ALBERT

Beschreibung: In a stratified water column, the nitracline is a layer where the nitrate concentration increases below the nutrient-depleted upper layer, exhibiting a strong vertical gradient in the euphotic zone. The subsurface chlorophyll maximum layer (SCML) forms near the bottom of the euphotic zone, acting as a trap to diminish the upward nutrient supply. Depth and steepness of the nitracline are important measurable parameters related to the vertical transport of nitrate into the euphotic zone. The correlation between the SCML and the nitracline has been widely reported in the literature, but the analytic solution for the relationship between them is not well established. By incorporating a piecewise function for the approximate Gaussian vertical profile of chlorophyll, we derive analytical solutions of a specified nutrient–phytoplankton model. The model is well suited to explain basic dependencies between a nitracline and an SCML. The analytical solution shows that the nitracline depth is deeper than the depth of the SCML, shoaling with an increase in the light attenuation coefficient and with a decrease in surface light intensity. The inverse proportional relationship between the light level at the nitracline depth and the maximum rate of new primary production is derived. Analytic solutions also show that a thinner SCML corresponds to a steeper nitracline. The nitracline steepness is positively related to the light attenuation coefficient but independent of surface light intensity. The derived equations of the nitracline in relation to the SCML provide further insight into the important role of the nitracline in marine pelagic ecosystems.

Beschreibung: Bedload transport measurements with acoustic sensors were obtained during summer 2015 in the Albula River in Switzerland. An impact plate measuring system was used with geophone and accelerometer sensors. This system provides indirect estimations of bedload transport in water courses. In April 2015, 30 impact sensors were installed in a new permanent measuring station to monitor continuously bedload transport in a mountain river with a large annual rate of sediment transport (around 90 000 m3 yr−1). Records of the first year of measurement showed that (i) the signal response in terms of geophone and accelerometer impulses is comparable for both types of sensors; (ii) there is a good correlation between discharge data and impulses recorded by both types of sensors; (iii) the critical discharge at the start of bedload transport is around 5 m3 s−1; (iv) a mean calibration factor for the geophone impulses can be estimated which is in a similar range as values determined from other sites with field calibration measurements.

Beschreibung: Since 2012, an array of 105 Biogeochemical-Argo (BGC-Argo) floats has been deployed across the world's oceans to assist in filling observational gaps that are required for characterizing open-ocean environments. Profiles of biogeochemical (chlorophyll and dissolved organic matter) and optical (single-wavelength particulate optical backscattering, downward irradiance at three wavelengths, and photosynthetically available radiation) variables are collected in the upper 1000 m every 1 to 10 days. The database of 9837 vertical profiles collected up to January 2016 is presented and its spatial and temporal coverage is discussed. Each variable is quality controlled with specifically developed procedures and its time series is quality-assessed to identify issues related to biofouling and/or instrument drift. A second database of 5748 profile-derived products within the first optical depth (i.e., the layer of interest for satellite remote sensing) is also presented and its spatiotemporal distribution discussed. This database, devoted to field and remote ocean color applications, includes diffuse attenuation coefficients for downward irradiance at three narrow wavebands and one broad waveband (photosynthetically available radiation), calibrated chlorophyll and fluorescent dissolved organic matter concentrations, and single-wavelength particulate optical backscattering. To demonstrate the applicability of these databases, data within the first optical depth are compared with previously established bio-optical models and used to validate remotely derived bio-optical products. The quality-controlled databases are publicly available from the SEANOE (SEA scieNtific Open data Edition) publisher at https://doi.org/10.17882/49388 and https://doi.org/10.17882/47142 for vertical profiles and products within the first optical depth, respectively.

Beschreibung: Since 2012, an array of 105 Biogeochemical (BGC) Argo floats has been deployed across the world’s oceans to fill the observational gap characterizing most of open-ocean environments. Profiles of biogeochemical (chlorophyll and fluorescent dissolved organic matter) and optical (single-wavelength particulate optical backscattering, downward irradiance at three wavelengths and photosynthetically available radiation) variables are collected in the upper 1000 m every 1 to 10 days. The global database of 9837 vertical profiles collected up to January 2016 is presented and its spatial and temporal coverage is discussed. Each variable is quality controlled with specifically-developed procedures and its time-series is quality-assessed to identify issues related to biofouling and/or instrumental drift. A second database of 5748 profile-derived products within the first optical depth (i.e. the layer of interest for satellite remote sensing) is also presented and its spatio-temporal distribution discussed. This database, devoted to field and remote ocean color applications, includes diffuse attenuation coefficients for downward irradiance at three narrow wavebands and one broad waveband (photosynthetically available radiation), calibrated chlorophyll and dissolved organic matter fluorescence, and single-wavelength particulate optical backscattering. To demonstrate the applicability of these global databases, data within the first optical depth are finally compared with previously established bio-optical models and used to validate remotely-derived bio-optical products. The quality-controlled databases are publicly available from SEANOE (SEA scieNtific Open data Edition) publisher at http://doi.org/10.17882/49388 and http://doi.org/10.17882/47142 for vertical profiles and products within the first optical depth, respectively.

