Niek Jesse Speetjens - Profile on Academia.edu (original) (raw)

Papers by Niek Jesse Speetjens

Microbial growth in a warming Arctic: Exploring controls and temperature responses in permafrost soils

Distribution Patterns of Pahs and Pcbs in Ice-Wedge Polygon Soils of a Canadian Coastal Tundra Catchment

Degradation of Ice-Wedge Polygons Leads to Increased Fluxes of Water and Doc

The Arctic is rapidly changing. Outside the Arctic, large-sample catchment databases have transfo... more The Arctic is rapidly changing. Outside the Arctic, large-sample catchment databases have transformed catchment science from focusing on local case studies to more systematic studies of watershed functioning. Here we present an integrated pan-ARctic CAtchments summary DatabasE (ARCADE) of >40,000 catchments that drain into the Arctic Ocean and range in size from 1 km 2 to 3.1 x 10 6 km 2 (Speetjens et al., 2022). These watersheds, delineated at a 90-m resolution, are provided with 103 geospatial, environmental, climatic, and physiographic catchment properties. ARCADE is the first aggregated database of pan-Arctic river catchments that also includes numerous small watersheds at a high resolution. These small catchments are experiencing the greatest climatic warming while also storing large quantities of soil carbon in landscapes that are especially prone to degradation of permafrost (i.e., ice-wedge polygon terrain) and associated hydrological regime shifts. ARCADE is a key step toward monitoring the pan-Arctic across scales and is publicly available: .

Frontiers in Earth Science, Mar 24, 2021

Climate warming is accelerating erosion along permafrost-dominated Arctic coasts. This results in... more Climate warming is accelerating erosion along permafrost-dominated Arctic coasts. This results in the additional supply of organic matter (OM) and nutrients into the coastal zone. In this study we investigate the impact of coastal erosion on the marine microbial community composition and growth rates in the coastal Beaufort Sea. Dissolved organic matter (DOM) derived from three representative glacial deposit types (fluvial, lacustrine, and moraine) along the Yukon coastal plain, Canada, were used as substrate to cultivate marine bacteria using a chemostat setup. Our results show that DOM composition (inferred from UV-Visible spectroscopy) and biodegradability (inferred from DOC concentration, bacterial production and respiration) significantly differ between the three glacial deposit types. DOM derived from fluvial and moraine types show clear terrestrial characteristics with low aromaticity (S r : 0.63 ± 0.02 and SUVA 254 : 1.65 ± 0.06 L mg C -1 m -1 & S r : 0.68 ± 0.01 and SUVA 254 : 1.17 ± 0.06 L mg C -1 m -1 , respectively) compared to the lacustrine soil type (S r : 0.71 ± 0.02 and SUVA 254 : 2.15 ± 0.05 L mg C -1 m -1 ). The difference in composition of DOM leads to the development of three different microbial communities. Whereas Alphaproteobacteria dominate in fluvial and lacustrine deposit types (67 and 87% relative abundance, respectively), Gammaproteobacteria is the most abundant class for moraine deposit type (88% relative abundance). Bacterial growth efficiency (BGE) is 66% for DOM from moraine deposit type, while 13 and 28% for DOM from fluvial and lacustrine deposit types, respectively. The three microbial communities therefore differ strongly in their net effect on DOM utilization depending on the eroded landscape type. The high BGE value for moraine-derived DOM is probably caused by a larger proportion of labile colorless DOM. These results indicate that the substrate controls marine microbial community composition and activities in coastal waters. This suggests that

Supplementary material to "The Pan-Arctic Catchment Database (ARCADE)

Landscape-related ground ice variability on the Yukon coastal plain inferred from computed tomography and potential implications on lateral permafrost carbon release

Warming in the Arctic causes strong environmental changes with permafrost degradation being among... more Warming in the Arctic causes strong environmental changes with permafrost degradation being among the most striking effects. Active layer deepening and permafrost erosion can result in the mobilization and lateral transport of organic carbon (OC), which potentially alters carbon cycles in the Arctic substantially. Although the understanding of ground ice contents and permafrost OC release is improving, still little is known of permafrost OC release rates, lateral transport pathways and its driving mechanisms on a landscape scale. In this study we investigate ground ice characteristics and OC composition of the most dominant landscape units of the Yukon coastal plain. In total, 12 permafrost cores were taken from moraine, lacustrine, fluvial and glaciofluvial deposits with a SIPRE corer. Ground ice and sediment contents were analysed using computed tomography and k-means classification. Active layer and upper permafrost were subsampled to analyse OC contents and isotopes of bulk material and a leaching-incubation experiment was conducted with active layer and permafrost sediments to assess potential dissolved OC export and degradation rates. Preliminary results show that ground ice contents vary significantly between landscape units. Ground ice contents in permafrost average 72.4 vol.-% with highest contents in moraines (78.3 vol.-%) and lowest contents in fluvial deposits (53.2 vol.-%). We expect highest dissolved OC leaching and loss rates from permafrost in contrast to active layer and from fluvial and lacustrine deposits, as they simply contain more OC. Yet, lateral OC transport is more likely for landscapes with a topographic gradient such as ground ice-rich moraines. We conclude that due to the high ground ice contents on the Yukon coastal plain, substantial changes of the permafrost landscape will occur under current warming trends. This will include subsidence, abrupt erosion, changes in hydrology and OC degradation processes, which will differ between landscape units

