Glass sponge reefs as a silicon sink. Marine Ecology Progress Series 441:1-14 (2011)
Supplementary Material – Prepared by Jackson W.F. Chu
I) Calculations of Si Reservoirs
Fraser Reef calculations:
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Ekman Grab = 0.00354 m3
Average dry sponge mass recovered from Fraser Reef: 69.3g
Therefore,
(69.3 g) / (0.00354 m3) = 19,576 g m-3 is the Density of Dry Sponge Mass
At Fraser Reef, the volumes of live sponges (79.3% bSi in dry sponge mass) and dead sponges
(62.7% bSi) are:
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8,264 m3 = volume of live sponge reef*
4,167 m3 = volume of dead sponge reef*
*Area of sponge coverage (Chu & Leys, 2010)* 0.6 m reef height
So,
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(0.793 bSi)*(19,576 g m-3) = 15,523 g m-3 is the density of bSi in live sponges
(0.627 bSi)*(19,576 g m-3) = 12,274 g m-3 is the density of bSi in dead sponges
(15,523 g m-3)*(8,264 m3) = 128,282,072 g, or 128,282 kg of bSi in live sponges
(12,274 g m-3)*(4,167 m3) = 51,145,758 g, or 51,146 kg of bSi in dead sponges
For Howe Reef:
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Average dry sponge in grabs = 60.1 g
Density of Dry Sponge Mass = 16,977 g m-3
Volume of live sponge reef = 6,145 m3
Volume of dead sponge reef = 5,450 m3
Mass of bSi in live sponge reef = 82,729 kg of bSi
Mass of bSi in dead sponge reef = 58,013 kg of bSi
For Galiano Reef:
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Average dry sponge in grabs = 94.2 g
Density of Dry Sponge Mass = 26,610 g m-3
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Volume of live sponge reef = 14,059 m3
Volume of dead sponge reef = 17,879 m3
Mass of bSi in live sponge reef = 296,669 kg of bSi
Mass of bSi in dead sponge reef = 298,302 kg of bSi
II) Calculations of Si input to Reef (from sponge growth)
Fraser Reef Calculations:
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Area of live sponge reef: 13,774 m2
Vertical Growth: 0.01 m year-1
So,
(13,774 m2)(0.01 m year-1) = 137.74 m3year-1 increase in volume of live sponge reef
Dry sponge mass in new growth:
(19,576 g m-3)*(137.74 m3 year-1) = 2,696,398 g year-1of dry sponge mass
bSi in new growth:
(0.793)(2,696,398 g year-1) = 2,138,244 g year-1of bSi
Molecular mass of bSi (silicon dioxide, SiO2) = 60.0843 g / mole
So,
(2,138,244 g year-1) / (60.0843 g mole) = 35,587 mole, or
3.56 x 104 mol of Si year-1 is added to Fraser Reef from live sponge growth
For Howe Reef:
Volume Increase = (10,242 m2)*(0.01 m year-1) = 102.42 m3
Dry sponge mass in new growth = (16,977 g m-3)*(102.42 m3) = 1,738,784 g year-1
bSi in new growth = 1,378,856 g of bSi (2.29 x 104 mol of Si year-1)
For Galiano Reef:
Volume Increase = (23,432 m2)*(0.01 m year-1) = 234.32 m3
Dry sponge mass in new growth = (26,610g m-3)*(234.32 m3) = 6,235,255 g year-1
bSi in new growth = 4,944,557 g of bSi (8.23 x 104 mol of Si year-1)
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III) Calculations of Si output from reef (from dissolution)
Fraser Reef Calculations
From Dissolution Experiments,
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Initial Mass of sponge bSi substrate = 0.025 g of bSi (SiO2, 60.0843 g mole-1)
Volume in experiment bottle = 0.05 L
Max dissolution observed = 10 µmol dSi L-1 after 8 months (242 days)
Therefore,
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Dissolution rate is calculated using initial: 1) volume, and 1.) initial mass of bSi
(10 µmol L-1)*(0.05 L) / (242 days) = 0.002066 µmol day-1
(0.002066 µmol day-1) / 0.025 g = 0.083 µmol dSi day-1 is released per gram of bSi
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Mass of bSi in dead sponge reef = 51,145,758 g bSi
So,
(0.083 µmol dSi day-1 per gram of bSi)*(51,145,758 g bSi) = 4,245,098 µmol dSi day-1
(4,245,098 µmol dSi day-1)*(365 days year-1) = 1,549,460,770 µmol dSi year-1, or
1,549 mol Si year-1 is released from dissolution of dead sponges at Fraser Reef
For Howe Reef:
Mass of bSi in dead sponge reef = 58,013,000 g of bSi
Annual rate of Si released = 1,758 mol Si year-1 (1.76 x 103 mol Si year-1)
For Galiano Reef:
Mass of bSi in dead sponge reef = 298,302,000 g of bSi
Annual rate of Si released = 9,037 mol Si year-1 (9.04 x 103 mol Si year-1)
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IV) Calculations of silicon sinks (Ratio of Si input to output)
Fraser Reef:
Input = 3.56 x 104 mol of Si year-1
Output = 1.55 x 103 mol Si year-1
= 23x silicon sink
Howe Reef:
Input: 2.29 x 104 mol of Si year-1
Output: 1.76 x 103 mol Si year= 13x silicon sink
Galiano Reef:
Input: 8.23 x 104 mol of Si year-1
Output: 9.04 x 103 mol Si year-1
= 9x silicon sink
For the 700 km2 area covered by glass sponge reefs:
Assuming a ratio of 50:50 live to dead sponge coverage over this area and using the “middle”
value of dry sponge mass density measured from Fraser Reef:
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Live Sponge Reef Si reservoir =
(0.793 bSi)*(19,576 g m-3)*(3.50 x 108 m2)*(0.6 m) = 3.26 x 1012 g bSi
(3.26 x 1012 g bSi) / (60.0843 g mol-1) = 5.43 x 1010 mol Si
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Dead Sponge Reef Si reservoir =
(0.627 bSi)*(19,576 g m-3)*(3.50 x 108 m2)*(0.6 m) = 2.58 x 1012 g bSi
(2.58 x 1012 g bSi) / (60.0843 g mol-1) = 4.29 x 1010 mol Si
Total Reservoir: (5.43 x 1010 mol Si) + (4.29 x 1010 mol Si) = 9.7 x 1010 mol Si
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Rate of Si input from sponge growth =
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(3.50 x 108 m2)*(0.01 m year-1) = 3.50 x 106 m3 year-1
(0.793 bSi)*(19,576 g m-3)*(3.50 x 106 m3 year-1) = 5.43 x 1010 g bSi year-1
(5.43 x 1010 g bSi year-1) / (60.0843 g / mole) = 9.04 x 108 mol Si year-1
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Rate of Si output from dissolution
(0.083 µmol Si day-1 is released per gram of bSi)*(2.58 x 1012 g bSi) = 2.14 x 105 mol Si day-1
(2.14 x 105 mol Si day-1)(365 days year-1) = 7.82 x 107 mol Si year-1
Silicon sink for 700 km2 of known glass sponge reefs:
(9.04 x 108 mol Si year-1) / (7.82 x 107 mol Si year-1)
= 12x silicon sink
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