Beschreibung: Arctic coastal zones serve as a sensitive filter for terrigenous matter input onto the shelves via river discharge and coastal erosion. This material is further distributed across the Arctic by ocean currents and sea ice. The coastal regions are particularly vulnerable to changes related to recent climate change. We compiled a pan-Arctic review that looks into the changing Holocene sources, transport processes and sinks of terrigenous sediment in the Arctic Ocean. Existing palaeoceanographic studies demonstrate how climate warming and the disappearance of ice sheets during the early Holocene initiated eustatic sea-level rise that greatly modified the physiography of the Arctic Ocean. Sedimentation rates over the shelves and slopes were much greater during periods of rapid sea-level rise in the early and middle Holocene, as a result of the relative distance to the terrestrial sediment sources. However, estimates of suspended sediment delivery through major Arctic rivers do not indicate enhanced delivery during this time, which suggests enhanced rates of coastal erosion. The increased supply of terrigenous material to the outer shelves and deep Arctic Ocean in the early and middle Holocene might serve as analogous to forecast changes in the future Arctic.

Beschreibung: Mobilization of Arctic permafrost carbon is expected to increase with warming-induced thawing. However, this effect is challenging to assess due to the diverse processes controlling the release of various organic carbon (OC) pools from heterogeneous Arctic landscapes. Here, by radiocarbon dating various terrestrial OC components in fluvially and coastally integrated...

Beschreibung: Warming in the Arctic is expected to be roughly twice as high as the global mean. Sea ice extent is declining dramatically over the last years and favors accelerating coastal erosion. With erosion rates as high as 25 m·yr-1, the release of organic carbon and nutrients from permafrost coasts has dramatic impacts on the global carbon cycle, on nearshore food webs and the local communities which are still relying on the marine biological resources. During the Holocene, the delivery of sediment, particulate organic carbon (POC) and dissolved organic carbon (DOC) varied in response to temperature and relative sea level changes. Such phases of increased or reduced material input could serve as an analogue for future erosion scenarios. In the past, changing inputs of sediments, carbon, and nutrients may have altered the biogeochemical setting on the upper arctic shelves and may have impacted the global carbon cycle. Recent flux estimates of sediment and POC from coastal erosion into the Arctic Ocean are ~430 Tg yr-1 sediment and 4.9-14 Tg yr-1 POC, which is comparable to if not higher than riverine fluxes. However, the fate of sediments and organic carbon once eroded from the cliff remains largely unknown and the release of DOC from melting ground ice in permafrost cliffs has not been considered yet. Material supply over the Holocene is difficult to quantify as it depends on erosion of a coastline whose original configuration is not known. For example, large parts of the circum-arctic shelves were subaerially exposed during the last glacial maximum (LGM) and became flooded rapidly. Thus, early Holocene erosion of coastal permafrost deposits was probably stronger than today and released more terrestrial material. With the retreat of the coastline, the depocenters moved further southward and thereby successively reducing accumulation rates in the distal shelf areas. In other parts of the Arctic, however, glacio-isostatic rebound was significant so that global transgression was outpaced and therefore reduced shore line retreat. Even after the modern sea-level highstand was approached around 5,000 cal BP, there is evidence that the depositional system on the shelves took time to stabilize. Quantitative estimates of erosion rates along Arctic coasts throughout the Holocene are still sparse and need substantial improvement to clarify the fate of terrigenous material in the Arctic Ocean.

Beschreibung: Arctic coastal zones serve as a sensitive filter for terrigenous matter input onto the shelves via river discharge and coastal erosion. This material is further distributed across the Arctic by ocean currents and sea ice. The coastal regions are particularly vulnerable to changes related to recent climate change. We compiled a pan-arctic review that looks into the changing Holocene sources, transport processes and sinks of terrigenous sediment in the Arctic Ocean. Existing paleoceanographic studies demonstrate how climate warming and the disappearance of ice sheets during the early Holocene initiated eustatic sea-level rise that greatly modified the physiography of the Arctic Ocean. Sedimentation rates over the shelves and slopes were much greater during periods of rapid sea-level rise in the early and middle Holocene, due to the relative distance to the terrestrial sediment sources. However, estimates of suspended sediment delivery through major Arctic rivers do not indicate enhanced delivery during this time, thus, suggesting enhanced rates of coastal erosion. The increased supply of terrigenous material to the outer shelves and deep Arctic Ocean in the early and middle Holocene might serve as analogous to forecast changes in the future Arctic.

Beschreibung: The rapidly changing East Siberian Arctic Shelf (ESAS) receives large amounts of terrestrial organic carbon (OC) from coastal erosion and Russian-Arctic rivers. Climate warming increases thawing of coastal Ice Complex Deposits (ICD) and can change both the amount of released OC, as well as its propensity to be converted to greenhouse gases (fueling further global warming) or to be buried in coastal sediments. This study aimed to unravel the susceptibility to degradation, and transport and dispersal patterns of OC delivered to the ESAS. Bulk and molecular radiocarbon analyses on surface particulate matter (PM), sinking PM and underlying surface sediments illustrate the active release of old OC from coastal permafrost. Molecular tracers for recalcitrant soil OC showed ages of 3.4–13 14C-ky in surface PM and 5.5–18 14C-ky in surface sediments. The age difference of these markers between surface PM and surface sediments is larger (i) in regions with low OC accumulation rates, suggesting a weaker exchange between water column and sediments, and (ii) with increasing distance from the Lena River, suggesting preferential settling of fluvially derived old OC nearshore. A dual-carbon end-member mixing model showed that (i) contemporary terrestrial OC is dispersed mainly by horizontal transport while being subject to active degradation, (ii) marine OC is most affected by vertical transport and also actively degraded in the water column, and (iii) OC from ICD settles rapidly and dominates surface sediments. Preferential burial of ICD-OC released into ESAS coastal waters might therefore lower the suggested carbon cycle climate feedback from thawing ICD permafrost.