This is a case of a 35-year-old gravida 1 para 0 at 39 weeks’ gestation who experienced a protracted active phase of the first stage of labor. The case reviews traditional definitions (based on the work of Friedman) and current Obstetrical Care Consensus guidelines related to the active phase of the first stage of labor. It includes discussion of the 5 Ps that can affect labor progress and interventions that have been shown to have a positive impact on the active phase. Slow but continued progress in the first stage of labor is not an indication for cesarean. To diagnose arrest of dilation in the active phase, the cervix must be ≥ 6 cm dilated with rupture of membranes and ≥ 4 hours of adequate contractions (≥ 200 MvU) or ≥ 6 hours of inadequate contractions.

Carbon is the vehicle for the collaboration between life on Earth and the climate of the planet. The Sun supplies the energy for plants to create organic carbon by linking reduced carbon atoms together with O, H, N, and minor amounts of many other elements in a vast variety of organic matter forms (see online Chapter 8 of Emerson and Hedges (2008), www.cambridge.org/emerson-hamme). Reduced organic carbon is thermodynamically unstable, and many organisms derive energy by oxidizing it to CO2, the most stable form of inorganic carbon in an oxygen-containing world. In our atmosphere, CO2 causes a strong greenhouse effect warming the planet, and paleoclimate observations indicate past changes in the concentration of atmospheric CO2 have driven profound climate shifts.

Concentrations both of the elements that make up most of the salinity of the oceans and of the major gases provide clues to the mechanisms that control their sources and sinks. The chemical perspective of oceanography revealed by major element concentrations is about processes that occur across ocean boundaries – weathering reactions on land, authigenic mineral formation in marine sediments, reactions with the crust at hydrothermal areas, and air–sea interaction. The amount of time some of the dissolved constituents remain in solution before they are removed chemically is very long, suggesting the possibility for chemical equilibrium between seawater and the minerals in ocean basins as a controlling factor. Conversely, energy from both the Sun and the Earth’s interior is constantly driving seawater constituents away from chemical equilibrium. This chapter is divided into two parts: ocean mass balances controlling the major ions in seawater and the processes controlling the distribution of gases between the atmosphere and ocean.

While photosynthesis and the production of organic matter dominate the surface ocean, respiration is the process that most influences the chemical perspective of oceanography in the deep ocean. For a chemist, respiration is simply photosynthesis (Eq. 3.10) run in reverse, with O2 consumed while CO2, nutrients, and energy are liberated. The flux of organic matter out of the surface ocean (the biological pump) is the driving force for the respiration reactions that occur in the deeper ocean. The delicate balance between the supply of organic matter via the biological pump and the renewal of water by mixing with ocean surface waters determines the distribution of metabolites below the euphotic zone. In this chapter, we explore how these processes interact to produce the complex and fascinating distributions of O2 and nutrients in the deep sea.

Patterns of chemical distributions within the ocean are primarily controlled by biological processes and ocean circulation. Sunlight penetrates only the top 100 meters or so of the ocean (the euphotic zone), just 4 percent of the average ocean depth, but supplies the energy for photosynthesis that is the basis for most marine chemical transformations. Much of the organic matter produced by photosynthesis is consumed by bacteria and animals in the euphotic zone, but some also escapes the sunlit upper waters into the dark sphere. Density stratification between the warmer surface mixed layer and colder deep waters helps to keep the metabolic products of photosynthesis and respiration separate.

The study of radioisotopes provides the added dimension of time to the chemical perspective of oceanography. Stable elements and isotopes (Chapter 6) are useful tracers of the sources and transformations of marine materials, but they carry no direct information about the rates and dates of their associated processes. However, such temporal distinctions are made possible by many different, naturally occurring radioactive isotopes with their wide range of elemental forms and decay rates. These highly dependable atomic clocks decay by nuclear processes that are insensitive to temperature and pressure and that allow them to be detected at very low concentrations. A fanciful analogy of how these tracers are used is an experiment in which you attach hundreds of clocks that operate only at pressures less than one atmosphere to helium-filled balloons and release them to float in the atmosphere. After the helium leaks out of the balloons, the clocks would fall to the Earth scattered across the landscape. Because each clock records only the time spent aloft, their position and time would convey information about the direction and speed of local winds.