Publication Date:
2015-11-18
Description:
In coastal waters and the ocean silicic acid (Si(OH)
4
) is a key nutrient for primary producers (
e.g
. diatoms)
and other siliceous organisms, because it is required for the formation of frustules and other hard parts
made of biogenic silica (bSi). Especially in shallow waters like the southern North Sea, dissolution of bSi
in surface sediments and the re
fl
ux of silicic acid from sediments into the water column is an important
feedback mechanism for sustaining primary production. We investigated the temporal variability of
benthic silicic acid
fl
uxes and the recycling ef
fi
ciency of bSi in surface sediments of the Helgoland Mud
Area (southern North Sea). For this purpose we used different methods including a benthic chamber
lander system for
in situ
fl
ux studies of Si(OH)
4
,
ex situ
sediment incubations, pore water studies
and sediment analysis. Our
in situ
measurements revealed considerable temporal variations with low
silicic acid
fl
uxes in winter (0.3
–
1.0 mmol m
�
2
d
�
1
in March 2013 and 2014), increased
fl
uxes of
2.0
–
4.0 mmol m
�
2
d
�
1
in November 2013, and high
fl
uxes in June and August 2012
(3.6
–
8.3 mmol m
�
2
d
�
1
). The relevance of biological mediated transport for the recycling of Si(OH)
4
was
underlined by comparing
in situ
and
ex situ
sediment incubations, pore water studies, as well as depth
pro
fi
les of benthic macrofauna. Mass budget calculations indicate that about 1.7
–
2.2 mol bSi m
�
2
settle
annually at the sea
fl
oor, off which about 60
–
81% are recycled within surface sediments and transported
back into the water column
Repository Name:
EPIC Alfred Wegener Institut
Type:
Article
,
isiRev
Format:
application/pdf
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