Robert M. DeConto

Bio: Robert M. DeConto is an academic researcher from University of Massachusetts Amherst. The author has contributed to research in topics: Ice sheet & Antarctic ice sheet. The author has an hindex of 48, co-authored 128 publications receiving 12585 citations. Previous affiliations of Robert M. DeConto include University of Colorado Boulder.

Contribution of Antarctica to past and future sea-level rise

Abstract: Polar temperatures over the last several million years have, at times, been slightly warmer than today, yet global mean sea level has been 6-9 metres higher as recently as the Last Interglacial (130,000 to 115,000 years ago) and possibly higher during the Pliocene epoch (about three million years ago). In both cases the Antarctic ice sheet has been implicated as the primary contributor, hinting at its future vulnerability. Here we use a model coupling ice sheet and climate dynamics-including previously underappreciated processes linking atmospheric warming with hydrofracturing of buttressing ice shelves and structural collapse of marine-terminating ice cliffs-that is calibrated against Pliocene and Last Interglacial sea-level estimates and applied to future greenhouse gas emission scenarios. Antarctica has the potential to contribute more than a metre of sea-level rise by 2100 and more than 15 metres by 2500, if emissions continue unabated. In this case atmospheric warming will soon become the dominant driver of ice loss, but prolonged ocean warming will delay its recovery for thousands of years.

Rapid Cenozoic glaciation of Antarctica induced by declining atmospheric CO2.

Abstract: The sudden, widespread glaciation of Antarctica and the associated shift towards colder temperatures at the Eocene/Oligocene boundary (approximately 34 million years ago) (refs 1-4) is one of the most fundamental reorganizations of global climate known in the geologic record. The glaciation of Antarctica has hitherto been thought to result from the tectonic opening of Southern Ocean gateways, which enabled the formation of the Antarctic Circumpolar Current and the subsequent thermal isolation of the Antarctic continent. Here we simulate the glacial inception and early growth of the East Antarctic Ice Sheet using a general circulation model with coupled components for atmosphere, ocean, ice sheet and sediment, and which incorporates palaeogeography, greenhouse gas, changing orbital parameters, and varying ocean heat transport. In our model, declining Cenozoic CO2 first leads to the formation of small, highly dynamic ice caps on high Antarctic plateaux. At a later time, a CO2 threshold is crossed, initiating ice-sheet height/mass-balance feedbacks that cause the ice caps to expand rapidly with large orbital variations, eventually coalescing into a continental-scale East Antarctic Ice Sheet. According to our simulation the opening of Southern Ocean gateways plays a secondary role in this transition, relative to CO2 concentration.

Modelling West Antarctic ice sheet growth and collapse through the past five million years

Abstract: Changes in Earth's orbit are known to influence climate shifts from cold glacials to warm interglacials. How the vast West Antarctic ice sheet responds to these fluctuations is uncertain but, because its collapse could raise sea levels by about 5 metres, of great interest. Naish et al. have analysed the AND-1B ocean sediment core, extracted from beneath the Ross Ice Shelf as part of the ANDRILL drilling project, and find evidence that the ice sheet collapsed periodically during the early Pliocene (3-5 million years ago), when atmospheric CO2 levels were similar to, or slightly higher than today's. The pattern of collapse suggests an influence of approximately 40,000-year cycles in the tilt of Earth's rotational axis (obliquity). Also in this issue of Nature, in a numerical modelling study focused on the past 5 million years in Antarctica, David Pollard and Robert DeConto combine ice sheet (land-supported) and ice shelf (water-supported) modelling approaches to simulate the movement of the grounding line — the border between land and sea ice. Their results show that over the past 5 million years, the West Antarctic ice sheet transitioned between full, intermediate, and collapsed states in just a few thousand years. This means that the ice sheet is likely to disintegrate if ocean temperatures in the area rise by 5 C. If the West Antarctic Ice Sheet (WAIS) melted, sea levels would rise by about 5 m; such changes are thought to have occurred in the past but could not be simulated by models. Pollard and DeConto combine ice-sheet with ice-shelf modelling, and show that over the past 5 million years, the WAIS transitioned among full, intermediate, and collapsed states in only a few thousand years, suggesting possible disintegration of the WAIS if ocean temperatures in the area rise by 5 °C. The West Antarctic ice sheet (WAIS), with ice volume equivalent to ∼5 m of sea level1, has long been considered capable of past and future catastrophic collapse2,3,4. Today, the ice sheet is fringed by vulnerable floating ice shelves that buttress the fast flow of inland ice streams. Grounding lines are several hundred metres below sea level and the bed deepens upstream, raising the prospect of runaway retreat3,5. Projections of future WAIS behaviour have been hampered by limited understanding of past variations and their underlying forcing mechanisms6,7. Its variation since the Last Glacial Maximum is best known, with grounding lines advancing to the continental-shelf edges around ∼15 kyr ago before retreating to near-modern locations by ∼3 kyr ago8. Prior collapses during the warmth of the early Pliocene epoch9 and some Pleistocene interglacials have been suggested indirectly from records of sea level and deep-sea-core isotopes, and by the discovery of open-ocean diatoms in subglacial sediments10. Until now11, however, little direct evidence of such behaviour has been available. Here we use a combined ice sheet/ice shelf model12 capable of high-resolution nesting with a new treatment of grounding-line dynamics and ice-shelf buttressing5 to simulate Antarctic ice sheet variations over the past five million years. Modelled WAIS variations range from full glacial extents with grounding lines near the continental shelf break, intermediate states similar to modern, and brief but dramatic retreats, leaving only small, isolated ice caps on West Antarctic islands. Transitions between glacial, intermediate and collapsed states are relatively rapid, taking one to several thousand years. Our simulation is in good agreement with a new sediment record (ANDRILL AND-1B) recovered from the western Ross Sea11, indicating a long-term trend from more frequently collapsed to more glaciated states, dominant 40-kyr cyclicity in the Pliocene, and major retreats at marine isotope stage 31 (∼1.07 Myr ago) and other super-interglacials.

