AMS 14C and calibrated ages of sediment core GeoB10426-1

Newly acquired bathymetric and seismic reflection data have revealed mass-transport deposits (MTDs) on the northeastern Cretan margin in the active Hellenic subduction zone. These include a stack of two submarine landslides within the Malia Basin with a total volume of approximately 4.6 km**3 covering an area of about 135 km**2. These two MTDs have different geometry, internal deformations and transport structures. The older and stratigraphic lower MTD is interpreted as a debrite that fills a large part of the Malia Basin, while the second, younger MTD, with an age of at least 12.6 cal. ka B.P., indicate a thick, lens-shaped, partially translational landslide. This MTD comprises multiple slide masses with internal structure varying from highly deformed to nearly undeformed. The reconstructed source area of the older MTD is located in the westernmost Malia Basin. The source area of the younger MTD is identified in multiple headwalls at the slope-basin-transition in 450 m water depth. Numerous faults with an orientation almost parallel to the southwest-northeast-trending basin axis occur along the northern and southern boundaries of the Malia Basin and have caused a partial steepening of the slope-basin-transition. The possible triggers for slope failure and mass-wasting include (i) seismicity and (ii) movement of the uplifting island of Crete from neotectonics of the Hellenic subduction zone, and (iii) slip of clay-mineral-rich or ash-bearing layers during fluid involvement.

(Table 1) AMS 14C dates from sediment cores RC12-10 and GYRE97-6PV-20

Proxy records from two piston cores in the Gulf of Mexico (GOM) provide a detailed (50-100 year resolution) record of climate variability over the last 14,000 years. Long-term (millennial-scale) trends and changes are related to the transition from glacial to interglacial conditions and movement of the average position of the Intertropical Convergence Zone (ITCZ) related to orbital forcing. The d18O of the surface-dwelling planktic foraminifer Globigerinoides ruber show negative excursions between 14 and 10.2 ka (radiocarbon years) that reflect influx of meltwater into the western GOM during melting of the Laurentide Ice Sheet. The relative abundance of the planktic foraminifer Globigerinoides sacculifer is related to transport of Caribbean water into the GOM. Maximum transport of Caribbean surface waters and moisture into the GOM associated with a northward migration of the average position of the ITCZ occurs between about 6.5 and 4.5 ka. In addition, abundance variations of G. sacculifer show century-scale variability throughout most of the Holocene. The GOM record is consistent with records from other areas, suggesting that century-scale variability is a pervasive feature of Holocene climate. The frequency of several cycles in the climate records is similar to cycles identified in proxy records of solar variability, indicating that at least some of the century-scale climate variability during the Holocene is due to external (solar) forcing.

(Table 2) Radiocarbon content and 14C AMS ages of planktonic foraminifera from sediment cores Louis_1900 and Louis_2023

North American freshwater runoff records have been used to support the case that climate flickers were caused by shutdowns of the ocean thermohaline circulation (THC) resulting from reversals of meltwater discharges. Inconsistencies in the documentation of these meltwater switches, however, continue to fuel the debate on the cause/s of the oscillatory nature of the deglacial climate. New oxygen and carbon isotope records from the northern Gulf of Mexico depict in exceptional detail the succession of meltwater floods and pauses through the southern routing during the interval 16 to 8.9 ka (14C years BP; ka, kiloannum). The records underscore the bimodal role played by the Gulf of Mexico as a destination of meltwater discharges from the receding Laurentide Ice Sheet. The evidence indicates that the Gulf of Mexico acted as the principal source of superfloods at 13.4, 12.6, and 11.9 ka that reached the North Atlantic and contributed significantly to density stratification, disruption of ocean ventilation, and cold reversals. Gulf of Mexico lapsed into a "relief valve" position in post-Younger Dryas time, when meltwater discharges were rerouted south at 9.9, 9.7, 9.4, and 9.1 ka, thus temporarily interrupting North Atlantic-bound freshwater discharges from Lake Agassiz. The history of meltwater events in the Gulf of Mexico contradicts the model that meltwater flow via the eastern outlets into the North Atlantic disrupted the ocean THC, causing cooling, while diversions to the Gulf of Mexico via the Mississippi River enhanced THC and warming.

Age determinations in Lena Delta

The age correlation between the three main geomorphological terraces in the Lena Delta, especially that of the second sandy terrace (Arga Island) and the third terrace (Ice Complex and underlying sands) is still being discussed, Knowledge about the age of the lee Complex and its underlying sands, and the Arga sands is necessary for understanding the past and modern structure of the delta. Geochronometrie data have been acguired for three sediment seguences from the Lena Delta by lumineseence dating using the potassium feldspar IR-OSL technique. Additionally, 14C dates are available for geochronological discussion. Typical sediments of the upper part of Arga Island as found in the area of Lake Nikolay are of Late Pleistoeene age (14.5-10.9 ka), Typical third terrace sediments from two seguenees located at the Olenyokskaya branch are older. At the profile "Nagym" sandy seguences were most probably deposited between about 65 ka and 50 ka before present. The lower part of the sandy seguence at "Kurungnakh Island" is possibly older than the sediments of the section at Nagym. However, methodological difficulties in luminescence dating (insufficient bleaching at the time of deposition) and younger 14C dates make the discussion of the results difficult.

(Table 1) AMS-14C ages determined in pairs of spreiten and directly adjacent host sediment of cores M39029-4 and M29039-8

he downward transport of surface sediment deep into the sediment column by the Zoophycos-producing animal leads not only to large age differences between the Zoophycos structure and surrounding host sediment but also to large differences in age between different foraminifer species found inside the trace fossil. In the late Quaternary material from the southwestern Portuguese continental slope examined in this study, age differences of up to 2590 years were observed between the planktic foraminifer species Globigerinoides ruber and Globigerina bulloides. These differences are caused by the mixing of surface and host material with different abundances of the two species. If there are differences in the abundance of the two species at the surface and/or in the host sediment, plenty of relatively young foraminifers may be mixed with few relatively old ones, or vice versa. The age differences between species caused by the combination of deep-reaching bioturbation by the Zoophycos producer and abundance variations may be considerably larger than the age differences caused by the homogenizing bioturbation in the mixed layer.