Page path:

Small "snow­flakes" in the sea play a big role

May 28, 2021

In the deep waters that underlie the productive zones of the ocean, there is a constant rain of organic material called 'marine snow'. Marine snow does not only look like real snow but also behaves similarly: Large flakes are rare and fall quickly while highly abundant smaller flakes take their time. Scientists from Bremen and Kiel have now discovered that precisely those features explain why small particles play an important role for the nutrient balance of the oceans. These findings have now been published in Nature Com­mu­nic­a­tions and will aid in the further development of biogeochemical models that include the marine nitrogen cycle.

 

A team of sci­ent­ists from the Max Planck In­sti­tute for Mar­ine Mi­cro­bi­o­logy, the Max Planck In­sti­tute for Met­eor­o­logy and the GEO­MAR – Helm­holtz Centre for Ocean Re­search Kiel have been study­ing biogeo­chem­ical pro­cesses in the oxy­gen min­imum zone of the east­ern South Pa­cific off Peru, one of the largest low oxy­gen re­gions of the world ocean. The re­search­ers fo­cused on so-called mar­ine snow particles of dif­fer­ent sizes, which are com­posed of algal debris and other or­ganic ma­ter­ial, aim­ing to un­der­stand how these particles af­fect the ni­tro­gen cycle in the oxy­gen min­imum zone. Thereby, they solved a long-stand­ing puzzle: How do the nu­tri­ents that are con­cen­trated in­side the particles reach anam­mox bac­teria that live freely sus­pen­ded in the wa­ter column.

Too much of a good thing can be bad

Oxy­gen min­imum zones are re­gions of the ocean where little to no oxy­gen is dis­solved in the wa­ter. As most an­im­als need oxy­gen to breathe, they can­not sur­vive in these wa­ter bod­ies. Not sur­pris­ingly, oxy­gen min­imum zones are also re­ferred to as mar­ine dead zones. Oxy­gen min­imum zones are a nat­ural phe­nomenon, but have been found to be ex­pand­ing in many re­gions of the ocean as a res­ult of hu­man activ­ity. Global warm­ing con­trib­utes to de­creas­ing oxy­gen con­cen­tra­tions, as warm wa­ter stores less oxy­gen. Warmer sur­face wa­ter also mix less with the deep, cool wa­ter be­low, thus lead­ing to stag­na­tion and re­duced vent­il­a­tion.

Small marine “snowflakes” are very important for the nutrient balance of the oceans. The particle shown here is highly magnified – in reality small particles are only about the size of a hair and thus barely visible. (© Max Planck Institute for Marine Microbiology/C. Karthäuser and S. Ahmerkamp)
Small marine “snowflakes” are very important for the nutrient balance of the oceans. The particle shown here is highly magnified – in reality small particles are only about the size of a hair and thus barely visible. No particle is like another and they have often bizarre forms.
Small marine “snowflakes” are very important for the nutrient balance of the oceans. The particle shown here is highly magnified – in reality small particles are only about the size of a hair and thus barely visible. (© Max Planck Institute for Marine Microbiology/C. Karthäuser and S. Ahmerkamp)
Small marine “snowflakes” are very important for the nutrient balance of the oceans. The particle shown here is highly magnified – in reality small particles are only about the size of a hair and thus barely visible. No particle is like another and they have often bizarre forms.
Small marine “snowflakes” are very important for the nutrient balance of the oceans. The particle shown here is highly magnified – in reality small particles are only about the size of a hair and thus barely visible. (© Max Planck Institute for Marine Microbiology/C. Karthäuser and S. Ahmerkamp)
Small marine “snowflakes” are very important for the nutrient balance of the oceans. The particle shown here is highly magnified – in reality small particles are only about the size of a hair and thus barely visible. No particle is like another and they have often bizarre forms.
Map with an overview of the oxygen minimum zones. The largest are located offshore Middle and South America, but oxygen depleted areas can also be found in the Baltic Sea. The red box marks the oxygen minimum zone off Peru where samples were collected for this study. (©Max Planck Institute for Marine Microbiology/S. Ahmerkamp)
Map with an overview of the oxygen minimum zones. The largest are located offshore Middle and South America, but oxygen depleted areas can also be found in the Baltic Sea. The red box marks the oxygen minimum zone off Peru where samples were collected for this study. (©Max Planck Institute for Marine Microbiology/S. Ahmerkamp)
Clarissa Karthäuser in the lab. On the screen you see a coloured and highly magnified particle. (© Max Planck Institute for Marine Microbiology/C. Karthäuser)
Clarissa Karthäuser in the lab. On the screen you see a coloured and highly magnified particle. (© Max Planck Institute for Marine Microbiology/C. Karthäuser)

