scholarly journals On the use of acoustic data to characterise the thermohaline stratification in a tropical ocean

2021 ◽  
Author(s):  
Ramilla Vieira Assunção ◽  
Anne Lebourges-Dhaussy ◽  
Alex Costa da Silva ◽  
Bernard Bourlès ◽  
Gary Vargas ◽  
...  
Keyword(s):  
Robust Estimation ◽  
Mixed Layer Depth ◽  
Ecosystem Structure ◽  
Tropical Ocean ◽  
Thermohaline Structure ◽  
Acoustic Data ◽  
Vertical Extension ◽  
The One ◽  
Thermohaline Stratification ◽  
The Vertical Distribution

Abstract. The use of active acoustic to monitor abiotic structures and processes in the ocean have been gaining ground in oceanography. In some systems, acoustics allow the robust estimation of the depth of the pycnocline or thermocline either directly or indirectly when the physical structures drive the one of organisms. Here, we examined the feasibility of extracting the thermohaline structure (mixed-layer depth, upper and lower thermocline) from echosounder data collected in the oligotrophic Southwestern tropical Atlantic region at two seasons (spring and fall), more precisely in two areas with different thermohaline conditions, at both day and night. For that, we tested three approaches: (i) the vertical extension of the epipelagic community; (ii) the use of acoustic gradients; and (iii) a cross-wavelet approach. Results show that, even if the thermohaline structure impacts the vertical distribution of acoustic scatters, the resultant structuring did not allow for a robust estimation of the thermohaline limits indicating that other oceanographic or biological processes are acting. This result prevents for a fine-scale representation of the upper-layer turbulence from acoustic data. However, studying the proportion of acoustic biomass within each layer provides interesting insights on ecosystem structure in different thermohaline, seasonal and diel scenarios.

Implications of a regional-scale process (the Lakshadweep low) on the mesozooplankton community structure of the Arabian Sea

2019 ◽  
Vol 70 (3) ◽  
pp. 345 ◽  
Author(s):  
K. K. Karati ◽  
G. Vineetha ◽  
T. V. Raveendran ◽  
P. K. Dineshkumar ◽  
K. R. Muraleedharan ◽  
...  
Keyword(s):  
Physical Process ◽  
Arabian Sea ◽  
Mixed Layer Depth ◽  
Regional Scale ◽  
Zooplankton Community ◽  
Ocean Basin ◽  
Zooplankton Biomass ◽  
Global Ocean ◽  
Mesozooplankton Community ◽  
Tropical Ocean

The Arabian Sea, a major tropical ocean basin in the northern Indian Ocean, is one of the most productive regions in the global ocean. Although the classical Arabian Sea ‘paradox’ describes the geographical and seasonal invariability in zooplankton biomass in this region, the effect of the Lakshadweep low (LL), a regional-scale physical process, on the zooplankton community has not yet been evaluated. The LL, characterised by low sea surface height and originating around the vicinity of the Lakshadweep islands during the mid-summer monsoon, is unique to the Arabian Sea. The present study investigated the effect of the LL on the zooplankton community. The LL clearly had a positive effect, with enhanced biomass and abundance in the mixed-layer depth of the LL region. Copepods and chaetognaths formed the dominant taxa, exhibiting strong affinity towards the physical process. Of the 67 copepod species observed, small copepods belonging to the families Paracalanidae, Clausocalanidae, Calanidae, Oncaeidae and Corycaeidae dominated the LL region. Phytoplankton biomass (chlorophyll-a) was the primary determinant influencing the higher preponderance of the copepod community in this region.

scholarly journals Characterization of the <sup>222</sup>Rn family turbulent transport in the convective atmospheric boundary layer

2007 ◽  
Vol 7 (3) ◽  
pp. 697-712 ◽  
Author(s):  
J.-F. Vinuesa ◽  
S. Galmarini
Keyword(s):  
Boundary Layer ◽  
Steady State ◽  
Vertical Distribution ◽  
Turbulent Transport ◽  
Radioactive Decay ◽  
Atmospheric Boundary Layers ◽  
Eddy Simulation ◽  
The One ◽  
The Vertical Distribution ◽  
Unsteady Conditions