High resolution mapping shows differences in soil carbon and nitrogen stocks in areas of varying landscape history in Canadian lowland tundra

Geoderma

Degradation of Ice-Wedge Polygons Leads to Increased Fluxes of Water and Doc

Permafrost soil organic matter (de)composition in times of global warming

The Arctic warms four times faster than the global average, resulting in widespread permafrost th... more The Arctic warms four times faster than the global average, resulting in widespread permafrost thaw. Organic matter that was stored in permanently frozen soil for up to millennia now becomes available to microbial decomposition. Warming might also alter microbial community composition and physiology and thus change the decomposition potential of soils. Our current knowledge about permafrost soil organic matter (SOM) composition and decomposition is limited, particularly in regard to the heterogeneity of permafrost landscapes, thus hampering our ability to predict possible permafrost soil feedbacks to climate change. The objective of this study was to characterize SOM and microbial community composition of the active layer and the upper permanently frozen soil from permafrost-affected polygonal lowland tundra.We collected more than 80 soil samples from four different soil layers (organic, mineral, cryoturbated, permanently frozen) from three developmental stages of ice-wedge polygons...

The Arctic is rapidly changing. Outside the Arctic, large-sample catchment databases have transfo... more The Arctic is rapidly changing. Outside the Arctic, large-sample catchment databases have transformed catchment science from focusing on local case studies to more systematic studies of watershed functioning. Here we present an integrated pan-ARctic CAtchments summary DatabasE (ARCADE) of > 40 000 catchments that drain into the Arctic Ocean and range in size from 1 to 3.1 × 10 6 km 2 . These watersheds, delineated at a 90 m resolution, are provided with 103 geospatial, environmental, climatic, and physiographic catchment properties. ARCADE is the first aggregated database of pan-Arctic river catchments that also includes numerous small watersheds at a high resolution. These small catchments are experiencing the greatest climatic warming while also storing large quantities of soil carbon in landscapes that are especially prone to degradation of permafrost (i.e., ice wedge polygon terrain) and associated hydrological regime shifts. ARCADE is a key step toward monitoring the pan-Arctic across scales and is publicly available:

Supplementary material to "The Pan-Arctic Catchment Database (ARCADE)

Subjecting permafrost microorganisms to short-term warming

EPIC3AGU Fall Meeting, Online, 2020-12-01-2020-12-17, Dec 9, 2020

Arctic environments are a prime example for ecosystems facing manifold vast and rapid changes in ... more Arctic environments are a prime example for ecosystems facing manifold vast and rapid changes in the wake of climate change, outpacing the global rate of temperature increases. The risk of thawing permafrost soils raises concerns about a positive feedback process being mediated by increased microbial activity that does not acclimate over time freeing greenhouse gases. However, the mechanistic understanding of the controls on microbial carbon cycling upon warming is still vague. In the following study we investigate microbial growth and soil organic matter decomposition in different soil horizons of the active layer and upper permafrost, covering different polygonal landscape units in two small catchments at the Canadian Yukon Coast. 81 soil samples were subjected to a short-term warming experiment under controlled temperature (4 °C and 14 °C) and moisture conditions. Microbial respiration was measured weekly whereas microbial biomass and physiological parameters were determined at the end of the incubation period and used to assess temperature responses. Microbial growth was estimated by measuring the incorporation of 18O from labelled water into DNA and used to calculate CUE. Microbial biomass was determined via chloroform fumigation. Potential activities of extracellular enzymes were measured using microplate fluorometric assays. Microbial biomass carbon was not affected by warming except for permafrost layers where it either increased or decreased depending on the examined catchment. Microbial respiration strongly responded to warming following the pattern organic layers > upper frozen permafrost > cryoturbated material > mineral layers. Mass specific growth and extracellular enzymatic activities were also enhanced with short-term warming in all soil horizons. This led to rather variable CUE being unaffected in mineral and cryoturbated layers whereas we could observe a minor reduction in organic and permafrost layers where the response of respiration outpaced the one of microbial growth. Our results are not indicative for any physiological acclimatization of permafrost microbes when subjected to 8 weeks of experimental warming and hence support the current concern for potential prolonged carbon losses from warming tundra soils. This work is part of the EU H2020 project “Nunataryuk”

