Reidar Nydal

Comparing Long-Term Atmospheric 14C and 3H Records near Groningen, The Netherlands with Fruholmen, Norway and Izaña, Canary Islands 14C Stations

We present the results of the (CO2)-C-14 atmospheric monitoring station at the Smilde observation station, near Groningen, the Netherlands, a typical continental station. We compared these data, for absolute values and annual variation, with data from Fruholmen, Nordkapp, Norway and Izana, Tenerife, Canary Islands, which are situated in areas less influenced by fossil-fuel CO2. The 20-yr Smilde record shows much seasonal variation (peak-to-trough variation is similar to 30% in contrast to similar to 12% for Fruholmen, and similar to 55% for Izana) and a lower overall value due to fossil-fuel consumption, in accordance with findings from similar stations in continental Western Europe. The Fruholmen and Izana data show fairly equal mean Delta(14)C levels, but differ in seasonal amplitude. This difference could be due partly to the elevation difference between the stations. The Izana station also has a slow exchange with the ground-level air because of an inversion layer. It is speculative whether annual injection of C-14 from the stratosphere also plays a role. We give the Groningen long record of tritium in precipitation, showing profound seasonality.

Further Application of Bomb 14C as a Tracer in the Atmosphere and Ocean

Bomb 14 C from nuclear tests in the atmosphere has proved to be a particularly useful tool in the study of the carbon cycle. We provide here a ca. 30-yr time series of 14 C concentrations in the atmosphere between 28°N and 71°N and in the ocean surface between 45°S and 45°N. More recently (since 1990), a north-south profile also has been obtained for 14 C in the surface waters of the Atlantic Ocean. The measurements were performed using the conventional technique of beta counting of large samples (4 to 5 liter CO 2 ) in CO 2 proportional counters. These data show that the 14 C concentration in the atmosphere is leveling off with a time constant of 0.055 yr -1 , and is now approaching that of the ocean surface at lower latitudes. Additional tracer studies have been concerned especially with the penetration of bomb 14 C into the deep ocean. The Norwegian and Greenland seas are of interest as a sink for atmospheric CO 2 and also a source of water for the deep Atlantic Ocean. During the last five years, several 14 C depth profiles have been measured from the Fram Strait (79°N) to south of Iceland (62°N), using the AMS technique available at the University of Arizona AMS Facility. We considered it important to repeat and compare a few of the profiles with those produced by the GEOSECS expedition in 1972 and the TTO expedition in 1981. The profiles show that water descending to the deep Atlantic Ocean is originating mainly from intermediate and surface depths in the Nordic Seas. However, the ventilation rate of the Norwegian Sea deepwater is too slow to be an important component in the transfer of water over the Greenland-Scotland Ridge.

A Time History Of Pre- And Post-Bomb Radiocarbon In The Barents Sea Derived From Arcto-Norwegian Cod Otoliths

Radiocarbon measured in seawater dissolved inorganic carbon (DIC) can be used to investigate ocean circulation, atmosphere/ocean carbon flux, and provide powerful constraints for the fine-tuning of general circulation models (GCMs). Time series of 14 C in seawater are derived most frequently from annual bands of hermatypic corals. However, this proxy is unavailable in temperate and polar oceans. Fish otoliths, calcium carbonate auditory, and gravity receptors in the membranous labyrinths of teleost fishes, can act as proxies for 14 C in most oceans and at most depths. Arcto-Norwegian cod otoliths are suited to this application due to the well-defined distribution of this species in the Barents Sea, the ability to determine ages of individual Arcto-Norwegian cod with a high level of accuracy, and the availability of archived otoliths collected for fisheries research over the past 60 years. Using measurements of 14 C derived from Arcto-Norwegian cod otoliths, we present the first pre- and post-bomb time series (1919-1992) of 14 C from polar seas and consider the significance of these data in relation to ocean circulation and atmosphere/ocean flux of 14 C. The data provide evidence for a minor Suess effect of only 0.2‰ per year between 1919 and 1950. Bomb 14 C was evident in the Barents Sea as early as 1957 and the highest 14 C value was measured in an otolith core from a cod with a birth date of 1967. The otolith 14 C data display key features common to records of 14 C obtained from a Georges Bank mollusc and corals from the tropical and subtropical North Atlantic.

Transfer of Bomb 14C to the Ocean Surface

Additional 14C data from the atmosphere and ocean have been provided since the ninth 14C conference in 1976. At the moment, one sampling station in the troposphere in each hemisphere seems to give sufficient accuracy for exchange studies. The 14C concentration in the troposphere in December 1978 constituted a mean value of 30 ± 1 percent (∆14C) above normal level, a concentration that has been reduced to about one half during 12 years, 14C measurements have been performed with intervals of 1 to 4 months in the surface water of the Atlantic, Pacific, and Indian Oceans. In addition to the 14C data observed, the salinity and temperature are also measured. Because of earlier objections against storing sea water in steel drums on board ships for months before treatment, the CO2 has now been flushed out immediately after collection. The reliability of previous measurements has been confirmed with 10 parallel samples. 14C concentration in ocean surface on each location shows some seasonal variation due to variable exchange of water with deeper layers.

14C Profiles in the Norwegian and Greenland Seas by Conventional and AMS Measurements

CO2 in the atmosphere is an important climate gas because of its absorption of infrared radiation. More knowledge about CO2 uptake in the ocean is of critical significance in predicting future climate development. For a period of approximately 30 years, radioactive carbon from nuclear tests has been a very useful tracer in CO2 exchange studies. Up to now, the measurements have been based mainly on the conventional counting technique with large CO2 samples (ca. 5 liters). Accelerator mass spectrometry (AMS) with small CO2 samples (1-2 ml) has made sampling much easier, and has especially stimulated the use of 14C as a tracer in the ocean.

Proportional Counting Technique for Radiocarbon Measurements

A proportional counting system for radiocarbon dating is described in this article. The CO2 counter has an effective volume of 1.2 liters and operates at a pressure of 2 atm. The total background is 1.10 counts/min and the standard net count on recent carbon is 16.0 counts/min. Maximum measureable age is 43 000 years. The end terminals of the counter have a few original details which serve to reduce inactive counter volume and the end effects. The ground capacity of the center wire has been reduced to a very small value (10 pF). Anticoincidence shielding is provided by a multiple‐anode proportional counter. It is filled with C3H8 to a pressure of 1.3 atm and can operate continuously for at least one year without refilling. The counter walls of the ring counter and the CO2 counter are connected together and supplied with the same high voltage. Shielding against γ rays is provided by a 22‐cm‐thick iron shield around the counting unit, and by a shell of 3.5‐cm old lead between the CO2 counter and the ring co...

Tracer studies of 14C in the Nordic Seas by AMS measurements

Abstract At a time of important interest in climate, the Nordic Seas are especially in focus as a sink for CO 2 and the further transfer to the deep water in the Atlantic Ocean. The relatively short time constant in this process provides possibilities to study the circulation by application of tracers. 14 C is one of the most representative isotopes in this study, and several deep sea profiles have been obtained in seven summer cruises during the last years. For modelling studies it has been especially important to repeat some GEOSECS profiles obtained 20 years earlier in this area. Some of the first 14 C profiles were obtained with conventional CO 2 counting technique based on 100–200 l seawater. Most of the later profiles have, however, been measured with the AMS technique at the Arizona AMS facility, based on 0.5 l seawater. The small samples make this technique especially preferable for sample collection on board ship and in further laboratory treatment. The precision in the isotope ratio measurements is generally 6%. for a counting time of 20 min per sample. Higher precision (3–5%.) has, however been achieved with several accelerator targets.