Nitrate and silicic acid in the world ocean: patterns and processes

Kamykowski, Daniel; Zentara, Sara-Joan

doi:10.3354/meps026047

Cited by 30 publications

(16 citation statements)

References 22 publications

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“…Switzer et al 2003, Kamykowski andZentara 1985), but this is not true for west Australian shelf waters where warmer winter temperatures are associated with greater surface nitrate concentrations ). In most of the world's oceans 110 convective cooling and increased wind during winter acts to deepen the seasonal thermocline and resupply the euphotic zone with nutrients including nitrate (Kamykowski and Zentara 1985).…”

Section: Introductionmentioning

confidence: 94%

Nutrients in an oligotrophic boundary current: Evidence of a new role for the Leeuwin Current

Thompson

Wild-Allen

Lourey

et al. 2011

Progress in Oceanography

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Section: Introductionmentioning

confidence: 94%

Nutrients in an oligotrophic boundary current: Evidence of a new role for the Leeuwin Current

Thompson

Wild-Allen

Lourey

et al. 2011

Progress in Oceanography

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“…The gradient in silicic acid within the nutncline throughout much of the ocean equals or exceeds that for nitrate (Kamykowski & Zentara 1985), such that mixing supplies at least as much silicic acid to the surface ocean as it does nitrate. That supply rate ratio of silicic acid:nitrate nearly equals the Si:N mole ratio within diatoms (Si:N = 0.8; Brzezinski 1985), suggesting that net depletion of the silicic acid in surface waters consumes a large fraction of the nitrate supply, resulting in a significant fraction of new production being carried out by diatoms.…”

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.

147

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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“…Three previous surveys that examined how nitrate (No3) and silicic acid (Si) concentrations co-vary in the Pacific Ocean (Zentara & Kamykowski 1977 and in the world ocean (Kamykowski & Zentara 1985, hereafter KZ 1985 emphasize the unique character of the Southern Ocean. This uniqueness is related to the large range of dissolved Si:N03 ratios (all units are mole-based) that occur between the Southern Subtropical Convergence and Antarctica.…”

Section: Introductionmentioning

confidence: 99%

Circumpolar plant nutrient covariation in the Southern Ocean: patterns and processes

Kamykowski¹,

Zentara²

1989

Mar. Ecol. Prog. Ser.

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Phosphate from the NODC data set is substituted for nitrate in a regression relationship with silicic acid based on the NODC data set to broaden a previous spatially-limited analysis of nitrogen and silicic acid fluxes in the Southern Ocean (30's to Antarctica) The log slope of the phosphate-silicic acid relation an index of plant nutrient utlization rates provides a complete circumpolar view and supports more detailed speculation on the processes that contribute to the spatial and temporal patterns A log PO4-Si slope cntenon of -1 6 parallels a previous log NO3-Si slope criterion of -0 5 where low log NOs-Si slopes more negative than the criterion were attributed to higher ammonium flux Three regions are distinguished by these criteria including an area of mixed low and high log slopes south of the Antarctic Divergence, an area of predominantly low log slopes between the Antarctic Divergence and the Antarctic Polar Front, and an area of piedommantly high log slopes north of the Antarctic Polar Front The middle low log slope legion is most restricted in austral winter and spring and most broadly distributed in austral summei and fall Based on recent information from the Southern Ocean the processes that are likely contributors to the occurrence of high or low log slopes are extended to include not only ammonium fluxes, but also particulate Si N molar ratios (and therefore implied Si N uptake ratios) ranging up to 4 1 and possible iron limitation The invoked processes apply both to NO3-Si and PO4-Si relationships except that excreted phosphorus atoms are not preferentially selected from the total phosphorus pool as occurs for ammonium from the total nitrogen pool The continuous presence of low log slopes in various regions of the Southern Ocean throughout the year suggests a strong potential for ammonium preference in response to a dominating ammonium supply or to iron limitation and/or for relatively high Si N uptake ratios to occur throughout the annual cycle The nutrient relationships from the Southern Ocean provide a record of the integrated processes that influence net plant nutrient utilization rates over the growth season However since a given log slope can represent a variety of process combinations more information will be required to accurately interpret the exact sequence of processes that contribute to the nutrient signature in the Southern Ocean at a given time and place

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Nitrate and silicic acid in the world ocean: patterns and processes

Cited by 30 publications

References 22 publications

Nutrients in an oligotrophic boundary current: Evidence of a new role for the Leeuwin Current

Nutrients in an oligotrophic boundary current: Evidence of a new role for the Leeuwin Current

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

Circumpolar plant nutrient covariation in the Southern Ocean: patterns and processes

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