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  • 1
    Online Resource
    Online Resource
    Organic nutrients and excess nitrogen in the North Atlantic subtropical gyre (2008)
    Associated volumes
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    In: Biogeosciences, Katlenburg-Lindau [u.a.] : Copernicus, 2004, 5(2008), 5, Seite 1199-1213, 1726-4189
    In: volume:5
    In: year:2008
    In: number:5
    In: pages:1199-1213
    Description / Table of Contents: To enable an accurate estimate of total excess nitrogen (N) in the North Atlantic, a new tracer TNxs is defined, which includes the contribution of organic nutrients to the assessment of N:P stoichiometric anomalies. We measured the spatial distribution of TNxs within the subtropical North Atlantic using data from a trans-Atlantic section across 24.5° N occupied in 2004. We then employ three different approaches to infer rates of total excess nitrogen accumulation using pCFC-12 derived ventilation ages (a TNxs vertical integration, a one end-member and a two-end member mixing model). Despite some variability among the different methods the dissolved organic nutrient fraction always contributes to about half of the TNxs accumulation, which is in the order of 9.38±4.18×10 11 mol N y-1. We suggest that neglecting organic nutrients in stoichiometric balances of the marine N and P inventories can lead to systematic errors when estimating deviations of nitrogen excess or deficit relative to the Redfield ratio in the oceans. For the North Atlantic the inclusion of the organic fraction to the excess nitrogen pool leads to an upward revision of the N supply by N2 fixation to 10.2±6.9×10 11 mol N y-1.
    Type of Medium: Online Resource
    Pages: graph. Darst
    ISSN: 1726-4189
    Language: English
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  • 2
    Electronic Resource
    Electronic Resource
    Fetal Cutaneous Myofibroblasts — Fact or Fallacy? (2005)
    Oxford, UK; Malden, USA : Blackwell Science Inc
    Wound repair and regeneration 13 (2005), S. 0 
    Details
    ISSN: 1524-475X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: It has been known for several decades that early gestational human fetuses will regenerate cutaneous wounds resulting in a scarless repair. In postnatal humans, myofibroblasts are known to play a central role in wound healing and in the pathology of fibrosis. The role of the profibrotic growth factor TGF-β1 in human fetal fibroblasts remains unclear, with recent data now showing that TGF-β1 is present in fetal wounds but for shorter periods. We have therefore examined the effects of TGF-β1 on fibroblasts isolated from early human fetuses (〈14week EGA). We have identified that stimulation with 5 ng/ml TGF-β1 induces a significant proportion of human fetal fibroblasts to differentiate into myofibroblasts (approximately 40%), as identified by staining of α-smooth muscle actin (n = 5). Interestingly, this response was earlier (peaking at day 2–3) and more transitory (over by day 4–5) than that seen with postnatal dermal fibroblasts (peaking at day 6–8 and dropping at day 10). We examined the effects of blocking various intracellular pathways involved in TGF-β1 signalling. The early and transitory myofibroblast induction seen in fetal cells is blocked by an inhibitor of p-JNK (n = 4; p =〈 0.05). In contrast, the later and more prolonged induction of myofibroblasts seen in postnatal cells was not affected by inhibition of p-JNK. Despite the fact that fetal fibroblasts do indeed differentiate into myofibroblasts they were further shown to exhibit differential behavior to postnatal myofibroblasts with respect to TGF-β1 stimulation of collagen expression, producing significantly less soluble collagen (approximately 50%, n = 4) after 24 or 48 hours of treatment with TGF-β1 in serum-free media. These results appear to indicate a role for TGF-β1 during cutaneous wound healing in the early fetus and show that the response of fetal cells to this important profibrotic cytokine is rapid and more controlled, being short lived. It is possible that a prolonged response to this cytokine may lead to the overblown nature of postnatal wound healing, resulting in fibrosis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1067-1927.2005.130117w.x
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  • 3
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    Simultaneous determination of dissolved organic carbon and total dissolved nitrogen on a coupled high-temperature combustion total organic carbon-nitrogen chemiluminescence detection (HTC TOC-NCD) system (2005)
    Hindawi Publ. Corp.
    In:  Journal of Automated Methods and Management in Chemistry, 2005 (4). pp. 240-246.
