Detection of El Nino and decade time scale variations of sea surface temperature from banded coral records: implications for the carbon dioxide cycle.

. Stable oxygen isotope ratios from annually banded corals are correlated with historical records of sea surface temperature in the central and eastern tropical Pacific Ocean. are de-tected using this method, but there are discrep- ancies corals and those determined using historical hydrographic and meteorologic data. The average annual depletion of 6(cid:127)s0 during E1Nino events is greater at the Galapagos Island sites (0.45ø/oo) than at the Fanning and Canton Island sites in the mid-Pacific (0.20-0.30ø/oo and <0.2ø/oo, respectively). Of prime importance is evidence of decade time scale variability of sea surface temperature (SST) in the tropical Pacific. In particular, annually averaged SST appears to have been 0.5ø-1øC higher in the eastern tropical Pacific during the 1930's than during subsequent years. A significant net flux of CO2 from the surface ocean to the atmosphere is envisioned during these periods of higher SST.

anthropogenic A•C levels in the tropical Pacific were 15-30ø/oo lower than at higher latitudes (Figure 1) due to upwelling of •C-depleted waters from subsurface depths. Keeling et al. [1965] showed that pC0• levels in these equatorial surface waters are 40-80 ppm above atmospheric equilibrium values. This is the result of an imbalance between sources (upwelling of CO•-enriched water) and sinks (photosynthetic production of biomass) of COz to the surface ocean and long air/sea equilibration times. High pCO2 indicates that the equatorial surface ocean acts as a net source of COz to the atmosphere, whereas temperate and most polar surface oceans are either in equilibrium or act as a net sink for COz. If the nature of upwelling in the equatorial ocean were to change, this delicate balance would be altered, thus changing the net flux of COz to the atmosphere and causing perturbations in atmospheric pCO• on a time scale of months to years.
If the equatorial ocean warms up markedly as a result of reduced upwelling, such as that which occurs during E1Nino, opposing effects on the COz balance are expected: (1) the solubility of CO• will be lo•er in warmer water, (2) rates of primary production will be lower as

Ca z+ + 2HCO• ' CaCO3 + Hz0 + COz
(1) Sources and sinks of C and 0 in this internal pool are controlled by three major processes: (1) input of dissolved inorganic carbon (DIC) and Hz0 from surrounding seawater, (2) uptake and release of COz by metabolic processes such as coral respiration and algal photosynthesis, and (

records (&TøC) and annual range in 6•0 values (A6•O) in coral bands from Hood Island (Galapagos Islands), Fanning Island, and Canton
Island. As the upward growth rates of these corals were not the same, sampling resolution varied among specimens. A growth rate of ~1.5-2.0 cm/yr for Fanning (CFAN), Canton, and Hood Island heads allowed sampling of 9-12 samples/yr whereas the second Fanning specimen (CTFN) grew less than 1.0 cm/yr, which reduced the sampling resolution to 6 samples/yr.   Superimposed on the long-term changes are the presence of strong (1957,1965,1972), moderate (1953,1969,1976 It is important to note that results of annual sampling of the 1972 event (-4.85•/oo) agree with the results obtained from subannual sampling (Figure 3) where the values ranged from -4.6 to -5.0ø/oo

Geophysical Monograph Series
The Carbon Cycle and Atmospheric CO₂: Natural Variations Archean to Present Vol. 32 Copyright American Geophysical Union  1920 1930 '1940 '1950 '1960 '1970 '1980 YEAR  The level of noise in the •'O values surrounding the HI baseline (-4.35+0.13ø/oo SD) is significantly higher than that surrounding the UB baseline (-3.97+0.06ø/oo SD, after removing the 0.12ø/oo depletion during the 1930's) (see Figure 6).
It  Figure 6. The reliability of the record can be improved by obtaining higher precision (•0.03ø/oo) and by implementing more careful sampling procedures on a high growth rate coral that exhibits minimal intraannual banding.
A major conclusion of this study is that there appears to have been decade time scale variability of SST in the eastern and central tropical Pacific over the past half century. Warmer (and/or less saline) waters, by about 0.5ø-1øC, apparently predominated in the Galapagos Islands during the 1930's than during the subsequent decade. In addition, sea surface temperature appears to have increased by about  and are believed to be a net source of COz to the atmosphere during non-ENSO conditions. Decreased upwelling might be expected to reduce pC02 in ocean water and as a result reduce the net flux of COz to the atmosphere. On the other hand, increased primary production