scholarly journals Temporal variations of zooplankton biomass in the Ligurian Sea inferred from long time series of ADCP data

Ocean Science ◽  
2014 ◽  
Vol 10 (1) ◽  
pp. 93-105 ◽  
Author(s):  
R. Bozzano ◽  
E. Fanelli ◽  
S. Pensieri ◽  
P. Picco ◽  
M. E. Schiano
Keyword(s):  
Time Series ◽  
Acoustic Doppler Current Profiler ◽  
Temporal Variations ◽  
Zooplankton Biomass ◽  
Mesopelagic Fish ◽  
Ligurian Sea ◽  
Time Frequency ◽  
Backscattering Strength ◽  
Current Profiler ◽  
Long Time

Abstract. Three years of 300 kHz acoustic doppler current profiler data collected in the central Ligurian Sea are analysed to investigate the variability of the zooplankton biomass and the diel vertical migration in the upper thermocline. After a pre-processing phase aimed at avoiding the slant range attenuation, hourly volume backscattering strength time series are obtained. Despite the lack of concurrent net samples collection, different migration patterns are identified and their temporal variability examined by means of time–frequency analysis. The effect of changes in the environmental condition is also investigated. The highest zooplankton biomasses are observed in April–May just after the peak of surface primary production in March–April. The main migration pattern found here points to a "nocturnal" migration, with zooplankton organisms occurring deeper in the water column during the day and shallower at night. Also, twilight migration is highlighted during this study. The largest migrations are recorded in November–December, corresponding to lowest backscattering strength values and they are likely attributable to larger and more active organisms (i.e. euphausiids and mesopelagic fish). The results suggest further applications of the available historical acoustic doppler current profiler time series.

scholarly journals Temporal variations of zooplankton biomass in the Ligurian Sea inferred from long time series of ADCP data

2013 ◽  
Vol 10 (4) ◽  
pp. 1367-1404 ◽  
Author(s):  
R. Bozzano ◽  
E. Fanelli ◽  
S. Pensieri ◽  
P. Picco ◽  
M. E. Schiano
Keyword(s):  
Time Series ◽  
Temporal Variations ◽  
Zooplankton Biomass ◽  
Mesopelagic Fish ◽  
Ligurian Sea ◽  
Time Frequency ◽  
Diel Vertical Migrations ◽  
Backscattering Strength ◽  
Long Time ◽  
Adcp Data

Abstract. Three years of 300 kHz ADCP data collected in the central Ligurian Sea are analyzed to investigate the variability of the zooplankton biomass and the Diel Vertical Migrations (DVM) in the upper thermocline. After a pre-processing aimed at avoiding the slant range attenuation, hourly volume backscattering strength time series are obtained. Despite the lack of concurrent net samples collection, different migration patterns are identified and their temporal variability examined by means of time-frequency analysis. The effect of changes in the environmental condition is also investigated. Highest zooplankton biomasses are observed in April–May just after the peak of surface primary production in March–April. The main migration pattern points to a "nocturnal" migration with zooplankton organisms occurring deeper in the water column during the day and shallower at night. Also twilight migration is highlighted during this study. The largest migrations are recorded in November–December, corresponding to lowest backscattering strength values and are likely attributable to larger and more active organisms (i.e. euphausiids and mesopelagic fish). The results suggest further applications of the historical ADCP time series available.

scholarly journals Acoustic and optical methods to infer water transparency at Time Series Station Spiekeroog, Wadden Sea

Ocean Science ◽  
2016 ◽  
Vol 12 (6) ◽  
pp. 1155-1163 ◽  
Author(s):  
Anne-Christin Schulz ◽  
Thomas H. Badewien ◽  
Shungudzemwoyo P. Garaba ◽  
Oliver Zielinski
Keyword(s):  
Time Series ◽  
Wadden Sea ◽  
Acoustic Doppler Current Profiler ◽  
Water Transparency ◽  
Optical Observations ◽  
Optical Methods ◽  
Acoustic Measurements ◽  
Data Set ◽  
Backscatter Signal ◽  
Current Profiler

Abstract. Water transparency is a primary indicator of optical water quality that is driven by suspended particulate and dissolved material. A data set from the operational Time Series Station Spiekeroog located at a tidal inlet of the Wadden Sea was used to perform (i) an inter-comparison of observations related to water transparency, (ii) correlation tests among these measured parameters, and (iii) to explore the utility of both acoustic and optical tools in monitoring water transparency. An Acoustic Doppler Current Profiler was used to derive the backscatter signal in the water column. Optical observations were collected using above-water hyperspectral radiometers and a submerged turbidity metre. Bio-fouling on the turbidity sensors optical windows resulted in measurement drift and abnormal values during quality control steps. We observed significant correlations between turbidity collected by the submerged metre and that derived from above-water radiometer observations. Turbidity from these sensors was also associated with the backscatter signal derived from the acoustic measurements. These findings suggest that both optical and acoustic measurements can be reasonable proxies of water transparency with the potential to mitigate gaps and increase data quality in long-time observation of marine environments.

