Lithium Isotopes
Lithium (Li) has two stable isotopes, 6Li (7.59%) and 7Li (92.41%). Because of their relatively large mass differences, remarkable isotopic fractionations (>60‰) can be expected in natural environments. Li isotopes are, therefore, becoming powerful tracers for various geochemical processes, including chemical weathering, hydrothermal alteration, magmatic differentiation, arc magmatism and recycling of mantle-crust in global scale. I have developed a new high-precision Li isotopic analysis on MC-ICP-MS (Huang et al., 2010), which allows me to investigate silicate weathering processes in mountainous rivers of Taiwan and other low- or high-temperature geochemical processes (Tsai et al., 2014). This technique has been significantly improved by using a new generation MC-ICP-MS (Neptune Plus) at AS-IES (Liu et al., submitted), and is currently used to evaluate the utility of the Li isotopic composition as tracers for silicate weathering intensity and other geochemical processes. Furthermore, Li isotopes in biogenic carbonates (e.g., foraminifera, surface and deep-sea corals) are under investigation in order to fully understand the main controls on the Li isotopic variations in biogenic carbonates (through an international collaborative research among AS-IES, WHOI, Rutgers University and National Cheng Kung University).
Boron Isotopes Boron (B) has two naturally occurring stable isotopes, 10B (19.9%) and 11B (80.1%). By means of relatively large mass difference and high volatility, the B isotopic compositions span a wide range in natural materials, ranging from -30 to +60‰, and therefore has been extensively used as a tracer for investigating surface weathering process, dehydration of subducted materials, early diagenesis, fluid-rock interaction and anthropogenic pollution in groundwater. The B isotopes also have received much attention in paleoceanographic studies, mainly due to its potential for the reconstruction of oceanic pH value. I have been involved in several studies using high-precision B isotopic analyses in marine pore waters, river waters, hydrothermal vent fluids and biogenic carbonates (corals and foraminifera) in order to better constrain the geochemical behaviors of elemental B and B isotopes in the hydrosphere (Huang et al., 2005; Wang et al., 2010; Liu et al., 2012) and the utility of the B isotopes in deep-sea corals as a reliable proxy for seawater pH (Anagnostou et al., 2012). By using surface corals from Guam Island, a l50 yr-long seawater pH record was reconstructed to evaluate the long-term ocean acidification in the western Pacific (Shinjo et al., 2013). At AS-IES, we have successfully developed a new accurate and high-precision B isotope technique for a variety of geological materials (Liu et al., submitted). Through a combination of the coralline B isotopes and clumped isotopes, as well as biogeochemical modeling, we are also trying to answer the questions about how shallow-water corals can regulate their calcifying fluid pH (or saturation state) in respond to ocean acidification/ocean warming (Mollica et al., in revision).
Strontium Isotopes
In tropical estuaries, plumes of freshened waters derived from runoffs or episodic floods (e.g., those caused by typhoons) greatly influence the physical (sediment dynamics), chemical (elements and nutrients), and biological conditions of these systems. They may also have profound effects on biogeochemical cycles in coastal environments. In addition to the riverine transport, submarine groundwater discharge may also have a significant impact on elemental inputs to the ocean. Tracing fresh water plumes is therefore critical for better understanding nutrient and chemical supplies in the coastal region. I have developed a new technique that is capable of measuring Sr isotope ratios with unprecedentedly high precision and applied it to trace the migration of the fresh water plume and water-mass mixing in the coastal ocean (Huang and You, 2007; Huang et al., 2011). I am currently collaborating with Prof. Chen-Feng You and Dr. Hou-Chun Liu at NCKU to further our understandings about the natural Sr isotopic fractionation in the hydrosphere/lithosphere through the combination of the stable Sr isotopes (δ88/86Sr) and radiogenic Sr isotopes (87Sr/86Sr), and investigate their potential applications for weathering processes (Liu et al., 2012; Liu et al., 2017). More recently, we have applied δ88/86Sr and 87Sr/86Sr (together with the Li-Mg isotope systems) to one of the most widespread carbon isotopic excursions in the Cambrian, Steptoean Positive Carbon Isotope Excursion (SPICE, ~500 Ma), to better constrain possible mechanisms for driving the SPICE event (in collaboration with Prof. Tin-Wai Ng at NTUE).