    Details
    Publication Date: 2020-07-27
    Description: The marine biogeochemistries of carbon and nitrogen have come under increased scrutiny because of their close involvement in climate change and coastal eutrophication. Recent studies have shown that the high-temperature combustion (HTC) technique is suitable for routine analyses of dissolved organic matter due to its good oxidation efficiency, high sensitivity, and precision. In our laboratory, a coupled HTC TOC-NCD system with a sample changer was used for the automated and simultaneous determination of dissolved organic carbon (DOC) and total dissolved nitrogen (TDN)in seawater samples. TOC control software was used for TOC instrument control, DOC data acquisition, and data analysis. TDN data acquisition and manipulation was undertaken under LabVIEW. The combined system allowed simultaneous determination of DOC and TDN in the same sample using a single injection and provided low detection limits and excellent linear ranges for both DOC and TDN. The risk of contamination has been remarkably reduced due to the minimal sample manipulation and automated analyses. The optimised system provided a reliable tool for the routine determination of DOC and TDN in marine waters. © 2005 Hindawi Publishing Corporation.
    Type: Article , PeerReviewed
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  • 4
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    Ocean fertilization: A potential means of geoengineering? (2008)
    Royal Society of London
    In:  Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, 366 (1882). pp. 3919-3945.
    Details
    Publication Date: 2020-06-12
    Description: The oceans sequester carbon from the atmosphere partly as a result of biological productivity. Over much of the ocean surface, this productivity is limited by essential nutrients and we discuss whether it is likely that sequestration can be enhanced by supplying limiting nutrients. Various methods of supply have been suggested and we discuss the efficacy of each and the potential side effects that may develop as a result. Our conclusion is that these methods have the potential to enhance sequestration but that the current level of knowledge from the observations and modelling carried out to date does not provide a sound foundation on which to make clear predictions or recommendations. For ocean fertilization to become a viable option to sequester CO 2, we need more extensive and targeted fieldwork and better mathematical models of ocean biogeochemical processes. Models are needed both to interpret field observations and to make reliable predictions about the side effects of large-scale fertilization. They would also be an essential tool with which to verify that sequestration has effectively taken place. There is considerable urgency to address climate change mitigation and this demands that new fieldwork plans are developed rapidly. In contrast to previous experiments, these must focus on the specific objective which is to assess the possibilities of CO 2 sequestration through fertilization. © 2008 The Royal Society.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1098/rsta.2008.0139
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 5
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    The role of calcite in enhancing the flux of particulate organic carbon into the deep ocean (2009)
    In:  [Poster] In: AGU Chapman Conference on the Biological Carbon Pump of the Oceans, 01.-04.09.2009, Brockenhurst, Hampshire, UK .
    Details
    Publication Date: 2015-01-07
    Type: Conference or Workshop Item , NonPeerReviewed
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    OceanRep: Poster
  • 6
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    Large-scale physical controls on phytoplankton growth in the Irminger Sea Part I: Hydrographic zones, mixing and stratification (2006)
    Elsevier
    In:  Journal of Marine Systems, 59 (3-4). pp. 201-218.
    Details
    Publication Date: 2015-09-22
    Description: Hydrographic surveys in three consecutive seasons in the Irminger Sea in 2001/2002 have revealed six physical regimes (zones) in which different surface mixing and spring re-stratification processes dominate. They are the South Irminger Current, the North Irminger Current, the Central Irminger Sea, the Polar-origin East Greenland Current, the Atlantic-origin East Greenland Current and the Reykjanes Ridge. The variations in restratification processes in particular have significant implications for the timing of shallow spring mixed layer development and therefore the timing and strength of the spring bloom. The relative roles of heat and freshwater in controlling re-stratification are examined for each hydrographic zone, and it is shown that the simplest concept of solar warming generating spring stratification is appropriate for the Irminger Current and the central Irminger Sea. However in the East Greenland Current and the Reykjanes Ridge zones, the springtime arrival of fresh or saline water at the surface dominates re-stratification and generates the earliest and strongest spring blooms of the region. In the cool fresh centre of the Irminger Sea the relatively low chlorophyll-a throughout the year cannot be wholly explained by stratification or nutrient concentrations. Details of the annual cycle in temperature, salinity, chlorophyll-a and nutrients are presented for each hydrographic zone
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1016/j.jmarsys.2005.10.004
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 7
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    N2 fixation in the North Atlantic: a new geochemical estimate (2007)
    In:  [Talk] In: EGU General Assembly, 20.04, Vienna, Austria .
    Details
    Publication Date: 2012-02-23
    Type: Conference or Workshop Item , NonPeerReviewed
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    OceanRep: Talk
  • 8
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    Organic nutrients and excess nitrogen in the North Atlantic subtropical gyre (2008)
    Copernicus Publications (EGU)
    In:  Biogeosciences (BG), 5 . pp. 1199-1213.
