Tune in on 11.57 µHz and listen to primary production
In this paper we present an elegant approach to reconstruct slowly varying gross primary production (GPP) as a function of time, based on O<sub>2</sub> time series. The approach, called complex demodulation, is based on a direct analogy with amplitude-modulated (AM) radio signals. The...
| Main Authors: | , , |
|---|---|
| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2017-11-01
|
| Series: | Biogeosciences |
| Online Access: | https://www.biogeosciences.net/14/5271/2017/bg-14-5271-2017.pdf |
| _version_ | 1819055171347415040 |
|---|---|
| author | T. J. S. Cox T. J. S. Cox J. E. E. van Beusekom K. Soetaert |
| author_facet | T. J. S. Cox T. J. S. Cox J. E. E. van Beusekom K. Soetaert |
| author_sort | T. J. S. Cox |
| collection | DOAJ |
| description | In this paper we present an elegant approach to reconstruct slowly
varying gross primary production (GPP) as a function of time, based on O<sub>2</sub> time series. The
approach, called complex demodulation, is based on a direct analogy with
amplitude-modulated (AM) radio signals. The O<sub>2</sub> concentrations
oscillating at the diel frequency (or 11.57 µHz) can be seen as a
<q>carrier wave</q>, while the time variation in the amplitude of this carrier
wave is related to the time-varying GPP. The relation follows from an
analysis in the frequency domain of the governing equations of O<sub>2</sub>
dynamics. After the theoretical derivation, we assess the performance of the
approach by applying it to three artificial O<sub>2</sub> time series, generated
with models representative of a well-mixed vertical water column, a river
and an estuary. These models are forced with hourly observed incident
irradiance, resulting in a variability of GPP on scales from hours to months.
The dynamic build-up of algal biomass further increases the seasonality.
Complex demodulation allows for reconstruction, with great precision, of time-varying
GPP of the vertical water column and the river model. Surprisingly, it is
possible to derive daily averaged GPP – complex demodulation thus
reconstructs the amplitude of every single diel cycle. Also, in estuaries time-varying GPP can be reconstructed to a great extent. But there, the influence
of the tides prevent achieving the same temporal resolution. In particular, the combination of horizontal O<sub>2</sub> gradients with quasi-diurnal harmonics in the tides
interferes with the complex demodulation procedure and introduces spurious amplitude variation
that can not be attributed to GPP. We demonstrate that these spurious effects also occur in real-world
time series (Hörnum Tief, Germany). The spurious effects due to K1 and P1 quasi-diurnals
can not be distinguished from GPP. However, the spurious fluctuations introduced by O1 and Q1
can be removed to a large extent by increasing the averaging time to 15 days. As such, we
demonstrate that a good estimate of the running 15-day average of GPP can be
obtained in tidal systems. Apart from the direct merits of estimating GPP
from O<sub>2</sub> time series, the analysis in the frequency domain enhances
our insights into O<sub>2</sub> dynamics in tidal systems in general, and into the
performance of O<sub>2</sub> methods to estimate GPP in particular. |
| first_indexed | 2024-12-21T13:03:17Z |
| format | Article |
| id | doaj.art-f56b88ef0f6c4257a7eb0bed5cce4a28 |
| institution | Directory Open Access Journal |
| issn | 1726-4170 1726-4189 |
| language | English |
| last_indexed | 2024-12-21T13:03:17Z |
| publishDate | 2017-11-01 |
| publisher | Copernicus Publications |
| record_format | Article |
| series | Biogeosciences |
