We are all familiar with the lush green landscapes and rugged mountains that characterize our planet, but when viewed from space, Earth appears as a predominantly blue planet, owing to its vast oceans. Despite their extreme salinity, unpredictable nature, and significant impact on our climate, these expansive bodies of water are indispensable to all life on Earth. British oceanographer and broadcaster Helen Czerski has dedicated her career to studying the ocean, and her latest book, "The Blue Machine: How the Ocean Works" (W. W. Norton & Company, 2023), delves into the profound influence of the ocean on our planet's evolution. She explores why certain regions are teeming with life while others are not, how civilizations have thrived along ocean currents, and how the ocean serves as Earth's engine, driving its weather systems.
In this interview, Czerski discusses the forces that drive this oceanic engine, likening it to a complex cocktail. She explains the unique structure of the ocean, with its warm surface layer and colder, stratified layer below. While these layers are typically separated, there are channels near the poles where they connect, driving a circulation where water descends, travels along the ocean floor for centuries, and resurfaces elsewhere. This process plays a crucial role in transporting heat from the equator to the poles, influencing global weather patterns.
Czerski explains that two factors power this engine: Earth's rotation and water density. Despite the perception that water is easily mixed, it actually requires energy to do so, much like stirring a cocktail. In the ocean, warmer, less dense water remains on top, while colder, denser water stays below, with minimal mixing between them. This stratification is essential, as nutrients vital for life often sink out of the warm, mixed layer. However, life thrives where these layers mix, such as near coastlines and polar regions.
She describes how the ocean's lateral movement, driven by wind and Earth's rotation, creates intricate currents that redistribute heat worldwide. The ocean essentially acts as Earth's battery, storing solar energy and influencing weather patterns. Czerski emphasizes that while water can mix, the vast ocean requires significant energy to fully homogenize, resulting in a dynamic but stable system.
Reflecting on Earth's history, Czerski notes that ocean circulation has varied over time. There have been periods when heat was more evenly distributed, and the deep ocean was warmer. However, the Arctic Ocean defies this pattern, with warmer water beneath the cold surface layer due to its high salinity, a result of ice formation.
Regarding the future, Czerski underscores the need to understand how the ocean will change under climate change. Shifts in circulation patterns could impact oxygen levels and marine life. She emphasizes the importance of working with, rather than against, Earth's natural systems.
Czerski's book offers a captivating narrative of the ocean's profound influence on life, from underwater waterfalls to its impact on civilizations.