Beschreibung: Eastern boundary upwelling systems are characterized by high productivity that often leads to subsurface hypoxia on the shelf. Mesoscale eddies are important, frequent, and persistent features of circulation in these regions, transporting physical, chemical and biological properties from shelves to the open ocean. In austral fall of 2011, during the Tara Oceans expedition, a subsurface layer (200–400 m) in which the concentration of oxygen was very low (〈 2 μmol kg−1 of O2) was observed in the eastern South Pacific, ~ 900 km offshore (30° S, 81° W). Satellite altimetry combined with CTD observations associated the local oxygen anomaly with an intrathermocline, anticyclonic, mesoscale eddy with a diameter of about 150 km. The eddy contained Equatorial Subsurface Water (ESSW) that at this latitude is normally restricted near the coast. Undersaturation (44 %) of nitrous oxide (N2O) and nitrite accumulation (〉 0.5 μM) gave evidence for denitrification in this water mass. Based on satellite altimetry, we tracked the eddy back to its region of formation on the coast of central Chile (36.1° S, 74.6° W). We estimate that the eddy formed in April 2010. Field studies conducted on the Chilean shelf in June 2010 provided approximate information on initial O2 and N2O concentrations of "source water" in the region at the time of eddy formation. Concentrations of both O2 and N2O in the oxygen minimum zone (OMZ) of the offshore eddy were lower than its surroundings or "source water" on the shelf, suggesting that these chemical species were consumed as the eddy moved offshore. Estimates of apparent oxygen utilization rates at the OMZ of the eddy ranged from 0.29 to 44 nmol L−1 d−1 and the rate of N2O consumption was 3.92 nmol L−1 d−1. Our results show that mesoscale eddies in the ESP not only transport physical properties of the ESSW from the coast to the ocean interior, but also export and transform biogeochemical properties, creating suboxic environments in the oligotrophic region of the eastern South Pacific. Suboxic water masses that are advected by eddies act as hotspots for denitrification and loss of fixed nitrogen from the system.

Beschreibung: Mesoscale eddies are important, frequent, and persistent features of the circulation in the eastern South Pacific (ESP) Ocean, transporting physical, chemical and biological properties from the productive shelves to the open ocean. Some of these eddies exhibit subsurface hypoxic or suboxic conditions and may serve as important hotspots for nitrogen loss, but little is known about oxygen consumption rates and nitrogen transformation processes associated with these eddies. In the austral fall of 2011, during the Tara Oceans expedition, an intrathermocline, anticyclonic, mesoscale eddy with a suboxic (

Beschreibung: In a stratified water column, the nitracline is a layer where the nitrate concentration increases below the nutrient-depleted upper layer, exhibiting a strong vertical gradient in the euphotic zone. The subsurface chlorophyll maximum layer (SCML) forms near the bottom of euphotic zone, acting as a trap to diminish the upward nutrient supply. Depth and steepness of the nitracline are important measurable parameters related to the vertical transport of nitrate into the euphotic zone. The correlation between the SCML and the nitracline has been widely reported in the literature, but the analytic solution for the relationship between them is not well established. By incorporating a piecewise function for the approximate Gaussian vertical profile of chlorophyll, we derive analytical solutions for the system of phytoplankton and nutrient. The analytical solution shows that the nitracline depth is deeper than the depth of SCML, shoaling with an increase in light attenuation coefficient and with a decrease in surface light intensity. The inverse proportional relationship between the light level at the nitracline depth and the maximum rate of new primary production is derived, suggesting that the light level at the nitracline can be used as an indicator for integrated new primary production. Analytic solutions also show that a thinner SCML corresponds to a steeper nitracline. The nitracline steepness is positively related to light attenuation coefficient, but independent of surface light intensity. The derived equations of the nitracline in relation to the SCML provide further insight into the important role of the nitracline in marine pelagic ecosystems.

