Distribution of nitrate, phosphate and silicate in the world oceans

Levitus, Sydney; Conkright, Margarita E.; Reid, Joseph L.; Najjar, Raymond G.; Mantyla, Arnold W.

doi:10.1016/0079-6611(93)90003-v

Cited by 221 publications

(143 citation statements)

References 16 publications

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“…Within the Antarctic Ocean proper, south of the Polar Front, major nutrients are present all year; typical concentrations in surface waters are in the order of 1.6 to 2.0 mM phosphate, 20 to 30 Ž mM nitrate and 30 to 100 mM silicate Gordon et al, 1986;Kamykowski and Zentara, 1989;Levitus et al, . 1993 .…”

Section: Major Nutrientsmentioning

confidence: 99%

Low dissolved Fe and the absence of diatom blooms in remote Pacific waters of the Southern Ocean

et al. 1999

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The remote waters of the Pacific region of the Southern Ocean are the furthest away from any upstream and upwind Ž continental Fe sources. This prime area for expecting Fe limitation of the plankton ecosystem was studied March-April . 1995 along a north-south transect at ; 898W. At the end of the austral summer the upper wind-mixed layers were in the order of ; 100 m deep, thus mixing the algae down into the dimly lit part of the euphotic zone where photosynthesis is severely restricted. The dissolved Fe was found at low concentrations ranging from 0.05 nM near the surface to 0.5 nM in Ž . deeper waters. Along the transect 528S-698S , the dissolved iron was enhanced in the Polar Front, as well as near the Ž . Antarctic continental margin 0.6-1.0 nM . In between, the southern ACC branch was depleted with iron; here the concentrations in surface waters were quite uniform at about 0.21 nM. This is only somewhat lower than the 0.49 nM Ž . Ž . October 1992 and 0.31 nM November 1992 averages in early spring in the southern ACC part of Atlantic 68W sections wde Baar, H.J.W., de Jong, J.T.M., Bakker, D.C.E.. Loscher, B.M., Veth, C., Bathmann, U., Smetacek, V., 1995. Importancë of iron for phytoplankton spring blooms and CO drawdown in the Southern Ocean. Nature 373, 412-415; Loscher, B.M., 2 de Jong, J.T.M., de Baar, H.J.W., Veth, C., Dehairs, F., 1997. The distribution of iron in the Antarctic Circumpolar Current.x Deep-Sea Research II 44, 143-188. . First, the lower ; 0.21 nM in March-April 1995 may partly be due to continuation of the seasonal trend where the phytoplankton growth, albeit modest, was removing Fe from the surface waters. Secondly, the 898W Pacific stations are further downstream continental or seafloor sources than the Atlantic 68W section. In the latter case, the ACC water had passed through the Drake Passage and also over the Sandwich Plateau. Indeed for Drake Passage, intermediate Fe concentrations have been reported by others. The generally somewhat lower surface water Fe at the ACC and PF at 898W is consistent with the distance from sources and the late summer. It also would explain the very low Ž . abundance of phytoplankton Chl a in the region and the conspicuous absence of plankton blooms. In the subAntarctic waters north of the Polar Front there are no diatoms, let alone diatom blooms, due to low availability of silicate. Thus, it Baar et al.r Marine Chemistry 66 1999 1-34 2 appears the biological productivity is suppressed due to iron deficiency, in combination with the severe seasonal effects of wind mixing on the light climate, as well as regional silicate limitation for diatoms. q

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Section: Major Nutrientsmentioning

confidence: 99%

Low dissolved Fe and the absence of diatom blooms in remote Pacific waters of the Southern Ocean

et al. 1999

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“…This observation has been explained by assuming that upward migration of the fluid carries with it heat, maintaining a warm channel where gas can be transported through what would otherwise be thermodynamically hostile territory 526 D. Archer: Methane hydrate stability and anthropogenic climate change Hydrate solubility temperature is given by the long-dashed line. Offshore water column temperatures are from Levitus et al (1993), given by the solid black lines. Nearshore, the sea floor impinges on the water column, so that temperature follows the geotherm (short dashes).…”

Section: Gas Migrationmentioning

confidence: 99%

Methane hydrate stability and anthropogenic climate change

2007

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Abstract. Methane frozen into hydrate makes up a large reservoir of potentially volatile carbon below the sea floor and associated with permafrost soils. This reservoir intuitively seems precarious, because hydrate ice floats in water, and melts at Earth surface conditions. The hydrate reservoir is so large that if 10% of the methane were released to the atmosphere within a few years, it would have an impact on the Earth's radiation budget equivalent to a factor of 10 increase in atmospheric CO 2 .Hydrates are releasing methane to the atmosphere today in response to anthropogenic warming, for example along the Arctic coastline of Siberia. However most of the hydrates are located at depths in soils and ocean sediments where anthropogenic warming and any possible methane release will take place over time scales of millennia. Individual catastrophic releases like landslides and pockmark explosions are too small to reach a sizable fraction of the hydrates. The carbon isotopic excursion at the end of the Paleocene has been interpreted as the release of thousands of Gton C, possibly from hydrates, but the time scale of the release appears to have been thousands of years, chronic rather than catastrophic.The potential climate impact in the coming century from hydrate methane release is speculative but could be comparable to climate feedbacks from the terrestrial biosphere and from peat, significant but not catastrophic. On geologic timescales, it is conceivable that hydrates could release as much carbon to the atmosphere/ocean system as we do by fossil fuel combustion.

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“…Both fractions of the phytoplankton use NO 3 and NH 4 , only diatoms use Si(OH) 4 which is not regenerated in the model (a procedure justified by a sensitivity analysis that showed only very low regeneration values gave reasonable steady state solutions; Dugdale et al, in press a). The model was initialized with mean nutrients from Levitus et al (1993) at 120m for the Wyrtki box (90-180ºW,5ºN-5ºS) and with rate constants and biomass from the literature (Chai et al, in press). The model is very stable and steady state values are generally close to observations, as shown in the model and field data from JGOFS cruise TT011 (Murray et al 1995), describing the vertical distribution of Si(OH) 4 and NO 3 (Fig.…”

Section: Evolution Of Models For the Eep Incorporating The Si-pumpmentioning

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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Distribution of nitrate, phosphate and silicate in the world oceans

Cited by 221 publications

References 16 publications

Low dissolved Fe and the absence of diatom blooms in remote Pacific waters of the Southern Ocean

Low dissolved Fe and the absence of diatom blooms in remote Pacific waters of the Southern Ocean

Methane hydrate stability and anthropogenic climate change

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

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