scholarly journals Effects of iron on the elemental stoichiometry during EIFEX and in the diatoms <i>Fragilariopsis kerguelensis</i> and <i>Chaetoceros dichaeta</i>

2007 ◽  
Vol 4 (1) ◽  
pp. 249-275 ◽  
Author(s):  
L. J. Hoffmann ◽  
I. Peeken ◽  
K. Lochte
Keyword(s):  
Laboratory Experiments ◽  
Iron Limitation ◽  
Iron Availability ◽  
Diatom Species ◽  
Fertilization Experiment ◽  
High Iron ◽  
Iron Fertilization ◽  
Elemental Stoichiometry ◽  
Fertilization Experiments

Abstract. The interaction between iron availability and the phytoplankton elemental composition was investigated during the in situ iron fertilization experiment EIFEX and in laboratory experiments with the Southern Ocean diatom species Fragilariopsis kerguelensis and Chaetoceros dichaeta. Contrary to other in situ iron fertilization experiments we observed an increase in the bPSi : POC, bPSi : PON, and bPSi : POP ratios within the iron fertilized patch during EIFEX. This is possibly caused by a relatively stronger increase in diatom abundance compared to other phytoplankton groups and does not necessarily represent the amount of silicification of single diatom cells. In laboratory experiments with F. kerguelensis and C. dichaeta no changes in the POC : PON, PON : POP, and POC : POP ratios were found with changing iron availability in both species. BPSi : POC, bPSi : PON, and bPSi : POP ratios were significantly lower in the high iron treatments compared to the controls. In F. kerguelensis this is caused by a decrease in cellular bPSi concentrations and therefore possibly less silicification. In C. dichaeta no change in cellular bPSi concentration was found. Here lower bPSi : POC, bPSi : PON, and bPSi : POP ratios were caused by an increase in cellular C, N, and P under high iron conditions. We therefore assume that iron limitation does not generally increase silicification of diatoms and that changes in the bPSi : POC, bPSi : PON, and bPSi : POP ratios under iron fertilization in the field are caused by a variety of different mechanisms. These results imply that the effect of iron on nutrient uptake is more complex than hitherto assumed.

scholarly journals Effects of iron on the elemental stoichiometry during EIFEX and in the diatoms <i>Fragilariopsis kerguelensis</i> and <i>Chaetoceros dichaeta</i>

2007 ◽  
Vol 4 (4) ◽  
pp. 569-579 ◽  
Author(s):  
L. J. Hoffmann ◽  
I. Peeken ◽  
K. Lochte
Keyword(s):  
Laboratory Experiments ◽  
Iron Availability ◽  
Diatom Species ◽  
Elemental Ratios ◽  
Fertilization Experiment ◽  
High Iron ◽  
Iron Fertilization ◽  
Elemental Stoichiometry ◽  
Fertilization Experiments

Abstract. The interaction between iron availability and the phytoplankton elemental composition was investigated during the in situ iron fertilization experiment EIFEX and in laboratory experiments with the Southern Ocean diatom species Fragilariopsis kerguelensis and Chaetoceros dichaeta. Contrary to other in situ iron fertilization experiments we observed an increase in the BSi:POC, BSi:PON, and BSi:POP ratios within the iron fertilized patch during EIFEX. This is possibly caused by a relatively stronger increase in diatom abundance compared to other phytoplankton groups and does not necessarily represent the amount of silicification of single diatom cells. In laboratory experiments with F. kerguelensis and C. dichaeta no changes in the POC:PON, PON:POP, and POC:POP ratios were found with changing iron availability in both species. BSi:POC, BSi:PON, and BSi:POP ratios were significantly lower in the high iron treatments compared to the controls. In F. kerguelensis this was caused by a decrease in cellular BSi concentrations and therefore possibly less silicification. In C. dichaeta no change in cellular BSi concentration was found. Here lower BSi:POC, BSi:PON, and BSi:POP ratios were caused by an increase in cellular C, N, and P under high iron conditions. These results indicate that iron limitation does not always increase silicification in diatoms and that changes in the BSi:POC, BSi:PON, and BSi:POP ratios under iron fertilization in the field are caused by a variety of different mechanisms. Our results therefore imply that simple cause-and-effect relationships are not always applicable for modeling of elemental ratios.

scholarly journals Effects of high CO2 levels on the ecophysiology of the diatom Thalassiosira weissflogii differ depending on the iron nutritional status

2016 ◽  
Vol 73 (3) ◽  
pp. 680-692 ◽  
Author(s):  
Koji Sugie ◽  
Takeshi Yoshimura
Keyword(s):  
High Pco2 ◽  
Natural Seawater ◽  
Iron Availability ◽  
Thalassiosira Weissflogii ◽  
Carbonate Chemistry ◽  
High Co2 ◽  
High Iron ◽  
Linear Relationships ◽  
Elemental Stoichiometry ◽  
Co2 Levels

