Description: Wildfires and incomplete combustion of fossil fuel produce large amounts of black carbon. Black carbon production and transport are essential components of the carbon cycle. Constraining estimates of black carbon exported from land to ocean is critical, given ongoing changes in land use and climate, which affect fire occurrence and black carbon dynamics. Here, we present an inventory of the concentration and radiocarbon content (∆14C) of particulate black carbon for 18 rivers around the globe. We find that particulate black carbon accounts for about 15.8 ± 0.9% of river particulate organic carbon, and that fluxes of particulate black carbon co-vary with river-suspended sediment, indicating that particulate black carbon export is primarily controlled by erosion. River particulate black carbon is not exclusively from modern sources but is also aged in intermediate terrestrial carbon pools in several high-latitude rivers, with ages of up to 17,000 14C years. The flux-weighted 14C average age of particulate black carbon exported to oceans is 3,700 ± 400 14C years. We estimate that the annual global flux of particulate black carbon to the ocean is 0.017 to 0.037 Pg, accounting for 4 to 32% of the annually produced black carbon. When buried in marine sediments, particulate black carbon is sequestered to form a long-term sink for CO2.

Description: During the Pleistocene, glaciers advanced repeatedly from the Alps onto the Swiss Plateau. Numeric age control for the last glaciation is good and thus the area is well suited to test a method which has so far not been applied to till in Switzerland. In this study, we apply in situ produced cosmogenic 10Be depth profile dating to several till deposits. Three sites lie inside the assumed Last Glacial Maximum (LGM) extent of the Rhône and Aare glaciers (Bern, Deisswil, Steinhof) and two lie outside (Niederbuchsiten, St. Urban). All sites are strongly affected by denudation, and all sites have reached steady state, i.e., the 10Be production is in equilibrium with radioactive decay and denudational losses. Deposition ages can therefore not be well constrained. Assuming constant denudation rates of 5 cm/kyr, total denudation on the order of 100 cm for sites within the extent of the LGM and up to tens of meters for older moraines are calculated. Denudation events, for example related to periglacial conditions during the LGM, mitigate the need to invoke such massive denudation and could help to explain high 10Be concentrations at great depths, which we here dub "pseudo-inheritance". This term should be used to distinguish conceptionally from "true inheritance", i.e., high concentrations derived from the catchment.

Description: Oxygen and Carbon isotope data from Globigerinoides ruber from sediment core SHAK06-5K. Between 6 and 12 specimens of G. ruber were measured with a Gas Bench II connected to a Delta V Plus isotope ratio mass spectrometer at the Stable Isotope Laboratory of Climate Geology, ETH Zurich. Calibration to the Vienna Pee Dee Belemnite (VPDB) scale was accomplished using two in‐house standards previously calibrated against the NBS‐18 and NBS‐19 international standards. The associated long‐term standard deviation is 〈0.07‰. This isotopic record was concluded to be affected by the coupled effect of bioturbation with changes in the abundance of G. ruber. We refer potential users to the published article.

Description: Oxygen and Carbon isotope data from Globigerina bulloides from sediment core SHAK06-5K. Between 6 and 12 specimens of each species were measured with a Gas Bench II connected to a Delta V Plus isotope ratio mass spectrometer at the Stable Isotope Laboratory of Climate Geology, ETH Zurich. Calibration to the Vienna Pee Dee Belemnite (VPDB) scale was accomplished using two in‐house standards previously calibrated against the NBS‐18 and NBS‐19 international standards. The associated long‐term standard deviation is 〈0.07‰.

Description: Age model for core SHAK06-5K based on monospecific samples of the planktonic foraminifera Globigerina bulloides. Convention radiocarbon ages and associated 1σ uncertainties have been rounded according to convention

Description: Radiocarbon ages and associated 1-σ confidence level (68.2% probability), and corresponding age discrepancies. * Stands for untreated samples. Numbers marked with # indicate age offsets that can be explained within the 1-σ confidence level of the associated dates.

Description: Influence of the sample preparation method on radiocarbon ages. 14C ages and associated 1-σ confidence level (68.2% probability), and corresponding age discrepancies. Age offsets that can be explained within the 1-σ confidence level of the associated dates are indicated with #.

Description: Land cover transformations have accompanied the rise and fall of civilizations for thousands of years, exerting strong influence on the surrounding environment. Soil erosion and the associated outwash of nutrients are a main cause of eutrophication of aquatic ecosystems. Despite the great challenges of water protection in the face of climate change, large uncertainties remain concerning the timescales for recovery of aquatic ecosystems impacted by hypoxia. This study seeks to address this issue by investigating the sedimentary record of Lake Murten (Switzerland), which witnessed several phases of intensive human land-use over the past 2000 years. Application of geophysical and geochemical methods to a 10 m-long sediment core revealed that soil erosion increased drastically with the rise of the Roman City of Aventicum (30 CE). During this period, the radiocarbon age of the bulk sedimentary organic carbon (OC) increasingly deviated from the modeled deposition age, indicating rapid flushing of old soil OC from the surrounding catchment driven by intensive land-use. Enhanced nutrient delivery resulted in an episode of cultural eutrophication, as shown by the deposition of varved sediments. Human activity drastically decreased towards the end of the Roman period (3rd century CE), resulting in land abandonment and renaturation. Recovery of the lake ecosystem from bottom-water hypoxia after the peak in human activity took around 50 years, while approximately 300 years passed until sediment accumulation reached steady state conditions on the surrounding landscape. These findings suggest that the legacy of anthropogenic perturbation to watersheds may persist for centuries.

