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Old permafrost carbon dumps just offshore

Eroding Arctic coasts drop ancient organic carbon into a 100–300 m nearshore strip, while farther surface waters carry younger carbon.

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How much OC can pan-Arctic coastal erosion release per year, as cited?

Up to 14 Tg OC per year.

Where is the field site?

Herschel Island–Qikiqtaruk, Yukon coast, Beaufort Sea.

How have mean erosion rates changed?

0.45 m yr−1 (1970–2000) to 0.68 m yr−1 (2000–2011).

How many locations were sampled?

49 over two weeks in July–August 2017, including 37 nearshore sites to 20 m depth.

What mean POC do thaw streams carry?

2,200 mg L−1 (range 136–5,350).

How wide/deep is the turbid resuspension zone?

About 100–300 m offshore, up to 5–6 m depth.

How old is resuspension-zone surface POC?

Mean Δ14C −867‰, about 16,400 14C years.

How old is thaw-stream POC?

Mean Δ14C −803‰ (8,300 to 25,000 14C years).

How do deposition-zone surface POC concentrations compare?

Much lower: <1.0 mg L−1 (mean 0.3) versus 1.5–15.9 (mean 4.8) in the resuspension zone.

What fraction of nearshore sediment OC is terrestrial?

More than 90%, matching earlier Herschel Basin studies.

What do the authors conclude about the nearshore zone?

It can be a sink for old, permafrost-derived POC via mineral association and burial, though waves can resuspend it.