POM is defined as suspended organic matter that remains on 0.2–1.0 μm pore filters during PCI-32765 price the filtering of sea water ( Turnewitsch et al. 2007). Nominally, therefore, POM consists of phyto- and zooplankton cells, detritus and bacteria ( Chen & Wagnersky 1993, Hygum et al. 1997, Nagata 2000, Dzierzbicka-Głowacka et al. 2010a). Processes supplying organic matter to seawater are especially intensive in coastal areas and land-locked seas. This is attributed to the elevated supply of terrestrial nutrients, which enhances primary productivity. As a result, POC concentrations in land-locked seas like the Baltic are 3–4

times higher than in the oceans (Pempkowiak et al. 1984, Grzybowski & Pempkowiak 2003, Kuliłski & Pempkowiak 2008). Quantification of factors influencing POC concentrations in seawater based on actual measurements is tedious owing to the natural variability of POC (Dzierzbicka-Głowacka et al. 2010a). Therefore, experimental assessment of long-term

organic matter changes in seawater is unrealistic, unless an extensive survey of several years’ duration is carried out. An obvious solution to the problem of assessing seasonal dynamics and changes in long-term organic matter concentrations is modelling. This enables the concentration dynamics due to specific factors of environmental regimes to be studied (Dzierzbicka-Głowacka et filipin al. 2010a,

Kuliński et al. 2011). Validation of results, GSK-3 phosphorylation based on the comparison of the modelled and the measured POC concentrations in the Gdańsk Deep, Baltic Sea, proved successful (Dzierzbicka-Głowacka et al. 2010a). The POC model used in this work is based on the 1D Coupled Ecosystem Model, forced by a 3D hydrodynamic model, developed by Dzierzbicka-Głowacka (2005), Dzierzbicka-Głowacka et al. (2006, 2010b) and further parameterized by Kuliński et al. (2011). Another advantage of POC modelling is the possibility of assessing changes that may be brought about by future regime shifts. The most certain regime shift that is being experienced in today’s world is due to the increasing concentration of atmospheric CO2-Directly or indirectly, this shift will influence several factors important to organic matter levels in seawater: they include river run-off, river water nutrient concentrations, primary productivity, phytoplankton species composition and succession, seawater pH, and a number of others grouped under the general heading of climate change. The impact of future climate change on the physical conditions of the Baltic Sea and the dynamics of the deepwater inflows has been investigated in several studies (e.g. Meier 2006, Meier et al. 2006, BACC Author Team 2008). Biogeochemical models of this impact are also available (e.g. Omstedt et al. 2009).