Sea-levelchange and shore-line evolution in Aegean Greecesince UPPer Palaeolithic time Kunr LAvtgncr* - not been 'As the glaciation ended, the ice melted and the sea-Ievelrose'' Yes but it has surface-Ioads as simp"leas that, ss the'Earth has adjusted in several ways to the changing in a it siffers under ice and under weight of water. The important issuesare set out Greeceand simple'mathematical treatment, and theii varied consequencesare shown fot islands, where the impact on Lspecialtyfor the Greek coastalplains and the Greek human settlement has been latge' about 20,000 to Nature and consequences ofPostglacial sea- the Last Glacial Maximum, lowerthan level change 18,000 years ago, were sufficiently plains that have Sea-Ievelshave changed significantly since Late today tó leave exposed coastal appearc to have Palaeolithic time, primarily in response to the since flooded. But less attention and rates of change melting of the gréat ice-sheets that covered been focused on the timing the great ice-sheets. northern Europe and North America. These ice- after the onset of melting of - with the exception sheets*et" of a sufficiently large volume that, What discussion there is by van Andel & upon melting, sea-level rose globally by about of the important paper (1982) (see van Andel tg89J tàoaso m. Releaseof this ice into the oceans Shackletor also - that this was initiated at about 18,000 years before present often leavesthe distinct impression quickly with (b.p.), although the majority of the-melting oc- change in level occurred early and cuired betwebn about 16,000 and 8000 b.p.1 rather minimal human imPact. using the Aegean Ratesof global sea-levelrise reached 15-20 mm This paper sets out to describe, model of p*r y"ut-dn.ing this interval. As the sea-levels Sea region as an example, a realistic migration for the ior", to did the shorelines migrate with time, sea-IevLl change and shoreline a frame- at rates that for some low-lying regions reached past 20,000 ye¿Irs,one that canprovide of such chalge on about a kilometre per year. Examples of where work for discussing impacts such rapid ettcro"chtoent of the sea occurred huma¡r movements ald settlement. ice sheets, the include the Persian GuIf and the Gulf of If, during the decay of the uniformly over Carpentaria of northern Australia, between about meltwater vòIume is distributed change at time f 12,ô00 and t0,000 years b.p. In some areasof the oceans, then the sea-level the world the sea-Ievelspeaked at about 6000 would be years b.p., inundating now low-Iying areasbe- A("(t)= changein oceanvolume/ocean surface area (1) iore falling slowly to their present position, The consequencesof these changes on human.set- 'eustatic This sea-levelchange'is a function of tlement ánd movement have been recognized time. It represents only a zero-order approxi- in the archaeological and pre-historic records' mation because sea-Ievel does not respond Thus it is widely accepted that levels during uniformly to the melting of the ice caps: the rates of rise are spatially variable, and in some are in conventional radiocarbon years unless 1 All ages may actually be falling rela- otherwise specified. Iocalities sea-levél ACT 0200, Australia' * Research school ofEarthsciences, Australian Nalional university, canberra Received 23 January 1996, accepted 26 April 1996' ANrrQUrrY 70 (1996): SEA-LEVEL CHANGE & SHORE-LINE EVOLUTION IN,A,EGEAN GREECE SINCE UPPER PALAEOLITHIC TIME 58S tive to the land. This is a consequence of the Because of the viscous nature of the planet's adjustment of the Earth to the changing sur- interior, the crustal defo¡mation continues lons face-Ioads of ice and meltwater. fhé eãrth,s after the melting of the Late pleistocene icel response can be ilescribed as that of an elastic sheetshas ceased;and shorelines have contin- (the layer lithosphere which includes the crust) ued to change up to the present. overlying a viscoelastic mantle. When changes This combined behaviour of the eustatic in the mass distribution occur on the Eart-h's change a¡ld the crustal rebound describes a first- surface,the lithosphere and mantle respond to order solution to the question of what happens the new stress state in different *uys: elastic to sea-levelwhen ice sheetsmelt. A more ôurrr- deformation primarily occurs in the lithosphere plete description requires consideration of two and viscous flow occurs prirnarily in thè un- additional effects: derlying mantle. The characteristic time-scale . the fact that newly added meltwater loads of this flow is of the order of a few thousand the sea floor and stressesthe mantle. re- years. The deformation of the Earth's surface sulting in further mantle flow and surface under a changing load therefore exhibits both displacement; an instantaneous elastic responseand a viscous r the gravity field of the earth is changing; first, response. Such behaviour iì well documented because of the changing gravitalioñal at- by other geophysical observations: gravitational