Trade-offs between deep (magmatic) and shallow (hydrological) forcings on volcanic unrest at La Soufrière de Guadeloupe (Lesser Antilles)

2021 ◽  
Author(s):  
David Jessop ◽  
Roberto Moretti ◽  
Séverine Moune ◽  
Vincent Robert
Keyword(s):  
Time Series ◽  
Hydrothermal System ◽  
Temporal Variations ◽  
Temperature Record ◽  
Trade Offs ◽  
External Forcings ◽  
Seismic Swarms ◽  
Long Time ◽  
Deep Activity

<p>Fumarolic gas composition and temperature record deep processes that generate and transfer heat and mass towards the surface.  These processes are a result of the emplacement, degassing and cooling of magma and the overturning of the above hydrothermal system.  A reasonable expectation, and too often an unproved assumption, is that fumarole temperatures and the deep heat sources vary on similar timescales.  Yet signals from deep and shallow processes have vastly different temporal variations.  This indicates that signals arising from deep activity may be masked or modified by intervening hydrothermal processes, such as fluid-groundrock reactions in which secondary minerals play a major role.  Clearly, this complicates the interpretation of the signals such as the joint variation of fumarole vent temperature and geochemical ratios in terms of what is occurring at depth.  So what do the differences between the timescales governing deep and shallow processes tell us about the intervening transport mechanisms?</p><p>At the volcanic dome of La Soufrière de Guadeloupe, the Observatoire Volcanologique et Sismologique de la Guadeloupe has performed weekly-to-monthly in-situ vent gas sampling over many years.  These analyses reliably track several geochemical species ratios over time, which provide important information about the evolution of deep processes.  Vent temperature is measured as part of the in-situ sampling, giving a long time series of these measurements.  Here, we look to exploit the temporal variations in these data to establish the common processes, and also to determine why these signals differ.  By fitting sinusoids to the gas-ratio time series we find that several of the deep signals are strongly sinusoidal.  For example, the He/CH<sub>4</sub> and CO<sub>2</sub>/CH<sub>4</sub> ratios, which involve conservative components and mark the injection of deep and hot magmatic fluids, oscillate on a timescale close to 3 years. We also analyse the frequency content of the temperature measurements since 2011 and find that such long signals are not seen.  This may be due to internal buffering by the hydrothermal system, but other external forcings are also present.  From these data we build up a more informed model of the heat-and-mass supply chain from depth to the surface.  This will potentially allow us to predict future unrest (e.g. thermal crises, seismic swarms), and distinguish between sources of unrest.</p>

scholarly journals Seiche excitation in a highly stratified fjord of southern Chile: the Reloncaví fjord

Ocean Science ◽  
2017 ◽  
Vol 13 (1) ◽  
pp. 145-160 ◽  
Author(s):  
Manuel I. Castillo ◽  
Oscar Pizarro ◽  
Nadin Ramírez ◽  
Mario Cáceres
Keyword(s):  
Time Series ◽  
Sea Level ◽  
Low Frequency ◽  
Phase Speed ◽  
Acoustic Doppler Current Profiler ◽  
Southern Chile ◽  
Density Profiles ◽  
Level Data ◽  
Spectral Peaks ◽  
Current Profiler

Abstract. We describe a seiche process based on current, temperature, and sea-level data obtained from the Reloncaví fjord (41.6° S, 72.5° W) in southern Chile. We combined 4 months of acoustic Doppler current profiler (ADCP) data with sea-level, temperature, and wind time series to analyze the dynamics of low-frequency (periods > 1 day) internal oscillations in the fjord. Additionally, seasonal conductivity, temperature, and depth (CTD) data from 19 along-fjord stations were used to characterize the seasonality of the density field. The density profiles were used to estimate the internal long-wave phase speed (c) using two approximations: (1) a simple reduced gravity model (RGM) and (2) a continuously stratified model (CSM). No major seasonal changes in c were observed using either approximation (e.g., the CSM yielded 0.73 < c < 0.87 m s−1 for mode 1). The natural internal periods (TN) were estimated using Merian's formula for a simple fjord-like basin and the above phase speeds. Estimated values of TN varied between 2.9 and 3.5 days and were highly consistent with spectral peaks observed in the along-fjord currents and temperature time series. We conclude that these oscillations were forced by the wind stress, despite the moderate wind energy. Wind conditions at the end of winter gave us an excellent opportunity to explore the damping process. The observed damping time (Td) was relatively long (Td =  9.1 days).

