Kinetics of silicic acid uptake by natural diatom assemblages in two Gulf Stream warm-core rings

Dm, Nelson; Brzezinski, MA

doi:10.3354/meps062283

Cited by 79 publications

(28 citation statements)

References 28 publications

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“…In our 1-D model for the EEP, we do not include Fe as a limiting nutrient explicitly, but rather consider it's role implicitly through the parameters that determine the growth rate of diatoms. There are two parameters in our current model reflecting Fe limitation, alpha, α, the slope of the photosynthetic rate over irradiance at low irradiance, and K Si(OH)4 , the halfsaturation for Si(OH) 4 uptake which varies considerably (Nelson and Brzezinski, 1990;Nelson and Treguer, 1992). When the model was run to mimic an Fe enrichment experiment ecological behaviors similar to these observed during the field Fe enrichment experiments (Martin et al, 1994;Coale et al, 1996;Boyd et al, 2000) resulted (Chai et al, in press).…”

Section: The Role Of Iron In Si Limitation Of Diatomsmentioning

confidence: 99%

Sources and fates of silicon in the ocean: the role of diatoms in the climate and glacial cycles

Dugdale

Wilkerson

2001

Sci. Mar.

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INTRODUCTIONThe biogeochemistry of silicon (Si) is the focus of considerable contemporary attention by geochemists, paleoceanographers and paleoclimatologists. Biologists are showing revived interest in the Si cycle in relation to diatom productivity as it's very strong role in marine productivity (e.g. Smetacek, 1999) and effect on ocean-atmosphere processes becomes apparent, following a period in which the focus was almost exclusively on smaller and smaller planktonic organisms. The objective of this communication is to review the role of biological processes in the formation of the ocean Si environment first at the broad scale and then in more detail in two special settings, the equatorial Pacific and the Southern Ocean. In doing so, we will follow the evolution of a set of nitrogen (N) based models, that conclude with inclusion of Si and it's impact on global carbon cycles and paleoclimatology. We will examine the differences between the oceanic Si and N cycle, the existence of areas of unusually low silicate relative to nitrate concentrations and how we think they are formed. The concept of the Pacific equatorial upwelling area as a Si limited chemostatlike system and the model complexity necessary to describe its functioning will be presented. SUMMARY: Diatoms with their fast growth rates and obligate requirement for Si have a unique relationship to the oceanic Si cycle with the potential for controlling the nutrient and CO 2 environment of large important areas of the ocean. The new production of diatoms based on both new nitrogen and Si sources is described using a Si-pump based upon the differential regeneration of the two elements. This approach, applied to the eastern equatorial Pacific, showed diatoms to respond as in a Si-limited chemostat, to the low source Si(OH) 4 in the Equatorial UnderCurrent. Increased Si(OH) 4 results in increased diatom productivity, suppression of non-diatom populations and decreased surface pCO 2 . The deficiency in source concentrations of Si(OH) 4 results from low Si(OH) 4 :NO 3 water originating in the vicinity of the Antarctic Polar Front, a consequence of the extraordinary trapping of Si by the Southern Ocean. In glacial periods this trapping is reduced several fold and likely results in increased Si(OH) 4 export to the north, and increased Si(OH) 4 production and deposition at the equatorial Pacific which can be expected to reduce surface pCO 2 . The connections between the eastern equatorial Pacific export production and Southern Ocean Si trapping may provide a major biogeochemical feedback system with implications for contemporary and paleoclimatology.

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Section: The Role Of Iron In Si Limitation Of Diatomsmentioning

confidence: 99%

Sources and fates of silicon in the ocean: the role of diatoms in the climate and glacial cycles

Dugdale

Wilkerson

2001

Sci. Mar.

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“…Goering et al 1973, Azam & Chisholm 1976, Nelson et al 1981, Nelson & Brzezinski 1990. These studies have shown the Michaelis-Menten hyperbola (Eq.…”

Section: Introductionmentioning

confidence: 99%

“…For diatoms from all areas of the ocean examined to date the dependence of the specific uptake rate of silicic acid ( V ) and the division rate (p) on the extracellular silicic acid concentration can be fit reasonably well by hyperbolic saturation functions of the form of the Michaelis-Menten equation for enzyme kinetics or the Monod equation for the substratelimited growth of bacteria (e.g. Paasche 1973a, b, Nelson et al 1976, Nelson & Brzezinski 1990 where V, , , represents the maximum uptake rate, p,,, the maximum growth rate and km and k, the silicic acid concentrations that respectively limit V and p to % of their maximum values. Eqs.…”

Section: Introductionmentioning

confidence: 99%

Role of silicon as a limiting nutrient to Antarctic diatoms: evidence from kinetic studies in the Ross Sea ice-edge zone

Nelson¹,

Tréguer²

1992

Mar. Ecol. Prog. Ser.

