Factors controlling aggregate formation in the benthic boundary layer of the Mecklenburg Bight (western Baltic Sea)

Studies on aggregate formation and size distribution in relation to bottom water composition and flow regime were carried out in November 1994 at two transects in the inner and outer Mecklenburg Bight (Baltic Sea). The bottom water sampler ‘BIOPROBE' (BWS) was used to collect 10-dm³ water samples at 5, 10, 20 and 40 cm above the seabed. The outer transect samples tended to be more influenced by the open western Baltic Sea, whereas the inner transect samples were more affected by the coastal hydrography. Aggregate size distribution was investigated using a newly developed particle camera allowing identification of particles down to 150 μm size. Increasing concentrations of total particulate matter (TPM), particulate organic carbon (POC) and chlorophyll pigment equivalents (CPE) towards the seafloor together with a low proportion of POC/TPM (<5%) implied that the material was of resuspended origin. Aggregate size in both transects was positively correlated with TPM, transparent exopolymer particles (TEP) and bacterial cell abundance. Higher particle concentrations and aggregate numbers in the outer transect indicated a higher resuspension frequency, or lateral advection processes. The higher concentration of aggregates at the outer transect may reflect the larger amount of near-bottom transported material.