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Particle flux in the oceans: Challenging the steady state assumption
Author(s) -
Giering Sarah L. C.,
Sanders Richard,
Martin Adrian P.,
Henson Stephanie A.,
Riley Jennifer S.,
Marsay Chris M.,
Johns David G.
Publication year - 2017
Publication title -
global biogeochemical cycles
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.512
H-Index - 187
eISSN - 1944-9224
pISSN - 0886-6236
DOI - 10.1002/2016gb005424
Subject(s) - mesopelagic zone , sediment trap , flux (metallurgy) , photic zone , environmental science , oceanography , atmospheric sciences , remineralisation , phytodetritus , spring bloom , geology , water column , pelagic zone , chemistry , benthic zone , phytoplankton , nutrient , inorganic chemistry , fluoride , organic chemistry , foraminifera
Atmospheric carbon dioxide levels are strongly controlled by the depth at which the organic matter that sinks out of the surface ocean is remineralized. This depth is generally estimated from particle flux profiles measured using sediment traps. Inherent in this analysis is a steady state assumption that export from the surface does not significantly change in the time it takes material to reach the deepest trap. However, recent observations suggest that a significant fraction of material in the mesopelagic zone sinks slowly enough to bring this into doubt. We use data from a study in the North Atlantic during July/August 2009 to challenge the steady state assumption. An increase in biogenic silica flux with depth was observed which we interpret, based on vertical profiles of diatom taxonomy, as representing the remnants of the spring diatom bloom sinking slowly (<40 m d −1 ). We were able to reproduce this behavior using a simple model using satellite‐derived export rates and literature‐derived remineralization rates. We further provide a simple equation to estimate “additional” (or “excess”) particulate organic carbon supply to the dark ocean during nonsteady state conditions, which is not captured by traditional sediment trap deployments. In seasonal systems, mesopelagic net organic carbon supply could be wrong by as much as 25% when assuming steady state. We conclude that the steady state assumption leads to misinterpretation of particle flux profiles when input fluxes from the upper ocean vary on the order of weeks, such as in temperate and polar regions with strong seasonal cycles in export.