Environmental Control of Phytoplankton Patchiness

The relative importance of the various biological, chemical, and physical factors for the control of the phytoplankton patchiness in the environment has been studied for the near-surface waters of a small coastal embayment. It was found that during periods of low turbulent mixing (wind speed [Formula: see text]), the phytoplankton patchiness was induced by local differences (taxonomic or physiological) in its production efficiency which was linked to the dynamic fluctuation in the physicochemical characteristics of the medium. For periods of high winds [Formula: see text] it is indicated that the physical turbulent transport processes were responsible for damping out the spatial variations in the phytoplankton distribution.Key words: phytoplankton biomass, P/B ratio, spatial distribution, turbulence, wind stress

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Adaptive Thermal Image Velocimetry of spatial wind movement on landscapes using near target infrared cameras

10.5194/amt-2021-335 ◽

2021 ◽

Author(s):

Benjamin Schumacher ◽

Marwan Katurji ◽

Jiawei Zhang ◽

Peyman Zawar-Reza ◽

Benjamin Adams ◽

...

Keyword(s):

Spatial Information ◽

Turbulent Transport ◽

Surface Wind ◽

Infrared Camera ◽

Thermal Image ◽

Transport Processes ◽

Near Surface ◽

Remote Sensing Technique ◽

Sonic Anemometers ◽

Image Velocimetry

Abstract. Thermal Image Velocimetry (TIV) is a near-target remote sensing technique for estimating two- dimensional near-surface wind velocity based on spatiotemporal displacement of fluctuations in surface brightness temperature captured by an infrared camera. The addition of an automated parameterization and the combination of ensemble TIV results into one output made the method more suitable to changing meteorological conditions and less sensitive to noise stemming from the airborne sensor platform. Three field campaigns were carried out to evaluate the algorithm over turf, dry grass and wheat stubble. The derived velocities were validated with independently acquired observations from fine wire thermocouples and sonic anemometers. It was found that the TIV technique correctly derives atmospheric flow patterns close to the ground. Moreover, the modified method resolves wind speed statistics close to the surface at a higher resolution than the traditional measurement methods. Adaptive Thermal Image Velocimetry (A-TIV) is capable of providing contact-less spatial information about near-surface atmospheric motion and can help to be a useful tool in researching turbulent transport processes close to the ground.

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Investigation of the Hydrogen Transport Processes in Crystalline Silicon of n-Type Conductivity

Solid State Phenomena ◽

10.4028/www.scientific.net/ssp.131-133.425 ◽

2007 ◽

Vol 131-133 ◽

pp. 425-430 ◽

Cited By ~ 1

Author(s):

Anis M. Saad ◽

Oleg Velichko ◽

Yu P. Shaman ◽

Adam Barcz ◽

Andrzej Misiuk ◽

...

Keyword(s):

Hydrogen Concentration ◽

Room Temperature ◽

Crystalline Silicon ◽

Transport Processes ◽

Concentration Profiles ◽

Hydrogen Transport ◽

Hydrogen Atoms ◽

Near Surface ◽

Type Conductivity ◽

Hydrogen Molecules

The silicon substrates were hydrogenated at approximately room temperature and hydrogen concentration profiles vs. depth have been measured by SIMS. Czochralski grown (CZ) wafers, both n- and p-type conductivity, were used in the experiments under consideration. For analysis of hydrogen transport processes and quasichemical reactions the model of hydrogen atoms diffusion and quasichemical reactions is proposed and the set of equations is obtained. The developed model takes into account the formation of bound hydrogen in the near surface region, hydrogen transport as a result of diffusion of hydrogen molecules 2 H , diffusion of metastable complexes * 2 H and diffusion of nonequilibrium hydrogen atoms. Interaction of 2 H with oxygen atoms and formation of immobile complexes “oxygen atom - hydrogen molecule” (O - H2 ) is also taken into account to explain the hydrogen concentration profiles in the substrates of n-type conductivity. The computer simulation based on the proposed equations has shown a good agreement of the calculated hydrogen profiles with the experimental data and has allowed receiving a value of the hydrogen molecules diffusivity at room temperature.

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Sediment transport processes across the Tibetan Plateau inferred from robust grain-size end members in lake sediments

Climate of the Past ◽

10.5194/cp-10-91-2014 ◽

2014 ◽

Vol 10 (1) ◽

pp. 91-106 ◽

Cited By ~ 61

Author(s):

E. Dietze ◽

F. Maussion ◽

M. Ahlborn ◽

B. Diekmann ◽

K. Hartmann ◽

...