Changes to the ni­tro­gen cycle also have de­le­ter­i­ous ef­fects on ocean oxy­gen con­cen­tra­tions. Ni­tro­gen is a vi­tal nu­tri­ent that an­im­als and plants need in or­der to grow. Nor­mally rare in the ocean, ni­tro­gen com­pounds that can be pro­cessed have be­come in­creas­ingly avail­able in many coastal re­gions. Hu­mans use large amounts of fer­til­izers with ni­tro­gen com­pounds such as am­monium and ni­trate for ag­ri­cul­ture and these nu­tri­ents find their way to the ocean via rivers and the at­mo­sphere in ever in­creas­ing amounts. This has severe con­sequences. The ad­di­tional nu­tri­ents en­hance phyto­plank­ton growth. When the plank­tonic or­gan­isms die, they are de­com­posed by bac­teria. Dur­ing this pro­cess the bac­teria con­sume oxy­gen, driv­ing a de­cline in oxy­gen con­cen­tra­tions. Once oxy­gen is fully con­sumed, an­aer­obic mi­cro­bial pro­cesses take over, dur­ing which mi­crobes es­sen­tially “breathe” ni­tro­gen com­pounds in place of oxy­gen, and as a res­ult con­vert ni­trate, ni­trite and am­monium back to ni­tro­gen gas and re­lease it to the at­mo­sphere.

Which factors drive the loss of ni­tro­gen?

Com­bined, the an­aer­obic mi­cro­bial res­pir­a­tion pro­cesses of anam­mox and de­ni­tri­fic­a­tion in oxy­gen min­imum zones lead to the loss of up to 40 per­cent of the oceans ni­tro­gen. However the reg­u­la­tion of mi­cro­bial N-loss pro­cesses in oxy­gen min­imum zones is still poorly un­der­stood. This study is fo­cused on the anam­mox pro­cess, i.e. an­aer­obic am­monium ox­id­a­tion with ni­trite. In their pro­ject, the re­search­ers fol­lowed up on the ob­ser­va­tion that the anam­mox pro­cess is par­tic­u­larly high when or­ganic ma­ter­ial in the form of mar­ine snow particles is es­pe­cially abund­ant. Their hy­po­thesis was that the or­ganic ma­ter­ial, which con­tains a large amount of fixed ni­tro­gen, serves as a source of am­monium for the anam­mox re­ac­tion. Strangely enough, anam­mox bac­teria do not seem to live on the mar­ine snow it­self, but in the wa­ter column. So how do these bac­teria find their nu­tri­ents?

To un­ravel this puzzle, the sci­ent­ists used un­der­wa­ter cam­eras to meas­ure particle abund­ances over depth pro­files at dif­fer­ent sta­tions in the oxy­gen min­imum zone off Peru. “We ob­served that the anam­mox pro­cess oc­curs mainly in places where the smal­ler particles are abund­ant,” says Clarissa Karthäuser, shared first au­thor of the pa­per with So­eren Ah­merkamp. “This in­dic­ates that the smal­ler particles are more im­port­ant for the anam­mox pro­cess than the lar­ger ones – whereby small means that they are about the size of a hair and thus barely vis­ible”.

These small particles are very abund­ant in the wa­ter column and sink slowly, thus they stay in the oxy­gen min­imum zone longer. Also, the or­ganic ma­ter­ial is packed more densely in smal­ler particles and as a res­ult the small flakes trans­port a sim­ilar amount of ma­ter­ial per particle as the lar­ger clumps, which means that over­all they trans­port sig­ni­fic­antly more ni­tro­gen. “We es­tim­ated that the am­monium con­cen­tra­tion around the particles is sig­ni­fic­antly in­creased,” says So­eren Ah­merkamp. “This in­dic­ates two things: First, that the higher num­ber and longer res­id­ence times of the smal­ler particles in the wa­ter column in­crease the like­li­hood that bac­teria will en­counter a small particle by chance. Secondly, the high am­monium con­cen­tra­tions in the bound­ary layer of the particle can then provide nour­ish­ment to the bac­teria.”

Im­port­ant res­ults for earth sys­tem mod­els

The new find­ings are cru­cial for the im­prove­ment of Earth sys­tem mod­els. “With this study, we have re­solved an im­port­ant as­pect of the anam­mox pro­cess and thus made an im­port­ant con­tri­bu­tion to a bet­ter un­der­stand­ing of the nu­tri­ent bal­ance in the oceans,” says Mar­cel Kuypers, head of the De­part­ment of Biogeo­chem­istry of the Max Planck In­sti­tute for Mar­ine Mi­cro­bi­o­logy in Bre­men. “With this im­proved pro­cess un­der­stand­ing, we provide the link between particle-as­so­ci­ated pro­cesses and N-cyc­ling in oxy­gen min­imum zones which can be ad­ap­ted in biogeo­chem­ical Earth sys­tem mod­els to bet­ter as­sess the ef­fects of an­thro­po­genic deoxy­gen­a­tion on the ni­tro­gen cycle.”

