Beaches in McMurdo Sound, Antarctica

<p>Modern beaches in McMurdo Sound can be divided into 3 process regimes. Beaches on Ross Island (eastern McMurdo Sound) are characterised by marine processes with little ice modification. On ice-bound western McMurdo Sound, coastal orientation is of paramount importance. Ice thrust features are prominent on south facing beaches, which are open to the predominant wind direction and receive relatively small waves from the fetch restricted south. A greater degree of marine dominance is exhibited by beaches on north facing coasts where sea ice is blown offshore and the beaches are open to the larger storm waves from the eastern Ross Sea. The single most useful indicator of the relative importance of marine and ice processes on the beaches is the roundness of the beach material. Unlike the modern beaches, raised beach ridges at all sites comprise poorly sorted cobbles in a mixed sand and gravel matrix. These are inferred to be storm ridges. In contrast with the raised beaches, the modern beaches on the western side of the Sound have evidence of ice processes on them. This suggests that the modem beach has not experienced the same magnitude storms that produced the raised beaches. The size and frequency of the ridges is a product of the local wave climate. The number of raised beaches at any site is a useful indicator of the paleo-wave climate. More ridges occur in sheltered south facing locations, because they are more protected from open marine conditions, than on beaches in ice-free or north facing locations. When determining the marine limit of a site the most useful features are, low energy marine bedding features (such as flaser bedding) and boulder pavements. Based on inferred process information at the time of deposition, revised estimates of marine limits in McMurdo Sound and a new marine limit at Cape Barne are presented. Because the nature of the raised beaches has not been fully considered by previous authors sea level curves are inaccurate. The reconstruction of the retreat of the Ross Ice Shelf from marine limits in McMurdo Sound shows a three stage stepwise southward retreat of the Ross Ice Shelf. A breakout from somewhere north of Cape Roberts and south of Cape Ross back to Marble Point (on the western side of the Sound) while remaining north of Cape Bird (on the eastern side of the Sound), occurred sometime around 8,000 years ago. Another breakout cleared ice from Cape Bird to somewhere south of Cape Barne and south of Cape Bernacchi around 5,000 years ago. This differs with other authors work (Hall and Denton, 1999, Kellogg et al., 1996, Stuiver et al., 1981) by suggesting a considerably older date for the Ross Ice Sheet retreating from McMurdo Sound. The data presented here suggests that much of McMurdo Sound was ice free about 1,500 years before earlier estimates at about 6,500 years. The effect of the change in deglaciation timing is to reduce isostatic rebound rates. This suggests that there was less ice in McMurdo Sound during the Last Glacial Maximum.</p>

Beaches in McMurdo Sound, Antarctica

<p>Modern beaches in McMurdo Sound can be divided into 3 process regimes. Beaches on Ross Island (eastern McMurdo Sound) are characterised by marine processes with little ice modification. On ice-bound western McMurdo Sound, coastal orientation is of paramount importance. Ice thrust features are prominent on south facing beaches, which are open to the predominant wind direction and receive relatively small waves from the fetch restricted south. A greater degree of marine dominance is exhibited by beaches on north facing coasts where sea ice is blown offshore and the beaches are open to the larger storm waves from the eastern Ross Sea. The single most useful indicator of the relative importance of marine and ice processes on the beaches is the roundness of the beach material. Unlike the modern beaches, raised beach ridges at all sites comprise poorly sorted cobbles in a mixed sand and gravel matrix. These are inferred to be storm ridges. In contrast with the raised beaches, the modern beaches on the western side of the Sound have evidence of ice processes on them. This suggests that the modem beach has not experienced the same magnitude storms that produced the raised beaches. The size and frequency of the ridges is a product of the local wave climate. The number of raised beaches at any site is a useful indicator of the paleo-wave climate. More ridges occur in sheltered south facing locations, because they are more protected from open marine conditions, than on beaches in ice-free or north facing locations. When determining the marine limit of a site the most useful features are, low energy marine bedding features (such as flaser bedding) and boulder pavements. Based on inferred process information at the time of deposition, revised estimates of marine limits in McMurdo Sound and a new marine limit at Cape Barne are presented. Because the nature of the raised beaches has not been fully considered by previous authors sea level curves are inaccurate. The reconstruction of the retreat of the Ross Ice Shelf from marine limits in McMurdo Sound shows a three stage stepwise southward retreat of the Ross Ice Shelf. A breakout from somewhere north of Cape Roberts and south of Cape Ross back to Marble Point (on the western side of the Sound) while remaining north of Cape Bird (on the eastern side of the Sound), occurred sometime around 8,000 years ago. Another breakout cleared ice from Cape Bird to somewhere south of Cape Barne and south of Cape Bernacchi around 5,000 years ago. This differs with other authors work (Hall and Denton, 1999, Kellogg et al., 1996, Stuiver et al., 1981) by suggesting a considerably older date for the Ross Ice Sheet retreating from McMurdo Sound. The data presented here suggests that much of McMurdo Sound was ice free about 1,500 years before earlier estimates at about 6,500 years. The effect of the change in deglaciation timing is to reduce isostatic rebound rates. This suggests that there was less ice in McMurdo Sound during the Last Glacial Maximum.</p>

