Variations in the elemental ratio of organic matter in the central Baltic Sea: Part I—Linking primary production to remineralization

The air‐water CO2 exchange of a coastal sea—A sensitivity study on factors that influence the absorption and outgassing of CO2 in the Baltic Sea

“…Kreus et al . [] allowed in their model formulation a continuous CO 2 assimilation—followed by DOC exudation and coagulation—in periods of nutrient depletion. This has the effect that pCO 2 in the central Baltic Sea may continuously be drawn down after the DIN depletion in mid‐April without the need for “cold fixation” by cyanobacteria [cf.…”

“…Several possible explanations have been investigated, such as early fixation of atmospheric nitrogen [e.g., Schneider et al, 2009;Kuznetsov et al, 2011], uptake of dissolved organic nutrients [Edman and Anderson, 2014], as well as large deviations from the Redfield ratios [Kreus et al, 2014]. A number of different phytoplankton species are, in addition, able to migrate vertically and could thus collect limiting nutrients from below the seasonal thermocline.…”

“…Additional problems however arise from these parameterizations; in particular, there are discrepancies between simulated and observed concentrations of organic nutrients and carbon. Kreus et al [2014] allowed in their model formulation a continuous CO 2 assimilation-followed by DOC exudation and coagulation-in periods of nutrient depletion. This has the effect that pCO 2 in the central Baltic Sea may continuously be drawn down after the DIN depletion in mid-April without the need for ''cold fixation'' by cyanobacteria [cf.…”

A nitrogen source in spring in the surface mixed-layer of the Baltic Sea: Evidence from total nitrogen and total phosphorus data

“…They conclude that this pattern does not require N 2 -fixation but can be sufficiently achieved when considering variable cellular C:N:P stoichiometry of phytoplankton and a temporal decoupling between nutrient uptake and phytoplankton growth. However, the contribution of this process seems to be overestimated as the simulated surface water POC:PON ratios by Kreus et al (2014) are as high as 15 in spring and thus much higher than the measured values of 8 to 9 in spring 2001 by Schneider et al (2003).…”

“…With this approach they could improve the model's ability to reproduce seasurface phosphate and pCO 2 dynamics in spring. Also Kreus et al (2014) performed one-dimensional model experiments for the Gotland Sea to explain the observed drawdown in DIP and pCO 2 levels after the spring-bloom. They conclude that this pattern does not require N 2 -fixation but can be sufficiently achieved when considering variable cellular C:N:P stoichiometry of phytoplankton and a temporal decoupling between nutrient uptake and phytoplankton growth.…”