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262

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During the austral summer of 1990 an intense, diatom-dominated, ice-edge phytoplankton bloom in the southwestern Ross Sea resulted in depletion of silicic acid, nitrate and phosphate to concentrations much lower than is typical for Antarctic surface waters. Silicic acid was depleted to <6 FM within the core of the meltwater field, where biogenic particulate silica concentrations exceeded 20 pm01 1-' Three Si uptake kinetic experiments were conducted on natural phytoplankton assemblages from the nutrient-depleted zone; 30Si-labeled Si(OH), was used to measure the uptake rate at concentrations ranging from 1 to 20 PM above ambient. Dependence of the spec~fic uptake rate ( V ) on silicic acid concentration conformed well to a Michaelis-Menten saturation model; maximum uptake rates (V,,,,,) ranged from 0.0022 to 0.0028 h-' which corresponds to maximum growth rates of 0.08 to 0.10 doublings d-l. Half-saturation constants (km) ranged from 1.1 to 4.6 PM, a range similar to values found in other areas of the ocean and considerably lower than those previously reported for several Antarctic d~atom species in culture studies. Results indicate detectable, but weak, substrate limitation of s~llcic acid uptake rate by the naturally occurring diatom assemblage in the western Ross Sea. Significant Si limitation in other subsystems of the Southern Ocean would be possible only if their resident diatom assemblages had much lower affinity for silicic acid than we observed.

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“…The availability of dissolved Si has been shown to control diatom silica production rates, at least at times, in every natural system examined to date (Nelson et aI. 1976, Nelson & Brzezinski 1990, Nelson & Treguer 1992, Brzezinski & Nelson 1996, Nelson & Dortch 1996. Limitation of diatom metabolism by the supply rate of silicic acid results in a physiological cascade that affects diatom primary productivity and nitrogen use (Dugdale et al 1981), potentially altering regional nitrogen and carbon cycling.…”

Section: Introductionmentioning

confidence: 99%

Silica production and the contribution of diatoms to new and primary production in the central North Pacific

Brzezinski¹,

Villareal²,

Lipschultz³

1998

Mar. Ecol. Prog. Ser.

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149

100

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The silica cycle in the upper 200 m of the central North Pacific was examined to further assess the role of oligotrophic mid-ocean gyres in the global marine silica cycle and to evaluate the role of diatoms in the regional carbon and nitrogen cycles. Siliceous biomass in the upper 200 m was very low (generally c50 nmol S1 1. ' of biogenic silica) with, higher concentrations (100 to 280 nmol Si 1.') observed occasionally in the deep chlorophyll maximum and in the nitracline Doubling times for biogenic silica were generally between 2 and 5 d, suggesting fairly rapid diatom growth. Ki~ieiic experiments showed widespread limitation of silica production rates by ambient silicic acid concentrations (0.9 to 3.0 pM). Inputs of iron inferred from high concentrations of lithogenic silica (up to 300 nmol Si 1-l) in surface waters did not stimulate silica production. lntegrated silica production rates averaged 1.24 mm01 Si m-' d-' (range 0.47 to 2.9 mm01 Si m-' d-') This average is 2 to 3 times higher than those reported for other oligotrophic mid-ocean gyres, significantly increasing estimates of the fraction of global silica production occurring in these systems. A pronounced diatom bloom dominated by Mastogloia woodiana and Hemiaulus hauckLi was observed ca 200 km north of the Joint Global Ocean Flux Study (JGOFS) Hawaii Ocean Time-series (HOT) site in August 1995. A doming of isopycnals within the nutricline beneath the bloom suggested the presence of a cyclonic eddy that was enhancing local diatom production through eddy pumping. The exceptionally high biomass levels (up to 250 nmol Si I-') and high silica product~on rates (1.8 mm01 Si m-' d-') within the bloom suggest that diatom blooms triggered by the mesoscale flow field may contribute significantly to regional silica production. Diatom primary production in the central North Pacific estimated from the overall average integrated silica production rate and diatom Si:C ratios is 9.5 mm01 C m-2 d-' (= 114 mg C m-' d-'), which is 25% of the average primary productivity at the JGOFS HOT site. Silicic acid and nitrate supply rates to the euphotic zone inferred from the gradients of the 2 solutes in the nutricline are in about the same proportion as diatom cellular S1:N ratios. Thus, net consumption of the silicic a c~d supplied to the surface layer requires that diatoms account for a significant fraction of new production in the central North Pacific.

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Kinetics of silicic acid uptake by natural diatom assemblages in two Gulf Stream warm-core rings

Cited by 79 publications

References 28 publications

Sources and fates of silicon in the ocean: the role of diatoms in the climate and glacial cycles

Sources and fates of silicon in the ocean: the role of diatoms in the climate and glacial cycles

Role of silicon as a limiting nutrient to Antarctic diatoms: evidence from kinetic studies in the Ross Sea ice-edge zone

Silica production and the contribution of diatoms to new and primary production in the central North Pacific

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