scholarly journals Absence of ice-bonded permafrost beneath an Arctic lagoon revealed by electrical geophysics

2020 ◽  
Vol 6 (43) ◽  
pp. eabb5083
Author(s):  
Micaela N. Pedrazas ◽  
M. Bayani Cardenas ◽  
Cansu Demir ◽  
Jeffery A. Watson ◽  
Craig T. Connolly ◽  
...  
Keyword(s):  
The Arctic ◽  
Biogeochemical Processes ◽  
Climate Feedbacks ◽  
Potential Source ◽  
Permafrost Table ◽  
Coastal Shelf ◽  
Near Shore ◽  
Ice Wedge ◽  
Physical Degradation ◽  
Subsea Permafrost

Relict permafrost is ubiquitous throughout the Arctic coastal shelf, but little is known about it near shore. The presence and thawing of subsea permafrost are vital information because permafrost stores an atmosphere’s worth of carbon and protects against coastal erosion. Through electrical resistivity imaging across a lagoon on the Alaska Beaufort Sea coast in summer, we found that the subsurface is not ice-bonded down to ~20 m continually from within the lagoon, across the beach, and underneath an ice-wedge polygon on the tundra. This contrasts with the broadly held idea of a gently sloping ice-bonded permafrost table extending from land to offshore. The extensive unfrozen zone is a marine talik connected to on-land cryopeg. This zone is a potential source and conduit for water and dissolved organic matter, is vulnerable to physical degradation, and is liable to changes in biogeochemical processes that affect carbon cycling and climate feedbacks.

scholarly journals The East Siberian Arctic Shelf: towards further assessment of permafrost-related methane fluxes and role of sea ice

2015 ◽  
Vol 373 (2052) ◽  
pp. 20140451 ◽  
Author(s):  
Natalia Shakhova ◽  
Igor Semiletov ◽  
Valentin Sergienko ◽  
Leopold Lobkovsky ◽  
Vladimir Yusupov ◽  
...  
Keyword(s):  
Arctic Shelf ◽  
The Arctic ◽  
Permafrost Degradation ◽  
Run Off ◽  
Heating Effects ◽  
Siberian Arctic ◽  
Methane Fluxes ◽  
Near Shore ◽  
Permafrost Thawing ◽  
Subsea Permafrost

Sustained release of methane (CH 4 ) to the atmosphere from thawing Arctic permafrost may be a positive and significant feedback to climate warming. Atmospheric venting of CH 4 from the East Siberian Arctic Shelf (ESAS) was recently reported to be on par with flux from the Arctic tundra; however, the future scale of these releases remains unclear. Here, based on results of our latest observations, we show that CH 4 emissions from this shelf are likely to be determined by the state of subsea permafrost degradation. We observed CH 4 emissions from two previously understudied areas of the ESAS: the outer shelf, where subsea permafrost is predicted to be discontinuous or mostly degraded due to long submergence by seawater, and the near shore area, where deep/open taliks presumably form due to combined heating effects of seawater, river run-off, geothermal flux and pre-existing thermokarst. CH 4 emissions from these areas emerge from largely thawed sediments via strong flare-like ebullition, producing fluxes that are orders of magnitude greater than fluxes observed in background areas underlain by largely frozen sediments. We suggest that progression of subsea permafrost thawing and decrease in ice extent could result in a significant increase in CH 4 emissions from the ESAS.

scholarly journals Distribution and Driving Mechanism of N2O in Sea Ice and Its Underlying Seawater during Arctic Melt Season

Water ◽  
2022 ◽  
Vol 14 (2) ◽  
pp. 145
Author(s):  
Jian Liu ◽  
Liyang Zhan ◽  
Qingkai Wang ◽  
Man Wu ◽  
Wangwang Ye ◽  
...  
Keyword(s):  
Sea Ice ◽  
Arctic Ocean ◽  
Ice Core ◽  
The Arctic ◽  
First Year ◽  
Driving Mechanism ◽  
Biogeochemical Processes ◽  
Ice Melting ◽  
Detailed Mechanism ◽  
The Arctic Ocean

