Temporal changes in terrestrial organic matter loading to coastal sediments of the Baltic Sea

Early diagenesis in coastal marine sediments is primarily controlled by inputs of organic matter. These inputs may be derived from a range of autochthonous and allochthonous sources, which display variable reactivity in the sediment column and thus affect the balance between carbon burial and regeneration. In the low-salinity Baltic Sea, eutrophication and associated loading of autochthonous carbon have led to marked shoaling of sedimentary redox zones, promoting methane release and compromising the function of marine sediments as a carbon sink. However, up to 30% of organic matter in sediments of the Baltic Sea is estimated to be of allochthonous origin (Miltner & Emeis, GCA 65, 2001). Human activities in catchment areas, including forest clearance and ditching, may have significantly impacted fluxes of terrestrial organic matter across the land-sea interface, yet the scale of these impacts on carbon loading to marine sediments remains unknown. Here I will discuss new data from CuO extractions of dated sediment cores in the northern Baltic Sea, showing coherent temporal changes in the magnitude and composition of lignin inputs to sediments over the past five decades. These changes reflect the evolution of land use and forest industry activities during this period, suggesting a direct signal of changes in terrestrial organic matter inputs to marine sediments. Furthermore, porewater data from key locations show that this material has contributed to overall carbon loading and stimulation of methanogenesis in the upper sediment column.    

Presentation Preference: Oral

Primary Presenter: Tom Jilbert, University of Helsinki (tom.jilbert@helsinki.fi)

Authors:

Tom Jilbert, University of Helsinki, Finland  (tom.jilbert@helsinki.fi)

Rahat Riaz, University of Helsinki, Finland  (rahat.riaz@helsinki.fi)

Gregory Cowie, University of Edinburgh, Scotland, UK  (dr.greg.cowie@ed.ac.uk)

Joonas Virtasalo, Geological Survey of Finland  (joonas.virtasalo@gtk.fi)

Anna Sobek, Stockholm University, Sweden  (anna.sobek@aces.su.se)

Alf Norkko, Tvärminne Zoological Station, University of Helsinki, Finland  (alf.norkko@helsinki.fi)