Silicon isotope and silicic acid uptake in surface waters of Marguerite Bay, West Antarctic Peninsula

Cassarino, Lucie; Hendry, Katharine R.; Meredith, Michael P. ORCID: https://orcid.org/0000-0002-7342-7756; Venables, Hugh J. ORCID: https://orcid.org/0000-0002-6445-8462; De La Rocha, Christina L.. 2017 Silicon isotope and silicic acid uptake in surface waters of Marguerite Bay, West Antarctic Peninsula. Deep Sea Research II: Topical Studies in Oceanography, 139. 143-150. 10.1016/j.dsr2.2016.11.002

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This article has been accepted for publication and will appear in a revised form in Deep Sea Research II, published by Elsevier. Copyright Elsevier.
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Abstract/Summary

The silicon isotope composition (δ30Si) of dissolved silicon (DSi) and biogenic silica (BSi) provides information about the silicon cycle and its role in oceanic carbon uptake in the modern ocean and in the past. However, there are still questions outstanding regarding the impact of processes such as oceanic mixing, export and dissolution on the isotopic signature of seawater, and the impacts on sedimentary BSi. This study reports the δ30Si of DSi from surface waters at the Rothera Time Series (RaTS) site, Ryder Bay, in a coastal region of the West Antarctic Peninsula (WAP). The samples were collected at the end of austral spring through the end of austral summer/beginning of autumn over two field seasons, 2004/5 and 2005/6. Broadly, for both field seasons, DSi diminished and δ30Si of DSi increased through the summer, but this was accomplished during only a few short periods of net nutrient drawdown. During these periods, the δ30Si of DSi was negatively correlated with DSi concentrations. The Si isotope fractionation factor determined for the net nutrient drawdown periods, ɛuptake, was in the range of -2.26 to -1.80‰ when calculated using an open system model and -1.93 to -1.33‰ when using a closed system model. These estimates of ɛ are somewhat higher than previous studies that relied on snapshots in time rather than following changes in δ30Si and DSi over time, which therefore were more likely to include the effects of mixing of dissolved silicon up into the mixed layer. Results highlight also that, even at the same station and within a single growing season, the apparent fractionation factor may exhibit significant temporal variability because of changes in the extent of biological removal of DSi, nutrient source, siliceous species, and mixing events. Paleoceanographic studies using silicon isotopes need careful consideration in the light of our new results.

Item Type:	Publication - Article
Digital Object Identifier (DOI):	10.1016/j.dsr2.2016.11.002
Programmes:	BAS Programmes > BAS Programmes 2015 > Polar Oceans
ISSN:	0967-0645
Additional Keywords:	silicon, isotopes, fractionation, time series, Ryder Bay, Southern Ocean
NORA Subject Terms:	Marine Sciences Chemistry
Date made live:	08 Nov 2016 13:26 +0 (UTC)
URI:	https://nora.nerc.ac.uk/id/eprint/512258

Item Type:

Publication - Article

Digital Object Identifier (DOI):

10.1016/j.dsr2.2016.11.002

Programmes:

BAS Programmes > BAS Programmes 2015 > Polar Oceans

ISSN:

0967-0645

Additional Keywords:

silicon, isotopes, fractionation, time series, Ryder Bay, Southern Ocean

NORA Subject Terms:

Marine Sciences
Chemistry