Late Holocene Carbonate Dissolution in the Equatorial Pacific: Reef Growth or Neoglaciation?
- E.T. Sundquist and
- W.S. Broecker
Published Online: 18 MAR 2013
Copyright 1985 by the American Geophysical Union.
The Carbon Cycle and Atmospheric CO: Natural Variations Archean to Present
How to Cite
Keir, R. S. and Berger, W. H. (2013) Late Holocene Carbonate Dissolution in the Equatorial Pacific: Reef Growth or Neoglaciation?, in The Carbon Cycle and Atmospheric CO: Natural Variations Archean to Present (eds E.T. Sundquist and W.S. Broecker), American Geophysical Union, Washington, D. C.. doi: 10.1029/GM032p0208
- Published Online: 18 MAR 2013
- Published Print: 1 JAN 1985
Print ISBN: 9780875900605
Online ISBN: 9781118664322
- Carbon cycle (Biogeochemistry)—Congresses;
- Atmospheric carbon dioxide—Congresses;
- Geological time—Congresses;
- Geology, Stratigraphic—Congresses
Equatorial Pacific sediments in water depths greater than 4 km exhibit increased calcium carbonate dissolution and anomalously old 14C ages in the upper ˜5–10 cm of sediment. This suggests that these sediments have been “chemically” eroded by unusually high dissolution rates within the recent past. An atmosphere-ocean-sediment model is employed to evaluate the effect of Holocene carbonate reef growth on deep sea sediment accumulation/erosion rate as well as the resulting carbonate fraction and radiocarbon stratigraphies. This model also predicts the temporal atmospheric CO2 content. We assume that about 6 g CaCO3 cm−2 of ocean bottom is extracted to produce lowered carbonate values and anomalous 14C ages. The model assumes a continuous supply of settling particles throughout the Holocene, and that the anomalously old sediment is produced by a sudden increase in reef growth within the last 3 kyr. This time interval corresponds to the turnover time of the particulate carbonate influx in the upper mixed layer of sediment. In cases where a burst of reef growth ends before 3 kyr B.P. the aging effect on the mixed layer is subsequently eradicated by the settling young carbonate. The result is a “normal” mixed layer age of 3 to 5 kyr overlying a discontinuous age jump or hiatus. Slow continuous reef growth throughout the Holocene produces a similar result. This type of 14C profile is not observed. However, a burst of reef growth in the last 3 kyr would not only produce the peculiar radiocarbon profile which is observed, but also a pulse-like increase of greater than 70 ppm in the atmospheric CO2 concentration. This is not seen in published data on interstitial air trapped in ice cores. Accordingly, it appears that basin-to-shelf transfer by reef growth is not the cause of the recent erosional event in the Pacific. Rather, a mechanism must be found which produces undersaturation of deep waters in some other fashion, for example, by an increase in productivity caused by global cooling (“neoglaciation”).