Trace gas disequilibria during deep-water formation

• Published in: Deep-sea research. Part I, Oceanographic research papers Oceanographic research papers, 2007-06, Vol.54 (6), p.939-950
• Main Authors: Hamme, Roberta C., Severinghaus, Jeffrey P.
• Format: Article
• Language: English
• Subjects: Air–sea gas exchange; Animal and plant ecology; Animal, plant and microbial ecology; Biological and medical sciences; Bubbles; Deep-water formation; Dissolved gases; Earth sciences; Earth, ocean, space; Exact sciences and technology; External geophysics; Fundamental and applied biological sciences. Psychology; Gases; Geochemistry; Inert gases; Isotopes; Marine; Mineralogy; Oceanography; Oceans; Physical and chemical properties of sea water; Physics of the oceans; Sea water ecosystems; Silicates; Solubility pump; Synecology; Water geochemistry
• ISSN: 0967-0637; 1879-0119
• DOI: 10.1016/j.dsr.2007.03.008

We present high-precision measurements by a new isotope dilution technique of a suite of inert gases in the North Pacific. Remarkably smooth gradients in Ar, Kr and Xe from near equilibrium in intermediate waters to several percent undersaturated in deep waters were observed. The general pattern in the deepest waters was that Ar, Kr and Xe were undersaturated (Ar least and Xe most), while N 2 was close to equilibrium, and Ne was supersaturated. We propose that this pattern was produced by the interaction between the different physical properties of the gases (solubility and the temperature dependence of solubility) with the rapid cooling and high wind speeds that characterize deep-water formation regions. In a simple model of deep-water formation by convection, the saturations of the more temperature-sensitive gases were quickly driven down by rapid cooling and could not reequilibrate with the atmosphere before the end of the winter. In contrast, the gas exchange rate of the more bubble-sensitive gases (Ne and N 2) was able to meet or exceed the drawdown by cooling. Our simple convection model demonstrates that the heavier noble gases (Ar, Kr and Xe) are sensitive on seasonal timescales to the competing effects of cooling and air–sea gas exchange that are also important to setting the concentration of CO 2 in newly formed waters.