Quantifying importance of macrobenthos for benthic-pelagic coupling in a
temperate coastal shelf sea
Abstract
Benthic oxygen fluxes consist of advective and diffusive terms. Both
terms in the south-eastern North Sea exhibit a prominent annual cycle
but with opposite variation patterns. To understand the driving
mechanisms quantitatively, a novel 3-D benthic-pelagic coupled model
resolving interactions among macrobenthos, bioturbation, oxygen
consumption and carbon early diagenesis was applied to reconstruct the
benthic states. Simulation results show a satisfactory agreement with
field data and reveal that the benthic oxygen flux is determined by not
only pelagic drivers but also by internal dynamics associated with the
interaction between organic carbon and macrobenthos, and bedform
morphodynamics. Variation of advective flux, characterized by summer-low
and winter-high, is mainly driven by hydrodynamics and bedform
morphodynamics, while variation of diffusive flux, featured by
summer-high and winter-low, is a compound effect of pelagic and benthic
drivers with a dominant control by macrobenthos through bioturbation.
The role of bioturbation in benthic oxygen consumption is twofold: (i)
on the one hand, it alters the particulate organic carbon (POC)
distribution in surface sediments, thereby changing the availability of
POC to oxygen consumption; (ii) on the other hand, it mixes oxygen down
into sediments, thereby facilitating oxygen consumption. Our results
indicate that the first role prevails in sandy seafloor characterized by
energetic hydrodynamics, while the second role becomes increasingly
important along with a weakening of bottom currents. We found that
bioturbation-induced oxygen consumption contributes to more than 85%
and 52% of the total benthic oxygen fluxes in muddy seabed and at a
regional scale, respectively.