Recent decades have shown phases of very rapid warming in the Canadian Arctic. This raises a conc... more Recent decades have shown phases of very rapid warming in the Canadian Arctic. This raises a concern, also in reference to potential changes in permafrost active layer deepening, enhancing the fact that seawater, snow and soils are becoming important secondary sources remobilizing persistent organic pollutants (POPs). This work investigates the potential influence of permafrost on POPs distribution in the soils of two small coastal catchments at the Canadian Beaufort coast. One catchment is located south of Herschel Island on the mainland and was covered by the Laurentide ice sheet during the last glacial maximum (LGM), the second catchment is located westerly at Komakuk Beach and was ice-free during the LGM.

Frontiers in Earth Science, 2021

Climate warming is accelerating erosion along permafrost-dominated Arctic coasts. This results in... more Climate warming is accelerating erosion along permafrost-dominated Arctic coasts. This results in the additional supply of organic matter (OM) and nutrients into the coastal zone. In this study we investigate the impact of coastal erosion on the marine microbial community composition and growth rates in the coastal Beaufort Sea. Dissolved organic matter (DOM) derived from three representative glacial deposit types (fluvial, lacustrine, and moraine) along the Yukon coastal plain, Canada, were used as substrate to cultivate marine bacteria using a chemostat setup. Our results show that DOM composition (inferred from UV-Visible spectroscopy) and biodegradability (inferred from DOC concentration, bacterial production and respiration) significantly differ between the three glacial deposit types. DOM derived from fluvial and moraine types show clear terrestrial characteristics with low aromaticity (Sr: 0.63 ± 0.02 and SUVA254: 1.65 ± 0.06 L mg C−1 m−1 & Sr: 0.68 ± 0.01 and SUVA254: 1.17 ±...