scholarly journals Morphodynamic change analysis of bedforms in the Lower Orinoco River, Venezuela

2018 ◽  
Vol 377 ◽  
pp. 41-50 ◽  
Author(s):  
Santiago Paul Yepez ◽  
Alain Laraque ◽  
Carlo Gualtieri ◽  
Frédéric Christophoul ◽  
Claudio Marchan ◽  
...  
Keyword(s):  
Time Series ◽  
Hydrological Regime ◽  
Acoustic Doppler Current Profiler ◽  
Dual Frequency ◽  
Mean Flow ◽  
Change Analysis ◽  
Sand Waves ◽  
Orinoco River ◽  
Current Profiler ◽  
The Right

Abstract. The Orinoco River has the third largest discharge in the world, with an annual mean flow of 37 600 m3 s−1 at its outlet to the Atlantic Ocean. Due to the presence of the Guiana Shield on the right bank, the lower reach of the Orinoco has a plan form characterized by contraction and expansion zones. Typical 1–1.5 km wide narrow reaches are followed by 7–8 km wide reaches. A complex pattern of bed aggradation and degradation processes takes place during the annual hydrological regime. A series of Acoustic Doppler Current Profiler (ADCP) transects were collected on an expansion channel in the Orinoco River, specifically over a fluvial island, representative of the lower Orinoco. In this study, temporal series of bathymetric cartography obtained by ADCP profiles combined with Differential Global Position System (DGPS) measurements (with dual-frequency), were used to recover the local displacement of bed forms in this island. The principal aims of this analysis were: (1) to understand the dynamics and evolution of sand waves and bars at this section and (2) to quantify the volume (erosion vs. accretion) of a mid-channel bar with dunes by applying DEM of Difference (DoD) maps on time series of bathymetric data. This required sampling with ADCP transects during the months of: May 2016; November 2016 and April 2017. Each bathymetric transect was measured twice, 1 day apart and on the same trajectory obtained by a GPS receptor. The spatial analysis of these ADCP transects is presented as a novel tool in the acquisition of time series of bathymetry for a relatively deep section (∼20 m) and under variable flow conditions.

Detecting and Correcting Biases in Long-Term Ocean Observatory Time Series: Case Study on Current Directions Estimated From Acoustic Doppler Current Profiler Data

2016 ◽  
Vol 50 (3) ◽  
pp. 109-113
Author(s):  
Michael G. Morley ◽  
Marlene A. Jeffries ◽  
Steven F. Mihály ◽  
Reyna Jenkyns ◽  
Ben R. Biffard
Keyword(s):  
Time Series ◽  
Acoustic Doppler Current Profiler ◽  
Lessons Learned ◽  
Ocean Current ◽  
Data Types ◽  
Current Profiler ◽  
Future Data ◽  
Multiple Deployments

AbstractOcean Networks Canada (ONC) operates the NEPTUNE and VENUS cabled ocean observatories to collect continuous data on physical, chemical, biological, and geological ocean conditions over multiyear time periods. Researchers can download real-time and historical data from a large variety of instruments to study complex earth and ocean processes from their home laboratories. Ensuring that the users are receiving the most accurate data is a high priority at ONC, requiring QAQC (quality assurance and quality control) procedures to be developed for a variety of data types (Abeysirigunawardena et al., 2015). Acquiring long-term time series of oceanographic data from remote locations on the seafloor presents significant challenges from a QAQC perspective. In order to identify and study important scientific events and trends, data consolidated from multiple deployments and instruments need to be self-consistent and free of biases due to changes to instrument configurations, calibrations, metadata, biofouling, or a degradation in instrument performance. As a case study, this paper describes efforts at ONC to identify and correct systematic biases in ocean current directions measured by ADCPs (acoustic Doppler current profilers), as well as the lessons learned to improve future data quality.

