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

Surprisingly heavy silicon isotopes in the surface and deep Arctic Ocean

Brzezinski and his colleagues report on a comprehensive study of the Arctic Ocean silicic acid concentrations and silicon isotopic composition…

14.09.2021

Science Highlights

Unique winter dataset of particulate and dissolved cadmium in the Indian sector of the Southern Ocean

Cloete and collaborators analysed particulate and dissolved cadmium at 7 stations in austral winter along a North South section off South Africa.

06.09.2021

Science Highlights

A new proxy for ocean iron bioavailability

The approach established and verified in this study, opens a new way for determining dissolved iron bioavailability in samples across the ocean.

23.07.2021

Science Highlights

Scavenging differentiates the distribution of cadmium, nickel, zinc and copper in the North Pacific Ocean

Zheng and co-authors observed sectional distributions of cadmium, nickel, zinc, and copper in the North Pacific Ocean during three GEOTRACES related cruises…

19.07.2021

Rechercher