GEOTRACES intercalibration of the stable silicon isotope composition of dissolved silicic acid in seawater

Dissolved silicon (Si) is a major oceanic nutrient and variations of its stable isotope values are reflecting the intensity of surface primary production. As for other isotopes, agreement between the different laboratories is crucial. Here, the first intercalibration study of the stable silicon (Si) isotopes in seawater (δ30Si(OH)4) is presented as a contribution to the international GEOTRACES programme.

Eleven laboratories from seven countries participated in the study. Si isotope measurements were performed on three different mass spectrometer types Neptune MC-ICP-MS, Nu Plasma MC-ICP-MS and a MAT 252 IRMS.

Two seawater samples from the North Pacific subtropical gyre (Station ALOHA) collected at 300 m (9 μmol Si L-1; ALOHA300) and at 1000 m (113 μmol Si L -1; ALOHA1000) water depth were analyzed.

Agreement among laboratories is considered very good with mean values for δ30Si(OH)4:

  • ALOHA300 = +1.68 ± 0.35 (2 s.d.; Median: +1.66 ± 0.13)
  • ALOHA1000 = +1.24 ± 0.20 (2 s.d.; Median: +1.25 ± 0.06)

For future studies analyzing δ30Si(OH)4 in seawater it is recommended to analyze ALOHA300 and ALOHA1000 and report these results to facilitate and evaluate comparability of data between laboratories.

17 Grasse l

Figure: δ30Si(OH)4 results from all groups for ALOHA300 (red circles) and ALOHA1000 (blue circles). The vertical lines indicates the mean value of all measurements for ALOHA1000 (blue) and for ALOHA300 (red). The data points represent the individual δ30Si(OH)4 values for Si isotopes measurements. Short vertical solid lines are the means obtained by individual laboratories for the two samples. Uncertainty in the mean for all measurements (2 s.d.) is indicated by the horizontal bars at the top of the figure (Modified from Grasse et al. 2017, JAAS). Click here to view the figure larger.

Reference:

Grasse, P., Brzezinski, M. A., Cardinal, D., de Souza, G. F., Andersson, P., Closset, I., et al. (2017). GEOTRACES inter-calibration of the stable silicon isotope composition of dissolved silicic acid in seawater. Journal of Analytical Atomic Spectrometry, 32, 562–578. DOI: 10.1039/C6JA00302H

Latest highlights

Science Highlights

Decline of the anthropogenic lead imprint to the ocean confirmed by data from the South West Atlantic Ocean

This study reveals that the mean lead concentrations in the surface waters of the western South Atlantic Ocean decreased by 34 % between the 1990s and 2011.

29.03.2023

Science Highlights

Irradiance-normalized non-photochemical quenching (NPQ): a new proxy of iron stress for phytoplankton

Ryan-Keogh and his colleagues used NPQ to fingerprint the photo-physiological response of phytoplankton to their environment.

06.03.2023

Science Highlights

Exhaustive modelling study of the oceanic neodymium parameters

The conclusion of this study reinforces the important role of the solid particles in driving the neodymium oceanic cycle.

02.03.2023

Science Highlights

Dissolved manganese distribution in the Arabian Sea reveals many variable triggers

Analysis of dissolved manganese on samples collected on GEOTRACES cruises allowed Singh and colleagues to establish its basin-wide distribution in the Arabian Sea.

01.03.2023

Rechercher