Sedimentary phosphorus and iron cycling in and below the oxygen minimum zone of the northern Arabian Sea

Abstract. In this study, we investigate phosphorus (P) and iron (Fe) cycling in sediments along a depth transect from within to well below the oxygen minimum zone (OMZ) in the northern Arabian Sea (Murray Ridge). Pore-water and solid-phase analyses show that authigenic formation of calcium phosphate minerals (Ca-P) is largely restricted to where the OMZ intersects the seafloor topography, likely due to higher depositional fluxes of reactive P. Nonetheless, increased ratios of organic carbon to organic P (Corg/Porg) and to total reactive P (Corg/Preactive) in surface sediments indicate that the overall burial efficiency of P relative to Corg decreases under the low bottom water oxygen concentrations (BWO) in the OMZ. The relatively constant Fe/Al ratio in surface sediments along the depth transect suggest that corresponding changes in Fe burial are limited. Sedimentary pyrite contents are low throughout the ~25 cm sediment cores at most stations, as commonly observed in the Arabian Sea OMZ. However, pyrite is an important sink for reactive Fe at one station in the OMZ. A reactive transport model (RTM) was applied to quantitatively investigate P and Fe diagenesis at an intermediate station at the lower boundary of the OMZ (bottom water O2: ~14 μmol L−1). The RTM results contrast with earlier findings in showing that Fe redox cycling can control authigenic apatite formation and P burial in Arabian Sea sediment. In addition, results suggest that a large fraction of the sedimentary Ca-P is not authigenic, but is instead deposited from the water column and buried. Dust is likely a major source of this Ca-P. Inclusion of the unreactive Ca-P pool in the Corg/P ratio leads to an overestimation of the burial efficiency of reactive P relative to Corg along the depth transect. Moreover, the unreactive Ca-P accounts for ~85% of total Ca-P burial. In general, our results reveal large differences in P and Fe chemistry between stations in the OMZ, indicating dynamic sedimentary conditions under these oxygen-depleted waters.

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Sedimentary phosphorus and iron cycling in and below the oxygen minimum zone of the northern Arabian Sea

Biogeosciences Discussions ◽

10.5194/bgd-9-3829-2012 ◽

2012 ◽

Vol 9 (3) ◽

pp. 3829-3880 ◽

Cited By ~ 3

Author(s):

P. Kraal ◽

C. P. Slomp ◽

D. C. Reed ◽

G.-J. Reichart ◽

S. W. Poulton

Keyword(s):

Arabian Sea ◽

Bottom Water ◽

Surface Sediments ◽

Lower Boundary ◽

Oxygen Minimum Zone ◽

Apatite Formation ◽

Northern Arabian Sea ◽

Minimum Zone ◽

Oxygen Minimum ◽

Burial Efficiency

Abstract. In this study, we investigate phosphorus (P) and iron (Fe) cycling in sediments along a depth transect from within to well below the oxygen minimum zone (OMZ) in the northern Arabian Sea (Murray Ridge). Pore-water and solid-phase analyses show that authigenic formation of calcium phosphate minerals (Ca-P) is largely restricted to where the OMZ intersects the seafloor topography, likely due to higher depositional fluxes of reactive P. Nonetheless, increased ratios of organic carbon to organic P (Corg/Porg) and to total reactive P (Corg/Preactive) in surface sediments indicate that the overall burial efficiency of P relative to Corg decreases under the low bottom water oxygen concentrations (BWO) in the OMZ. The relatively constant Fe/Al ratio in surface sediments along the depth transect suggest that corresponding changes in Fe burial are limited. Sedimentary pyrite contents are low throughout the ~25-cm sediment cores at most stations, as commonly observed in the Arabian Sea OMZ. However, pyrite is an important sink for reactive Fe at one station in the OMZ. A reactive transport model (RTM) was applied to quantitatively investigate P and Fe diagenesis at an intermediate station at the lower boundary of the OMZ (bottom water O2: ~14 μ mol l−1). The RTM results contrast with earlier findings in showing that Fe redox cycling can control authigenic apatite formation and P burial in Arabian Sea sediment. In addition, results suggest that a large fraction of the sedimentary Ca-P is not authigenic, but is instead deposited from the water column and buried. Dust is likely a major source of this Ca-P. Inclusion of the unreactive Ca-P pool in the Corg/P ratio leads to an overestimation of the burial efficiency of reactive P relative to Corg along the depth transect. Moreover, the unreactive Ca-P accounts for ~85% of total Ca-P burial. In general, our results reveal large differences in P and Fe chemistry between stations in the OMZ, indicating dynamic sedimentary conditions under these oxygen-depleted waters.

