Radiocarbon in annual coral rings from the eastern Tropical Pacific Ocean

Sixty radiocarbon measurements were performed on aragonite from annually banded corals collected from three sites in the Galapagos Islands. Preanthropogenic Δ14C values of coral that grew around A.D. 1930 averaged −70‰. This is substantially lower than average values previously reported (−51‰) for corals from Florida and Belize in the western North Atlantic Ocean. A decrease of 6‰ was noticed in coral that grew from 1930 to 1954. This decrease could be interpreted as a Suess effect in surface ocean water. The 100‰ increase in Δ14C for coral that grew from 1954 to 1973 is the result of bomb-produced 14C that was introduced to the surface ocean waters. The 14C levels in corals that grew during El Nino years were considerably higher than those for normal years. These higher values are attributed to the absence of up welling at the equator during El Nino events.

nite does not dissolve in surface ocean waters to any significant degree. Thus, coral skeletons are permanent records of the radiocarbon levels that were present in the DIOC in the sea water.
Glynn and Wellington (in preparation) studied Pavona clavus from the Galhpagos Islands and revealed that dense aragonitic bands form during the warm water months of January through March. Thicker, less dense bands form during the cold, upwelling season, which usually is April through December.
These workers observed that Pavona clavus exhibits increased growth rates during most E1 Niho years. An E1 Niho event is the appearance of warm, low salinity water to the surface in the eastern tropical Pacific Ocean (Wyrtki, et al., 1976). Just as stress bands in Montastrea annularis from the Florida Straits depict recorded Cold Fronts that occur on the reef (Hudson, et al., 1976;Druffel, 1980b), unusually high rates of coral growth provide markers of growth during known E1 Niho years. Slabs of the above mentioned coral heads (5 mm thick) were

Samples
x-rayed to depict annual variations in the density of the aragonite. The x-ray positives of three of these slabs are shown in Figure 2. The annual nature of these density band pairs was established by using alizarin staining techniques, field observations (Glynn and Wellington, in prep.) and •aCp2C and •so/•60 measurements (Druffel, unpublished data). The x-rays revealed that HI-6 grew from 1961 to 1976 and HI-7 grew from 1966 to 1976 (Figure 2). Fifteen samples, each of which represented growth during one individual year (midpoint July) were used from HI-6. Eleven samples were taken from HI-7; five of these samples consisted of growth during five individual years. The remaining six samples from HI-7 represented growth during individual six-month periods. This was done in order to detect seasonal fluctuations of the •4C/C ratio. The x-ray of UB-16 revealed that this head grew from 1929 to 1954. Twenty-one samples were run from this coral head. In some cases, coral that grew during consecutive years were combined in order to obtain enough material to perform the •4C analyses. The x-ray of D-12 revealed that this coral head grew from 1966 to 1977. Eleven samples were run from this coral head; each represented growth during a single year.   (Druffel, 1980a) where waters have been at the surface for considerably longer.

these years (see below). Values for the non-E1 Niho years steadily rose from -59%o in 1961 to +25%o in 1972. If-75%o is taken to be the pre-bomb A•4C value (Figure 3), an overall rise of 100%o is observed by 1972. Atmospheric •4CO2 concentration nearly doubled by 1963 due to the input of bomb-produced •4C. By 1972, the •4C value had decreased to about 500%0 and at present (1980) is about 300% o. The increase in Ax4C due to bomb •4C in the eastern
tropical Pacific is much smaller than that observed for North Atlantic corals (214% o increase) ( Figure 5) (Druffel and Linick, 1978;Druffel, 1980a). The smaller rise is attributable to the undefined thermocline in equatorial areas, which allows increased mixing with subsurface waters that contain lower Ax4C values than those at the surface.
E1 Niho The appearance of warm, low salinity waters to the surface in the equatorial Pacific is known as E1 Niho (Wyrtki, et al., 1976). These waters come from north of the equator and contain higher levels of x4C than the upwelled surface waters normally present in the Gal/•pagos area. E1 Niho events start in January of certain years and last up to nine months. Results from seasonal samples were used to observe the difference of x4C concentrations between the normal upwelled and E1 Niho surface waters.
The A14C value for growth from HI-6 during 1969 was 31%o (Figure 4) I  I  I  I  I  I  I  I  I  I  I  I 1925 1930 1935 1940 1945 1950 1955 1960 1965 1970 1975 1980  The differences between the A•4C records for tropical Pacific coral and North Atlantic coral are due to varying degrees of upwelling for the two sites. The density structure of waters near the Galhpagos Islands allows subsurface waters from 60 to 180 m depth to rise to the surface (Eastropac Atlas, 1971, 1975. Equatorial surface waters have been in contact with the atmosphere for relatively short periods of time. This is characterized by the low oxygen content and the high nutrient concentrations in these waters (Eastropac Atlas, 1971, 1975