Oceanography The Official Magazine of
The Oceanography Society
Volume 22 Issue 01

View Issue TOC
Volume 22, No. 1
Pages 26 - 43

OpenAccess

Cascades in Mediterranean Submarine Grand Canyons

By Miquel Canals , Roberto Danovaro, Serge Heussner, Vasilios Lykousis, Pere Puig, Fabio Trincardi , Antoni M. Calafat , Xavier Durrieu de Madron, Albert Palanques , and Anna Sànchez-Vidal 
Jump to
Article Abstract Citation References Copyright & Usage
Article Abstract

Continuous monitoring of water-column and near-bottom hydrosedimentary processes in the Mediterranean Sea over the last 15 years has resulted in a novel view of the functioning of this land-locked sea. Destratification of the water column and fast, dense, organic-matter-rich, and sediment-laden near-bottom currents occurring in late winter to early spring efficiently transfer matter and energy from the continental shelf and the upper ocean layers to the deep basin. These currents, known as dense shelf water cascading (DSWC), have been repeatedly measured by moored instrumentation during concurrent field experiments in the Gulf of Lion (northwestern Mediterranean Sea) and the Adriatic Sea (central Mediterranean). Physical oceanography observations made in the eastern Mediterranean in the early 1990s, together with observations of large-scale bed forms on the shelf floor, indicate that this phenomenon also occurs in the Aegean Sea (eastern Mediterranean) where it impacts the neighboring deep basins.

The source areas of DSWC are the northernmost shelves of the Mediterranean Sea. Due to their location and inland topography, they are more exposed to the cold, persistent, intense northerly winter winds that cool shelf (and offshore) waters enough to make them denser than underlying waters, thus triggering their sinking once a density threshold is reached. It has also been observed that low river discharge on these shelves favors late winter-early spring cascading as shelf waters become denser than they would be under high river discharge. While offshore convection cells bring only “blue water” to the deep basin, DSWC events carry huge amounts of organic and inorganic substances as they scour the shelf and slope seafloor while sinking. Cascades of DSW may last for several weeks, and cascading waters sink continually deeper until they find their density equilibrium level, which changes from year to year. It has been observed that particularly intense DSWC events that carry shelf waters to the deepest parts of the western Mediterranean basin occur at subdecadal frequency.

The influence of seafloor topography on the path followed by DSWC is best illustrated by submarine canyons. At specific locations, canyons are the main conduits for the cascading shelf waters, and from this developed the concept of “flushing submarine canyons.” If the volume of cascading waters in a given event is too large, the canyons may be unable to accommodate it, and, therefore, those waters may escape from the canyons—especially where they are less entrenched. It has been also observed that DSW may cascade as sheet flows, sweeping continental slopes along tens of kilometers or more before spreading over the deep basin.

The findings reported in this paper are just the tip of the iceberg in terms of the consequences of DSWC on deep-water mass formation and on the deep ecosystem of the Mediterranean Sea. As cascades often occur simultaneously with spring phytoplankton blooms in the various Mediterranean regions, there is no doubt that their role as a natural mechanism for carbon sequestration from the shallow ocean layers will demand the attention of the scientific community in the coming years.

Citation

Canals, M., R. Danovaro, S. Heussner, V. Lykousis, P. Puig, F. Trincardi, A.M. Calafat, X. Durrieu de Madron, A. Palanques, and A. Sànchez-Vidal. 2009. Cascades in Mediterranean submarine grand canyons. Oceanography 22(1):26–43, https://doi.org/10.5670/oceanog.2009.03.

