Pan-Arctic Patterns in Black Carbon Sources and Fluvial Discharges Deduced From Radiocarbon and PAH Source Apportionment Markers In Estuarine Surface Sediments

A pan-arctic geospatial picture of black carbon (BC) characteristics was obtained from the seven largest arctic rivers by combining with molecular combustion markers (polycyclic aromatic hydrocarbons) and radiocarbon ((14)C) analysis. The results suggested that the contribution from modern biomass burning to BC ranged from low in the Yukon (8%) and Lena (5%) Rivers to high in the Yenisey River (88%). The Mackenzie River contributed almost half of the total arctic fluvial BC export of 202 kton a(-1) (kton = 10(9) g), with the five Russian-Arctic rivers contributing 10-36 kton a(-1) each. The (14)C-based source estimate of fluvially exported BC to the Arctic Ocean, weighted by the riverine BC fluxes, amount to about 20% from vegetation/biofuel burning and 80% from (14)C-extinct sources such as fossil fuel combustion and relict BC in uplifted source rocks. Combining these pan-arctic data with available estimates of BC export from other rivers gave a revised estimate of global riverine BC export flux of 26 x 10(3) kton a(-1). This is twice higher than a single previous estimate and confirms that river export of BC is a more important pathway of BC to the oceans than direct atmospheric deposition

Evidence and estimates of significant warming-associated methane release on the East Siberian Arctic shelf

The Tenth Symposium on Polar Science/Ordinary sessions: [OG] Polar Geosciences, Wed. 4 Dec. / Entrance Hall (1st floor), National Institute of Polar Researc

Cold-seep carbonates of the Laptev Sea continental slope: Constraints from fluid sources and environment of formation

This study presents results of the petrographic, mineralogical, stable isotopes of oxygen and carbon, and trace element investigation of authigenic carbonates collected at newly discovered active cold seeps on the Laptev Sea continental slope at ∼300 m water depth. These carbonates are mainly represented by Mg-calcite with MgCO3 content from 9.1 mol% to 14.0 mol%. The low δ13C values of carbonates ranging from −50.6 ‰ to −32.4 ‰ (V-PDB) indicate that they were formed from anaerobic oxidation of biogenic methane and minor participation of other carbon sources. The difference between measured (from 4.7 ‰ to 5.5 ‰) and calculated (4.0 ‰) δ18Ocarb values might be inherited from fluids enriched in 18O due to dissociation of gas hydrates, which could be the source of methane. The carbonates exhibit weak enrichment in Co, moderate and strong enrichments in As, Mo, and Sb, and strong enrichment in U. Interestingly, As, Sb, and Co correlate with the pyrite content. This indicates that authigenic iron sulfides promote the immobilization of these redox-sensitive elements in seep sediments. The (Mo/U)EF values and anomalies of concentration of Mo and U probably indicate variations in the redox conditions during carbonate formation due to episodically seepage activity changes. Ascending methane-bearing fluids were the main contributor to the enrichment of cold-seep carbonates in As, Mo, Sb, and U at the Laptev Sea continental slope. However additional input from the particulate shuttle process can not be ruled out

北極海マカロフ海盆での冬季水増加に伴う栄養塩躍層の浅化

北極海における近年の急激な海氷減少は北極海の気候や生態系にさまざまな変化を引き起こしてきた。例えば、カナダ海盆では海氷融解に伴う淡水化や酸性化、海洋循環の強化、栄養塩躍層の深化とそれに伴う生物生産の低下、巨大渦の出現とその影響による植物プランクトン量の増加などが観測されるようになってきた。これらの現象はいずれもアラスカ側北極海で観測されたものである。しかし、シベリア側北極海はデータが少なく、どのような変化が起きているのかはほとんど分かっていない。本研究ではロシアEEZ海域のデータを含む複数船舶のデータを活用し、シベリア側北極海での海氷減少に伴う水塊構造の変化と低次生態系への影響について議論する。要旨 ; 2013年度日本海洋学会春季大会（2013年3月21日～3月25日, 東京海洋大学）http://www.godac.jamstec.go.jp/darwin/cruise/mirai/mr04-05/ehttp://www.godac.jamstec.go.jp/darwin/cruise/mirai/mr08-04/

Spatial patterns and distributional controls of total and methylated mercury off the Lena River in the Laptev Sea sediments

A warmer climate is predicted to accelerate the export of mercury (Hg) from Siberian rivers to the Arctic Ocean, yet there is a dearth of process-oriented studies on the speciation and fate of Hg in the shelf sea system. Here, we present data on total Hg (HgT) and methylmercury (MeHg) in Laptev Sea surface sediments along a cross-shelf transect starting at the mouth of the Lena River. Concentrations of HgT along the 330 km cross-shelf transect ranged within a fairly narrow span from 480 to 150 pmol g−1 d.w., while concentrations of MeHg decreased one hundredfold from 13 pmol g−1 d.w. near the Lena river to 0.095 pmol g−1 d.w. in the more distall stations. The highest concentrations of HgT and MeHg were observed close to the river delta and were associated with a high supply of organic carbon (OC). Enrichment of the OC normalized HgT concentration (HgTOC) and depletion of the OC normalized MeHg concentration (MeHgOC) across the shelf suggests bulk OC content to not be the only driver of the HgT and MeHg spatial distributions. Based on correlations observed between HgTOC and MeHgOC and proxies for sediment physics and organic matter pools we suggest the spatial distribution of Hg and MeHg to also be influenced by hydrodynamic sorting of riverine-derived material. For MeHg, depletion of the MeHgOC across the shelf is likely driven by the trapping of terrestrial MeHg in sediments close to the river delta before it is degraded in the water column