Nitrous oxide (N2O) is the third most important greenhouse gas in the atmosphere, and the ocean is an important source of N2O. As the Arctic Ocean is strongly affected by global warming, rapid ice melting can have a significant impact on the N2O pattern in the Arctic environment. To better understand this impact, N2O concentration in ice core and underlying seawater (USW) was measured during the seventh Chinese National Arctic Research Expedition (CHINARE2016). The results showed that the average N2O concentration in first-year ice (FYI) was 4.5 ± 1.0 nmol kg−1, and that in multi-year ice (MYI) was 4.8 ± 1.9 nmol kg−1. Under the influence of exchange among atmosphere-sea ice-seawater systems, brine dynamics and possible N2O generation processes at the bottom of sea ice, the FYI showed higher N2O concentrations at the bottom and surface, while lower N2O concentrations were seen inside sea ice. Due to the melting of sea ice and biogeochemical processes, USW presented as the sink of N2O, and the saturation varied from 47.2% to 102.2%. However, the observed N2O concentrations in USW were higher than that of T-N2OUSW due to the sea–air exchange, diffusion process, possible N2O generation mechanism, and the influence of precipitation, and a more detailed mechanism is needed to understand this process in the Arctic Ocean.

scholarly journals INFLUENCE OF THE PALEOCLIMATIC RECONSTRUCTIONS UNCERTAINTY ON THE SUBMARINE PERMAFROST DYNAMICS

2019 ◽  
Vol 4 (1) ◽  
pp. 99-105
Author(s):  
Valentina Malakhova ◽  
Alexey Eliseev
Keyword(s):  
Time Series ◽  
Sea Level ◽  
Air Temperature ◽  
Climate Changes ◽  
Arctic Shelf ◽  
The Arctic ◽  
Time Intervals ◽  
Ocean Level ◽  
Subsea Permafrost ◽  
Uncertainty Coefficient

The estimates of the subsea permafrost sensitivity to the uncertainty of paleoclimatic reconstructions of air temperature and ocean level have been obtained. This was done by using the model for thermophysical processes in the subsea sediments and the scenario for climate changes at the Arctic shelf for the last 400 kyr. This model was forced by four time series of temperature at the sediment top, by using different combinations of air temperature and sea level. The uncertainty coefficient of the response of the permafrost base depth is less than 0,3, with the exception of isolated time intervals and / or the deepest areas of the shelf.

scholarly journals Microtopographic control on the ground thermal regime in ice wedge polygons

2018 ◽  
Vol 12 (6) ◽  
pp. 1957-1968 ◽  
Author(s):  
Charles J. Abolt ◽  
Michael H. Young ◽  
Adam L. Atchley ◽  
Dylan R. Harp
Keyword(s):  
Thermal Conditions ◽  
Ground Temperature ◽  
The Arctic ◽  
Near Surface ◽  
Hydrologic Processes ◽  
Ground Temperatures ◽  
Air Temperatures ◽  
Winter Temperatures ◽  
Ice Wedge ◽  
Prudhoe Bay

