ALBERT

Description: Thaumarchaeota are one of the most abundant groups of Archaea in the marine water column. Their membrane consists of isoprenoid glycerol dibiphytanyl glycerol tetraethers (GDGTs) which are applied in the widely used TEX86 proxy to reconstruct past sea surface temperatures (SSTs). However, in some specific marine systems, such as the Mediterranean Sea, core-top TEX86-derived temperatures do not seem to reflect annual mean SSTs. This has been attributed to contributions of deep-water dwelling Thaumarchaeota. Here, we investigate the potential causes of this bias by studying both the archaeal diversity as well as the intact polar lipid (IPL) GDGT composition in the Mediterranean water column by a combined 16S rRNA gene amplicon sequencing and a lipidomic approach on suspended particulate matter (SPM) at different water depths. The archaeal distribution showed a dominance of archaea other than Thaumarchaeota, i.e. Marine Euryarchaeota group II and III in the upper epipelagic waters (0-100 meters deep), while Thaumarchaeota (Marine group I; MGI) dominated the subsurface and the deeper waters. This shift in the archaeal community composition coincided with a decrease in IPL GDGT-0 and increase of IPL crenarchaeol. The ratio of GDGT-2/GDGT-3 increased with water depth, but values were lower than observed in deep marine waters of some other regions. The increase of the GDGT-2/GDGT-3 ratio coincided with the high relative abundance of deep-water MGI, which may be linked to the high temperature and salinity found in specific water masses of the Mediterranean Sea. We conclude that these particularities of the Mediterranean Sea are responsible for the overestimated SST based on TEX86.

Description: Turbulent mixing and energy dissipation have important roles in the global circulation but are not resolved by ocean models. We use direct numerical simulations of a geostrophic circulation, resolving turbulence and convection, to examine the rates of dissipation and mixing. As a starting point, we focus on circulation in a rotating rectangular basin forced by a surface temperature difference but no wind stress. Emphasis is on the geostrophic regime for the horizontal circulation, but also on the case of strong buoyancy forcing (large Rayleigh number), which implies a turbulent convective boundary layer. The computed results are consistent with existing scaling theory that predicts dynamics and heat transport dependent on the relative thicknesses of thermal and Ekman boundary layers, hence on the relative roles of buoyancy and rotation. Scaling theory is extended to describe the volume-integrated rate of mixing, which is proportional to heat transport and decreases with increasing rotation rate or decreasing temperature difference. In contrast, viscous dissipation depends crucially on whether the thermal boundary layer is laminar or turbulent, with no direct Coriolis effect on the turbulence unless rotation is extremely strong. For strong forcing, in the geostrophic regime, the mechanical energy input from buoyancy goes primarily into mixing rather than dissipation. For a buoyancy-driven circulation in a basin comparable to the North Atlantic we estimate that the total rate of mixing accounts for over $95$\% of the mechanical energy supply, implying that buoyancy is an efficient driver of mixing in the oceans. This article is protected by copyright. All rights reserved.

Description: With an ever-increasing demand for natural resources and the societal need to understand and predict natural disasters, soil water content (SWC) observations remain a critical variable to monitor in order to optimally allocate resources, establish early warning systems, and improve weather forecasts. However, routine agricultural production practices of soil cultivation, planting, and harvest make the operation and maintenance of direct contact point sensors for long-term monitoring challenging. In this work, we explore the use of the newly established Cosmic-Ray Neutron Probe (CRNP) and method to monitor landscape average SWC in a mixed agricultural land use system in northeast Austria. The calibrated CRNP landscape SWC values compare well against an independent in situ SWC probe network (MAE = 0.0286 m3/m3) given the challenge of continuous in situ monitoring from probes across a heterogeneous agricultural landscape. The ability of the CRNP to provide real-time and accurate landscape SWC measurements makes it an ideal method for establishing long-term monitoring sites in agricultural ecosystems to aid in agricultural water and nutrient management decisions at the small tract of land scale as well as aiding in management decisions at larger scales.

