Dr. Marc Hijma
Dr. Marc Hijma, Postdoctoral Fellow in the Department of Earth and Environmental Sciences, Tulane University, presented an excellent and very well attended (standing-room only) invited talk on "sea-level jumps" at the XVIII Congress of the International Union for Quaternary Research (INQUA), Bern, Switzerland, on July 26, 2011. The title of Marc's presentation was "Magnitude and timing of the sea-level jumps preluding the 8.2 ka climate event."
The 8.2 cooling event is generally considered to be caused by the sudden drainage of proglacial lakes Agassiz and Ojibway that freshened the North Atlantic Ocean and resulted in the temporary shutdown of the thermohaline circulation. Ongoing debate concerns the magnitude of the associated sea-level rise as well as its timing in relation to the start of the 8.2 event. High-resolution sea-level data from the Rhine-Meuse Delta, The Netherlands, indicate a fingerprint corrected magnitude of 3.0 ± 1.25 m that exceeds previous modeled estimates. This is a value for total accelerated rise leading up to the 8.2 event, narrowly 14C dated to have started at 8.45 ka, so centuries before the 8.2 event.
Marc gave an up-to-date overview of the knowledge his research team has acquired on rapid sea-level rise between 8.5-8.2 ka, including sea-level data (Rhine and Mississippi deltas), drainage-event data (Hudson Bay/North Atlantic) and modeling results. The evidence is increasingly pointing towards two-staged drainage. Potentially, this not only solves the problem that the first drainage event predates the 8.2 event by two centuries, but it can also explain the magnitude of the sea-level jump: two events may add up to 3 m of abrupt sea-level rise.
New data from the Mississippi Delta time the second event between 8.31-8.18 ka with a fingerprint corrected sea-level rise of 1.5 ± 0.7 m. The derived 3.0 ± 1.25 m jump in The Netherlands occurred between 8.45-8.25 ka, hereby capturing both events, and this tentatively suggests that the two sea-level jumps were of similar size. Besides (recharging) amounts of lake water, huge amounts of disintegrating Hudson-bay ice are needed to produce the observed sea-level signature from the source area, as also concluded from 8.2-event simulations in general circulation models. High resolution sea-level data are therefore urgently needed to settle this matter, specifically from areas such as Southeast-Asia and Australia where the relative rise would have been largest.
Once every four years, Quaternary researchers from all over the world meet at the INQUA Congress to exchange their latest research results and develop agendas for the years to come. Marc Hijma is a member of the Tulane Quaternary research group, under the direction of Professor Torbjörn Törnqvist, who also presented at the Congress.
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