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On-Shelf Nutrient Trapping Enhances the Fertility of the Southern Benguela Upwelling System.

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Title: On-Shelf Nutrient Trapping Enhances the Fertility of the Southern Benguela Upwelling System.
Authors: Flynn, R. F.1 flyraq001@myuct.ac.za, Granger, J.2, Veitch, J. A.3,4,5, Siedlecki, S.2, Burger, J. M.1, Pillay, K.5, Fawcett, S. E.1
Source: Journal of Geophysical Research. Oceans. Jun2020, Vol. 125 Issue 6, p1-24. 24p.
Subject Terms: *Fisheries, *Denitrification, *Oceanography, *Ocean dynamics, Methodology
Abstract: The southern Benguela upwelling system (SBUS) supports high rates of primary productivity that sustain important commercial fisheries. The exceptional fertility of this system is reportedly fueled not only by upwelled nutrients but also by nutrients regenerated on the broad and shallow continental shelf. We measured nutrient concentrations and the nitrogen (N) and oxygen (O) isotope ratios (δ15N and δ18O) of nitrate along four zonal lines in the SBUS in late summer and early winter to evaluate the extent to which regenerated nutrients augment the upwelled nutrient reservoir originating offshore. During summer upwelling, a decrease in on-shelf nitrate δ18O revealed that 0-48% of the subsurface nutrients derived from in situ remineralization. The nitrate regenerated on-shelf in the more quiescent winter (0-63% of total nitrate) extended further offshore along the mid-shelf. A shoreward increase in subsurface nitrate δ15N and a greater N deficit in on-shelf bottom waters further indicated N loss to benthic (and at times, watercolumn) denitrification coincident with the on-shelf remineralization. Our data show that remineralized nutrients get trapped on the SBUS shelf in summer through early winter, enhancing the nutrient pool that can be upwelled to support surface production. We hypothesize that this process is aided by a number of equatorward-flowing hydrographic fronts that impede the lateral exchange of surface waters. The extent to which nutrients remain trapped on the shelf has implications for the occurrence of hypoxic events in the SBUS. [ABSTRACT FROM AUTHOR]
Copyright of Journal of Geophysical Research. Oceans is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)
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  Data: On-Shelf Nutrient Trapping Enhances the Fertility of the Southern Benguela Upwelling System.
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  Data: <searchLink fieldCode="AR" term="%22Flynn%2C+R%2E+F%2E%22">Flynn, R. F.</searchLink><relatesTo>1</relatesTo><i> flyraq001@myuct.ac.za</i><br /><searchLink fieldCode="AR" term="%22Granger%2C+J%2E%22">Granger, J.</searchLink><relatesTo>2</relatesTo><br /><searchLink fieldCode="AR" term="%22Veitch%2C+J%2E+A%2E%22">Veitch, J. A.</searchLink><relatesTo>3,4,5</relatesTo><br /><searchLink fieldCode="AR" term="%22Siedlecki%2C+S%2E%22">Siedlecki, S.</searchLink><relatesTo>2</relatesTo><br /><searchLink fieldCode="AR" term="%22Burger%2C+J%2E+M%2E%22">Burger, J. M.</searchLink><relatesTo>1</relatesTo><br /><searchLink fieldCode="AR" term="%22Pillay%2C+K%2E%22">Pillay, K.</searchLink><relatesTo>5</relatesTo><br /><searchLink fieldCode="AR" term="%22Fawcett%2C+S%2E+E%2E%22">Fawcett, S. E.</searchLink><relatesTo>1</relatesTo>
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  Data: <searchLink fieldCode="JN" term="%22Journal+of+Geophysical+Research%2E+Oceans%22">Journal of Geophysical Research. Oceans</searchLink>. Jun2020, Vol. 125 Issue 6, p1-24. 24p.
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  Data: *<searchLink fieldCode="DE" term="%22Fisheries%22">Fisheries</searchLink><br />*<searchLink fieldCode="DE" term="%22Denitrification%22">Denitrification</searchLink><br />*<searchLink fieldCode="DE" term="%22Oceanography%22">Oceanography</searchLink><br />*<searchLink fieldCode="DE" term="%22Ocean+dynamics%22">Ocean dynamics</searchLink><br /><searchLink fieldCode="DE" term="%22Methodology%22">Methodology</searchLink>
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  Data: The southern Benguela upwelling system (SBUS) supports high rates of primary productivity that sustain important commercial fisheries. The exceptional fertility of this system is reportedly fueled not only by upwelled nutrients but also by nutrients regenerated on the broad and shallow continental shelf. We measured nutrient concentrations and the nitrogen (N) and oxygen (O) isotope ratios (δ15N and δ18O) of nitrate along four zonal lines in the SBUS in late summer and early winter to evaluate the extent to which regenerated nutrients augment the upwelled nutrient reservoir originating offshore. During summer upwelling, a decrease in on-shelf nitrate δ18O revealed that 0-48% of the subsurface nutrients derived from in situ remineralization. The nitrate regenerated on-shelf in the more quiescent winter (0-63% of total nitrate) extended further offshore along the mid-shelf. A shoreward increase in subsurface nitrate δ15N and a greater N deficit in on-shelf bottom waters further indicated N loss to benthic (and at times, watercolumn) denitrification coincident with the on-shelf remineralization. Our data show that remineralized nutrients get trapped on the SBUS shelf in summer through early winter, enhancing the nutrient pool that can be upwelled to support surface production. We hypothesize that this process is aided by a number of equatorward-flowing hydrographic fronts that impede the lateral exchange of surface waters. The extent to which nutrients remain trapped on the shelf has implications for the occurrence of hypoxic events in the SBUS. [ABSTRACT FROM AUTHOR]
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  Data: <i>Copyright of Journal of Geophysical Research. Oceans is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract.</i> (Copyright applies to all Abstracts.)
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        Value: 10.1029/2019JC015948
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        Text: English
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        PageCount: 24
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        Type: general
      – SubjectFull: Denitrification
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      – SubjectFull: Oceanography
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      – TitleFull: On-Shelf Nutrient Trapping Enhances the Fertility of the Southern Benguela Upwelling System.
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              Text: Jun2020
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              Y: 2020
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