Abstract. Bottom trawling in the deep sea is one of the main
drivers of sediment resuspension, eroding the seafloor and altering the
content and composition of sedimentary organic matter (OM). The physical and
biogeochemical impacts of bottom trawling were studied on the continental
slope of the Gulf of Castellammare, Sicily (southwestern Mediterranean),
through the analysis of two triplicate sediment cores collected at trawled
and untrawled sites (∼550 m water depth) during the summer of
2016. Geochemical and sedimentological parameters (excess 210Pb, excess
234Th, 137Cs, dry bulk density, and grain size), elemental
(organic carbon and nitrogen) and biochemical composition of sedimentary OM
(proteins, carbohydrates, lipids), as well as its freshness (phytopigments)
and degradation rates were determined in both coring locations. The
untrawled site had a sedimentation rate of 0.15 cm yr−1 and
presented a 6 cm thick surface mixed layer that contained siltier sediment
with low excess 210Pb concentrations, possibly resulting from the
resuspension, posterior advection, and eventual deposition of coarser and
older sediment from adjacent trawling grounds. In contrast, the trawled site
was eroded and presented compacted century-old sediment highly depleted in
OM components, which were between 20 % and 60 % lower than those in the
untrawled site. However, the upper 2 cm of the trawled site consisted of
recently accumulated sediments enriched in excess 234Th, excess
210Pb, and phytopigments, while OM contents were similar to those from
the untrawled core. This fresh sediment supported protein turnover rates of
0.025 d−1, which doubled those quantified in surface sediments of the
untrawled site. The enhancement of remineralization rates in surface
sediment of the trawled site was associated with the arrival of fresh
particles on a chronically trawled deep-sea region that is generally
deprived of OM. We conclude that the detrimental effects of bottom trawling
can be temporarily and partially abated by the arrival of fresh and
nutritionally rich OM, which stimulate the response of benthic communities.
However, these ephemeral deposits are likely to be swiftly eroded due to the
high trawling frequency over fishing grounds, highlighting the importance of
establishing science-based management strategies to mitigate the impacts of
bottom trawling.