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07.12.2010 Car­bon Fluxes in the Oceans

Car­bon Fluxes in the Oceans
Size mat­ters: The strange be­ha­vior of small particles at dens­ity in­ter­faces
 
Carbon Fluxes in the Oceans
Size matters: The strange behavior of small particles at density interfaces

Re­search­ers from the Max Planck Institute for Marine Microbiology in Bre­men, Ger­many and the Mas­sachu­setts In­sti­tute of Tech­no­logy (M.I.T.) in Cam­bridge, Mas­sachu­setts have found a re­mark­able ef­fect while study­ing how mar­ine particles sink, which could af­fect the way sci­ent­ists as­sess global car­bon fluxes. Their ques­tion - How fast does or­ganic ma­ter­ial and debris clumped to­gether form­ing por­ous particles settle to the sea floor? Mi­crobes col­on­iz­ing these particles de­grade the or­ganic mat­ter and re­lease car­bon di­ox­ide back to the wa­ter. The down­ward ve­lo­city of the particles de­term­ines the amount of car­bon ex­por­ted to the deep sea. The res­ults from this study are now presen­ted in the Proceedings of the National Academy of Sciences (DOI: 10.1073/​pnas.1012319108).

Struc­tured like sponges, the mar­ine particles are por­ous ag­greg­ates that are mostly void and made of wa­ter to 95% or more. Be­cause the world's oceans are strat­i­fied due to tem­per­at­ure and/​or sa­lin­ity, wa­ter dens­ity in­creases with depth. On their way down to the deep ocean, mar­ine ag­greg­ates can reach a depth where they ap­proach neut­ral buoy­ancy, stop­ping in their des­cent un­til the ex­change of low-dens­ity wa­ter and heav­ier am­bi­ent wa­ter al­lows set­tling to re­sume. Kolja Kindler, a sci­ent­ist at the Max Planck In­sti­tute for Mar­ine Mi­cro­bi­o­logy and the Mas­sachu­setts In­sti­tute of Tech­no­logy, points out that al­though thin lay­ers of mar­ine ag­greg­ates have of­ten been ob­served in nature, this ef­fect has been pre­vi­ously neg­lected in particle trans­port mod­els.
Porous Particle
Figure: An aquatic aggregate of one centimeter diameter from Lake Constance, Germany (courtesy of Hans-Peter Grossart, IGB, Leibniz-Institute of Freshwater Ecology and Inland Fisheries)
In this study by Kind­ler and col­leagues, the res­ults from labor­at­ory ex­per­i­ments and a math­em­at­ical model demon­strate this ef­fect for the first time. As the particles are im­per­meable to flow, the only means of ex­chan­ging wa­ter is by dif­fu­sion. As a res­ult, the lar­ger the size of the ag­greg­ates, the more time they spend in the strat­i­fied layer.

Arzhang Khalili from the Max Planck In­sti­tute for Mar­ine Mi­cro­bi­o­logy says, "Large mar­ine ag­greg­ates may have a longer res­id­ence time in the wa­ter column than pre­vi­ously ex­pec­ted. This shows that we should re­visit cur­rent ap­proaches to particle set­tling to in­clude the ef­fect of poros­ity, if we want to im­prove our es­tim­ate of the car­bon flux in the ocean."

“The deeper we look at mi­cro­scale phe­nom­ena in the ocean, the more we dis­cover that they are the pro­cesses that really gov­ern how the Oceans work. Our chances of de­vel­op­ing a sus­tain­able ap­proach to how we in­ter­act with and use the Oceans hinge on how well we can un­der­stand pro­cesses at these small scales” adds Roman Stocker from the Mas­sachu­setts In­sti­tute of Tech­no­logy.

Manfred Schloesser
Fur­ther ques­tions to be ad­dressed to:

Prof. Ar­zhang Khalili
Max Planck In­sti­tute for Mar­ine Mi­cro­bi­o­logy, Celsi­usstr. 1, D-28359 Bre­men, Ger­many
E-Mail: akhalili@mpi-bre­men.de
Tel.: +49 (0)421 2028 – 636

Pro­fessor of Com­pu­ta­tional Sci­ence
Jac­obs Uni­versity Bre­men
School of En­gin­eer­ing & Sci­ence
Life Sci­ences
E-Mail: a.khalili@jac­obs-uni­versity.de
Tel.: +49 421 200-3256


Prof. Ro­man Stocker
Mas­sachu­setts In­sti­tute of Tech­no­logy, 77 Mas­sachu­setts Av­enue, 02139 Cam­bridge MA, U.S.A.
E-Mail: ro­mans@mit.edu
Tel.:+1 617 253 3726


and Public relation officers:
Man­fred Schlösser
Max Planck In­sti­tute for Mar­ine Mi­cro­bi­o­logy, Celsi­usstr. 1, D-28359 Bre­men
mschloes@mpi-bre­men.de
Tel.: +49 (0)421 2028 - 704

Den­ise Brehm
MIT De­part­ment of Civil and En­vir­on­mental En­gin­eer­ing
brehm@mit.edu
Tel. +1 617 253 8069


Original title:
“Dif­fu­sion-lim­ited re­ten­tion of por­ous particles at dens­ity in­ter­faces”, by Kolja Kind­ler, Ar­zhang Khalili and Ro­man Stocker (2010).


Contributing Institutes:
Dept. of Biogeochemistry, Max Planck In­sti­tute for Mar­ine Mi­cro­bi­o­logy, Bre­men, Ger­many
Earth & Space Sciences Program, Jac­obs Uni­versity Bre­men, Bre­men, Ger­many
Department of Civil and Environmental Engineering, Mas­sachu­setts In­sti­tute of Tech­no­logy, Cam­bridge, MA, USA
 
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