Radiocarbon ages, dose rates, water isotopic composition and hydrochemistry of samples from Komakuk Beach and Herschel Island

Terrestrial permafrost archives along the Yukon Coastal Plain (northwest Canada) have recorded landscape development and environmental change since the Late Wisconsinan at the interface of unglaciated Beringia (i.e. Komakuk Beach) and the northwestern limit of the Laurentide Ice Sheet (i.e. Herschel Island). The objective of this paper is to compare the late glacial and Holocene landscape development on both sides of the former ice margin based on permafrost sequences and ground ice. Analyses at these sites involved a multi-proxy approach including: sedimentology, cryostratigraphy, palaeoecology of ostracods, stable water isotopes in ground ice, hydrochemistry, and AMS radiocarbon and infrared stimulated luminescence (IRSL) dating. AMS and IRSL age determinations yielded full glacial ages at Komakuk Beach that is the northeastern limit of ice-free Beringia. Herschel Island to the east marks the Late Wisconsinan limit of the northwest Laurentide Ice Sheet and is composed of ice-thrust sediments containing plant detritus as young as 16.2 cal ka BP that might provide a maximum age on ice arrival. Late Wisconsinan ice wedges with sediment-rich fillings on Herschel Island are depleted in heavy oxygen isotopes (mean d18O of -29.1 per mil); this, together with low d-excess values, indicates colder-than-modern winter temperatures and probably reduced snow depths. Grain-size distribution and fossil ostracod assemblages indicate that deglaciation of the Herschel Island ice-thrust moraine was accompanied by alluvial, proluvial, and eolian sedimentation on the adjacent unglaciated Yukon Coastal Plain until ~11 cal ka BP during a period of low glacio-eustatic sea level. The late glacial-Holocene transition was marked by higher-than-modern summer temperatures leading to permafrost degradation that began no later than 11.2 cal ka BP and caused a regional thaw unconformity. Cryostructures and ice wedges were truncated while organic matter was incorporated and soluble ions were leached in the thaw zone. Thermokarst activity led to the formation of ice-wedge casts and deposition of thermokarst lake sediments. These were subsequently covered by rapidly accumulating peat during the early Holocene Thermal Maximum. A rising permafrost table, reduced peat accumulation, and extensive ice-wedge growth resulted from climate cooling starting in the middle Holocene until the late 20th century. The reconstruction of palaeolandscape dynamics on the Yukon Coastal Plain and the eastern Beringian edge contributes to unraveling the linkages between ice sheet, ocean, and permafrost that have existed since the Late Wisconsinan.

The interstitial subsoil fauna on the beach of Sarso Island, Red Sea

The scope of this research was to find out, how important is the presence of brackish water for the formation of the characteristical littoral subsoil fauna in the interstitial spaces of beaches. There is little precipitation in the Red Sea area and therefore little influence of freshwater on the beach. Moreover, the sandy beach of Sarso Island (Farasan Archipelago) is bordered landwards and underneath by solid limestone, preventing subsoil fresh water, if there is any, from penetrating into the beach region. The salinity of the interstitial water from Sarso beach lies a little above the salinity of the adjacent sea. The microfauna of Sarso beach is composed to a rather big proportion of such species that are known to be characteristical littoral subsoil water species, partially of world wide distribution. The ecological analysis of this fauna, i.e. the freeliving Nematodes, reveals the presence of two distinct associations: 1. the association of the low level subsoil region, close to the sea, with clear interstitial water, subject to regular exchange with the water of the adjcent sea. 2. the association of the high level subsoil region, 4-10 meter distant from the sea, with brownish water. Contrary to earlier results there is no distinction in salinity between the two associations, so it is not longer justified to apply the term brackish water fauna on the animals living in the association of the high level subsoil region.

