FEST: Titrating System Earth with Carbon Dioxide

Friday Earth Sciences Talk

Speaker: Prof. Dr Jack Middelburg

Atmospheric carbon dioxide concentrations have varied over much of the geological history and are increasing at unprecedented in the Anthropocene. Uptake and storage of anthropogenic carbon dioxide in the ocean is related to the reaction of dissolved carbon dioxide with water to form bicarbonate (and minor quantities of carbonic acid and carbonate). Alkalinity, the excess of bases in solution, governs the efficiency at which this occurs and provides buffering capacity towards acidification.

Here I present the biogeochemical processes impacting the ocean carbonate system over multiple timescales. Over geological time scales alkalinity input to the ocean from weathering should be in balance with removal via carbonate mineral burial in the sea. However, a re-evaluation of the modern oceanic alkalinity balance revealed that the so far neglected riverine delivery of particulate inorganic carbon should be included to balance inputs and outputs.

Next I present a retrodiction of ocean alkalinity, dissolved inorganic carbon and pH over the last 50 million years. At intermediate time scales (decades to thousands of years), the marine carbon system is governed by carbonate compensation mechanisms, i.e. changes in calcium carbonate production and dissolution, and I argue that we need to distinguish between biological and chemical carbonate compensation. At the shortest time scale, ocean chemistry is buffered by proton transfer among various dissolved species. These processes are well understood and can be used to quantify the impact of individual biogeochemical processes on the pH of seawater.

With the Friday Earth Sciences Talks (FEST) we intend to bring the departments of Earth Sciences and Physical Geography together. The aim is to present (mostly) Utrecht-based Earth Sciences in an accessible way in order to stay familiar with each other’s work across disciplines. Alumni and students are also invited, in particular MSc students in Earth Sciences.