Abstract Iron availability in seawater, namely the concentration of dissolved inorganic iron ([Fe′]), is affected by changes in pH. Such changes in the availability of iron should be taken into account when investigating the effects of ocean acidification on phytoplankton ecophysiology because iron plays a key role in phytoplankton metabolism. However, changes in iron availability in response to changes in ocean acidity are difficult to quantify specifically using natural seawater because these factors change simultaneously. In the present study, the availability of iron and carbonate chemistry were manipulated individually and simultaneously in the laboratory to examine the effect of each factor on phytoplankton ecophysiology. The effects of various pCO2 conditions (∼390, ∼600, and ∼800 µatm) on the growth, cell size, and elemental stoichiometry (carbon [C], nitrogen [N], phosphorus [P], and silicon [Si]) of the diatom Thalassiosira weissflogii under high iron ([Fe′] = ∼240 pmol l−1) and low iron ([Fe′] = ∼24 pmol l−1) conditions were investigated. Cell volume decreased with increasing pCO2, whereas intracellular C, N, and P concentrations increased with increasing pCO2 only under high iron conditions. Si:C, Si:N, and Si:P ratios decreased with increasing pCO2. It reflects higher production of net C, N, and P with no corresponding change in net Si production under high pCO2 and high iron conditions. In contrast, significant linear relationships between measured parameters and pCO2 were rarely detected under low iron conditions. We conclude that the increasing CO2 levels could affect on the biogeochemical cycling of bioelements selectively under the iron-replete conditions in the coastal ecosystems.

Iron effects on colonization behavior, motility, and enzymatic activity of marine bacteria

2007 ◽  
Vol 53 (8) ◽  
pp. 968-974 ◽  
Author(s):  
Kam W. Tang ◽  
Hans-Peter Grossart
Keyword(s):  
Marine Bacteria ◽  
Laboratory Experiments ◽  
Large Fraction ◽  
Iron Limitation ◽  
Colonization Rate ◽  
Particle Interactions ◽  
Iron Availability ◽  
Free Living ◽  
Attached Bacteria ◽  
Colonization Behavior

Iron availability in the ocean has been shown to affect the growth and production of phytoplankton and free-living bacteria. A large fraction of marine bacteria are specialized in colonizing and living on particles and aggregates, but the effects of iron limitation on these bacteria are not fully known. We conducted laboratory experiments to study the effects of iron availability on particle colonization behavior, motility, and enzymatic activities of 4 strains of marine bacteria. Iron depletion reduced the bacterial particle colonization rate by 1.7%–43.1%, which could be attributed to reduced swimming speeds in 2 of the 4 strains. Protease activity was not affected by iron availability. However, attached bacteria did show higher protease activities than their free counterparts. Our results suggest that iron limitation in the ocean could in some cases reduce bacteria–particle interactions by reducing bacterial motility and colonization rate.

scholarly journals Design of a small-scale in situ iron fertilization experiment

1991 ◽  
Vol 36 (8) ◽  
pp. 1960-1965 ◽  
Author(s):  
Andrew Watson ◽  
Peter Liss ◽  
Robert Duce
Keyword(s):  
Small Scale ◽  
Fertilization Experiment ◽  
Iron Fertilization

scholarly journals Reviews and syntheses: Ocean iron fertilization experiments – past, present, and future looking to a future Korean Iron Fertilization Experiment in the Southern Ocean (KIFES) project

2018 ◽  
Vol 15 (19) ◽  
pp. 5847-5889 ◽  
Author(s):  
Joo-Eun Yoon ◽  
Kyu-Cheul Yoo ◽  
Alison M. Macdonald ◽  
Ho-Il Yoon ◽  
Ki-Tae Park ◽  
...  
Keyword(s):  
Side Effects ◽  
Southern Ocean ◽  
Field Experiments ◽  
Dimethyl Sulfide ◽  
Mixed Layer Depth ◽  
Design Guidelines ◽  
Fertilization Experiment ◽  
Iron Fertilization ◽  
In Situ Conditions

