Radiocarbon in dissolved organic carbon of the Atlantic Ocean

Druffel, Ellen R. M.; Griffin, Sheila; Coppola, Alysha I.; Walker, Brett D.

doi:10.1002/2016gl068746

Cited by 57 publications

(74 citation statements)

References 42 publications

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“…Oceanic DBC is generally more radiocarbon depleted (Δ 14 C age: 18,000–23,000 yr; Ziolkowski and Druffel ; Coppola and Druffel ) than the bulk DOC (Δ 14 C age: 4000–6000 yr; Druffel et al ). Previous studies observed anomalously high DOC concentrations in the deep Southern Ocean (Druffel and Bauer ; Follett et al ), especially in the Indian Ocean Sector adjacent to Prydz Bay (Bercovici and Hansell ).…”

Section: Discussionmentioning

confidence: 99%

Transport of dissolved black carbon from the Prydz Bay Shelf, Antarctica to the deep Southern Ocean

Fang

Yang

Chen

et al. 2018

Limnology & Oceanography

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Dissolved black carbon (DBC) is one of the largest pools of molecularly identifiable carbon in the ocean. In the deep ocean, DBC appears to persist for millennia, whereas it can be rapidly degraded by sunlight in surface waters. In Antarctica, the downward transport of dense shelf water (DSW) exports a massive volume of water to the deep Southern Ocean each year. If this sinking DSW is enriched in DBC, it may allow a route for DBC to escape degradation by sunlight in the surface ocean and become sequestered in the deep waters of the global ocean. To investigate this possibility, we quantified dissolved organic carbon (DOC), DBC, and ancillary properties in the waters of an Antarctic shelf sea (Prydz Bay) and adjacent waters. DBC concentrations in Prydz Bay DSW (1.2 ± 0.3 μmol L−1) were elevated compared to those in circumpolar deep water (0.49 ± 0.07 μmol L−1). The water column distribution of DBC in Prydz Bay suggested that sediments were the main source of DBC in DSW. A mixing model incorporating seawater oxygen isotopes (H2δ18O) indicated that Prydz Bay DSW transported DBC and DOC into the deep Southern Ocean. We estimate that the downward transport of DSW from Prydz Bay could contribute 4–9% (66–150 Gg yr−1) and 2–4% (3700–8500 Gg yr−1) to the DBC and DOC concentrations in Antarctic Bottom Water, respectively. Thus, the downward transport of DBC along the Antarctic shelf/slope is likely a significant source of DBC to the deep waters of the Southern and Global Ocean.

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Section: Discussionmentioning

confidence: 99%

Transport of dissolved black carbon from the Prydz Bay Shelf, Antarctica to the deep Southern Ocean

Fang

Yang

Chen

et al. 2018

Limnology & Oceanography

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“…On the other hand, both the DOC latitudinal gradients and modeling approach do not explicitly measure the microbial degradation but infer it indirectly from subsurface spatial gradients in DOC and temperature. However, it can be assumed that these approaches assess the temperature effects on microbial consumption of DOC, as long as abiotic particle-DOC scavenging or solubilization processes are minimal (Druffel et al, 1992(Druffel et al, , 2016.…”

Section: Discussionmentioning

confidence: 99%

Large Stimulation of Recalcitrant Dissolved Organic Carbon Degradation by Increasing Ocean Temperatures

et al. 2018

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More than 96% of organic carbon in the ocean is in the dissolved form, most of it with lifetimes of decades to millennia. Yet, we know very little about the temperature sensitivity of dissolved organic carbon (DOC) degradation in a warming ocean. Combining independent estimates from laboratory experiments, oceanographic cruises and a global ocean DOC cycling model, we assess the relationship between DOC decay constants and seawater temperatures. Our results show that the apparent activation energy of DOC decay (E a ) increases by three-fold from the labile (lifetime of days) and semi-labile (lifetime of months) to the semi-refractory (lifetime of decades) DOC pools, with only minor differences between the world's largest ocean basins. This translates into increasing temperature coefficients (Q 10 ) from 1.7-1.8 to 4-8, showing that the generalized assumption of a constant Q 10 of ∼2 for biological rates is not universally applicable for the microbial degradation of DOC in the ocean. Therefore, rising ocean temperatures will preferentially impact the microbial degradation of the more recalcitrant and larger of the three studied pools. Assuming a uniform 1 • C warming scenario throughout the ocean, our model predicts a global decrease of the DOC reservoir by 7 ± 1 Pg C. This represents a 15% reduction of the semi-labile + semi-refractory DOC pools.

