Environmental control of phytoplankton production on the southeastern U.S. continental shelf

1985 ◽  
pp. 93-103 ◽  
Author(s):  
J. A. Yoder
Keyword(s):  
Continental Shelf ◽  
Environmental Control ◽  
Phytoplankton Production

Evidence that increased nitrogen efflux from wave-influenced marine sediment enhances pelagic phytoplankton production on the inner continental shelf of Western Australia

2010 ◽  
Vol 61 (5) ◽  
pp. 625 ◽  
Author(s):  
Jim Greenwood
Keyword(s):  
Continental Shelf ◽  
Surface Waves ◽  
Water Column ◽  
Chlorophyll A ◽  
Wave Height ◽  
Western Australia ◽  
Regional Scale ◽  
Reaction Rates ◽  
Phytoplankton Production ◽  
Biogeochemical Model

Increased biological and chemical reaction rates within permeable continental-shelf sediment can result from the action of passing surface waves, especially when the seabed is rippled. The effect of this on the exchange of nitrogen between the sediment and water column is the focus of the present paper. The continental shelf of Western Australia is used as an example. A time series of chlorophyll a is compared with surface-wave height revealing seasonal and sub-seasonal correlation between the two variables. At the same time, results from a coupled pelagic–benthic biogeochemical model show that temperature-controlled changes in sedimentary nitrogen efflux cannot account for the observed seasonal changes in chlorophyll a in the overlying water column. It is proposed that enhanced pore-water circulation within the sediment, caused by the action of passing surface waves, results in an increase in the efflux of nitrogen from the sediment during winter, supporting higher pelagic phytoplankton production. The parameterisation of sedimentary nitrogen mineralisation as a function of the square of wave height is suggested for the inclusion of this effect in regional-scale continental shelf models.

Size-fractionated phytoplankton production in western Agulhas Bank continental shelf waters

1993 ◽  
Vol 13 (2-3) ◽  
pp. 307-329 ◽  
Author(s):  
Helen F. McMurray ◽  
R.A. Carter ◽  
M.I. Lucas
Keyword(s):  
Continental Shelf ◽  
Phytoplankton Production

Controls on oxygen response to climate change on the Northwest European Continental Shelf

2020 ◽  
Author(s):  
Sarah L. Wakelin ◽  
Yuri Artioli ◽  
Momme Butenschön ◽  
Jason Holt ◽  
Jeremy Blackford
Keyword(s):  
Climate Change ◽  
Continental Shelf ◽  
Water Column ◽  
Ecosystem Processes ◽  
Phytoplankton Production ◽  
Biogeochemical Model ◽  
Biological Cycling ◽  
Increasing Temperature ◽  
The Impact ◽  
Oxygen Concentrations

<p>Dissolved oxygen in the ocean is an indicator of water quality and low concentrations can threaten ecosystem health. The main sources of marine oxygen are diffusion from the atmosphere and phytoplankton photosynthesis. Biological respiration and decomposition act to reduce oxygen concentrations. Under conditions of vertical stratification, the water column below the pycnocline is isolated from oxygen exchange with the atmosphere, photosynthesis may be limited by light availability and oxygen concentrations decrease. Climate change influences the oxygen cycle in two ways: 1) changing the hydrodynamic climate and 2) affecting rates of biogeochemical processes. The hydrodynamic climate affects the nutrient supply and so controls phytoplankton production while changes to water column stratification affects vertical mixing. Gas solubility decreases with increasing temperature so that oxygen uptake from the atmosphere is expected to decrease under increasing oceanic temperatures. Biological cycling rates increase with increasing temperature affecting photosynthesis, respiration and bacterial decomposition. It is not obvious whether changes in oxygen concentrations due to changing ecosystem processes will mitigate or reinforce the projected reduction from solubility changes.</p><p>The Northwest European Continental shelf (NWES) is a region of the northeast Atlantic that experiences seasonal stratification. We use the physics-biogeochemical model NEMO-ERSEM to study near-bed oxygen concentrations on the NWES under a high greenhouse gas emissions scenario (Representative Concentration Pathway (RCP) 8.5). We show that much of the NWES could experience low oxygen concentrations by 2100 and assess the relative impacts of changing temperature and ecosystem processes. Until about 2040 the impact of solubility dominates the oxygen change. The mean near-bed oxygen concentration is projected to decrease by 6.3% by 2100, of which 73% is due to solubility changes and the remainder to changes in the ecosystem. In the oxygen-depleted region in the eastern North Sea, 77% of the near-bed oxygen reduction is due to ecosystem processes.</p>

scholarly journals Environmental control and potential fate of size-fractionated phytoplankton production in the Greenland Sea (75° N)

1993 ◽  
Vol 98 ◽  
pp. 297-313 ◽  
Author(s):  
L Legendre ◽  
M Gosselin ◽  
H-J Hirche ◽  
G Kattner ◽  
G Rosenberg
Keyword(s):  
Environmental Control ◽  
Phytoplankton Production ◽  
Greenland Sea

scholarly journals Intra-annual variability of carbon and nitrogen stable isotopes in suspended organic matter in waters of the western continental shelf of India

