Did you know that microscopic molecules in marine sediments can record past climate changes? A type of algal organic compound called alkenone is widely used as a paleothermometer via an index known as UK’37 since the 90s. In this study, IONTU master’s student Chia-Yu Chung and her supervisor, associate professor Sze Ling Ho, evaluate the sensitivity of the UK’37 paleothermometer to seasonal sea surface temperature variations in the northern South China Sea associated with the East Asian Monsoon system.
To achieve this goal, they analyzed sinking particulate samples collected at 2000 m and 3500 m water depths between 2017 and 2020 to examine variations in alkenone fluxes and UK’37 values at the South East Asian Time-series Study (SEATS) site. Interestingly, the temperatures recorded in sinking particles do not correspond well to the sea-surface temperatures above them, being higher during winter and lower during summer. Likewise, sedimentary UK’37 values at the seafloor fail to capture the cooler conditions of the winter monsoon, even though alkenone production is highest during that season due to the East Asian Winter Monsoon. This mismatch arises because alkenones can remain suspended in the water column for several months before settling, blending signals from different times of the year (Figure 1). Consequently, the sedimentary record in this region reflects a broad, multi-season temperature average instead of being skewed toward winter conditions. These results indicate that, in the northern South China Sea, UK’37 is more reliable for reconstructing long-term mean temperatures than for detecting seasonal monsoon-related variations. Therefore, simply being located in a monsoon region does not guarantee that UK’37 values in the sediment cores will capture monsoon-related variability.
This study was published in American Geophysical Union journal Geophysical Research Letters.
Further reading:
Chung, C.-Y., & Ho, S. L. (2025). Sedimentary UK’37 in the South China Sea reflects mean sea surface temperatures despite substantial winter monsoon-driven alkenone flux variability. Geophysical Research Letters, 52, e2025GL117936. https://doi.org/10.1029/2025GL117936
Figure 1: Conceptual diagram illustrating the processes that shape the alkenone sedimentary record.
