Abstract

The polar regions are home to important and dynamic components of the silicon cycle, from subglacial weathering to biological production and carbon sequestration in marine sediments by silicifiers. The Arctic, parts of the Antarctic, and glaciated mountain ranges (the ‘third pole’) are also some of the most climatically sensitive locations on Earth, where the most dramatic warming and associated physical and chemical changes have been observed in recent decades. If we are to comprehend the implications of anthropogenic climate change for future oceans, we need to examine how such rapid change in the polar regions could be either amplified or mitigated by silicon cycle feedback mechanisms. Here, we will explore polar silicon cycling through the lens of isotope studies.

Subglacial weathering in polythermal (“wet-based”) glacial systems—mobilises silicon, both in dissolved form (DSi) and as reactive, amorphous particulates. However, the degree to which (and rate at which) this bioavailable silicon reaches the ocean or remains trapped within coastal fjord systems by physical, chemical and biological processes remains a matter of debate. Another major unknown is the role of fjord and marine sediments in silicon cycling: are particulate reactive silica phases (glacial weathering products, biogenic opal) preserved within sediments, or does sedimentary cycling release DSi back into the overlying water? We can use stable silicon isotopes to begin the careful disentangling of these different processes, each of which results in different—but overlapping—fractionation. We use Arctic and Chilean Patagonian case studies to illustrate how these silicon isotope measurements can be coupled together with trace metals and their stable isotopes, and radioisotopes, to build a more complete picture of the nature and rates of important silicon cycling components that are active in glaciated environments