Temporal variations of CO2 efflux continuous monitoring at the summit cone of Teide volcano (Tenerife, Canary Islands) during the period1999-2021

2021 ◽  
Author(s):  
Germán D. Padilla ◽  
Nemesio M. Perez ◽  
Pedro A. Hernández ◽  
Eleazar Padrón ◽  
José Barrancos ◽  
...  
Keyword(s):  
Time Series ◽  
Canary Islands ◽  
Seismic Activity ◽  
Temporal Variations ◽  
Hydrothermal Systems ◽  
Co2 Efflux ◽  
Time Frequency ◽  
Tenerife Island ◽  
Efflux Time ◽  
Teide Volcano

&lt;p&gt;Tenerife Island (2034 km&lt;sup&gt;2&lt;/sup&gt;), the largest of the Canarian archipelago, is characterized by three main volcano-tectonic axes: the NS, NE and NW rifts and a central caldera, Las Ca&amp;#241;adas, hosting the twin stratovolcanoes Pico Viejo and Teide. Although Teide volcano hosts a weak fumarolic system, volcanic gas emissions from the summit cone consist mostly of diffuse CO&lt;sub&gt;2&lt;/sub&gt; degassing. The first continuous automatic geochemical station in Canary Islands was installed at the south-eastern foot of summit cone of Teide volcano in 1999, with the aim of improving the volcanic monitoring system and providing a multidisciplinary approach to the surveillance program of Teide volcano. The 1999-2020 time series shows diffuse CO&lt;sub&gt;2&lt;/sub&gt; emission values ranging between 0 and 62.8 kgm&lt;sup&gt;-2&lt;/sup&gt;d&lt;sup&gt;-1&lt;/sup&gt;, with a mean value of 4.3 kgm&lt;sup&gt;-2&lt;/sup&gt;d&lt;sup&gt;-1&lt;/sup&gt;. Inspection of the CO&lt;sub&gt;2&lt;/sub&gt; efflux time series shows significant temporal variations with anomalous values of more than 20 kgm&lt;sup&gt;-2&lt;/sup&gt;d&lt;sup&gt;-1&lt;/sup&gt; centred at years 2000, 2003, 2005, 2007, 2008, 2012, 2015 and 2016, always before a significant increase in the seismic activity beneath Tenerife Island. With the aim to filter out environmental variables, a multiple regression analysis (MRA) was applied to the first 12 years of the diffuse CO&lt;sub&gt;2&lt;/sub&gt; flux time series (1999-2011), recorder on an hourly basis by the station, and we found that soil temperature, soil water content, wind speed and barometric pressure explained 16.7% of variability. The comparison between filtered CO&lt;sub&gt;2&lt;/sub&gt; efflux (continuous, hourly, automated station) versus the temporal evolution of diffuse CO&lt;sub&gt;2&lt;/sub&gt; emission estimated by ground CO&lt;sub&gt;2&lt;/sub&gt; efflux surveys of summit cone of Teide (during summer season on an area of around 0.11 km&lt;sup&gt;2&lt;/sup&gt;) for the period 1999-2011 (P&amp;#233;rez et al., 2013), shows a nearly coincident marked peak in December 2001 and a similar shaped evolution from each sampling type as the increase from ~2005 to 2009 and the subsequent decrease from ~2009 to 2011, reaching maximum values of 161.6 and 179.9 t d&lt;sup&gt;-1&lt;/sup&gt;, respectively. Seismic activity displayed as of monthly earthquakes (M&gt;1) occurring in and around Tenerife island is well correlated with diffuse CO&lt;sub&gt;2&lt;/sub&gt; efflux relevant peaks. In average, the seismicity recorded during the study period was mainly preceded by geochemical anomalies of the registered surface CO&lt;sub&gt;2&lt;/sub&gt; efflux by about one year. After we analysed the CO&lt;sub&gt;2&lt;/sub&gt; efflux time series by using the Continuous Wavelet Transform (Ricker wavelet) to detect relevant time-frequency patterns in the signal, we found at low frequencies quasi-periodical oscillations with periods of 3-4 years, which might reflect the internal dynamics of the magmatic-hydrothermal system. Moreover, during the intervals of highest levels of CO&lt;sub&gt;2&lt;/sub&gt; efflux, the analysis evidenced also oscillations with a period of about 6 months during the interval 1999-2011. Our study reveals that continuous geochemical monitoring data is representative of the same trends in flux that are quantitatively captured by annual surveys, and provides the basis for accurate determination of background values. This combined approach offers a useful template for application to other volcanic systems for the purposes of constructing quantitative dynamic models of hydrothermal systems and identifying processes at depth in near-real-time.&lt;/p&gt;

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