DRIFT SIMULATIONS: Numerical simulations of the temporal and special evolution of sediment drifts
Description:
To gain a detailed understanding of the temporal and spatial evolution of the Antarctic Peninsula drifts, extensive numerical process simulations are essential to reconstruct the geological as well as oceanographic framework over long-time periods during the Neogene. This project will be directly connected to the IODP initiative - extreme climates.
Numerical models enable a wide spectrum of scenarios to be tested, specifically to evaluate (a) current conditions, and (b) sediment input variations in space and time for sediment transport processes in particular to quantify the along-slope vs. down-slope component. Accordingly, simulations obtain detailed information about past oceanic circulation and environmental conditions to identify climate shifts. However, sediment physics as well as erosion and deposition criteria are only partially implemented in ocean circulation models.
Thus, this project focuses on two major aspects:
- improvement of the sediment transport module in ROMS (Regional Ocean Circulation Model), and
- development of a high-resolution 3D forward model to investigate the evolution of Drift 7.
We have selected the area of ODP Leg 178 because a dense grid of seismic profiles and numerous high-resolution cores document extreme climate episodes. These considerable sedimentological and geophysical data supply information about:
- a event horizons,
- seismostratigraphic unit thicknesses,
- grain-size distributions within seismostratigraphic units, and
- physical properties of sediments at event horizons
and will serve as an excellent model input.
Using information maps of reflectors depth and seismic unit thickness were compiled and interpreted regarding the controlling depositional processes. The depositional model shows an initially major along-slope sediment transport by a SW-setting bottom current (25-15 Ma), which deflected sediment supplied from the continental shelf (Figure 2). Between 15 Ma and 9 Ma down-slope transport took over as a result of the growth of the Antarctic Peninsula ice sheet. The SW setting bottom current appears to have broken down. Down-slope transport has decreased since 9 Ma, but a re-onset of the bottom current can only be observed since 5.3 Ma. The analysis has further shown that the nucleus of the drift is connected to a basement ridge. We hence infer that basement topography played a major role in the formation of this sediment drift.
Figures:
Figure 2: Depositional model for Drift 7. Major outline of each unit’s base (solid area) and depocentre (hatched area) are displayed. The open arrow shows the along-slope transport, while the closed arrow shows the down-slope transport. Thickness and length of the arrows indicate the importance of the process (Uenzelmann-Neben, in review).
Figure 1: Swath bathymetric map of Drift 7 (Rebesco et al., in revision). The insert map shows the location of Drift 7 at the continental margin of the Antarctic Peninsula (black box, bathymetry according to Smith and Sandwell, 1997), of the southern ACC front (dashed line, according to Orsi et al., 1995) and the inferred southwest setting bottom current (thin arrows, according to Giorgetti et al., 2003).
References:
Uenzelmann-Neben, G.(2006).Depositional patterns at Drift 7, Antarctic Peninsula: along-slope versus down-slope sediment transport as indicators for oceanic currents and climatic conditions, Marine geology, 233(1-4), 49-62, doi:10.1016/j.margeo.2006.08.008.