Neogene to Quaternary stratigraphic evolution of the Antarctic Peninsula, Pacific Margin offshore of Adelaide Island:Transitions from a non-glacial, through glacially-influenced to a fully glacial state

A detailed morphologic and seismic stratigraphic analysis of the continental margin offshore of Adelaide Island on the Pacific Margin of the Antarctic Peninsula (PMAP) is described based on the study of a regular network of reflection multichannel seismic profiles and swath bathymetry. We present an integrated study of the margin spanning the shelf to the continental rise and establish novel chronologic constraints and offer new interpretations on tectonic evolution and environmental changes affecting the PMAP. The stratigraphic stacking patterns record major shifts in the depositional style of the margin that outline three intervals in its evolution. The first non-glacial interval (Early Cretaceous to middle Miocene) encompasses a transition from an active to a passive margin (early Miocene). The second glacially-influenced interval (middle to late Miocene) is marked by pronounced aggradational sedimentary stacking and subsidence. Ice sheets advanced over the middle shelf of the margin at the end of this second interval, while the outer shelf experienced rare progradational events. The third, fully glaciated interval shows clear evidence of glacially dominated conditions on the margin. This interval divides into three minor stages. During the first stage (late Miocene to the beginning of the early Pliocene), frequent grounded ice advances to the shelf break began, depositing an initial progradational unit. A major truncation surface marked the end of this stage, which coincided with extensive mass transport deposits at the base of the slope. During the second progradational glacial margin stage (early Pliocene to middle Pleistocene), stacking patterns record clearly prograding glacial sequences. The beginning of the third aggradational glacial margin stage (middle Pleistocene to present) corresponded to an important shift in global climate during the Mid-Pleistocene Transition. Morphosedimentary characteristics observed along the margin today began to develop during the latest Miocene but did not become fully established until sometime during the interval between the end of the Pliocene and middle Pleistocene. Between these two time intervals, the northeast lateral migration of the Marguerite Trough also played a critical role in margin evolution, as it controlled ice sheet drainage pathways across the shelf, which in turn influenced development of slope and rise morphologies. Areas offshore from Adelaide Island differ from other areas of the PMAP due to changes in sedimentary processes that resulted from migration of the trough. This study confirms that the PMAP represents an exceptional locality for decoding, reconstructing and linking past tectonic and climatic changes. The study area specifically records not only the most relevant changes in depositional style, but also the relative importance of persistent along- and down-slope sedimentary processes. Our study approach can be extended to other areas and integrated with additional techniques to understand the evolution and the global linkages of the entire Antarctic continental margin and the ice sheets

Drake-Scotia Sea gateways: onset and evolution of the Drake Passage and Scotia Sea, implications for global ocean circulation and climate

Australasian IODP Regional Planing Workshop (2017. Sidney)Instituto Geológico y Minero de España, EspañaInstituto Andaluz de Ciencias de la Tierra, Consejo Superior de Investigaciones Científicas, EspañaIstituto Nazionale di Oceanografia e Geofisica Sperimentale, ItaliaSan Diego State University, Estados UnidosPeer reviewe

Drought response in Arabidopsis displays synergistic coordination between stems and leaves

The synergy between drought-responsive traits across different organs is crucial in the whole-plant mechanism influencing drought resilience. These organ interactions, however, are poorly understood, limiting our understanding of drought response strategies at the whole-plant level. Therefore, we need more integrative studies, especially on herbaceous species that represent many important food crops but remain underexplored in their drought response. We investigated inflorescence stems and rosette leaves of six Arabidopsis thaliana genotypes with contrasting drought tolerance, and combined anatomical observations with hydraulic measurements and gene expression studies to assess differences in drought response. The soc1ful double mutant was the most drought-tolerant genotype based on its synergistic combination of low stomatal conductance, largest stomatal safety margin, more stable leaf water potential during non-watering, reduced transcript levels of drought stress marker genes, and reduced loss of chlorophyll content in leaves, in combination with stems showing the highest embolism resistance, most pronounced lignification, and thickest intervessel pit membranes. In contrast, the most sensitive Cvi ecotype shows the opposite extreme of the same set of traits. The remaining four genotypes show variations in this drought syndrome. Our results reveal that anatomical, ecophysiological, and molecular adaptations across organs are intertwined, and multiple (differentially combined) strategies can be applied to acquire a certain level of drought tolerance.NWOPlant sciencesNaturali

