Nearshore arctic subsea permafrost in transition

Rachold, Volker; Bolshiyanov, Dimitry Yu; Grigoriev, Mikhail N.; Hubberten, Hans‐Wolfgang; Junker, R.; Kunitsky, V.; Merker, F.; Overduin, Paul; Schneider, Waldemar

doi:10.1029/2007eo130001

Cited by 86 publications

(80 citation statements)

References 8 publications

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“…The Lena basin is generally located in the continuous permafrost zone where the frozen layer depth varies from 50 to 1500 m. In the delta area the permafrost extends down to 600 m, though large lakes and rivers can be underlain by taliks extending through permafrost (Grigoriev and Kunitsky, 2000). It is assumed that under the Laptev Sea the depth of the offshore layer of relict permafrost varies between 50 and 200 m. Note that estimation of the subsea permafrost distribution is mostly based on modeling, but some geophysical and borehole data show that the subsea permafrost is the most fragile component of the modern cryosphere because the mean temperature of the upper 100 m subsea sediment layer is roughly − 1 • C, compared to ∼ −12 • C onshore (see discussion in Shakhova et al, 2010a, b;Nicolsky and Shakhova, 2010;Rachold et al, 2007). A vast amount of buried OM containing an average 3-5 % C by weight is presently reentering biological cycling due to thawing and erosion of onshore and offshore permafrost.…”

Section: General Description Of the Lena River Basinmentioning

confidence: 99%

Carbon transport by the Lena River from its headwaters to the Arctic Ocean, with emphasis on fluvial input of terrestrial particulate organic carbon vs. carbon transport by coastal erosion

et al. 2011

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Abstract. The Lena River integrates biogeochemical signals from its vast drainage basin, and the integrated signal reaches far out over the Arctic Ocean. Transformation of riverine organic carbon (OC) into mineral carbon, and mineral carbon into the organic form in the Lena River watershed, can be considered to be quasi-steady-state processes. An increase in Lena discharge exerts opposite effects on total organic (TOC) and total inorganic (TCO 2 ) carbon: TOC concentration increases, while TCO 2 concentration decreases. Significant inter-annual variability in mean values of TCO 2 , TOC, and their sum (total carbon, TC) has been found. This variability is determined by changes in land hydrology which cause differences in the Lena River discharge. There is a negative correlation in the Lena River between TC in September and its mean discharge in August; a time shift of about one month is required for water to travel from Yakutsk to the Laptev Sea. Total carbon entering the sea with the Lena discharge is estimated to be almost 10 Tg C yr −1 . The annual Lena River discharge of particulate organic carbon (POC) can be as high as 0.38 Tg (moderate to high estimate). If we instead accept Lisytsin's (1994) statement that 85-95 % of total particulate matter (PM) (and POC) precipitates on the marginal "filter", then only about 0.03-0.04 Tg of Lena River POC reaches the Laptev Sea. The Lena's POC export would then be two orders of magnitude less than the annual input of eroded terrestrial carbon onto the shelf of the Laptev and East SiberianCorrespondence to: I. P. Semiletov (igorsm@iarc.uaf.edu) seas, which is estimated to be about 4 Tg. Observations support the hypothesis of a dominant role for coastal erosion (Semiletov, 1999a, b) in East Siberian Arctic Shelf (ESAS) sedimentation and the dynamics of the carbon/carbonate system. The Lena River is characterized by relatively high concentrations of the primary greenhouse gases, dissolved carbon dioxide (CO 2 ) and methane (CH 4 ). During all seasons the river is supersaturated in CO 2 compared to the atmosphere, by up to 1.5-2 fold in summer, and 4-5 fold in winter. This results in a significant CO 2 supersaturation in the adjacent coastal sea. Localized areas of dissolved CH 4 along the Lena River and in the Lena delta channels may reach 100 nM, but the CH 4 concentration decreases to 5-20 nM towards the sea, which suggests that riverborne export of CH 4 plays but a minor role in determining the ESAS CH 4 budget in coastal waters. Instead, the seabed appears to be the source that provides most of the CH 4 to the Arctic Ocean.

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Section: General Description Of the Lena River Basinmentioning

confidence: 99%

Carbon transport by the Lena River from its headwaters to the Arctic Ocean, with emphasis on fluvial input of terrestrial particulate organic carbon vs. carbon transport by coastal erosion

et al. 2011

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“…8c). Observing submarine permafrost depends on direct observation by drilling, sampling and temperature measurements (Fartyshev, 1993;Rachold et al, 2007) coupled with indirect observations using geophysical methods sensitive to property changes between frozen and unfrozen sediment. Since the coastal zone is highly dynamic, especially during spring melt and autumn freeze-up, the logistics of measurements and continuous monitoring are difficult, requiring innovative new instrumentation and platforms for use in shallow water.…”

