Reduction of thermohaline circulation during deglaciation: the effect on atmospheric radiocarbon and CO2

A two-? ocean reservoir model is employed to examine the combined effects of vertical ocean circulation, organic matter extraction and cosmic ray production on the¹⁴C/¹²C in the atmosphere, ocean and sediment. In this model, dissolution of deep-sea calcium carbonate sediment is assumed to respond to the supply of particulate carbonate from the surface ocean and to the dissolved carbonate-ion concentration of the deep-sea.If the vertical ocean circulation decreased by 50% during the maximum rate of deglaciation, the atmospheric¹⁴C/¹²C would have increased concurrently by 10% relative to the pre-bomb present. Further, if cosmic ray production of¹⁴C was 50% greater than present at about 7800 years B.P. as suggested by archeomagnetic measurements, a double maximum of 10% occurs. The first is at about 10.5 ka and the second at 6.5 ka. This result is similar to the variation of¹⁴C/¹²C over the last 10,000 years calculated from the¹⁴C dates measured by Stuiver on the varved Lake of the Clouds. The result is not sensibly altered if 10¹⁷ moles of organic carbon is extracted from the ocean during sea-level rise.Reduction of the thermohaline ocean circulation by 50% over a one- to two-thousand-year interval would not be sensibly detected in the dating of deep-sea sediment. If Broecker's organic nutrient extraction occurs in conjunction with reduction of vertical circulation, a decrease in the atmospheric P_CO2 will precede the eventual rise.