Hagi BucknWise at 23:33, 11 May 2026

2026-05-11T23:33:03Z

← Older revision		Revision as of 16:33, 11 May 2026
Line 1:		Line 1:
	{{DISPLAYTITLE:H<sub>2</sub> supersaturation}}		{{DISPLAYTITLE:H<sub>2</sub> supersaturation}}
	{{BreadcrumbsNFixation}}		{{BreadcrumbsNFixation}}

			{{BreadcrumbsPrimaryProduction}}

			* [[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;"
			! H<sub>2</sub> supersaturation (N<sub>2</sub> fixation proxy)
			\|-
			\| '''Approach:''' dissolved H<sub>2</sub> gas measurement by reduction gas analyzer
			\|-
			\| '''Context:''' ''in situ''
			\|-
			\| '''Spatial scale:''' point sample to continuous underway
			\|-
			\| '''Temporal scale:''' minutes
			\|-
			\| '''Units:''' H<sub>2</sub> saturation (%)
			\|-
			\| '''Community captured:''' bulk
			\|-
			\| '''Co-measurements:''' temperature, pressure, salinity (for equilibrium saturation calculation)
			\|}
			</div>
			<div style="clear:both"></div>

			== Method Overview ==

			Nitrogenase produces molecular hydrogen (H<sub>2</sub>) as a stoichiometric by-product of N<sub>2</sub> fixation. Dissolved H<sub>2</sub> supersaturation relative to the atmospheric equilibrium therefore indicates that N<sub>2</sub> fixation is occurring in the water column. Dissolved H<sub>2</sub> is measured using a UV reduction gas analyzer interfaced with a membrane inlet system that equilibrates the dissolved gas phase with a carrier gas stream. Samples of ~1 mL of seawater are sufficient per measurement, and the method can be adapted for continuous underway operation<ref name="Moore2014">Moore, C. M., Seeyave, S., Hickman, A. E., Allen, J. T., Lucas, M. I., Planquette, H., Pollard, R. T., & Poulton, A. J. (2014). Extensive hydrogen supersaturations in the western South Atlantic Ocean suggest substantial underestimation of nitrogen fixation. ''Journal of Geophysical Research: Oceans'', 119, 4340–4350. https://doi.org/10.1002/2014JC010017</ref>.

			=== Scale of measurement ===

			Sample volumes are ~1 mL, but continuous membrane inlet systems allow underway surveys at kilometer-scale resolution. Because H<sub>2</sub> is produced and consumed rapidly, the signal represents a near-instantaneous snapshot of diazotrophic activity, though air-sea exchange integrates over the mixed layer gas exchange timescale.

			=== Data generated ===

			H<sub>2</sub> supersaturation expressed as a percentage above atmospheric equilibrium. Conversion to N<sub>2</sub> fixation rates requires knowledge of the H<sub>2</sub>:N<sub>2</sub> production ratio and the air-sea gas transfer velocity for H<sub>2</sub>.

			=== Units & currency ===

			Units are H<sub>2</sub> saturation (%). The currency is hydrogen.

			=== Sample size ===

			Typical samples are ~1 mL per discrete measurement.

			=== Repositories & databases ===

			== Limitations ==

			The ratio of H<sub>2</sub> production to N<sub>2</sub> fixation varies among diazotroph taxa (some unicellular diazotrophs may have uptake hydrogenases that recycle H<sub>2</sub>) and with physiological state. No data exist on H<sub>2</sub> release rates for several important unicellular diazotroph groups. Converting H<sub>2</sub> supersaturation to a quantitative N<sub>2</sub> fixation flux requires gas transfer parameterisations that introduce significant uncertainty. The method cannot identify which taxa are responsible for the observed supersaturation.

			== Example Applications & Protocols ==

			=== Classic examples ===
			* Moore et al. (2014) ''Extensive hydrogen supersaturations in the western South Atlantic Ocean suggest substantial underestimation of nitrogen fixation'' <ref name="Moore2014" />

			=== Recent applications ===
			*

			=== Common calculations/conversions ===
			* H<sub>2</sub> supersaturation (%) = ([H<sub>2</sub>]<sub>measured</sub> / [H<sub>2</sub>]<sub>equilibrium</sub> − 1) × 100; equilibrium calculated from temperature, salinity, and atmospheric H<sub>2</sub> mixing ratio (~0.53 ppm).
			* N<sub>2</sub> fixation flux = k × ρ × [H<sub>2</sub>]<sub>sat</sub> × ΔH<sub>2</sub> / H<sub>2</sub>:N<sub>2</sub> ratio.

			== References ==

			[[Category:Main Pages\|Model types]]

Kate Evans at 19:34, 11 February 2026

2026-02-11T19:34:57Z

← Older revision		Revision as of 12:34, 11 February 2026
Line 1:		Line 1:
	{{DISPLAYTITLE:H<sub>2</sub> supersaturation}}		{{DISPLAYTITLE:H<sub>2</sub> supersaturation}}
			{{BreadcrumbsNFixation}}

Hagi BucknWise at 21:15, 2 February 2026

2026-02-02T21:15:20Z

← Older revision		Revision as of 14:15, 2 February 2026
Line 1:		Line 1:
	{DISPLAYTITLE:H<sub>2</sub> supersaturation}		{{DISPLAYTITLE:H<sub>2</sub> supersaturation}}

Hagi BucknWise: Created page with "{DISPLAYTITLE:H₂ supersaturation}"

2026-02-02T21:14:11Z

Created page with "{DISPLAYTITLE:H<sub>2</sub> supersaturation}"

New page

{DISPLAYTITLE:H<sub>2</sub> supersaturation}

H2 supersaturation - Revision history

Hagi BucknWise at 23:33, 11 May 2026

Kate Evans at 19:34, 11 February 2026

Hagi BucknWise at 21:15, 2 February 2026

Hagi BucknWise: Created page with "{DISPLAYTITLE:H2 supersaturation}"

Hagi BucknWise: Created page with "{DISPLAYTITLE:H₂ supersaturation}"