References
    Amblàs, D., M. Canals, G. Lastras, S. Berné, and B. Loubrieu. 2004. Imaging the seascapes of the Mediterranean. Oceanography 17(4):144–155.
  1. Arnau, P., C. Liquete, and M. Canals. 2004. River mouth plume events and their dispersal in the northwestern Mediterranean Sea. Oceanography 17(3):22–31.
  2. Bignami, F., R. Sciarra, S. Carniel, and R. Santoleri. 2007. Variability of Adriatic Sea coastal turbid waters from SeaWiFS imagery. Journal of Geophysical Research 112, C03S10, doi:10.1029/2006JC003518.
  3. Canals, M., J.L. Casamor, G. Lastras, A. Monaco, J. Acosta, S. Berné, B. Loubrieu, P.P.E. Weaver, A. Grehan, and B. Dennielou. 2004. The role of canyons in strata formation. Oceanography 17(4):80–91.
  4. Canals, M., P. Puig, X. Durrieu de Madron, S. Heussner, A. Palanques, and J. Fabrés. 2006. Flushing submarine canyons. Nature 444:354–357.
  5. Company, J.B., P. Puig, F. Sardà, A. Palanques, M. Latasa, and R. Scharek. 2008. Climate influence on deep sea populations. PLoS ONE 3(1):e1431, doi:10.1371/journal.pone.0001431.
  6. Cushman-Roisin, B., M. Gacic, P.-M. Poulain, and A. Artegiani, eds. 2001. Physical Oceanography of the Adriatic Sea: Past, Present and Future. Kluwer Academic Publishers, Dordrecht/Boston/London, 304 pp.
  7. Durrieu de Madron, X. 1994. Hydrography and nepheloid structures in the Grand-Rhône canyon. Continental Shelf Research 14:457–477.
  8. Durrieu de Madron, X., F. Nyffeler, E.T. Balopoulos, and G. Chronis. 1992. Circulation and distribution of suspended matter in the Sporades Basin (northwestern Aegean Sea). Journal of Marine Systems 3:237–248.
  9. Durrieu de Madron, X., F. Nyffeler, and C.H. Godet. 1990. Hydrographic structure and nepheloid spatial distribution in the Gulf of Lions continental margin. Continental Shelf Research 10:915–929.
  10. Ferré, B., X. Durrieu de Madron, C. Estournel, C. Ulses, and G. Le Corre. 2008. Impact of natural and anthropogenic (trawl) resuspension on the export of particulate matter to the open ocean. Application to the Gulf of Lion (NW Mediterranean). Continental Shelf Research 28(15):2,071–2,091, doi:10.1016/j.csr.2008.02.002.
  11. Flexas, M., X. Durrieu de Madron, M.A. García, M. Canals, and P. Arnau. 2002. Flow variability in the Gulf of Lions during the MATER HFF Experiment (March–May 1997). Journal of Marine Systems 33–34:197–214.
  12. Hermann, M., C. Estournel, M. Déqué, P. Marsaleix, F. Sevault, and S. Somot. 2008. Dense water formation in the Gulf of Lions shelf: Impact of atmospheric interannual variability and climate change. Continental Shelf Research 28(25):2,092–2,112, doi:10.1016/j.csr.2008.03.003.
  13. Heussner, S., A. Calafat, and M. Canals. 1996. Quantitative and qualitative features of particle fluxes in the North-Balearic Basin, Pp. 43–66 in EUROMARGE-NB Final Report, MAST II Programme, vol. II. M. Canals, J.L. Casamor, I. Cacho, A. Calafat, and A. Monaco, eds, European Union, Brussels.
  14. Heussner, S., X. Durrieu de Madron, A. Calafat, M. Canals, J. Carbonne, N. Delsaut, and G. Saragoni. 2006. Spatial and temporal variability of downward particle fluxes on a continental slope: Lessons from an 8-yr experiment in the Gulf of Lions (NW Mediterranean). Marine Geology 234:63–92.
  15. Ivanov, V.V., G.I. Shapiro, J.M. Huthnance, D.L. Aleynik, and P.N. Golovin. 2004. Cascades of dense water around the world ocean. Progress in Oceanography 60:47–98.
  16. Kerherve, P., S. Heussner, B. Charriere, S. Stavrakakis, J.-L. Fernard, A. Monaco, and N. Delsaut. 1999. Biochemistry and dynamics of settling particle fluxes at the Antikythira Strait (Eastern Mediterranean). Progress in Oceanography 44(4):651–677.