Herschel Island -about 70 km east of the Yukon-Alaska border -occurs as the only major elevation ... more Herschel Island -about 70 km east of the Yukon-Alaska border -occurs as the only major elevation on the Yukon Coastal Plain facing the Southern Beaufort Sea and represents the likely westernmost edge of Wisconsin Glaciation in northwestern Canada. Being accumulated as a terminal moraine during the Early to Middle Wisconsin the island has been intensively affected by periglacial processes for a period of time that probably dates back to 50 ka BP but is still of great uncertainty. Multi-proxy analyses on sediments and stable isotope determinations (δD, δ 18 O) on ground ice samples have been performed to reconstruct the island's paleoenvironmental evolution and paleoclimatic variations through time. Distinct stages in landscape succession are addressed with regard to permafrost/ground ice aggradation and its degradation through time as well as to link these processes to distinct periods of climate change. Sediments generally consist of clayey diamicton and silty loams with a quite uniform origin as near-shore marine beds that have been glacially redeposited and set as a terminal moraine that makes up the body of the modern island. Stratigraphic appraisals are difficult due to the deformed nature of Herschel Island sediments by glacial ice thrust. However, even these deformations give evidence that deeper strata remained unaffected by postglacial thaw and reworking, thus representing original Pleistocene deposits. Climate amelioration during the early Holocene Thermal Maximum (HTM) between 11 and 8 ka BP led to increased thermokarst processes and an enhanced accumulation of peat. Extensive active layer thickening is recorded by a widespread thaw unconformity along the Yukon coast at depths between 1.5 to 2.5 m below surface. Increased bioproductivity, Holocene cryoturbation and recent mass wasting have produced an upper diamicton with deviant cryostructures and significantly more organics than below the discontinuity. Different types of ground ice have been recovered that range widely regarding their isotopic composition, thus reflecting different types of water and strongly variable climatic conditions during their genesis. Holocene ice wedges vary in δ 18 O between -24 and -20 ‰ (VSMOW). A fossil wedge truncated at 1.5 m below surface, revealed low δ 18 O values between -30 and -27 ‰ and is therefore supposed to have formed during an icefree period of more severe climatic conditions prior to HTM. Texture ice within sediment sequences might be an applicable tool for paleoclimate reconstructions as isotope values show clear dependency with depth and enable the recognition of afore-identified boundaries in paleoenvironmental development like the prominent thaw unconformity. Buried glacier ice and ice of unknown origin with low isotope values (< -30 ‰) seem to contribute to ground ice spectrum on Herschel Island, too. Up to the present day, the study area is affected by extensive coastal erosion and ongoing melt of ground ice, that both leads to a strong geomorphological alteration of the landscape. Herschel Island -etwa 70 km östlich der Grenze zwischen Alaska und Kanada -tritt als einzige wesentliche Erhebung auf der Yukon Coastal Plain an der südlichen Beaufortsee in Erscheinung und befindet sich am westlichen Rand der maximalen Wisconsin-Vereisung im Nordwesten Kanadas. Die Insel wurde während des Früh-bis Mittel-Wisconsin als Endmoräne geschüttet und über einen langen Zeitraum von periglazialen Prozessen stark beeinflusst, der möglicherweise bis 50 ka BP zurückreicht aber noch immer mit großer Unsicherheit behaftet ist. Multidisziplinäre Analysen an Sedimenten und die Bestimmung stabiler Isotope (δD, δ 18 O) am Grundeis wurden vor dem Hintergrund durchgeführt, die Paläoumweltentwick-lung der Insel und Paläoklima-Variationen entlang der Yukon Coastal Plain über die Zeit zu rekonstruieren. Unterschiedliche Stadien der Landschaftsentwicklung werden mit Blick auf Bildungs-und Degradationsprozesse von Permafrost und Grundeis untersucht und wie diese Prozesse mit bestimmten Klimaveränderungen in Verbindung stehen. Die untersuchten Sedimente bestehen im allgemeinen aus tonigen Diamikten und siltigen Lehmen mit relativ einheitlichem Ursprung als küstennahe Flachmeerablagerungen, die glazial umgelagert wurden und als Stauchendmoräne den Korpus der Insel bilden. Aufgrund der deformierten Struktur vorliegender Sedimente infolge des Eisschubs ist eine stratigraphische Einordnung schwierig. Jedoch zeugen eben diese Deformationen davon, dass tiefere Schichten von postglazialen Tau-und Umlagerungsprozessen unbeeinflusst blieben und somit die ursprünglichen pleistozänen Ablagerungen repräsentieren. Die Klimaerwärmung während des (früh)holozänen Klimaoptimums zwischen 11 und 8 ka BP führte zu verstärkten Thermokarstprozessen und einer gesteigerten Torfakkumulation. Eine flächendeckende Mächtigkeitszunahme der Auftauzone bis auf 1,5-2,5 m unter Flur ist durch eine weitverbreitete Auftaudiskordanz entlang der Yukon Coastal Plain dokumentiert. Erhöhte Bioproduktivität, holozäne sowie rezente Kryoturbationsprozesse und Massenverlagerungen haben eine oberen Diamikt geschaffen, der sich durch signifikant höhere Organikgehalte und verschiedenartige Kryostrukturen auszeichnet als sie unterhalb der Diskordanz auftreten. Verschiedene Typen Grundeis wurden vorgefunden, die in ihrer isotopischen Zusammensetzung stark variieren und somit unterschiedliche Wassertypen und stark schwankende Klimabedingungen während der Eisgenese widerspiegeln. Holozäne Eiskeile schwanken im δ 18 O-Wert zwischen -20 und -24 ‰ (VSMOW). Ein fossiler Eiskeil, der bei 1,5 m unter Flur gekappt wurde, weist δ 18 O-Werte von -30 bis -27 ‰ auf und scheint daher während einer eisfreien Periode strengerer Klimabedingungen vor dem holozänen Klimaoptimum gebildet worden zu sein. Das Textureis in Sedimentsequenzen stellt möglicherweise ein geeignetes Instrument in der Paläoklimarekonstruktion dar. Denn zum einen zeigen die Isotopenwerte eine klaren Zusammenhang mit der Tiefe an und zum anderen lassen sich die zuvor identifizierten Grenzen in der Paläoumweltentwicklung, wie IX jene markante Auftau-diskordanz, nachvollziehen. Begrabenes Gletschereis und Grundeis unbekannter Herkunft mit niedrigen Isotopenwerten (< -30 ‰) scheinen ebenfalls zum Grundeisspektrum von Herschel Island beizutragen, was noch bis vor wenigen Jahren als umstritten galt. Bis in die Gegenwart hinein wurde das Untersuchungsgebiet durch umfassende Küstenerosionsprozesse und anhaltendes Schmelzen von Grundeis beeinflusst. Beide Prozesse haben zu starken geomorphologischen Veränderungen der Landschaft geführt.

