2024 CSDMS meeting-080
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On the Origin of Holocene Sea Level Transgressions in Formerly Glaciated Regions
Sam Chester,
(He/Him),Columbia University New York , United States. schester@ldeo.columbia.edu
Jacqueline Austermann, Columbia University New York New York, United States. jausterman
William D'Andrea, Columbia University New York New York, United States. dandrea@ldeo.columbia.edu
Andrew Lloyd, Columbia University New York New York, United States. alloyd@ldeo.columbia.edu
Roger Creel, Columbia University New York New York, United States. Roger.creel@whoi.edu
Glacial isostatic adjustment creates characteristic patterns of relative sea level change (RSL) as a function of distance to melting ice sheets (Clark et al., 1978). During the last termination and through the Holocene, regions formerly covered by large ice sheets experienced rapidly falling RSL due to the processes involved in glacial isostatic adjustment (GIA), primarily isostatic uplift. Surrounding this region of uplift is a narrow band that similarly records RSL fall but is interrupted at sometime during the Holocene by a period of sea level rise (i.e. a transgressions) culminating in a high stand. Holocene transgressions and highstands have been well documented in many locations including Norway, Canadian Atlantic coast, the Canadian Pacific coast, Svalbard, the Baltic Sea, and the British Isles (Forman, 2004; Smith et al., 2011; Shugar et al., 2014; Shennan et al., 2018; Vacchi et al., 2018; Rosentau et al., 2021; Creel et al., 2022). We investigate the origins of these Holocene transgressions using GIA/sea level modeling and test the hypothesis that they are the direct result of solid Earth deformation. Our modeling results highlight a unique pattern of solid Earth deformation in which the region of subsidence (peripheral bulge) surrounding the ice sheet migrates first towards and then away from the melted ice mass. We show how this effect, we term ’reverse migration’, is the direct result of the contrast in viscosity between the upper and lower mantle. We compare our GIA model predictions of RSL change to 1) RSL data since the last glacial maximum and 2) constrains on the transgression magnitude in Norway and eastern Canada. Both tests show a preference for GIA models that include a mantle with a substantial (1-2 orders of magnitude) increase in vicosity with depth. This suggests that, in contrast to the conventional view that Holocene transgressions record GMSL temporarily outpacing isostatic uplift, solid Earth deformation and specifically reverse migration played an important role in generating nearfield Holocene transgressions. Finally, by comparing GIA model results to RSL observations, we show how Holocene transgressions can be used to constrain the vertical viscosity structure of the mantle. Our findings suggest that a significant increase in viscosity with depth (1-2 orders of magnitude) likely exists below continents with nearfield transgressions.
