Nutrient Supply and Phytoplankton Growth:
During glacial periods, the global ocean circulation changed, resulting in increased nutrient upwelling from the deep ocean to the surface waters. This nutrient enrichment stimulated phytoplankton growth, leading to higher rates of photosynthesis. As phytoplankton convert carbon dioxide (CO2) into organic matter through photosynthesis, a greater amount of CO2 was removed from the atmosphere and stored in the ocean.
Increased Organic Carbon Export:
The increased phytoplankton growth during colder periods resulted in higher production of organic matter in the surface ocean. A substantial portion of this organic matter sank to the deep sea, a process known as organic carbon export. As organic carbon is transported to the deep ocean, it effectively sequesters carbon away from the atmosphere for long periods of time. Deep-sea corals living on the seafloor record these variations in organic carbon flux through their growth patterns and geochemical composition.
Reduced Carbon Cycling in Deep Ocean:
During colder intervals, deep-water formation occurred at higher rates, leading to increased deep-ocean ventilation. This ventilation process transported oxygenated water to the deep sea, enhancing the decomposition of organic matter. However, the colder temperatures also slowed down the decomposition rates of organic matter, allowing more carbon to remain stored in the deep ocean. Deep-sea corals provide a record of past deep-ocean ventilation and organic matter degradation, helping scientists understand the role of the deep ocean in carbon storage.
Changes in Ocean Circulation:
The variations in ocean circulation patterns during glacial and interglacial periods had profound effects on carbon cycling. Deep-sea corals record these changes in circulation through their oxygen isotope composition, providing information about the origin and transport of water masses. Shifts in water mass formation and transport influence the distribution of nutrients, temperature, and carbon dioxide, all of which impact atmospheric carbon levels.
By studying deep-sea corals, scientists gain valuable information about past changes in oceanographic conditions, nutrient cycling, and carbon fluxes. These insights contribute to a comprehensive understanding of why atmospheric carbon was reduced during colder time periods and help improve our understanding of the complex interplay between climate, ocean processes, and the global carbon cycle.
