Biogeochemical consequences of vertical and lateral transport of particulate organic matter in the southern North Sea: A multiproxy approach

Abstract

Vertical and lateral transports are of importance in continental shelf systems such as the North Sea and play a major role in the processing of organic matter. We investigated the biogeochemical consequences of these transports on particulate organic matter at the molecular level in the southern North Sea. We analysed suspended particulate matter and surface sediments for organic carbon, pigments and phospholipid derived fatty acids at 10 stations sampled in September 2011 along the particle transport route. The particulate organic matter in both suspended particulate matter and surface sediment was mainly from marine phytoplankton origin but of fresher quality in the water column. Particulate organic matter quality did not change from south to north in the suspended particulate matter, whereas it 2 clearly decreased towards the north in the surface sediments, reflecting a decreased intensity of benthic-pelagic coupling. However, we also observed strong deposition of fresh organic matter in the northern station denoting that occasionally, intense benthic-pelagic coupling can occur. Finally, our study highlights the necessity to use a multiproxy approach covering multiple characteristic time scales, when investigating both suspended particulate matter and surface sediments.

A seasonal study of particulate organic matter composition and quality along an offshore transect in the southern North Sea

“…1) deposited on the seafloor and/or the OM originating in the southern area, where primary production also mainly occurs during spring ( Fig. 1) (Dauwe and Middelburg, 1998;Le Guitton et al, 2015), was deposited on the surface sediment of Oyster Grounds.…”

“…1); its waters are stratified in summer (Bale et al, 2013). The Coastal Station is situated along the major OM transport route Dauwe and Middelburg, 1998;Le Guitton et al, 2015) (Fig. 1).…”

“…Short time scales -Pigments have higher degradation rates compared to lipids (Cowie and Hedges, 1994), thus we used pigments-derived parameters to assess the freshness of POM (Le Guitton et al, 2015): the chlorophyll a to phaeopigment ratio (CHLA/PHAEOs), and the intact to total pigments ratio (ITPIG) (Woulds and Cowie, 2009). Here the phaeopigments are defined as the sum of pheophytin and phaeophorbide, and intact pigments are the sum of chlorophyll a, alloxanthin, diatoxanthin, zeaxanthin and β carotene.…”

“…Reproducibility is ~2 % for OC and N; detection limits are about 2 µg C and 0.4 µg N, respectively, related to about 0.02 and <0.01 wt% C and N for sediment samples. The pigments were extracted from SPM and SS samples and analyzed by reversed phase chromatography using the method described in Le Guitton et al (2015) modified from Jeffrey et al (1997). The PLFAs were extracted from SPM and SS samples using the method described in Boschker et al (1999) modified from Bligh and Dyer (1959).…”

“…Dauwe and Middelburg (1998) were the first to clearly document the compositional consequences of the repetitive deposition-resuspension cycles of OM, a process called OM spiralling, during OM transport from the main primary production area in the Southern Bight to the main deposition area in the Skagerrak. In a recent study covering a set of stations along this main OM transport route, Le Guitton et al (2015) showed how spiralling of particles leaves a clear imprint on the biogeochemical composition of watercolumn and sedimentary OM. Whereas this previous study focused on large scale spatial patterns during one single period, a clear temporal signal is also expected, e.g.…”