Keyword(s):

Grain Size ◽

Sediment Transport ◽

Tibetan Plateau ◽

Transport Processes ◽

The Tibetan Plateau ◽

Dust Deposition ◽

Northerly Wind ◽

Near Surface ◽

Depositional Processes ◽

End Members

Abstract. Grain-size distributions offer powerful proxies of past environmental conditions that are related to sediment sorting processes. However, they are often of multimodal character because sediments can get mixed during deposition. To facilitate the use of grain size as palaeoenvironmental proxy, this study aims to distinguish the main detrital processes that contribute to lacustrine sedimentation across the Tibetan Plateau using grain-size end-member modelling analysis. Between three and five robust grain-size end-member subpopulations were distinguished at different sites from similarly–likely end-member model runs. Their main modes were grouped and linked to common sediment transport and depositional processes that can be associated with contemporary Tibetan climate (precipitation patterns and lake ice phenology, gridded wind and shear stress data from the High Asia Reanalysis) and local catchment configurations. The coarse sands and clays with grain-size modes >250 μm and <2 μm were probably transported by fluvial processes. Aeolian sands (~200 μm) and coarse local dust (~60 μm), transported by saltation and in near-surface suspension clouds, are probably related to occasional westerly storms in winter and spring. Coarse regional dust with modes ~25 μm may derive from near-by sources that keep in longer term suspension. The continuous background dust is differentiated into two robust end members (modes: 5–10 and 2–5 μm) that may represent different sources, wind directions and/or sediment trapping dynamics from long-range, upper-level westerly and episodic northerly wind transport. According to this study grain-size end members of only fluvial origin contribute small amounts to mean Tibetan lake sedimentation (19± 5%), whereas local to regional aeolian transport and background dust deposition dominate the clastic sedimentation in Tibetan lakes (contributions: 42 ± 14% and 51 ± 11%). However, fluvial and alluvial reworking of aeolian material from nearby slopes during summer seems to limit end-member interpretation and should be crosschecked with other proxy information. If not considered as a stand-alone proxy, a high transferability to other regions and sediment archives allows helpful reconstructions of past sedimentation history.

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Technical Note: Mesocosm approach to quantify dissolved inorganic carbon percolation fluxes

Biogeosciences ◽

10.5194/bg-11-1077-2014 ◽

2014 ◽

Vol 11 (4) ◽

pp. 1077-1084 ◽

Cited By ~ 4

Author(s):

E. M. Thaysen ◽

S. Jessen ◽

P. Ambus ◽

C. Beier ◽

D. Postma ◽

...

Keyword(s):

Inorganic Carbon ◽

Dissolved Inorganic Carbon ◽

Experimental Period ◽

Technical Note ◽

Transport Processes ◽

Carbon Dioxide Partial Pressure ◽

Physical Factors ◽

Soil Carbon Dioxide ◽

Promising Tool ◽

Unplanted Soil

Abstract. Dissolved inorganic carbon (DIC) fluxes across the vadose zone are influenced by a complex interplay of biological, chemical and physical factors. A novel soil mesocosm system was evaluated as a tool for providing information on the mechanisms behind DIC percolation to the groundwater from unplanted soil. Carbon dioxide partial pressure (pCO2), alkalinity, soil moisture and temperature were measured with depth and time, and DIC in the percolate was quantified using a sodium hydroxide trap. Results showed good reproducibility between two replicate mesocosms. The pCO2 varied between 0.2 and 1.1%, and the alkalinity was 0.1–0.6 meq L−1. The measured cumulative effluent DIC flux over the 78-day experimental period was 185–196 mg L−1 m−2 and in the same range as estimates derived from pCO2 and alkalinity in samples extracted from the side of the mesocosm column and the drainage flux. Our results indicate that the mesocosm system is a promising tool for studying DIC percolation fluxes and other biogeochemical transport processes in unsaturated environments.

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Environmental control on the variability of DMS and DMSP in the Mauritanian upwelling region

Biogeosciences ◽

10.5194/bg-9-1041-2012 ◽

2012 ◽

Vol 9 (3) ◽

pp. 1041-1051 ◽

Cited By ~ 22

Author(s):

C. Zindler ◽

I. Peeken ◽

C. A. Marandino ◽

H. W. Bange

Keyword(s):

Surface Waters ◽

Coastal Upwelling ◽

Environmental Control ◽

Hot Spot ◽

Local Source ◽

Surface Seawater ◽

Near Surface ◽

Northwest Africa ◽

N:P Ratios ◽

A Minor

Abstract. Dimethylsulphide (DMS) and dissolved and particulate dimethylsulfoniopropionate (DMSPd, DMSPp) were measured in near-surface waters along the Mauritanian coast, Northwest Africa, during the upwelling season in February 2008. DMS, DMSPd and DMSPp surface concentrations of up to 10 nmol L−1, 15 nmol L−1 and 990 nmol L−1, respectively, were measured. However, the DMS concentrations measured are in the low range compared to other upwelling regions. The maximum DMSPp concentration is the highest reported from upwelling regions so far, which might indicate that the Mauritanian upwelling is a hot spot for DMSP. Within the phytoplankton groups, dinoflagellates were identified as important contributors to DMS concentrations, while other algae seemed to have only a minor or no influence on DMS and DMSP concentrations. A pronounced switch from high DMSP to high DMS concentrations was observed when the nitrogen to phosphorus ratio (N:P) was below 7. The high DMS/DMSP ratios at N:P ratios <7 indicate that nitrogen limitation presumably triggered a switch from DMSP to DMS independent of the species composition. Our results underline the importance of coastal upwelling regions as a local source for surface seawater sulphur.

