Benthic phosphorus cycling in the Peruvian oxygen minimum zone
Oxygen minimum zones (OMZs) that impinge on continental margins favor the release of phosphorus (P) from the sediments to the water column, enhancing primary productivity and the maintenance or expansion of low-oxygen waters. A comprehensive field program in the Peruvian OMZ was undertaken to identi...
| Main Authors: | , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2016-03-01
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| Series: | Biogeosciences |
| Online Access: | http://www.biogeosciences.net/13/1367/2016/bg-13-1367-2016.pdf |
| Summary: | Oxygen minimum zones (OMZs) that impinge on continental margins favor the
release of phosphorus (P) from the sediments to the water column, enhancing
primary productivity and the maintenance or expansion of low-oxygen waters. A
comprehensive field program in the Peruvian OMZ was undertaken to identify
the sources of benthic P at six stations, including the analysis of particles
from the water column, surface sediments, and pore fluids, as well as in situ
benthic flux measurements. A major fraction of solid-phase P was bound as
particulate inorganic P (PIP) both in the water column and in sediments.
Sedimentary PIP increased with depth in the sediment at the expense of
particulate organic P (POP). The ratio of particulate organic carbon (POC) to
POP exceeded the Redfield ratio both in the water column (202 ± 29) and
in surface sediments (303 ± 77). However, the POC to total particulate
P (TPP = POP + PIP) ratio was close to Redfield in the water column
(103 ± 9) and in sediment samples (102 ± 15). This suggests that
the relative burial efficiencies of POC and TPP are similar under low-oxygen
conditions and that the sediments underlying the anoxic waters on the Peru
margin are not depleted in P compared to Redfield. Benthic fluxes of
dissolved P were extremely high (up to
1.04 ± 0.31 mmol m<sup>−2</sup> d<sup>−1</sup>), however, showing that a lack of
oxygen promotes the intensified release of dissolved P from sediments, whilst
preserving the POC / TPP burial ratio. Benthic dissolved P fluxes were
always higher than the TPP rain rate to the seabed, which is proposed to be
caused by transient P release by bacterial mats that had stored P during
previous periods when bottom waters were less reducing. At one station
located at the lower rim of the OMZ, dissolved P was taken up by the
sediments, indicating ongoing phosphorite formation. This is further
supported by decreasing porewater phosphate concentrations with sediment
depth, whereas solid-phase P concentrations were comparatively high. |
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| ISSN: | 1726-4170 1726-4189 |