Microbial growth in a warming Arctic: Exploring controls and temperature responses in permafrost soils

Distribution Patterns of Pahs and Pcbs in Ice-Wedge Polygon Soils of a Canadian Coastal Tundra Catchment

Degradation of Ice-Wedge Polygons Leads to Increased Fluxes of Water and Doc

The Arctic is rapidly changing. Outside the Arctic, large-sample catchment databases have transfo... more The Arctic is rapidly changing. Outside the Arctic, large-sample catchment databases have transformed catchment science from focusing on local case studies to more systematic studies of watershed functioning. Here we present an integrated pan-ARctic CAtchments summary DatabasE (ARCADE) of >40,000 catchments that drain into the Arctic Ocean and range in size from 1 km 2 to 3.1 x 10 6 km 2 (Speetjens et al., 2022). These watersheds, delineated at a 90-m resolution, are provided with 103 geospatial, environmental, climatic, and physiographic catchment properties. ARCADE is the first aggregated database of pan-Arctic river catchments that also includes numerous small watersheds at a high resolution. These small catchments are experiencing the greatest climatic warming while also storing large quantities of soil carbon in landscapes that are especially prone to degradation of permafrost (i.e., ice-wedge polygon terrain) and associated hydrological regime shifts. ARCADE is a key step toward monitoring the pan-Arctic across scales and is publicly available: .

Frontiers in Earth Science, Mar 24, 2021

Climate warming is accelerating erosion along permafrost-dominated Arctic coasts. This results in... more Climate warming is accelerating erosion along permafrost-dominated Arctic coasts. This results in the additional supply of organic matter (OM) and nutrients into the coastal zone. In this study we investigate the impact of coastal erosion on the marine microbial community composition and growth rates in the coastal Beaufort Sea. Dissolved organic matter (DOM) derived from three representative glacial deposit types (fluvial, lacustrine, and moraine) along the Yukon coastal plain, Canada, were used as substrate to cultivate marine bacteria using a chemostat setup. Our results show that DOM composition (inferred from UV-Visible spectroscopy) and biodegradability (inferred from DOC concentration, bacterial production and respiration) significantly differ between the three glacial deposit types. DOM derived from fluvial and moraine types show clear terrestrial characteristics with low aromaticity (S r : 0.63 ± 0.02 and SUVA 254 : 1.65 ± 0.06 L mg C -1 m -1 & S r : 0.68 ± 0.01 and SUVA 254 : 1.17 ± 0.06 L mg C -1 m -1 , respectively) compared to the lacustrine soil type (S r : 0.71 ± 0.02 and SUVA 254 : 2.15 ± 0.05 L mg C -1 m -1 ). The difference in composition of DOM leads to the development of three different microbial communities. Whereas Alphaproteobacteria dominate in fluvial and lacustrine deposit types (67 and 87% relative abundance, respectively), Gammaproteobacteria is the most abundant class for moraine deposit type (88% relative abundance). Bacterial growth efficiency (BGE) is 66% for DOM from moraine deposit type, while 13 and 28% for DOM from fluvial and lacustrine deposit types, respectively. The three microbial communities therefore differ strongly in their net effect on DOM utilization depending on the eroded landscape type. The high BGE value for moraine-derived DOM is probably caused by a larger proportion of labile colorless DOM. These results indicate that the substrate controls marine microbial community composition and activities in coastal waters. This suggests that

Supplementary material to "The Pan-Arctic Catchment Database (ARCADE)

Landscape-related ground ice variability on the Yukon coastal plain inferred from computed tomography and potential implications on lateral permafrost carbon release

Warming in the Arctic causes strong environmental changes with permafrost degradation being among... more Warming in the Arctic causes strong environmental changes with permafrost degradation being among the most striking effects. Active layer deepening and permafrost erosion can result in the mobilization and lateral transport of organic carbon (OC), which potentially alters carbon cycles in the Arctic substantially. Although the understanding of ground ice contents and permafrost OC release is improving, still little is known of permafrost OC release rates, lateral transport pathways and its driving mechanisms on a landscape scale. In this study we investigate ground ice characteristics and OC composition of the most dominant landscape units of the Yukon coastal plain. In total, 12 permafrost cores were taken from moraine, lacustrine, fluvial and glaciofluvial deposits with a SIPRE corer. Ground ice and sediment contents were analysed using computed tomography and k-means classification. Active layer and upper permafrost were subsampled to analyse OC contents and isotopes of bulk material and a leaching-incubation experiment was conducted with active layer and permafrost sediments to assess potential dissolved OC export and degradation rates. Preliminary results show that ground ice contents vary significantly between landscape units. Ground ice contents in permafrost average 72.4 vol.-% with highest contents in moraines (78.3 vol.-%) and lowest contents in fluvial deposits (53.2 vol.-%). We expect highest dissolved OC leaching and loss rates from permafrost in contrast to active layer and from fluvial and lacustrine deposits, as they simply contain more OC. Yet, lateral OC transport is more likely for landscapes with a topographic gradient such as ground ice-rich moraines. We conclude that due to the high ground ice contents on the Yukon coastal plain, substantial changes of the permafrost landscape will occur under current warming trends. This will include subsidence, abrupt erosion, changes in hydrology and OC degradation processes, which will differ between landscape units

