Observations and Modelling Needs to Understand the Impacts of Nitrogen

Inputs to the OceansTim Jickells

On behalf of GESAMP WG 38 sponsored by NSF, SCOR, SOLAS and WMO

Altieri, K., Baker, A.R., Capone, D., Buitenhuis, E., Duce, R.A., Dentener, F., Fennel, K., Kanakidou, M., LaRoche, J., Lee, K., Liss, P., Middelburg, J. B.M., Moore, J.K., Nickovic, S., Okin, G., Oschlies, A.,

Sarin, M., Seitzinger, S., Sharples, J., Suntharalingam, P., Uematsu, M., Zamora, L.M.

1850 2005 2050

Soluble Reactive Nitrogen deposition to the ocean – TM4-ECPL MODEL results

Atmospheric nitrogen deposition fields for 1850, 2005 and 2050 from Jickells et al 2017 Global Biogeochemical Cycles 31, 289-305

Validating Atmospheric N Deposition Models

NO3- wet deposition from ACCMIP multi-model mean

• How do we validate model performance over the (remote) ocean?

Lamarque et al., ACP, 2013

mg N m-2 yr-1

STUDY REGIONS

Database of Aerosol NO3- and NH4

+ Concentrations

~ 2800 aerosol samples collected aboard ships between 1995 and 2012.

Atmospheric Deposition Fluxes, Observations vs models - Nitrogen

North Atlantic

South Atlantic

Baker et al 2010

483 259

Dentener et al., 2006

492 244

Nitrogen Deposition (90% wet) Gmol yr -1

Comparison of the Observations to ACCMIP?Database:

NO3- and NH4

+ Concentrations

ACCMIP product: NOy and NHx Dry Deposition Flux

Compare to a different model – TM4-EPCL

Available fields: NO3

- and NH4+ Concentrations

NO3- and NH4

+ Dry Deposition FluxNOy and NHx Dry Deposition Flux

Concentration Comparison (TM4)

𝑅𝑅𝐴𝐴,𝑛𝑛 =∑ ⁄𝑀𝑀 𝑂𝑂 𝐴𝐴𝐴𝐴

∑𝐴𝐴𝐴𝐴 𝑁𝑁𝑀𝑀𝑁𝑁 = 100∑ 𝑀𝑀 − 𝑂𝑂

∑𝑂𝑂

Baker et al., “Observation- and Model- Based Estimates of Particulate Dry Nitrogen Deposition to the Oceans“, ACPD, doi:10.5194/acp-2016-1123, 2017.

Concentration Comparison (TM4)

NO3-

NH4+

Baker et al., 2017

Deposition Comparison (ACCMIP and TM4)

NO3- NH4

+

Baker et al., 2017

1850 2005 2050

Soluble Reactive Nitrogen deposition to the ocean – TM4-ECPL MODEL results

Atmospheric nitrogen deposition fields for 1850, 2005 and 2050 from Jickells et al 2017 Global Biogeochemical Cycles 31, 289-305

Nitrate34%

NHx38%

OrganicN28%

Gross Nitrogen Deposition to the OceansTotal Deposition 53 TgN yr-1

Jickells et al 2017

Note that up to 40% of the gross NHx and Organic N deposition may be recycled,i.e. emitted from the oceans and redeposited

Net Nitrogen Inputs to the Oceans TgN yr-1Jickells et al 2017

Source Total Flux to the ocean TgN yr-1

Flux to the open ocean TgN yr-1

Atmosphere 39 >30

Fluvial 34 17-28

N2 Fixation 164 164

Much of the oceans are nitrogen limited with the atmosphere the dominant external source of nitrogen to the oceans and current atmospheric supply enhancing productivity (and C uptake) by about 0.4%, equivalent to 0.15PgC yr-1 ocean uptake.

Possible Hot Spots of ImpactsN W Pacific - Deposition appears to have increased nitrogen concentrations and possibly productivity

North Indian Ocean – high and increasing nitrogen deposition region in proximity to major oxygen minimum zone and associated N2O source region

Easter Mediterranean and Tropical North Atlantic - Phosphorus limited ocean regions and increased nitrogen deposition will enhance this possibly with impacts on planktonic species composition

Conclusions

• Atmospheric inputs of nitrogen to the oceans are important,• Oxidised, reduced and organic N species are important,• We need to quantify the scale of ocean emissions,• There are some key regional hot spots where inputs can have

particularly important biogeochemical impacts,• Flux estimates are dependent on models and models need

validation,• Data from island stations and ships of aerosol and rainwater

composition is particularly valuable.

Thank You for listening

Goals of WG38 are to quantify atmospheric inputs to the oceans and their effects.• Our recent work has focussed particularly on impacts of atmospherically

deposited nutrients including nitrogen, iron and phosphorus.• We now know that over about 30% of the oceans productivity is iron

limited with the atmosphere a major supply route for iron to eliminate the limitation.

• Much of the remainder of the oceans are nitrogen limited with the atmosphere the dominant external source of nitrogen to the oceans and current atmospheric supply enhancing productivity (and C uptake) by about 0.4%, equivalent to 0.15PgC/yr ocean uptake.

• So atmospheric inputs are important for ocean biogeochemistry• First step in assessing the impact is to define the inputs field.

1850 2005 2050

NOy

NHx

Organic N

Atmospheric nitrogen deposition fields for 1850, 2005 and 2050 from Jickells et al 2017 Global Biogeochemical Cycles 31, 289-305