GLOBAL DISTRIBUTION OF TRITIUM
The
667
increase of tritium concentration toward the northern mid-
latitudes is clear.
Southern-hemisphere tritium data for the Pacific is represented
by Canton Island (LJ) and Kaitoke, New Zealand (NZ) (Figs. 2 and 7).
Canton at 02°46’S shows typical southern-hemisphere values for 1963,
averaging 9.4 T.U. At Kaitoke the mean tritium concentration for the
same period is 24.2 T.U. There is no evidence of a peak at Canton, but
a spring peak is clearly defined at Kaitoke. Although Kaitoke may be
influenced by the land mass of New Zealand to some extent, this effect
would not appear to be very Significant because of the overwhelming
ratio of water over land area. Kaitoke is a coastal location (near
Wellington). Thus it appears that the higher mean concentrations at
Kaitoke may represent a true latitude effect. This would suggest the
entry of the annual tritium fallout pulse at the higher southern latitudes
and gradual migration of the pulse northward.
The Americas
The highest tritium concentrations in the entire survey with the
single exception of Nord, Greenland, are found in northern Canada
(Fig. 8). Although the 1961-1962 record for Canada is not complete,
it seems fairly certain that these northern sites showed the same im-
mediate response to the Oct. 23 to 30, 1961, testing that was observed
in the Arctic regions of Europe. In January 1962, for example, the
tritium measurement at Whitehorse, Yukon (CR), was 1010 T.U., and
at Goose Bay, Labrador (CR), it was 1680 T.U.
The single highest monthly tritium measurement found throughout
the entire survey was the 10,000 T.U. value for April 1963 at Whitehorse.
The effect of the prevailing cross-continent direction of air circulation may be observed in Canada where west and east stations are
located at approximately the same latitude. The difference is most
marked in 1961
when the influx of spring tritium was minimum (com-
pared to later years)
and reevaporated tritium showed its maximum
effect. Between Edmonton (53°34’N, 113°31'W) and Goose Bay (53°19'N,
60°25 W), an apparent time difference of approximately one month
existed between the fall tritium decay curves, with the summer peak
persisting longer at Goose Bay. This was as expected.
The same effect is not observed in 1963 for Edmonton and Goose
Bay, but it is suggested for Whitehorse and Goose Bay. Presumably,
as the proportionate input of stratospheric tritium decreases and the
reevaporation component increases, in 1964 and 1965 the delay of the
annual tritium decline in the east as compared to the west should reappear.