Increased typhoon activity led to higher land-to-sea organic carbon export in the deglacial northwest subtropical Pacific: Insights from lipid biomarkers and sediment geochemistry

The evolution of typhoon activity in Taiwan at glacial-interglacial timescales remains poorly constrained, as modelling past typhoon trajectories is challenging and terrestrial archives rarely extend beyond the Holocene due to high erosion rates. However, the land-to-sea transfer of terrestrial material is mainly controlled by typhoons, with more than 75% of the annual flux occurring within less than 1% of the year. Particulate organic carbon (POC) transferred during typhoon-induced floods represents 77 to 92% of the annual biospheric (vegetation- and soil-derived) POC flux. Consequently, investigating changes in the flux of biospheric terrestrial POC in marine sediments off eastern Taiwan, where rivers connect directly to the canyon regardless of the relative sea-level due to the absence of a broad continental shelf, provides an opportunity to assess past variations in typhoon activity.

At this end, we analyzed lipid biomarkers together with sedimentological and geochemical parameters from a sediment core collected offshore eastern Taiwan. Coarser grain sizes, higher TOC, long chain n-alkanes and soil-derived brGDGTs (IIIa/IIa < 0.59) accumulation rates during the deglaciation relative to the Holocene indicate substantially enhanced land-to-sea carbon transport linked to more frequent and/or more energetic turbidity activity. In addition, higher CPI values and reduced age offsets between planktonic foraminifera and bulk organic matter radiocarbon dating over the same interval point to a larger fraction of biospheric terrestrial POC transfer to the marine sediments compared to the Holocene. Together, these results point to an enhanced typhoon activity affecting Taiwan during the deglaciation, in agreement with recent model simulations indicating a higher typhoon genesis potential at that time. Given the difficulties in simulating past typhoon activity in Taiwan, or in recording it from terrestrial archives, our approach provides an alternative way to constrain past changes in typhoon activity affecting the island. This also raises the possibility that, if typhoon activity affecting Taiwan were to increase due to a northward shift in typhoon pathways as projected under ongoing global warming, the eastern margin of Taiwan could turn into a carbon sink.