Early Career Spotlight

Mebrahtu Fisseha Weldeghebriel

Tell us about yourself:

My name is Mebrahtu Fisseha Weldeghebriel. I am a doctoral candidate at Binghamton University, working with Tim Lowenstein on drivers of secular variability in the chemical composition of seawater during the Phanerozoic Eon. I received my undergraduate degree in Geology at Eritrea Institute of Technology (EIT), Eritrea, where I worked on my project on sedimentology and geochemistry of Pleistocene potash-bearing marine evaporites in the Danakil Depression. After undergrad, I was hired as a graduate teaching assistant in the department of Earth Sciences in EIT for 4 years before I came to the USA in summer 2016.

What is your research about?

I am broadly interested in documenting major, minor, and trace element composition of seawater in the Phanerozoic using direct measurements in fluid inclusions trapped in marine halite and to better understand what controls long-term changes in the elemental composition of seawater on multimillion-year timescales. The main goal of this research is to examine which global processes, continental weathering or seafloor hydrothermal systems, played a significant role in controlling the long-term oscillations of major element and isotopic composition of seawater. For my PhD, I measured more than 3000 fluid inclusions in halites collected from ~35 Phanerozoic marine evaporite basins using combined laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) and cryogenic-scanning electron microscopy-energy dispersive spectroscopy (cryo-SEM-EDS). One of my goals is to understand how long-term changes in seawater chemistry links to variations in atmospheric CO2 and climate.         

What excites you about your research?

I am most excited about the analytical technique that we improved to extract minor and trace element composition of ancient seawater preserved unaltered in fluid inclusions in marine halite, over geologic time scale as old as 830 million years. We can use this new data combined with other records such as major ion and isotopic composition of seawater to constrain major fluxes to the ocean and link these records to marine biological evolution, atmospheric CO2, and climate. Another exciting part of this research is the prospect of unraveling ancient oceanic and atmospheric conditions using MATLAB based reverse modeling constrained by the invaluable elemental composition of ancient seawater obtained from direct measurement of fluid inclusion in marine halite. 

What broader importance does your research have for society?

This research has scientific and societal significance in two aspects. First, this study will provide a new data on minor and trace element concentrations in ancient seawater which may shed new light on the long-term controls of seawater composition. Earlier studies disagreed on the drivers of secular variability in chemical composition of Phanerozoic seawater based on major element and isotopic composition of seawater. Understanding the long-term controls of seawater chemistry may advance our understanding of the global carbon cycle and the sources and sinks of carbon in the hydrosphere and atmosphere. Secondly, the Mg/Ca ratio of seawater controls which carbonate, calcite or aragonite, is favored to precipitate. This research investigates the major transition periods in the Mg/Ca ratios of Phanerozoic seawater and evaluate how such changes in the major and minor element compositions of seawater link to the evolution of marine shell-building organisms.

What inspired you to pursue a career in Earth science?

I became interested in Earth Science in high school after I visited a rare mineral, rock, and fossil show by a group of geologists in the annual Eritrea Festival. Following my undergrad in Geology, I liked seismology after I worked on several projects with Prof. Ghebrebrhan Ogubazghi and Dr. Berhe Goitiom in monitoring seismicity and crustal deformations in Eritrea related to tectonics in Afar triple junction. I was later inspired to pursue my PhD in low-temperature geochemistry in evaporite minerals with Tim Lowenstein.    

What are you looking to do after you complete your PhD or postdoc?

After finishing up my PhD, I would like to go for a postdoc position or pursue a career in academia at research institutions. 

Given unlimited funding and access to resources, what is your dream project that you would pursue?

Can I select two? Firstly, I would work with a team of researchers from atmospheric, ocean, and earth sciences interested in climate on the details of how the carbon cycle evolved in the Phanerozoic and how that affects atmospheric carbon dioxide. Because atmospheric CO2 is the primary driver of global temperature change. Secondly, I would create a repository of the chemical compositions of Phanerozoic seawater obtained from fluid inclusions in marine halite and calcite cements (analytical technique in progress). To fill gaps in the record, I would also revisit global evaporite deposits and carbonate platforms of marine origin to collect more basal halites precipitated early during the evaporation of seawater and marine calcite cements, respectively. Fluid inclusions in marine calcite cements contain unevaporated pristine seawater. Therefore, chemical analysis of these fluid inclusions would give first-time data on the major element chemistry of ancient seawater before evaporative concentration. Such information would be an improvement over results from fluid inclusions in halite, which are highly evaporated and have evolved through gypsum/anhydrite and halite precipitation.

What else do you do?  Any hobbies or interests outside of work?

I love playing and watching soccer games. I also like hiking and visiting nature preserves. 


Mebrahtu Weldeghebriel looking at gypsum-halite spring tufa in the Dead Sea shoreline during December 2019-January 2020 field trip to study halite sequences in a deep hypersaline lake. A collaborative project between Binghamton University and Geological Survey of Israel. Photo credit: Nadav Lensky.