Science Highlights

Short-Term Variability of Dissolved Rare Earth Elements and Neodymium Isotopes in the Entire Water Column of the Panama Basin

Patricia Grasse and co-workers (2017, see reference below) present new dissolved neodymium isotope compositions (εNd) and rare earth element (REE) concentrations from the Panama Basin.

REE concentrations peak at the surface reflect high lithogenic inputs from the nearby Central American Arc (CAA) resulting in highly radiogenic εNd signatures, with the observation of the most radiogenic value measured for seawater to date (+4.3). Intermediate and deep waters of the Panama Basin (mean εNd value = 0) are significantly more radiogenic than the inflowing water masses from the Peruvian Basin (−1.1 to −6.6 εNd). This demonstrates that the highly radiogenic Nd isotope compositions must result from release of radiogenic Nd through partial dissolution of volcanic material of the CAA. The re-occupation of one station demonstrates that the high amounts of radiogenic Nd released from these particles can reset water mass Nd isotope and REE signatures of the entire Panama Basin water column within 3.5 years, clearly an area where water masses acquire their signatures before they are advected to the open ocean.

Large amounts of REEs readily released from volcanic particles on such short time scales may require a different parameterization of the Nd isotope signal acquisition processes of water masses in models of the oceanic Nd isotope distribution and are important for the seawater Nd budget.

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Figure: (a) Map of sampling locations during Meteor Cruise M90 (Oct./Nov. 2012) in the Panama Basin together with the location of re-occupied station 160 sampled previously during Cruise M77-4 in February 2009. The dashed grey line indicates the approximate position of the Intertropical Convergence Zone (ITCZ) in spring and late summer (b) Water column distribution of St. 1555 eNd (filled black circles) and Nd concentrations (open black circles) together with previously occupied St.160 eNd (filled red squares) and Nd concentrations (open red squares) (Grasse et al., 2012). Please click here to view the figure larger.


Grasse, P., Bosse, L., Hathorne, E. C., Böning, P., Pahnke, K., & Frank, M. (2017). Short-term variability of dissolved rare earth elements and neodymium isotopes in the entire water column of the Panama Basin. Earth and Planetary Science Letters, 475, 242–253. DOI: 10.1016/j.epsl.2017.07.022


Manganese in the west Atlantic Ocean in the context of the first global ocean circulation model of manganese

Marco van Hulten and co-workers (2017, see reference below) ran a global ocean model to understand manganese (Mn), a biologically essential element. The model shows that:

(i) in the deep ocean, dissolved [Mn] is mostly homogeneous ~0.10—0.15 nM. The model reproduces this with a threshold on MnO₂ of 25 pM, suggesting a minimal particle concentration is needed before aggregation and removal become efficient.

(ii) The observed distinct hydrothermal signals are produced by assuming both a strong source and a strong removal of Mn near hydrothermal vent.

17 vanHulten l2Figure: (A) The modelled dissolved [Mn] (nM) at the Zero-Meridian section component of the GIPY5 cruise dataset, and the West Atlantic GA02 GEOTRACES section cruise (annual average). Observations at the transects are presented as coloured dots. (B) Worldmap showing cruise transects for GA02 (red) and GIPY5 (green, in the Atlantic sector of the Southern Ocean). Please click here to view the figure larger. Modified from Biogeosciences.


van Hulten, M., Middag, R., Dutay, J.-C., de Baar, H., Roy-Barman, M., Gehlen, M., Tagliabue, A., and Sterl, A. (2017) Manganese in the west Atlantic Ocean in the context of the first global ocean circulation model of manganese, Biogeosciences, 14, 1123-1152. DOI: 10.5194/bg-14-1123-2017.

Surprising cadmium isotope results north of the Subantarctic Front in the South West Atlantic Ocean

Xie and co-workers (2017, see reference below) report cadmium (Cd) isotopic compositions from five stations and 15 tow-Fish surface waters from 50ºS to the equator along GEOTRACES GA02 Leg 3. Along this transect, the coupled Cd concentrations and Cd isotopes reflect classical behaviour dominated by preferential uptake of light Cd by the biological species at the surface, release in the twilight zone and water mass mixing deeper. Surprisingly, ε112/110Cd displays a "flattening off" pattern in the surface and subsurface waters of stations north of the Subantarctic Front, while Cd concentrations decrease to low levels; this observation can be extended to the global Cd isotope dataset at hand for Cd concentrations below a nominal value of 0.1 nmol kg-1. Two explanations are proposed for this behaviour: 1) either Cd is bound by organic detritus, colloids or ligands and passes the 0.2μm filtration of the samples, products which could dominate ε112/110Cd over that of the dissolved pool; or 2) the ε112/110Cd values result from a simple open system, steady-state model for the (sub)surface layer, fed with an in-flux of Cd from deeper waters.

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Map of the five super stations (color circles) and tow-Fish surface sites (crosses) for Cd isotopes along GA02 Leg 3 (Left), and Cd isotope systematics in the western South Atlantic (Middle) and the global ocean (right). Color circles for profile samples, and open circles for tow-Fish seawater samples (this study). In the right-hand panel: grey diamonds – North Atlantic (Boyle et al., 2012; Conway and John 2015a; John and Conway, 2014); open triangles – North (Conway and John, 2015b; Ripperger et al., 2007) and South Pacific (New Zealand (Gault-Ringold et al., 2012), South China Sea and Philippine Sea (Yang et al., 2012, 2014)); open squares – Southern Ocean (Abouchami et al., 2011, 2014; Xue et al., 2013). Red dashed lines in the middle and right-hand panels schematically highlight the evolution of seawater e112/110Cd toward low Cd concentrations. Error bars (2s) are shown. Click here to view the figure larger.


