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Fluvial sediments are important archives of paleoenvironments. However, variations in sediment production and transport processes greatly influence sediment geochemistry and resultant interpretations of ancient conditions. Tectonically-active tropical regions are particularly sensitive to climate feedbacks because these areas are often characterized by high precipitation rates, rapid erosion and short sediment residence times. We analyzed the hydrogen and carbon isotope composition of plant-derived n-alkanes (δ2Hn-alkane and δ13Cn-alkane) in sediment cores along the Gaoping River-submarine canyon system in southwestern Taiwan to examine climatic and geomorphic controls on isotope geochemical signatures of fluvial sedimentary archives. These records span the last ∼26 kyr and provide critical insight into the temporal and spatial variations in sedimentary biomarker isotopes within a source-to-sink system. Isotope data are coupled with new results from an iCESM 1.2 Earth System Model of precipitation isotopes during the last glacial-interglacial cycle. Biomarker isotope and modeling results support two important conclusions. First, biomarker isotope values change by ∼10 to 15‰ in δ2Hn-alkane and ∼1 to 2‰ δ13Cn-alkane in offshore SW Taiwan through the late Quaternary deglaciation. These shifts are consistent with iCESM predictions and other records from the South China Sea and are best explained by a shift in isotope hydrology due to regional warming and biologic responses to increased atmospheric pCO2. Second, the δ2Hn-alkane of biomarkers preserved in onshore sediments proximal to the mountain range is ∼15 to 20‰ more negative than biomarkers deposited in offshore sites, and the temporal change in carbon isotopes exceeds that observed in the offshore deposits. The onshore core locality is proximal to the orogen and characterized by a mean elevation > 1 km compared to the offshore site, which has a mean catchment elevation of ∼500 m. These data show that depositional setting and catchment hypsometry strongly bias the geochemical signature of sediments transported through the river system. The magnitude of isotopic variability generated by catchment geometry and sediment integration greatly exceeds the change associated with warming during deglaciation. This result suggests that catchment integration processes may play a similar or larger role in shaping fluvial geochemical records in tropical mountain systems than climatic factors.

Submarine canyons are major conduits for delivery of sediments originating from the continental margin into the deep sea. Here we analyze the effects of changing sea levels and climate (e.g. sediment supply) on the frequency of turbidites over the last 26 kyr. Our study is based on high resolution age controls for turbidites in core MD178-10-3291 from a water depth of 2070 m on the flank of the Gaoping Canyon offshore in SW Taiwan. Unlike most other submarine canyons worldwide, the head of the Gaoping Canyon has remained connected to the river mouth during the recent flooding of the continental shelf. Our results reveal that turbidity currents are less frequent during periods of sea-level lowstand. In contrast, turbidity currents have been more frequent since ~ 12 kyr BP, during the final stage of rising sea level and sea-level highstands. This may be the result of increased terrestrial sediment delivery due to enhanced rainfall intensity. Moreover, comparing to other source-to-sink systems, the turbidite occurrence in the flank of Gaoping Canyon through the last glacial cycle might have been more strongly influenced by climatic changes due to short sediment storage/response time.

A compressed fossil seed, described as Carpolithes sp., is found in the coal-bearing Miocene Shihti Formation from the Lifeng coal mine, Sanshia District of the New Taipei City. The fossil is generally rounded with a diameter of ca. 10 mm in lateral view. The anatomical features of the testa epidermal cells were observed using anatomical analysis. The anatomical features of the megafossil organ from the Formation are reported for the first time.