墨西哥湾北部的卫星图像, “死亡地带”可以达到新泽西州那么大. 图片来源:NASA
缺氧的海洋“死亡区”,鱼和动物无法生存, have been expanding in the open ocean and coastal waters for several decades as a result of human agricultural and industrial activity. 试图预测未来死亡地带的规模和位置, 科学家们从过去寻找历史线索.
今天最大的公海死亡地带, 位于东太平洋, emerged eight million years ago as a result of increasing nutrient content in the ocean, 一个国际科学家小组在 美国国家科学院院刊.
虽然今天营养丰富的来源可能不同, the mechanics that created what scientists call “oxygen-deficient zones” remain the same, according to 电子游戏软件 Assistant Professor of Earth and Environmental Sciences Xingchen “Tony” Wang, 该报告的主要作者. Better understanding ocean dead zones in the past, may help future ocean conservation efforts.
王星晨“托尼”(李·佩莱格里尼)
“为了更好地保护海洋生态系统和管理渔业, it is critical to predict how an ocean ‘dead zone’ will evolve in the future,王说.
A coastal ocean dead zone is mainly caused by the flow of excess nutrients humans use on land, 例如施肥. 在墨西哥湾北部, anthropogenic nutrients delivered by the Mississippi River annually produce a dead zone as big as the state of New Jersey.
这些区域也自然地出现在开阔的海洋中, 在东太平洋发现的最大的. “It remains unclear how these dead zones will change as the planet warms. So, we studied the history of the eastern Pacific dead zone in order to better predict its future behavior,王说.
来自美国各大学的电子游戏正规平台人员.S., 加拿大, 台湾, 德国, and Australia set out to determine the evolution of open ocean dead zones before human activity began to impact the ocean, 王说. 此外，这些死区是否一直存在? 如果有，为什么??
The team examined the chemical composition of ocean sediments near today’s largest ocean dead zone, 位于东太平洋. The team obtained sediment samples—the “history books” of ocean activity—going back 12 million years and analyzed nitrogen contained in microfossils, 被称为有孔虫.
“Fossil foraminifera in ocean sediments are mainly made of calcium carbonate and they have been used to study past climate change for decades,孔天舒说, a doctoral student in Wang’s lab who studies foraminifera in her research. “Most foraminifera found in ocean sediments actually came from the surface water, 所以它们可以告诉我们上层海洋发生了什么.”
电子游戏正规平台小组在死亡区寻找反硝化的迹象, which occurs when oxygen content is so low that microbes instead use nitrate to power their biological activity. 氮有两种稳定的同位素, 氮14和氮15, and microbes prefer to consume the lighter isotope of nitrogen-14 during denitrification.
当缺氧区扩大时, 反硝化区也扩大了, 提高剩余硝酸盐中氮-15和氮-14的比例, which is then recorded in ocean organisms such as foraminifera through the cycling of nitrogen in the marine ecosystems, 根据报告.
“By analyzing the nitrogen-15 to nitrogen-14 ratio of foraminifera in ocean sediments, 我们可以重建缺氧区范围的历史,王说, 他在这个项目上的工作部分由西蒙斯基金会资助.
除了, the researchers analyzed the phosphorus and iron content of the same sediments, 揭示了太平洋深处古代的营养成分, 根据报告.
“Deep-ocean nutrient content is hard to reconstruct and our record is the first of its kind over the past 12 million years; its trends have important implications for the global carbon cycle and climate change,伍德沃德说. Fischer, a co-author of the study and professor at the California Institute of Technology.
今天最大的“死亡区”位于东太平洋. Symbols and colors indicate the location and thickness of oxygen-deficient water, 颜色越深表示“死区”越厚.图片来源:孔天舒.
The sedimentary records showed the team that the largest open ocean dead zones gradually expanded over the past eight million years, 王说, who was joined on the project by colleagues from the Max Planck Institute for Chemistry, 普林斯顿大学, 国立台湾大学, 多伦多大学, 德克萨斯州的一个&M大学、西澳大利亚大学和加州理工学院.
“Further, the expansion of these dead zones was mainly caused by nutrient enrichment,” he said. “This mechanism is similar to the formation of dead zones in today’s coastal waters, 除了人类对目前的营养富集负有责任.”
These findings may help better predict the future behavior of open ocean dead zones, 根据报告. For example, human activities have been adding more and more nitrogen to the ocean. They can support the need to improve climate and ocean models to better gauge the impact of anthropogenic nitrogen on the deoxygenation processes in the open ocean.
The researchers were struck by data that showed much lower nutrient content in the ocean prior to eight million years ago.
“The nutrient increase since eight million years ago was likely caused by increased weathering and erosion on land which would increase the delivery of phosphorus to the ocean,费希尔说。.
“除了, terrestrial ecosystems underwent a major transition between eight and six million years ago,王说. “Many forests were replaced by less dense grassland, known as the expansion of C4 ecosystems. 有更多的草地, 在此期间，土壤侵蚀可能增加了, and it would have triggered a greater transfer of organic nutrients to the ocean.”
王说 a likely next step in this research would be to determine how the flow of nitrogen into the ocean from human activity can impact the ocean’s nutrient cycle.
“关键问题在于我们的沿海地区, 哪里是进入海洋最多的人为氮,王说. “If most of anthropogenic nitrogen is removed in coastal regions—essentially by denitrification taking place in the sediments—then that could lessen the impact on the whole ocean. Our research group at BC is currently doing some work in the Northern Gulf of Mexico to better understand the fate of anthropogenic nitrogen in the ocean.”
Ed Hayward |大学传播| 2023年1月