Xie, R. C., Galer, S. J. G., Abouchami, W., Rijkenberg, M. J. A., de Baar, H. J. W., De Jong, J., & Andreae, M. O. (2017). Non-Rayleigh control of upper-ocean Cd isotope fractionation in the western South Atlantic. Earth and Planetary Science Letters (Vol. 471). DOI: 10.1016/j.epsl.2017.04.024

Shelf sediment dissolved iron source via non-reductive dissolution in the Gulf of Alaska

Crusius and co-workers (2017, see reference below), reveal temporal and spatial variability in the sources of iron (Fe) to the northern Gulf of Alaska, based on data from cruises from three different seasons from the Copper River (AK) mouth to beyond the shelf break.  April data are the first to describe late winter Fe behavior before surface-water nitrate depletion began.  Sediment resuspension during winter and spring storms generated high “total dissolvable Fe” (TDFe) concentrations of ~1000 nmol kg-1 along the entire continental shelf, which decreased beyond the shelf break.  In July, high TDFe concentrations were similar on the shelf, but more spatially variable, and driven by low-salinity glacial meltwater.  Conversely, dissolved Fe (DFe) concentrations in surface waters were far lower and more seasonally consistent, ranging from ~4 nmol kg-1 in nearshore waters to ~0.6-1.5 nmol kg-1 seaward of the shelf break during April and July, despite dramatic depletion of nitrate over that period. The April DFe data can be simulated using a simple numerical model that assumes a DFe flux from shelf sediments, horizontal transport by eddy diffusion, and removal by scavenging.  Calculations suggest dust is an important Fe source beyond the shelf break.

17 Crusius lFigure:  Seasonal and spatial variability in Fe in the northern Gulf of Alaska: a) Sampling region in the northern Gulf of Alaska extending from the Copper River Mouth to ~50 km beyond the shelf break.  The surface water transect was carried out along the line defined by the green dots (which define sampling stations).  This is superimposed upon a MODIS image from 9 April, 2010 that shows resuspended sediments (light blue) landward of the 500-m depth contour (orange line).  b) Surface water total dissolvable Fe (TDFe) concentrations and salinity plotted versus distance from shore during April, May and July.  c) Dissolved Fe (DFe) data (blue squares) from April, along with several time-dependent model simulations that bracket the data, with varying flux of DFe from the shelf sediments, horizontal eddy diffusion, and removal by chemical scavenging. Click here to view the figure larger.


Crusius, J., A. W. Schroth, J. A. Resing, J. Cullen, and R. W. Campbell (2017), Seasonal and spatial variabilities in northern Gulf of Alaska surface-water iron concentrations driven by shelf sediment resuspension, glacial meltwater, a Yakutat eddy, and dust, Global Biogeochem. Cycles, 31, doi:10.1002/2016GB005493.

Low iron sulfide precipitation rate in hydrothermal fluids during the early stage of mixing

Waeles and co-authors (2017, see reference below) report for the first time on the dissolved-particulate partition of iron (Fe) after in situ filtration at the early stage of mixing of hydrothermal fluids with seawater. This study was performed at three hydrothermal fields on the Mid-Atlantic Ridge (Lucky Strike, TAG and Snakepit). For the different vents examined, Fe predominantly occurred (>90%) in the dissolved fraction and dissolved Fe showed a strictly conservative behavior, arguing for low iron-bearing sulfide precipitation in basalt-hosted systems with low Fe:H2S ratios. The small part of Fe being precipitated as sulfides in the mixing gradient (<10%) is restricted to the inclusion of Fe in minerals of high copper (Cu) and zinc (Zn) content because the kinetic of pyrite formation is slow compared to the time scale of mixing processes. Their works also show that secondary venting, i.e. lower temperature clear smokers and diffusive venting, is a source of Fe-depleted hydrothermal fluids and provide new constrains on Fe fluxes from hydrothermal venting one of the main present issue of the GEOTRACES programme.

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 Dissolved Fe (dFe), particulate Fe (pFe) and other chemical species concentrations measured at Aisics, a black smoker vent on the Lucky Strike vent field. Concentrations are given as a function of temperature and dissolved Mn (dMn) which is used as the conservative tracer. a) Dissolved Fe occurs essentially as Fe(II) species and coexists with sulfide until the coldest part of the mixing gradient due to the kinetically limited formation of pyrite particles. b) As opposed to Fe, Zn and Cu precipitate quantitatively before venting and/or during the very early stage of mixing (T > 150°C); Zn and Cu were mainly found as particulate rather than as dissolved species over the studied gradients. c) The data also showed that secondary venting, i.e. lower temperature auxiliary smokers and diffusive venting, is a source of Fe-depleted fluids. Click here to view the figure larger.


Waeles, M., L. Cotte, B. Pernet‐Coudrier, V. Chavagnac, C. Cathalot, T. Leleu, A. Laës‐Huon, A. Perhirin, R. Riso, and P. Sarradin (2017), On the early fate of hydrothermal iron at deep‐sea vents: a reassessment after in‐situ filtration, Geophysical Research Letters. DOI: 10.1002/2017GL073315.


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 Data Assembly Centre (GDAC)


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