Abstract. The combined effect of turbulent transport and radioactive decay on the distribution of 222Rn and its progeny in convective atmospheric boundary layers (CBL) is investigated. Large eddy simulation is used to simulate their dispersion in steady state CBL and in unsteady conditions represented by the growth of a CBL within a pre-existing reservoir layer. The exact decomposition of the concentration and flux budget equations under steady state conditions allowed us to determine which processes are responsible for the vertical distribution of 222Rn and its progeny. Their mean concentrations are directly correlated with their half-life, e.g. 222Rn and 210Pb are the most abundant whereas 218Po show the lowest concentrations. 222Rn flux decreases linearly with height and its flux budget is similar to the one of inert emitted scalar, i.e., a balance between on the one hand the gradient and the buoyancy production terms, and on the other hand the pressure and dissipation at smaller scales which tends to destroy the fluxes. While 222Rn exhibits the typical bottom-up behavior, the maximum flux location of the daughters is moving upwards while their rank in the 222Rn progeny is increasing leading to a typical top-down behavior for 210Pb. We also found that the relevant radioactive decaying contributions of 222Rn short-lived daughters (218Po and 214Pb) act as flux sources leading to deviations from the linear flux shape. In addition, while analyzing the vertical distribution of the radioactive decay contributions to the concentrations, e.g. the decaying zone, we found a variation in height of 222Rn daughters' radioactive transformations. Under unsteady conditions, the same behaviors reported under steady state conditions are found: deviation of the fluxes from the linear shape for 218Po, enhanced discrepancy in height of the radioactive transformation contributions for all the daughters. In addition, 222Rn and its progeny concentrations decrease due to the rapid growth of the CBL. The analysis emphasizes the crucial role of turbulent transport in the behavior of 222Rn n morning concentrations, in particular the ventilation at the top of the boundary layer that leads to the dilution of 222Rn by mixing with radon low concentration air.

scholarly journals Hydromorphological restoration stimulates river ecosystem metabolism

2016 ◽  
Author(s):  
Benjamin Kupilas ◽  
Daniel Hering ◽  
Armin W. Lorenz ◽  
Christoph Knuth ◽  
Björn Gücker
Keyword(s):  
Open Channel ◽  
Ecosystem Respiration ◽  
Gross Primary Production ◽  
Ecosystem Metabolism ◽  
Ecosystem Structure ◽  
Third Order ◽  
Goods And Services ◽  
Ecosystem Structure And Functioning ◽  
The One ◽  
Substantial Effort

Abstract. Both, ecosystem structure and functioning determine ecosystem status and are important for the provision of goods and services to society. However, there is a paucity of research that couples functional measures with assessments of ecosystem structure. In mid-sized and large rivers, effects of restoration on key ecosystem processes, such as ecosystem metabolism, have rarely been addressed and remain poorly understood. We compared three reaches of the third-order, gravel-bed river Ruhr in Germany: two reaches restored with moderate (R1) and substantial effort (R2) and one upstream degraded reach (D). Hydromorphology, habitat composition and hydrodynamics were assessed. We estimated gross primary production (GPP) and ecosystem respiration (ER) using the one-station open-channel diel dissolved oxygen change method over a 50-day period at the end of each reach. Values for hydromorphological variables increased with restoration intensity (D 

scholarly journals Spatial Distribution and Problems in the Interpretation of Radiocarbon Dates of the Sungir Site, Russia

Radiocarbon ◽  
2019 ◽  
Vol 61 (4) ◽  
pp. e1-e15
Author(s):  
Taisiya Soldatova
Keyword(s):  
Horizontal Distribution ◽  
Upper Paleolithic ◽  
Russian Plain ◽  
Cultural Layer ◽  
Human Occupation ◽  
Radiocarbon Dates ◽  
Lithic Industry ◽  
The One ◽  
The Vertical Distribution

ABSTRACTThe Upper Paleolithic open-air site Sungir is located in the central Russian Plain. The blank production of the lithic industry is characterized by parallel reduction with flakes being the main blank type. The tool assemblage has two components: archaic types (Mousterian-like) on the one hand and Upper Paleolithic types on the other. The available data does not allow for a confident determination of the chronological position of the Sungir site, nor does it enable researchers to distinguish different stages of human occupation. The horizontal distribution of the dated samples demonstrates the almost complete absence of radiocarbon (14C) dates for household features identified at the site (fireplaces, fire and ritual pits, large accumulations of bones, etc.). In addition, the vertical distribution of 14C dates in the rather thick cultural layer points to the exposure of the site to solifluction.

