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Co-limitation of diatoms by iron and silicic acid in the equatorial Pacific

Co-limitation of diatoms by iron and silicic acid in the equatorial Pacific
Co-limitation of diatoms by iron and silicic acid in the equatorial Pacific
The relative roles of silicon (Si) and iron (Fe) as limiting nutrients in the eastern equatorial Pacific (EEP) were examined in a series of nine microcosm experiments conducted over two years between 110°W and 140°W longitude. Si and Fe additions had consistently different but synergistic effects on macronutrient use, phytoplankton biomass and phytoplankton community structure. Silicon addition increased silicic acid use and biogenic silica production, but had no significant effect on the use of inorganic nitrogen or orthophosphate, chlorophyll accumulation, particulate inorganic (PIC) carbon accumulation, or plankton community composition relative to controls. That result, together with observations that Si addition increased the cellular Si content of the numerically dominant diatom by not, vert, similar50%, indicates that the main effect of Si was to regulate diatom silicification. Like the effect of Si, Fe addition increased the rate of silicic acid use and biogenic silica production and had no effect on PIC production. Unlike the effect of Si, Fe addition also enhanced rates of organic matter production, had no effect on cellular Si content of diatoms, and resulted in the growth of initially rare, large (>40 ?m) diatoms relative to controls, indicating that Fe limitation acts mainly through its effects on growth rate and phytoplankton community composition. A pennate diatom of the genus Pseudo-nitzschia dominated the diatom assemblage in situ, grew readily in the controls and did not show a strong growth response to either Fe or Si addition suggesting that its growth was regulated by other factors such as grazing or light. Addition of germanium, an inhibitor of diatom cell division, eliminated the effects of Fe on macronutrient use, biogenic silica production and chlorophyll accumulation and phytoplankton community composition, consistent with a predominantly diatom response to Fe addition. The lack of a response of PIC production to Fe suggests that coccolithophores were not Fe limited. Addition of Fe and Si together resulted in the greatest levels of nutrient drawdown and biomass accumulation through the effect of Fe in promoting the growth of large diatoms. The results suggest a form of co-limitation with Si regulating diatom silicification and the rate of biogenic silica production while Fe regulates the production of organic matter through limitation of phytoplankton growth rates, in particular those of large diatoms. The results argue against Si regulation of new production in the EEP under average upwelling conditions. Iron addition was necessary and sufficient to stimulate complete removal of nitrate within the equatorial upwelling zone suggesting that new production was restricted by low ambient dissolved Fe consistent with results from in situ Fe fertilization experiments conducted to the south of the equator outside of the equatorial upwelling zone.
Co-limitation, Nutrient limitation, Silicon, Iron, Equatorial upwelling, Diatoms, Pacific Ocean, eastern equatorial Pacific
0967-0645
493-511
Brzezinski, Mark A.
9d492cdc-c042-4e03-a95c-413306b28874
Baines, Stephen B.
ce771517-bff9-4286-9206-9acc19763176
Balch, William M.
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Beucher, Charlotte P.
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Chai, Fei
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Dugdale, Richard C.
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Krause, Jeffrey W.
ac5eb1a3-66e3-4c7f-a57d-8f69438e6399
Landry, Michael R.
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Marchi, Albert
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Measures, Chris I.
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Nelson, David M.
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Parker, Alexander E.
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Poulton, Alex J.
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Selph, Karen E.
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Strutton, Peter G.
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Taylor, Andrew G.
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Twining, Benjamin S.
480e107b-8504-4251-b650-d0a3ffccd9db
Brzezinski, Mark A.
9d492cdc-c042-4e03-a95c-413306b28874
Baines, Stephen B.
ce771517-bff9-4286-9206-9acc19763176
Balch, William M.
18270567-fc45-4bc9-bd82-253d473e9564
Beucher, Charlotte P.
a5972a6a-de7d-4976-827f-8d3e734b6102
Chai, Fei
a396fa21-9b57-455f-841a-3ffbb0fb2bbb
Dugdale, Richard C.
7c44a008-5f02-4284-8097-5a3b1f4292b1
Krause, Jeffrey W.
ac5eb1a3-66e3-4c7f-a57d-8f69438e6399
Landry, Michael R.
17fdae52-4f30-4541-9d96-3ee9918384d1
Marchi, Albert
fc963ce9-a457-4bab-b394-7ff19eaf9293
Measures, Chris I.
9f8e1866-4690-46f1-b5af-856a58f78c5a
Nelson, David M.
10949db8-c5d3-4ffe-b8f6-60febec6ae95
Parker, Alexander E.
da008878-086b-449c-9475-6d922df5662a
Poulton, Alex J.
14bf64a7-d617-4913-b882-e8495543e717
Selph, Karen E.
70cbf564-8633-4fae-896d-c0aebbc3705a
Strutton, Peter G.
8ab6c4b3-ad21-41ae-b64a-9cff50d515e5
Taylor, Andrew G.
13726b5f-c661-4129-a545-42a9d6077d0e
Twining, Benjamin S.
480e107b-8504-4251-b650-d0a3ffccd9db

