CO2 uptake via chemical weathering of glacial particles in the ocean.

Photo by N. Webster

PROJECT

CO2 uptake via chemical weathering of glacial particles in the ocean.

Overview

Chemical weathering of primary silicate minerals removes CO2 from the atmosphere. CDR
proposals envision widespread addition of fine-grained particles to the ocean to accelerate
weathering. Natural glacial melting adds fine weatherable particles to the coastal ocean and
can test this approach, without mining, milling, or particle distribution. Prince William Sound
(PWS), AK, is a deep estuary where multiple glaciers discharge particles into fjords. Each
fjord offers semi-independent experimental conditions with unique particle mineralogy, water
flow rates, and biogeochemical fluxes. We have identified candidate PWS fjords that span a
range of sediment input rates, including a control without glacial inputs, some with glaciers
overlying granitic rocks, and another with a glacier overlying rapidly weathering tholeitic
metabasalt. Additionally, acid mine drainage, localized to specific fjords, can test whether pH
reduction is a viable strategy to accelerate weathering. Glacial fjords follow classic estuarine
circulation with sediment-laden water flowing outward along the surface and new seawater
flowing inward at depth. This well-characterized circulation makes fjords a natural reactor and
an ideal location to measure rates. Distance along the outward flow path represents longer
particle weathering times and allows for cumulatively longer air-sea gas exchange, while
estuarine return flow accumulates fluxes from particle weathering in the sediments. We will
measure alkalinity fluxes, geochemical proxies for weathering, and dissolved trace metals
along these flow paths as well as tracers for weathering in sediment pore waters. We will also

measure CO2 uptake in the surface water together with geochemical proxies that can attribute
this uptake to specific processes. Using this natural laboratory we will determine the rate of
alkalinity addition from particle weathering in real world seawater conditions; test the link
between alkalinity addition and atmospheric CO2 removal; and evaluate how metals released
during weathering impact marine systems. These data will inform feasibility studies, uncover
scaling issues, and provide a proof of concept in support of future CDR efforts.