Alfred Wegener Institute for Polar and Marine Research
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Analysis of micro-climate variation and feedbacks in an Arctic tundra landscape on Disko Island, Western Greenland
Get PDFThe Arctic tundra is experiencing rapid changes due to climate warming, with profound implications for permafrost ecosystems and their feedbacks to the global climate. Vegetation changes driven by recipitation and temperature increases include extended shrub cover and increases in plant primary production. Changes in vegetation and climate alter soil moisture and temperature on small spatial scales (< 1 m), which mediate greenhouse gas sequestration and emission processes during summer. Understanding these interactions is essential for identifying climate feedback mechanisms and supporting global assessments using remote sensing data.
This study examines the relationships between vegetation cover, topography, surface soil moisture and their effects on soil temperature in an Arctic tundra landscape on Disko Island (Qeqertarsuaq), Western Greenland. Data were collected from 24 sites (1 m²) in a southern valley on Disko Island during field studies conducted between September 2022 and September 2024. It includes visually assessed vegetation cover, a digital terrain model and continuous temperature-moisture data collected using TOMST TMS-4 sensors. I derived variables describing vegetation (vegetation height, vegetation density, forb, graminoid, lichen, moss and shrub cover) and topography (elevation, geomorphon type and slope). I quantified the spatial and annual variation of summer mean soil temperature and moisture at the study site during the summer seasons of 2023 and 2024. I then used single linear regression models to identify the variables which explained most of the variance in the moisture and temperature data of the summer season 2023.
Mean summer surface soil moisture varied between 14% and 60%, mean summer soil temperatures between 1.9°C and 6.5°C. The linear regression models revealed that geomorphon type (R = 0.35), graminoid cover (R2 = 0.35) and slope (R2 = 0.28) were most important predictors of summer soil surface moisture, with higher soil moisture in sheltered and flatter locations with high graminoid cover. Summer soil temperature was best explained by slope (R2 = 0.25), elevation (R2 = 0.23), graminoid cover (R2 = 0.15) and lichen (R2 = 0.12), exhibiting cooler soils at higher elevations with steeper terrain and less graminoid cover whereas high lichen cover indicated warmer soils in summer. Contrary to prior expectations, shrub and moss cover explained little variance in both soil moisture and temperature (< 10% and < 5%, respectively).
These findings underscore the dominant role of topography in shaping summer soil microclimate, while also highlighting the influence of vegetation, particularly graminoid cover. Future vegetation changes in Arctic landscapes are likely to alter soil thermal and hydrological regimes, with implications for greenhouse gas fluxes. Investigating interactions between vegetation, soil moisture, and temperature across diverse topographic settings is essential for predicting feedbacks to climate change
An overview of the vertical structure of the atmospheric boundary layer in the central Arctic during MOSAiC
Get PDFObservations collected during the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) provide an annual cycle of the vertical thermodynamic and kinematic structure of the atmospheric boundary layer (ABL) in the central Arctic. A self-organizing map (SOM) analysis conducted using radiosonde observations shows a range in the Arctic ABL vertical structure from very shallow and stable, with a strong surface-based virtual potential temperature (θv) inversion, to deep and near neutral, capped by a weak elevated θv inversion. The patterns identified by the SOM allowed for the derivation of criteria to categorize stability within and just above the ABL, which revealed that the Arctic ABL during MOSAiC was stable and near neutral with similar frequencies, and there was always a θv inversion within the lowest 1km, which usually had strong to moderate stability. In conjunction with observations from additional measurement platforms, including a 10m meteorological tower, ceilometer, and microwave radiometer, the radiosonde observations and SOM analysis provide insight into the relationships between atmospheric vertical structure and stability, as well as a variety of atmospheric thermodynamic and kinematic features. A low-level jet was observed in 76% of the radiosondes, with stronger winds and low-level jet (LLJ) core located more closely to the ABL corresponding with weaker stability. Wind shear within the ABL was found to decrease, and friction velocity was found to increase, with decreasing ABL stability. Clouds were observed within the 30min preceding the radiosonde launch 64% of the time. These were typically low clouds, corresponding to weaker stability, where high clouds or no clouds largely coincided with a stable ABL
Observational and Numerical Modeling Constraints on the Global Ocean Biological Carbon Pump
