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

<p><strong>Abstract: EGU 2020</strong></p><p><strong>Session: BG4.1: Biogeochemistry of coastal seas and continental shelves (Helmuth Thomas)</strong></p><p>Mona Norbisrath<sup>1</sup>, Kirstin Dähnke<sup>1</sup>, Andreas Neumann<sup>1</sup>, Justus van Beusekom<sup>1</sup>, Nele Treblin<sup>1</sup>, Bryce van Dam<sup>1</sup>, Helmuth Thomas<sup>1</sup></p><p><sup>1</sup>Institute for Coastal Research, Helmholtz-Zentrum Geesthacht</p><p>Contact: [email protected]</p><p> </p><p><strong>In-situ investigation of alkalinity - denitrification coupling in the sediment - water column interface</strong></p><p> </p><p>As a shallow shelf sea, the North Sea is very vulnerable to anthropogenic impacts like rising CO<sub>2</sub> concentrations, increasing nutrient inflows and coincident oxygen loss.</p><p>Two important processes that determine the role of the coastal ocean as a net sink for anthropogenic CO<sub>2</sub> are alkalinity and denitrification. Alkalinity, the acid binding capacity of the ocean, buffers natural and anthropogenic changes in the oceans’ CO<sub>2</sub> and pH system. Denitrification, an anaerobic microbial process in which organic matter is respired, uses NO<sub>3</sub><sup>-</sup> instead of O<sub>2</sub> as a terminal electron acceptor. Denitrification reduces NO<sub>3</sub><sup>-</sup> to N<sub>2</sub> and in turn produces alkalinity.</p><p>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<sub>2</sub>. However, the quantitative relationship between denitrification and alkalinity production and its control under changing environmental conditions is yet to be determined.</p><p>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<sub>2</sub> isotope species (<sup>28</sup>N<sub>2</sub>, <sup>29</sup>N<sub>2</sub> and <sup>30</sup>N<sub>2</sub>) 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<sub>2</sub> in the atmosphere.</p><p> </p>

scholarly journals Advanced experimental approaches to marine water-column biogeochemical processes

2017 ◽  
Vol 75 (1) ◽  
pp. 30-42 ◽  
Author(s):  
Louis Legendre ◽  
Richard B Rivkin ◽  
Nianzhi Jiao
Keyword(s):  
Water Column ◽  
Numerical Models ◽  
Free Water ◽  
Sea Surface ◽  
Biogeochemical Processes ◽  
In Situ Experiments ◽  
Technological Developments ◽  
Approaches To Study ◽  
Experimental Approaches

Abstract This “Food for Thought” article examines the potential uses of several novel scientific and technological developments, which are currently available or being developed, to significantly advance or supplement existing experimental approaches to study water-column biogeochemical processes (WCB-processes). After examining the complementary roles of observation, experiments and numerical models to study WCB-processes, we focus on the main experimental approaches of free-water in situ experiments, and at-sea and on-land meso- and macrocosms. We identify some of the incompletely resolved aspects of marine WCB-processes, and explore advanced experimental approaches that could be used to reduce their uncertainties. We examine three such approaches: free-water experiments of lengthened duration using bioArgo floats and gliders, at-sea mesocosms deployed several 100s m below the sea-surface using new biogeochemical sensors, and 50 m-tall on-land macrocosms. These approaches could lead to significant progress in concepts related to marine WCB-processes.

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.

In Situ Investigation of Orientation Changes during Heating of Extruded AZ31

2007 ◽  
Vol 561-565 ◽  
pp. 183-186
Author(s):  
Sang Bong Yi ◽  
Heinz Günter Brokmeier ◽  
Jens Homeyer
Keyword(s):  
Heating Temperature ◽  
Extrusion Direction ◽  
Fiber Texture ◽  
Post Heat Treatment ◽  
Change Rate ◽  
Soaking Time ◽  
In Situ Investigation ◽  
In Situ Experiments ◽  
Exponential Relation

The orientation changes during heating of extruded AZ31 were investigated using synchrotron Xrays by in-situ experiments. The as-extruded sample shows a strong <10.0>-fiber texture which is generally observed after round extrusion. The initial <10.0>-fiber texture, in which the <10.0> direction of the hexagonal crystallites is parallel to extrusion direction, starts to change to <11.0>- fiber component at 300 °C. The orientation change rate shows an exponential relation to the heating temperature and the soaking time. The microstructure observations, prior and post heat treatment, indicate that the texture changes occur mainly during grain growth.

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.