Section: Submarine Permafrost Degradationmentioning

confidence: 99%

Coastal dynamics and submarine permafrost in shallow water of the central Laptev Sea, East Siberia

et al. 2016

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Abstract. Coastal erosion and flooding transform terrestrial landscapes into marine environments. In the Arctic, these processes inundate terrestrial permafrost with seawater and create submarine permafrost. Permafrost begins to warm under marine conditions, which can destabilize the sea floor and may release greenhouse gases. We report on the transition of terrestrial to submarine permafrost at a site where the timing of inundation can be inferred from the rate of coastline retreat. On Muostakh Island in the central Laptev Sea, East Siberia, changes in annual coastline position have been measured for decades and vary highly spatially. We hypothesize that these rates are inversely related to the inclination of the upper surface of submarine ice-bonded permafrost (IBP) based on the consequent duration of inundation with increasing distance from the shoreline. We compared rapidly eroding and stable coastal sections of Muostakh Island and find permafrost-table inclinations, determined using direct current resistivity, of 1 and 5 %, respectively. Determinations of submarine IBP depth from a drilling transect in the early 1980s were compared to resistivity profiles from 2011. Based on borehole observations, the thickness of unfrozen sediment overlying the IBP increased from 0 to 14 m below sea level with increasing distance from the shoreline. The geoelectrical profiles showed thickening of the unfrozen sediment overlying ice-bonded permafrost over the 28 years since drilling took place. We use geoelectrical estimates of IBP depth to estimate permafrost degradation rates since inundation. Degradation rates decreased from over 0.4 m a −1 following inundation to around 0.1 m a −1 at the latest after 60 to 110 years and remained constant at this level as the duration of inundation increased to 250 years. We suggest that long-term rates are lower than these values, as the depth to the IBP increases and thermal and porewater solute concentration gradients over depth decrease. For the study region, recent increases in coastal erosion rate and changes in benthic temperature and salinity regimes are expected to affect the depth to submarine permafrost, leading to coastal regions with shallower IBP.

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“…In addition, the extensive shallow-water areas of the Arctic continental shelf are underlain by permafrost, which was formed under terrestrial conditions and subsequently submerged by post-glacial rises in sea level. Methane trapped within this permafrost, as well as below its base (Rachold et al, 2007), can serve as yet another source of this greenhouse gas.…”

Section: Introductionmentioning

confidence: 99%

Methane distribution and oxidation around the Lena Delta in summer 2013

et al. 2017

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Abstract. The Lena River is one of the largest Russian rivers draining into the Laptev Sea. The predicted increases in global temperatures are expected to cause the permafrost areas surrounding the Lena Delta to melt at increasing rates. This melting will result in high amounts of methane reaching the waters of the Lena and the adjacent Laptev Sea. The only biological sink that can lower methane concentrations within this system is methane oxidation by methanotrophic bacteria. However, the polar estuary of the Lena River, due to its strong fluctuations in salinity and temperature, is a challenging environment for bacteria. We determined the activity and abundance of aerobic methanotrophic bacteria by a tracer method and by the quantitative polymerase chain reaction. We described the methanotrophic population with a molecular fingerprinting method (monooxygenase intergenic spacer analysis), as well as the methane distribution (via a headspace method) and other abiotic parameters, in the Lena Delta in September 2013.The median methane concentrations were 22 nmol L −1 for riverine water (salinity (S) < 5), 19 nmol L −1 for mixed water (5 < S < 20) and 28 nmol L −1 for polar water (S > 20). The Lena River was not the source of methane in surface water, and the methane concentrations of the bottom water were mainly influenced by the methane concentration in surface sediments. However, the bacterial populations of the riverine and polar waters showed similar methane oxidation rates (0.419 and 0.400 nmol L −1 d −1 ), despite a higher relative abundance of methanotrophs and a higher estimated diversity in the riverine water than in the polar water. The methane turnover times ranged from 167 days in mixed water and 91 days in riverine water to only 36 days in polar water. The environmental parameters influencing the methane oxidation rate and the methanotrophic population also differed between the water masses. We postulate the presence of a riverine methanotrophic population that is limited by sub-optimal temperatures and substrate concentrations and a polar methanotrophic population that is well adapted to the cold and methane-poor polar environment but limited by a lack of nitrogen. The diffusive methane flux into the atmosphere ranged from 4 to 163 µmol m 2 d −1 (median 24). The diffusive methane flux accounted for a loss of 8 % of the total methane inventory of the investigated area, whereas the methanotrophic bacteria consumed only 1 % of this methane inventory. Our results underscore the importance of measuring the methane oxidation activities in polar estuaries, and they indicate a population-level differentiation between riverine and polar water methanotrophs.

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Nearshore arctic subsea permafrost in transition

Cited by 86 publications

References 8 publications

Carbon transport by the Lena River from its headwaters to the Arctic Ocean, with emphasis on fluvial input of terrestrial particulate organic carbon vs. carbon transport by coastal erosion

Carbon transport by the Lena River from its headwaters to the Arctic Ocean, with emphasis on fluvial input of terrestrial particulate organic carbon vs. carbon transport by coastal erosion

Coastal dynamics and submarine permafrost in shallow water of the central Laptev Sea, East Siberia

Methane distribution and oxidation around the Lena Delta in summer 2013

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