Abstract.With the accumulation of anthropogenic carbon dioxide (CO 2 ), a proceeding decline in seawater pH has been induced that is referred to as ocean acidification. The ocean's capacity for CO 2 storage is strongly affected by biological processes, whose feedback potential is difficult to evaluate. The main source of CO 2 in the ocean is the decomposition and subsequent respiration of organic molecules by heterotrophic bacteria. However, very little is known about potential effects of ocean acidification on bacterial degradation activity. This study reveals that the degradation of polysaccharides, a major component of marine organic matter, by bacterial extracellular enzymes was significantly accelerated during experimental simulation of ocean acidification. Results were obtained from pH perturbation experiments, where rates of extracellular α-and β-glucosidase were measured and the loss of neutral and acidic sugars from phytoplanktonderived polysaccharides was determined. Our study suggests that a faster bacterial turnover of polysaccharides at lowered ocean pH has the potential to reduce carbon export and to enhance the respiratory CO 2 production in the future ocean.
Please cite this article as: Engel, Anja, Händel, Nicole, A novel protocol for determining the concentration and composition of sugars in particulate and in high molecular weight dissolved organic matter (HMW-DOM) in seawater, Marine Chemistry (2011Chemistry ( ), doi: 10.1016Chemistry ( /j.marchem.2011 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. Here, we show that desalting by membrane dialysis (1kDa) is an efficient alternative to ion exchange resins and yields recoveries of >90% for HMW carbohydrates. We conducted several tests to determine the accuracy and reproducibility of the method. Sugar concentrations determined with our protocol were compared to results obtained with the colorimetric TPTZ-method, and with earlier HPAEC-PAD protocols using cation/ anion exchange resins. Applications of our protocol to field samples indicated that acidic sugars can comprise a substantial fraction (30-50%) of HMW dissolved carbohydrates in seawater.The simultaneous analysis of the three classes of sugars appears promising to detect a larger fraction of marine combined carbohydrates, and thus to improve our understanding of organic matter cycling in the ocean.
The present study investigates the combined effect of phosphorous limitation, elevated partial pressure of CO 2 (pCO 2 ) and temperature on a calcifying strain of Emiliania huxleyi (PML B92/11) by means of a fully controlled continuous culture facility. Two levels of phosphorous limitation were consecutively applied by renewal of culture media (N:P = 26) at dilution rates (D) of 0. . CO 2 and temperature conditions were 300, 550 and 900 μatm pCO 2 at 14°C and 900 μatm pCO 2 at 18°C. In general, the steady state cell density and particulate organic carbon (POC) production increased with pCO 2 , yielding significantly higher concentrations in cultures grown at 900 μatm pCO 2 compared to 300 and 550 μatm pCO 2 . At 900 μatm pCO 2 , elevation of temperature as expected for a greenhouse ocean, further increased cell densities and POC concentrations. In contrast to POC concentration, C-quotas (pmol C cell , a reduction of C-quotas by up to 15% was observed in the 900 μatm pCO 2 at 18°C culture. As a result of growth rate reduction, POC:PON:POP ratios deviated strongly from the Redfield ratio, primarily due to an increase in POC. Ratios of particulate inorganic and organic carbon (PIC:POC) ranged from 0.14 to 0.18 at D = 0.3 d , cell volume was reduced by up to 22% in cultures grown at 900 μatm pCO 2 . Our results indicate that changes in pCO 2 , temperature and phosphorus supply affect cell density, POC concentration and size of E. huxleyi (PML B92/11) to varying degrees, and will likely impact bloom development as well as biogeochemical cycling in a greenhouse ocean.
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