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“…Δ 14 C versus δ 13 C values of DOC and DIC in samples collected from the YBH and reference site in the South China Sea. Data from the Changjiang and Huanghe (Wang et al, , 2016), Northwest Pacific (Ge et al, ), South Pacific (Druffel & Griffin, ), Pacific (Druffel et al, ), and Atlantic (Druffel et al, ) are shown for comparison. Solid shapes are from this study; unfilled shapes are from previous studies.…”

Section: Discussionmentioning

confidence: 99%

“…DOC in the YBH is also unusually old, as shown by the Δ 14 C‐DOC values, for a shallow high salinity ocean environment which could be attributed to extensive degradation, chemoheterotrophic and/or chemoautotrophic production. In the open ocean, Δ 14 C‐DOC values usually decrease steadily with depth from −200‰ to −400‰ in surface waters to lower values at depths below 1,000 m (−400‰ to −550‰) and then remain relatively constant (Figure S7) (Bauer et al, ; Druffel et al, ; Hansell et al, ). Oceanic profiles of DOC ages thus increase from ~2,000 years in surface waters to ~6,000 years at depth.…”

Section: Discussionmentioning

confidence: 99%

“…The relatively high DOC concentrations and low DOC Δ 14 C values from the depths of 230 and 270 m in the YBH indicate that continuous supply as well as consumption and aging processes are likely responsible for the accumulation of older DOC. This does not, however, exclude the possibility of an additional source of DOC with potentially different DOC isotopic signatures in the deep waters of the blue hole, for example, heterotrophic/autotrophic production in anoxic waters (Sarbu et al, ; Druffel & Bauer, ; Loh et al, ; Mccarthy et al, 2011; Follett et al, ; Bercovici & Hansell, ; Druffel et al, ).…”

Section: Discussionmentioning

confidence: 99%

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Carbon Cycling in the World's Deepest Blue Hole

et al. 2020

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Blue holes are unique geomorphological features with steep biogeochemical gradients and distinctive microbial communities. Carbon cycling in blue holes, however, remains poorly understood. Here we describe potential mechanisms of dissolved carbon cycling in the world's deepest blue hole, the Yongle Blue Hole (YBH), which was recently discovered in the South China Sea. In the YBH, we found some of the lowest concentrations (e.g., 22 μM) and oldest ages (e.g., 6,810 years before present) of dissolved organic carbon, as well as the highest concentrations (e.g., 3,090 μM) and the oldest ages (e.g., 8,270 years before present) of dissolved inorganic carbon observed in oceanic waters. Sharp gradients of dissolved oxygen, H2S, and CH4 and changes in bacterially mediated sulfur cycling with depth indicated that sulfur‐ and/or methane‐based metabolisms are closely linked to carbon cycling in the YBH. Our results showed that the YBH is a unique and easily accessible natural laboratory for examining carbon cycling in anoxic systems, which has potential for understanding carbon dynamics in both paleo and modern oceans—particularly in the context of global change.

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Radiocarbon in dissolved organic carbon of the Atlantic Ocean

Cited by 57 publications

References 42 publications

Transport of dissolved black carbon from the Prydz Bay Shelf, Antarctica to the deep Southern Ocean

Transport of dissolved black carbon from the Prydz Bay Shelf, Antarctica to the deep Southern Ocean

Large Stimulation of Recalcitrant Dissolved Organic Carbon Degradation by Increasing Ocean Temperatures

Carbon Cycling in the World's Deepest Blue Hole

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