The relationship between lysocline depth and in situ carbonate ion concentration

Abstract

The relationship between the carbonate ion content of deep seawater and the depths of the lysoclines for calcite and for aragonite in the open ocean has been re-examined using Geochemical Ocean Sections Study (GEOSECS) data. It is concluded that the lysocline horizons are located where the carbonate ion versus depth curve passes through critical carbonate ion curves given by the following relationships: (CO3=)critcalc(μMkg-1)=90exp{0.16(Z-4)}(CO3=)critarag(μMkg-1)=120exp{0.15(Z-4)}where Z is the depth of water expressed in km. The slopes of these curves arc consistent with those predicted from partial molar volume data. The surface intercept of the calcite curve coincides with the solubility of calcite in seawater reported by Ingle, Culberson, Hawley and Pytkowicz, (Marine Chemistry I. 295–307, 1973). Using the above equations and the GEOSECS carbonate ion data, the topography of critical carbonate ion horizons (and hence presumably of the lysoclines for calcite and aragonite) have been mapped along the GEOSECS tracks in the Atlantic and Pacific oceans.