Direct effects of CO2 concentration on growth and isotopic composition of marine plankton.

The assessment of direct effects of anthropogenic CO2 increase on the marine biota has received relatively little attention compared to the intense research on CO2-related responses of the terrestrial biosphere. Yet, due to the rapid air–sea gas exchange, the observed past and predicted future rise in atmospheric CO2 causes a corresponding increase in seawater CO2 concentrations, [CO2], in upper ocean waters. Increasing [CO2] leads to considerable changes in the surface ocean carbonate system, resulting in decreases in pH and the carbonate concentration, [CO2−3]. These changes can be shown to have strong impacts on the marine biota. Here we will distinguish between CO2-related responses of the marine biota which (a) potentially affect the ocean's biological carbon pumps and (b) are relevant to the interpretation of diagnostic tools (proxies) used to assess climate change on geological times scales. With regard to the former, three direct effects of increasing [CO2] on marine plankton have been recognized: enhanced phytoplankton growth rate, changing elemental composition of primary produced organic matter, and reduced biogenic calcification. Although quantitative estimates of their impacts on the oceanic carbon cycle are not yet feasible, all three effects increase the ocean's capacity to take up and store atmospheric CO2 and hence, can serve as negative feedbacks to anthropogenic CO2 increase. With respect to proxies used in palaeo-reconstructions, CO2-sensitivity is found in carbon isotope fractionation by phytoplankton and foraminifera. While CO2- dependent isotope fractionation by phytoplankton may be of potential use in reconstructing surface ocean pCO2 at ancient times, CO2-related effects on the isotopic composition of foraminiferal shells confounds the use of the difference in isotopic signals between planktonic and benthic shells as a measure for the strength of marine primary production. The latter effect also offers an alternative explanation for the large negative swings in δ13C of foraminiferal calcite between glacial and interglacial periods. Changes in [CO2−3] affect the δ18O in foraminiferal shells. Taking this into account brings sea surface temperature estimates for the glacial tropics closer to those obtained from other geochemical proxies

Lattice-Gas Cellular Automaton Models for Biology: From Fluids to Cells

Lattice-gas cellular automaton (LGCA) and lattice Boltzmann (LB) models are promising models for studying emergent behaviour of transport and interaction processes in biological systems. In this chapter, we will emphasise the use of LGCA/LB models and the derivation and analysis of LGCA models ranging from the classical example dynamics of fluid flow to clotting phenomena in cerebral aneurysms and the invasion of tumour cell

Simulating the distribution of stable silicon isotopes in the Last Glacial Maximum

Variations in the silicon stable isotopic composition (δ30Si) of sedimentary biogenic silica (BSi) are used to reconstruct the utilization level of dissolved silicic acid (DSi) by diatoms in the geological past and to explore the influence of diatoms on past oceanic biogeochemistry and climate. A Last Glacial Maximum (LGM) climate simulation has been performed with a coupled ocean-sediment model that includes a prognostic formulation of BSi production with concurrent silicon isotopic fractionation. The model results show reduced DSi utilization by diatoms in high latitudes during the LGM, likely due to the extended ice cover in the model. There is a decrease in BSi export production in the Southern Ocean during the LGM compared to a present-day climate experiment. This leads to an increased equator-ward transport of DSi in Subantarctic Mode Water and Antarctic Intermediate Water, and a shift in the distribution of DSi from the deep Pacific into the deep Atlantic. The mean δ30Si value of DSi in the upper ocean shows a 0.14 per mil decrease in the LGM experiment, while there is an increase in the low-latitude Pacific compared with the present-day experiment. In the Pacific and Indian Ocean the slopes of the surface Si(OH)4

A model of photosynthetic 13C fractionation in marine phytoplankton based on diffusive molecular CO2 uptake

A predictive model of carbon isotope fractionation (sigma p) and abundance (delta13C phyto) is presented under circumstances where photosynthesis is strictly based on CO2(aq) that passively diffuses into marine phytoplankton cells. Similar to other recent models, the one presented here is based on a formulation where the expression of intracellular enzymatic isotope fractionation relative to that imposed by CO2(aq) transport is scaled by the ratio of intracellular to external [CO2(aq)], ci/ce. Unlike previous models, an explicit calculation of ci is made that is dependent on ce as well as cell radius, cell growth rate, cell membrane permeability to CO2(aq), temperature, and, to a limited extent, pH and salinity. This allows direct scaling of ci/ce to each of these factors, and thus a direct prediction of sigma p and delta13C phyto responses to changes in each of these variables. These responses are described, and, where possible, compared to recent experimental and previous modeling results

Laboratory study on coprecipitation of phosphate with ikaite in sea ice

Ikaite (CaCO3�6H2O) has recently been discovered in sea ice, providing first direct evidence of CaCO3 precipitation in sea ice. However, the impact of ikaite precipitation on phosphate (PO4) concentration has not been considered so far. Experiments were set up at pH from 8.5 to 10.0, salinities from 0 to 105, temperatures from 24°C to 0°C, and PO4 concentrations from 5 to 50 mmol kg-1 in artificial sea ice brine so as to understand how ikaite precipitation affects the PO4 concentration in sea ice under different conditions. Our results show that PO4 is coprecipitated with ikaite under all experimental conditions. The amount of PO4 removed by ikaite precipitation increases with increasing pH. Changes in salinity (S >=35) as well as temperature have little impact on PO4 removal by ikaite precipitation. The initial PO4 concentration affects the PO4 coprecipitation. These findings may shed some light on the observed variability of PO4 concentration in sea ice

Comment on "Scrutinizing the carbon cycle and CO2residence time in the atmosphere" by H. Harde

Harde (2017) proposes an alternative accounting scheme for the modern carbon cycle and concludes that only 4.3% of today's atmospheric CO2 is a result of anthropogenic emissions. As we will show, this alternative scheme is too simple, is based on invalid assumptions, and does not address many of the key processes involved in the global carbon cycle that are important on the timescale of interest. Harde (2017) therefore reaches an incorrect conclusion about the role of anthropogenic CO2 emissions. Harde (2017) tries to explain changes in atmospheric CO2 concentration with a single equation, while the most simple model of the carbon cycle must at minimum contain equations of at least two reservoirs (the atmosphere and the surface ocean), which are solved simultaneously. A single equation is fundamentally at odds with basic theory and observations. In the following we will (i) clarify the difference between CO2 atmospheric residence time and adjustment time, (ii) present recently published information about anthropogenic carbon, (iii) present details about the processes that are missing in Harde (2017), (iv) briefly discuss shortcoming in Harde's generalization to paleo timescales, (v) and comment on deficiencies in some of the literature cited in Harde (2017)