Researchers discover the mystery of the level of iron in the ocean

The middle of the Earth's oceans is filled with vast systems of rotating currents called subtropical gyres. These regions occupy 40% of the Earth's surface and have long been regarded as remarkably stable biological deserts, with little variation in chemical composition or nutrients required for survival.

However, there is a strange anomaly in the subtropical gyre ecosystem of the North Pacific, which has intrigued scientists for years. In this region that occupies the Pacific Ocean between China and the United States, the chemistry changes periodically. There is a particularly notable fluctuation in phosphorus and iron levels, which affects the overall composition of nutrients and, ultimately, biological productivity.

In a new study published in the Proceedings of the National Academy of Sciences, a group of researchers has discovered the reason for these variations in the ecosystem of subtropical gyres in the North Pacific. The group includes Matthew Church, a microbial ecologist from the Flathead Lake Biological Station of the University of Montana, as well as Ricardo Letelier of Oregon State University and David Karl of the University of Montana. Hawaii, among others.

"Variations in ocean climate appear to regulate iron supply, altering the types of plankton growing in these waters, which ultimately control nutrient concentrations in the ocean," he said. Church. "My lab has been working for many years on issues related to the role of plankton in controlling the availability of nutrients in the oceans, and this study puts much of this work in context with long-term, long-term observations. , our work confirms how plankton biology consists of providing nutrients, especially iron, released from the atmosphere. "

Using three decades of observation data from the ALOHA station, a six-mile zone in the Pacific Ocean north of Hawaii dedicated to oceanographic research, the team discovered that the Periodic variation in iron levels resulted from iron intake from Asian dust, which accounted for the chemical variances. and provide varying amounts of nutrients to maintain life.

The key to the variance is the Pacific Decadal Oscillation, an ocean-atmosphere relationship that varies between the weak and strong phases of atmospheric pressure in the northeastern Pacific Ocean.

In years when the depression is decreasing in the northeastern Pacific, winds from Asia are strengthening and are moving further south. This brings more dust from the Asian continent, "fertilizing" the ocean surrounding the ALOHA station. When the pressure increases, the opposite happens.

Nutrient supply is a fundamental regulator of ocean productivity. Phosphorus and iron are essential components of life. As a rule, the upper water column of the ocean is fertilized by nutrient rich water mixing with depths. This is a difficult process in the subtropical gyres ecosystem of the North Pacific, as the waters are highly stratified and there is little mixing.

When strong Asian winds bring significant amounts of iron, organisms are allowed to grow and use phosphorus in the upper layers of the ocean. When Asian winds weaken and iron intake decreases, organisms are forced to return to a deep-water nutrient distribution system. This creates periodic ebb and flow of iron and phosphorus levels in the North Pacific Gyre.

Church said the results of this study underscore the critical need to include the variability of atmospheric and ocean circulation in predicting the impact of climate change on ocean ecosystems.

"This reaffirms the need to reflect on the extent to which plankton biology is closely linked to climate change and, ultimately, changes in land use, which can have a direct impact on intake. dust in the sea, "he said.

As the Earth's temperature continues to warm up, researchers expect long-term changes in wind patterns in the North Pacific. Changes in land use and anthropogenic pollution in Asia will also affect the sources and magnitude of iron and other nutrients transported by wind across the ocean.

Further research is needed to better understand the impact of these changes on the ecosystems of this ocean region, as well as those around the world.