Abstract
Abstract. Climate warming is amplified in the land-sea system of the East Siberian Arctic, which also holds large pools of vulnerable carbon in permafrost. This coastal area is strongly influenced by sediment and carbon transport from both its large rivers and extensive erosion of Pleistocene permafrost along its coastline. This study is investigating the coastal fate of the sediment and organic carbon delivered to the Buor-Khaya Gulf, which is the first recipient of the overwhelming fluvial discharge from the Lena River and is additionally receiving large input from extensive erosion of the coastal ice-complex (permafrost a.k.a. Yedoma; loess soil with high organic carbon content). Both water column suspended particulate matter (SPM) and surface sediments were sampled at about 250 oceanographic stations in the Gulf in this multi-year effort, including one winter campaign, and analyzed for the distribution and sorting of sediment size, organic carbon content, and stable carbon isotope signals. The composition of the surface sediment suggests an overwhelmingly terrestrial contribution from both river and coastal erosion. The objective of this paper is to improve our understanding of the seasonal (i.e., winter vs summer) and interannual variability of these coastal sedimentation processes and the dynamics of organic carbon (OC) distribution in both the water column SPM and the surface sediments of the Buor-Khaya Gulf. Based on data collected during several years in the period 2000–2008, two different sedimentation regimes were revealed for the Buor-Khaya Gulf, the relative importance of each at a given time depend on hydrometeorological conditions, the Lena River water discharge and sea-ice regime: Type 1 erosion-accumulation and Type 2 accumulation. The Type 1 erosion-accumulation sedimentation regime is typical (2000–2006) for the ice-free period of the year (here considered in detail for August 2005). Under such conditions terrigenous sources of SPM and particulate organic carbon (POC) stem predominantly from river discharge, thermal erosion of coastal ice-complex and remobilized bottom sediments. The Type 2 accumulation sedimentation regime develops under ice-covered conditions, and only occasionally during the ice-free period (August 2008). In Type 2 winter, combined terrigenous and marine-biogenic SPM and POC sources are dominating due to relatively low overall terrigenous input (April 2007). In Type 2 summer, river alluvium becomes the major SPM and POC source (August 2008). The water column SPM and POC loadings vary by more than a factor of two between the two regimes. This study underscores the necessity of multi-year investigations to better understand the functioning of the primary recipient of terrestrially expulsed matter in the East Siberian Arctic.
Highlights
The Arctic Ocean receives >10 % of the global river sediment discharge while only hosting 1 % of the total ocean volume
One publication states that only 10–17 % of the sediment in the lower Lena River at Kyusur makes it through the Lena Delta (Alabyan et al, 1995), whereas another paper argues that essentially all suspended sediments reach the Laptev Sea (Rachold et al, 2000)
The particulate organic carbon (OC) (POC) composition was analyzed on samples filtered on pre-combusted (12 h, 450 ◦C) glass fiber filters (GF/F 0.7 μm, Whatman) of 47 mm or 142 mm diameters, respectively, which were upon filtration immediately transferred to pre-combusted aluminum envelopes, frozen and kept at −18 ◦C until analysis
Summary
The Arctic Ocean receives >10 % of the global river sediment discharge while only hosting 1 % of the total ocean volume. The East Siberian Arctic Shelf (ESAS) is the world’s largest continental shelf sea system and it is unusually shallow making the coastal system strongly influenced by terrestrial input. The Buor-Khaya Gulf in the SE Laptev Sea was targeted for this study as it is both the primary recipient of the Lena River discharge and a hotspot for erosional input from the thermo-abraded coastal ice-complex of Pleistocene permafrost. There are discussions concerning how much of the sediment transported by the Lena River reaches the Laptev Sea (Are et al, 2000). One publication states that only 10–17 % of the sediment in the lower Lena River at Kyusur makes it through the Lena Delta (Alabyan et al, 1995), whereas another paper argues that essentially all suspended sediments reach the Laptev Sea (Rachold et al, 2000)
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