Relative sea-level history of Marguerite Bay, Antarctic Peninsula derived from optically stimulated luminescence-dated beach cobbles

Calmette Bay within Marguerite Bay along the western side of the Antarctic Peninsula contains one of the most continuous flights of raised beaches described to date in Antarctica. Raised beaches extend to 40.8 m above sea level (masl) and are thought to reflect glacial isostatic adjustment due to the retreat of the Antarctic Peninsula Ice Sheet. Using optically stimulated luminescence (OSL), we dated quartz extracts from cobble surfaces buried in raised beaches at Calmette Bay. The beaches are separated into upper and lower beaches based on OSL ages, geomorphology, and sedimentary fabric. The two sets of beaches are separated by a prominent scarp. One of our OSL ages from the upper beaches dates to 9.3 thousand years ago (ka; as of 1950) consistent with previous extrapolation of sea-level data and the time of ice retreat from inner Marguerite Bay. However, four of the seven ages from the upper beaches date to the timing of glaciation. We interpret these ages to represent reworking of beaches deposited prior to the Last Glacial Maximum (LGM) by advancing and retreating LGM ice. Ages from the lower beaches record relative sea-level fall due to Holocene glacial-isostatic adjustment. We suggest a Holocene marine limit of 21.7 masl with an age of 5.5-7.3 ka based on OSL ages from Calmette Bay and other sea-level constraints in the area. A marine limit at 21.7 masl implies half as much relative sea-level change in Marguerite Bay during the Holocene as suggested by previous sea-level reconstructions. No evidence for a relative sea-level signature of neoglacial events, such as a decrease followed by an increase in RSL fall due to ice advance and retreat associated with the Little Ice Age, is found within Marguerite Bay indicating either: (1) no significant neoglacial advances occurred within Marguerite Bay; (2) rheological heterogeneity allows part of the Antarctic Peninsula (i.e. the South Shetland Islands) to respond to rapid ice mass changes while other regions are incapable of responding to short-lived ice advances; or (3) the magnitude of neoglacial events within Marguerite Bay is too small to resolve through relative sea-level reconstructions. Although the application of reconstructing sea-level histories using OSL-dated raised beach deposits provides a better understanding of the timing and nature of relative sea-level change in Marguerite Bay, we highlight possible problems associated with using raised beaches as sea-level indices due to post-depositional reworking by storm waves.

(Table 2) Grain composition of sediments from ODP Hole 161-974B and from beach samples

Miocene to Pleistocene sand and sandstone were recovered at Ocean Drilling Program Site 974 in the Tyrrhenian Basin and Sites 976 and 977 in the Alboran Basin. Sand detrital modes were determined for 45 samples from these sites, as well as 10 samples of Spanish beach sand. At Site 974, the Pleistocene section includes a number of volcaniclastic (vitric ash) and terrigenous sand layers; the latter are heterogeneous and contain sedimentary and metamorphic lithic fragments. Submarine canyon and onshore drainage patterns suggest that the most likely source of this sediment is the Tiber River drainage basin in central Italy, where a Pleistocene volcanic field is superimposed on Apennine orogenic rocks. In contrast, the Miocene sand in Unit III at Site 974 may have been derived from local basement highs. The quartzolithic composition and preponderance of metamorphic and sedimentary lithic debris in sand samples from Unit II at Site 976, Unit I at Sites 977 and 978, and Unit I at Site 979 are consistent with derivation from metamorphic rocks and sedimentary cover sequences that crop out in the Betic Cordillera of southern Spain (976-978) and in the Rif of Northern Africa (979). The sedimentary to metamorphic lithic fragment ratios in these samples reflect the relative proportion of metamorphic and sedimentary rocks exposed in onshore source terranes. In contrast, the source of the few quartzose Pleistocene sands at Site 976 was likely the Flysch Trough Units that crop out near Gibraltar. The significant volcanic component in certain intervals at Sites 976 (upper Miocene) and 977 (lower Pliocene to Miocene) is consistent with widespread volcanic activity during basin inception and development. Mean sand detrital modes for sand subgroups from both the Alboran and Tyrrhenian Basin sites plot in the Recycled Orogenic and Magmatic Arc compositional fields of Dickinson et al. (1983, doi:10.1130/0016-7606(1983)94<222:PONAPS>2.0.CO;2), reflecting the hybrid tectonic histories of these basins.