Brzezinski, Mark A., Baines, Stephen B., Balch, William M., Beucher, Charlotte P., Chai, Fei, Dugdale, Richard C., Krause, Jeffrey W., Landry, Michael R., Marchi, Albert, Measures, Chris I., Nelson, David M., Parker, Alexander E., Poulton, Alex J., Selph, Karen E., Strutton, Peter G., Taylor, Andrew G. and Twining, Benjamin S. (2011) Co-limitation of diatoms by iron and silicic acid in the equatorial Pacific. Deep Sea Research Part II: Topical Studies in Oceanography, 58 (3-4), 493-511. (doi:10.1016/j.dsr2.2010.08.005).

Record type: Article

Abstract

The relative roles of silicon (Si) and iron (Fe) as limiting nutrients in the eastern equatorial Pacific (EEP) were examined in a series of nine microcosm experiments conducted over two years between 110°W and 140°W longitude. Si and Fe additions had consistently different but synergistic effects on macronutrient use, phytoplankton biomass and phytoplankton community structure. Silicon addition increased silicic acid use and biogenic silica production, but had no significant effect on the use of inorganic nitrogen or orthophosphate, chlorophyll accumulation, particulate inorganic (PIC) carbon accumulation, or plankton community composition relative to controls. That result, together with observations that Si addition increased the cellular Si content of the numerically dominant diatom by not, vert, similar50%, indicates that the main effect of Si was to regulate diatom silicification. Like the effect of Si, Fe addition increased the rate of silicic acid use and biogenic silica production and had no effect on PIC production. Unlike the effect of Si, Fe addition also enhanced rates of organic matter production, had no effect on cellular Si content of diatoms, and resulted in the growth of initially rare, large (>40 ?m) diatoms relative to controls, indicating that Fe limitation acts mainly through its effects on growth rate and phytoplankton community composition. A pennate diatom of the genus Pseudo-nitzschia dominated the diatom assemblage in situ, grew readily in the controls and did not show a strong growth response to either Fe or Si addition suggesting that its growth was regulated by other factors such as grazing or light. Addition of germanium, an inhibitor of diatom cell division, eliminated the effects of Fe on macronutrient use, biogenic silica production and chlorophyll accumulation and phytoplankton community composition, consistent with a predominantly diatom response to Fe addition. The lack of a response of PIC production to Fe suggests that coccolithophores were not Fe limited. Addition of Fe and Si together resulted in the greatest levels of nutrient drawdown and biomass accumulation through the effect of Fe in promoting the growth of large diatoms. The results suggest a form of co-limitation with Si regulating diatom silicification and the rate of biogenic silica production while Fe regulates the production of organic matter through limitation of phytoplankton growth rates, in particular those of large diatoms. The results argue against Si regulation of new production in the EEP under average upwelling conditions. Iron addition was necessary and sufficient to stimulate complete removal of nitrate within the equatorial upwelling zone suggesting that new production was restricted by low ambient dissolved Fe consistent with results from in situ Fe fertilization experiments conducted to the south of the equator outside of the equatorial upwelling zone.

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More information

Published date: February 2011
Keywords: Co-limitation, Nutrient limitation, Silicon, Iron, Equatorial upwelling, Diatoms, Pacific Ocean, eastern equatorial Pacific
Organisations: Marine Biogeochemistry

Identifiers

Local EPrints ID: 176521
URI: http://eprints.soton.ac.uk/id/eprint/176521
ISSN: 0967-0645
PURE UUID: f9ed75e5-f647-4a64-a9f9-96f4069b68ed

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Date deposited: 08 Mar 2011 09:51
Last modified: 14 Mar 2024 02:39

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Contributors

Author: Mark A. Brzezinski
Author: Stephen B. Baines
Author: William M. Balch
Author: Charlotte P. Beucher
Author: Fei Chai
Author: Richard C. Dugdale
Author: Jeffrey W. Krause
Author: Michael R. Landry
Author: Albert Marchi
Author: Chris I. Measures
Author: David M. Nelson
Author: Alexander E. Parker
Author: Alex J. Poulton
Author: Karen E. Selph
Author: Peter G. Strutton
Author: Andrew G. Taylor
Author: Benjamin S. Twining

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