Nitrogen isotope dynamics of the Cariaco Basin, Venezuela

Thunell, Robert C.; Sigman, Daniel M.; Muller‐Karger, Frank E.; Astor, Yrene; Varela, Ramón

doi:10.1029/2003gb002185

Cited by 150 publications

(137 citation statements)

References 72 publications

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“…Disentangling the factors involved in δ 15 N fractionation during phytoplankton growth is simplified by the fact that nitrate utilization in the vicinity of the Northeast Channel is complete under the influence of both WSW and LSW, despite initial differences in nitrate concentrations in the two water masses (SI Text). Because the pool of nitrate is exhausted to completion, the accumulated phytoplankton biomass takes on the δ 15 N of the source nitrate, regardless of the species involved in nitrate assimilation or the rate of growth (31,32). Therefore, in this system, interannual variability in coral δ 15 N may be attributed either to a change in δ 15 N of source nitrate or to changes in trophic structure of the coral's food source.…”

Section: Resultsmentioning

confidence: 99%

Nutrient regime shift in the western North Atlantic indicated by compound-specific δ ¹⁵ N of deep-sea gorgonian corals

Sherwood

Lehmann

Schubert

et al. 2011

Proc. Natl. Acad. Sci. U.S.A.

155

172

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Despite the importance of the nitrogen (N) cycle on marine productivity, little is known about variability in N sources and cycling in the ocean in relation to natural and anthropogenic climate change. Beyond the last few decades of scientific observation, knowledge depends largely on proxy records derived from nitrogen stable isotopes ( δ 15 N) preserved in sediments and other bioarchives. Traditional bulk δ 15 N measurements, however, represent the combined influence of N source and subsequent trophic transfers, often confounding environmental interpretation. Recently, compound-specific analysis of individual amino acids ( δ 15 N-AA) has been shown as a means to deconvolve trophic level versus N source effects on the δ 15 N variability of bulk organic matter. Here, we demonstrate the first use of δ 15 N-AA in a paleoceanographic study, through analysis of annually secreted growth rings preserved in the organic endoskeletons of deep-sea gorgonian corals. In the Northwest Atlantic off Nova Scotia, coral δ 15 N is correlated with increasing presence of subtropical versus subpolar slope waters over the twentieth century. By using the new δ 15 N-AA approach to control for variable trophic processing, we are able to interpret coral bulk δ 15 N values as a proxy for nitrate source and, hence, slope water source partitioning. We conclude that the persistence of the warm, nutrient-rich regime since the early 1970s is largely unique in the context of the last approximately 1,800 yr. This evidence suggests that nutrient variability in this region is coordinated with recent changes in global climate and underscores the broad potential of δ 15 N-AA for paleoceanographic studies of the marine N cycle.

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Section: Resultsmentioning

confidence: 99%

Nutrient regime shift in the western North Atlantic indicated by compound-specific δ ¹⁵ N of deep-sea gorgonian corals

Sherwood

Lehmann

Schubert

et al. 2011

Proc. Natl. Acad. Sci. U.S.A.

155

172

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“…This increase is likely due to isotopic fractionations during NH 4 + release and partial oxidation in pore waters (Moebius, 2013;Prokopenko et al, 2006). In contrast, diagenesis under anoxic conditions, or under oxic conditions with high sedimentation rates, only imparts small isotopic fractionations of <1‰, making bulk sedimentary nitrogen slightly lighter (Altabet et al, 1999;Lehman et al, 2002;Thunell et al, 2004). Anoxic diagenesis therefore has minimal effect on the utility of the δ 15 N proxy in deep time.…”

Section: Preservation Of Nitrogen Isotopes In the Rock Recordmentioning

confidence: 98%

“…Fractionations associated with NO 3 -assimilation are often not expressed because assimilation typically goes to completion (Altabet and Francois, 1994;Thunell et al, 2004), except in modern Arctic settings (Somes et al, 2010). Under oxic conditions, marine sediments therefore approach the isotopic composition of NO 3 -in the overlying water column (Altabet and Francois, 1994;Thunell et al, 2004). This value is on average +5‰ in the modern ocean (range mostly between +3‰ and +14‰), which is largely a result of isotopic fractionations imparted by denitrification.…”