Mineralcomposition of beach sediments from the area "Fähre Großenbrode-Kliff Wulfen" on Fehmarn

Um die Insel Fehmarn und an der Nordküste Wagriens wurden rund 2500 Strand-, Flachwasser- und Seesandproben zum Erkennen der Materialtransportwege sedimentpetrographisch untersucht. Für die Schwermineralbestimmung wurde hauptsächlich die Fraktion 0,2-0,1 mm herangezogen, da diese für die vorliegenden Sedimente charakteristisch ist. Da die Mineralzusammensetzung der Sedimente im gesamten Untersuchungsgebiet gleich ist, also nirgends örtlich sog. Leitminerale zugeführt werden, wurden bei der Auswertung der Analysenergebnisse die hydrographischen Verhältnisse der westlichen Ostsee und die Abhängigkeit des Sedimentes von der Kraft des bewegten Meerwassers beachtet. Bezüglich der Abhängigkeit des transportierten Materials von der Wasserkraft werden drei voneinander abweichende Systeme, nämlich der Strand, die Brandungszone und das tiefere Wassergebiet, erkannt. Am Strand ist die angewandte Untersuchungsmethode sowohl an langgestreckten Küsten als auch in stark untergliederten Ufergebieten zum Erkennen der Sandwanderbahnen geeignet. Erosion und Neuzuführung von Material auf dem Transportwege zeigen das gleiche mineralische Bild, und eine Entscheidung, welcher dieser beiden Fälle tatsächlich vorliegt, kann nur im Gelände getroffen werden. Die Korngrößenanalyse allein ist zur Beantwortung vorliegender Fragestellungen nicht brauchbar, weil durch gegebene hydrographische Bedingungen die Korngröße in Transportrichtung sowohl abnehmen als auch zunehmen kann. In Strandgebieten mit veränderter natürlicher Beschaffenheit der Sedimente und an Küsten mit ausgedehnten vorgelagerten materialliefernden Abrasionsflächen ist die Grenze der Methode aufgezeigt. Höfte, Haken und Sandinseln zeigen jeweils typische mineralische Zusammensetzungen ihres Strandes, aus welchen die Entstehung der betreffenden Anlandungsformen abgeleitet werden kann. Quer über die Brandungszone weisen die Sedimente auf engem Raum wechselnde Mineralzusammensetzung auf, aus der auf die örtlichen hydrographischen Verhältnisse geschlossen werden kann. Zum Vergleich sedimentpetrographischer Ergebniswerte sind nur Sande, die unter gleichen Ablagerungsbedingungen entstanden sind, geeignet. Zum Erkennen der Materialwanderwege wurden entweder Sandproben von den Riffkämmen oder aus den Rinnen zwischen zwei Sandanhäufungszonen untersucht. In beiden Fällen wurden die Transportrichtungen erkannt. In Gebieten, in denen die Strandsanduntersuchungen negativ verliefen, ließen die Riffsandproben Schlüsse auf die Materialschüttungsrichtungen zu. An exponierten Küsten mit mehreren wirksamen Windrichtungen darf jedoch nicht von dem einen auf das andere Wandersystem geschlossen werden. Eine Umkehr der Materialvertriftung zwischen Flachwasser und Strand kann vorliegen. Im tieferen Wasser ist es möglich, mit gleicher Methode unter Berücksichtigung der Morphologie des Meeresgrundes die Materialschüttungsrichtung zu erkennen. Zur Sedimentuntersuchung auf Linienprofilen sind nur Proben gleicher Wassertiefe geeignet; die Sonderung des Materials nach der Tiefe muß beachtet werden. Aus den ermittelten sedimentpetrographischen Werten lassen sich eine Reihe von Beziehungen ablesen, die zur Deutung der Mineralgesellschaft und für die Auswertung der Untersuchungsergebnisse herangezogen werden können. Als regionales Ergebnis der vorstehenden Untersuchung kann eine Karte der Küsten Fehmarns und Nordoldenburgs vorgelegt werden, in der die Sandwanderungswege am Strand, in der Flachwasserzone und in den daran anschließenden tieferen Wassergebieten dargestellt sind.