Diffusion-limited retention of porous particles at density interfaces
Downward carbon flux in the ocean is largely governed by particle settling. Most marine particles settle at low Reynolds numbers and are highly porous, yet the fluid dynamics of this regime have remained unexplored. We present results of an experimental investigation of porous particles settling thr...
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| Format: | Article |
| Language: | en_US |
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National Academy of Sciences (U.S.)
2013
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| Online Access: | http://hdl.handle.net/1721.1/77977 https://orcid.org/0000-0002-3199-0508 |
| _version_ | 1826200340475674624 |
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| author | Kindler, Kolja Khalili, Arzhang Stocker, Roman |
| author2 | Massachusetts Institute of Technology. Department of Civil and Environmental Engineering |
| author_facet | Massachusetts Institute of Technology. Department of Civil and Environmental Engineering Kindler, Kolja Khalili, Arzhang Stocker, Roman |
| author_sort | Kindler, Kolja |
| collection | MIT |
| description | Downward carbon flux in the ocean is largely governed by particle settling. Most marine particles settle at low Reynolds numbers and are highly porous, yet the fluid dynamics of this regime have remained unexplored. We present results of an experimental investigation of porous particles settling through a density interface at Reynolds numbers between 0.1 and 1. We tracked 100 to 500 μm hydrogel spheres with 95.5% porosity and negligible permeability. We found that a small negative initial excess density Δp[subscript p] relative to the lower (denser) fluid layer, a common scenario in the ocean, results in long retention times of particles at the interface. We hypothesized that the retention time was determined by the diffusive exchange of the stratifying agent between interstitial and ambient fluid, which increases excess density of particles that have stalled at the interface, enabling their settling to resume. This hypothesis was confirmed by observations, which revealed a quadratic dependence of retention time on particle size, consistent with diffusive exchange. These results demonstrate that porosity can control retention times and therefore accumulation of particles at density interfaces, a mechanism that could underpin the formation of particle layers frequently observed at pycnoclines in the ocean. We estimate retention times of 3 min to 3.3 d for the characteristic size range of marine particles. This enhancement in retention time can affect carbon transformation through increased microbial colonization and utilization of particles and release of dissolved organics. The observed size dependence of the retention time could further contribute to improve quantifications of vertical carbon flux. |
| first_indexed | 2024-09-23T11:34:57Z |
| format | Article |
| id | mit-1721.1/77977 |
| institution | Massachusetts Institute of Technology |
| language | en_US |
| last_indexed | 2024-09-23T11:34:57Z |
| publishDate | 2013 |
| publisher | National Academy of Sciences (U.S.) |
| record_format | dspace |
| spelling | mit-1721.1/779772022-09-27T20:28:59Z Diffusion-limited retention of porous particles at density interfaces Kindler, Kolja Khalili, Arzhang Stocker, Roman Massachusetts Institute of Technology. Department of Civil and Environmental Engineering Kindler, Kolja Stocker, Roman Downward carbon flux in the ocean is largely governed by particle settling. Most marine particles settle at low Reynolds numbers and are highly porous, yet the fluid dynamics of this regime have remained unexplored. We present results of an experimental investigation of porous particles settling through a density interface at Reynolds numbers between 0.1 and 1. We tracked 100 to 500 μm hydrogel spheres with 95.5% porosity and negligible permeability. We found that a small negative initial excess density Δp[subscript p] relative to the lower (denser) fluid layer, a common scenario in the ocean, results in long retention times of particles at the interface. We hypothesized that the retention time was determined by the diffusive exchange of the stratifying agent between interstitial and ambient fluid, which increases excess density of particles that have stalled at the interface, enabling their settling to resume. This hypothesis was confirmed by observations, which revealed a quadratic dependence of retention time on particle size, consistent with diffusive exchange. These results demonstrate that porosity can control retention times and therefore accumulation of particles at density interfaces, a mechanism that could underpin the formation of particle layers frequently observed at pycnoclines in the ocean. We estimate retention times of 3 min to 3.3 d for the characteristic size range of marine particles. This enhancement in retention time can affect carbon transformation through increased microbial colonization and utilization of particles and release of dissolved organics. The observed size dependence of the retention time could further contribute to improve quantifications of vertical carbon flux. National Science Foundation (U.S.) (Grant OCE-0744641-CAREER) National Science Foundation (U.S.) (Grant CBET-0966000) 2013-03-21T20:22:25Z 2013-03-21T20:22:25Z 2010-12 2010-08 Article http://purl.org/eprint/type/JournalArticle 0027-8424 1091-6490 http://hdl.handle.net/1721.1/77977 Kindler, K., A. Khalili, and R. Stocker. “Diffusion-limited Retention of Porous Particles at Density Interfaces.” Proceedings of the National Academy of Sciences 107.51 (2010): 22163–22168. ©2010 National Academy of Sciences https://orcid.org/0000-0002-3199-0508 en_US http://dx.doi.org/10.1073/pnas.1012319108 Proceedings of the National Academy of Sciences of the United States of America Article is made available in accordance with the publisher's policy and may be subject to US copyright law. Please refer to the publisher's site for terms of use. application/pdf National Academy of Sciences (U.S.) PNAS |
| spellingShingle | Kindler, Kolja Khalili, Arzhang Stocker, Roman Diffusion-limited retention of porous particles at density interfaces |
| title | Diffusion-limited retention of porous particles at density interfaces |
| title_full | Diffusion-limited retention of porous particles at density interfaces |
| title_fullStr | Diffusion-limited retention of porous particles at density interfaces |
| title_full_unstemmed | Diffusion-limited retention of porous particles at density interfaces |
| title_short | Diffusion-limited retention of porous particles at density interfaces |
| title_sort | diffusion limited retention of porous particles at density interfaces |
| url | http://hdl.handle.net/1721.1/77977 https://orcid.org/0000-0002-3199-0508 |
| work_keys_str_mv | AT kindlerkolja diffusionlimitedretentionofporousparticlesatdensityinterfaces AT khaliliarzhang diffusionlimitedretentionofporousparticlesatdensityinterfaces AT stockerroman diffusionlimitedretentionofporousparticlesatdensityinterfaces |