Beschreibung: Rain-on-snow (ROS) events in mountainous catchments can cause enhanced snowmelt, leading to destructive winter floods. However, due to differences in topography and vegetation cover, the generation of snowpack outflow and its contribution to streamflow is spatially and temporally variable during ROS events. In order to adequately predict such flood events with hydrological models, an enhanced process understanding of the contribution of rainwater and snowmelt to stream water is needed. In this study, we monitored and sampled snowpack outflow with fully automated snowmelt lysimeter systems installed at three different locations in a pre-Alpine catchment in Central Switzerland. We measured snowpack outflow volumes during the winters of 2017 and 2018, as well as snowpack outflow isotopic compositions for winter 2017. Snowpack outflow volumes were highly variable in time and space reflecting differences in snow accumulation and melt. In winter 2017, around 815 mm snowpack outflow occurred at our reference site (grassland 1220 m above sea level, m asl), whereas snowpack outflow was 16 % less at the nearby forest site (1185 m asl), and 62 % greater at another grassland site located 200-meter higher (1420 m asl). A detailed analysis of ten ROS events showed that the snowpack outflow volumes could be explained mainly by rainfall volume and initial snow depth. The isotope signal of snowpack outflow was more damped than that of incoming rainfall at all three sites, with the most damped signal at the high-elevation site because its snowpack was the thickest and residence times of liquid water in the snowpack were the longest, thus enhancing isotopic mixing in the snowpack. The contribution of snowpack outflow to streamflow, estimated by isotope-based two-component end member mixing analysis, differed substantially among the three lysimeter sites. Because the study catchment vegetation is a mixture of grassland and forest and altitudes range from 1000 to 1500 m asl, the catchment-average contribution of snowpack outflow to stream discharge is likely to lie between the end member mixing estimates derived from the three site-specific datasets. Thus, our hydrograph separation estimates based on the measurements from the three lysimeter sites provide a range of snowpack outflow contributions to discharge from different parts of the study area. This information may be useful for improving hydrological models in snow-dominated catchments.

Beschreibung: Light emerging from natural water bodies and measured by remote sensing radiometers contains information about the local type and concentrations of phytoplankton, non-algal particles and colored dissolved organic matter in the underlying waters. An increase in spectral resolution in forthcoming satellite and airborne remote sensing missions is expected to lead to new or improved capabilities to characterize aquatic ecosystems. Such upcoming missions include NASA's Plankton, Aerosol, Cloud, ocean Ecosystem (PACE) Mission; the NASA Surface Biology and Geology observable mission; and NASA Airborne Visible/Infrared Imaging Spectrometer – Next Generation (AVIRIS-NG) airborne missions. In anticipation of these missions, we present an organized dataset of geographically diverse, quality-controlled, high spectral resolution inherent and apparent optical property (IOP/AOP) aquatic data. The data are intended to be of use to increase our understanding of aquatic optical properties, to develop aquatic remote sensing data product algorithms, and to perform calibration and validation activities for forthcoming aquatic-focused imaging spectrometry missions. The dataset is comprised of contributions from several investigators and investigating teams collected over a range of geographic areas and water types, including inland waters, estuaries and oceans. Specific in situ measurements include coefficients describing particulate absorption, particulate attenuation, non-algal particulate absorption, colored dissolved organic matter absorption, phytoplankton absorption, total absorption, total attenuation, particulate backscattering, and total backscattering, as well as remote-sensing reflectance, and irradiance reflectance. The dataset can be downloaded from https://doi.pangaea.de/10.1594/PANGAEA.902230 (Casey et al., 2019).

Beschreibung: Rain-on-snow (ROS) events in mountainous catchments can cause enhanced snowmelt, leading to an increased risk of destructive winter floods. However, due to differences in topography and forest cover, the generation of snowpack outflow volumes and their contribution to streamflow are spatially and temporally variable during ROS events. In order to adequately predict such flood events with hydrological models, an enhanced process understanding of the contribution of rainwater and snowmelt to stream water is needed. In this study, we monitored and sampled snowpack outflow with fully automated snowmelt lysimeter systems installed at three different elevations in a pre-Alpine catchment in central Switzerland. We measured snowpack outflow volumes during the winters of 2017 and 2018, as well as snowpack outflow isotopic compositions in winter 2017. Snowpack outflow volumes were highly variable in time and space, reflecting differences in snow accumulation and melt. In winter 2017, around 815 mm of snowpack outflow occurred at our reference site (grassland 1220 m a.s.l. – metres above sea level), whereas snowpack outflow was 16 % less at the nearby forest site (1185 m a.s.l.), and 62 % greater at another grassland site located 200 m higher (1420 m a.s.l.). A detailed analysis of 10 ROS events showed that the differences in snowpack outflow volumes could be explained mainly by rainfall volumes and initial snow depths. The isotope signals of snowpack outflow were more damped than those of incoming rainwater at all three sites, with the most damped signal at the highest elevation site because its snowpack was the thickest and the residence times of liquid water in its snowpack were the longest, thus enhancing isotopic mixing in the snowpack. The contribution of snowpack outflow to streamflow, estimated with an isotope-based two-component end-member mixing model, differed substantially among the three lysimeter sites (i.e. between 7±4 and 91±21 %). Because the vegetation in our study catchment is a mixture of grassland and forest, with elevations ranging from 1000 to 1500 m a.s.l., our site-specific hydrograph separation estimates can only provide a range of snowpack outflow contributions to discharge from different parts of the study area. Thus, the catchment-average contribution of snowpack outflow to stream discharge is likely to lie between the end-member mixing estimates derived from the three site-specific data sets. This information may be useful for improving hydrological models in snow-dominated catchments.