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  • 2015-2019  (276)
  • 2010-2014  (264)
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  • 1
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    Biological and physical controls on N2, O2 and CO2 distributions in contrasting Southern Ocean surface waters (2015)
    Wiley
    Details
    Publication Date: 2015-06-17
    Description: We present measurements of p CO 2 , O 2 concentration, biological oxygen saturation (ΔO 2 /Ar) and N 2 saturation (ΔN 2 ) in Southern Ocean surface waters during austral summer, 2010–2011. Phytoplankton biomass varied strongly across distinct hydrographic zones, with high chlorophyll a (Chla) concentrations in regions of frontal mixing and sea-ice melt. p CO 2 and ΔO 2 /Ar exhibited large spatial gradients (range 90 to 450 µatm and −10 to 60%, respectively) and co-varied strongly with Chla. However, the ratio of biological O 2 accumulation to dissolved inorganic carbon (DIC) drawdown was significantly lower than expected from photosynthetic stoichiometry, reflecting the differential time-scales of O 2 and CO 2 air-sea equilibration. We measured significant oceanic CO 2 uptake, with a mean air-sea flux (~ −10 mmol m −2 d −1 ) that significantly exceeded regional climatological values. N 2 was mostly supersaturated in surface waters (mean ΔN 2 of +2.5 %), while physical processes resulted in both supersaturation and undersaturation of mixed layer O 2 (mean ΔO 2phys = 2.1 %). Box model calculations were able to reproduce much of the spatial variability of ΔN 2 and ΔO 2phys along the cruise track, demonstrating significant effects of air-sea exchange processes ( e . g . atmospheric pressure changes and bubble injection) and mixed layer entrainment on surface gas disequilibria. Net community production (NCP) derived from entrainment-corrected surface ΔO 2 /Ar data, ranged from ~ −40 to 〉 300 mmol O 2 m −2 d −1 and showed good coherence with independent NCP estimates based on seasonal mixed layer DIC deficits. Elevated NCP was observed in hydrographic frontal zones and stratified regions of sea-ice melt, reflecting physical controls on surface water light fields and nutrient availability.
    Print ISSN: 0886-6236
    Electronic ISSN: 1944-9224
    Topics: Biology , Chemistry and Pharmacology , Geography , Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 2
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    Ventilation of the equatorial Atlantic by the equatorial deep jets (2012)
    Wiley
    Details
    Publication Date: 2012-12-12
    Description: Equatorial deep jets (EDJs) are a prominent flow feature of the equatorial Atlantic below the Equatorial Undercurrent down to about 3000 m. Here we analyze long-term moored velocity and oxygen observations, as well as shipboard hydrographic and current sections acquired along 23°W and covering the depth range of the oxygen minimum zones of the eastern tropical North and South Atlantic. The moored zonal velocity data show high-baroclinic mode EDJ oscillations at a period of about 4.5 years. Equatorial oxygen observations which do not resolve or cover a full 4.5-yr EDJ cycle nevertheless reveal large variability, with oxygen concentrations locally spanning a range of more than 60 μmol kg−1. We study the effect of EDJs on the equatorial oxygen concentration by forcing an advection-diffusion model with the velocity field of the gravest equatorial basin mode corresponding to the observed EDJ cycle. The advection-diffusion model includes an oxygen source at the western boundary and oxygen consumption elsewhere. The model produces a 4.5-yr cycle of the oxygen concentration and a temporal phase difference between oxygen concentration and eastward velocity that is less than quadrature, implying a net eastward oxygen flux. The comparison of available observations and basin-mode simulations indicates that a substantial part of the observed oxygen variability at the equator can be explained by EDJ oscillations. The respective role of mean advection, EDJs, and other possible processes in shaping the mean oxygen distribution of the equatorial Atlantic at intermediate depth is discussed.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 3
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    Expansion of oxygen minimum zones may reduce available habitat for tropical pelagic fishes (2011)
    Springer Nature
    Details
    Publication Date: 2011-12-21
    Description: Expansion of oxygen minimum zones may reduce available habitat for tropical pelagic fishes Nature Climate Change 2, 33 04122011 doi: 10.1038/nclimate1304 Lothar Stramma Eric D. Prince Sunke Schmidtko Jiangang Luo John P. Hoolihan Martin Visbeck Douglas W. R. Wallace Peter Brandt Arne Körtzinger One of the impacts of ocean warming is a decrease in dissolved oxygen, with implications for valuable pelagic fish species. A study shows that the oxygenated upper ocean layer in the tropical northeast Atlantic thinned at a rate of around one metre per year between 1960 and 2010, and, by tracking individually tagged fish, demonstrates that this contraction in the oxygenated layer limited the movement of blue marlin.
