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- U and Th isotope constraints on the duration of Heinrich events H0-H4 in the southeastern Labrador SeaPublication . C. Veiga-Pires, C.; Hillaire-Marcel, C.The duration and sequence of events recorded in Heinrich layers at sites near the Hudson Strait source area fbr ice-rafted material are still poorly constrained, notably because of the limit and uncertainties of the C-14 chronology. Here we use high-resolution Th-230-excess measurements, in a 6 m sequence raised from Orphan Knoll (southern Labrador Sea), to constrain the duration of the deposition of the five most recent Heinrich (H) layers. On the basis of maximum/minimum estimates for the mean glacial Th-230-excess flux at the studied site a minimum/maximum duration of 1.0/0.6, 1.4/0.8, 1.3/0.8, 1.5/0.9, and 2.1/1.3 kyr is obtained for H0 (similar to Younger Dryas), H1, H2, H3, and H4, respectively. Thorium-230-excess inventories and other sedimentological features indicate a reduced but still significant lateral sedimentary supply by the Western Boundary Undercurrent during the glacial interval. U and Th series systematics also provide insights into source rocks of H layer sediments (i.e., into distal Irminger Basin/local Labrador Sea supplies).
- U and Th isotope constraints on the duration of Heinrich events H0-H4 in the southeastern Labrador SeaPublication . Veiga-Pires, C.; Hillaire-Marcel, C.The duration and sequence of events recorded in Heinrich layers at sites near the Hudson Strait source area for ice-rafted material are still poorly constrained, notably because of the limit and uncertainties of the 14C chronology. Here we use high-resolution 230Th-excess measurements, in a 6 m sequence raised from Orphan Knoll (southern Labrador Sea), to constrain the duration of the deposition of the five most recent Heinrich (H) layers. On the basis of maximum/minimum estimates for the mean glacial 230Th-excess flux at the studied site a minimum/maximum duration of 1.0/0.6, 1.4/0.8, 1.3/0.8, 1.5/0.9, and 2.1/1.3 kyr is obtained for H0 (∼Younger Dryas), Hl, H2, H3, and H4, respectively. Thorium-230-excess inventories and other sedimentological features indicate a reduced but still significant lateral sedimentary supply by the Western Boundary Undercurrent during the glacial interval. U and Th series systematics also provide insights into source rocks of H layer sediments (i.e., into distal Irminger Basin/local Labrador Sea supplies).
- Postglacial sea-level rise in South Portugal as recorded in Guadiana EstuaryPublication . Boski, T.; Moura, Delminda; Camacho, Sarita; Duarte, Duarte; Scott, David; Veiga-Pires, C.; Pedro, Paulo; Santana, PauloThe Guadiana River Estuary is located in the terminal part of a deeply incised river valley, which accumulated several tens of meters of sediments during the Holocenic transgression. Five cored boreholes (see Fig.1 for localisation) that reached the pre-Holocenic substratum were drilled recently in order to recognize the architecture of sedimentary facies and to quantify the accumulation of organic carbon trapped in sediments during the valley infilling by marine waters. It was assumed that due to structural constraints imposed by Palaeozoic and Mezozoic substratum, the main estuarine channel did not change its position significantly. Consequently borehole locations were chosen in order to represent different sedimentary environments in the estuary: proximity to the main channel (CM1 and CM3), external sea facing (CM4) and lagoonal (CM2 and CM5) environments.
- A glaciological perspective on Heinrich eventsPublication . Clarke, G. K. C.; Marshall, S. J.; Veiga-Pires, C.; Bilodeau, G.; Hillaire-Marcel, C.Heinrich events, the massive episodic disgorgement of sediment-laden ice from the Laurentide Ice Sheet to the North Atlantic Ocean, are a puzzling instability of the Ice-Age climate system. Although there is broad agreement on the defining characteristics of Heinrich events, the glaciological mechanisms remain controversial. Paleoceanographic records show that Heinrich events tend to occur at the culmination of a cooling cycle, termed the Bond cycle, and this has invited the interpretation that the events are a fast response of the Laurentide Ice Sheet to external atmospheric changes. A vexing issue for glaciologists is how a fast and timely response to an external forcing can possibly be reconciled with the known physics of glaciers and ice sheets. Fast changes in glacier behavior can only occur if some flow instability is excited. Thus glaciologists tend to favor the idea that the climate change occurring at the culmination of a Bond cycle is an atmospheric response to ice sheet instability. However, a free-running cyclic flow instability, such as that exhibited by surging glaciers, could not satisfy the timing requirements. Using computer modeling we explore ways to resolve these conflicts.