Whelk (Buccinum undatum) Movement and Its Implications for the Use of Tag–Recapture Methods for the Determination of Baited Trap Fishing Parameters

1991 ◽  
Vol 48 (5) ◽  
pp. 751-756 ◽  
Author(s):  
Bernard Sainte-Marie
Keyword(s):  
Experimental Conditions ◽  
Buccinum Undatum ◽  
North Shore ◽  
The North ◽  
In Situ Experiments ◽  
Two Parameters ◽  
Biased Estimates ◽  
Fishing Area

The tag–recapture method has been used to measure the field of attraction and the effective fishing area of a baited trap. The possibly conflicting experimental conditions required for the determination of these two parameters are, respectively, that tagged animals do not move and that they behave as undisturbed animals, prior to exposure to bait odour. Field observations and in situ experiments were conducted on the north shore of the Gulf of Saint Lawrence in 1988 and 1989 to compare behaviour of undisturbed and tagged whelks (Buccinum undatum). In the daytime, ~ 75% of undisturbed whelks were quiescent, being either buried and oriented randomly or static and oriented downstream, while the remainder moved across stream at 2–5 cm∙min−1. In contrast, > 97% of tagged whelks oriented in nonrandom directions and moved at equal or greater speeds, on average, 2.2–9.2 m from release points in less than 6 h. Because neither of the two basic conditions was met, tag–recapture experiments would produce biased estimates of baited trap fishing parameters.

scholarly journals Bioturbation, ecosystem functioning and community structure

2002 ◽  
Vol 6 (6) ◽  
pp. 999-1005 ◽  
Author(s):  
C. L. Biles ◽  
D. M. Paterson ◽  
R. B. Ford ◽  
M. Solan ◽  
D. G. Raffaelli
Keyword(s):  
Community Structure ◽  
Water Column ◽  
Ecosystem Functioning ◽  
Nutrient Concentration ◽  
Nutrient Release ◽  
Nutrient Concentrations ◽  
Infaunal Community ◽  
Significant Difference ◽  
In Situ Experiments

Abstract. The effect of community structure on the functioning of the ecosystem is an important issue in ecology due to continuing global species loss. The influence of infaunal community structure on the functioning of marine systems is proposed here to act primarily through bioturbation of the sediment. Nutrient concentration in the water column, generated by release from the sediment, was used as a measure of ecosystem functioning. In situ and laboratory experiments showed a significant difference in nutrient concentrations with different species treatments. Bioturbation profiles showing the incorporation of tracer particles also differed between communities with different dominant species. The behavioural differences between infaunal species, generating different modes and rates of bioturbation, are therefore proposed to influence nutrient release. The presence and quantity of bioturbating infauna also influenced the amount of sediment suspended in the water column. The increase in surface area available for microbial activity may generate an increase in nutrient cycling. Abiotic influences on sediment structure, such as flow, may have a similar effect on nutrient concentration. Annular flumes used in both laboratory and in situ experiments to generate flow conditions produced a significant increase in ammonia (NH4-N) production in macrofaunal treatments. Flow may influence the behaviour of macrofaunal species, causing changes in NH4-N production through modifying bioturbation of the sediment. Keywords: bioturbation, community structure, ccosystem functioning, estuaries, flow, infauna

scholarly journals RiverOceanPlastic: Land-ocean transfer of plastic debris in the North Atlantic, Cruise No. AL534/2, 05 March – 26 March 2020, Malaga (Spain) – Kiel (Germany)

2020 ◽  
Author(s):  
Aaron Beck
Keyword(s):  
Water Column ◽  
Water Samples ◽  
Western Europe ◽  
Suspended Particle ◽  
Plastic Debris ◽  
The North ◽  
Research Initiative ◽  
Different Depths ◽  
Calm Weather

Cruise AL534/2 is part of a multi-disciplinary research initiative as part of the JPI Oceans project HOTMIC and sought to investigate the origin, transport and fate of plastic debris from estuaries to the oceanic garbage patches. The main focus of the cruise was on the horizontal transfer of plastic debris from major European rivers into shelf regions and on the processes that mediate this transport. Stations were originally chosen to target the outflows of major European rivers along the western Europe coast between Malaga (Spain) and Kiel (Germany), although some modifications were made in response to inclement weather. In total, 16 stations were sampled along the cruise track. The sampling scheme was similar for most stations, and included: 1) a CTD cast to collect water column salinity and temperature profiles, and discrete samples between surface and seafloor, 2) sediment sampling with Van Veen grab and mini-multi corer (mini-MUC), 3) suspended particle and plankton sampling using a towed Bongo net and vertical WP3 net, and 4) surface neusten sampling using a catamaran trawl. At a subset of stations with deep water, suspended particles were collected using in situ pumps deployed on a cable. During transit between stations, surface water samples were collected from the ship’s underway seawater supply, and during calm weather, floating litter was counted by visual survey teams. The samples and data collected on cruise AL534/2 will be used to determine the: (1) abundance of plastic debris in surface waters, as well as the composition of polymer types, originating in major European estuaries and transported through coastal waters, (2) abundance and composition of microplastics (MP) in the water column at different depths from the sea surface to the seafloor including the sediment, (3) abundance and composition of plastic debris in pelagic and benthic organisms (invertebrates), (4) abundance and identity of biofoulers (bacteria, protozoans and metazoans) on the surface of plastic debris from different water depths, (5) identification of chemical compounds (“additives”) in the plastic debris and in water samples.