    Print ISSN: 1758-678X
    Electronic ISSN: 1758-6798
    Topics: Geosciences
    Published by Springer Nature
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  • 4
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    N2O emissions from the northern Benguela upwelling system (2019)
    Wiley
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    Publication Date: 2019
    Description: Abstract The Benguela Upwelling system (BUS) is the most productive of all eastern boundary upwelling ecosystems and it hosts a well‐developed oxygen minimum zone. As such, the BUS is a potential hotspot for production of N2O, a potent greenhouse gas derived from microbially‐driven decay of sinking organic matter. Yet, the extent at which near‐surface waters emit N2O to the atmosphere in the BUS is highly uncertain. Here we present the first high‐resolution surface measurements of N2O across the northern part of the BUS (nBUS). We found strong gradients with a three‐fold increase in N2O concentrations near the coast as compared with open ocean waters. Our observations show enhanced sea‐to‐air fluxes of N2O (up to 1.67 nmol m−2 s−1) in association with local upwelling cells. Based on our data we suggest that the nBUS can account for 13% of the total coastal upwelling source of N2O to the atmosphere.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 5
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    Food availability outweighs ocean acidification effects in juvenile Mytilus edulis: laboratory and field experiments (2012)
    Wiley
    Details
    Publication Date: 2012-12-04
    Description: Ocean acidification is expected to decrease calcification rates of bivalves. Nevertheless in many coastal areas high p CO 2 variability is encountered already today. Kiel Fjord (Western Baltic Sea) is a brackish (12-20 g kg -1 ) and CO 2 enriched habitat, but the blue mussel Mytilus edulis dominates the benthic community. In a coupled field and laboratory study we examined the annual p CO 2 variability in this habitat and the combined effects of elevated p CO 2 and food availability on juvenile M. edulis growth and calcification. In the laboratory experiment, mussel growth and calcification were found to chiefly depend on food supply, with only minor impacts of p CO 2 up to 3350 μatm. Kiel Fjord was characterized by strong seasonal p CO 2 variability. During summer, maximal p CO 2 values of 2500 μatm were observed at the surface and 〉3000 μatm at the bottom. However, the field growth experiment revealed seven times higher growth and calcification rates of M. edulis at a high p CO 2 inner fjord field station (mean p CO 2 ca. 1000 μatm) in comparison to a low p CO 2 outer fjord station (ca. 600 μatm). In addition, mussels were able to outcompete the barnacle Amphibalanus improvisus at the high p CO 2 site. High mussel productivity at the inner fjord site was enabled by higher particulate organic carbon concentrations. Kiel Fjord is highly impacted by eutrophication, which causes bottom water hypoxia and consequently high seawater p CO 2 . At the same time, elevated nutrient concentrations increase the energy availability for filter feeding organisms such as mussels. Thus M. edulis can dominate over a seemingly more acidification resistant species such as A. improvisus . We conclude that benthic stages of M. edulis tolerate high ambient p CO 2 when food supply is abundant and that important habitat characteristics such as species interactions and energy availability need to be considered to predict species vulnerability to ocean acidification. © 2012 Blackwell Publishing Ltd
    Print ISSN: 1354-1013
    Electronic ISSN: 1365-2486
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Published by Wiley
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  • 6
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    Ventilation of the equatorial Atlantic by the equatorial deep jets (2013)
    Wiley
    Details
    Publication Date: 2013-01-04
    Description: [1]  Equatorial deep jets (EDJs) are a prominent flow feature of the equatorial Atlantic below the Equatorial Undercurrent down to about 3000 m. Here we analyze long-term moored velocity and oxygen observations, as well as shipboard hydrographic and current sections acquired along 23°W and covering the depth range of the oxygen minimum zones of the eastern tropical North and South Atlantic. The moored zonal velocity data show high-baroclinic mode EDJ oscillations at a period of about 4.5 years. Equatorial oxygen observations which do not resolve or cover a full 4.5-yr EDJ cycle nevertheless reveal large variability, with oxygen concentrations locally spanning a range of more than 60 μ mol kg −1 . We study the effect of EDJs on the equatorial oxygen concentration by forcing an advection-diffusion model with the velocity field of the gravest equatorial basin mode corresponding to the observed EDJ cycle. The advection-diffusion model includes an oxygen source at the western boundary and oxygen consumption elsewhere. The model produces a 4.5-yr cycle of the oxygen concentration and a temporal phase difference between oxygen concentration and eastward velocity that is less than quadrature, implying a net eastward oxygen flux. The comparison of available observations and basin-mode simulations indicates that a substantial part of the observed oxygen variability at the equator can be explained by EDJ oscillations. The respective role of mean advection, EDJs, and other possible processes in shaping the mean oxygen distribution of the equatorial Atlantic at intermediate depth is discussed.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 7
