Michael James Henehan

Michael James Henehan
Helmholtz-Zentrum Potsdam - Deutsches GeoForschungsZentrum GFZ | GFZ · Section 3.3; Earth Surface Geochemistry

PhD, Palaeoclimate/Geochemistry
Research Scientist, GFZ Potsdam, and Head of HELGES Trace Metal Clean Lab

About

59
Publications
12,632
Reads
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Introduction
I study how the Earth's carbon cycle and silicate weathering feedback work, and the effect of carbon cycle changes on past climates. This scales from the mechanistic drivers of silicate weathering within the critical zone to the reconstruction of past pCO2 and biogeochemical cycling on global and multi-million year timescales. My tools of choice are primarily B, Li, Mg isotopes, and carbonate trace element ratios.
Additional affiliations
September 2017 - present
Helmholtz-Zentrum Potsdam - Deutsches GeoForschungsZentrum GFZ
Position
  • PostDoc Position
April 2014 - August 2017
Yale University
Position
  • PostDoc Position
Description
  • Undertook a Post-Doc under Dr. Pincelli Hull, working on quantifying carbon cycle changes between the late Cretaceous and early Palaeogene.
August 2013 - February 2014
University of Southampton
Position
  • PostDoc Position
Description
  • Worked on applying boron isotope and trace element proxies to the Middle Eocene Climatic Optimum, to determine the interaction between the carbon cycle and global climate during this time interval.
Education
December 2009 - September 2013
University of Southampton
Field of study
  • Palaeoclimate and Geochemistry
October 2005 - June 2009
University of Bristol
Field of study
  • Palaeontology and Evolution