Coupling Human - Earth Systems for Sustainability

2021 ◽  
Author(s):  
Bojie Fu
Keyword(s):  
Sustainable Development ◽  
Ecosystem Services ◽  
Social Systems ◽  
Research Priorities ◽  
Research Centre ◽  
Chinese Government ◽  
Ecosystem Structure ◽  
Earth Systems ◽  
The World ◽  
The One

&lt;p&gt;&lt;strong&gt;Coupling Human - Earth Systems for Sustainability&lt;/strong&gt;&lt;/p&gt;&lt;p&gt;&lt;strong&gt;&amp;#160;&lt;/strong&gt;&lt;strong&gt;Bojie Fu&lt;/strong&gt;&lt;/p&gt;&lt;p&gt;(State Key Lab of Urban and Regional Ecology, Research Centre for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China&lt;/p&gt;&lt;p&gt;Faculty of Geographical Science, Beijing Normal University, Beijing, China)&lt;/p&gt;&lt;p&gt;Abstract: Human influence on the natural environment has intensified, and the earth has entered the stage of Anthropocene. Earth surface processes are gradually dominated by human behavior, resulting in numerous resources, disasters and ecological problems. The ecosystem services of 60% are degradation in the world. The one of major challenges facing the world&amp;#8217;s people are meeting the needs of people today and in the future, and sustaining atmosphere, water, soil and biological products which provided by ecosystems. We will present how to coupling human-earth system and propose the research priorities. They are: (1) Integrating research on multiple processes of water, soil, air and ecosystem; (2) Cascades of ecosystem structure, functions and services; (3) Feedback mechanisms of natural and social systems; (4) Data, models and simulation of sustainable development;(5) Mechanism, approach and policy of sustainable development.&lt;strong&gt; &lt;/strong&gt;Finally, a case study in the Loess plateau of China, an area suffered from severe soil erosion in the world was taken. The changes in four key ecosystem services including water regulation, soil conservation, carbon sequestration, and grain production were assessed and the trade off among the ecosystem services were analysed under the changing landscapes due to the Chinese government&amp;#8217;s implementation of the Grain to Green Program (GTGP). We found that ecosystem services convert significantly. The adaptive management strategy was discussed aiming on restoring and improving the sustainable capability of ecosystems providing services, based on the understanding of structure, function and dynamics of ecosystem.&lt;/p&gt;

scholarly journals Understanding the performance of the FLake model over two African Great Lakes

2014 ◽  
Vol 7 (1) ◽  
pp. 317-337 ◽  
Author(s):  
W. Thiery ◽  
A. Martynov ◽  
F. Darchambeau ◽  
J.-P. Descy ◽  
P.-D. Plisnier ◽  
...  
Keyword(s):  
Mixed Layer ◽  
Prediction Models ◽  
Mixed Layer Depth ◽  
Wave Radiation ◽  
Contrast Model ◽  
Near Surface ◽  
Lake Kivu ◽  
Tropical Conditions ◽  
Meteorological Observations ◽  
The One

Abstract. The ability of the one-dimensional lake model FLake to represent the mixolimnion temperatures for tropical conditions was tested for three locations in East Africa: Lake Kivu and Lake Tanganyika's northern and southern basins. Meteorological observations from surrounding automatic weather stations were corrected and used to drive FLake, whereas a comprehensive set of water temperature profiles served to evaluate the model at each site. Careful forcing data correction and model configuration made it possible to reproduce the observed mixed layer seasonality at Lake Kivu and Lake Tanganyika (northern and southern basins), with correct representation of both the mixed layer depth and water temperatures. At Lake Kivu, mixolimnion temperatures predicted by FLake were found to be sensitive both to minimal variations in the external parameters and to small changes in the meteorological driving data, in particular wind velocity. In each case, small modifications may lead to a regime switch, from the correctly represented seasonal mixed layer deepening to either completely mixed or permanently stratified conditions from ~ 10 m downwards. In contrast, model temperatures were found to be robust close to the surface, with acceptable predictions of near-surface water temperatures even when the seasonal mixing regime is not reproduced. FLake can thus be a suitable tool to parameterise tropical lake water surface temperatures within atmospheric prediction models. Finally, FLake was used to attribute the seasonal mixing cycle at Lake Kivu to variations in the near-surface meteorological conditions. It was found that the annual mixing down to 60 m during the main dry season is primarily due to enhanced lake evaporation and secondarily to the decreased incoming long wave radiation, both causing a significant heat loss from the lake surface and associated mixolimnion cooling.

