Page 8 - Sea-level change_2004

ARTICLE IN PRESS
1976 K. Lambeck, A. Purcell / Quaternary Science Reviews 24 (2005) 1969–1988

isostatic adjustment and by the gravitational change. epoch are a consequence of the inclusion of the Alpine
The pattern of change remains the same as for the first- glaciation andprecise observations of the sea-level
iteration solution but the amplitudes are modified. gradient along the coast may be useful for placing
approximate limits on the magnitude of the Alpine ice
load. Along parts of the North African and Levantine
3.4. Relative sea-level change
coast, the two isostatic contributions are of opposite
sign with the water loadbeing dominant, resulting in
The relative sea-level change, including the gravita-
predictions of small-amplitude highstands in Late
tional anddeformational parts of both isostatic terms
Holocene time. Notably, the predicted levels along the
andthe esl contributions, is illustrated in Figs. 2d–f for
Gulfs of Sirte andGabe ` s coasts exhibit strong spatial
the epochs 20, 12 and6 ka BP, always for the nominal
gradients, for example, 4 m from Gabe ` s to Tunisia,
earth andice models, with equivalent levels at these
anddata from this region would be important for
epochs of 142, 54 and0 m, respectively. The local
evaluating model parameters appropriate for the region.
levels at the time of maximum glaciation vary from
Between Majorca and Sardinia, the predicted levels for
110 to 150 m across the region andare below the esl 6 ka BP lie as much as 8 m below present, andthe spatial
values near the centers of the sub-basins south of Italy, variability remains significant across the entire region
between Majorca andSardinia, andin the eastern andconsiderably greater than most observational
Mediterranean. The shallower values occur within the
Gulfs of Genoa andLion andin the northern Adriatic. uncertainties.
(See Fig. 3 for locations.) At 12 ka BP, the levels range
from 40 m in the northern Adriatic to o 68 m near
the centers of the above-mentionedbasins. The pattern 4. Precision of sea-level predictions
is similar to that at 20 ka BP, with the levels at the coast
4.1. Dependence on earth-model parameters
being mostly above the esl values whereas offshore they
are mostly below the esl values. At both epochs, the
The above predictions are based on the nominal earth
pattern follows closely the coastline geometry, indicative
model for a three-layered mantle. No systematic
of water loading contributing a major role to the spatial
inversion of sea-level data for the entire Mediterranean
variability of the overall isostatic signal (c.f. Fig. 2a).
has yet been attempted, but a number of regional
This pattern persists for other Late Glacial and
solutions—from France, Italy, Greece, andIsrael—all
Holocene periods. At 6 ka BP, for example, sea levels
indicate that parameters in the range given in Table 1
remain below present day across much of the region, the
yieldpredictions that are consistent with observations
two isostatic contributions being both negative. The
(Lambeck, 1995b; Lambeck andBard, 2000; Sivan et al.,
exceptions occur in the northernmost Adriatic and along
2001; Lambeck et al., 2004a). The earth-model depen-
segments where the North African coast is indented,
dence of the predictions for this parameter range is
such as in the Gulfs of Sirte andGabe ´ , andalong the
illustratedfor two epochs (6 and 12 ka BP) in Fig. 4,
easternmost Mediterranean coast (Fig. 2f). In the
along two profiles, a north–south profile from the
northern Adriatic, the small positive values at this
northern Adriatic to North Africa and an east–west
profile along 401N in the western Mediterranean. For
t ¼ 6 ka BP, some of the largest differences occur near
the centers of the sub-basins within the Mediterranean
(e.g. Menorca, or between Sicily andNorth Africa) but
they are smaller at the coasts of the larger landbodies
(e.g. North Africa or Castellan) andmostly no larger
than the observational uncertainties for Late Holocene
epochs. The pattern is similar for t ¼ 12 ka. Thus, within
the Mediterranean basin there are locations where the
predictions are relatively insensitive to earth-model
parameter choice anddata from these would constrain
primarily the esl function. Then there are other localities
Fig. 3. Location map of principal sites mentionedin text. 1: Castellan, where the earth-model dependence is substantial and by
Spain. 2: Majorca and Balearic Islands. 3: Golfe du Lion. 4: Coˆ te an appropriate selection of sites andepochs it shouldbe
d’Azur. 5: Golfo di Genova. 6: Versilia Plain, Italy. 7: Sardinia. 8: possible to invert sea-level data from the region to
Golfe de Gabe ´ s. 9: Lampedusa. 10: Malta. 11: Golfo do Salerno. 12: improve upon the rheological parameters, particularly if
Ortona. 13: North Adriatic. 14: Trieste. 15: Susak, Croatia. 16: Golfo
di Taranto. 17: Albania. 18: Peloponnisos. 19: Golfe de Sirte ´ . 20: basin-wide data are available for the entire post-LGM
Carmel Coast, Israel. The dashed lines correspond to the sections in interval. Until such an analysis is completed, we adopt
Figs. 4 and6. the nominal earth-model parameters defined in Table 1