Open Access Publications | Past Climate Change

The Response of Magnesium, Silicon, and Calcium Isotopes to Rapidly Uplifting and Weathering Terrains: South Island, New Zealand

Si, Ca and Mg isotopes do not really correlate with anything. These findings highlight that major (high concentration) elements are used by too many systems (including a nutrients) to be a tracer of a single process.

Trace systems like lithium and uranium isotopes (Robinson et al., 2004; Pogge von Strandmann and Henderson, 2015) show correlations with rock exposure rates, meaning they are useful weathering tracers.

Hydrothermal and Cold Spring Water and Primary Productivity Effects on Magnesium Isotopes: Lake Myvatn, Iceland

Lake Myvatn, Iceland, is one of the most biologically productive lakes in the northern hemisphere, despite seasonal ice cover. Hydrothermal and groundwater springs make up the dominant source to this lake, and we investigate their Mg isotope ratio to assess the effect of mid-ocean ridge hydrothermal springs, which are the primary modern sink of seawater magnesiumWe also examine a time series in the only outflow from this lake, the Laxa River, to assess the effects of seasonal primary productivity on Mg isotopes.

The effect of shell secretion rate on Mg / Ca and Sr / Ca ratios in biogenic calcite as observed in a belemnite rostrum

Belemites, an extinct type of cephalopod, are often used as archives of past seawater chemistry. However, their shells (‘rostrums’) are quite diverse and heterogeneous. This paper investigates how their growth rates influence what chemical signals they record.

Selenium isotope evidence for progressive oxidation of the Neoproterozoic biosphere

Examination of the redox state of the oceans in the late Neoproterozoic – the time known as the Neoproterozoic Oxygenation Event at about 600 million years ago – when oxygen levels dramatically increased. This led directly to the evolution and radiation of the animals. It was previously thought that oxygen levels rose rapidly at about 570 Myr ago. Instead we find that levels started rising much earlier (about 650 Myr ago), and took at least 100 million years to rise to the level that allowed animals to evolve.

Global climate stabilisation by chemical weathering during the Hirnantian glaciation

Analysis of silicate weathering behaviour through the Hirnantian glaciation and major mass extinction about 445 million years ago. Silicate weathering (the major CO2 drawdown mechanism and hence climate control) decreases during the cooler climate, meaning that less CO2 is removed from the atmosphere during that time. Eventually this allows the climate to recover back to warmer temperatures. This is one of the first demonstrations that the weathering thermostat operates in geological history.

Using Mg Isotopes to Estimate Natural Calcite Compositions and Precipitation Rates During the 2010 Eyjafjallajökull Eruption

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The dissolution of olivine added to soil: Implications for enhanced weathering

Silicate weathering is a primary natural method for removing atmospheric CO2, and hence controlling climate. Enhanced weathering is a potential geoengineering method for speeding up this removal, to combat man-made climate change, by grinding silicate rocks very finely, and ploughing them into fields. We investigate the dissolution rate of silicate materials when ‘ploughed’ into experimental rock cores.

Modern and Cenozoic records of seawater magnesium from foraminiferal Mg isotopes

The first examination of magnesium isotopes in seawater stretching over the past 40 million years. Magnesium is directly involved in the carbon cycle, as it is the precipitation of Mg-rich carbonates (such as dolomite) that sequesters atmospheric CO2. We find that dolomite formation dramatically decreased in the most recent 10 million years, meaning that CO2 must have been sequestered in other ways.