scholarly journals Provenance of tetraether membrane lipids in a large temperate lake (Loch Lomond, UK): implications for GDGT-based palaeothermometry

2014 ◽  
Vol 11 (3) ◽  
pp. 4187-4250 ◽  
Author(s):  
L. K. Buckles ◽  
J. W. H. Weijers ◽  
X.-M. Tran ◽  
S. Waldron ◽  
J. S. Sinninghe Damsté
Keyword(s):  
Lake Sediments ◽  
Water Column ◽  
Membrane Lipids ◽  
Lacustrine Sediments ◽  
Small Rivers ◽  
The South ◽  
Factors Affecting ◽  
The North ◽  
Loch Lomond

Abstract. The application of glycerol dialkyl glycerol tetraether (GDGT)-based palaeoenvironmental proxies, such as the BIT index, TEX86 and the MBT/CBT palaeothermometer, has lately been expanded to lacustrine sediments. Given recent research identifying the production of branched, bacterial GDGTs (brGDGTs) within lakes, it is necessary to ascertain the effect of this lacustrine production on GDGT-based proxies. This study profiles a temperate, monomictic lake (Loch Lomond, UK), analysing labile intact polar GDGT lipids (IPLs) and resilient core GDGT lipids (CLs) in catchment soils, small tributary rivers, lake water and lake sediments. Loch Lomond consists of two basins bisected by the Highland Boundary Fault, resulting in a mesotrophic to oligotrophic gradient from south to north. The north basin is fjord-like, while the south basin is shallow with a lowland catchment. Besides abundant influxes of allochthonous soil and peat-derived (CL) brGDGTs, brGDGTs are produced in a variety of settings in Loch Lomond. Rather than integrating a scattered soil signal, there is some evidence that small rivers may contribute to the brGDGT pool through addition of brGDGTs produced in situ in these streams. 300 days of settling particles and water column profiles of suspended particulate matter (SPM; March and September 2011) reveal brGDGT production throughout the water column, with (IPL and CL) brGDGT distributions varying by basin. In lake sediments, in situ brGDGT production affects the distributions of sedimentary brGDGTs despite high soil and peat-derived organic matter influxes from the catchment. MBT/CBT-derived mean annual air temperature (MAAT) estimates from soil, river and lake sediments vary widely. A strong bias towards higher MAATs in the south and lower MAATs in the north basin further complicates the application of the proxy. These results emphasise that caution must be exercised when applying the MBT/CBT palaeothermometer to individual lakes in which the use of the proxy has not been validated and therefore the factors affecting its application are not well understood. Despite elevated BIT indices, (partly) due to in situ brGDGT production, reliable TEX86 lake surface temperature (LST) estimates were obtained from SPM with BIT indices up to 0.9 but containing abundant crenarchaeol. Lower north basin sediments yielded accurate LST estimates but require further evaluation to properly constrain the application of the TEX86 proxy.

scholarly journals In-situ investigation of ion-implantation effects on radiation-induced segregation in Ni-Al alloys

1996 ◽  
Vol 54 ◽  
pp. 988-989
Author(s):  
M.J. Giacobbe ◽  
N.Q. Lam ◽  
P.R. Okamoto ◽  
N.J. Zaluzec ◽  
J.F. Stubbins
Keyword(s):  
Electron Beam ◽  
National Laboratory ◽  
Argonne National Laboratory ◽  
Beam Diameter ◽  
Total Electron ◽  
Radial Segregation ◽  
In Situ Investigation ◽  
In Situ Experiments ◽  
Radiation Induced

In-situ experiments using the HVEM (high voltage electron microscope)/Tandem accelerator facility at Argonne National Laboratory were performed to determine the effects of 400-keV Zr+ and 75-keV Ne+ implantation on electron radiation-induced segregation (RIS) in Ni-9at.%Al at 550°C and 450°C, respectively. The alteration of RIS kinetics by Ne implantation was studied at two different doses. A highly-focused 900-keV electron beam, which produces a radial defect flux away from the beam center, was used to induce segregation of Al atoms in the opposite direction via the inverse-Kirkendall effect. Within the irradiated zone, Al enrichment drives the formation of γ′-Ni3Al precipitates, and the radial segregation rate of Al was monitored by measuring the growth of the precipitate zone.When a thin film is subject to a focused, electron beam, a non uniform defect distribution is produced. The effective beam diameter, D∘, is defined by IT= I∘ (πD∘/2)2 where IT is the total electron current and I∘ is the peak electron flux.

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