Sampling in the oxygen minimum zone off Peru with a marine snow catcher. On the research vessel Meteor, Clarissa Karthäuser collects individual particles to determine detailed characteristics. (© GEOMAR/A. Paul)
Sampling in the oxygen minimum zone off Peru with a marine snow catcher. On the research vessel Meteor, Clarissa Karthäuser collects individual particles to determine detailed characteristics. (© GEOMAR/A. Paul)
 
 

Ori­ginal pub­lic­a­tion

Cla­ris­sa Kar­t­häu­ser*, Soe­ren Ah­mer­kamp*, Han­nah K Mar­chant, Lau­ra A Bris­tow, He­le­na Hauss, Mor­ten H Iver­sen, Rai­ner Kiko, Jo­eran Ma­erz, Gau­te La­vik, Mar­cel MM Kuy­pers: Small sinking particles control anammox rates in the Peruvian oxygen minimum zone, Na­tu­re Com­mu­ni­ca­ti­ons, May 2021

DOI: 10.1038/s41467-021-23340-4

*bei­de Au­tor:in­nen ha­ben gleich­be­rech­tigt bei­ge­tra­gen

Fund­ing

This study is part of the Collaborative Research Centre 754 (SFB 754) "Climate-Biogeochemistry Interactions in the Tropical Ocean" which was fun­ded by the Ger­man Re­search Found­a­tion (DFG) from 2008 to 2019 and the “Multiscale Ap­proach on the Role of Mar­ine Ag­greg­ates (MARMA)” pro­ject which was fun­ded by the Max Planck Society (MPG). This pro­ject in­volves sci­ent­ists from the Max-Planck-In­sti­tute for Mar­ine Mi­cro­bi­o­logy, the Chris­tian Al­brechts Uni­versity Kiel (CAU), and the GEO­MAR Helm­holtz Cen­ter for Ocean Re­search Kiel.

 

Par­ti­cip­at­ing in­sti­tu­tions

  • Max Planck Institute for Marine Microbiology, Bremen, Germany
  • Max Planck Institute for Meteorology, Hamburg, Germany
  • GEOMAR – Helmholtz Centre for Ocean Research, Kiel, Germany
  • MARUM – Centre for Marine Environmental Sciences at the University of Bremen, Germany
  • Alfred Wegener Institute - Helmholtz Centre for Polar and Marine Research, Bremerhaven, Germany

Video about the Col­lab­or­at­ive Re­search Cen­ter 754 "Cli­mate-Biogeo­chem­istry In­ter­ac­tions in the Trop­ical Ocean", show­ing the form­a­tion and ex­plor­a­tion of oxy­gen min­imum zones.

Fur­ther pub­lic­a­tions on the topic

- Call­beck CM, La­vik G, Stram­ma L, Kuy­pers MMM, Bris­tow LA (2017): Enhanced Nitrogen Loss by Eddy-Induced Vertical Transport in the Offshore Peruvian Oxygen Minimum Zone. PLoS ONE 12(1): e0170059.

 
 
- Kalvelage T, Lavik G, Jensen MM, Revsbech NP, Löscher C, Schunck H, et al. (2015): Aerobic Microbial Respiration In Oceanic Oxygen Minimum Zones. PLoS ONE 10(7): e0133526.
 
 
 
- Kalvelage, T., G. Lavik, P. Lam, S. Con­tre­ras, L. Ar­tea­ga, C. R. Lö­scher, A. Oschlies, A. Paul­mier, L. Stram­ma and M. M. Kuypers (2013): Ni­tro­gen cy­cling dri­ven by or­ga­nic mat­ter ex­port in the South Pa­ci­fic oxy­gen mi­ni­mum zone, Na­tu­re Geo­sci­ence, 6, 228-234.
 
 

Please dir­ect your quer­ies to:

Cla­ris­sa Kar­t­häu­ser

Bio­geo­che­mistry Group

Max Planck In­sti­tute for Ma­ri­ne Mi­cro­bio­lo­gy

E-Mail: ckarthae@mpi-bremen.de

Scientist

Department of Biogeochemistry

Dr. Soeren Ahmerkamp

MPI for Marine Microbiology
Celsiusstr. 1
D-28359 Bremen

Room: 

3130

Phone: 

+49 421 2028-6380

Dr. Soeren Ahmerkamp

Scientist

Biogeochemistry Group

Dr. Hannah Marchant

MPI for Marine Microbiology
Celsiusstr. 1
D-28359 Bremen
Germany

Room: 

3135

Phone: 

+49 421 2028-6306

Dr. Hannah Marchant
 
Back to Top