scholarly journals Turbulence and hypoxia contribute to dense zooplankton scattering layers in Patagonian Fjord System

2017 ◽  
Author(s):  
Iván Pérez-Santos ◽  
Leonardo Castro ◽  
Nicolás Mayorga ◽  
Lauren Ross ◽  
Luis Cubillos ◽  
...  
Keyword(s):  
Water Column ◽  
Vertical Mixing ◽  
Acoustic Doppler Current Profiler ◽  
Eddy Diffusivity ◽  
Future Research ◽  
Dense Layer ◽  
The North ◽  
Diel Vertical Migrations ◽  
And Migration

Abstract. The Puyuhuapi Fjord is an atypical fjord, with two mouths, located in northern Patagonia (44.7° S). One mouth lies to the south, close to the Pacific Ocean, whilst the second connects with the Jacaf Channel to the north where a shallow sill inhibits deep water ventilation contributing to the hypoxic conditions below ~ 100 m depth. Acoustic Doppler Current Profiler moorings, scientific echo sounder transects, and in-situ abundance measurements were used to study zooplankton assemblages and migration patterns along Puyuhuapi Fjord and Jacaf Channel. The acoustic records and in-situ zooplankton data revealed diel vertical migrations of siphonophores, euphausiids and copepods. A dense layer of zooplankton was observed along Puyuhuapi Fjord between the surface and the top of the hypoxic layer (~ 100 m), which acted as a physic-chemical barrier to the distribution and migration of the zooplankton. Aggregations of zooplankton and fishes were generally more abundant around the sill in Jacaf Channel than anywhere within Puyuhuapi Fjord. In particular, zooplanktons were distributed throughout the entire water column to ~ 200 m depth, with no evidence of a hypoxic boundary. Turbulence measurements taken near the sill in the Jacaf Channel indicated high turbulent kinetic energy dissipation rates (ε ~ 10−4 W kg−1) and vertical diapycnal eddy diffusivity (Kρ ~ 10−2 m2 s−1) values. These elevated vertical mixing ensures that the water column well oxygenated and promotes zooplanktons aggregation. The sill region represents a major topographic contrast between the two fjords, and we suggest that this is an feature for future research on carbon export and fluxes in these fjords.

scholarly journals Turbulence and hypoxia contribute to dense biological scattering layers in a Patagonian fjord system

Ocean Science ◽  
2018 ◽  
Vol 14 (5) ◽  
pp. 1185-1206 ◽  
Author(s):  
Iván Pérez-Santos ◽  
Leonardo Castro ◽  
Lauren Ross ◽  
Edwin Niklitschek ◽  
Nicolás Mayorga ◽  
...  
Keyword(s):  
Kinetic Energy ◽  
Water Column ◽  
Turbulent Kinetic Energy ◽  
Tidal Flow ◽  
Vertical Mixing ◽  
Acoustic Doppler Current Profiler ◽  
Marine Species ◽  
Eddy Diffusivity ◽  
Diel Vertical Migrations

Abstract. The aggregation of plankton species along fjords can be linked to physical properties and processes such as stratification, turbulence and oxygen concentration. The goal of this study is to determine how water column properties and turbulent mixing affect the horizontal and vertical distributions of macrozooplankton along the only northern Patagonian fjord known to date, where hypoxic conditions occur in the water column. Acoustic Doppler current profiler moorings, scientific echo-sounder transects and in situ plankton abundance measurements were used to study macrozooplankton assemblages and migration patterns along Puyuhuapi Fjord and Jacaf Channel in Chilean Patagonia. The dissipation of turbulent kinetic energy was quantified through vertical microstructure profiles collected throughout time in areas with high macrozooplankton concentrations. The acoustic records and in situ macrozooplankton data revealed diel vertical migrations (DVM) of siphonophores, chaetognaths and euphausiids. In particular, a dense biological backscattering layer was observed along Puyuhuapi Fjord between the surface and the top of the hypoxic boundary layer (∼100 m), which limited the vertical distribution of most macrozooplankton and their DVM, generating a significant reduction of habitat. Aggregations of macrozooplankton and fishes were most abundant around a submarine sill in Jacaf Channel. In this location macrozooplankton were distributed throughout the water column (0 to ∼200 m), with no evidence of a hypoxic boundary due to the intense mixing near the sill. In particular, turbulence measurements taken near the sill indicated high dissipation rates of turbulent kinetic energy (ε∼10-5 W kg−1) and vertical diapycnal eddy diffusivity (Kρ∼10-3 m2 s−1). The elevated vertical mixing ensures that the water column is well oxygenated (3–6 mL L−1, 60 %–80 % saturation), creating a suitable environment for macrozooplankton and fish aggregations. Turbulence induced by tidal flow over the sill apparently enhances the interchange of nutrients and oxygen concentrations with the surface layer, creating a productive environment for many marine species, where the prey–predator relationship might be favored.

