Research — Mebrahtu Weldeghebriel

Fluid Inclusions in Marine Halite as Archives of Ancient Seawater Chemistry

Fluid inclusions in marine halite are micrometer-scale droplets of ancient seawater — the most direct record of ocean chemistry available. From more than 1,300 inclusions across ~30 marine evaporite basins, I built 550-million-year records of seawater Mg/Ca, Ca²⁺, SO₄²⁻, Sr²⁺, Li⁺, and δ⁷Li.

Fluid inclusionsHaliteTrace elements

Map showing global distribution of marine evaporite deposits analyzed in this study.

Fluid inclusions along chevron growth zones in halite

Photomicrograph of halite crystal from Serravallian-Tortonian (~11.8 Ma) Gulf of Suez, Hurghada, Egypt, A) showing vertically oriented chevron crystal with dark and light bands; B) dark banded part of chevron structure contains a large number of primary fluid inclusions; C) close up view shows individual fluid inclusions with negative cubic shapes and varying size from 3 to 80 μm. D) Large fluid inclusions ablated by laser appear dark after fluid extraction.

Phanerozoic record of seawater [Ca²⁺], [Sr²⁺], Mg/Ca, [SO₄²⁻], and ⁸⁷Sr/⁸⁶Sr from fluid inclusions in halite, alongside pCO₂ proxies, tracking greenhouse–icehouse states, KCl versus MgSO₄ potash mineralogy, and aragonite versus calcite seas.

Mass Balance Modeling of Seawater Chemistry and Climate Evolution

A forward box model of the coupled carbon–magnesium–calcium–lithium (C–Mg–Ca–Li) cycles over the past 550 million years, identifying ocean-crust production tied to the supercontinent cycle as the first-order control on seawater chemistry and atmospheric CO₂.

Mass balanceModelingIsotopes

Seawater concentration and isotope systems constraining seawater chemistry and the carbon cycle

Multiple seawater concentration and isotope systems (Li, Sr, Mg, Ca, S) constrain the controls of seawater chemistry and the carbon cycle.

A 3-Billion-Year Lithium Isotope Record from Marine Dolostones

Extending the seawater lithium isotope record beyond the Neoproterozoic back toward 3 billion years using more than 500 marine dolostones.

Lithium isotopesDolostonesPrecambrian

Lithium isotope systematics of carbonate archives — δ⁷Li systematics across primary and diagenetically altered carbonates (modified from Wei et al., 2024).

Sequential leaching and column chemistry workflow for dolostone lithium isotope analysis — Sequential leaching workflow for δ⁷Li analysis in bulk carbonates and dolomites (modified from Cao et al., 2023).

Seawater Lithium Evolution and the Origins of Lithium-Rich Brines

Ancient seawater held 5 to 15 times more lithium than today, making evaporated Paleozoic–Mesozoic seas and the brines derived from them an underexplored, economically important lithium resource.

LithiumCritical mineralsBasinal brines

Cartoon comparing lithium concentration in ancient versus modern seawater and its evaporation into Li-rich basinal brine

Evolved seawater preserved in ancient evaporite basins as an underexplored lithium reservoir.

High-Resolution Chemical Imaging and Dating of Oldest Ice Using LA-ICP-MS

Developing a cryo-cell LA-ICP-MS method to chemically image and independently date folded, disturbed Antarctic blue ice (1–6 Ma), in support of COLDEX's goal of recovering a direct atmospheric sample from the mid-Pliocene.

LA-ICP-MSImpurity mappingSr isotopesBlue-ice areas

Allan Hills sample location and blue-ice stratigraphy, ice-core sample preparation and cryo-cell LA-ICP-MS workflow, the loaded cryo-cell holder, and elemental maps of Na, Mg, Al, Ca, and Sr

Blue-ice stratigraphy sampled by LA-ICP-MS for ⁸⁷Sr/⁸⁶Sr geochronology.