Vertical fluxes of sediment organic proxies over an annual cycle in the coastal Baltic Sea

• Main Author: Näppilä, Meeri
• Other Authors: Helsingin yliopisto, Bio- ja ympäristötieteellinen tiedekunta, University of Helsinki, Faculty of Biological and Environmental Sciences, Helsingfors universitet, Bio- och miljövetenskapliga fakulteten
• Format: Master Thesis
• Language: English
• Published: Helsingin yliopisto 2023
• Subjects: paleo proxy; dinocyst; stable isotopes; Baltic Sea; sea ice; spring bloom; Ympäristömuutoksen ja globaalin kestävyyden maisteriohjelma (ECGS); Master's Programme in Environmental Change and Global Sustainability; Magisterprogrammet i miljöförändringar och global hållbarhet; Ympäristömuutos; Environmental Change; Miljöförändring; Sea ice
• Online Access: http://hdl.handle.net/10138/562794

The coastal Baltic Sea hosts a very special ecosystem due to its brackish water and high seasonality. However, there is little research on the seasonality of the ecosystem and organic matter (OM) cycling, as many studies are conducted during summer or in areas without ice cover. This study is based on material collected continously over one year (Oct 2012-Oct 2013) by a sequencing sediment trap at 7-56 day intervals. It will provide knowledge of the seasonal variability in the vertical flux of organic material (TOC) and its sources (C:N, δ13C, δ15N) as well as dinoflagellate resting stages (dinocysts). Dinoflagellates are important primary producers in the Baltic Sea, some of which produce well-preserving resting stages (cysts). The seasonal changes in the fluxes and source of OM and dinoflagellate species' seasonal succession are not only ecologically interesting, but as both are used as sediment paleo proxies, provide more information for reliable reconstruction models for the Baltic Sea in the past. The seasonal sedimentation of the coastal Baltic Sea was strongly impacted by seasonality, with strong primary production causing high OM sedimentation rate during spring bloom and lack of primary production causing very small sediment flux in winter. During the fall resuspension played a big role in sedimentation. Only three species of dinocysts were present in the trap samples and most of the dinocyst flux of the whole year was formed by Biecheleria baltica. Most important drivers of B. baltica abundance and encystment were likely temperature signals for encystment at 6 °C and a small bloom under ice that got B. baltica a head start for competition in the spring bloom. Changes in terrestrial material input were not clearly visible in the sedimenting material, but primary production had an enriching influence on the OM stable isotopic composition and elevated the C:N ratio due to reaching limiting conditions of N. During winter long sea-ice cover and cold-water temperature created anomaly depleted isotopic ...