高频率分光法测定海水二氧化碳系统参数：需求，研发，和应用
Dr. Zhaohui Aleck Wang
Woods Hole Oceanographic Institution, Associate Scientist
The marine CO2 (inorganic carbon) system is characterized by four primary
parameters – partial pressure of CO2 (pCO2) or CO2 fugacity (fCO2), total dissolved
inorganic carbon (DIC), pH, and total alkalinity (TA). These parameters are central to
the study of the marine carbon cycle and ocean acidification. There is a high demand
for sensors and instruments that can make simultaneous measurements of multiple
CO2 parameters, as measurements of at least two parameters are required to fully
resolve the carbonate system through CO2 equilibrium calculations. The pair of
measured parameters is important to consider since different calculation errors may
result from different choices. Measurement frequency is also important to consider
depending on the deployment purpose. A new spectrophotometric method has been
developed to achieve continuous measurements of DIC and pCO2 in seawater. This
method improves the spatiotemporal resolution by more than one order of
magnitude compared to the existing spectrophotometric method. The level of
precision and accuracy of this method is comparable to that of the existing
spectrophotometric method. The characteristics of the new method make it
particularly suitable for high-frequency, submerged measurements required for
mobile observing platforms in the ocean. Based on the new method, an in-situ
sensor has recently been developed for simultaneous measurements of seawater DIC
and pH in subsurface marine environments. The sensor is among the first to achieve
high-frequency, simultaneous measurements of two CO2 system parameters with
sufficient accuracy for use in carbon and ocean acidification studies. Such a capability
allows the seawater CO2 system to be fully characterized at high resolution with
relatively small errors. Highly productive coastal wetlands are potentially important
DIC and TA sources to the ocean globally and regionally. However, current estimates
of these fluxes are either highly uncertain or lacking because high resolution
measurements are not yet available. The frequency of measurements is critical to
determine these fluxes that vary on minute scale. The new high frequency sensor
provides a powerful tool to realistically quantify DIC and TA fluxes and study
carbonate chemistry in these systems.