
Dr Joseph Stewart
PhD (Soton.), MESc (Oxon.)
Current positions
Research Fellow
School of Earth Sciences
Contact
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Research interests
My research lies at the intersection of geochemistry, paleoceanography, and biomineralisation, with a focus on how marine archives record and respond to past environmental change. I primarily use cold-water corals, stylasterid corals, and foraminifera as natural archives to reconstruct ocean circulation, climate variability, and seawater chemistry from a range of timeframes including the Holocene, the last deglaciation, and Cenozoic.
A major part of my work involves developing and refining geochemical proxies (e.g., boron isotopes, Ba/Ca, Sr/Ca, Li/Mg, radiocarbon) and calibrating them against environmental parameters such as pH, temperature, dissolved oxygen, and nutrients. This includes laboratory, field, and interlaboratory studies to improve proxy reliability and to better understand “vital effects” in biomineralisation.
I am also interested in the biological and physiological controls on coral calcification under variable ocean chemistry, including the impacts of ocean acidification, diagenesis, and disease. These studies provide insights into coral resilience and the mechanisms by which trace elements are incorporated into skeletal carbonates.
Another central theme of my research is the role of the Southern Ocean and polar regions in driving deglacial climate change, particularly through changes in ocean circulation, carbon storage, and heat transport. My contributions to studies on Antarctic meltwater fluxes, deep-ocean ventilation, and interhemispheric climate forcing highlight the importance of geochemical records in understanding Earth system feedbacks.
Taken together, my work advances understanding of both the fundamental processes of biomineralisation and the use of coral archives to reconstruct paleoclimate, ocean chemistry, and global carbon cycle dynamics.
Projects and supervisions
Thesis supervisions
Stylasterid coral geochemistry
Supervisors
Deep-sea coral records of the intermediate Atlantic Ocean during the last glacial cycle
Supervisors
Investigating paleoceanographic proxies in deep-sea corals: Implications for weathering, water mass evolution, and ocean oxygenation
Supervisors
Subpolar North Atlantic paleoceanography over the last millennium and Holocene using cold-water coral geochemistry
Supervisors
Exploring recent ocean ventilation and biogeochemical variations using deepsea corals
Supervisors
Publications
Selected publications
01/10/2020NIST RM 8301 Boron Isotopes in Marine Carbonate (Simulated Coral and Foraminifera Solutions)
Geostandards and Geoanalytical Research
Refining trace metal temperature proxies in cold-water scleractinian and stylasterid corals
Earth and Planetary Science Letters
CO2 storage and release in the deep Southern Ocean on millennial to centennial timescales
Nature
Recent publications
15/01/2025Delayed onset of ocean acidification in the Gulf of Maine
Scientific Reports
Radiocarbon evidence of a North Atlantic intermediate water reconfiguration between the 1960s and 1980s
Earth and Planetary Science Letters
Century-Long Records of Sedimentary Input on a Caribbean Reef From Coral Ba/Ca Ratios
Paleoceanography and Paleoclimatology
Contrasting responses of commercially important Northwest Atlantic bivalve species to ocean acidification and temperature conditions
PLOS Climate
Correlative geochemical imaging of Desmophyllum dianthus reveals biomineralisation strategy as a key coral vital effect
Scientific Reports