scholarly journals A 900-year New England temperature reconstruction from <i>in situ</i> seasonally produced branched glycerol dialkyl glycerol tetraethers (brGDGTs)

2018 ◽  
Author(s):  
Daniel R. Miller ◽  
M. Helen Habicht ◽  
Benjamin A. Keisling ◽  
Isla S. Castañeda ◽  
Raymond S. Bradley
Keyword(s):  
New England ◽  
Water Column ◽  
Lacustrine Sediments ◽  
Temperature Reconstruction ◽  
Early Spring ◽  
Pollen Record ◽  
The North ◽  
The North Atlantic Oscillation ◽  
Glycerol Dialkyl Glycerol Tetraethers

Abstract. Paleotemperature reconstructions are essential for distinguishing anthropogenic climate change from natural variability. An emerging method in paleoclimatology is the use of branched glycerol dialkyl glycerol tetraethers (brGDGTs) in lacustrine sediments to reconstruct temperature, but their application is hindered by a limited understanding of their sources, seasonal production, and transport. We report seasonally resolved measurements of brGDGT production within the water column, in catchment soils and in a sediment sequence from a small, deep inland lake in Maine, USA. BrGDGT distributions in the water column are distinct from catchment soils but similar to the distributions in lake sediments, suggesting that (1) brGDGTs are produced within the lake and (2) this in situ production dominates the downcore sedimentary signal. Seasonally, depth-resolved measurements indicate that the dominant production of brGDGTs occurs in late fall/early spring and at intermediate depths (18–30 meters) in the water column. We apply these observations to help interpret a 900-year-long brGDGT-based temperature reconstruction and find that it shows similar trends to a pollen record from the same site and to regional and global syntheses of terrestrial temperatures over the last millennium. However, the record also shows higher-frequency variability than has previously been captured by such an archive in the Northeastern United States, potentially attributed to the North Atlantic Oscillation and volcanic/solar activity. This is the first brGDGT- based multi-centennial paleoreconstruction from this region and contributes to our understanding of the production and fate of brGDGTs in lacustrine systems.

scholarly journals Quantifying Suspended Sediment using Acoustic Doppler Current Profiler in Tidung Island Seawaters

2021 ◽  
Vol 29 (1) ◽  
Author(s):  
Henry Munandar Manik ◽  
Randi Firdaus
Keyword(s):  
Water Column ◽  
Suspended Sediment ◽  
Suspended Solids ◽  
Acoustic Doppler Current Profiler ◽  
Sediment Concentration ◽  
In Situ Measurement ◽  
Ocean Current ◽  
Echo Intensity ◽  
Current Profiler

Tidung Island, located near Jakarta Bay, is a tourism and conservation area. It is necessary to keep these seawaters unpolluted. To calculate the level of pollution, it is necessary to know the sediment concentration. Quantifying concentration suspended sediment is important for knowledge of sediment transport. Researchers usually use water sample analysis and optical method for quantifying suspended sediment in seawater. Less accuracies of these methods are due to under sample of seawater and the existence of biological fouling. One promising method to measure concentration of suspended sediment is using Acoustic Doppler Current Profiler (ADCP). ADCP is usually used by oceanographer and hydrographer to measure ocean current. In this research, ADCP with 300 kHz operating frequency was used effectively to measure suspended sediment concentration (SSC) and ocean current simultaneously. The echo intensity received from suspended sediment was computed using sonar equations to quantify SSC. The empirical equation between echo intensity and SSC was found. The SSC value obtained by ADCP was also compared with in situ measurement. The result showed that quantified SSC value obtained by ADCP was nearly equal with SSC obtained from in situ measurement with coefficient correlation of 0.98. The high concentration ranged from 55 mg/L to 80 mg/L at the surface layer to a depth 12 m, moderate concentration ranged from 45 mg/L to 55 mg/L at a depth 12 m to 40 m, and low concentration less than 45 mg/L at a depth greater than 40 m. The distribution of SSC was correlated with ocean current condition. In small currents, suspended solids will settle faster so that the concentration in the water column will decrease. Conversely, if the velocity is high, suspended solids will continue to float carried by the current in the water column so that the concentration is high.