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Short-term fate of phytodetritus in sediments across the Arabian Sea Oxygen Minimum Zone

Biogeosciences ◽

10.5194/bg-5-43-2008 ◽

2008 ◽

Vol 5 (1) ◽

pp. 43-53 ◽

Cited By ~ 36

Author(s):

J. H. Andersson ◽

C. Woulds ◽

M. Schwartz ◽

G. L. Cowie ◽

L. A. Levin ◽

...

Keyword(s):

Arabian Sea ◽

Inorganic Carbon ◽

Surface Sediments ◽

Dissolved Inorganic Carbon ◽

Oxygen Minimum Zone ◽

Short Term ◽

Minimum Zone ◽

Algal Material ◽

Oxygen Minimum

Abstract. The short-term fate of phytodetritus was investigated across the Pakistan margin of the Arabian Sea at water depths ranging from 140 to 1850 m, encompassing the oxygen minimum zone (~100–1100 m). Phytodetritus sedimentation events were simulated by adding ~44 mmol 13C-labelled algal material per m2 to surface sediments in retrieved cores. Cores were incubated in the dark, at in situ temperature and oxygen concentrations. Overlying waters were sampled periodically, and cores were recovered and sampled (for organisms and sediments) after durations of two and five days. The labelled carbon was subsequently traced into bacterial lipids, foraminiferan and macrofaunal biomass, and dissolved organic and inorganic pools. The majority of the label (20 to 100%) was in most cases left unprocessed in the sediment at the surface. The largest pool of processed carbon was found to be respiration (0 to 25% of added carbon), recovered as dissolved inorganic carbon. Both temperature and oxygen were found to influence the rate of respiration. Macrofaunal influence was most pronounced at the lower part of the oxygen minimum zone where it contributed 11% to the processing of phytodetritus.

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A 225 kyr record of dust supply, paleoproductivity and the oxygen minimum zone from the Murray Ridge (northern Arabian Sea)

Palaeogeography Palaeoclimatology Palaeoecology ◽

10.1016/s0031-0182(97)00071-0 ◽

1997 ◽

Vol 134 (1-4) ◽

pp. 149-169 ◽

Cited By ~ 101

Author(s):

Gert Jan Reichart ◽

Maryke den Dulk ◽

Hendrik Jan Visser ◽

Cornelis H. van der Weijden ◽

Willem J. Zachariasse

Keyword(s):

Arabian Sea ◽

Oxygen Minimum Zone ◽

Northern Arabian Sea ◽

Minimum Zone ◽

Oxygen Minimum

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Sedimentary trace element records over the last 200 kyr from within and below the northern Arabian Sea oxygen minimum zone

Marine Geology ◽

10.1016/j.margeo.2006.05.013 ◽

2006 ◽

Vol 231 (1-4) ◽

pp. 69-88 ◽

Cited By ~ 32

Author(s):

Cornelis H. van der Weijden ◽

Gert-Jan Reichart ◽

Bertil J.H. van Os

Keyword(s):

Trace Element ◽

Arabian Sea ◽

Oxygen Minimum Zone ◽

Northern Arabian Sea ◽

Minimum Zone ◽

Oxygen Minimum

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Effects of bottom water oxygen concentrations on mercury distribution and speciation in sediments below the oxygen minimum zone of the Arabian Sea

Marine Chemistry ◽

10.1016/j.marchem.2016.07.005 ◽

2016 ◽

Vol 186 ◽

pp. 24-32 ◽

Cited By ~ 16

Author(s):

Parthasarathi Chakraborty ◽

Robert P. Mason ◽

Saranya Jayachandran ◽

Krushna Vudamala ◽

Kazip Armoury ◽

...

