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| Titel |
Erosion of soil organic carbon at high latitudes and its delivery to Arctic
Ocean sediments: New source to sink insight from radiocarbon dating |
| VerfasserIn |
Robert Hilton, Valier Galy, Jérôme Gaillardet, Mathieu Dellinger, Charlotte Bryant, Matt O'Regan, Darren Gröcke, Helen Coxall |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250133257
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| Publikation (Nr.) |
 EGU/EGU2016-13845.pdf |
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| Zusammenfassung |
| Soils of the northern high latitudes store carbon over thousands of years and contain
almost double the carbon stock of the atmosphere. Erosion processes can mobilise
this pre-aged soil organic carbon from the landscape and supply it to rivers. If it
escapes degradation during river transport and is delivered to the coastal ocean,
this carbon may be sequestered for much longer periods of time (>104 yr) as a
geological CO2 sink. Despite this recognition, the erosional flux and fate of particulate
organic carbon (POC) in large rivers draining the high latitudes remains poorly
constrained.
Using radiocarbon activity, we quantify POC source, flux and fate in the Mackenzie
River, the main sediment supplier to the Arctic Ocean. When combined with stable carbon
isotopes and element ratios, the radiocarbon activity of POC allows us to distinguish inputs of
POC from sedimentary rocks and quantify the average age of biospheric POC (from
vegetation and soil) transported through the river system. We find that the eroded biospheric
POC has resided in the basin for millennia, with a mean radiocarbon age of 5800±800
years. This is much older than large tropical rivers where we have equivalent data
(Amazon River, Ganges River), and likely reflects the longer residence time of
organic matter in cold, wet, high latitude soils. Based on the measured biospheric
POC content and annual sediment flux, we calculate a biospheric POC flux of 2.2
(+1.3/-0.9) TgC yr−1 from the Mackenzie River. This is the largest input of aged organic
carbon to the Arctic Ocean, more than the combined POC flux from the Eurasian
Rivers.
Offshore, we use a marine core to investigate organic carbon burial over the
Holocene period. Radiocarbon measurements of bulk organic carbon reveal a significant
offset from benthic foraminifera radiocarbon ages throughout the core, which is
dependent upon the grain size of the sediments. Organic matter in sediments >63μm are
offset from foraminifera by ∼ 6,000 14C years, while organic matter in materials
<63μm are offset by ∼10,000 14C years. The benthic-organic matter offsets are
relatively constant down core, suggesting pre-aged soil organic matter has been
eroded from parts of the Mackenzie Basin for at least 15,000 years. The 14C age
offsets are consistent with those seen in the modern river system, where we find fine
grained sediments containing older biosperhic POC (∼6-8 ka) than coarse grained
materials (∼3-5 ka). Together with the organic carbon content of these sediments,
these measurements suggest high burial efficiencies (>60%) of pre-aged terrestrial
organic matter in this core over the Holocene. We postulate that erosion of organic
carbon-rich, high latitude soils may result in a significant long term carbon sink. |
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