Telling the story of the Atlantic’s sargassum surge with 40 years of data

Researchers from the Oceanographic Institute Institute Oceanographic of Florida Atlantic University published a historic review drawing four decades of changes in the Pelagic Sargasse – floating brown algae which play a vital role in the ecosystem of the Atlantic Ocean.

Once considered mainly to be confined to the poor waters in nutrients from the Sargasse Sea, the Sargasse is now recognized as a rapidly growing and largely distributed marine organization, whose expansion through the Atlantic is closely linked to natural processes and the enrichment of nutrients induced by humans.

La Revue, published in the journal PestsDraw new light on the origins and the development of the large Atlantic Sargasse belt, a massive massive flowering of Sargasse which extends through the Atlantic Ocean from the Coast of West Africa to the Gulf of America.

Since its first appearance in 2011, this belt has been formed almost every year – except in 2013 – and in May has reached a new record biomass of 37.5 million tonnes. This does not include basic biomass of 7.3 million tonnes historically estimated in the Sargassus Sea.

By combining historical oceanographic observations, modern satellite images and advanced biogeochemical analyzes, this review provides a complete framework to understand spectacular changes in the distribution, productivity and dynamics of sargassus nutrients. It also highlights the broader implications of the anthropogenic enrichment of nutrients on oceanic ecology and the need for coordinated international efforts to monitor and manage the impacts of these massive flowers of algae.

“Our magazine plunged deeply into the changing history of Sargasse – how it develops, which fuels this growth and why we see such a spectacular increase in biomass across the North Atlantic,” said Brian Lapointe, Ph.D., principal author and research teacher at FAU Harbor Branch. “By examining the changes in its nutritional composition – in particular nitrogen, phosphorus and carbon – and how these elements vary in time and space, we start to understand the larger environmental forces in play.”

At the start of the journal, Lapointe and the co-authors Deanna F. Webber, research coordinator; And Rachel Brewton, Ph.D., deputy research professor, both with FAU Harbor Branch, explain that the first oceanographers traced the Sargassus Sea on the basis of Sargasse surface observations, believing that algae prospered in its warm, clear but poor in nutrients. However, this notion created a paradox when the mid -20th century oceanographers described the region as a “biological desert”.

However, recent satellite observations, ocean circulation models and field studies have resolved this paradox by drawing seasonal transport of sargasse from coastal areas rich in nutrients, in particular the Western Gulf of America, in the ocean opened via the loop current and the Gulf Stream. These results support the first theories by explorers who proposed that the Sargasse from the Gulf could feed the populations of the Sargassus Sea.

Remote design technology has played a central role in these discoveries. In 2004 and 2005, satellites captured extended sargassum winds – narrow lines or narrow floating sargasse strips – in the west of the Gulf of America, a region experiencing increased nutrient loads from river systems such as Mississippi and Atchafalaya.

“These water -rich waters have fueled high biomass events along the Gulf coast, which causes mass shutters, expensive beach cleanings and even the emergency closure of a Florida nuclear power plant in 1991,” said Lapointe. “A major objective of our review is the elementary composition of the sargassum fabric and how it has changed over time.”

Laboratory experiences and field research dating from the 1980s have confirmed that Sargasse developed more quickly and is more productive in neritic waters enriched in nutrients than in the oligotrophic waters of the open ocean. Controlled studies have revealed that the two primary species, sargassum natans and sargasse, can double their biomass in just 11 days in optimal conditions. These studies have also established that phosphorus is often the main nutrient limiting growth, although nitrogen also plays an essential role.

From the 1980s to the 2020s, the nitrogen content of the Sargasse increased by more than 50%, while the phosphorus content has decreased slightly, leading to a sharp increase in the nitrogen / phosphorus ratio (N: P).

“These changes reflect a distance from the sources of natural ocean nutrients such as upwelling and vertical mixture, and to land inputs such as agricultural runoff, wastewater discharge and atmospheric deposit,” said Lapointe. “Carbon levels in sargasse have also increased, contributing to changes in global stoichiometry and further emphasizing the impact of external nutrients on marine primary producers.”

The journal also explores how the recycling of nutrients in the Sargasse Windrows, including the excretion of associated marine organisms and the microbial degradation of organic matter, can support the growth of nutrient -poor environments. This micro-scale recycling is essential to maintain sargassum populations in certain parts of the ocean which, otherwise, would not support high productivity levels.

Sargassum data collected near the mouth of the Amazon river support the hypothesis that the outputs of nutrients in this large river significantly contribute to the development of the Gasb. The variations in the sargasse biomass were linked to the cycles of floods and drought in the Amazon basin, moreover connecting the entrances of land nutrients to the open ocean.

The Gasb formation seems to have been sown by an extreme atmospheric event – the negative phase of the North Atlantic oscillation in 2009 to 2010, which may have helped to move surface waters and the south south south south south south in the tropical Atlantic.

However, researchers warn that there is no direct evidence of this movement. In addition, genetic and morphological data suggest that certain Sargasse populations, in particular the S. Natans dominating Var. Wingei, was already present in the Tropical Atlantic before 2011, indicating that this region may have had a neglected role in the early development of the Gasb.

“The expansion of sargasse is not only an ecological curiosity – it has real impacts on coastal communities. Massive flowers can obstruct beaches, affect fisheries and tourism and pose health risks,” said Lapointe. “Understanding why Sargassum develops as much is crucial to manage these impacts. Our examination helps to link the points between pollution of land nutrients, ocean circulation and the unprecedented expansion of the Sargasse in an entire ocean basin.”