The simultaneous use of chemical tracers in oceanic studies II.A three-reservoir model of the North and South Pacific Oceans

Abstract

Salinity, oxygen, inorganic phosphorus, organic and inorganic carbon, carbonate alkalinity, insoluble carbonate, and radiocarbon are used simultaneously as tracers to investigate oceanic circulation, chemical processes within the ocean and chemical exchange at oceanic boundaries. Estimates of the rates of these processes are made using the equation for chemical transport in the simplest approximation which recognizes spatially variable exchange at the ocean-atmosphere boundary, horizontal and vertical advective and eddy diffusive transport, and gravitational settling of insoluble chemicals within the oceans. This approximation is a cyclic model with one atmospheric and three oceanic reservoirs between which tracers exchange by first-order kinetics. Data for the Pacific Ocean are used after having been averaged over time and the regions: warm surface water, cold surface water, and deep water. Northern and southern cold surface waters are treated as alternate cases. We deduce that: 1 The mass of deep water in the Pacific Ocean divided by its rate of production is about 1100 years, a time interval in close agreement with its average radiocarbon age relative to that of cold surface water. 2 In the South Pacific Ocean, the transfer of water between the deep ocean and the surface is principally by exchange with cold surface water. A small net circulation from warm surface water to cold surface water is suggested by the model, but the rate cannot be calculated with existing information. 3 The three-reservoir model cannot, even to a first approximation, explain the circulation of the North Pacific Ocean, because it overlooks the flow of deep water into the North Pacific Ocean from the South Pacific Ocean. 4 Both oxygen and carbon dioxide are evolved from surface waters at low latitudes and absorbed at high latitudes. The rates of exchange from warm surface water to cold surface water are of the order of 10¹⁷ mmol yr^?1. 5 About 10% of the inorganic carbon in deep water arrives there from surface water by gravitational settling of organic carbon and insoluble carbonate. The other 90% is transported there by the water itself. 6 The use of pH measurements to assay for dissolved inorganic carbon and alkalinity seriously limits the reliability of carbon data in the present study. Small errors in pH result in large uncertainties in the deduced rates of gravitational transport of organic carbon and insoluble carbonates and in the rate of exchange of CO₂ with the atmosphere. DOI: 10.1111/j.2153-3490.1968.tb00348.x