Middle Miocene to Pliocene History of Antarctica and the Southern Ocean

This chapter explores the Middle Miocene to Pliocene terrestrial and marine records of Antarctica and the Southern Ocean. The structure of the chapter makes a clear distinction between terrestrial and marine records as well as proximal (on or around Antarctica) and more distal records (Southern Ocean). Particular geographical regions are identified that reflect the areas for which the majority of palaeoenvironmental and palaeoclimatic information exist. Specifically, the chapter addresses the terrestrial sedimentary and fjordal environments of the Transantarctic Mountains and Lambert Glacier region, the terrestrial fossil record of Antarctic climate, terrestrial environments of West Antarctica, and the marine records of the East Antarctic Ice Sheet (EAIS), the West Antarctic Ice Sheet (WAIS) and the Antarctic Peninsula Ice Sheet (APIS), as well as the marine record of the Southern Ocean. Previous and current studies focusing on modelling Middle Miocene to Pliocene climate, environments and ice sheets are discussed.Published401-4631.8. Osservazioni di geofisica ambientale3.8. Geofisica per l'ambientereserve

Anaerobic microbial communities and their potential for bioenergy production in heavily biodegraded petroleum reservoirs

Most of the oil in low temperature, non‐uplifted reservoirs is biodegraded due to millions of years of microbial activity, including via methanogenesis from crude oil. To evaluate stimulating additional methanogenesis in already heavily biodegraded oil reservoirs, oil sands samples were amended with nutrients and electron acceptors, but oil sands bitumen was the only organic substrate. Methane production was monitored for over 3000 days. Methanogenesis was observed in duplicate microcosms that were unamended, amended with sulfate or that were initially oxic, however methanogenesis was not observed in nitrate‐amended controls. The highest rate of methane production was 0.15 μmol CH4 g−1 oil d−1, orders of magnitude lower than other reports of methanogenesis from lighter crude oils. Methanogenic Archaea and several potential syntrophic bacterial partners were detected following the incubations. GC–MS and FTICR–MS revealed no significant bitumen alteration for any specific compound or compound class, suggesting that the very slow methanogenesis observed was coupled to bitumen biodegradation in an unspecific manner. After 3000 days, methanogenic communities were amended with benzoate resulting in methanogenesis rates that were 110‐fold greater. This suggests that oil‐to‐methane conversion is limited by the recalcitrant nature of oil sands bitumen, not the microbial communities resident in heavy oil reservoirs

Cenozoic history of Antarctic glaciation and climate from onshore and offshore studies

The past three decades have seen a sustained and coordinated effort to refine the seismic stratigraphic framework of the Antarctic margin that has underpinned the development of numerous geological drilling expeditions from the continental shelf and beyond. Integration of these offshore drilling datasets covering the Cenozoic era with Antarctic inland datasets, provides important constraints that allow us to understand the role of Antarctic tectonics, the Southern Ocean biosphere, and Cenozoic ice sheet dynamics and ice sheet–ocean interactions on global climate as a whole. These constraints are critical for improving the accuracy and precision of future projections of Antarctic ice sheet behaviour and changes in Southern Ocean circulation. Many of the recent advances in this field can be attributed to the community-driven approach of the Scientific Committee on Antarctic Research (SCAR) Past Antarctic Ice Sheet Dynamics (PAIS) research programme and its two key subcommittees: Paleoclimate Records from the Antarctic Margin and Southern Ocean (PRAMSO) and Palaeotopographic-Palaeobathymetric Reconstructions. Since 2012, these two PAIS subcommittees provided the forum to initiate, promote, coordinate and study scientific research drilling around the Antarctic margin and the Southern Ocean. Here we review the seismic stratigraphic margin architecture, climatic and glacial history of the Antarctic continent following the break-up of Gondwanaland in the Cretaceous, with a focus on records obtained since the implementation of PRAMSO. We also provide a forward-looking approach for future drilling proposals in frontier locations critically relevant for assessing future Antarctic ice sheet, climatic and oceanic change.We thank many people who collaborated, by sharing data and ideas, on geoscience research projects under the umbrella of the highly successful Paleoclimate Records from the Antarctic Margin and Southern Ocean (PRAMSO) and Palaeotopographic-Palaeobathymetric Reconstructions subcommittees of the Scientific Committee on Antarctic Research (SCAR) Past Antarctic Ice Sheet scientific program. This synthesis, which reflects our views, would not have been possible without the efforts of these many investigators, most of whom continue their collaborative Antarctic studies, now under the successor SCAR INSTANT programme. Chris Sorlien is thanked for drafting Fig. 3.6. We thank John Anderson, Peter Barrett, Giuliano Brancolini and Alan Cooper for their useful comments and for their continuous dedication to the past Antarctic Ice Sheet evolution reconstructions. We thank Nigel Wardell, Frank Nitsche and Paolo Diviacco for maintaining the Seismic Data Library System and the National Antarctic funding agencies of many countries (Australia, China, Germany, Italy, Japan, Korea, New Zealand, Russia, Spain, the UK, the United States) for supporting geophysical and geological surveys essential for Paleotopographic and Paleobathymetric reconstructions. We thank the International Ocean Discovery Program (IODP) for its support of recent expeditions that arose out of PRAMSO discussions. R.M. was funded by the Royal Society Te Apārangi NZ Marsden Fund (grant 18-VUW-089). C.E. acknowledges funding by the Spanish Ministry of Economy, Industry and Competitivity (grants CTM2017-89711-C2-1/2-P), cofunded by the European Union through FEDER funds. L.D.S. and F.D. were funded by the Programma Nazionale delle Ricerche in Antartide (PNRA16_00016 project and PNRA 14_00119). R.Larter and C.D.H. were funded by the BAS Polar Science for Planet Earth Programme and NERC UK IODP grant NE/J006548/1. S.K. was supported by the KOPRI Grant (PE21050). L.P. was funded by the European Union’s Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No. 792773 WAMSISE. A.S. and S.G. were funded by NSF Office of Polar Programs (Grants OPP-1744970 (A.S.), -1143836 (A.S.), and -1143843 (S.G.). This is University of Texas Institute for Geophysics Contribution #3784. B.D. acknowledges funding from a Rutherford Foundation Postdoctoral Fellowship (RFT-VUW1804-PD). K.G. and G.K. were funded by AWI research programme Polar Regions and Coasts in the changing Earth System (PACES II) and the Sub-EIS-Obs programme by the Bundesanstalt für Geowissenschaften und Rohstoffe (BGR). RL, RM, TN acknowledge support from MBIE Antarctic Science Platform contract ANTA1801