High resolution mapping shows differences in soil carbon and nitrogen stocks in areas of varying landscape history in Canadian lowland tundra

Geoderma

Degradation of Ice-Wedge Polygons Leads to Increased Fluxes of Water and Doc

Permafrost soil organic matter (de)composition in times of global warming

The Arctic warms four times faster than the global average, resulting in widespread permafrost th... more The Arctic warms four times faster than the global average, resulting in widespread permafrost thaw. Organic matter that was stored in permanently frozen soil for up to millennia now becomes available to microbial decomposition. Warming might also alter microbial community composition and physiology and thus change the decomposition potential of soils. Our current knowledge about permafrost soil organic matter (SOM) composition and decomposition is limited, particularly in regard to the heterogeneity of permafrost landscapes, thus hampering our ability to predict possible permafrost soil feedbacks to climate change. The objective of this study was to characterize SOM and microbial community composition of the active layer and the upper permanently frozen soil from permafrost-affected polygonal lowland tundra.We collected more than 80 soil samples from four different soil layers (organic, mineral, cryoturbated, permanently frozen) from three developmental stages of ice-wedge polygons...

The Arctic is rapidly changing. Outside the Arctic, large-sample catchment databases have transfo... more The Arctic is rapidly changing. Outside the Arctic, large-sample catchment databases have transformed catchment science from focusing on local case studies to more systematic studies of watershed functioning. Here we present an integrated pan-ARctic CAtchments summary DatabasE (ARCADE) of > 40 000 catchments that drain into the Arctic Ocean and range in size from 1 to 3.1 × 10 6 km 2 . These watersheds, delineated at a 90 m resolution, are provided with 103 geospatial, environmental, climatic, and physiographic catchment properties. ARCADE is the first aggregated database of pan-Arctic river catchments that also includes numerous small watersheds at a high resolution. These small catchments are experiencing the greatest climatic warming while also storing large quantities of soil carbon in landscapes that are especially prone to degradation of permafrost (i.e., ice wedge polygon terrain) and associated hydrological regime shifts. ARCADE is a key step toward monitoring the pan-Arctic across scales and is publicly available:

Supplementary material to "The Pan-Arctic Catchment Database (ARCADE)

Subjecting permafrost microorganisms to short-term warming

EPIC3AGU Fall Meeting, Online, 2020-12-01-2020-12-17, Dec 9, 2020

Arctic environments are a prime example for ecosystems facing manifold vast and rapid changes in ... more Arctic environments are a prime example for ecosystems facing manifold vast and rapid changes in the wake of climate change, outpacing the global rate of temperature increases. The risk of thawing permafrost soils raises concerns about a positive feedback process being mediated by increased microbial activity that does not acclimate over time freeing greenhouse gases. However, the mechanistic understanding of the controls on microbial carbon cycling upon warming is still vague. In the following study we investigate microbial growth and soil organic matter decomposition in different soil horizons of the active layer and upper permafrost, covering different polygonal landscape units in two small catchments at the Canadian Yukon Coast. 81 soil samples were subjected to a short-term warming experiment under controlled temperature (4 °C and 14 °C) and moisture conditions. Microbial respiration was measured weekly whereas microbial biomass and physiological parameters were determined at the end of the incubation period and used to assess temperature responses. Microbial growth was estimated by measuring the incorporation of 18O from labelled water into DNA and used to calculate CUE. Microbial biomass was determined via chloroform fumigation. Potential activities of extracellular enzymes were measured using microplate fluorometric assays. Microbial biomass carbon was not affected by warming except for permafrost layers where it either increased or decreased depending on the examined catchment. Microbial respiration strongly responded to warming following the pattern organic layers > upper frozen permafrost > cryoturbated material > mineral layers. Mass specific growth and extracellular enzymatic activities were also enhanced with short-term warming in all soil horizons. This led to rather variable CUE being unaffected in mineral and cryoturbated layers whereas we could observe a minor reduction in organic and permafrost layers where the response of respiration outpaced the one of microbial growth. Our results are not indicative for any physiological acclimatization of permafrost microbes when subjected to 8 weeks of experimental warming and hence support the current concern for potential prolonged carbon losses from warming tundra soils. This work is part of the EU H2020 project “Nunataryuk”