Section: A Primer On Nitrogen Isotopes In Geological Samplesmentioning

confidence: 99%

The evolution of Earth's biogeochemical nitrogen cycle

Stüeken

Kipp

Koehler

et al. 2016

Earth-Science Reviews

312

287

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Nitrogen is an essential nutrient for all life on Earth and it acts as a major control on biological productivity in the modern ocean. Accurate reconstructions of the evolution of life over the course of the last four billion years therefore demand a better understanding of nitrogen bioavailability and speciation through time. The biogeochemical nitrogen cycle has evidently been closely tied to the redox state of the ocean and atmosphere. Multiple lines of evidence indicate that the Earth"s surface has passed in a non-linear fashion from an anoxic state in the Hadean to an oxic state in the later Phanerozoic. It is therefore likely that the nitrogen cycle has changed markedly over time, with potentially severe implications for the productivity and evolution of the biosphere. Here we compile nitrogen isotope data from the literature and review our current understanding of the evolution of the nitrogen cycle, with particular emphasis on the Precambrian. Combined with recent work on redox conditions, trace metal availability, sulfur and iron cycling on the early Earth, we then use the nitrogen isotope record as a platform to test existing and new hypotheses about biogeochemical pathways that may have controlled nitrogen availability through time. Among other things, we conclude that (a) abiotic nitrogen sources were likely insufficient to sustain a large biosphere, thus favoring an early origin of biological N 2 fixation, (b) evidence of nitrate in the Neoarchean and Paleoproterozoic confirm current views of increasing surface oxygen levels at those times, (c) abundant ferrous iron and sulfide in the midPrecambrian ocean may have affected the speciation and size of the fixed nitrogen reservoir, and (d) nitrate availability alone was not a major driver of eukaryotic evolution.

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“…Complete NO 3 Ϫ consumption (''closed-system kinetics'') would cause underexpression of the isotope effect at larger scales (21,22), because little or no 15 N-rich NO 3 Ϫ would escape the zone of denitrification to elevate the 15 N͞ 14 N of the larger plant-soil system.…”

Section: Elimination Of Two Competing Hypothesesmentioning

confidence: 99%

Isotopic evidence for large gaseous nitrogen losses from tropical rainforests

Houlton¹,

Sigman

Hedin³

2006

Proc. Natl. Acad. Sci. U.S.A.

Self Cite

306

358

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The nitrogen isotopic composition ( 15 N͞ 14 N) of forested ecosystems varies systematically worldwide. In tropical forests, which are elevated in 15 N relative to temperate biomes, a decrease in ecosystem 15 N͞ 14 N with increasing rainfall has been reported. This trend is seen in a set of well characterized Hawaiian rainforests, across which we have measured the 15 N͞ 14 N of inputs and hydrologic losses. We report that the two most widely purported mechanisms, an isotopic shift in N inputs or isotopic discrimination by leaching, fail to explain this climate-dependent trend in 15 N͞ 14 N. Rather, isotopic discrimination by microbial denitrification appears to be the major determinant of N isotopic variations across differences in rainfall. In the driest climates, the 15 N͞ 14 N of total dissolved outputs is higher than that of inputs, which can only be explained by a 14 N-rich gas loss. In contrast, in the wettest climates, denitrification completely consumes nitrate in local soil environments, thus preventing the expression of its isotope effect at the ecosystem scale. Under these conditions, the 15 N͞ 14 N of bulk soils and stream outputs decrease to converge on the low 15 N͞ 14 N of N inputs. N isotope budgets that account for such local isotopic underexpression suggest that denitrification is responsible for a large fraction (24 -53%) of total ecosystem N loss across the sampled range in rainfall.climate ͉ isotope ͉ tropics ͉ ecosystem ͉ global change

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Nitrogen isotope dynamics of the Cariaco Basin, Venezuela

Cited by 150 publications

References 72 publications

Nutrient regime shift in the western North Atlantic indicated by compound-specific δ ¹⁵ N of deep-sea gorgonian corals

Nutrient regime shift in the western North Atlantic indicated by compound-specific δ ¹⁵ N of deep-sea gorgonian corals

The evolution of Earth's biogeochemical nitrogen cycle

Isotopic evidence for large gaseous nitrogen losses from tropical rainforests

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Nitrogen isotope dynamics of the Cariaco Basin, Venezuela

Cited by 150 publications

References 72 publications

Nutrient regime shift in the western North Atlantic indicated by compound-specific δ 15 N of deep-sea gorgonian corals

Nutrient regime shift in the western North Atlantic indicated by compound-specific δ 15 N of deep-sea gorgonian corals

The evolution of Earth's biogeochemical nitrogen cycle

Isotopic evidence for large gaseous nitrogen losses from tropical rainforests

Contact Info

Product

Resources

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Nutrient regime shift in the western North Atlantic indicated by compound-specific δ ¹⁵ N of deep-sea gorgonian corals

Nutrient regime shift in the western North Atlantic indicated by compound-specific δ ¹⁵ N of deep-sea gorgonian corals