Abstract. The goal of this research is to constrain the influence of ice wedge polygon microtopography on near-surface ground temperatures. Ice wedge polygon microtopography is prone to rapid deformation in a changing climate, and cracking in the ice wedge depends on thermal conditions at the top of the permafrost; therefore, feedbacks between microtopography and ground temperature can shed light on the potential for future ice wedge cracking in the Arctic. We first report on a year of sub-daily ground temperature observations at 5 depths and 9 locations throughout a cluster of low-centered polygons near Prudhoe Bay, Alaska, and demonstrate that the rims become the coldest zone of the polygon during winter, due to thinner snowpack. We then calibrate a polygon-scale numerical model of coupled thermal and hydrologic processes against this dataset, achieving an RMSE of less than 1.1 ∘C between observed and simulated ground temperature. Finally, we conduct a sensitivity analysis of the model by systematically manipulating the height of the rims and the depth of the troughs and tracking the effects on ice wedge temperature. The results indicate that winter temperatures in the ice wedge are sensitive to both rim height and trough depth, but more sensitive to rim height. Rims act as preferential outlets of subsurface heat; increasing rim size decreases winter temperatures in the ice wedge. Deeper troughs lead to increased snow entrapment, promoting insulation of the ice wedge. The potential for ice wedge cracking is therefore reduced if rims are destroyed or if troughs subside, due to warmer conditions in the ice wedge. These findings can help explain the origins of secondary ice wedges in modern and ancient polygons. The findings also imply that the potential for re-establishing rims in modern thermokarst-affected terrain will be limited by reduced cracking activity in the ice wedges, even if regional air temperatures stabilize.

scholarly journals The contribution of heavy metal pollution derived from highway runoff to Guanabara Bay sediments: Rio de Janeiro / Brazil

2007 ◽  
Vol 79 (4) ◽  
pp. 739-750 ◽  
Author(s):  
Edisio Pereira ◽  
José A. Baptista-Neto ◽  
Bernard J. Smith ◽  
John J. Mcallister
Keyword(s):  
Heavy Metals ◽  
Particle Size ◽  
Particle Size Analysis ◽  
Anthropogenic Sources ◽  
Size Analysis ◽  
Guanabara Bay ◽  
Sedimentary Deposits ◽  
Potential Source ◽  
Run Off ◽  
Near Shore

In this study, geochemical and particle size analyses of thirty-four street sediment samples collected from an urban environment around Guanabara Bay, shows highway run-off to be a potential source of heavy metals for the pollution of near-shore sedimentary deposits. Concentrations of Fe, Mn, Zn, Cu, Pb, Cr and Ni were found to be higher in these sediments when compared to concentrations found in samples from the natural environment, where an Enrichment Factor (EF) index was used to distinguish between natural and anthropogenic sources. Particle size analysis shows these sediments to be predominantly composed of sand and no distribution pattern was observed between the sand, silt and clay fractions. High levels of organic matter and heavy metals would indicate that these street run-off materials are a potential source of pollution for the near-shore sediments of Guanabara Bay.

From concentrations requirements to emission committments: prospects and challenges for the Global Stocktake

2020 ◽  
Author(s):  
Kevin Bowman ◽  
Junjie Liu ◽  
Anthony Bloom ◽  
Sassan Saatchi ◽  
Liang Xu ◽  
...  
Keyword(s):  
Inverse Modeling ◽  
Greenhouse Gas Emission ◽  
State Of The Art ◽  
Paris Agreement ◽  
Biogeochemical Processes ◽  
Climate Feedbacks ◽  
Gas Emission ◽  
The Relationship ◽  
Data Assimilation System ◽  
Global Stocktake

<p>The Paris Agreement was a watershed moment in providing a framework to address the mitigation of climate change.  The Global Stocktake is a bi-decadal process to assess progress in greenhouse gas emission reductions in light of climate feedbacks and response.   However, the relationship between emission commitments and concentration requirements is confounded by complex natural biogeochemical processes potentially modulated by climate feedbacks.  We investigate the prospects and challenges of mediating between emissions and concentrations through the NASA Carbon Monitoring System Flux (CMS-Flux) project, which is an inverse modeling and data assimilation system that ingests a suite of observations including the Orbital Carbon Observatory (OCO-2) and state-of-the-art biomass change maps across the carbon cycle to attribute atmospheric carbon variability to anthropogenic and biogeochemical processes. We decompose the spatial drivers of CO2 accumulation since the beginning of the decade into component fluxes and emissions in the context of the historic 2010 and 2015 El Ninos, which had a tremendous influence on the CO2 growth rate.  These processes reshuffle the primary contributors of CO2 growth at Stocktake time scales that must be reconciled with Nationally Determine Contributions and concentration targets.  Based on these findings, we investigate how systems such as CMS-Flux can harness the carbon constellation to fill a vital gap between policy needs and scientific assessment needed for the Stocktake.</p>