Get PDFThis study characterized ocean biological carbon pump metrics in the second iteration of the REgional Carbon Cycle Assessment and Processes (RECCAP2) project. The analysis here focused on comparisons of global and biome-scale regional patterns in particulate organic carbon (POC) production and sinking flux from the RECCAP2 ocean biogeochemical model ensemble against observational products derived from satellite remote sensing, sediment traps, and geochemical methods. There was generally good model-data agreement in mean large-scale spatial patterns, but with substantial spread across the model ensemble and observational products. The global-integrated, model ensemble-mean export production, taken as the sinking POC flux at 100 m (6.08 ± 1.17 Pg C yr−1), and export ratio defined as sinking flux divided by net primary production (0.154 ± 0.026) both fell at the lower end of observational estimates. Comparison with observational constraints also suggested that the model ensemble may have underestimated regional biological CO2 drawdown and air-sea CO2 flux in high productivity regions. Reasonable model-data agreement was found for global-integrated, ensemble-mean sinking POC flux into the deep ocean at 1,000 m (0.65 ± 0.24 Pg C yr−1) and the transfer efficiency defined as flux at 1,000 m divided by flux at 100 m (0.122 ± 0.041), with both variables exhibiting considerable regional variability. The RECCAP2 analysis presents standard ocean biological carbon pump metrics for assessing biogeochemical model skill, metrics that are crucial for further modeling efforts to resolve remaining uncertainties involving system-level interactions between ocean physics and biogeochemistry
Informing the Plastic Treaty negotiations on science - experiences from the Scientists’ Coalition for an Effective Plastic Treaty
Get PDFThe ongoing international negotiations on a global plastics treaty will have pivotal implications for future efforts to transform the plastic economy. This is essential since the current use of plastic in the economy impacts the environment beyond the planetary carrying capacity. To ensure that the forthcoming Treaty can provide the foundation for this transition, the best available science must be made available in the negotiations, but with no formal scientific mechanism to inform the negotiations process, this is not ensured. The Scientists’ Coalition for an Effective Plastic Treaty serves as an example of how the global scientific community has self-organized and come together to address this task, working with five different categories of science-policy communication. The Scientists’ Coalition’s work is made transparent here with the hope that it can inspire organization of scientific input into other future policy areas
IceBird Summer 2024 Campaign Report
Get PDFScientific focus in summer 2024:
In addition to continuing long-term objectives of IceBird, a scientific focus of the IceBird Summer campaing in 2024 is to validate and improve novel satellite-based sea ice freeboard and thickness estimates from altimetry missions like CryoSat-2 during the melting phase. It was planned to conduct satellite underflights of CryoSat-2 and ICESat-2; however, poor weather conditions meant a lack of opportunities, and this goal was not achieved. Other goals of the 2024 campaign, to coordinate with scheduled field work (e.g. RV Kronprins Haakon servicing an oceanographic mooring in the Amundsen basin) and a separate airborne campaign, the NASA ARCSIX https://espo.nasa.gov/arcsix project, were achieved successfully. We also overflew an array of ice mass balance (CRREL) and weather buoys (UiT) www.cryosphereinnovation.com/data deployed by twin otter landings in April 2024
Air mass transport to the tropical western Pacific troposphere inferred from ozone and relative humidity balloon observations above Palau
Get PDFKelp forest community structure and demography in Kongsfjorden (Svalbard) across 25 years of Arctic warming
Get PDFThe Arctic archipelago of Svalbard is a hotspot of global warming and many fjords experience
a continuous increase in seawater temperature and glacial melt while sea-ice
cover declines. In 1996/1998, 2012–2014, and 2021 macroalgal biomass and species
diversity were quantified at the study site Hansneset, Kongsfjorden (W-Spitsbergen)
in order to identify potential changes over time. In 2021, we repeated the earlier studies
by stratified random sampling (1 × 1 m2, n = 3) along a sublittoral depth transect (0,
2.5, 5, 10, and 15 m) and investigated the lower depth limits of dominant brown algae
between 3 and 19 m. The maximum fresh weight (FW) of all seaweeds was 11.5 kg m−2
at 2.5 m and to 99.9% constituted of kelp. Although biomass distribution along the
depth transect in 2021 was not significantly different compared to 2012/2013, the
digitate kelp community (Laminaria digitata/Hedophyllum nigripes) had transformed
into an Alaria esculenta-dominated
kelp forest. Consequently, a pronounced shift
in kelp forest structure occurred over time as we demonstrate that biomass allocation
to thallus parts is kelp species-specific.
