Rhythmically laminated sublittoral lake sediments in an eutrophicated bay

The annual rhytmic lamination of sediments is a widely known and throughly studied feature, but observations have mostly been made on core samples obtained from the deepest part of a lake basin or from a depth of at least 15 m. In Olkkolanlahti Bay and northern Tiirinselkä, which are hypertrophic water bodies and parts of the large lake Päijänne (Central Finland), clearly stratifed sediments have been found in the sublittoral zone at water depths of 1.2 and 2.2 m. All of the sediment cores obtained here exhibit light and dark laminae with varying diatom abundance. They may therefore be regarded as rhythmical laminations. Their thickness (+20 mm per couplet) was considerable in comparison to most laminae recorded in annually laminated sediments.