Hawaiian imprint on trace elements and isotopes in the central North Pacific: local and seasonal study


(Henning Fröllje, PhD Student)

The central North Pacific is poorly investigated with respect to its Nd isotope signature and REE cycling, and little is known about the contributions of volcanic islands, such as Hawaii, relative to dust input from Asian deserts to the surface water REE budgets. In this study, we used dissolved Nd isotope and REE data along with long-lived radium isotope activities from Hawaii Ocean Time-Series Station ALOHA and coastal waters from Oahu. The data are supplemented with seasonal samples from ALOHA, to potential study seasonal changes in dust input.

Fröllje, H., Pahnke, K., Schnetger, B., Brumsack, H.-J., Dulai, H., Fitzsimmons, J.N., 2016. Hawaiian imprint on dissolved Nd and Ra isotopes and rare earth elements in the central North Pacific: local survey and seasonal variability Geochimica et Cosmochimica Acta 189, 110-131.

Trace element input and cycling in the western subtropical to tropical Pacific

(Melanie Behrens, PhD Student)

The distributions of REE and e_Nd in the Pacific Ocean are still very rudimentary and the extent of different factors controlling these distributions are largely unknown. We measured dissolved REE and e_Nd along R/V SONNE transect SO223T in the western subtropical to tropical Pacific to study the relative influence of major water masses, the zonal current system of the equatorial Pacific, and element input from continents and volcanic islands on their distributions.

Rare earth elements in small volumes of seawater: new method and intercomparison

(Melanie Behrens, PhD Student)

The low (picomolar level) concentration of dissolved REE in seawater as well as time-consuming methods for their analysis have so far hindered their extensive use in marine studies. This study reports the first application of the automated seaFAST-pico system (Elemental Scientific Inc.) in offline mode and using multi-element isotope dilution inductively coupled plasma-mass spectrometry (ID ICP-MS) for the robust and rapid pre-concentration, purification, and analysis of dissolved REEs from small volumes of seawater (11-12 mL). In order to check the accuracy of the new method, we conducted an intercomparison among 4 laboratories using seawater from GEOTRACES intercalibration station SAFe from 3000 m water depth.

Behrens, M.K., Muratli, J., Pradoux, C., Wu, Y., Böning, P., Brumsack, H.-J., Goldstein, S.L., Haley, B., Jeandel, C., Paffrath, R., Pena, L.D., Schnetger, B., Pahnke, K. (2016).  Rapid and precise analysis of rare earth elements in small volumes of seawater - method and intercomparison. Marine Chemistry, 186, 110-120.dx.doi.org/10.1016/j.marchem.2016.08.006

Rare earth element and neodymium isotope distributions in the Central Arctic Ocean: trace element sources and transport (EU GEOTRACES)

(Ronja Paffrath, PhD student)

The Arctic Ocean is a unique ocean basin: it is almost land-locked with only restricted connections to the Atlantic and Pacific, and is marked by extended shelves, seasonal sea ice cover, high river input, and very low particle fluxes. Climate and ocean monitoring over the recent decades have shown that the Arctic is highly sensitive to climate change. Improving our understanding of geochemical processes in the Arctic and their interactions with the physical changes is therefore pivotal. As part of the EU GEOTRACES (www.geotraces.org) (add link) cruise P94 with R/V Polarstern, we collected seawater, suspended particles, dirty ice, and surface sediments to study the factors impacting the distribution of REE and e_Nd and to better understand the sources and mechanisms supplying trace elements to the Arctic. We are closely collaborating with other GEOTRACES scientists and in particular Dr. Michiel Rutgers van der Loeff, Dr. Walter Geibert, and Ole Veit (AWI Bremerhaven) on this project, who are measuring dissolved and particulate Pa and Th isotopes.

Biogeochemistry of silicon in the Central Arctic Ocean (EU GEOTRACES)

(Bianca Torres Liguori Pires, PhD Student / Claudia Ehlert, Scientist)

Silicon (Si) is a major element and an important nutrient mainly for diatoms. Diatoms are important primary producer that take up dissolved Si from the water to build a siliceous skeleton and that are responsible for the production of the majority of organic carbon in the oceans, which shows the importance of diatoms in both the global carbon and Si cycles. The stable Si isotope composition of different reservoirs like seawater or diatoms bears information on the dominant pathways and processes by which Si is transported to and cycled within the ocean. In most oceanic regions, the Si isotope composition of water masses varies as a function of input from land, primary productivity of diatoms in surface waters and the dissolution of their skeletons in deeper waters, and physical water mass circulation and mixing. The Arctic Ocean is a unique environment characterized by low biological productivity and highly seasonal Si utilization, extended shelf areas, high river discharge yet low particle fluxes, and seasonal sea-ice cover. This work is going to provide a baseline study on the present day Si isotope distribution in the Arctic for a better understanding of the general biogeochemistry of Si in the ocean and for future evaluation of the impact of climate change on the Si cycle.

Behavior of dissolved rare earth elements in the (near) absence of particle fluxes: GEOTRACES Process study in the oligotrophic South Pacific gyre

(Matthias Rehbein, MSc Student)

Due to its extreme remoteness from any continents, surface waters of the South Pacific Subtropical Gyre (SPG) are the most oligotrophic in the global ocean, with the lowest sea surface chlorophyll a concentrations and extremely low terrigenous input. Using seawater and surface sediment samples from R/V Sonne cruise SO245 (Antofagasta, Chile to Wellington, New Zealand), crossing the center of the SPG, we will examine the behavior of REEs and Nd isotopes in the absence of particle scavenging (in collaboration with R. Anderson’s group at LDEO measuring dissolved Pa, Th isotopes on the same samples), characterize the e_Nd signature of major Southern Ocean water masses, investigate the incorporation of bottom water e_Nd signals in surface sediments, and determine the source of the terrigenous component of the marine sediments in the SPG.