scholarly journals Development of CarbonTracker Europe-CH<sub>4</sub> – Part 2: global methane emission estimates and their evaluation for 2000–2012

2016 ◽  
Author(s):  
Aki Tsuruta ◽  
Tuula Aalto ◽  
Leif Backman ◽  
Janne Hakkarainen ◽  
Ingrid T. van der Laan-Luijkx ◽  
...  
Keyword(s):  
North American ◽  
Transport Model ◽  
Vertical Mixing ◽  
Total Carbon ◽  
In Situ Observation ◽  
Convection Scheme ◽  
Temperate Region ◽  
Northern Latitude ◽  
The North

Abstract. Gobal methane emissions were estimated for 2000–2012 using the CarbonTracker Europe-CH4 (CTE-CH4) data assimilation system. In CTE-CH4, the anthropogenic and biosphere emissions of CH4 are simultaneously constrained by global atmospheric in-situ methane mole fraction observations. We use three configurations developed in Tsuruta et al. (2016) to assess the sensitivity of the CH4 flux estimates to (a) the number of unknown flux scaling factors to be optimized which in turn depends on the choice of underlying land-ecosystem map, and (b) on the parametrization of vertical mixing in the 30 atmospheric transport model TM5. The posterior emission estimates were evaluated by comparing simulations to surface in-situ observation sites, to profile observations made by aircraft, to dry air total column-averaged mole fractions (XCH4) observations from the Total Carbon Column Observing Network (TCCON), and to XCH4 retrievals from the Greenhouse gases Observing SATellite (GOSAT). Our estimated posterior mean global total emissions during 2000–2012 are 516 ± 51 Tg CH4 yr−1, and emission estimates during 2007–2012 are 18 Tg CH4 yr−1 greater than those from 2001–2006, mainly driven by an 35 increase in emissions from the south America temperate region, the Asia temperate region and Asia tropics. The sensitivity of the flux estimates to the underlying ecosystem map was large for the Asia temperate region and Australia, but not significant in the northern latitude regions, i.e. the north American boreal region, the north American temperate region and Europe. Instead, the posterior estimates for the northern latitude regions show larger sensitivity to the choice of convection scheme in TM5. The Gregory et al. (2000) mixing scheme with faster interhemispheric exchange leads to higher estimated CH4 emissions at northern latitudes, and lower emissions in southern latitudes, compared to the estimates using Tiedtke (1989) convection scheme. Our evaluation with non-assimilated observations showed that posterior mole fractions were better matched with the 5 observations when Gregory et al. (2000) convection scheme was used.

scholarly journals On the Variability of the Circulation and Water Mass Properties in the Eastern Levantine Sea between September 2016–August 2017

Water ◽  
2019 ◽  
Vol 11 (9) ◽  
pp. 1741 ◽  
Author(s):  
Mauri ◽  
Sitz ◽  
Gerin ◽  
Poulain ◽  
Hayes ◽  
...  
Keyword(s):  
High Salinity ◽  
Autonomous Systems ◽  
Vertical Mixing ◽  
The North ◽  
Levantine Sea ◽  
Surface Circulation ◽  
Basin Scale ◽  
Geographical Position ◽  
Surface Drifters