| spelling | doaj.art-f56b88ef0f6c4257a7eb0bed5cce4a282022-12-21T19:03:06ZengCopernicus PublicationsBiogeosciences1726-41701726-41892017-11-01145271528010.5194/bg-14-5271-2017Tune in on 11.57 µHz and listen to primary productionT. J. S. Cox0T. J. S. Cox1J. E. E. van Beusekom2K. Soetaert3University of Antwerp, Department of Biology, Ecosystem Management research group, Universiteitsplein 1, 2610 Anwerpen, BelgiumRoyal Netherlands Institute of Sea Research (NIOZ) and University of Utrecht, Korringaweg 7, P.O. Box 140, 4400 AC Yerseke, the NetherlandsHelmholtz-Zentrum Geesthacht. Institute for Coastal Research, Max-Planck-Strasse 1, 21502 Geesthacht, GermanyRoyal Netherlands Institute of Sea Research (NIOZ) and University of Utrecht, Korringaweg 7, P.O. Box 140, 4400 AC Yerseke, the NetherlandsIn this paper we present an elegant approach to reconstruct slowly varying gross primary production (GPP) as a function of time, based on O<sub>2</sub> time series. The approach, called complex demodulation, is based on a direct analogy with amplitude-modulated (AM) radio signals. The O<sub>2</sub> concentrations oscillating at the diel frequency (or 11.57 µHz) can be seen as a <q>carrier wave</q>, while the time variation in the amplitude of this carrier wave is related to the time-varying GPP. The relation follows from an analysis in the frequency domain of the governing equations of O<sub>2</sub> dynamics. After the theoretical derivation, we assess the performance of the approach by applying it to three artificial O<sub>2</sub> time series, generated with models representative of a well-mixed vertical water column, a river and an estuary. These models are forced with hourly observed incident irradiance, resulting in a variability of GPP on scales from hours to months. The dynamic build-up of algal biomass further increases the seasonality. Complex demodulation allows for reconstruction, with great precision, of time-varying GPP of the vertical water column and the river model. Surprisingly, it is possible to derive daily averaged GPP – complex demodulation thus reconstructs the amplitude of every single diel cycle. Also, in estuaries time-varying GPP can be reconstructed to a great extent. But there, the influence of the tides prevent achieving the same temporal resolution. In particular, the combination of horizontal O<sub>2</sub> gradients with quasi-diurnal harmonics in the tides interferes with the complex demodulation procedure and introduces spurious amplitude variation that can not be attributed to GPP. We demonstrate that these spurious effects also occur in real-world time series (Hörnum Tief, Germany). The spurious effects due to K1 and P1 quasi-diurnals can not be distinguished from GPP. However, the spurious fluctuations introduced by O1 and Q1 can be removed to a large extent by increasing the averaging time to 15 days. As such, we demonstrate that a good estimate of the running 15-day average of GPP can be obtained in tidal systems. Apart from the direct merits of estimating GPP from O<sub>2</sub> time series, the analysis in the frequency domain enhances our insights into O<sub>2</sub> dynamics in tidal systems in general, and into the performance of O<sub>2</sub> methods to estimate GPP in particular.https://www.biogeosciences.net/14/5271/2017/bg-14-5271-2017.pdf |
| spellingShingle | T. J. S. Cox T. J. S. Cox J. E. E. van Beusekom K. Soetaert Tune in on 11.57 µHz and listen to primary production Biogeosciences |
| title | Tune in on 11.57 µHz and listen to primary production |
| title_full | Tune in on 11.57 µHz and listen to primary production |
| title_fullStr | Tune in on 11.57 µHz and listen to primary production |
| title_full_unstemmed | Tune in on 11.57 µHz and listen to primary production |
| title_short | Tune in on 11.57 µHz and listen to primary production |
| title_sort | tune in on 11 57 µhz and listen to primary production |
| url | https://www.biogeosciences.net/14/5271/2017/bg-14-5271-2017.pdf |
| work_keys_str_mv | AT tjscox tuneinon1157μhzandlistentoprimaryproduction AT tjscox tuneinon1157μhzandlistentoprimaryproduction AT jeevanbeusekom tuneinon1157μhzandlistentoprimaryproduction AT ksoetaert tuneinon1157μhzandlistentoprimaryproduction |