Description: Abstract Volume transport in the presence of fully resolved convection and turbulence is investigated in a reentrant channel model of the Southern Ocean. The response of the meridional overturning and zonal transport to variations in wind and buoyancy forcing is quantified. Our simulations show two overturning cells—a buoyancy‐driven lower cell and a wind‐driven upper cell. The lower overturning cell is much larger in meridional extent and magnitude than the upper cell. The mean component of the overturning transport is smaller than the fluctuating component in the lower overturning cell, indicating that transport is dominated by eddies and/or turbulent convective flow. In contrast, the upper cell can be primarily described as a mean flow (indicating minimal eddy compensation). Both cells strengthen with increasing winds, with the upper cell being more sensitive to increasing wind intensity than the lower cell. Scaling for the mean upper overturning is also derived and matches previous theories which predict a linear sensitivity of the upper cell to wind. Zonal transport remains insensitive to increasing wind stress, suggesting that the system is eddy saturated when turbulence and eddies are resolved. These results suggest that fine‐scale flows control zonal transport and abyssal meridional overturning in the Southern Ocean, while wind stress drives the upper meridional overturning transport, highlighting the importance of accurately characterizing turbulence and convection in large‐scale models.

Description: Previous validation studies have demonstrated the accuracy of the Metop-A ASCAT soil moisture (SM) product, although over- and underestimation during different seasons of the year suggest a need for improving the retrieval algorithm. In this study, we analyzed whether adapting the vegetation characterization based on global parameters to regional conditions improves the seasonal representation of SM and vegetation optical depth ( τ ). SM and τ are retrieved from ASCAT using both a seasonal (mean climatological) and a dynamic vegetation characterization that allows for year-to-year changes. The retrieved SM and τ are compared with in situ and satellite SM, and with vegetation products (SMAP, AMSR2, and SPOT-VGT/PROBA-V). The study region is set in an agricultural area of Lower Austria that is characterized by heterogeneous land cover and topography, and features an experimental catchment equipped with a SM network (HOAL SoilNet). We found that a stronger vegetation correction within the SM retrieval improves the SM product considerably (increase of the Spearman correlation coefficient r s by 0.15 on average, and r s comparable to SMAP and AMSR2). The vegetation product derived with a dynamic vegetation characterization compares well to the reference datasets and reflects vegetation dynamics such as start and peak of season and harvest. Although some vegetation effects cannot be corrected by the adapted vegetation characterization, our results demonstrate the benefits of a parameterization optimized for regional conditions in this temperate climate zone.

Description: Remote Sensing, Vol. 10, Pages 1396: Sensitivity of Sentinel-1 Backscatter to Vegetation Dynamics: An Austrian Case Study Remote Sensing doi: 10.3390/rs10091396 Authors: Mariette Vreugdenhil Wolfgang Wagner Bernhard Bauer-Marschallinger Isabella Pfeil Irene Teubner Christoph Rüdiger Peter Strauss Crop monitoring is of great importance for e.g., yield prediction and increasing water use efficiency. The Copernicus Sentinel-1 mission operated by the European Space Agency provides the opportunity to monitor Earth’s surface using radar at high spatial and temporal resolution. Sentinel-1’s Synthetic Aperture Radar provides co- and cross-polarized backscatter, enabling the calculation of microwave indices. In this study, we assess the potential of Sentinel-1 VV and VH backscatter and their ratio VH/VV, the cross ratio (CR), to monitor crop conditions. A quantitative assessment is provided based on in situ reference data of vegetation variables for different crops under varying meteorological conditions. Vegetation Water Content (VWC), biomass, Leaf Area Index (LAI) and height are measured in situ for oilseed-rape, corn and winter cereals at different fields during two growing seasons. To quantify the sensitivity of backscatter and microwave indices to vegetation dynamics, linear and exponential models and machine learning methods have been applied to the Sentinel-1 data and in situ measurements. Using an exponential model, the CR can account for 87% and 63% of the variability in VWC for corn and winter cereals. In oilseed-rape, the coefficient of determination ( R 2 ) is lower ( R 2 = 0.34) due to the large difference in VWC between the two growing seasons and changes in vegetation structure that affect backscatter. Findings from the Random Forest analysis, which uses backscatter, microwave indices and soil moisture as input variables, show that CR is by and large the most important variable to estimate VWC. This study demonstrates, based on a quantitative analysis, the large potential of microwave indices for vegetation monitoring of VWC and phenology.

Description: The nuclear hormone receptor superfamily acts as a genomic sensor of diverse signals. Their actions are often intertwined with other transcription factors. Nuclear hormone receptors are targets for many therap...

Description: Journal of Physical Oceanography, Ahead of Print. 〈br/〉