The surface circulation and the thermohaline properties of the water masses of the eastern Levantine Sea (Mediterranean Sea) were monitored with mobile autonomous systems (surface drifters and gliders) during the period September 2016–August 2017. The drifters provided data for more than a year and revealed complex circulation features at scales ranging from the basin scale to the sub-mesoscale. Three drifters were captured in a semi-permanent gyre (Cyprus Eddy) allowing a quantitative study of its kinematics. During the experiment, three gliders were operated, in two different periods: September to December 2016 and February to March 2017. The autonomous instruments crossed the prevailing sub-basin structures several times. The collected in-situ observations were analyzed and interpreted in concert with remote sensing products (sea surface temperature and altimetry). The evolution of some of the prevailing features confirmed the complexity of the circulation of the basin. The Cyprus Eddy is the most persistent anticyclone, moving its geographical position and sometimes merging with the North Shikmona Eddy in a bigger structure. The gliders sampled this wide anticyclonic feature revealing its vertical structure in the two different periods. In fall, in stratified conditions, a high salinity core is evident below the thermocline. The isopycnals are characterized by an upward bending over the high salinity lens and a downward bending below it, typical of an anticyclonic modewater eddy. In winter, the core disappears following the vertical mixing that, homogenizes the upper Cyprus Eddy water down to 300 m.

In-situ investigation of alkalinity - denitrification coupling in the sediment - water column interface

2020 ◽  
Author(s):  
Mona Norbisrath
Keyword(s):  
Water Column ◽  
German Bight ◽  
Anthropogenic Impacts ◽  
Binding Capacity ◽  
Quantitative Relationship ◽  
Terminal Electron Acceptor ◽  
The North ◽  
In Situ Investigation ◽  
In Situ Experiments

&lt;p&gt;&lt;strong&gt;Abstract: EGU 2020&lt;/strong&gt;&lt;/p&gt;&lt;p&gt;&lt;strong&gt;Session: BG4.1: Biogeochemistry of coastal seas and continental shelves (Helmuth Thomas)&lt;/strong&gt;&lt;/p&gt;&lt;p&gt;Mona Norbisrath&lt;sup&gt;1&lt;/sup&gt;, Kirstin D&amp;#228;hnke&lt;sup&gt;1&lt;/sup&gt;, Andreas Neumann&lt;sup&gt;1&lt;/sup&gt;, Justus van Beusekom&lt;sup&gt;1&lt;/sup&gt;, Nele Treblin&lt;sup&gt;1&lt;/sup&gt;, Bryce van Dam&lt;sup&gt;1&lt;/sup&gt;, Helmuth Thomas&lt;sup&gt;1&lt;/sup&gt;&lt;/p&gt;&lt;p&gt;&lt;sup&gt;1&lt;/sup&gt;Institute for Coastal Research, Helmholtz-Zentrum Geesthacht&lt;/p&gt;&lt;p&gt;Contact: [email protected]&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;&lt;strong&gt;In-situ investigation of alkalinity - denitrification coupling in the sediment - water column interface&lt;/strong&gt;&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;As a shallow shelf sea, the North Sea is very vulnerable to anthropogenic impacts like rising CO&lt;sub&gt;2&lt;/sub&gt; concentrations, increasing nutrient inflows and coincident oxygen loss.&lt;/p&gt;&lt;p&gt;Two important processes that determine the role of the coastal ocean as a net sink for anthropogenic CO&lt;sub&gt;2&lt;/sub&gt; are alkalinity and denitrification. Alkalinity, the acid binding capacity of the ocean, buffers natural and anthropogenic changes in the oceans&amp;#8217; CO&lt;sub&gt;2&lt;/sub&gt; and pH system. Denitrification, an anaerobic microbial process in which organic matter is respired, uses NO&lt;sub&gt;3&lt;/sub&gt;&lt;sup&gt;-&lt;/sup&gt; instead of O&lt;sub&gt;2&lt;/sub&gt; as a terminal electron acceptor. Denitrification reduces NO&lt;sub&gt;3&lt;/sub&gt;&lt;sup&gt;-&lt;/sup&gt; to N&lt;sub&gt;2&lt;/sub&gt; and in turn produces alkalinity.&lt;/p&gt;&lt;p&gt;Eutrophication, caused by leaching of excess fertilizer nutrients into coastal seas, leads to enhanced denitrification and therefore to enhanced alkalinity as well as an increased uptake of CO&lt;sub&gt;2&lt;/sub&gt;. However, the quantitative relationship between denitrification and alkalinity production and its control under changing environmental conditions is yet to be determined.&lt;/p&gt;&lt;p&gt;In the German Bight, denitrification is usually restricted to anoxic sediments. In this study, we therefore focus on in-situ experiments in the sediment - water column interface. Batch core incubations in combination with the isotope pairing technique (IPT) and labelled nitrate additions were used to detect denitrification and gauge its effect on alkalinity production during a cruise on RV Heincke (HE541) in September 2019 in the German Bight. To quantify denitrification, the production of all three N&lt;sub&gt;2&lt;/sub&gt; isotope species (&lt;sup&gt;28&lt;/sup&gt;N&lt;sub&gt;2&lt;/sub&gt;, &lt;sup&gt;29&lt;/sup&gt;N&lt;sub&gt;2&lt;/sub&gt; and &lt;sup&gt;30&lt;/sup&gt;N&lt;sub&gt;2&lt;/sub&gt;) is measured using a membrane inlet mass spectrometer (MIMS). We expect an increase of denitrification rates with nitrate concentrations and incubation times, and we will quantify benthic denitrification. We will further evaluate the assumption of concurrent increases in alkalinity production and will investigate the benthic-pelagic coupling of these processes. Investigating the in-situ interaction of metabolic alkalinity and denitrification will give an estimation of the alkalinity impact on the reduction of anthropogenic CO&lt;sub&gt;2&lt;/sub&gt; in the atmosphere.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;