Over the past decade, kelp demography
changed and in 2021 a balanced age structure of kelps (juveniles plus many older kelp
individuals) was only apparent at 2.5 m. In addition, the abundances and lower depth
limits of all dominant brown algae declined noticeably over the last 25 years while the
red algal flora abundance remained unchanged at depth. We propose that the major
factor driving the observed changes in the macroalgal community are alterations in
underwater light climate, as in situ data showed increasing turbidity and decreasing irradiance
since 2012 and 2017, respectively. As a consequence, the interplay between
kelp forest retreat to lower depth levels caused by coastal darkening and potential
macroalgal biomass gain with increasing temperatures will possibly intensify in the
future with unforeseen consequences for melting Arctic coasts and fjord ecosystem
services. The Arctic archipelago of Svalbard is a hotspot of global warming and many fjords experience
a continuous increase in seawater temperature and glacial melt while sea-ice
cover declines. In 1996/1998, 2012–2014, and 2021 macroalgal biomass and species
diversity were quantified at the study site Hansneset, Kongsfjorden (W-Spitsbergen)
in order to identify potential changes over time. In 2021, we repeated the earlier studies
by stratified random sampling (1 × 1 m2, n = 3) along a sublittoral depth transect (0,
2.5, 5, 10, and 15 m) and investigated the lower depth limits of dominant brown algae
between 3 and 19 m. The maximum fresh weight (FW) of all seaweeds was 11.5 kg m−2
at 2.5 m and to 99.9% constituted of kelp. Although biomass distribution along the
depth transect in 2021 was not significantly different compared to 2012/2013, the
digitate kelp community (Laminaria digitata/Hedophyllum nigripes) had transformed
into an Alaria esculenta-dominated
kelp forest. Consequently, a pronounced shift
in kelp forest structure occurred over time as we demonstrate that biomass allocation
to thallus parts is kelp species-specific.
Over the past decade, kelp demography
changed and in 2021 a balanced age structure of kelps (juveniles plus many older kelp
individuals) was only apparent at 2.5 m. In addition, the abundances and lower depth
limits of all dominant brown algae declined noticeably over the last 25 years while the
red algal flora abundance remained unchanged at depth. We propose that the major
factor driving the observed changes in the macroalgal community are alterations in
underwater light climate, as in situ data showed increasing turbidity and decreasing irradiance
since 2012 and 2017, respectively. As a consequence, the interplay between
kelp forest retreat to lower depth levels caused by coastal darkening and potential
macroalgal biomass gain with increasing temperatures will possibly intensify in the
future with unforeseen consequences for melting Arctic coasts and fjord ecosystem
services
Novel approach to estimate the water isotope diffusion length in deep ice cores with an application to Marine Isotope Stage 19 in the Dome C ice core
Get PDFAbstract. Accurate estimates of water isotope diffusion lengths are crucial when reconstructing and interpreting water isotope records from ice cores. This is especially true in the deepest, oldest sections of deep ice cores, where thermally enhanced diffusive processes have acted over millennia on extremely thinned ice. Previous statistical estimation methods, used with great success in shallower, younger ice cores, falter when applied to these deep sections, as they fail to account for the statistics of the climate on millennial timescales. Here, we present a new method to estimate the diffusion length from water isotope data and apply it to the Marine Isotope Stage 19 (MIS 19) interglacial at the bottom of the EPICA Dome C (EDC, Dome Concordia) ice core. In contrast to the conventional estimator, our method uses other interglacial periods taken from further up in the ice core to estimate the structure of the variability before diffusion. Through use of a Bayesian framework, we are able to constrain our fit while propagating the uncertainty in our assumptions. We estimate a diffusion length of 31±5 cm for the MIS 19 period, which is significantly smaller than previously estimated (40–60 cm). Similar results were obtained for each interglacial used to represent the undiffused climate signal, demonstrating the robustness of our estimate. Our result suggests better preservation of the climate signal at the bottom of EDC and likely other deep ice cores, offering greater potentially recoverable temporal resolution and improved reconstructions through deconvolution.
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