Other Traditional and Non-traditional Isotopes
My PhD and postdoc work also focuses on developing the state-of-the-arts isotope techniques to the fields of Marine Chemistry, Paleoceanography and Environmental Sciences. Other than the Li, B and Sr isotopes, I have been working on some other high-precision isotopic techniques (i.e., Mg, Ca, V, Zn, Cd, Nd, Hf, Pb and U-series isotopes), which can be widely applied to the fields of Geosciences and Marine Chemistry (Huang et al., 2012; 2014a). More recently, I am working closely with scientists from WHOI, US-GEOTRACES Pa-Th team, and AS-IES to develop and investigate the utilities of these traditional and non-traditional metal isotopes in a variety of natural materials in order to fully understand controlling mechanisms for their isotopic fractionations in natural environments, and the potential uses of these metal stable isotopes for environmental forensics. I expect that these new results can substantially improve our knowledge of the biogeochemical cycles of these trace elements and their isotopes on Earth surface, and applications of these isotope tracers for Geo- and Ocean Sciences (Hayes et al., 2015a, 2015b; Lerner et al., 2016; Anderson et al., 2016).
Trace Elements and Their Isotopes (TEIs) in Biogenic Carbonates and Paleo-applications
Reliable paleo-reconstruction obtained from the proxy-based approach relies on how much we know about these geochemical proxies and the proxy carriers. In addition to the theoretical perspectives, the empirical calibration is one of the key approaches to better understand mechanisms of TEIs incorporations and their relationships with environmental parameters. In the past few years, I have been involved in the calibration work on trace element ratios (Huang et al., 2008) and B-Sr isotopes in planktonic foraminifera using sediment-trap and core-top samples in the South China Sea (Huang et al., submitted). During my postdoc appointment at WHOI, I focused on core-top calibrations of trace element ratios and Nd isotopes in planktonic/benthic foraminifera, and further reconstruct the ocean state and deep ocean circulation over the last 25,000 years (Huang et al., 2014b). Our down-core records reveal similar glacial and interglacial contributions of Antarctic Intermediate Water (AAIW), and a pronounced decrease in the AAIW fraction during the North Atlantic deglacial cold episodes, Heinrich Stadial 1 and Younger Dryas, in the western Atlantic Ocean (Huang et al., 2014b; Howe et al., 2016; Howe et al., in revision), in response to the reduced Atlantic Meridional Overturning Circulation strength. On the other hand, I am also interested in the TEIs of the coral skeletons because of their potentials for extracting high-resolution climatic signals on annual/decadal/centennial timescales. The coral records can be used to understand the linkage between surface ocean state and abrupt climate events, such as El Niño/La Niña and typhoon events, and thus evaluate the impacts of these climatic events on coral growth. I am currently working with an international team (WHOI, Bristol University, and Rutgers University) to re-visit some trace elements and isotopic compositions in surface/deep-sea corals and planktonic/benthic foraminifera as proxies for environmental parameters in the ocean (Anagnastou et al., 2012).
Climate impacts on weathering intensity in mountainous rivers of Taiwan: Insights from Li-B-Mg-Sr-U isotope systems
Located on a collision boundary between the Eurasian Plate and Philippine Sea Plate, together with frequent earthquakes and extreme weather events, Taiwan is characterized by disproportionately high physical and chemical denudation rates over a variety of timescales. Therefore, a detailed investigation on riverine chemistry of Taiwan offers a great opportunity to study the interplay among climate, tectonic activity, and weathering intensity, and their impacts on geochemical behaviors of elements and isotopes in the drainage basins, as well as to provide critical constraints on intensities and rates of chemical/physical weathering within the river catchments. One of my on-going projects is to conduct a 3-year time-series study (2015-2018) using the multi-tracer approach (Li-B-Mg-Sr-U) in the selected river catchments of Taiwan. The results from this project not only provide an improved understanding of how climate influences weathering intensity in small mountainous rivers of Taiwan, but also further constrain the main controls on the isotopic fractionations of Li-B-Mg-Sr-U isotopes in the river catchments.