Recent decades have shown phases of very rapid warming in the Canadian Arctic. This raises a conc... more Recent decades have shown phases of very rapid warming in the Canadian Arctic. This raises a concern, also in reference to potential changes in permafrost active layer deepening, enhancing the fact that seawater, snow and soils are becoming important secondary sources remobilizing persistent organic pollutants (POPs). This work investigates the potential influence of permafrost on POPs distribution in the soils of two small coastal catchments at the Canadian Beaufort coast. One catchment is located south of Herschel Island on the mainland and was covered by the Laurentide ice sheet during the last glacial maximum (LGM), the second catchment is located westerly at Komakuk Beach and was ice-free during the LGM.

Frontiers in Earth Science, 2021

Climate warming is accelerating erosion along permafrost-dominated Arctic coasts. This results in... more Climate warming is accelerating erosion along permafrost-dominated Arctic coasts. This results in the additional supply of organic matter (OM) and nutrients into the coastal zone. In this study we investigate the impact of coastal erosion on the marine microbial community composition and growth rates in the coastal Beaufort Sea. Dissolved organic matter (DOM) derived from three representative glacial deposit types (fluvial, lacustrine, and moraine) along the Yukon coastal plain, Canada, were used as substrate to cultivate marine bacteria using a chemostat setup. Our results show that DOM composition (inferred from UV-Visible spectroscopy) and biodegradability (inferred from DOC concentration, bacterial production and respiration) significantly differ between the three glacial deposit types. DOM derived from fluvial and moraine types show clear terrestrial characteristics with low aromaticity (Sr: 0.63 ± 0.02 and SUVA254: 1.65 ± 0.06 L mg C−1 m−1 & Sr: 0.68 ± 0.01 and SUVA254: 1.17 ±...

