(Table 6) Sulfate ion concentration and alkalinity in interstitial waters from bottom sediments of Core DM9-666, Gulf of California

New data on phosphorites collected by dredging and trawling at depths from 2700 to 520 m in the open Atlantic Ocean (i.e. outside of the shelf and the continental slope) are reported. Aphanitic, granular, brecciated, and conglomerate-like types are distinguished among the phosphorites. A comparison of the studied phosphorites with ones from the Atlantic shelf of Africa and from seamounts of other oceans is made.

Detection of a variable intracellular acid-labile carbon pool in Thalassiosira weissflogii (Heterokontophyta) and Emiliania huxleyi (Haptophyta) in response to changes in the seawater carbon system

Accumulation of an intracellular pool of carbon (C(i) pool) is one strategy by which marine algae overcome the low abundance of dissolved CO2 (CO2 (aq) ) in modern seawater. To identify the environmental conditions under which algae accumulate an acid-labile C(i) pool, we applied a (14) C pulse-chase method, used originally in dinoflagellates, to two new classes of algae, coccolithophorids and diatoms. This method measures the carbon accumulation inside the cells without altering the medium carbon chemistry or culture cell density. We found that the diatom Thalassiosira weissflogii [(Grunow) G. Fryxell & Hasle] and a calcifying strain of the coccolithophorid Emiliania huxleyi [(Lohmann) W. W. Hay & H. P. Mohler] develop significant acid-labile C(i) pools. C(i) pools are measureable in cells cultured in media with 2-30 µmol/l CO2 (aq), corresponding to a medium pH of 8.6-7.9. The absolute C(i) pool was greater for the larger celled diatoms. For both algal classes, the C(i) pool became a negligible contributor to photosynthesis once CO2 (aq) exceeded 30 µmol/l. Combining the (14) C pulse-chase method and (14) C disequilibrium method enabled us to assess whether E. huxleyi and T. weissflogii exhibited thresholds for foregoing accumulation of DIC or reduced the reliance on bicarbonate uptake with increasing CO2 (aq) . We showed that the C(i) pool decreases with higher CO2 :HCO3 (-) uptake rates.

Interactive effects of light, nitrogen source, and carbon dioxide on energy metabolism in the diatom Thalassiosira pseudonana

Due to the ongoing effects of climate change, phytoplankton are likely to experience enhanced irradiance, more reduced nitrogen, and increased water acidity in the future ocean. Here, we used Thalassiosira pseudonana as a model organism to examine how phytoplankton adjust energy production and expenditure to cope with these multiple, interrelated environmental factors. Following acclimation to a matrix of irradiance, nitrogen source, and CO2 levels, the diatom's energy production and expenditures were quantified and incorporated into an energetic budget to predict how photosynthesis was affected by growth conditions. Increased light intensity and a shift from inline image to inline image led to increased energy generation, through higher rates of light capture at high light and greater investment in photosynthetic proteins when grown on inline image. Secondary energetic expenditures were adjusted modestly at different culture conditions, except that inline image utilization was systematically reduced by increasing pCO2. The subsequent changes in element stoichiometry, biochemical composition, and release of dissolved organic compounds may have important implications for marine biogeochemical cycles. The predicted effects of changing environmental conditions on photosynthesis, made using an energetic budget, were in good agreement with observations at low light, when energy is clearly limiting, but the energetic budget over-predicts the response to inline image at high light, which might be due to relief of energetic limitations and/or increased percentage of inactive photosystem II at high light. Taken together, our study demonstrates that energetic budgets offered significant insight into the response of phytoplankton energy metabolism to the changing environment and did a reasonable job predicting them.

Combined effects of CO2 and temperature on carbon uptake and partitioning by the marine diatoms Thalassiosira weissflogii and Dactyliosolen fragilissimus

Carbon uptake and partitioning of two globally abundant diatom species, Thalassiosira weissflogii and Dactyliosolen fragilissimus, was investigated in batch culture experiments under four conditions: ambient (15°C, 400 µatm), high CO2 (15°C, 1000 µatm), high temperature (20°C, 400 µatm), and combined (20°C, 1000 µatm). The experiments were run from exponential growth into the stationary phase (six days after nitrogen depletion), allowing us to track biogeochemical dynamics analogous to bloom situations in the ocean. Elevated CO2 had a fertilizing effect and enhanced uptake of dissolved inorganic carbon (DIC) by about 8% for T. weissflogii and by up to 39% for D. fragilissimus. This was also reflected in higher cell numbers, build-up of particulate and dissolved organic matter, and transparent exopolymer particles. The CO2 effects were most prominent in the stationary phase when nitrogen was depleted and CO2(aq) concentrations were low. This indicates that diatoms in the high CO2 treatments could take up more DIC until CO2 concentrations in seawater became so low that carbon limitation occurs. These results suggest that, contrary to common assumptions, diatoms could be highly sensitive to ongoing changes in oceanic carbonate chemistry, particularly under nutrient limitation. Warming from 15 to 20 °C had a stimulating effect on one species but acted as a stressor on the other species, highlighting the importance of species-specific physiological optima and temperature ranges in the response to ocean warming. Overall, these sensitivities to CO2 and temperature could have profound impacts on diatoms blooms and the biological pump.

Effects of increasing seawater carbon dioxide concentrations on chain formation of the diatom Asterionellopsis glacialis

Diatoms can occur as single cells or as chain-forming aggregates. These two strategies affect buoyancy, predator evasion, light absorption and nutrient uptake. Adjacent cells in chains establish connections through various processes that determine strength and flexibility of the bonds, and at distinct cellular locations defining colony structure. Chain length has been found to vary with temperature and nutrient availability as well as being positively correlated with growth rate. However, the potential effect of enhanced carbon dioxide (CO2) concentrations and consequent changes in seawater carbonate chemistry on chain formation is virtually unknown. Here we report on experiments with semi-continuous cultures of the freshly isolated diatom Asterionellopsis glacialis grown under increasing CO2 levels ranging from 320 to 3400 µatm. We show that the number of cells comprising a chain, and therefore chain length, increases with rising CO2 concentrations. We also demonstrate that while cell division rate changes with CO2 concentrations, carbon, nitrogen and phosphorus cellular quotas vary proportionally, evident by unchanged organic matter ratios. Finally, beyond the optimum CO2 concentration for growth, carbon allocation changes from cellular storage to increased exudation of dissolved organic carbon. The observed structural adjustment in colony size could enable growth at high CO2 levels, since longer, spiral-shaped chains are likely to create microclimates with higher pH during the light period. Moreover increased chain length of Asterionellopsis glacialis may influence buoyancy and, consequently, affect competitive fitness as well as sinking rates. This would potentially impact the delicate balance between the microbial loop and export of organic matter, with consequences for atmospheric carbon dioxide.