carbon isotope anomalies also occurred throughout the surface ocean and atmosphere, but their timing relative to AMOC collapse and the underlying drivers have remained unclear. Here we evaluate the lead-lag relationship between AMOC variability and surface oceanδ13C signals using high resolution benthic and planktonic stable isotope records from two Brazil Margin cores (located at 1.8 km and 2.1 km water depth). In each case, the decrease in benthicδ13C during HS1 leads planktonicδ13C by 800 ± 200 years. Because the records are based on the same samples, the relative timing is constrained by the core stratigraphy. Our results imply that AMOC collapse initiates a chain of events that propagates through the oceanic carbon cycle in less than 1 kyr. Direct comparison of planktonic foraminiferal and atmospheric records implies a portion of the surface oceanδ13C signal can be explained by temperature-dependent equilibration with a13C-depleted atmosphere, with the remainder due to biological productivity, input of carbon from the abyss, or reduced air-sea equilibration.
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In situ carbon uptake of marine macrophytes is highly variable among species, taxa, and morphology
Macroalgae form important coastal ecosystems and are considered to be highly productive, yet individual macrophyte carbon uptake rates are poorly documented and methodologies forin situassessments of productivity are not well developed. In this study, we employ a13C enrichment method in benthic chambers to calculate carbon uptake rates and assessδ13C signatures of a large stock of nearshore benthic macroalgae varying in taxa and morphology in Southern California. Our objectives are to 1) identify the variability of carbon uptake and inorganic carbon use among individuals of the same species or morphology, and 2) establish accurate and accessible carbon uptake procedures for coastal benthic primary producers. We found no significant relationship between the observed ranges of environmental factors such as nutrient concentrations, PAR, temperature, conductivity, and productivity rates, suggesting that unique physiological complexions underpin the high variability of carbon uptake andδ13C in studied macrophyte samples. We consider three reasons our experimental carbon uptake rates are 3–4 orders of magnitude lower than existing literature, which reports carbon uptake in the same units despite using different methods: 1) underrepresentation ofPmax, 2) incomplete carbon fractionation corrections, and 3) reduced hydrodynamics within the benthic chambers.
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- Award ID(s):
- 1950350
- PAR ID:
- 10506981
- Publisher / Repository:
- Frontiers
- Date Published:
- Journal Name:
- Frontiers in Marine Science
- Volume:
- 10
- ISSN:
- 2296-7745
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.3389/fmars.2023.1290054
