The Late Pleistocene and Holocene glacial and postglacial sediments of the Baltic Sea basin are conventionally classified into units according to the so‐called Baltic Sea stages: Baltic Ice Lake, Yoldia Sea, Ancylus Lake and Litorina Sea. The Baltic Sea stages have been identified in offshore sediment cores by fundamentally different criteria, precluding detailed comparisons of the sediment units amongst different sea areas and studies. Here, long sediment cores and reflection seismic and pinger sub‐bottom profiles were studied from an offshore area in the Gulf of Finland, northern Baltic Sea. The strata are divided on the basis of sedimentological criteria into three allostratigraphical formations with subordinate allostratigraphical members and lithostratigraphical formations, following the combined allostratigraphical and lithostratigraphical (CUAL) approach. Sedimentological features are recommended as the primary stratigraphical classification criteria because they do not require the palaeoenvironmental inferences of salinity and water level that are inherent in the conventional classification practice. The presented stratigraphical division is proposed as a flexible template for future stratigraphical work on the Baltic Sea basin, whereby lower‐rank allounits and lithounits can be included and removed locally, while the alloformations will remain at the highest hierarchical level and guarantee regional correlatability. The stratigraphical division is compatible with international guidelines, facilitating communication to the wider scientific community and comparison with other similar basins.
The mosaic archipelagoes, high water turbidity, variable benthic habitats and very long shoreline of the Northern Baltic Sea make it costly and technically challenging to collect data that is useful for decision making concerning conservation and sustainable use
of the marine environment.
The Finnish Inventory Programme for the Underwater Marine Environment (VELMU) has gathered information on species, communities and habitats during 2004-2016 from over 122,000 observation points. The data consists of 95,600 points made with drop-video or ROV, 23,200 with dive line points (from ca.
2000 dive sites), 1850 fish larvae sampling sites, >1000 benthos samples, 780 geological sediment samples, and 20,000 km of acoustic profiling (e.g. echosounding). In addition, satellite observations, LIDAR, aerial imaging with drones and automatic video platforms were used or tested. The
majority of the data has been published in an open map service (https://paikkatieto.ymparisto.fi/velmu).
We present our national sampling design, by which the majority of data was collected cost-effectively in a 5 year time span (2011-2015). We show examples of our results, such as geographical distribution maps and spatial models for species, habitats, biodiversity and environmental factors. We also
explain how the VELMU data has been used in marine spatial planning in the Finnish sea area. In the planning process, areas with high nature values were identified and given a high conservation priority, while other areas were identified as more suitable for human activities, such as aquaculture,
wind energy production and ecotourism.
Based on our 13 years long experience we review the challenges of mapping species and habitats in complex marine environments, and provide a checklist for establishing a successful inventory programme in such conditions.
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