Abstract

The North Atlantic Ocean is characterized by an intense meridional circulation cell carrying near-surface waters of tropical and subtropical origin northward and deep waters of arctic and subarctic origin southward. The related overturning is driven by the sinking of water masses at high latitudes. The overturning rate and thus the intensity of the meridional transports of mass, heat, and salt, is an important control parameter for the modeling of the ocean's role in climate. Certainly such estimates require more than one survey of the study area; therefore, the Research Vessel (R/V) Meteor Cruise 18/1 was one in a series of cruises in the North Atlantic that started in March 1991 and continued until 1995 (Meincke 1993).

This data documentation discusses the procedures and methods used to measure total carbon dioxide (TCO₂) and total alkalinity (TALK) at hydrographic stations, as well as underway partial pressure of CO₂ (pCO₂) measured during the R/V Meteor Cruise 18/1 in the North Atlantic Ocean (Section A1E). Conducted as part of the World Ocean Circulation Experiment (WOCE) and the German North Atlantic Overturning Rate Determination expedition, the cruise began in Reykjavik, Iceland, on September 2, 1991, and ended after 24 days at sea in Hamburg, Germany, on September 25, 1991. WOCE Zonal Section A1E began at 60^o N and 42^o 30' W (southeast of Greenland) and continued southeast with a closely spaced series of hydrocasts to 52^o 20' N and 14^o 15' W (Porcupine Shelves). Measurements made along WOCE Section A1E included pressure, temperature, salinity, and oxygen measured by a conductivity, temperature and depth (CTD) sensor; bottle salinity; oxygen; phosphate; nitrate; nitrite; silicate; TCO₂; TALK; and underway pCO₂. A total of 61 CTD casts were made, including 59 bottle casts and 2 calibration stations. Replicate samples from seven Niskin bottles at five stations were also collected for later shore-based reference analyses of TCO₂ by vacuum extraction and manometry and TALK in the laboratory of Dr. Charles D. Keeling, Scripps Institution of Oceanography; these results are also included in this report.

TCO₂ was measured by using an automated sample processor, to extract CO₂ from seawater samples, coupled to a coulometer, to detect the extracted gas. The precision and accuracy of the system was ± 1.60 µ mol/kg. Samples collected for TALK were measured using standard potentiometric techniques; precision was ± 2.0 µ mol/kg. Underway pCO₂ was measured by infrared photometry; precision was ± 2 µ atm.

The R/V Meteor Cruise 18/1 data set is available free of charge as a numeric data package (NDP) from the Carbon Dioxide Information Analysis Center. The NDP consists of three oceanographic data files, three FORTRAN 77 data retrieval routine files, a readme file, and this printed documentation, which describes the contents and format of all files as well as the procedures and methods used to obtain the data.

Keywords: carbon dioxide; alkalinity; pCO₂; World Ocean Circulation Experiment; North Atlantic Ocean; hydrographic measurements; carbon cycle

Reference

• Johnson, K. M., B. Schneider, L. Mintrop, and D. W. R. Wallace. 1996. Carbon Dioxide, Hydrographic, and Chemical Data Obtained During the R/V Meteor Cruise 18/1 in the North Atlantic Ocean (WOCE Section A1E, September 1991). ORNL/CDIAC-91, NDP-056. Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory, Oak Ridge, Tennessee. doi: 10.3334/CDIAC/otg.ndp056