Description: The last deglaciation was characterized by rising concentration in atmospheric CO2 (CO2atm) and a decrease in its radiocarbon content (Δ14Catm). Mobilization of 14C-depleted terrestrial organic carbon, which was previously frozen in extensive boreal permafrost soils, might have contributed to both changes, and was potentially caused by coastal erosion during deglacial sea-level rise and warming. Since parts of this potentially mobilized organic carbon was reburied in marine sediments, records of accumulation of terrigenous biomarkers and their compound-specific radiocarbon ages can provide insights into the timing and controls on permafrost decomposition. We present data from three marine sediment cores, two cores off the Amur River draining into the Sea of Okhotsk, and one core from the Northeastern Bering Sea adjacent to the Bering shelf (one the largest shelf areas flooded during the deglaciation) receiving input from the Yukon River. During the Last Glacial Maximum all catchments were completely covered with permafrost. Today, the Amur drainage basin is free of permafrost while the Yukon catchment is covered by discontinuous permafrost. All sites show three distinct deglacial maxima (at 16.5, 14.5, 11.5 ka BP) in accumulation of old terrigenous biomarkers (5-20 kyr old at the time of deposition). The peaks occurred during meltwater pulses suggesting that sea-level rise remobilized old terrestrial carbon from permafrost on the flooded shelfs. In the Bering Sea fossil, mature organic matter, mobilized by erosion of organic rich rocks during the retreat of Brooks Range glaciers and the Laurentide ice sheet additionally contributed to the first peak via increased fluvial runoff. Deglacial changes in abundance ratios of long-chain n-alkanes record gradual changes in vegetation type and wetland extent in the Amur-river catchment. Since wetland expansion is closely linked to permafrost thaw this implies that permafrost decomposition in the Amur drainage basin was a gradual process. By contrast sea-level rise caused abrupt decomposition events across the Okhotsk and Bering Shelfs. We extrapolate our localized findings to an overall potential carbon release during deglaciation of 285 PgC from coastal erosion in the Arctic Ocean and the related permafrost decomposition. By analysing some idealized scenarios using the global carbon cycle model BICYCLE we estimate the impact of such a release on the atmosphere. We find that it might have accounted for a deglacial rise in CO2atm of up to 15 ppm, and to a decline in ∆14Catm of 15‰. These results, if restricted to the three peak events connected to rapid sea-level rise, as supported by our data, might have contributed particularly to abrupt changes in CO2atm and ∆14Catm, corresponding to 15-20% of both, the observed rise in CO2atm of ~90 ppm, and the residual in ∆14Catm that is unexplained by changes in the 14C production rate.

Description: The last deglaciation was characterized by rising concentrations in atmospheric CO2 (CO2atm) and a decrease in its radiocarbon content (∆14Catm). Mobilization of 14C-depleted terrestrial organic carbon, which was previously frozen in extensive boreal permafrost soils, might have contributed to both changes. Since parts of this potentially mobilized organic carbon was reburied in marine sediments, records of accumulation of terrigenous biomarkers and their compound-specific radiocarbon ages can provide insights into the timing of, and controls on permafrost decomposition. We present data from marine sediment cores covering the last deglaciation that were retrieved from key locations potentially receiving terrigenous material mobilized from hotspot areas of permafrost thaw. In the North Pacific, we studied two cores off the Amur River draining into the Okhotsk Sea, and one core from the Northeastern Bering Sea adjacent to the Bering shelf (one of the largest shelf areas flooded during the deglaciation), which receives input from the Yukon River. During the Last Glacial Maximum these catchments were completely covered with permafrost. Today, the Amur drainage basin is free of permafrost while the Yukon catchment is covered by discontinuous permafrost. Besides, we investigated one core from the northwestern Black Sea as a record of terrigenous material released from the thawing European tundra. All sites show distinct deglacial maxima in accumulation of old terrigenous biomarkers (5-20 kyr old at the time of deposition). In the Black Sea, one early maximum of terrigenous organic matter accumulation occurred during HS1. In the North Pacific region, two more pronounced maxima occurred later during meltwater pulses suggesting that sea-level rise remobilized old terrestrial carbon from permafrost on the flooded shelfs. Sea-level rise thus likely caused abrupt decomposition events across the Okhotsk and Bering Shelfs. We extrapolate our localized findings to an overall potential carbon release during deglaciation of 285 Pg C from coastal erosion in the Arctic Ocean and the related permafrost decomposition. By analysing some idealized scenarios using the global carbon cycle model BICYCLE we estimate the impact of carbon release from thawing permafrost on the atmosphere. We find that it might have accounted for a deglacial rise in CO2atm of up to 15 ppm, and to a decline in ∆14Catm of 15 T ̇hese results, if restricted to the three peak events as supported by our data, might have contributed particularly to abrupt changes in CO2atm and ∆14Catm, corresponding to 15-20% of both, the observed rise in CO2atm of ∼90 ppm, and the residual in ∆14Catm that is unexplained by changes in the 14C production rate.