scholarly journals Vertical distribution and aggregation patterns of krill (Crustacea: Euphausiacea) in the Bay of Biscay: interannual and seasonal variability

2019 ◽  
Vol 97 (7) ◽  
pp. 619-630 ◽  
Author(s):  
M. Peña ◽  
R. González-Quirós ◽  
I. Munuera-Fernández ◽  
F. González ◽  
S. Romero-Romero ◽  
...  
Keyword(s):  
Vertical Distribution ◽  
Vertical Migration ◽  
Seasonal Variations ◽  
Seasonal Variability ◽  
Shelf Area ◽  
Bay Of Biscay ◽  
Acoustic Data ◽  
Epipelagic Zone ◽  
Acoustic Recording ◽  
The Vertical Distribution

Studies of krill (Crustacea: Euphausiacea) in oceanic waters of the Bay of Biscay are scarce and restricted to the epipelagic zone, overlooking vertical dynamics such as diurnal vertical migration (DVM). There is a growing interest in acoustically evaluating the biomass of krill in this area, but this requires a good knowledge of its vertical dynamics and aggregation patterns. In this work we employed acoustic data and net samples from two consecutive annual surveys covering a wide off-shelf area of the Bay of Biscay (JUVENA surveys of 2013 and 2014) and four seasonal surveys covering slope and oceanic waters in the Cantabrian Sea (SCAPA surveys of 2015). Vertical dynamics of krill were analyzed in the frame of the environmental seascape. High interannual and seasonal variations in the vertical distribution and aggregation patterns (small swarms, dense aggregations, or loose layers) of krill were observed. The vertical distribution covaried with dissolved oxygen and salinity. According to our findings, the best season to acoustically evaluate krill in the Bay of Biscay is spring, with the bulk of the biomass located above 600 m depth. Moreover, extending the acoustic recording beyond the epipelagic zone is mandatory for any season.

scholarly journals Impact of Variations in Upper-Level Shear on Simulated Supercells

2017 ◽  
Vol 145 (7) ◽  
pp. 2659-2681 ◽  
Author(s):  
Robert A. Warren ◽  
Harald Richter ◽  
Hamish A. Ramsay ◽  
Steven T. Siems ◽  
Michael J. Manton
Keyword(s):  
Mixed Layer Depth ◽  
Vertical Wind Shear ◽  
Cold Pool ◽  
Slight Reduction ◽  
Upper Troposphere ◽  
Surface Precipitation ◽  
Storm Intensity ◽  
Upper Level ◽  
High Precipitation ◽  
The Vertical Distribution

It has previously been suggested, based on limited observations, that vertical wind shear in the upper troposphere is a key control on supercell morphology, with the low-precipitation, high-precipitation, and classic archetypes favored under strong, weak, and moderate shear, respectively. The idea is that, with increasing upper-level shear (ULS), hydrometeors are transported farther from the updraft by stronger storm-relative anvil-level winds, limiting their growth and thereby reducing precipitation intensity. The present study represents the first attempt to test this hypothesis, using idealized simulations of supercells performed across a range of 6–12-km shear profiles. Contrary to expectations, there is a significant increase in surface precipitation and an associated strengthening of outflow winds as ULS magnitude is increased from 0 to 20 m s−1. These changes result from an increase in storm motion, which drives stronger low-level inflow, a wider updraft, and enhanced condensation. A further increase in ULS magnitude to 30 m s−1 promotes a slight reduction in storm intensity associated with surging rear-flank outflow. However, this transition in behavior is found to be sensitive to other factors that influence cold-pool strength, such as mixed-layer depth and model microphysics. Variations in the vertical distribution and direction of ULS are also considered, but are found to have a much smaller impact on storm intensity than variations in ULS magnitude. Suggestions for the disparity between the current results and the aforementioned observations are offered and the need for further research on supercell morphology—in particular, simulations in drier environments—is emphasized.

Efficient and robust estimation for the one-sided stable distribution of index

2004 ◽  
Vol 66 (3) ◽  
pp. 251-257 ◽  
Author(s):  
Panagiotis Besbeas ◽  
Byron J.T. Morgan
Keyword(s):  
Robust Estimation ◽  
Stable Distribution ◽  
The One
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