The production of giant marine diatoms and their export at oceanic frontal zones: implications for Si and C flux in stratified oceans.

• Published in: Global Biogeochemical Cycles
• Main Authors: Kemp, Alan, Pearce, Richard, Grigorov, Ivo, Rance, J., Lange, Carina, Quilty, Patrick, Salter, Ian
• Other Authors: School of Ocean and Earth Sciences (SOES-NOC), University of Southampton, Université de Brest (UBO), Center for Oceanographic Research in the Eastern South Pacific (FONDAP-COPAS), Universidad de Concepción - University of Concepcion Chile, School of Earth Sciences Hobart, University of Tasmania Hobart, Australia (UTAS)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2006
• Subjects: Giant diatoms; Equatorial front; Polar front; Deep chlorophyll maximum; Stratification; Export production; Thalassiothrix; Rhizosolenia; Ethmodiscus; [SDU.STU.OC]Sciences of the Universe [physics]/Earth Sciences/Oceanography; Pacific; Southern Ocean
• Online Access: https://hal.univ-brest.fr/hal-00460241; https://hal.univ-brest.fr/hal-00460241v2/document; https://hal.univ-brest.fr/hal-00460241v2/file/Kemp_et_al_2006_Global_Biogeochemical_Cycles_20.pdf; https://doi.org/10.1029/2006GB002698

International audience From a synthesis of recent oceanic observations and paleo-data it is evident that certain species of giant diatoms including Rhizosolenia spp. Thalassiothrix spp. and Ethmodiscus rex may become concentrated at oceanic frontal zones and subsequently form episodes of mass flux to the sediment. Within the nutrient bearing waters advecting towards frontal boundaries, these species are generally not dominant but they appear selectively segregated at fronts, and thus may dominate the export flux. Ancient Thalassiothrix diatom mat deposits in the eastern Equatorial Pacific and beneath the Polar Front in the Southern Ocean record the highest open ocean sedimentation rates ever documented and represent vast sinks of silica and carbon. Several of the species involved are adapted to a stratified water column and may thrive in Deep Chlorophyll Maxima. Thus in oceanic regions and/ or at times prone to enhanced surface water stratification (e.g. during meltwater pulses) they provide a mechanism for generating substantial biomass at depth and its subsequent export with concomitant implications for Si export and C draw-down. This ecology has important implications for ocean biogeochemical models suggesting that more than one diatom “functional type” should be used. In spite of the importance of these giant diatoms for biogeochemical cycling, their large size coupled with the constraints of conventional oceanographic survey schemes and techniques means that they are under-sampled. An improved insight of these key species will be an important prerequisite for enhancing our understanding of marine biogeochemical cycling and for assessing the impacts of climate change on ocean export production.