Abstract
Abstract. Total dissolved inorganic carbon (CT) is one of the most frequently measured parameters used to calculate the partial pressure of carbon dioxide in seawater. Its determination has become increasingly important because of the rising interest in the biological effects of ocean acidification. Coulometric and infrared detection methods are currently favored in order to precisely quantify CT. These methods however are not sufficiently validated for CT measurements of biological experiments manipulating seawater carbonate chemistry with an extended CT measurement range (~1250–2400 μmol kg–1) compared to natural open ocean seawater (~1950–2200 μmol kg−1). The requirement of total sample amounts between 0.1–1 L seawater in the coulometric- and infrared detection methods potentially exclude their use for experiments working with much smaller volumes. Additionally, precise CT analytics become difficult with high amounts of biomass (e.g., phytoplankton cultures) or even impossible in the presence of planktonic calcifiers without sample pre-filtration. Filtration however, can alter CT concentration through gas exchange induced by high pressure. Addressing these problems, we present precise quantification of CT using a small, basic and inexpensive gas chromatograph as a CT analyzer. Our technique is able to provide a repeatability of ±3.1 μmol kg−1, given by the pooled standard deviation over a CT range typically applied in acidification experiments. 200 μL of sample is required to perform the actual CT measurement. The total sample amount needed is 12 mL. Moreover, we show that sample filtration is applicable with only minor alteration of the CT. The method is simple, reliable and with low cumulative material costs. Hence, it is potentially attractive for all researchers experimentally manipulating the seawater carbonate system.
Highlights
Oceanic absorption of anthropogenic carbon dioxide (CO2) in the past and during the decades leads to seawater acidification (Caldeira and Wickett, 2003), which will increasingly influence biological and biochemical processes in the open oceans (Doney et al, 2009; Houghton, 1995; Kroeker et al, 2010) and in coastal waters (Melzner et al, 2012)
Our technique is able to provide a repeatability of ±3.1 μmol kg−1, given by the pooled standard deviation over a CT range typically applied in acidification experiments. 200 μL of sample is required to perform the actual CT measurement
Analysis is the most preferred method in oceanographic research with the highest precision of ±0.06 %, which equals ±1.5 μmol kg−1 (Table 1) for a typical open ocean water measurement range (Johnson et al, 1993). This precision is needed because present ocean acidification causes only a small increase of ∼ 1 μmol kg−1 yr−1, which is added to a CT background of ∼ 2100 μmol kg−1 (Houghton, 1995)
Summary
Oceanic absorption of anthropogenic carbon dioxide (CO2) in the past and during the decades leads to seawater acidification (Caldeira and Wickett, 2003), which will increasingly influence biological and biochemical processes in the open oceans (Doney et al, 2009; Houghton, 1995; Kroeker et al, 2010) and in coastal waters (Melzner et al, 2012). Due to this fact, scientific interest in precise measurements of CT has increased. Such experiments often contain non-negligible quantities of biomass (e.g., from phytoplankton cultures), which require sample filtration (Mueller et al, 2012; Matthiessen et al, 2012) before precise CT measurement can be performed
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