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The importance of tides for sediment dynamics in the deep sea—Evidence from the particulate-matter tracer 234Th in deep-sea environments with different tidal forcing

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dc.contributor.authorPeine, Florian
dc.contributor.authorTurnewitsch, Robert
dc.contributor.authorMohn, Christian
dc.contributor.authorReichelt, Theresa
dc.contributor.authorSpringer, Barbara
dc.contributor.authorKaufmann, Manfred
dc.date.accessioned2021-10-07T15:03:40Z
dc.date.available2021-10-07T15:03:40Z
dc.date.issued2009
dc.description.abstractKey aspects of deep-ocean fluid dynamics such as basin-scale (residual) and tidal flow are believed to have changed over glacial/interglacial cycles, with potential relevance for climatic change. To constrain the mechanistic links, magnitudes and temporal succession of events analyses of sedimentary paleo-records are of great importance. Efforts have been underway for some time to reconstruct residual-flow patterns from sedimentary records. Attempts to reconstruct tidal flow characteristics from deep-sea sediment deposits, however, are at a very early stage and first require a better understanding of the reflection of modern tides in sediment dynamics. In this context internal (baroclinic) tides, which are formed by the surface (barotropic) tide interacting with seafloor obstacles, are believed to play a particularly important role. Here we compare two modern deep-sea environments with respect to the effect of tides on sediment dynamics. Both environments are influenced by kilometre-scale topographic features but with vastly different tidal forcing: (1) two sites in the Northeast Atlantic (NEA) being surrounded by, or located downstream of, fields of short seamounts (maximum barotropic tidal current velocities 5 cm s 1 ); and (2) a site next to the Anaximenes seamount in the Eastern Mediterranean (EMed) (maximum barotropic tidal current velocities 0.5 cm s 1 ). With respect to other key fluid-dynamical parameters both environments are very similar. Signals of sedimentary particle dynamics, as influenced by processes taking place in the bottom boundary layer, were traced by the vertical water-column distribution of radioactive disequilibria (daughter/parent activity ratiosa1) between the naturally occurring, short-lived (half-life: 24.1 d) particulate matter tracer 234Th relative to its very long-lived and non-particle-reactive parent nuclide 238U. Activity ratios of 234Th/238Uo1 in water samples collected near the seafloor indicate fast 234Th scavenging onto particles followed by fast settling of these particles from the sampled parcel of water and, therefore, imply active sediment resuspension and dynamics on time scales of up to several weeks. In the Northeast Atlantic study region tides (in particular internal tides) are very likely to locally push total current velocities near the seafloor across the critical current velocity threshold for sediment erosion or resuspension whereas in the Eastern Mediterranean the tides aremuch too weak for this to happen. This difference in tidal forcing is reflected in a difference of the frequency of the occurrence of radioactive disequilibria o1 between total 234Th and 238U: In the near-bottom water column of the Northeast Atlantic region 59% of samples had detectable 234Th/238U disequilibria whereas at the Eastern Mediterranean site this fraction was only 7% (including a few disequilibria 41). The results of this study, therefore, add to the evidence suggesting that tides in the deep sea of the open oceans are more important for sediment dynamics than previously thought. It is hypothesised that (a) tide/seamount interactions in the deep open ocean control the local distribution of erosivity proxies (e.g., distributions of sediment grain sizes, heavy minerals and particle-reactive radionuclides) in sedimentary deposits and (b) the aforementioned topographically controlled sedimentary imprints of (internal) tides are useful in the reconstruction of past changes of tidal forcing in the deep seapt_PT
dc.description.versioninfo:eu-repo/semantics/publishedVersionpt_PT
dc.identifier.citationPeine, F., Turnewitsch, R., Mohn, C., Reichelt, T., Springer, B., & Kaufmann, M. (2009). The importance of tides for sediment dynamics in the deep sea—Evidence from the particulate-matter tracer 234Th in deep-sea environments with different tidal forcing. Deep Sea Research Part I: Oceanographic Research Papers, 56(7), 1182-1202. https://doi.org/10.1016/j.dsr.2009.03.009pt_PT
dc.identifier.doi10.1016/j.dsr.2009.03.009pt_PT
dc.identifier.urihttp://hdl.handle.net/10400.13/3709
dc.language.isoengpt_PT
dc.peerreviewedyespt_PT
dc.publisherElsevierpt_PT
dc.rights.urihttp://creativecommons.org/licenses/by-nc-nd/4.0/pt_PT
dc.subjectThorium-234/uranium-238 disequilibriapt_PT
dc.subjectSediment dynamicspt_PT
dc.subjectBottom boundary layerpt_PT
dc.subjectTopographypt_PT
dc.subjectSeamountspt_PT
dc.subjectInternal tidespt_PT
dc.subjectNortheast Atlanticpt_PT
dc.subjectEastern Mediterraneanpt_PT
dc.subject.pt_PT
dc.subjectFaculdade de Ciências da Vidapt_PT
dc.titleThe importance of tides for sediment dynamics in the deep sea—Evidence from the particulate-matter tracer 234Th in deep-sea environments with different tidal forcingpt_PT
dc.typejournal article
dspace.entity.typePublication
oaire.citation.endPage1202pt_PT
oaire.citation.issue7pt_PT
oaire.citation.startPage1182pt_PT
oaire.citation.titleDeep Sea Research Part I: Oceanographic Research Paperspt_PT
oaire.citation.volume56pt_PT
person.familyNameKaufmann
person.givenNameManfred
person.identifier.ciencia-idA316-A34A-F7AF
person.identifier.orcid0000-0001-6213-3229
person.identifier.ridA-7561-2013
person.identifier.scopus-author-id35264346100
rcaap.rightsopenAccesspt_PT
rcaap.typearticlept_PT
relation.isAuthorOfPublication041c8f9b-d342-4678-938d-9c95a4fd19de
relation.isAuthorOfPublication.latestForDiscovery041c8f9b-d342-4678-938d-9c95a4fd19de

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