Abstract. Since the start of the industrial revolution, human activities have caused a rapid increase in atmospheric carbon dioxide (CO2) concentrations, which have, in turn, had an impact on climate leading to global warming and ocean acidification. Various approaches have been proposed to reduce atmospheric CO2. The Martin (or iron) hypothesis suggests that ocean iron fertilization (OIF) could be an effective method for stimulating oceanic carbon sequestration through the biological pump in iron-limited, high-nutrient, low-chlorophyll (HNLC) regions. To test the Martin hypothesis, 13 artificial OIF (aOIF) experiments have been performed since 1990 in HNLC regions. These aOIF field experiments have demonstrated that primary production (PP) can be significantly enhanced by the artificial addition of iron. However, except in the Southern Ocean (SO) European Iron Fertilization Experiment (EIFEX), no significant change in the effectiveness of aOIF (i.e., the amount of iron-induced carbon export flux below the winter mixed layer depth, MLD) has been detected. These results, including possible side effects, have been debated amongst those who support and oppose aOIF experimentation, and many questions concerning the effectiveness of scientific aOIF, environmental side effects, and international aOIF law frameworks remain. In the context of increasing global and political concerns associated with climate change, it is valuable to examine the validity and usefulness of the aOIF experiments. Furthermore, it is logical to carry out such experiments because they allow one to study how plankton-based ecosystems work by providing insight into mechanisms operating in real time and under in situ conditions. To maximize the effectiveness of aOIF experiments under international aOIF regulations in the future, we therefore suggest a design that incorporates several components. (1) Experiments conducted in the center of an eddy structure when grazing pressure is low and silicate levels are high (e.g., in the SO south of the polar front during early summer). (2) Shipboard observations extending over a minimum of ∼40 days, with multiple iron injections (at least two or three iron infusions of ∼2000 kg with an interval of ∼10–15 days to fertilize a patch of 300 km2 and obtain a ∼2 nM concentration). (3) Tracing of the iron-fertilized patch using both physical (e.g., a drifting buoy) and biogeochemical (e.g., sulfur hexafluoride, photosynthetic quantum efficiency, and partial pressure of CO2) tracers. (4) Employment of neutrally buoyant sediment traps (NBST) and application of the water-column-derived thorium-234 (234Th) method at two depths (i.e., just below the in situ MLD and at the winter MLD), with autonomous profilers equipped with an underwater video profiler (UVP) and a transmissometer. (5) Monitoring of side effects on marine/ocean ecosystems, including production of climate-relevant gases (e.g., nitrous oxide, N2O; dimethyl sulfide, DMS; and halogenated volatile organic compounds, HVOCs), decline in oxygen inventory, and development of toxic algae blooms, with optical-sensor-equipped autonomous moored profilers and/or autonomous benthic vehicles. Lastly, we introduce the scientific aOIF experimental design guidelines for a future Korean Iron Fertilization Experiment in the Southern Ocean (KIFES).

scholarly journals Listener-Position and Orientation Dependency of Auditory Perception in an Enclosed Space: Elicitation of Salient Attributes

2021 ◽  
Vol 11 (4) ◽  
pp. 1570
Author(s):  
Bogdan Ioan Băcilă ◽  
Hyunkook Lee
Keyword(s):  
Auditory Perception ◽  
Laboratory Experiments ◽  
Head Orientation ◽  
Repertory Grid Technique ◽  
Apparent Source ◽  
Grid Technique ◽  
Subjective Study ◽  
Enclosed Space ◽  
Orientation Dependency

This paper presents a subjective study conducted on the perception of auditory attributes depending on listener position and head orientation in an enclosed space. Two elicitation experiments were carried out using the repertory grid technique—in-situ and laboratory experiments—which aimed to identify perceptual attributes among 10 different combinations of the listener’s positions and head orientations in a concert hall. It was found that, between the in-situ and laboratory experiments, the listening positions and head orientations were clustered identically. Ten salient perceptual attributes were identified from the data obtained from the laboratory experiment. Whilst these included conventional attributes such as ASW (apparent source width) and LEV (listener envelopment), new attributes such as PRL (perceived reverb loudness), ARW (apparent reverb width) and Reverb Direction were identified, and they are hypothesised to be sub-attributes of LEV (listener envelopment). Timbral characteristics such as Reverb Brightness and Echo Brightness were also identified as salient attributes, which are considered to potentially contribute to the overall perceived clarity.

scholarly journals Natural dimethyl sulfide gradients would lead marine predators to higher prey biomass

2021 ◽  
Vol 4 (1) ◽  
Author(s):  
Kylie Owen ◽  
Kentaro Saeki ◽  
Joseph D. Warren ◽  
Alessandro Bocconcelli ◽  
David N. Wiley ◽  
...  
Keyword(s):  
Laboratory Experiments ◽  
Dimethyl Sulfide ◽  
Zooplankton Biomass ◽  
Foraging Success ◽  
Spatially Correlated ◽  
Prey Biomass ◽  
Marine Predators ◽  
Predator Foraging ◽  
The Impact

AbstractFinding prey is essential to survival, with marine predators hypothesised to track chemicals such as dimethyl sulfide (DMS) while foraging. Many predators are attracted to artificially released DMS, and laboratory experiments have shown that zooplankton grazing on phytoplankton accelerates DMS release. However, whether natural DMS concentrations are useful for predators and correlated to areas of high prey biomass remains a fundamental knowledge gap. Here, we used concurrent hydroacoustic surveys and in situ DMS measurements to present evidence that zooplankton biomass is spatially correlated to natural DMS concentration in air and seawater. Using agent simulations, we also show that following gradients of DMS would lead zooplankton predators to areas of higher prey biomass than swimming randomly. Further understanding of the conditions and scales over which these gradients occur, and how they are used by predators, is essential to predicting the impact of future changes in the ocean on predator foraging success.

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