scholarly journals Observations of Near-Surface Mixing Behind a Headland

2020 ◽  
Vol 8 (2) ◽  
pp. 68
Author(s):  
Preston Spicer ◽  
Kimberly Huguenard
Keyword(s):  
Vertical Mixing ◽  
Acoustic Doppler Current Profiler ◽  
Bottom Layer ◽  
Eddy Diffusivity ◽  
Vertical Shear ◽  
Small Island ◽  
Streamwise Vorticity ◽  
Near Surface ◽  
Surface Mixing ◽  
Complex Features

Field observations were collected near the mouth of the Bagaduce River, Maine, in order to understand how complex features affect the intratidal and lateral variability of turbulence and vertical mixing. The Bagaduce River is a low-inflow, macrotidal estuary that features tidal islands, tidal flats and sharp channel bends. Profiles of salinity, temperature, and turbulent kinetic energy dissipation (ε) were collected for a tidal cycle across the estuary with a microstructure profiler. Lateral distributions of current velocities were obtained with an acoustic doppler current profiler. Results showed intratidal asymmetries in bottom-generated vertical eddy diffusivity and viscosity, with larger values occurring on ebb (Kz: 10−2 m2; Az: 10−2 m2/s) compared to flood (Kz: 10−5 m2/s; Az: 10−4 m2/s). Bottom-generated mixing was moderated by the intrusion of stratified water on flood, which suppressed mixing. Elevated mixing (Kz: 10−3 m2; Az: 10−2.5 m2/s) occurred in the upper water column in the lee of a small island and was decoupled from the bottom layer. The near-surface mixing was a product of an eddy formed downstream of a headland, which tended to reinforce vertical shear by laterally straining streamwise velocities. These results are the first to show near-surface mixing caused by vertical vorticity induced by an eddy, rather than previously reported streamwise vorticity associated with lateral circulation.

scholarly journals Volumetric Mapping of Methane Concentrations at the Bush Hill Hydrocarbon Seep, Gulf of Mexico

2021 ◽  
Vol 9 ◽  
Author(s):  
William P. Meurer ◽  
John Blum ◽  
Greg Shipman
Keyword(s):  
Gulf Of Mexico ◽  
Water Column ◽  
Acoustic Doppler Current Profiler ◽  
Field Studies ◽  
Methane Seepage ◽  
Current Profiler ◽  
Methane Fluxes ◽  
Methane Concentrations