Space-time dynamics of carbon stocks and environmental parameters related to carbon dioxide emissions in the Buor-Khaya Bay of the Laptev Sea

This study aims to improve understanding of carbon cycling in the Buor-Khaya Bay (BKB) by studying the inter-annual, seasonal, and meso-scale variability of carbon stocks and related hydrological and biogeochemical parameters in the water, as well as factors controlling carbon dioxide (CO2) emission. Here we present data sets obtained on summer cruises and winter expeditions during 12 yr of investigation. Based on data analysis, we suggest that in the heterotrophic BKB area, coastal erosion and river discharge serve as predominant drivers of the organic carbon (OC) cycle, determining OC input and transformation, dynamics of nutrients, carbon stocks in the water column, and atmospheric emissions of CO2

Understanding the Permafrost–Hydrate System and Associated Methane Releases in the East Siberian Arctic Shelf

This paper summarizes current understanding of the processes that determine the dynamics of the subsea permafrost–hydrate system existing in the largest, shallowest shelf in the Arctic Ocean; the East Siberian Arctic Shelf (ESAS). We review key environmental factors and mechanisms that determine formation, current dynamics, and thermal state of subsea permafrost, mechanisms of its destabilization, and rates of its thawing; a full section of this paper is devoted to this topic. Another important question regards the possible existence of permafrost-related hydrates at shallow ground depth and in the shallow shelf environment. We review the history of and earlier insights about the topic followed by an extensive review of experimental work to establish the physics of shallow Arctic hydrates. We also provide a principal (simplified) scheme explaining the normal and altered dynamics of the permafrost–hydrate system as glacial–interglacial climate epochs alternate. We also review specific features of methane releases determined by the current state of the subsea-permafrost system and possible future dynamics. This review presents methane results obtained in the ESAS during two periods: 1994–2000 and 2003–2017. A final section is devoted to discussing future work that is required to achieve an improved understanding of the subject

Remobilization of dormant carbon from Siberian-Arctic permafrost during three past warming events.

Carbon cycle models suggest that past warming events in the Arctic may have caused large-scale permafrost thaw and carbon remobilization, thus affecting atmospheric CO2 levels. However, observational records are sparse, preventing spatially extensive and time-continuous reconstructions of permafrost carbon release during the late Pleistocene and early Holocene. Using carbon isotopes and biomarkers, we demonstrate that the three most recent warming events recorded in Greenland ice cores-(i) Dansgaard-Oeschger event 3 (~28 ka B.P.), (ii) Bølling-Allerød (14.7 to 12.9 ka B.P.), and (iii) early Holocene (~11.7 ka B.P.)-caused massive remobilization and carbon degradation from permafrost across northeast Siberia. This amplified permafrost carbon release by one order of magnitude, particularly during the last deglaciation when global sea-level rise caused rapid flooding of the land area thereafter constituting the vast East Siberian Arctic Shelf. Demonstration of past warming-induced release of permafrost carbon provides a benchmark for the sensitivity of these large carbon pools to changing climate

Ebullition-Driven Fluxes of Methane from Shallow Hot Spots in the East Siberian Arctic Shelf

The maximum concentration of atmospheric methane (CH4) occurs over the Arctic: the value of CH4 over Greenland exceeds that over Antarctica by 8-10%; an absolute maximum is measured during wintertime (Steel et. al., 1987; Fung et. al., 1991). Geologic evidence provides insight into possible climate change effects from a warmer Arctic, suggesting that enhanced Arctic CH4 emissions during warm periods played a key role in past rapid climate change.This work was supported by the International Arctic Research Center of the University Alaska Fairbanks (by the Cooperative Institute for Arctic Research through NOAA Cooperative Agreement NA17RJ1224 and the National Science Foundation Agreement No OPP-0327664), the Russian Foundation for Basic Research (No.04-05-64819) and the Far-Eastern Branch of Russian Academy of Sciences, RAS (Project: Environmental changes in the East-Siberian region)

Sonar gas flux estimation by bubble insonification: application to methane bubble flux from seep areas in the outer Laptev Sea

Sonar surveys provide an effective mechanism for mapping seabed methane flux emissions, with Arctic submerged permafrost seepage having great potential to significantly affect climate. We created in situ engineered bubble plumes from 40 m depth with fluxes spanning 0.019 to 1.1 L s−1 to derive the in situ calibration curve (Q([sigma])). These nonlinear curves related flux (Q) to sonar return ([sigma]) for a multibeam echosounder (MBES) and a single-beam echosounder (SBES) for a range of depths. The analysis demonstrated significant multiple bubble acoustic scattering - precluding the use of a theoretical approach to derive Q([sigma]) from the product of the bubble [sigma] (r) and the bubble size distribution where r is bubble radius. The bubble plume σ occurrence probability distribution function ([PSI]([sigma])) with respect to Q found [PSI] ([sigma]) for weak σ well described by a power law that likely correlated with small-bubble dispersion and was strongly depth dependent. [PSI] ([sigma]) for strong σ was largely depth independent, consistent with bubble plume behavior where large bubbles in a plume remain in a focused core. [PSI] ([sigma]) was bimodal for all but the weakest plumes