High rates of organic carbon burial in fjord sediments globally
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The deposition and long-term burial of organic carbon in marine sediments has played a key role in controlling atmospheric O-2 and CO2 concentrations over the past 500 million years(1). Marine carbon burial represents the dominant natural mechanism of long-term organic carbon sequestration(1,2). Fjords-deep, glacially carved estuaries at high latitudes-have been hypothesized to be hotspots of organic carbon burial, because they receive high rates of organic material fluxes from the watershed(3). Here we compile organic carbon concentrations from 573 fjord surface sediment samples and 124 sediment cores from nearly all fjord systems globally. We use sediment organic carbon content and sediment delivery rates to calculate rates of organic carbon burial in fjord systems across the globe. We estimate that about 18 Mt of organic carbon are buried in fjord sediments each year, equivalent to 11% of annual marine carbon burial globally(4). Per unit area, fjord organic carbon burial rates are twice as large as the global ocean average, and fjord sediments contain twice as much organic carbon as biogenous sediments underlying the upwelling regions of the ocean(1). We conclude that fjords may play an important role in climate regulation on glacial-interglacial timescales.