Ph.D., Utrecht University, 1993 M.S., Utrecht University, 1988
Dr. Törnqvist's research interests include Quaternary geology, Sea-level change, Coastal sustainability, Fluvial and deltaic sedimentology, Sequence stratigraphy, Applied geochronology and Paleoclimatology
Holocene ice sheet‒sea level connections.
The sedimentary record of the Mississippi Delta offers unique opportunities to investigate Holocene relative sea-level (RSL) change at very high resolution, and to develop connections with paleoclimate records. Our past efforts have focused, among others, on an abrupt sea-level rise associated with the 8.2 ka cooling event that was likely caused by the final drainage of proglacial Lake Agassiz. Currently ongoing research is pushing this record back beyond 10 ka, providing one of the first high-resolution RSL curves for the early Holocene. Combined with glacial isostatic adjustment (GIA) modeling, this can potentially shed light on the relative contribution of the North American and Antarctic ice sheets to global sea-level rise during the second half of the last deglaciation.
Mechanisms and rates of subsidence in low-elevation coastal zones.
Subsidence in rapidly urbanizing, low-lying coastal environments is evolving into a “slow-motion catastrophe”. Our primary focus is on coastal Louisiana and involves the collection and analysis of field data (both geological and instrumental) that is combined with various modeling approaches (GIA models, compaction models) which involves several collaborators. Our Holocene RSL records are a cornerstone of this work, more recently augmented by surface-elevation table – marker horizon data available from the unparalleled Coastwide Reference Monitoring System. A recent addition is the “subsidence superstation” near Myrtle Grove, Louisiana, where a wide range of instrumental and geological methods are integrated to gain a more fundamental understanding about subsidence mechanisms and rates over a range of depth and timescales.
Holocene delta evolution.
There is a resurgence of interest in delta evolution over timescales longer than the instrumental record, motivated by the increasing challenge to successfully manage deltas throughout this century and beyond. Our research involves a variety of projects concerned with rates of delta growth (both vertically and horizontally) as well as patterns of material (sediment, organic carbon) dispersal and burial in the Mississippi Delta. This work relies heavily on geochronology as provided by 14C dating (including novel methods such as ramped PyrOx 14C) and optically stimulated luminescence dating. Much of this research is closely tied to questions that emanate from coastal restoration efforts, such as deciphering the patterns and rates of fluviodeltaic deposition that can serve as analogs for coastal restoration projects by means of river diversions.
Coastal wetland sustainability.
The wetland loss problem in coastal Louisiana is widely documented and there is an enormous interest in the future fate of these highly valuable ecosystems. Our research attempts to determine, among others, which rates of RSL rise coastal wetlands can withstand. One recent finding is that over short (annual to decadal) timescales, coastal marshes and swamps may keep up with rates as high as ~1 cm/yr. However, over longer (multi-decadal to centennial) timescales sudden marsh collapse occurs at rates of RSL rise that are much lower. Many intriguing questions remain, including the need for a better understanding of the conditions that cause marsh drowning and subsequent re-emergence (including possible hysteresis effects), both in coastal Louisiana and elsewhere.
The continental margin as a critical interface for earthscape processes.
Sea-level positions during the Last Glacial Maximum, obtained by means of GIA modeling, serve as the foundation for a GIS-based analysis of the spatial relationship between the lowstand shoreline and the shelf edge along passive margins worldwide. Our studies so far have shown that the relationship between these two features varies widely from one margin to the next, yet it is critical for material fluxes from continents to oceans on a global scale. Our objectives therefore include, among others, to understand the nature of source-to-sink sediment flux during glacial-interglacial cycles and to elucidate the currently poorly understood mechanisms of shelf-edge formation.
For more information, please visit the website of the Quaternary research group.
Selected Recent Publications
Törnqvist, T.E., Jankowski, K.L., Li, Y.-X. and González, J.L., 2020. Tipping points of Mississippi Delta marshes due to accelerated sea-level rise. Science Advances, 6: eaaz5512.
Nienhuis, J.H., Ashton, A.D., Edmonds, D.A., Hoitink, A.J.F., Kettner, A.J., Rowland, J.C. and Törnqvist, T.E., 2020. Global-scale human impact on delta morphology has led to net land area gain. Nature, 577: 514-518.
Keogh, M.E. and Törnqvist, T.E., 2019. Measuring rates of present-day relative sea-level rise in low-elevation coastal zones: a critical evaluation. Ocean Science, 15: 61-73.
Chamberlain, E.L., Törnqvist, T.E., Shen, Z., Mauz, B. and Wallinga, J., 2018. Anatomy of Mississippi Delta growth and its implications for coastal restoration. Science Advances, 4: eaar4740.
Jankowski, K.L., Törnqvist, T.E. and Fernandes, A.M., 2017. Vulnerability of Louisiana’s coastal wetlands to present-day rates of relative sea-level rise. Nature Communications, 8: 14792.
You can find these as well as my other papers at ResearchGate.