    Details
    Publication Date: 2012-07-06
    Description: To enable an accurate estimate of total excess nitrogen (N) in the North Atlantic, a new tracer TNxs is defined, which includes the contribution of organic nutrients to the assessment of N:P stoichiometric anomalies. We measured the spatial distribution of TNxs within the subtropical North Atlantic using data from a trans-Atlantic section across 24.5° N occupied in 2004. We then employ three different approaches to infer rates of total excess nitrogen accumulation using pCFC-12 derived ventilation ages (a TNxs vertical integration, a one end-member and a two-end member mixing model). Despite some variability among the different methods the dissolved organic nutrient fraction always contributes to about half of the TNxs accumulation, which is in the order of 9.38±4.18×1011 mol N y−1. We suggest that neglecting organic nutrients in stoichiometric balances of the marine N and P inventories can lead to systematic errors when estimating deviations of nitrogen excess or deficit relative to the Redfield ratio in the oceans. For the North Atlantic the inclusion of the organic fraction to the excess nitrogen pool leads to an upward revision of the N supply by N2 fixation to 10.2±6.9×1011 mol N y−1.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.5194/bg-5-1199-2008
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 9
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    Phosphorus cycling in the North and South Atlantic Ocean subtropical gyres (2008)
    Nature Publishing Group
    In:  Nature Geoscience, 1 (7). pp. 439-443.
    Details
    Publication Date: 2017-02-23
    Description: Despite similar physical properties, the Northern and Southern Atlantic subtropical gyres have different biogeochemical regimes. The Northern subtropical gyre, which is subject to iron deposition from Saharan dust1, is depleted in the nutrient phosphate, possibly as a result of iron-enhanced nitrogen fixation2. Although phosphate depleted, rates of carbon fixation in the euphotic zone of the North Atlantic subtropical gyre are comparable to those of the South Atlantic subtropical gyre3, which is not phosphate limited. Here we use the activity of the phosphorus-specific enzyme alkaline phosphatase to show potentially enhanced utilization of dissolved organic phosphorus occurring over much of the North Atlantic subtropical gyre. We find that during the boreal spring up to 30% of primary production in the North Atlantic gyre is supported by dissolved organic phosphorus. Our diagnostics and composite map of the surface distribution of dissolved organic phosphorus in the subtropical Atlantic Ocean reveal shorter residence times in the North Atlantic gyre than the South Atlantic gyre. We interpret the asymmetry of dissolved organic phosphorus cycling in the two gyres as a consequence of enhanced nitrogen fixation in the North Atlantic Ocean4, which forces the system towards phosphorus limitation. We suggest that dissolved organic phosphorus utilization may contribute to primary production in other phosphorus-limited ocean settings as well.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1038/ngeo232
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 10
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    Distribution of dissolved organic nutrients and their effect on export production over the Atlantic Ocean (2009)
    American Geophysical Union (AGU)
    In:  Global Biogeochemical Cycles, 23 (4).
    Details
    Publication Date: 2020-07-30
    Description: A synthesis is provided of dissolved organic nitrogen (DON) and phosphorus (DOP) distributions over the Atlantic Ocean based upon field data from eight recent transects, six meridional between 50°N and 50°S and two zonal at 24° and 36°N. Over the entire tropical and subtropical Atlantic, DON and DOP provide the dominant contributions to total nitrogen and phosphorus pools for surface waters above the thermocline. Elevated DON and DOP concentrations (〉5 and 〉0.2 μ mol L−1, respectively) occur in surface waters on the eastern side of the North Atlantic subtropical gyre and equatorial sides of both the North and South Atlantic subtropical gyres, while particularly low concentrations of DOP (〈0.05 μ mol L−1) occur over the northern flank of the North Atlantic subtropical gyre along 36°N. This distribution is consistent with organic nutrients formed at the gyre margins supporting carbon export as they are redistributed via the gyre circulation. The effect of DON and DOP transport and cycling on export production is examined in an eddy‐permitting, coupled physical and nutrient model integrated for 40 years: organic nutrients are produced in the upwelling zones off North Africa and transferred laterally into the gyre interior, facilitated in part by the mesoscale eddy circulation, as well as fluxed northward from the tropics as part of the overturning circulation. Inputs of semilabile DON and DOP to the tropical and subtropical Atlantic Ocean play an important role in sustaining up to typically 40 and 70% of the modeled particulate N and P export, particularly on the eastern and equatorward sides of the subtropical gyres.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1029/2008GB003389
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    OceanRep: Article in a Scientific Journal - peer-reviewed
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