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    Characterization of a novel autonomous analyzer for seawater total alkalinity: Results from laboratory and field tests (2019)
    Wiley
    Details
    Publication Date: 2019
    Description: Abstract High‐quality seawater total alkalinity (AT) measurements are essential for reliable ocean carbon and acidification observations. Well‐established manual multipoint potentiometric titration methods already fulfill these requirements. The next step in the improvement of these observations is the increase of the spatial and temporal measuring resolution with minimal personnel and instrumental effort. For this, a rapid, automated underway analyzer meeting the same high requirements as the traditional method is necessary. In this study, we carried out a comprehensive characterization of the flow‐through analyzer CONTROS HydroFIA® TA (Kongsberg Maritime Contros GmbH, Kiel, Germany) for automated seawater AT measurements in the laboratory and in field with overall more than 5000 measurements. Under laboratory conditions, the analyzer featured a precision of ± 1.5 μmol kg−1 and an accuracy of ± 1.0 μmol kg−1, combined in an uncertainty of 1.6 – 2.0 μmol kg−1. High precision (± 1.1 μmol kg−1) and accuracy (−0.3 ± 2.8 μmol kg−1), and low uncertainty (2.0 – 2.5 μmol kg−1) were also achieved during field trials of 4 and 6 weeks duration. Although a linear drift appears to be the typical behavior of the system, this can be corrected for by regular reference measurements giving consistent measurement results. Another advantage of regular reference measurements is the early detection of any kind of malfunction due to its direct impact on the measurement performance. Based on the present study, recommendations for automated long‐term deployments are provided in order to gain optimal performance characteristics, aiming at the requirements for AT measurements.
    Electronic ISSN: 1541-5856
    Topics: Biology , Geosciences
    Published by Wiley on behalf of The Association for the Sciences of Limnology and Oceanography (ASLO).
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  • 8
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    Nitrous oxide during the onset of the Atlantic Cold Tongue (2016)
    Wiley
    Details
    Publication Date: 2016-11-12
    Description: The tropical Atlantic exerts a major influence in climate variability through strong air-sea interactions. Within this region, the eastern side of the equatorial band is characterized by strong seasonality, whereby the most prominent feature is the annual development of the Atlantic Cold Tongue (ACT). This band of low sea surface temperatures (∼22-23°C) is typically associated with upwelling-driven enhancement of surface nutrient concentrations and primary production. Based on a detailed investigation of the distribution and sea-to-air fluxes of N 2 O in the eastern equatorial Atlantic (EEA), we show that the onset and seasonal development of the ACT can be clearly observed in surface N 2 O concentrations, which increase progressively as the cooling in the equatorial region proceeds during spring-summer. We observed a strong influence of the surface currents of the EEA on the N 2 O distribution, which allowed identifying “high” and “low” concentration regimes that were, in turn, spatially delimited by the extent of the warm eastward-flowing North Equatorial Countercurrent and the cold westward-flowing South Equatorial Current. Estimated sea-to-air fluxes of N 2 O from the ACT (mean 5.18±2.59 µmol m −2 d −1 ) suggests that in May-July 2011 this cold-water band doubled the N 2 O efflux to the atmosphere with respect to the adjacent regions, highlighting its relevance for marine tropical emissions of N 2 O. This article is protected by copyright. All rights reserved.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 9
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    Computation of nitrate concentrations in turbid coastal waters using an in situ ultraviolet spectrophotometer (2011)
    Elsevier
    Details
    Publication Date: 2011-05-01
    Print ISSN: 1385-1101
    Electronic ISSN: 1873-1414
    Topics: Biology , Geosciences , Physics
    Published by Elsevier
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  • 10
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    Future ocean acidification will be amplified by hypoxia in coastal habitats (2012)
    Springer
    Details
    Publication Date: 2012-05-29
    Print ISSN: 0025-3162
    Electronic ISSN: 1432-1793
    Topics: Biology
    Published by Springer
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