Keyword(s):

Arabian Sea ◽

Bottom Water ◽

Oxygen Minimum Zone ◽

Mercury Distribution ◽

Water Oxygen ◽

Minimum Zone ◽

Oxygen Minimum ◽

Oxygen Concentrations

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Flux and accumulation of sedimentary particles off the continental slope of Pakistan: a comparison of water column and seafloor estimates from the oxygen minimum zone, NE Arabian Sea

Biogeosciences Discussions ◽

10.5194/bgd-10-12417-2013 ◽

2013 ◽

Vol 10 (7) ◽

pp. 12417-12449

Author(s):

H. Schulz ◽

U. von Rad

Keyword(s):

Water Column ◽

Water Depth ◽

Arabian Sea ◽

Lower Boundary ◽

Oxygen Minimum Zone ◽

High Mass ◽

Sediment Surface ◽

Accumulation Rates ◽

Minimum Zone ◽

Oxygen Minimum

Abstract. Due to the lack of bioturbation, the laminated muds from the oxygen-minimum zone (OMZ) off Pakistan provide a unique opportunity to precisely determine the vertical and lateral sediment fluxes in the near shore part of the northeastern Arabian Sea, and to explore the effects of the margin topography and the low oxygen conditions on the accumulation of organic matter and other particles. West of Karachi, in the Hab river area of EPT and WPT (Eastern and Western PAKOMIN Traps), 16 short sediment profiles from water depths between 250 m and 1970 m on a depth transect crossing the OMZ (~ 120 to ~ 1200 m water depth) were investigated, and correlated on the basis of a thick, light-gray- to reddish-colored turbidite layer. Varve counting yielded a date for this layer of AD 1905 to 1888. We adopted the young age which agrees with 210Pb- dating, and used this isochronous stratigraphic marker bed to calculate sediment accumulation rates, that we could directly compare with the flux rates from the sediment traps installed within the water column above. All traps in the area show exceptionally high, pulsed winter fluxes of up to 5000 mg m−2 d−1 in this margin environment. The lithic flux at the sea floor is as high as 4000 mg m−2 d−1 , and agrees remarkably well with the bulk winter flux of material. This holds as well for the individual bulk components (organic carbon, calcium carbonate, opal, lithic fraction). However, the high winter flux events (HFE) by their extreme mass of remobilized matter terminated the recording in the shallow traps by clogging the funnels. Based on our comparisons, we argue that HFE for the past 5000 yr most likely occurred as regular events within the upper OMZ off Pakistan. Coarse fraction and foraminiferal accumulation rates from sediment surface samples along the Hab transect show distribution patterns that seem to be a function of water depth and distance from the shelf. Some of these sediment fractions show sudden shifts at the lower boundary of the OMZ. However, the potential effect of the OMZ on carbon preservation in the area would by masked by high mass of fine-grained matter laterally advected, and by the pulsed nature of the resuspension events.

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Temporal variability in the northern Arabian Sea oxygen minimum zone (OMZ) during the last 225,000 years

Paleoceanography ◽

10.1029/98pa02203 ◽

1998 ◽

Vol 13 (6) ◽

pp. 607-621 ◽

Cited By ~ 199

Author(s):

G. J. Reichart ◽

L. J. Lourens ◽

W. J. Zachariasse

Keyword(s):

Temporal Variability ◽

Arabian Sea ◽

Oxygen Minimum Zone ◽

Northern Arabian Sea ◽

Minimum Zone ◽

Oxygen Minimum

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Short-term fate of phytodetritus across the Arabian Sea Oxygen Minimum Zone

Biogeosciences Discussions ◽

10.5194/bgd-4-2493-2007 ◽

2007 ◽

Vol 4 (4) ◽

pp. 2493-2523 ◽

Cited By ~ 1

Author(s):

J. H. Andersson ◽

C. Woulds ◽

M. Schwartz ◽

G. L. Cowie ◽

L. A. Levin ◽

...

Keyword(s):

Arabian Sea ◽

Inorganic Carbon ◽

Surface Sediments ◽

Dissolved Inorganic Carbon ◽

Oxygen Minimum Zone ◽

Short Term ◽

Minimum Zone ◽

Algal Material ◽

Oxygen Minimum

Abstract. The short-term fate of phytodetritus was investigated across the Pakistan margin of the Arabian Sea at water depths ranging from 140 to 1850 m, encompassing the oxygen minimum zone (~100–1100 m). Phytodetritus sedimentation events were simulated by adding 13C-labelled algal material to surface sediments in retrieved cores. Cores were incubated at in situ temperature and oxygen concentrations. Overlying waters were sampled periodically, and cores were recovered and sampled (for organisms and sediments) after durations of two and five days. The labelled carbon was subsequently traced into bacterial lipids, foraminiferan and macrofaunal biomass, and dissolved organic and inorganic pools. The majority of the label was left unprocessed in the sediment at the surface. The largest pool of processed carbon was found to be respiration, recovered as dissolved inorganic carbon. Both temperature and oxygen were found to influence the rate of respiration. Macrofaunal influence was most pronounced at the lower part of the oxygen minimum zone where it dominated the processing of phytodetritus.

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