Publications

Publications (59)
Article
Full-text available
Lithium isotopes are used to trace weathering intensity, but little is known about the processes that fractionate them in highly weathered settings, where secondary minerals play a dominant role in weathering reactions. To help fill this gap in our knowledge of Li isotope systematics, we investigated Li isotope fractionation at an andesitic catchme...
Article
In a small, forested catchment underlain by gneiss (Conventwald, Black Forest, Germany), we found that the magnesium isotope composition (δ²⁶Mg) of creek water did not show seasonal variability, despite variations in dissolved Mg concentrations. To investigate the potential controlling factors on water δ²⁶Mg values, we studied the Mg isotope compos...
Article
Boron isotope ratios – as measured in marine calcium carbonate – are an established tracer of past seawater and calcifying fluid pH, and thus a powerful tool for probing marine calcifier physiology and reconstructing past atmospheric CO2 levels. For such applications, understanding the inorganic baseline upon which foraminiferal vital effects or co...
Article
Full-text available
The stable isotopes of lithium (Li) serve as a robust proxy of silicate weathering. The fate and transport of these isotopes in the dissolved load of major rivers have been characterized to infer changes in both contemporary weathering regimes and paleo-conditions. In this contribution, we deconvolve this integrated signal into the individual proce...
Code
seacarbx is a seacarb extension written in R, which enables to use seacarb (Gattuso et al., 2019) for deep-time carbonate system calculations or for culturing studies carried out in seawater with modified [Mg2+] and [Ca2+]. For this, the functions carb, K0, K1, K2, Ks, Kw, Kb, Kspa, and Kspc were modfied to account for the effect of seawater [Mg2+]...
Article
In this study, to better understand the factors controlling the concentration and isotope composition of lithium (Li) in the ocean, we investigated the behaviour of Li during interaction of kaolinite with artificial seawater. Dissolution of kaolinite in Li-free seawater at acidic conditions (exp. 1) results in a strong preferential release of light...
Article
Full-text available
The boron isotopic (δ11BSRM951) and trace element composition of marine carbonates are key proxies for understanding carbon cycling (pH) and palaeoceanographic change. However, comparability of results between laboratories requires carbonate reference materials. Here we report results of an inter‐laboratory comparison study to both assign δ11BSRM95...
Article
Full-text available
The early Paleogene represents the most recent interval in Earth's history characterized by global greenhouse warmth on multi-million year timescales, yet our understanding of long-term climate and carbon cycle evolution in the low latitudes, and in particular the Indian Ocean, remains very poorly constrained. Here we present the first long-term su...
Article
Full-text available
The Middle Eocene Climatic Optimum (MECO) was a gradual warming event and carbon cycle perturbation that occurred between 40.5 and 40.1 Ma. A number of characteristics, including greater-than-expected deep-sea carbonate dissolution, a lack of globally-coherent negative δ 13 40 C excursion in marine carbonates, a duration longer than the characteris...
Article
The cause of the end-Cretaceous mass extinction is vigorously debated, owing to the occurrence of a very large bolide impact and flood basalt volcanism near the boundary. Disentangling their relative importance is complicated by uncertainty regarding kill mechanisms and the relative timing of volcanogenic outgassing, impact, and extinction. We used...
Article
Full-text available
Boron incorporated in marine biogenic carbonates records the pH of seawater during precipitation. From reconstructing atmospheric CO2 beyond ice-core records to deciphering the ocean's role in storing and releasing carbon, boron is proving to be a vital tool in paleoclimate research.
Article
Full-text available
Mass extinction at the Cretaceous-Paleogene (K-Pg) boundary coincides with the Chicxulub bolide impact and also falls within the broader time frame of Deccan trap emplacement. Critically, though, empirical evidence as to how either of these factors could have driven observed extinction patterns and carbon cycle perturbations is still lacking. Here,...
Article
In most chemical reactions, stable isotopes are fractionated in a mass-dependent manner, yielding correlated isotope ratios in elements with three or more stable isotopes. The proportionality between isotope ratios is set by the triple isotope fractionation exponent, θ, that can be determined precisely for e.g. sulfur and oxygen by IRMS, but not fo...
Article
Full-text available
Planktonic foraminiferal species identification is central to many paleoceanographic studies, from selecting species for geochemical research to elucidating the biotic dynamics of microfossil communities relevant to physical oceanographic processes and interconnected phenomena such as climate change. However, few resources exist to train students i...
Article
Full-text available
Paleoclimate records suggest that a rapid major transient Antarctic glaciation occurred across the Oligocene‐Miocene transition (OMT; ca. 23 Ma; ~50 m sea level equivalent in 200‐300 kyrs). Orbital forcing has long been cited as an important factor determining the timing of the OMT glacial event. A similar orbital configuration occurred 1.2 million...
Article
Full-text available
The clustering of mitochondria near pores in the test walls of foraminifera suggests that these perforations play a critical role in metabolic gas exchange. As such, pore measurements could provide a novel means of tracking changes in metabolic rate in the fossil record. However, in planktonic foraminifera, variation in average pore area, density,...
Article
Full-text available
The clustering of mitochondria near pores in the test walls of foraminifera suggests that these perforations play a critical role in metabolic gas exchange. As such, pore measurements could provide a novel means of tracking changes in metabolic rate in the fossil record. However, in planktonic foraminifera, variation in pore size, density, and poro...
Article
Full-text available
The response of the marine carbon cycle to changes in atmospheric CO2 concentrations will be determined, in part, by the relative response of calcifying and non-calcifying organisms to global change. Planktonic foraminifera are responsible for a quarter or more of global carbonate production, therefore understanding the sensitivity of calcification...
Article
The boron isotope-pH proxy has been widely used to reconstruct past ocean pH values. In both planktic foraminifera and corals, species-specific calibrations are required in order to reconstruct absolute values of pH, due to the prevalence of so-called vital effects — physiological modification of the primary environmental signals by the calcifying...
Article
Full-text available
Boron isotope ratios, as measured in planktic foraminifera, can be a useful tracer of past ocean pH, and hence help to discern the concentration of CO2 in the ancient atmosphere. However, different species of planktic foraminifera demonstrate different patterns of boron isotope variation with ambient seawater pH. Therefore when applying the proxy t...
Article
Full-text available
The chromium isotope system ((53) Cr/(52) Cr expressed as δ(53) Cr relative to NIST SRM 979) is potentially a powerful proxy for the redox state of the ocean-atmosphere system, but a lack of temporally continuous, well-calibrated archives has limited its application to date. Marine carbonates could potentially serve as a common and continuous Cr is...
Article
Full-text available
One contribution of 17 to a theme issue 'Biodiversity and ecosystem functioning in dynamic landscapes'. Pelagic ecosystem function is integral to global biogeochemical cycling, and plays a major role in modulating atmospheric CO2 concentrations (pCO2). Uncertainty as to the effects of human activities on marine ecosystem function hinders projectio...
Article
Full-text available
Much of our knowledge of past ocean temperatures comes from the foraminifera Mg / Ca palaeothermometer. Several nonthermal controls on foraminifera Mg incorporation have been identified, of which vital effects, salinity, and secular variation in seawater Mg / Ca are the most commonly considered. Ocean carbonate chemistry is also known to influence...
Data
Pelagic ecosystem function is integral to global biogeochemical cycling, and plays a major role in modulating atmospheric CO2 concentrations (pCO2). Uncertainty as to the effects of human activities on marine ecosystem function hinders projection of future atmospheric pCO2. To this end, events in the geological past can provide informative case stu...
Article
Full-text available
B/Ca ratios in foraminifera have attracted considerable scientific attention as a proxy for past ocean carbonate system. However, the carbonate system controls on B/Ca ratios are not straightforward, with Δ[CO32−] ([CO32−]in situ – [CO32−]at saturation) correlating best with B/Ca ratios in benthic foraminifera, rather than pH, or (as a simple model...
Article
Full-text available
Atmospheric CO2 fluctuations over glacial–interglacial cycles remain a major challenge to our understanding of the carbon cycle and the climate system. Leading hypotheses put forward to explain glacial–interglacial atmospheric CO2 variations invoke changes in deep-ocean carbon storage1, 2, probably modulated by processes in the Southern Ocean, wher...
Article
Biweekly sediment trap samples and concurrent hydrographic measurements collected between March 2005 and October 2008 from the Cariaco Basin, Venezuela, are used to assess the relationship between [CO32−] and the area densities (ρA) of two species of planktonic foraminifera (Globigerinoides ruber (pink) and Globigerinoides sacculifer). Calcificatio...
Data
Biweekly sediment trap samples and concurrent hydrographic measurements collected between March 2005 and October 2008 from the Cariaco Basin, Venezuela, are used to assess the relationship between [CO3]2- and the area densities (ho A) of two species of planktonic foraminifera (Globigerinoides ruber (pink) and Globigerinoides sacculifer). Calcificat...

Questions

Question (1)
Question
Unfortunately the Clay Mineral Society (clays.org) no longer have any pure illite in stock, and we need some for some experiments. If anyone knows where to find some, or has any of the old IMt-1 or IMt-2 CMS reference materials gathering dust in their lab, I'd really appreciate the input.
Thanks all,
Michael

Network

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Projects

Project (1)
Project
An international program designed to explore the mass extinction at the Cretaceous-Paleogene boundary in the classic El Kef section in Tunisia - http://www.ktboundary.org/