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Validation of farm-scale methane emissions using nocturnal boundary layer budgets

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-15-21765-2015 ◽

2015 ◽

Vol 15 (15) ◽

pp. 21765-21802 ◽

Cited By ~ 1

Author(s):

J. Stieger ◽

I. Bamberger ◽

N. Buchmann ◽

W. Eugster

Keyword(s):

Boundary Layer ◽

Nocturnal Boundary Layer ◽

Methane Emissions ◽

Emission Factors ◽

Transport Processes ◽

Tethered Balloon ◽

Near Surface ◽

Time Space ◽

Farm Scale ◽

Balloon System

Abstract. This study provides the first experimental validation of Swiss agricultural methane emission estimates at the farm scale. We measured CH4 concentrations at a Swiss farmstead during two intensive field campaigns in August 2011 and July 2012 to (1) quantify the source strength of livestock methane emissions using a tethered balloon system, and (2) to validate inventory emission estimates via nocturnal boundary layer (NBL) budgets. Field measurements were performed at a distance of 150 m from the nearest farm buildings with a tethered balloon system in combination with gradient measurements at eight heights on a 10 m tower to better resolve the near-surface concentrations. Vertical profiles of air temperature, relative humidity, CH4 concentration, wind speed and wind direction showed that the NBL was strongly influenced by local transport processes and by the valley wind system. Methane concentrations showed a pronounced time course, with highest concentrations in the second half of the night. NBL budget flux estimates were obtained via a time–space kriging approach. Main uncertainties of NBL budget flux estimates were associated with instationary atmospheric conditions and the estimate of the inversion height zi (top of volume integration). The mean NBL budget fluxes of 1.60 ± 0.31 μg CH4 m-2 s-1 (1.40 ± 0.50 and 1.66 ± 0.20 μg CH4 m-2 s-1 in 2011 and 2012, respectively) were in good agreement with local inventory estimates based on current livestock number and default emission factors, with 1.29 ± 0.47 and 1.74 ± 0.63 μg CH4 m-2 s-1 for 2011 and 2012, respectively. This indicates that emission factors used for the national inventory reports are adequate, and we conclude that the NBL budget approach is a useful tool to validate emission inventory estimates.

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Physical Transport Processes that Affect the Distribution of Oil in the Gulf of Mexico: Observations and Modeling

Oceanography ◽

10.5670/oceanog.2021.117 ◽

2021 ◽

Vol 34 (1) ◽

pp. 58-75

Author(s):

Michel Boufadel ◽

◽

Annalisa Bracco ◽

Eric Chassignet ◽

Shuyi Chen ◽

...

Keyword(s):

Gulf Of Mexico ◽

Physical Environment ◽

Large Scale ◽

Transport Processes ◽

Small Scale ◽

Surface Mixed Layer ◽

Physical Processes ◽

Mixing Processes ◽

Near Surface ◽

Wide Range

Physical transport processes such as the circulation and mixing of waters largely determine the spatial distribution of materials in the ocean. They also establish the physical environment within which biogeochemical and other processes transform materials, including naturally occurring nutrients and human-made contaminants that may sustain or harm the region’s living resources. Thus, understanding and modeling the transport and distribution of materials provides a crucial substrate for determining the effects of biological, geological, and chemical processes. The wide range of scales in which these physical processes operate includes microscale droplets and bubbles; small-scale turbulence in buoyant plumes and the near-surface “mixed” layer; submesoscale fronts, convergent and divergent flows, and small eddies; larger mesoscale quasi-geostrophic eddies; and the overall large-scale circulation of the Gulf of Mexico and its interaction with the Atlantic Ocean and the Caribbean Sea; along with air-sea interaction on longer timescales. The circulation and mixing processes that operate near the Gulf of Mexico coasts, where most human activities occur, are strongly affected by wind- and river-induced currents and are further modified by the area’s complex topography. Gulf of Mexico physical processes are also characterized by strong linkages between coastal/shelf and deeper offshore waters that determine connectivity to the basin’s interior. This physical connectivity influences the transport of materials among different coastal areas within the Gulf of Mexico and can extend to adjacent basins. Major advances enabled by the Gulf of Mexico Research Initiative in the observation, understanding, and modeling of all of these aspects of the Gulf’s physical environment are summarized in this article, and key priorities for future work are also identified.

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