  17. Klein, B., W. Roether, N. Kress, B. Manca, M.R. Alcala, A. Souvermezoglou, A. Theocharis, G. Civitarese, and A. Luchetta. 2003. Accelerated oxygen consumption in eastern Mediterranean deep waters following the recent changes in thermohaline circulation. Journal of Geophysical Research 108(C9), 8107, doi:10.1029/2002JC001454.
  18. Lykousis, V. 2001. Subaqueous bedforms on the Cyclades Plateau (NE Mediterranean). Evidence of Cretan Deep Water formation? Continental Shelf Research 21:495–507.
  19. Lykousis, V., G. Chronis, A. Tselepides, B. Price, A. Theocharis, I. Siokou-Frangou, F. Van Wambeke, R. Danovaro, S. Stavrakakis, G. Duineveld, and others. 2002. Major outputs of the recent multidisciplinary biogeochemical researches in the Aegean Sea. Journal of Marine Science 33–34:313–334.
  20. Manca, B.B., V. Kovacevic, M. Gacic, and D. Viezzoli. 2002. Dense water formation in the southern Adriatic Sea and interaction with the Ionian Sea in the period 1997–1999. Journal of Marine Systems 33–34:133–154.
  21. Minisini, D., F. Trincardi, and A. Asioli. 2006. Evidence of slope instability in the South-Western Adriatic margin. Natural Hazards and Earth System Sciences 6(1):1–20.
  22. Palanques, A., X. Durrieu de Madron, P. Puig, J. Fabrés, J. Guillén, A. Calafat, M. Canals, and J. Bonnin. 2006. Suspended sediment fluxes and transport processes in the Gulf of Lions submarine canyons: The role of storms and dense water cascading. Marine Geology 234:43–61.
  23. Palanques, A., J. Guillén, and P. Puig. 2001. Impact of bottom trawling on water turbidity and muddy sediment of an unfished continental shelf. Limnology and Oceanography 46(5):1,100–1,110
  24. Palanques, A., J. Martin, P. Puig, J. Guillén, J.B. Company, and F. Sardà. 2006. Evidence of sediment gravity flows induced by trawling in the Palamos (Fonera) submarine canyon (northwestern Mediterranean). Deep-Sea Research Part I 53:201–214.
  25. Puig, P., A. Palanques, D.L. Orange, G. Lastras, and M. Canals. 2008. Dense shelf water cascades and sedimentary furrow formation in the Cap de Creus Canyon, northwestern Mediterranean Sea. Continental Shelf Research 28(15):2,017–2,030, doi:10.1016/j.csr.2008.05.002/
  26. Roether, W., B.B. Manca, B. Klein, D. Bregant, D. Georgopoulos, V. Beitzel, V. Kovacevic, and A. Luchetta. 1996. Recent changes in Eastern Mediterranean Deep Waters. Science 271:333–335.
  27. Sànchez-Vidal, A., C. Pascual, P.A. Kerhervé, A. Calafat, S. Heussner, A. Palanques, X. Durrieu de Madron, M. Canals, and P. Puig. 2008. Impact of dense shelf water cascading on the transfer of organic matter to the deep Western Mediterranean Basin. Geophysical Research Letters 35, L05605, doi:10.1029/2007GL032825.
  28. Shepard, F.P. 1981. Submarine canyons: Multiple causes and long time persistence. American Association of Petroleum Geologists Bulletin 65(6):1,062–1,077.
  29. Somot, S., F. Sevault, and M. Déqué. 2006. Transient climate change scenario simulation of the Mediterranean Sea for the twenty-first century using a high-resolution ocean circulation model. Climate Dynamics 27:851–879, doi:10.1007/s00382-006-0167-z.
  30. Tesi, T., L. Langone, M.A. Goñi, M. Turchetto, S. Miserocchi, and A. Boldrin. 2008. Source and composition of organic matter in the Bari canyon (Italy): Dense water cascading versus particulate export from the upper ocean. Deep-Sea Research Part I 55:813–831.
  31. Theocharis, A., and D. Georgopoulos. 1993. Dense water formation over the Samothraki and Lemnos plateaux in the North Aegean Sea (Eastern Mediterranean Sea). Continental Shelf Research 13(8/9):919–939.
