Dataset: The role of the Southern Ocean in the carbon cycle


Description

Metadata record for data from ASAC Project 133
See the link below for public details on this project.

Surface carbon dioxide (CO2) observations are integral to understanding the role of the Southern Ocean in the global carbon cycle, and to developing reliable predictions of biogeochemical responses to altered climatic conditions. Carbon dioxide (CO2) observations made in surface waters of the Australian sector of the Southern Ocean between the years 1991 and 2002 were used to estimate the seasonal variability in the fugacity of CO2 (fCO2) and net air-sea carbon fluxes. The results showed a net annual uptake of CO2 by the surface ocean over the entire region. The greatest seasonal uptake and lowest fCO2 values were observed in Spring/Summer in the sub-Antarctic zone (SAZ: 44 degrees S-50 degrees S) and in the Seasonal Sea-ice Zone (SIZ: south of 62 degrees S). The seasonal maximum in uptake for these regions is consistent with increased phytoplankton biomass and shoaling mixed layers over the Spring/Summer period. The High Nutrient Low Chlorophyll waters between 50 degrees S and 62 degrees S, also had maximum uptake in summer, but less compared to the SAZ and SIZ regions. Winter surface waters were close to or slightly above equilibrium, with respect to atmospheric CO2. The reduced uptake in winter appeared due to deeper mixing, lower biomass, and air-sea CO2 exchange. The highest fCO2 values in Winter were observed under or near the seasonal sea-ice where entrainment of deeper CO2-rich waters and ice cover would maintain high surface fCO2 values. The smallest seasonal amplitude in the surface fCO2 and net air-sea fluxes was found from 51 degrees S to 54 degrees S, a region on the southern edge of the SAZ and between the North sub-Antarctic Front and North Polar Front. The uptake estimates derived from the data were in good agreement with the CO2 flux climatology of Takahashi (2002), except in the SAZ and SIZ where we observed greater and less uptake, respectively.

Data for this project are available for download - the dataset consists of a data files, and some excel files, which provide further information about each data file (cruise, dates, etc).

Furthermore, the column headings used in the data files are as follows:

Cruise - name of the cruise which collected the data
Date - UTC
Time - in UTC
Latitude - decimal
Longitude - decimal
Sst - Sea Surface Temperature in degrees C
Teq - Temperature of surface water at which the CO2 measurement is made.
Sal - Salinity
Patm - atmospheric pressure in hectopascals
Shipspd - ship speed in knots
Windspd - wind speed in knots
Winddir - wind direction in degrees
xCO2 - Mole fraction of CO2 in air (dry) equilibrated with surface water and at equilibrator water temperature
xCO2air - Mole fraction of CO2 in atmosphere, dry
pCO2 - partial pressure of carbon dioxide in surface water

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