No abstract

The impact of Quaternary climate cycles on denudation rates and fluvial aggradation and incision is debated, especially in non-glaciated regions. Here we present paleo-denudation rates and geochronological constraints on aggradation and incision from the Sfakia and Elafonisi alluvialfan sequences on Crete, Greece. We report seven optically stimulated luminescence (OSL), ten radiocarbon ages, and eight 10 Be and eight 36 Cl denudation rates from modern and terrace sediments. For five samples, 10 Be and 36 Cl were measured on the same sample by measuring 10 Be on cherts and 36 Cl on calcite. Results indicate relatively steady denudation rates throughout the past 80kyr, but the aggradation and incision history indicate a link with shifts in climate. At the Elafonisi fan, we identify four periods of aggradation coinciding with Marine Isotope Stages (MIS) 2, 4, 5a/b, and likely 6, and three periods of incision coinciding with MIS 1, 3, and likely 5e. At the Sfakia fan, rapid aggradation occurred during MIS 2 and 4, analogous to aggradation periods at the Elafonisi fan system, followed by up to 50 m of incision during MIS 1. Nearby climate and vegetation records show that MIS 2, 4, and 6 were characterized by cold and dry climates with sparse vegetation, whereas forest cover and wet conditions prevailed during MIS 1, 3, and 5. Our data thus suggest that past changes in climate had little effect on landscape-wide denudation rates, but exerted a strong control on the aggradation-incision behaviour of alluvial channels on Crete. During glacial stages, we attribute aggradation to hillslope sediment release promoted by reduced vegetation cover and decreased river sediment transport capacity; conversely, incision occurred during relatively warm and wet stages due to increased river transport capacity. We conclude that, in this landscape, past hydroclimate variations outcompeted changes in sediment supply as the primary driver of alluvial deposition and incision.

<p>The impact of Quaternary climate cycles on denudation as well as fluvial aggradation and incision is debated, especially in regions that did not experience glaciation. Here we present a record of paleo-denudation rates, and geochronologic data constraining aggradation and incision from the Sfakia and Elafonisi alluvial sequences on the island of Crete, Greece. We report seven new optically stimulated luminescence (OSL) and ten new radiocarbon ages, as well as eight <sup>10</sup>Be and eight <sup>36</sup>Cl denudation rates from modern and terrace sediments. At the Elafonisi fan system, we identify four periods of aggradation, where marine isotope stages (MIS) 2, 4, and likely 6 correspond to aggradation periods, and MIS 1, 3, and likely 5e are characterized by incision. The dating of paleoshorelines indicates constant uplift over the past 71 ka, at rates of 1.2 mm/a. Aggradation occurred throughout the entire glacial cycle at the Sfakia fan, followed by up to 50 m of incision in the past 10 ka. Chronological constraints indicate that aggradation rates were particularly high during MIS 2 and 4, analogous to the Elafonisi fan system. However, our paleo-denudation rates indicate mostly constant denudation throughout the past 80 ka; with only two samples indicating an up to 50% increase in paleo-denudation rates compared to modern rates. Nearby climate and vegetation records show that MIS 2, 4, and 6 were characterized by cold and dry climate with sparse vegetation, whereas forest cover and wet conditions prevailed during MIS 1, 3, and 5. Our data suggest that variations in climate and vegetation cover were not sufficient to markedly alter landscape-wide denudation rates, but that changes in hydroclimate and vegetation exerted a strong control on the aggradation-incision behavior of the drainages. During relatively cold stages, low vegetation cover and river sediment transport capacity led to aggradation, whereas the increased river transport capacity during relatively warm stages caused subsequent incision. We therefore hypothesize that the studied catchments show a decoupling between transport-limited streams responding to climate forcing and near-steady hillslope denudation.</p>

The impact of Quaternary climate cycles on denudation rates and fluvial aggradation and incision is debated, especially in non-glaciated regions. Here we present paleo-denudation rates and geochronological constraints on aggradation and incision from the Sfakia and Elafonisi alluvial-fan sequences on Crete, Greece. We report seven optically stimulated luminescence (OSL), ten radiocarbon ages, and eight 10Be and eight 36Cl denudation rates from modern and terrace sediments. For five samples, 10Be and 36Cl were measured on the same sample by measuring 10Be on cherts and 36Cl on calcite. Results indicate relatively steady denudation rates throughout the past 80kyr, but the aggradation and incision history indicate a link with shifts in climate. At the Elafonisi fan, we identify four periods of aggradation coinciding with Marine Isotope Stages (MIS) 2, 4, 5a/b, and likely 6, and three periods of incision coinciding with MIS 1, 3, and likely 5e. At the Sfakia fan, rapid aggradation occurred during MIS 2 and 4, analogous to aggradation periods at the Elafonisi fan system, followed by up to 50 m of incision during MIS 1. Nearby climate and vegetation records show that MIS 2, 4, and 6 were characterized by cold and dry climates with sparse vegetation, whereas forest cover and wet conditions prevailed during MIS 1, 3, and 5. Our data thus suggest that past changes in climate had little effect on landscape-wide denudation rates, but exerted a strong control on the aggradation-incision behaviour of alluvial channels on Crete. During glacial stages, we attribute aggradation to hillslope sediment release promoted by reduced vegetation cover and decreased river sediment transport capacity; conversely, incision occurred during relatively warm and wet stages due to increased river transport capacity. We conclude that, in this landscape, past hydroclimate variations outcompeted changes in sediment supply as the primary driver of alluvial deposition and incision.