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Phosphate cycling in Bering Sea sediments

Phosphate cycling in Bering Sea sediments. Background Questions Results Bering Sea Domains Importance of Benthos. Emily S Davenport, David H Shull and Allan H Devol. Image: C. Ashjian. 40-50%. 40-50%. Dissolved phosphate. Fe-bound phosphate. Organic phosphorus. Oxic sediments

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Phosphate cycling in Bering Sea sediments

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  1. Phosphate cycling in Bering Sea sediments Background Questions Results Bering Sea Domains Importance of Benthos Emily S Davenport, David H Shull and Allan H Devol Image: C. Ashjian

  2. 40-50% 40-50% Dissolved phosphate Fe-bound phosphate Organic phosphorus Oxic sediments (Oxygen present) Dissolved phosphate Fe-bound phosphate Organic phosphorus Fe-bound phosphate Organic phosphorus Dissolved phosphate Anoxic sediments (Minimal oxygen present) Authigenic apatite Sediment surface Adapted from Sundby et al. 1992

  3. The role of the benthos in phosphorus geochemistry

  4. Overlying water column Overlying water column HPO4+ Fe(OH)3 HPO4+ Fe(OH)3 HPO4+ Fe(OH)3 Oxic zone Oxic zone HPO42- Fe2+ HPO42- Fe2+ Anoxic zone Anoxic zone HPO42- Fe2+

  5. Questions • Does phosphate flux co-vary with oxygen flux? • Does phosphate flux co-vary with amorphous iron-hydroxide concentrations? • Does phosphate flux co-vary with burrow numbers?

  6. St. Lawrence Island Alaska Image: S. Dahle, NOAA

  7. 50m 100m 200m St. Lawrence Island Northern Bering shelf Alaska Outer shelf Middle shelf Off shelf- Continental slope and Aleutian Basin

  8. Phosphate adsorption

  9. Shake for 24 hours 20mL sediment 0µM, 10µM, 20µM, 30µM, 40µM or 50µM Centrifuge Filter HPO42- Image: D. Shull

  10. 80 120 60 100 25 0 2 4 6 8 10 40 80 20 60 15 20 40 10 0 20 5 0 -20 0 0 2 4 6 -20 -5 -10 0 5 10 15 20 Outer-shelf domain Freundlich isotherm: C*=KC K= linear adsorption coefficient Station 31 Station 79 Station 106 y=61.1x-393 R2=0.824 y=3.10x-37.9 R2=0.608 C* (µmole kg-1) Mass of phosphate adsorbed/desorbed C (µmole L-1) Final concentration of dissolved phosphate *All linear regressions are statistically significant at the α = 0.05 level

  11. 100 80 60 40 20 Station 21 Station 27 Station 59 0 60 50 40 80 30 60 20 40 20 10 0 0 -20 Middle-shelf domain C* (µmole kg-1) Mass of phosphate adsorbed/desorbed 0 2 4 6 8 10 0 1 2 3 4 0 2 4 6 8 10 12 14 C (µmole L-1) Final concentration of dissolved phosphate

  12. 30 25 25 20 0 15 30 45 0 5 10 15 20 25 30 20 40 15 35 15 30 10 10 25 5 20 5 15 0 0 10 0 5 10 15 20 25 30 35 5 -5 0 Middle-shelf domain Station 21 Station 27 Station 59 ΔC (Cfinal-Cinitial; µmole L-1) y=0.983x-6.14 R2=0.986 y=0.994x-2.98 R2=0.999 y=1.01x-9.35 R2=0.976 Cinitial (µmole L-1) *All linear regressions are statistically significant at the α = 0.05 level

  13. Phosphate fluxes:Whole-core incubations

  14. SmartChem M.I.M.S. Images: D. Shull, A. Devol

  15. Amorphous iron-hydroxides Ammonium oxalate, oxalic acid mixture Chao and Zhou, 1983 25mL Shake, 4 hours in the dark Centrifuge, dilute to 50mls and analyze for iron on flame AAS

  16. Outer shelf vs. middle shelf:Phosphate flux

  17. 120 100 80 60 40 20 0 -20 Outer shelf: Phosphate flux co-varies with sediment oxygen consumption Phosphate flux (µmole m-2 d-1) y=-0.260x+9.25 R2=0.604 p=0.00819 0 -500 -1000 -1500 -2000 -2500 -3000 -3500 -4000 Sediment oxygen consumption (µmole m-2 d-1)

  18. Outer shelf 8 7 6 5 Top 0.5-cm pore-water dissolved phosphate (µmole L-1) 4 3 y=-0.0279x+7.93 R2=0.352 F[1,8]=5.43 p=0.0421 2 1 0 0 50 100 150 200 Top 0.5-cm sediment amorphous iron-hydroxides (µmole g-1)

  19. 60 50 40 30 Phosphate flux (µmole m-2 d-1) 20 y= 2.07x-17.8 R2=0.751 p= 0.00117 10 0 Burrow numbers 0 5 10 15 20 25 30 35 Middle shelf: Phosphate flux co-varies with burrow numbers

  20. Stn 21 Stn 27 Stn 59 Dissolved phosphate (µmole L-1) 0 20 40 60 80 100 0 5 10 Depth (cm) 15 20 25

  21. A special thanks to: Dr. Suzanne Strom Funding from NSF The captain and crew of the USCGC Healy Bonnie Chang and Heather Whitney for assistance with sample processing Erin Macri and Calvin Mordy for assistance with sample analysis My family and friends for all their encouragement and support QUESTIONS?

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