The highest proportion of mud (>10%) was found at sites 2, and 3 in the offshore part of the cable route and at sites 32 and 39 in the inshore part of the cable route. The proportions varied from 14 to 15% for the former sites and from 22 to 41% for the latter sites respectively. These sites were described as gravelly muddy sand (gmS) or as slightly gravelly muddy sand ((g)mS). Only two sites were recorded as sandy gravel (sG) (17 and 18), located offshore in the middle part of the cable route. The sediments in the area vary between very poorly sorted (vps), with a high sorting coefficient, and well sorted (ws), with a low sorting coefficient. Other sorting categories such as poorly sorted (ps), moderately sorted (ms) and well sorted (ws) were also recorded. Well sorted sediments can indicate a consistent input of energy with little fluctuation, on the contrary poorly sorted sediments can indicate the reverse, i.e. an inconsistent energy input and a consequently wide fluctuation in the sediment matrix.
98.
Data were further analysed using multivariate techniques. Figure 3.2 presents the ordinations of per cent fractional weight sediment data based on a Euclidean distance resemblance matrix. The symbology indicates the statistically significant groups highlighted by the PRIMER SimProf routine set to a significance level of 1% (a) and the Folk sediment groupings (b), whilst the bubble plots show those sites associated with the highest proportions of medium sand (500 μm) (c) and fine sand (250 μm) (d), the components accounting for the variability of the sediments.
99.
Application of the PRIMER SimProf routine, (Figure 3.2) highlighted five statistically significant groups (a to e). The majority of the sites (17) were included in group a and were characterised by medium to fine sand, mainly classified as slightly gravelly sand ((g)S), with four sites classified as gravelly sand (gS). Group b and c included nine sites each, the first one characterised by fine sand and coarse gravel, mainly classified as gravelly sand (gS) with two sites classified as slightly gravelly sand ((g)S and one as slightly gravelly muddy sand ((g)mS). Group d included the single site 39 classified as slightly gravelly muddy sand ((g)mS), whilst group e included three sites. This last group was characterised by medium sand and find sand, but in lower proportions compared to group a, and the three sites were classified as gravelly muddy sand (gmS), slightly gravelly sand ((g)S) and gravelly sand (gS). Sediment at sites in group a ranged from moderately sorted (ms) to moderately well sorted (mws) to well sorted (ws). Only site 34 was described as poorly sorted (ps). In the other groups sediments were predominantly described as poorly sorted (ps) or very poorly sorted (vps).
Benthic Characterisation Report November 2013
East Anglia THREE and FOUR Offshore Cable Corridor
