Canadian Marine Reservoir Ages

Objective:

GSC has attemped to define the "reservoir age" in Canadian waters from the Pacific, through the Arctic, to the Atlantic. The reservoir age is essentially the residence time of CO2, and the bicarbonate formed from it, in the ocean; that is, the length of time spent in transit in the ocean between the time of absorption of the gas from the atmosphere and its ventilation back to the atmosphere at sites of ocean upwelling. During this transit time, the radioactive isotope of carbon (C-14) decays, imparting an "age" to the carbon in the water. Previously there were only a few measurements available from the Canadian sector of the Northwest Atlantic-Arctic Ocean.

Carbon cycle

Rationale:

Marine mollusc shells are the best materials to use in addressing this problem, primarily because the carbonate in marine mollusc shells is deposited in isotopic equilibrium with the bicarbonate in the surrounding water. The shells therefore capture the reservoir age. Thus the problem of measuring reservoir ages should be a simple one of collecting shells where we need them and radiocarbon dating them to determine their "apparent ages". Unfortunately, nuclear bomb testing has spiked the atmosphere and the oceans with large amounts of artificial C-14. Hence, today the reservoir ages can only be determined on shells collected live prior to bomb testing (ca. 1955). Therefore, only material in museum collections such as the Canadian Museum of Nature can be used to resolve this problem. We have been fortunate to acquire a large number of shell samples that were collected live pre-bomb that can be dated by the AMS technique.

Carbon cycle

Clientele:

Quaternary researchers, who need to establish time-series of events, such as sea level change or ice sheet retreat, require valid estimates of the regional reservoir age to ascertain an integrated marine / terrestrial chronology and develop models for their syntheses; Canadian Marine Reservoir Ages, GSC Open File 5049 [ZIP, 3.8 Mb] or GeoPub download Open File 5049.

Reservoir samples [PDF, 1.4 Mb, viewer]

For example, there was an urgent need to firmly establish the reservoir age for Hudson Bay-Foxe Basin-Hudson Strait. This arises from the recent discovery of a large 8200 calendar year (7400 rcybp) event (cooling) in the Greenland Ice Sheet ice cores. Several researchers feel that the most reasonable explanation (cause) of this event in Greenland was the rapid deglaciation of Hudson Bay, which is presently placed at about 8000 rcybp; that is, 500 to 600 years too early. However, the timing of the deglaciation of Hudson Bay relies on an assumed reservoir age correction of 400 years. Our new data provided a possible range of reservoir ages in this region and the forgoing hypothesis was published in Nature.

D.C. Barber, A.S. Dyke, C. Hillaire-Marcel, A.E. Jennings, J.T. Andrews, M.W. Kerwin, G. Bilodeau, R. McNeely, J. Southon, M.D. Morehead, J-M. Gagnon

Forcing of the Cold Event 8200 years ago by Catastrophic Drainage of Laurentide Lakes 1999:
Nature, vol. 400, no. 22, p. 344-348