2011 ◽  
Vol 8 (11) ◽  
pp. 3441-3456 ◽  
Author(s):  
M. V. Maya ◽  
S. G. Karapurkar ◽  
H. Naik ◽  
R. Roy ◽  
D. M. Shenoy ◽  
...  
Keyword(s):  
Organic Matter ◽  
Continental Shelf ◽  
Phytoplankton Production ◽  
Terrestrial Organic Matter ◽  
Monsoon Period ◽  
Isotopic Signatures ◽  
Carbon And Nitrogen ◽  
Annual Variability ◽  
Post Monsoon ◽  
Sw Monsoon

Abstract. Intra-annual variations of δ13C and δ15N of water-column suspended particulate organic matter (SPOM) have been investigated to understand the biogeochemical cycling of C and N in the Western Continental Shelf of India (WCSI). The key issues being addressed are: how the δ15N of SPOM is affected by seasonally varying processes of organic matter production and respiration and how it relates to the δ15N of sedimentary organic matter that appears to show a decreasing trend despite an apparent intensification of seasonal oxygen deficiency over the past few decades? A secondary objective was to evaluate the sources of organic carbon. Elemental carbon and nitrogen concentrations, C/N ratios in SPOM, along with ancillary chemical and biological variables including phytoplankton pigment abundance were also determined on a seasonal basis (from March 2007 to September 2008), with the partial exception of the southwest (SW) monsoon period. The results reveal significant shifts in isotopic signatures, especially δ15N, of SPOM before and after the onset of SW monsoon. Very low δ15N values, reaching a minimum of −4.17 ‰, are found during the pre-monsoon period. Our results provide the first direct evidence for the addition of substantial amounts of isotopically light nitrogen by the diazotrophs, especially Trichodesmium, in the region. The δ15N of SPOM is generally lower than the mean value (7.38 ‰) for surficial sediments, presumably because of diagenetic enrichment. The results support the view that sedimentary δ15N may not necessarily reflect denitrification intensity in the overlying waters due to diverse sources of nitrogen and variability of its isotopic composition. The observed intra-annual variability of δ13C of SPOM during the pre-monsoon and post-monsoon periods is generally small. Phytoplankton production and probably species composition could drive some of the observed changes. The largest changes (depletion of δ13C and increase in C/N) appear to occur during the pre- and post-monsoon seasons, presumably through episodic deposition of terrestrial organic matter from the atmosphere. During the SW monsoon, when a large input of terrestrial organic matter is expected through runoff from land, the C/N ratio remains low, but significant difference is observed between δ13C data in 2007 and 2008. Inputs of soil organic matter that may have elemental and isotopic signatures different from those of the conventional (C3 plant derived) organic matter could explain the constancy of the C/N ratio.

Thermal Considerations in Lens Regulator Systems

1970 ◽  
Vol 28 ◽  
pp. 358-359
Author(s):  
K.C. Newton
Keyword(s):  
Electron Microscope ◽  
Thermal Effects ◽  
Environmental Control ◽  
Reference Networks ◽  
Better Than

Thermal effects in lens regulator systems have become a major problem with the extension of electron microscope resolution capabilities below 5 Angstrom units. Larger columns with immersion lenses and increased accelerating potentials have made solutions more difficult by increasing the power being handled. Environmental control, component choice, and wiring design provide answers, however. Figure 1 indicates with broken lines where thermal problems develop in regulator systemsExtensive environmental control is required in the sampling and reference networks. In each case, stability better than I ppm/min. is required. Components with thermal coefficients satisfactory for these applications without environmental control are either not available or priced prohibitively.

Disentangling the role of shared ancestry and the environment on leaf stable isotopes

2019 ◽  
Author(s):  
Marko J. Spasojevic ◽  
Sören Weber1
Keyword(s):  
Stable Isotopes ◽  
Environmental Conditions ◽  
Evolutionary History ◽  
Environmental Control ◽  
Phylogenetic Signal ◽  
Individual Species ◽  
Habitat Types ◽  
Δ13c And Δ15n ◽  
Environmental Controls ◽  
Shared Ancestry

Stable carbon (C) and nitrogen (N) isotopes in plants are important indicators of plant water use efficiency and N acquisition strategies. While often regarded as being under environmental control, there is growing evidence that evolutionary history may also shape variation in stable isotope ratios (δ13C and δ15N) among plant species. Here we examined patterns of foliar δ13C and δ15N in alpine tundra for 59 species in 20 plant families. To assess the importance of environmental controls and evolutionary history, we examined if average δ13C and δ15N predictably differed among habitat types, if individual species exhibited intraspecific trait variation (ITV) in δ13C and δ15N, and if there were a significant phylogenetic signal in δ13C and δ15N. We found that variation among habitat types in both δ13C and δ15N mirrored well-known patterns of water and nitrogen limitation. Conversely, we also found that 40% of species exhibited no ITV in δ13C and 35% of species exhibited no ITV in δ15N, suggesting that some species are under stronger evolutionary control. However, we only found a modest signal of phylogenetic conservatism in δ13C and no phylogenetic signal in δ15N suggesting that shared ancestry is a weaker driver of tundra wide variation in stable isotopes. Together, our results suggest that both evolutionary history and local environmental conditions play a role in determining variation in δ13C and δ15N and that considering both factors can help with interpreting isotope patterns in nature and with predicting which species may be able to respond to rapidly changing environmental conditions.

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