Seafloor carbon

(Image credited to: NOAA Vents Program, the Institute of Geological & Nuclear Sciences and NOAA-OE)

Deep-sea carbon cycling is poorly constrained, not least because this remote environment is so difficult to explore. In this web focus we highlight the prevalence and diversity of seabed carbon sources.



Deep-sea discoveries p1


The sea floor is emerging as a source of carbon to the overlying ocean. Scientific exploration of the sea bed is essential for a full understanding of the global carbon budget and the safety of deep-sea carbon storage proposals.


News and Views

Oceanography: Carbon cycle at depth pp9 - 11

Katrina J. Edwards


The existence of a microbial community in the ocean crust has long been hypothesized. Isotopic evidence indicates that a deep biosphere of microbes both scrubs oceanic fluids of organic matter and produces new, yet old, organic carbon in situ.

Volcanology: Carbon below the sea floor pp11 - 12

David Goldberg


Magma from the mantle meets the ocean at seafloor spreading centres. At young rifts, basalt sills may heat overlying sediments and induce natural carbon release; basalt flows elsewhere may offer secure reservoirs for sequestration of anthropogenic carbon.



Chemosynthetic origin of 14C-depleted dissolved organic matter in a ridge-flank hydrothermal system pp32 - 36

Matthew D. McCarthy, Steven R. Beaupré, Brett D. Walker, Ian Voparil, Thomas P. Guilderson & Ellen R. M. Druffel


Hydrothermal fluids circulate through the upper portion of the oceanic crust. Isotopic analyses suggest that chemosynthetic microbial communities in the crust synthesize dissolved organic carbon in hydrothermal ridge-flank fluids.

Methane hydrate-bearing seeps as a source of aged dissolved organic carbon to the oceans pp37 - 41

John W. Pohlman, James E. Bauer, William F. Waite, Christopher L. Osburn & N. Ross Chapman


Marine sediments contain large quantities of carbon, primarily in the form of gas hydrate. Isotopic analyses suggest that carbon derived from fossil methane accounts for up to 28% of the dissolved organic carbon in sea water overlying hydrate-bearing seeps in the northeastern Pacific Ocean.

Carbon release by off-axis magmatism in a young sedimented spreading centre pp50 - 54

Daniel Lizarralde, S. Adam Soule, Jeff S. Seewald & Giora Proskurowski


Continental rifting creates narrow ocean basins, where coastal ocean upwelling and enhanced silicate weathering remove carbon dioxide from the atmosphere. Evidence from seismic data, sonar backscatter and seafloor images, and geochemical water analyses suggest that in young sedimented rifts, active magmatism occurs in a broader region than appreciated and releases carbon from the sediments.


From the archives



Kick-starting ancient warming

E. G. Nisbet, S. M. Jones, J. Maclennan, G. Eagles, J. Moed, N. Warwick, S. Bekki, P. Braesicke, J. A. Pyle & C. M. R. Fowler


Rapid global warming marked the boundary between the Palaeocene and Eocene periods 55.6 million years ago, but how the temperature rise was initiated remains elusive. A catastrophic release of greenhouse gases from the Kilda basin could have served as a trigger.


News and Views

Biogeochemistry: Life in the deep sea

Cara M. Santelli


Volcanic rocks on the sea floor are home to diverse and abundant microbial communities. Microscopic and spectroscopic analyses suggest that iron and manganese derived from hydrothermal venting support microbial colonization of the ocean crust.

Palaeoclimate: Enigmatic Earth

David J. Beerling


Global warming 55 million years ago was accompanied by a massive injection of carbon into the ocean–atmosphere system, but the resulting climatic warming was much greater than expected from the modelled rise in atmospheric carbon dioxide alone.



A heat-induced molecular signature in marine dissolved organic matter

Thorsten Dittmar & Jiyoung Paeng


Marine dissolved organic matter contains roughly as much organic carbon as all living biota on land and in the oceans combined. New techniques in analytical chemistry show that a significant portion of this material has undergone thermal alteration, either on land or in sediments deep below the sea floor.



Asphalt volcanoes as a potential source of methane to late Pleistocene coastal waters

David L. Valentine, Christopher M. Reddy, Christopher Farwell, Tessa M. Hill, Oscar Pizarro, Dana R. Yoerger, Richard Camilli, Robert K. Nelson, Emily E. Peacock, Sarah C. Bagby, Brian A. Clarke, Christopher N. Roman & Morgan Soloway


Natural petroleum seepage emits large volumes of oil and methane to the oceans every year, accompanied by the formation of asphalt volcanoes on the sea floor. The discovery of seven asphalt volcanoes off the coast of southern California may help to explain high methane emissions recorded during the late Pleistocene.

Considerable methane fluxes to the atmosphere from hydrocarbon seeps in the Gulf of Mexico

Evan A. Solomon, Miriam Kastner, Ian R. MacDonald & Ira Leifer


The flux of methane — a greenhouse gas — from submarine hydrocarbon seeps to the atmosphere is not well quantified. Direct measurements of methane concentrations and isotopic depth profiles in deepwater hydrocarbon plumes indicate that a significant amount of methane from deep-ocean sources could reach the surface ocean.

Carbon dioxide forcing alone insufficient to explain Palaeocene–Eocene Thermal Maximum warming

Richard E. Zeebe, James C. Zachos & Gerald R. Dickens


About 55 million years ago global surface temperatures increased by 5–9 °C within a few thousand years, following a pulse of carbon released to the atmosphere. Analysis of existing data with a carbon cycle model indicates that this carbon pulse was too small to cause the full amount of warming at accepted values for climate sensitivity.

Metabolic variability in seafloor brines revealed by carbon and sulphur dynamics

Samantha B. Joye, Vladimir A. Samarkin, Beth! N. Orcutt, Ian R. MacDonald, Kai-Uwe Hinrichs, Marcus Elvert, Andreas P. Teske, Karen G. Lloyd, Mark A. Lever, Joseph P. Montoya & Christof D. Meile


Brine fluids supply the sea floor with energy-rich substrates. Geochemical and genetic analyses indicate that the associated microbial communities — and their dominant metabolisms — vary between seep sites with different supplies of sulphate and organic matter.

Preservation of iron(II) by carbon-rich matrices in a hydrothermal plume

Brandy M. Toner, Sirine C. Fakra, Steven J. Manganini, Cara M. Santelli, Matthew A. Marcus, James W. Moffett, Olivier Rouxel, Christopher R. German & Katrina J. Edwards


Hydrothermal vents release significant quantities of dissolved iron into the oceans. Spectromicroscopic examination of a hydrothermal plume suggests that carbon-rich matrices protect this iron from oxidation and precipitation.

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