High-resolution Boron and beyond Geologic reconstructions for carbon and climate processes

Introduction

The link between climate and CO2 is not always straightforward, particularly during periods of multiple climatic and environmental changes. However, atmospheric carbon dioxide (CO2) plays an important part in determining climate on human and geological timescales.

Climate Sensitivity

For example, the state dependency of climate sensitivity, which is the response of Earth’s temperature to CO2, is a critical unknown for future climate projections and policy strategies.

Antarctic Ice Sheet Response

Another unknown is the response of the Antarctic Ice Sheet (AIS) at different CO2 thresholds for its melting and growth, known as “hysteresis.” This response will ultimately determine the magnitude of future sea level rise.

Historical Records

Existing records suggest that the ice sheet margin waxed and waned since the Eocene, approximately 50 million years ago (Ma), while CO2 varied within the likely range projected for the year 2100 and Earth’s temperature progressively cooled.

Project Goals

HighBorG aims to resolve climate-AIS-CO2 unknowns during three periods of the geologic past:

1. 52-46 Ma: Hot Earth, high CO2, likely ice-free.
2. 39-23 Ma: Largely unexplored period when AIS was established.
3. 17-13 Ma: Cold Earth, low CO2, dynamic AIS.

Methodology

HighBorG focuses on reconstructing CO2-climate feedbacks at millennial/orbital timescales. This represents a medium risk, high gain opportunity necessary to resolve warming and cooling periods at different climate states.

To achieve this, a new automated system for purification-analysis will be developed, accompanied by a laser ablation split-stream approach. This will utilize new marine archives and cutting-edge methodologies.

Seasonal Reconstructions

Seasonal reconstructions from contemporaneous tropical corals will provide a novel way to constrain seawater composition, which is necessary to obtain accurate estimates of CO2.

Earth System Modelling

Earth system modelling incorporating these reconstructions will provide a new understanding of the mechanisms driving state-dependent interactions between Earth’s orbit, CO2, temperature, cryosphere, and carbon cycling. This will increase our confidence in sea level and temperature projections for the future.