  32. Theocharis, A., E. Balopoulos, S. Kioroglou, H. Kontoyiannis, and A. Iona. 1999. A synthesis of the circulation and hydrography of the South Aegean Sea and the Straits of the Cretan Arc (March 1994–January 1995). Progress in Oceanography 44(4):469–509.
  33. Trincardi, F., F. Foglini, G. Verdicchio, A. Asioli, A. Correggiari, S. Minisini, A. Piva, A. Remia, D. Ridente, and M. Taviani. 2007a. The impact of cascading currents on the Bari Canyon System, SW-Adriatic Margin (Central Mediterranean). Marine Geology 246:208–230.
  34. Trincardi, F., G. Verdicchio, and S. Miserocchi. 2007b. Sea-floor evidence for the interaction between cascading and along-slope bottom-water masses. Journal of Geophysical Research (Earth Surface) 112, F03011, doi:10.1029/2006JF000620.
  35. Turchetto, M., A. Boldrin, L. Langone, S. Miserocchi, T. Tesi, and F. Foglini. 2007. Particle transport in the Bari Canyon (southern Adriatic Sea). Marine Geology 246:231–247.
  36. Ulses, C., C. Estournel, P. Puig, X. Durrieu de Madron, and P. Marsaleix. 2008. Dense shelf water cascading in the northwestern Mediterranean during the cold winter 2005. Quantification of the export through the Gulf of Lion and the Catalan margin. Geophysical Research Letters 35, L07610, doi:10.1029/2008GL033257.
  37. UNEP/MAP/MED POL. 2003. Riverine transport of water, sediments and pollutants to the Mediterranean Sea. MAP Technical Reports Series No. 141, UNEP/MAP, Athens.
  38. Ünlüata, U., T. Oguz, M.A. Latif, and E. Öszoy. 1990. On the physical oceanography of the Turkish Straits. Pp. 25–60 in The Physical Oceanography of Sea Straits. L.J. Pratt, ed., Kluwer, Dordrecht.
  39. Van Wambeke, F., S. Heussner, F. Díaz, P. Raimbault, and P. Conan. 2002. Small-scale variability in the coupling/uncoupling of bacteria, phytoplankton and organic carbon fluxes along the continental margin of the Gulf of Lions, Northwestern Mediterranean Sea. Journal of Marine Systems 33–34:411-429.
  40. Verdicchio, G., and F. Trincardi. 2006. Short-distance variability in slope bed-forms along the Southwestern Adriatic Margin (Central Mediterranean). Marine Geology 234:271–292.
  41. Verdicchio, G., F. Trincardi, and A. Asioli. 2007. Mediterranean bottom current deposits: An example from the Southwestern Adriatic Margin. Geological Society of London, Special Publication 276:199–224.
  42. Vilibic, I. 2003. An analysis of dense water production on the North Adriatic shelf. Estuarine, Coastal and Shelf Science 56:697–707.
  43. Vilibic, I., and N. Supic. 2005. Dense water generation on a shelf: The case of the Adriatic Sea. Ocean Dynamics 55(5–6):403–415.
  44. Zore-Armanda, M. 1963. Les masses d’eau de la mer Adriatique. Acta Adriatica 10:5–88.
  45. Zoccolotti, L., and E. Salusti. 1987. Observations of a vein of very dense marine water in the southern Adriatic Sea. Continental Shelf Research 7:535–551.
Copyright & Usage

This is an open access article made available under the terms of the Creative Commons Attribution 4.0 International License (https://creativecommons.org/licenses/by/4.0/), which permits use, sharing, adaptation, distribution, and reproduction in any medium or format as long as users cite the materials appropriately, provide a link to the Creative Commons license, and indicate the changes that were made to the original content. Images, animations, videos, or other third-party material used in articles are included in the Creative Commons license unless indicated otherwise in a credit line to the material. If the material is not included in the article’s Creative Commons license, users will need to obtain permission directly from the license holder to reproduce the material.