GEOTRACES

GEOTRACES is an international scientific program dedicated to mapping the global distributions of trace elements and their isotopes in the world's oceans. Launched in 2006, it represents a major collaborative effort to understand the fundamental biogeochemical cycles that govern the composition of seawater and influence marine ecosystems. The program builds upon the legacy of earlier oceanographic expeditions like the Geochemical Ocean Sections Study and aims to provide a comprehensive, high-resolution dataset for the international scientific community. Its findings are critical for addressing contemporary issues such as ocean acidification, the efficiency of the biological pump, and the impacts of anthropogenic inputs on marine environments.

Overview and objectives

The primary goal of the program is to quantify the processes that control the distributions of key trace elements and isotopes, which act as sensitive tracers of oceanic processes. These include essential micronutrients like iron, zinc, and cobalt, whose availability can limit phytoplankton growth across vast regions of the ocean such as the Southern Ocean and the North Pacific Ocean. A core objective is to distinguish between natural sources, such as hydrothermal vents, atmospheric deposition, and sediment resuspension, and anthropogenic inputs from industrial activity. The program also seeks to improve the incorporation of these chemical tracers into global climate models to better predict the ocean's response to environmental change, providing data that informs assessments by the Intergovernmental Panel on Climate Change.

Scientific approach and methodology

The program employs a highly coordinated, basin-scale section approach, conducting precision measurements during dedicated research cruises aboard vessels like those operated by the U.S. National Science Foundation and the British Antarctic Survey. State-of-the-art ultraclean sampling techniques are mandatory to avoid contamination when measuring elements present at extremely low concentrations. Analytical methods involve advanced mass spectrometry, including inductively coupled plasma mass spectrometry and thermal ionization mass spectrometry, often conducted in dedicated laboratories like those at the University of California, Santa Cruz or the University of Southampton. This standardized methodology ensures data comparability across different ocean basins and international teams, a principle championed by early proponents in the Scientific Committee on Oceanic Research.

Key findings and discoveries

Research has revolutionized the understanding of iron cycling, revealing its complex sources from aeolian dust, hydrothermal plumes along the Mid-Atlantic Ridge, and melting ice sheets in the Arctic Ocean. Studies in the South Pacific Ocean have detailed the extensive shadow zones of trace elements emanating from hydrothermal systems, impacting nutrient stoichiometry thousands of kilometers away. The program has also provided the first basin-scale maps of anthropogenic inputs, such as lead from historic leaded gasoline use, tracing its transport and decline following the Montreal Protocol. Furthermore, work on isotopes like neodymium has refined knowledge of ocean circulation and water mass mixing, offering insights complementary to physical measurements from programs like Argo.

International collaboration and cruises

The program is a model of global cooperation, governed by an International Project Office and guided by a Scientific Steering Committee with members from over 35 nations. Major collaborative cruises have traversed all major ocean basins, including iconic expeditions in the Indian Ocean, the Mediterranean Sea, and the Weddell Sea. These efforts often involve joint missions between agencies such as NASA, the National Oceanic and Atmospheric Administration, and the European Science Foundation. The integration of scientists from diverse institutions, including the Woods Hole Oceanographic Institution, the Alfred Wegener Institute, and the University of Tokyo, ensures a multidisciplinary approach combining chemical oceanography, marine biology, and atmospheric science.

Data management and legacy

All data generated are curated and made freely available through a central Data Management Committee and an online Data Assembly Centre, adhering to the FAIR principles for scientific data. This open-access policy has created an invaluable resource, the GEOTRACES Intermediate Data Product, which is used by thousands of researchers worldwide for studies ranging from paleoceanography to marine pollution assessment. The program's legacy includes training a new generation of marine geochemists and establishing a foundational observational framework that will serve as a benchmark for decades, much like the World Ocean Circulation Experiment did for physical oceanography.

Category:Scientific organizations Category:Oceanography Category:International research projects