The Role of Geomorphology in the Quaternary

The advances in understanding of Quaternary geomorphology in the latter half of the 20th Century were closely linked with the improved knowledge of Quaternary climatic fluctuation, principally derived from isotopic evidence from ocean and ice cores. An important goal was finding terrestrial sedimentary records that can be correlated with the globally applicable isotopic sequence. From a geomorphological viewpoint, river terraces are paramount, particularly since they can provide semi-continuous sequences that record palaeoclimate and landscape evolution throughout the Quaternary, as well as the interaction of rivers with glaciation, sea-level change and notable geomorphological events. In coastal areas, shoreline terraces and raised beaches can provide similar sequences. The chapter discusses the progress made in understanding these archives and, in particular, the various mechanisms for dating and correlation, as well as touching upon contributions from other environments, namely slopes and karstic systems, as well as the role of soils in deciphering geomorphological evidence.

Multibeam Bathymetry and Distribution of Clay Minerals on Surface Sediments of a Small Bay in Terra Nova Bay, Antarctica

The second Antarctic station of South Korea was constructed at Terra Nova Bay, East Antarctica, but local seafloor morphology and clay mineralogical characteristics are still not fully understood. Its small bay is connected to a modern Campbell Glacier, cliffs, and raised beaches along the coastline. Fourteen sampling sites to collect surface sediments were chosen in the small bay for grain size and clay mineral analyses to study the sediment source and sediment-transport process with multibeam bathymetry and sub-bottom profiles. Under the dominant erosional features (streamlined feature and meltwater channel), icebergs are the major geological agent for transport and deposition of coarse-sized sediments along the edge of glaciers in summer, and thus the study area can reveal the trajectory of transport by icebergs. Glacier meltwater is an important agent to deposit the clay-sized detritus and it results from the dominance of the illite content occurring along the edge of Campbell Glacier Tongue. The high smectite content compared to Antarctic sediments may be a result of the source of the surrounding volcanic rocks around within the Melbourne Volcanic Province.

MIS 5e sea-level proxies in the eastern Mediterranean coastal region

Mediterranean raised beaches were subject to Quaternary research since the early years of the 20th century. The uniqueness of a warm-loving molluscs fauna immigrating into the Mediterranean made the coastline a prime subject for studying Quaternary sea-level changes. Today, we have a detailed picture of this historically important coastline characterised by tectonically dormant coastal zone alternating with zones that are subject to subsidence or uplift. As part of the Word Atlas of last interglacial shorelines (WALIS) database we compiled 21 MIS 5e proxies for the for the eastern Mediterranean area available at http://doi.org/10.5281/zenodo.4274178 (Israel; Sivan and Galili, 2020) and at http://doi.org/10.5281/zenodo.4283819 (Turkey, Egypt, Tunisia; Mauz, 2020). All these datapoints are sea-level indicators of variable quality situated between −1 ± 4 m and 7 ± 2 m resulting in a reconstructed MIS 5e palaeo-sea level situated between −1 ± 4 m and 13 ± 10 m.