Microbotanical residues for the study of early hominin tools

More than 2 million years ago in East Africa, the earliest hominin stone tools evolved amidst changes in resource base, with pounding technology playing a key role in this adaptive process. Olduvai Gorge (now Oldupai) is a famed locality that remains paramount for the study of human evolution, also yielding some of the oldest battering tools in the world. However, direct evidence of the resources processed with these technologies is lacking entirely. One way to obtain this evidence is through the analysis of surviving residues. Yet, linking residues with past processing activities is not simple. In the case of plant exploitation, this link can only be established by assessing site-based reference collections inclusive of both anthropogenic and natural residues as a necessary first step and comparative starting point. In this paper, we assess microbotanical remains from rock clasts sourced at the same quarry utilized by Oldowan hominins at Oldupai Gorge. We mapped this signal and analysed it quantitatively to classify its spatial distribution objectively, extracting proxies for taxonomic identification and further comparison with freestanding soils. In addition, we used blanks to manufacture pounding tools for blind, controlled replication of plant processing. We discovered that stone blanks are in fact environmental reservoirs in which plant remains are trapped by lithobionts, preserved as hardened accretions. Tool use, on the other hand, creates residue clusters; however, their spatial distribution can be discriminated from purely natural assemblages by the georeferencing of residues and statistical analysis of resulting patterns. To conclude, we provide a protocol for best practice and a workflow that has the advantage of overcoming environmental noise, reducing the risk of false positive, delivering a firm understanding of residues as polygenic mixtures, a reliable use of controls, and most importantly, a stronger link between microbotanical remains and stone tool use. © 2022. The Author(s).Materials and methods Results - Blanks as environmental reservoirs - Utilization creates residue clusters - Anthropogenic residue distribution - Of lichen habitability, proxy palimpsests, and hardened accretions - A protocol to study plant residue from Oldowan pounding tool

Evidence of marine ice-cliff instability in Pine Island Bay from iceberg-keel plough marks.

Marine ice-cliff instability (MICI) processes could accelerate future retreat of the Antarctic Ice Sheet if ice shelves that buttress grounding lines more than 800 metres below sea level are lost. The present-day grounding zones of the Pine Island and Thwaites glaciers in West Antarctica need to retreat only short distances before they reach extensive retrograde slopes. When grounding zones of glaciers retreat onto such slopes, theoretical considerations and modelling results indicate that the retreat becomes unstable (marine ice-sheet instability) and thus accelerates. It is thought that MICI is triggered when this retreat produces ice cliffs above the water line with heights approaching about 90 metres. However, observational evidence confirming the action of MICI has not previously been reported. Here we present observational evidence that rapid deglacial ice-sheet retreat into Pine Island Bay proceeded in a similar manner to that simulated in a recent modelling study, driven by MICI. Iceberg-keel plough marks on the sea-floor provide geological evidence of past and present iceberg morphology, keel depth and drift direction. From the planform shape and cross-sectional morphologies of iceberg-keel plough marks, we find that iceberg calving during the most recent deglaciation was not characterized by small numbers of large, tabular icebergs as is observed today, which would produce wide, flat-based plough marks or toothcomb-like multi-keeled plough marks. Instead, it was characterized by large numbers of smaller icebergs with V-shaped keels. Geological evidence of the form and water-depth distribution of the plough marks indicates calving-margin thicknesses equivalent to the threshold that is predicted to trigger ice-cliff structural collapse as a result of MICI. We infer rapid and sustained ice-sheet retreat driven by MICI, commencing around 12,300 years ago and terminating before about 11,200 years ago, which produced large numbers of icebergs smaller than the typical tabular icebergs produced today. Our findings demonstrate the effective operation of MICI in the past, and highlight its potential contribution to accelerated future retreat of the Antarctic Ice Sheet