Herschel Island -about 70 km east of the Yukon-Alaska border -occurs as the only major elevation ... more Herschel Island -about 70 km east of the Yukon-Alaska border -occurs as the only major elevation on the Yukon Coastal Plain facing the Southern Beaufort Sea and represents the likely westernmost edge of Wisconsin Glaciation in northwestern Canada. Being accumulated as a terminal moraine during the Early to Middle Wisconsin the island has been intensively affected by periglacial processes for a period of time that probably dates back to 50 ka BP but is still of great uncertainty. Multi-proxy analyses on sediments and stable isotope determinations (δD, δ 18 O) on ground ice samples have been performed to reconstruct the island's paleoenvironmental evolution and paleoclimatic variations through time. Distinct stages in landscape succession are addressed with regard to permafrost/ground ice aggradation and its degradation through time as well as to link these processes to distinct periods of climate change. Sediments generally consist of clayey diamicton and silty loams with a quite uniform origin as near-shore marine beds that have been glacially redeposited and set as a terminal moraine that makes up the body of the modern island. Stratigraphic appraisals are difficult due to the deformed nature of Herschel Island sediments by glacial ice thrust. However, even these deformations give evidence that deeper strata remained unaffected by postglacial thaw and reworking, thus representing original Pleistocene deposits. Climate amelioration during the early Holocene Thermal Maximum (HTM) between 11 and 8 ka BP led to increased thermokarst processes and an enhanced accumulation of peat. Extensive active layer thickening is recorded by a widespread thaw unconformity along the Yukon coast at depths between 1.5 to 2.5 m below surface. Increased bioproductivity, Holocene cryoturbation and recent mass wasting have produced an upper diamicton with deviant cryostructures and significantly more organics than below the discontinuity. Different types of ground ice have been recovered that range widely regarding their isotopic composition, thus reflecting different types of water and strongly variable climatic conditions during their genesis. Holocene ice wedges vary in δ 18 O between -24 and -20 ‰ (VSMOW). A fossil wedge truncated at 1.5 m below surface, revealed low δ 18 O values between -30 and -27 ‰ and is therefore supposed to have formed during an icefree period of more severe climatic conditions prior to HTM. Texture ice within sediment sequences might be an applicable tool for paleoclimate reconstructions as isotope values show clear dependency with depth and enable the recognition of afore-identified boundaries in paleoenvironmental development like the prominent thaw unconformity. Buried glacier ice and ice of unknown origin with low isotope values (< -30 ‰) seem to contribute to ground ice spectrum on Herschel Island, too. Up to the present day, the study area is affected by extensive coastal erosion and ongoing melt of ground ice, that both leads to a strong geomorphological alteration of the landscape. Herschel Island -etwa 70 km östlich der Grenze zwischen Alaska und Kanada -tritt als einzige wesentliche Erhebung auf der Yukon Coastal Plain an der südlichen Beaufortsee in Erscheinung und befindet sich am westlichen Rand der maximalen Wisconsin-Vereisung im Nordwesten Kanadas. Die Insel wurde während des Früh-bis Mittel-Wisconsin als Endmoräne geschüttet und über einen langen Zeitraum von periglazialen Prozessen stark beeinflusst, der möglicherweise bis 50 ka BP zurückreicht aber noch immer mit großer Unsicherheit behaftet ist. Multidisziplinäre Analysen an Sedimenten und die Bestimmung stabiler Isotope (δD, δ 18 O) am Grundeis wurden vor dem Hintergrund durchgeführt, die Paläoumweltentwick-lung der Insel und Paläoklima-Variationen entlang der Yukon Coastal Plain über die Zeit zu rekonstruieren. Unterschiedliche Stadien der Landschaftsentwicklung werden mit Blick auf Bildungs-und Degradationsprozesse von Permafrost und Grundeis untersucht und wie diese Prozesse mit bestimmten Klimaveränderungen in Verbindung stehen. Die untersuchten Sedimente bestehen im allgemeinen aus tonigen Diamikten und siltigen Lehmen mit relativ einheitlichem Ursprung als küstennahe Flachmeerablagerungen, die glazial umgelagert wurden und als Stauchendmoräne den Korpus der Insel bilden. Aufgrund der deformierten Struktur vorliegender Sedimente infolge des Eisschubs ist eine stratigraphische Einordnung schwierig. Jedoch zeugen eben diese Deformationen davon, dass tiefere Schichten von postglazialen Tau-und Umlagerungsprozessen unbeeinflusst blieben und somit die ursprünglichen pleistozänen Ablagerungen repräsentieren. Die Klimaerwärmung während des (früh)holozänen Klimaoptimums zwischen 11 und 8 ka BP führte zu verstärkten Thermokarstprozessen und einer gesteigerten Torfakkumulation. Eine flächendeckende Mächtigkeitszunahme der Auftauzone bis auf 1,5-2,5 m unter Flur ist durch eine weitverbreitete Auftaudiskordanz entlang der Yukon Coastal Plain dokumentiert. Erhöhte Bioproduktivität, holozäne sowie rezente Kryoturbationsprozesse und Massenverlagerungen haben eine oberen Diamikt geschaffen, der sich durch signifikant höhere Organikgehalte und verschiedenartige Kryostrukturen auszeichnet als sie unterhalb der Diskordanz auftreten. Verschiedene Typen Grundeis wurden vorgefunden, die in ihrer isotopischen Zusammensetzung stark variieren und somit unterschiedliche Wassertypen und stark schwankende Klimabedingungen während der Eisgenese widerspiegeln. Holozäne Eiskeile schwanken im δ 18 O-Wert zwischen -20 und -24 ‰ (VSMOW). Ein fossiler Eiskeil, der bei 1,5 m unter Flur gekappt wurde, weist δ 18 O-Werte von -30 bis -27 ‰ auf und scheint daher während einer eisfreien Periode strengerer Klimabedingungen vor dem holozänen Klimaoptimum gebildet worden zu sein. Das Textureis in Sedimentsequenzen stellt möglicherweise ein geeignetes Instrument in der Paläoklimarekonstruktion dar. Denn zum einen zeigen die Isotopenwerte eine klaren Zusammenhang mit der Tiefe an und zum anderen lassen sich die zuvor identifizierten Grenzen in der Paläoumweltentwicklung, wie IX jene markante Auftau-diskordanz, nachvollziehen. Begrabenes Gletschereis und Grundeis unbekannter Herkunft mit niedrigen Isotopenwerten (< -30 ‰) scheinen ebenfalls zum Grundeisspektrum von Herschel Island beizutragen, was noch bis vor wenigen Jahren als umstritten galt. Bis in die Gegenwart hinein wurde das Untersuchungsgebiet durch umfassende Küstenerosionsprozesse und anhaltendes Schmelzen von Grundeis beeinflusst. Beide Prozesse haben zu starken geomorphologischen Veränderungen der Landschaft geführt.