ABSTRACT The distribution and taxonomy of modern benthic foraminifera are described for the western Sunda Shelf, southern South China Sea off northeast peninsular Malaysia. This study provides baseline foraminiferal data that can be utilized in paleoenvironmental reconstructions of Neogene sediments from the Sunda Shelf and elsewhere in the Indo-Pacific. The uppermost centimeter of 60 surface sediment samples (> 150 µm) from nearshore (8 m) to inner shelf (60 m) water depths yielded 125 species. The distribution of these species is described and 120 species are illustrated with color light microscope digital images and scanning electron microscope imagery. Five sample assemblages, CGT1-CGT5 are interpreted from the results of the cluster analysis of total (live plus dead) foraminiferal relative abundance data. Discriminant analysis demonstrates that these five groups are statistically distinguishable at the 95% confidence level. The distribution of groups is related to variations in depth and substrate grain-size. This relationship is reaffirmed by canonical correspondence analysis. Closest to shore (8–14 m water depth), the high diversity (49 species) assemblage (CGT1), characterized by Amphistegina radiata and Amphistegina lessonii , occurs in medium to coarse quartz sand substrates, likely derived from the nearby Terengganu River. In slightly deeper water (21–22 m) and in gravelly quartz sand substrates, the lower diversity (33 species) assemblage of CGT2 is strongly dominated by Amphistegina radiata and Amphistegina lessonii . CGT3 occurs in shelly muddy quartz sand substrates (32–41 m), has a high diversity assemblage (46 species), and is characterized by Assilina ammonoides , Amphistegina radiata and Discorbinella bertheloti . Berthierine internal molds of Amphistegina lessonii and Amphistegina radiata are common in CGT1, CGT2 and CGT3, possibly indicating reworking from Pleistocene deposits in the region. High diversity (51 species) assemblage CGT4 occurs in mud substrates (44–59 m) and is characterized by Heterolepa dutemplei and Asterorotalia milletti ; the nearshore, sandy substrate taxa Amphistegina radiata and Amphistegina lessonii are absent. CGT5, located farthest from shore at 60 m water depth and in shelly sandy mud and shelly muddy sand, has a high diversity assemblage (46 species) characterized by Heterolepa dutemplei and Assilina ammonoides , with rare Asterorotalia milletti . This assemblage may be, in part, a lag deposit associated with modern bottom currents. The results of this study were combined with previously published research to identify nine foraminifera-based environmental subdivisions in the southern South China Sea: mangrove swamps in Terengganu and Sabah, Malaysia; high salinity lagoonal and inlet assemblages in Terengganu, Malaysia; low salinity estuarine assemblages in Terengganu, Malaysia; Mekong Delta assemblages; nearshore areas in the northern Gulf of Thailand off the mouths of rivers; inner shelf environments off the Mekong delta and off Johore, Malaysia dominated by Asterorotalia pulchella ; shallow inner shelf (<40 m water depth) environments from Terengganu and Johore, Malaysia; inner shelf environments (40–100 m water depth) off Terengganu, Malaysia and on the east-central Sunda Shelf; outer shelf environments (100–200 m water depth) on the east-central Sunda Shelf. The subdivisions are related mainly to salinity in marginal marine environments and substrate type and depth/distance from shore in shelf environments.

Abstract The Institute Ice Stream (IIS) in West Antarctica may be increasingly vulnerable to melting at the grounding line through modifications in ocean circulation. Understanding such change requires knowledge of grounding-line boundary conditions, including the topography on which it rests. Here, we discuss evidence from new radio-echo sounding (RES) data on the subglacial topography adjacent to the grounding line of the IIS. In doing so, we reveal a previously unknown subglacial embayment immediately inland of the IIS grounding zone which is not represented in the Bedmap2 compilation. We discuss whether there is an open-water connection between the embayment and the ice-shelf cavity. The exact location of the grounding line over the embayment has been the subject of considerable uncertainty, with several positions being proposed recently. From our compilation of data, we are able to explain which of these grounding lines is most likely and, in doing so, highlight the need for accurate bed topography in conjunction with satellite observations to fully comprehend ice-sheet processes in this region and other vulnerable locations at the grounded margin of Antarctica.