Sea Level and Ice Volume Changes

Lithostratigraphic data from Antarctic margin drill cores show clear evidence on the shelf (PB, RS) for linked sea-level and ice-volume changes. This is best shown in the Oligocene through early Miocene record of cyclic glacial and interglacial lithologies near the coast in Cape Roberts cores (WRS) (Barrett, 2007). Lithostratigraphic data from the slope (PB) and rise (PB, AP) show additional direct evidence for cyclic ice-volume changes. Seismic-reflection data provide indirect evidence across the entire margin for the linked sea-level and ice-volume fluctuations that have been noted by many investigators and have been modelled in the RS (Bartek et al., 1991) and presented conceptually for all margins (ten Brink et al., 1995). The Antarctic drill cores are too limited, however, to establish the timing, magnitude and extent of individual ice sheet advances onto the continental shelf, other than for the LGM.

A comparison of the Antarctic margin proximal stratigraphic record with the global record of sea-level variations (and linked ice-volume variations) from coastal onlap, backstripping, and isotopic records since the middle

Figure D-1: Graph showing sea-level and isotope curves and principal stratigraphic events for the Antarctic continental margin. Curves are from Miller et al. (2005). Events are from text and Tables D-1 and D-2. Curve A is for benthic foraminifera. Curve B is derived from stratigraphic backstripping (>9 M.a.) and isotopic measurements (0-9 M.a.); Curve C is from Haq et al. (1987). Curves B and C have different sea-level change scales. For some periods, Antarctic stratigraphic events correlate with isotopic shifts (e.g. PB: early Oligocene unconformity and first ice sheets at the coast and mid-Miocene lithology changes and ice buildup) and with the Haq Curve (e.g. mid-to-late Miocene shelf erosion and early Pliocene and younger slope fan development with long-term sea-level lowerings).

Eocene is shown in Fig. D-1. Large differences appear between the global sea-level curves (see Miller et al. (2005) for the explanation), yet the Antarctic stratigraphic features can potentially be linked to parts of all of the curves principally because of the current uncertainty in ages of Antarctic features, especially for the Paleogene. The closest links of Antarctic features with the global curves are:

• Late Eocene and early Oligocene lowering of sea-level (first glaciers into PB and RS), followed by sea-level rise in the early Oligocene (flooding of PB).

• A long period from the Oligocene into the late Miocene of cyclic sea-level, seen in cyclic coastal deposits (WRS) and as glacial/interglacial rise-drift deposits (PB, AP)

• Abrupt sea-level lowering in the middle Miocene, seen in lithologies of rise-drift deposits (PB), followed by further sea-level lowering (with ice buildup) and enhanced erosional deepening and prograding of continental shelves by glaciers (as seen in seismic profiles from all areas).

• The systematic decrease in sea-level (and increase in ice) from the mid-Miocene to the present that corresponds with the decrease in sedimentation rates on the rise and increase in sedimentation rates on the slope. This is most pronounced since early Pliocene time, when an extensive system of shelf erosional troughs and upper-slope fans developed.

Greater resolution of the link between ice-volume variations and sea-level changes requires further drilling on the Antarctic margin.

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