The role of methane as a green-house gas is widely recognized and has sparked considerable efforts to quantify the contribution from natural methane sources including submarine seeps. A variety of techniques and approaches have been directed at quantifying methane fluxes from seeps from just below the sediment water interface all the way to the ocean atmosphere interface. However, there have been no systematic efforts to characterize the amount and distribution of dissolved methane around seeps. This is critical to understanding the fate of methane released from seeps and its role in the submarine environment. Here we summarize the findings of two field studies of the Bush Hill mud volcano (540 m water depth) located in the Gulf of Mexico. The studies were carried out using buoyancy driven gliders equipped with methane sensors for near real time in situ detection. One glider was equipped with an Acoustic Doppler Current Profiler (ADCP) for simultaneous measurement of currents and methane concentrations. Elevated methane concentrations in the water column were measured as far away as 2 km from the seep source and to a height of about 100 m above the seep. Maximum observed concentrations were ∼400 nM near the seep source and decreased away steadily in all directions from the source. Weak and variable currents result in nearly radially symmetric dispersal of methane from the source. The persistent presence of significant methane concentrations in the water column points to a persistent methane seepage at the seafloor, that has implications for helping stabilize exposed methane hydrates. Elevated methane concentrations in the water column, at considerable distances away from seeps potentially support a much larger methane-promoted biological system than is widely appreciated.

scholarly journals Turbulent Exchange Characteristics in the Hypolimnion Layer of Lake Ontario

2001 ◽  
Vol 32 (1) ◽  
pp. 13-28 ◽  
Author(s):  
Messon B. Gbah ◽  
Y.R. Rao ◽  
Raj C. Murthy
Keyword(s):  
Kinetic Energy ◽  
Water Column ◽  
Sediment Resuspension ◽  
Surface Wind ◽  
Vertical Mixing ◽  
Acoustic Doppler Current Profiler ◽  
Lake Ontario ◽  
Mean Flow ◽  
Turbulent Structures ◽  
Nepheloid Layer

Flow regime and turbulence characteristics in a hypolimnion of Lake Ontario are determined using time series current measurements from a vertical string of moored current meters and a bottom mounted Acoustic Doppler Current Profiler (ADCP). The diffusion and turbulent structures of the water column are parameterised in terms of horizontal exchange coefficients for momentum (Kx and Ky) during these deployments. The analysis suggests that the structure of the turbulent fluctuations is isotropic. The kinetic energy and horizontal exchange coefficients decrease with depth. The mean flow at all moorings appears to be strongly correlated with the zonal surface wind stress. Fifteen to twenty metres above the bottom, the flow is marked by an increase in kinetic energy, turbulence intensities, and eddy viscosity coefficients. Strong episodic wind impulse decreases horizontal exchange coefficients through the water column but probably enhances the vertical mixing due to increase in current shear. It is suggested that the associated current-induced sediment resuspension may contribute to the establishment and maintenance of a Nepheloid layer in Lake Ontario.

Krill diel vertical migration fine dynamics, nocturnal overturns, and their roles for aggregation in stratified flows

2008 ◽  
Vol 65 (4) ◽  
pp. 574-587 ◽  
Author(s):  
M Sourisseau ◽  
Y Simard ◽  
F J Saucier
Keyword(s):  
Water Column ◽  
Vertical Migration ◽  
Acoustic Doppler Current Profiler ◽  
Day Length ◽  
Data Set ◽  
Vertical Movements ◽  
Lawrence Estuary ◽  
Diel Vertical Migrations ◽  
Current Profiler ◽  
Feeding Bout

A set of high-resolution observations on short-term dynamics of krill diel vertical migrations (DVM) in the St. Lawrence Estuary are presented here, including vertical mass transfer measurements from multifrequency echo sounding coupled with stratified net sampling and tracers of individual vertical movements from stomach pigments over a 72 h period. The data set is supplemented by vertical migration speeds and biomass diel patterns from ADCP (acoustic Doppler current profiler) time series lasting up to 3 months. All krill always rapidly migrated to the surface in synchrony at sunset. Soon after the ascent, fed krill started to swim downward. A scattering layer was then formed at their daytime depth with sometimes a significant backscatter at intermediate depths, especially around midnight. A reorganisation in the upper water column then occurs, likely for a predawn feeding bout. At dawn, the krill mass still feeding in upper water column synchronously swam downward to their daytime depth. This nocturnal asynchronous vertical behaviour, conforming to the DVM hunger-satiation hypothesis, repeated between August and October in two different years, the DVM timing being determined by day length.

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