Marine Isotope Laboratory
Research
Here is an overview of what we are working on at the NTU MISO
Tracing barium cycling in the ocean using Ba stable isotopes​
The ocean barium cycles are tightly linked with a wide range of oceanic processes, including marine productivity, barite cycling, weathering, riverine inputs, hydrothermal dynamics, cold seeps, submarine groundwater discharge, and ocean circulation. Thus, Ba has been commonly used as an ocean tracer to explore these complex marine systems. Ba stable isotopes have been recently developed as a new tool to help us to understand the marine Ba cycles. In MISO, we are particularly interested in studying what controls the variations in Ba isotopes in the ocean. We are also interested in developing new applications with Ba isotopes to improve our understanding of the Earth's surface systems.
Seawater Ba concentration and isotope distribution in the Atlantic Ocean. In the upper ocean, the isotopically heavy Ba is mainly due to the formation of pelagic barite (BaSO4) which preferentially removes isotonically light Ba. In the deep ocean, barite dissolution releases the isotopically light Ba back into the water column. Ba concentration and isotope composition are generally following the distribution of water masses, except in areas where the influences of hydrothermal and riverine inputs are strong. Figure adapted from Hsieh and Henderson (2017).
Clocking the ocean with U-series meters
How fast ocean currents flow; how soon marine particles sink; how quick seafloor sediments accumulate; how much carbon is drawn from the surface to the deep ocean; how much nutrients are transported in and out the ocean? These key questions determine how the ocean functions, however it is extremely challenging to assess the rates of these processes in the ocean. The radioactive decay chains of uranium-series nuclides provide a suite of natural meters to help us to clock the rates of these oceanic processes on different time scales. In MISO, we are interested in using thorium isotopes to trace seasonal or annual atmospheric dust inputs and particle sinking rates; we are also interested in using uranium-thorium isotopes to determine sedimentation rates or marine chronology on the glacial-interglacial time scale. In addition to the long-lived nuclides, we are also working on the applications of short-lived radium isotopes for monitoring ocean mixing and continental runoffs to the ocean (Hsieh et al., 2021).
Schematic diagram of U-series meters in the ocean. U-series nuclides can be used to trace and quantify the inputs of atmospheric dust, continental runoffs (submarine groundwater discharge SGD and rivers), and sediments. The radioactive decay of these nuclides and their chemical behavior can also be used as powerful meters to estimate ocean mixing and particle scavenging/sinking rates in the ocean.
Understanding the ocean in the past, present and future
In addition to modern oceanography, we are also interested in developing new tracers in marine paleo archives, which help us to understand the changes of the ocean in the past. Our ongoing work in marine carbonates and sediments allows us to reconstruct the changes of seawater compositions in the past and to understand the drivers behind these changes and their links with climate conditions. Constraining the processes that may affect the paleo records is also of interest (e.g., vital effects or sediment diagenesis). With intensified global warming and climate change, the ability to accurately forecast the ocean conditions in the future becomes crucial. In MISO, we aim to work closely with collaborators using ocean modeling to understand the past changes and to predict ocean dynamics in the future.
Images of coral slices from Singapore (the Kusu Island). Corals can be used as a paleo archive to record seawater compositions in the past. These Singapore corals were used to calibrate the compositions of Ba isotopes between coral skeletons and in-situ seawater (collaboration with Dr Jani Tanzil from National University of Singapore). Singapore seawater Ba isotopes may reflect the changes of regional water mixing in the past and hence the dynamics of the South East Asian monsoon, which plays an important role in driving the flow of surface currents in this area. Figure adapted from Hsieh et al. (2022).
Please refer to our publications for references.
