Biological carbon pump revisited: Feedback mechanisms between climate and the Redfield ratio

Biological activity gives rise to a difference in carbon concentration between the ocean surface and the deep waters. This difference is determined by the carbon:nutrient ratio of the sinking organic material and it is crucial in determining the distribution of CO2 between the atmosphere and the ocean. For this reason, it is interesting to determine whether the physical environment affects the carbonrnitrogen ratio of phytoplankton. Using a model with a novel representation of the effect of temperature on phytoplankton stoichiometry, we have investigated the influence of mixed-layer depth and water temperature on the elemental composition of an algal community. In the light-limited regime, the carbon:nutrient ratio turns out to decrease with increasing mixed-layer depth and temperature. Hence our model suggests the existence of a positive feedback between temperature and atmospheric CO 2 content through the stoichiometry of phytoplankton. This feedback may have contributed to the glacial/ interglacial cycles in the atmospheric CO2 concentration. Copyright 2006 by the American Geophysical Union

Quantifying nutrient throughput and DOM production by algae in continuous culture

© 2020 Freshwater and marine algae can balance nutrient demand and availability by regulating uptake, accumulation and exudation. To obtain insight into these processes under nitrogen (N) and phosphorus (P) limitation, we reanalyze published data from continuous cultures of the chlorophyte Selenastrum minutum. Based on mass budgets, we argue that much of the non‐limiting N and P had passed through the organisms and was present as dissolved organic phosphorus or nitrogen (DOP or DON). We construct a model that describes the production of biomass and dissolved organic matter (DOM) as a function of the growth rate. A fit of this model against the chemostat data suggests a high turnover of the non‐limiting N and P: at the highest growth rates, N and P atoms spent on average only about 3 h inside an organism, before they were exuded as DON and DOP, respectively. This DOM exudation can explain the observed trends in the algal stoichiometric ratios as a function of the dilution rate. We discuss independent evidence from isotope experiments for this apparently wasteful behavior and we suggest experiments to quantify and characterize DON and DOP exudation further

Ion-ing out the details

The timescale on which the hydrogen bonds formed by a water molecule in a salt solution switch between ions and other water molecules is revealed for the first time

Surface evolution of manganese chloride aqueous droplets resulting in self-suppressed evaporation

The exchange kinetics of liquid water, which are of fundamental interest and have potential applications, remain unclear. A fantastic and extraordinary phenomenon was observed during the evaporation of a water droplet doped with manganese chloride. As observed from the evolution of this type of droplet, a thin film was formed on the surface with an exothermic phase transition, resulting in self-suppressed evaporation. The MnCl(2)-doped water droplets were maintained in a relative humidity (RH) of 50% at 40 °C for more than a week and for longer than two months at a temperature of 25 °C. In contrast, a pure water droplet can only be sustained for a few minutes. The self-suppressed evaporation of doped water may be due to the special hydration of the accumulated manganese and chloride ions at the surface, decreasing the surface tension