Comparative zinc and lead toxicity tests with Arctic marine invertebrates and implications for toxicant discharges

Polar Record ◽  
1993 ◽  
Vol 29 (168) ◽  
pp. 45-54 ◽  
Author(s):  
Peter M. Chapman ◽  
Cathy McPherson
Keyword(s):  
Literature Review ◽  
Marine Invertebrates ◽  
Lead Toxicity ◽  
Temperature Tolerance ◽  
The Arctic ◽  
Toxicity Tests ◽  
Test Conditions ◽  
Near Shore ◽  
Cornwallis Island ◽  
Point Source Discharges

ABSTRACTEpontic and benthic amphipods (Onisimus litoralis, Onisimus juveniles, Gammarus setosus, Anonyx nugax, and A. makarovi) and a pelagic mysid (Mysis oculatus) were collected under ice at Little Cornwallis Island, Northwest Territories, Canada. They were exposed, on site, to dissolved zinc and lead to determine lethal concentrations (LC50s). Incidental information was obtained on salinity and temperature tolerance. Subsequent testing of a temperate amphipod and oyster larvae exposed to the two metals provided comparative data to augment a literature review. The Arctic invertebrates were surprisingly insensitive under all test conditions. The implications for Arctic developments, particularly those involving near-shore, point-source discharges, are discussed and recommendations are made for effectively expanding a presently depauperate Arctic marine toxicity database.

scholarly journals The origin of methane in the East Siberian Arctic Shelf unraveled with triple isotope analysis

2016 ◽  
Author(s):  
Célia J. Sapart ◽  
Natalia Shakhova ◽  
Igor Semiletov ◽  
Joachim Jansen ◽  
Sönke Szidat ◽  
...  
Keyword(s):  
Water Column ◽  
Large Scale ◽  
Age Determination ◽  
Arctic Shelf ◽  
Climate Feedback ◽  
The Arctic ◽  
Small Contribution ◽  
Isotope Data ◽  
Siberian Arctic ◽  
Subsea Permafrost

Abstract. Methane (CH4) is a strong greenhouse gas emitted by human activity and natural processes that are highly sensitive to climate change. The Arctic Ocean, especially the East Siberian Arctic Shelf (ESAS) overlays large areas of subsea permafrost that is degrading. The release of large amount of CH4 originally stored or formed there could create a strong positive climate feedback. Large scale CH4 super-saturation has been observed in the ESAS waters, pointing to leakages of CH4 through the sea floor and possibly to the atmosphere, but the origin of this gas is still debated. Here, we present CH4 concentration and triple isotope data analyzed on gas extracted from sediment and water sampled over the shallow ESAS from 2007 to 2013. We find high concentrations (up to 500 μM) of CH4 in the pore water of the partially thawed subsea permafrost of this region. For all sediment cores, both hydrogen and carbon CH4 isotope data reveal the predominant presence of CH4 that is not of thermogenic/natural gas origin as it has long been thought, but resultant from microbial CH4 formation using as primary substrate glacial water and old organic matter preserved in the subsea permafrost or below. Radiocarbon data demonstrate that the CH4 present in the ESAS sediment is of Pleistocene age or older, but a small contribution of highly 14C-enriched CH4, from unknown origin, prohibits precise age determination for one sediment core and in the water column. Our data suggest that at locations where bubble plumes have been observed, CH4 can escape anaerobic oxidation in the surface sediment. CH4 will then rapidly migrate through the very shallow water column of the ESAS to escape to the atmosphere generating a positive radiative feedback.

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