Timing and magnitude of Holocene sea-level changes along the middle and south Patagonian Atlantic coast derived from beach systems, littoral terraces and valley-mouth terraces
Geomorphologic and chronostratigraphic investigations in various coastal localities along the middle and south Patagonian Atlantic coast, from Bahía Vera (44°S) in the north to San Julián (49°S) in the south, confirm a rich sequence of Holocene beach ridge systems and littoral and valley-mouth terraces. Beach ridges are present up to 10 m above current highest tide level (hTw) and date to the early mid-Holocene transgression maximum. Beach-ridge deposits represent high-energy, wave dominated coastal environments, whereas valley-mouth terraces and littoral terraces (elevations of 5.5–6.5 m above hTw) developed in wave-protected coastal environments. The surface elevation of these littoral forms suggest that the middle and south Patagonian Atlantic coast is likely undergoing a slow glacio-isostatic uplift on the order of 0.3–0.4 mm/a since the mid-Holocene. The early Holocene sea-level rise reached the modern coastline by 8100 14C years ago (c. 8600 cal BP) at the latest. Sea level at that time was most likely near its present position. The Holocene transgression maximum lasted from 6900 to at least 6200 14C BP (c. 7400 to 6600 cal BP), raising relative sea level to about 2 m to a maximum of 3 m above the present level, after which sea level declined to the present level. Two significant sea-level falls of at most 1 m occurred: a) between 6200 and 6000 14C BP (c. 6600 to 6400 cal BP), and b) between 2600 and 2400 14C BP (c. 2300 to 2050 cal BP). We assume, that both significant sea-level falls were predominantly driven by eustatic changes of ocean volume, whereas both thermo-steric changes and changes of tides may also have contributed to these relatively strong sea-level drops. Gravitational changes driven by Greenland ice growth (sensu Mitrovica et al., 2001) may also have amplified any eustatic portion of sea-level fall. The trend of a general sea-level decline since the mid-Holocene transgression maximum seems to be predominantly glacio-isostatically driven.
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