traction between the ice, water and land attraction of the Sun and Moon raises tides in as the ice sheetsmelt, and second,because the solid Earth; ocean tides load the sea floor of theredishibution of masswithinthe solid and contribute to the deformation of the Earth's Earth in response to the mantle flow and zurface; atmospheric pressure fluctuations over surface deflection. the continents induce deformations in the solid The total effect ofthese various processesis Earth. These displacements, when measured called glacio-hydro-isostasy'after the (regional) with precision scientific instruments, show both isostatic response of the Earth's surfacJto the an.elasticand a viscous component, with the ice and water loads. It leads to a complex spa- latter becoming increasingly important as the tial temporal pattern of sea-level change duration of the load or force .and increãses.Changes as the ice sheets wax and wane, making tñe in the ice and water loads occurring a! times concept of a uniform global eustatic change of of major deglaciation are much largãr and oc- only very limited value. This complexity is ñtore cur on longer time-scales than these small at- than a scientific curiosity, as iti understand- mospheric and tidal perturbations, butthe tleory ing has broad scientific impacts. In geophys- underpinning the formulation of the surface re- ics, for example, the spatial changesinieallevel bound problem is similar and has been tested provide a valuable insight into physical prop- against a range of different observations (e.g, erties of the Earth that cannot otherwiie 6e Lambeck 198s). measured. In environmental studies they pro- When the ice-sheets melt, the surface load vide a framework for separating naturai 6om is changedin two ways. Ice is removed, thereby man-caused changesin sea-level.In prehistory unloading the formerly glaciated crust, and thä and archaeology, they provide a baiis for de- meltwater is added into the oceans,loading the tailed geographic reconstructions of coastal oceanic _lithosphere. The resulting changã in regions and for assessingthe impact of chang- sea-level relative to the land is a cãmbinátion ing sea-levelson past societies. of two reactions: the increase in ocean volume, and the deflection of the land surface.Depending Models for sea-level change on which contribution is greater, sea-level ii The evaluation of the evolution of shorelines seen to rise or fall relative to the land. In re- during-times of glaciation and deglaciation re- gions near or within the former centres of gla- quires knowledge of several quantities: ciation, the crustal adjustment is one of uplift; ¡ the change in sea-level relãtive to the land it is usually the more important, and sea-level for the region in question, a change that here is seen to fall. Further away from the ice is usually regionally variable; sheets,the crustal rebound is small and gener- . the present topography of the low-lying land ally one of subsidence;here the chanqeinãcean areas and shallow sea-floorbathymetry for volume dominates, and sea-levelis séento rise. the region; KURT LAMBECK = a("(t)+^Çía,Ð+AÇ@'Ð (2) . any information on tectonics, sedimentation ^ç@,t) or erosion that may have changed the ge- where A("(t) is the previously defined-eustatic ometry of the coastal zone. "(t) sea-Ievel , AÇ,@,t)is the combined glacio- Because of the spatial variability of the sea-level hydro-isostatic contributi on, and A(r(E,t) is any change, the beJt way to establish a record of additionai tectonic contribution. This last con- the pãst positions at a particular location is to tribution is discussed further below and the infei it frbm the geoiogical, geomorphological emphasis here is on the isostatic function, which and archaeological record. But observations that b" written as the sum of three parts: permit a quantitative estimate of the changing "ati exist for the þosition olfthe sea surface seldom Açía,Ð = ^Ç@,Ð+ ^(,@,Ð + a(*(tP,t) t3l ärea of interest and - at best - it probably consists of a partial time series. Also, such The total sea-levelchange is expressedas: records become increasingly rare and impre- cise the further one goesback in time. What is AKa,t)= A("(t) + A(,,@,t)+ Aqq,t) + Aç,@,t)+ AÇ{EÐ t+l required is a physical model for inte-rpolation in is a function of beiween the available fragments of information The eustatic term A("(t) [a) volume a¡rd its evalu- so as to be able to predict sea-Ievelat any place the rate of change in oðean of the rate of melt- and time. For tectonically stable regions the ation requires ã knowledge ice caps. The second glacio-hydro-isostatic theory provides- a rela- ing of thi totality of the the departures of sea- [ively smoothly varying and predictable func- rclrn A(,(E,t) describes on a rigid planet by tion ôf such change in time and spacethat can level chänge lrom eustasy in gravitational attrac- be used to interpolate between isolated obser- allowing for the change water as the ice sheets vations.