Global cooling during the eocene-oligocene climate transition.

Abstract: About 34 million years ago, Earth's climate shifted from a relatively ice-free world to one with glacial conditions on Antarctica characterized by substantial ice sheets. How Earth's temperature changed during this climate transition remains poorly understood, and evidence for Northern Hemisphere polar ice is controversial. Here, we report proxy records of sea surface temperatures from multiple ocean localities and show that the high-latitude temperature decrease was substantial and heterogeneous. High-latitude (45 degrees to 70 degrees in both hemispheres) temperatures before the climate transition were ∼20°C and cooled an average of ∼5°C. Our results, combined with ocean and ice-sheet model simulations and benthic oxygen isotope records, indicate that Northern Hemisphere glaciation was not required to accommodate the magnitude of continental ice growth during this time.

Obliquity-paced Pliocene West Antarctic ice sheet oscillations

Abstract: Thirty years after oxygen isotope records from microfossils deposited in ocean sediments confirmed the hypothesis that variations in the Earth's orbital geometry control the ice ages, fundamental questions remain over the response of the Antarctic ice sheets to orbital cycles. Furthermore, an understanding of the behaviour of the marine-based West Antarctic ice sheet (WAIS) during the 'warmer-than-present' early-Pliocene epoch ( approximately 5-3 Myr ago) is needed to better constrain the possible range of ice-sheet behaviour in the context of future global warming. Here we present a marine glacial record from the upper 600 m of the AND-1B sediment core recovered from beneath the northwest part of the Ross ice shelf by the ANDRILL programme and demonstrate well-dated, approximately 40-kyr cyclic variations in ice-sheet extent linked to cycles in insolation influenced by changes in the Earth's axial tilt (obliquity) during the Pliocene. Our data provide direct evidence for orbitally induced oscillations in the WAIS, which periodically collapsed, resulting in a switch from grounded ice, or ice shelves, to open waters in the Ross embayment when planetary temperatures were up to approximately 3 degrees C warmer than today and atmospheric CO(2) concentration was as high as approximately 400 p.p.m.v. (refs 5, 6). The evidence is consistent with a new ice-sheet/ice-shelf model that simulates fluctuations in Antarctic ice volume of up to +7 m in equivalent sea level associated with the loss of the WAIS and up to +3 m in equivalent sea level from the East Antarctic ice sheet, in response to ocean-induced melting paced by obliquity. During interglacial times, diatomaceous sediments indicate high surface-water productivity, minimal summer sea ice and air temperatures above freezing, suggesting an additional influence of surface melt under conditions of elevated CO(2).

疟原虫var基因转换速率变化导致抗原变异[英]／Paul H, Robert P, Christodoulou Z, et al//Proc Natl Acad Sci U S A

Abstract: 抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1（PfPMP1）与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用，在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员，通过启动转录不同的var基因变异体为抗原变异提供了分子基础。

Climate Change 2007: The Physical Science Basis.

Abstract: Cause, conseguenze e strategie di mitigazione Proponiamo il primo di una serie di articoli in cui affronteremo l’attuale problema dei mutamenti climatici. Presentiamo il documento redatto, votato e pubblicato dall’Ipcc - Comitato intergovernativo sui cambiamenti climatici - che illustra la sintesi delle ricerche svolte su questo tema rilevante.

Early-warning signals for critical transitions

Abstract: Complex dynamical systems, ranging from ecosystems to financial markets and the climate, can have tipping points at which a sudden shift to a contrasting dynamical regime may occur. Although predicting such critical points before they are reached is extremely difficult, work in different scientific fields is now suggesting the existence of generic early-warning signals that may indicate for a wide class of systems if a critical threshold is approaching.

The impact of climate change on the world's marine ecosystems.

Abstract: Marine ecosystems are centrally important to the biology of the planet, yet a comprehensive understanding of how anthropogenic climate change is affecting them has been poorly developed. Recent studies indicate that rapidly rising greenhouse gas concentrations are driving ocean systems toward conditions not seen for millions of years, with an associated risk of fundamental and irreversible ecological transformation. The impacts of anthropogenic climate change so far include decreased ocean productivity, altered food web dynamics, reduced abundance of habitat-forming species, shifting species distributions, and a greater incidence of disease. Although there is considerable uncertainty about the spatial and temporal details, climate change is clearly and fundamentally altering ocean ecosystems. Further change will continue to create enormous challenges and costs for societies worldwide, particularly those in developing countries.

Chapter 12 - Long-term climate change: Projections, commitments and irreversibility

Abstract: This chapter assesses long-term projections of climate change for the end of the 21st century and beyond, where the forced signal depends on the scenario and is typically larger than the internal variability of the climate system. Changes are expressed with respect to a baseline period of 1986-2005, unless otherwise stated.