Hagi BucknWise: Created page with "{{BreadcrumbsNutrients}} * Page authors: PRIMO * Responsible curator: Hagen Buck-Wiese ---- TOC
{| class="model-ib" style="float:right; margin-left:1em; margin-bottom:1em;" ! Urea uptake (regenerated production) |- | '''Approach:''' ¹⁵N tracer incubation, EA-IRMS |- | '''Context:''' incubation, simulated ''in situ'' |- | '''Spatial scale:''' point sample |- | ''..."

2026-05-12T17:47:10Z

Created page with "{{BreadcrumbsNutrients}} * Page authors: PRIMO * Responsible curator: Hagen Buck-Wiese ---- __TOC__ <div class="model-box"> {| class="model-ib" style="float:right; margin-left:1em; margin-bottom:1em;" ! Urea uptake (regenerated production) |- | '''Approach:''' 15N tracer incubation, EA-IRMS |- | '''Context:''' incubation, simulated ''in situ'' |- | '''Spatial scale:''' point sample |- | ''..."

New page

{{BreadcrumbsNutrients}}

* [[Page authors|Page authors]]: [[PRIMO]]
* [[Responsible curator|Responsible curator]]: [[User:Hagi BucknWise|Hagen Buck-Wiese]]
----

__TOC__
<div class="model-box">
{| class="model-ib" style="float:right; margin-left:1em; margin-bottom:1em;"
! Urea uptake (regenerated production)
|-
| '''Approach:''' 15N tracer incubation, EA-IRMS
|-
| '''Context:''' incubation, simulated ''in situ''
|-
| '''Spatial scale:''' point sample
|-
| '''Temporal scale:''' 12–24 h
|-
| '''Units:''' µmol N L-1 d-1; µmol N m-2 d-1 (depth-integrated)
|-
| '''Community captured:''' all (usually > 0.2 µm)
|-
| '''Co-measurements:''' background δ15N (PON), ambient [urea], temperature, PAR, Chl, initial blank; can couple with 13C uptake
|}
</div>
<div style="clear:both"></div>

== Method Overview ==

15N-labelled urea (CO(15NH2)2) is added at tracer concentrations to seawater incubated under simulated ''in situ'' conditions. Urea is an important dissolved organic nitrogen (DON) source for phytoplankton, particularly in low-nitrate environments. After incubation, the particulate fraction is filtered onto GFF filters; EA-IRMS measures the 15N enrichment in PN, and the urea uptake rate (ρurea) is calculated using the constant-flux model<ref name="Dugdale1986">Dugdale, R. C., & Wilkerson, F. P. (1986). The use of 15N to measure nitrogen uptake in eutrophic oceans; experimental considerations. ''Limnology and Oceanography'', 31(4), 673–689. https://doi.org/10.4319/lo.1986.31.4.0673</ref>. In the Eppley & Peterson framework, urea uptake is classified as regenerated production<ref name="Eppley1979">Eppley, R. W., & Peterson, B. J. (1979). Particulate organic matter flux and planktonic new production in the deep ocean. ''Nature'', 282, 677–680. https://doi.org/10.1038/282677a0</ref>.

=== Scale of measurement ===

Point sample; 12–24 h incubation.

=== Data generated ===

Urea uptake rates in µmol N L-1 d-1. When measured alongside nitrate and ammonium uptake, urea provides the third component of the total dissolved inorganic and organic nitrogen uptake budget.

=== Units & currency ===

Units are µmol N L-1 d-1. The currency is nitrogen.

=== Sample size ===

Typical samples are 0.5–2 L in volume.

=== Repositories & databases ===

== Limitations ==

Ambient urea concentrations in the euphotic zone are often very low (nM), which can violate the tracer requirement and cause underestimation. As with ammonium, microbial regeneration of urea during the incubation can dilute the 15N pool (isotope dilution), leading to underestimation. Bottle effects apply.

== Example Applications & Protocols ==

=== Classic examples ===
* Dugdale & Goering (1967) ''Uptake of new and regenerated forms of nitrogen in primary productivity'' <ref name="Dugdale1967">Dugdale, R. C., & Goering, J. J. (1967). Uptake of new and regenerated forms of nitrogen in primary productivity. ''Limnology and Oceanography'', 12(2), 196–206. https://doi.org/10.4319/lo.1967.12.2.0196</ref>
* Dugdale & Wilkerson (1986) ''The use of 15N to measure nitrogen uptake in eutrophic oceans'' <ref name="Dugdale1986" />

=== Recent applications ===
* Varela et al. (2013) ''Pelagic primary productivity and upper ocean nutrient dynamics across subarctic and Arctic seas'' <ref name="Varela2013">Varela, D. E., Crawford, D. W., Wrohan, I. A., Wyatt, S. N., & Carmack, E. C. (2013). Pelagic primary productivity and upper ocean nutrient dynamics across subarctic and Arctic seas. ''Journal of Geophysical Research: Oceans'', 118, 7132–7152. https://doi.org/10.1002/2013JC009211</ref>

=== Common calculations/conversions ===
* ρurea is calculated identically to ρNO3- using the 15N-urea enrichment in PN and the initial PN concentration.

== References ==

[[Category:Main Pages|Model types]]

(15N-ρurea) uptake Regenerated Production - Revision history