The center of oceans of the Earth are covered with an enormous arrangement of rotating currents known as subtropical gyres, which occupy 40% of the Earth’s surface. They have been considered as stable biological deserts with little deviation in chemical composition or the nutrients needed to sustain life.
The region in the North Pacific Subtropical Gyre ecosystem that occupies the Pacific Ocean between China and the United States has confused scientists over the years by its strange abnormality in chemistry that changes periodically. There is a remarkable variation in the levels of phosphorus and iron which affects the entire nutrient composition and eventually biological productivity.
The research team has found out the explanation behind the variations in the North Pacific Subtropical Gyre ecosystem. It includes Matthew Church, a microbial ecologist with the University of Montana’s Flathead Lake Biological Station, Ricardo Letelier from Oregon State University and David Karl from the University of Hawaii. The work appears in the Proceedings of the National Academy of Sciences.
Church said that the variations in the ocean climate arise to basically control ocean nutrient concentrations by regulating iron supply and altering the kinds of plankton growing in these waters. He also said that after constant, long-term observations on the role of plankton in controlling ocean nutrient availability, their team has finally confirmed that tightly linked plankton supplies nutrients, particularly iron, delivered from the atmosphere.
With the help of three decades of observational data from Station ALOHA, a six-mile area in the Pacific Ocean, the researchers discovered that the periodic shift in the level of iron is due to iron input from Asian dust, accounting for the chemical variances and varying amounts of nutrients to sustain life.
The ocean-atmosphere relationship known as The Pacific Decadal Oscillation varies between weak and strong stages of atmospheric pressure in the northeast Pacific Ocean which is the major factor of the variance. The winds from Asia become stronger and move in a more southern direction in years when the low pressure weakens in the northeast Pacific bringing more dust from Asia and fertilizing the ocean around ALOHA. The opposite occurs when the pressure strengthens.
Phosphorous and iron are the essential components of life and the supply of nutrients is a fundamental controller of ocean productivity. The process of fertilizing the ocean’s upper water level by mixing nutrient-rich water from the bottom is challenging in the North Pacific Subtropical Gyre ecosystem because the waters are very layered and very less mixing takes place. The creatures are allowed to grow and use phosphorus in the upper layers of the ocean when strong Asian winds bring in substantial quantity of iron while they are forced to return to a bottom-water-mixing nutrient delivery system when the Asian winds weaken and iron quantity is reduced creating the periodic ebb and flow of iron and phosphorus levels in the North Pacific Gyre.
Church said that the results from the study highlight the crucial need to include both atmospheric and ocean circulation variability for forecasting the climate change impact on ocean ecosystems. He also added that it confirms the necessity to think about the biology of tightly connected plankton to changes in climate as well as land use which can directly impact dust supply to the ocean.
Researchers hope to see long-term changes in wind patterns across the North Pacific as Earth’s temperature continues to increase. The sources and quantity of iron and other nutrients carried by the wind across the ocean will get affected by the evolution of land use and pollution caused by human activity in Asia.
To know the impact of the changes on ecosystems around the ocean region as well as others around the world, more research is needed.
Journal Reference: Proceedings of the National Academy of Sciences.