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High-Latitude Controls on the Silicon Isotope Composition of Silicic Acid in the South Pacific
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DOI：10.1029/2025GB009008.png)
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Abstract
En 中文
We present measurements of silicon isotopes in silicic acid, δ30Si, from GEOTRACES GP17OCE between 20°S and 60°S along 152°W. The section sampled key water masses, allowing assessment of controls on large-scale δ30Si features. Observational data paralleled results of a data-constrained Si isotope model and are consistent with nutrient trapping and partial nutrient consumption in polar surface waters leading to the accumulation of light silicon isotopes in the deep Southern Ocean (SO) and transport of the residually heavy fraction northward within Sub-Antarctic Mode Water (SAMW) and Antarctic Intermediate Water (AAIW). Deep-water δ30Si values were nearly constant along isopycnals in the South Pacific, with vertical gradients driven by an increasing fractional contribution of isotopically light regenerated silicic acid with depth. Isotope values in deep waters from the SO to Tahiti exhibited a greater range than previously observed in the South Pacific or predicted by models, with δ30Si falling between 1.19‰ and 1.45‰. SAMW and AAIW exhibited relatively heavy, uniform δ30Si. Model results suggest that these mode waters are composed of preformed silicic acid subducted in the outcropping region and regenerated silicic acid sourced in roughly equal measure from polar waters and northern distal sources. Distal input is mainly through entrainment of underlying Upper Circumpolar Deep Water into AAIW.
Keywords:
nutrient trapping
mode waters
silicon isotopes
southern ocean
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