Associate Professor David Heslop

My research focuses on a wide variety of topics, but is founded in the fields of palaeomagnetism and rock magnetism. I'm also working on a number of collaborative projects to develop data inference methods in several different research areas, including paleoclimate reconstruction. The following sections describe some of my recent research.

Climate Sensitivity

As atmospheric CO₂ increases due to human activities, the Earth will warm. But how much warming can be expected? Climate sensitivity describes how much global average surface temperature will warm with a given increase in atmospheric CO₂. While this is a simple definition, estimating climate sensitivity is difficult because Earth's climate system is complex with several poorly understood interacting parts. One approach to estimating climate sensitivity is to quantify how Earth's climate changed because of variations in atmospheric CO₂ through geological time. This information is invaluable, but it is patchy and has large uncertainties that make estimating climate sensitivity challenging. Existing statistical techniques may underestimate climate sensitivity and, thus, underestimate future warming. We developed an alternative Bayesian approach to determining climate sensitivity that overcomes the underestimation problem and demonstrated its performance using geological data from the Eocene epoch. This work was published in Paleoceanography and Paleoclimatology (doi:10.1029/2024PA004880) with the figure below used as the cover image.

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Estimation of climate sensitivity based on Eocene atmospheric CO₂ radiative forcing and global mean surface temperature (GMST). Our published Bayesian errors-in-variables (EIV) approach overcomes the underestimation bias used in more traditional approaches such as ordinary least squares (OLS). 

Palaeomagnetic Bootstrap Statistics

Statistical inference is the process of using observations to infer the properties of an unobserved population. An example of this process in paleomagnetism (the study of Earth's ancient magnetic field based on information preserved in geological materials) is a test of whether two sets of field directions have a common mean. Traditional statistical methods used to address this question make assumptions about the properties of the observations, which are known to be invalid in many cases. An alternative approach is so-called bootstrapping, which relaxes assumptions about the observations and can then be applied more widely. In this study, we show how bootstrapping can be applied to paleomagnetic observations within the interpretational structure of existing paleomagnetic statistics, thus, providing a consistent inference framework. Furthermore, using numerical experiments we investigate how many paleomagnetic observations are required for bootstrapping to yield reliable results. This work was published in the Journal of Geophysical Research: Solid Earth (doi:10.1029/2023JB026983). 

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Paleomagnetic directions from the Hector Formation, Mojave Block as reported by MacFadden et al. (1990) (filled and open symbols represent normal and reversed polarity directions, respectively). Small gray points represent example pseudosample mean directions for the normal polarity directions. The 95% confidence regions (ellipses) estimated using the bootstrap approach described in using our new bootstrap and the approach of Tauxe & Constable 1991 are shown in black and red, respectively.

Estimating Plio-Pleistocene North African monsoon runoff into the Mediterranean Sea and temperature impacts

We investigated long-term changes in monsoon rains over North Africa, which annually result in freshwater flowing into the Mediterranean Sea. Over geological time, Earth's orbital variations have played a significant role in shaping the monsoon and, consequently, the quantity of freshwater entering the Mediterranean. Foraminifera, small marine organisms, record the oxygen isotope composition of their environment in their shells. Notably, the oxygen isotope balance in North African monsoon rains and the Mediterranean Sea differ, but eventually mix upon the freshwater entering into the Mediterranean. Our research combines a statistical analysis of oxygen isotope data preserved in foraminifera shells with a numerical model of the Mediterranean Sea, enabling us to estimate changes in monsoon freshwater input into the Mediterranean over the past 5 million years. This information not only enhances our understanding of monsoon evolution but also provides insights into the potential for hominin migrations in a more lush North African landscape characterized by higher rainfall than today. This work was published in Paleoceanography and Paleoclimatology (doi:10.1029/2023PA004677).

Quantile regression of the ODP Site 967 d18O record was used to deconvolve the signal into components related to sea-level change and freshwater runoff from North Africa.

Assessing Paleosecular Variation Averaging and Correcting Paleomagnetic Inclination Shallowing

Paleomagnetic vectors recorded by rocks and archeological materials yield information on the structure of the magnetic field through Earth's history. The geomagnetic field mostly resembles a geocentric dipole aligned with the spin axis, but the directions at any given time and place generally deviate from this simple model. Data sets produced over several decades help define global magnetic field behavior. We updated a compilation of paleomagnetic data and used it to establish a new field model representative of the last 10 million years. Prior or emerging data sets can be tested against the model to see whether the two agree in terms of field structure and variability. We tested data sets as old as 1.1 billion years and found them compatible with the model. Moreover, this model can also assess, and potentially correct data from sedimentary rocks that may have suffered from inclination shallowing. Although other correction methods exist, our approach employs a more complete description of the geometry of directional data, thereby allowing a more quantitative comparison of empirical and predicted distributions. Corrected inclinations and their uncertainties define paleolatitudes more accurately, key for plate tectonic and paleoclimatic reconstructions. This work was published in the Journal of Geophysical Research: Solid Earth (doi:10.1029/2024JB029502).

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Global magnetic field model results for scatter (S) vs. latitude, including results for our new THG24 model. (b) Number of studies that passed the consistency tests as a function of model and κappa.