scholarly journals Penguin heat-retention structures evolved in a greenhouse Earth

2010 ◽  
Vol 7 (3) ◽  
pp. 461-464 ◽  
Author(s):  
Daniel B. Thomas ◽  
Daniel T. Ksepka ◽  
R. Ewan Fordyce
Keyword(s):  
Cold Water ◽  
Global Climate ◽  
Extreme Environments ◽  
Ice Sheets ◽  
Global Cooling ◽  
Polar Ice Sheets ◽  
Subsurface Waters ◽  
Glacial Environments ◽  
Retention Structures ◽  
Counter Current

Penguins (Sphenisciformes) inhabit some of the most extreme environments on Earth. The 60+ Myr fossil record of penguins spans an interval that witnessed dramatic shifts in Cenozoic ocean temperatures and currents, indicating a long interplay between penguin evolution and environmental change. Perhaps the most celebrated example is the successful Late Cenozoic invasion of glacial environments by crown clade penguins. A major adaptation that allows penguins to forage in cold water is the humeral arterial plexus, a vascular counter-current heat exchanger (CCHE) that limits heat loss through the flipper. Fossil evidence reveals that the humeral plexus arose at least 49 Ma during a ‘Greenhouse Earth’ interval. The evolution of the CCHE is therefore unrelated to global cooling or development of polar ice sheets, but probably represents an adaptation to foraging in subsurface waters at temperate latitudes. As global climate cooled, the CCHE was key to invasion of thermally more demanding environments associated with Antarctic ice sheets.

Provenance of Cenozoic glaciomarine sediments of East Greenland: constraints to the cryosphere evolution and continental margin erosion

2020 ◽  
Author(s):  
Silvia Cattò ◽  
Valerio Olivetti ◽  
Massimiliano Zattin
Keyword(s):  
Continental Margin ◽  
Late Miocene ◽  
Global Climate ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Sediment Provenance ◽  
Polar Ice ◽  
East Greenland ◽  
Continental Scale ◽  
Polar Ice Sheets

<p>Understanding the evolution and dynamics of polar ice sheets is of the utmost importance for reconstructing the climatic development in the past and estimating the future global climate changes. The Cenozoic climatic evolution has been characterized by repeated fluctuations between somewhat warmer and colder conditions. While the first appearance of continental-scale polar ice sheets on Antarctica is widely inferred and well constrained (Eocene‐Oligocene Transition, EOT; Miller et al., 2009; Cramer et al., 2012), the onset of the glaciation in the Northern Hemisphere remains much more enigmatic and controversial. It is commonly accepted that small ice sheets have been present on Greenland since late Miocene (Larsen et al., 1994) with an intensification of the glaciation and development of extensive polar ice sheets in the late Pliocene (Bailey et al., 2013). Although glacier ice was likely to be present on Greenland at the EOT (Moran et al., 2006; Tripati et al., 2005, 2008) it is still debated if it derived from scattered coastal outlet glaciers or from an actual ice sheet.</p><p>In this work we present detrital apatite fission-tracks analysis (AFT) on offshore deposits in order to reconstruct the sediment provenance. In detrital samples, grain-age distributions can be decomposed by statistical means into different main grain-age components or peaks (e.g. Galbraith and Green 1990) thus discerning the provenance of the sediments eroded at the time. Age peaks trends throughout the section also provide information about the exhumation rate and tectonic evolution of the source rock.</p><p>We collected detrital apatites from some sites of ODP Leg 152 and ODP Leg 162, conveniently located near the East Greenland coast (southern and central East Greenland, respectively), in order to obtain a continuous record from Eocene to middle Oligocene and from middle Miocene to present. The age peaks inferred for the offshore samples have been compared with the thermochronological data available onshore to find the potential sources. Our results point out a common provenance (at least since late Miocene) for both central and southern East Greenland offshore sediments, despite the distance of >1200 km between the two locations. Moreover, both samples display a mutually consistent trend of increasingly older AFT ages moving up the section, indicative of provenance changes. Such trend seems compatible with ice-rafting from icebergs calved from the Scoresby Sound outlet glaciers and drifting along the East Greenland Current that, should this be the case, would be active with the same modalities as now since the late Miocene. We tentatively argue that the “older ages upwards” trend is determined by climate variations, specifically by the expansion/thickening of the ice sheet. Any change due to tectonic events, if present, cannot be resolved. Conversely, the Eocene to middle Oligocene record displays a younging upwards trend with decreasing lagtime typical of an eroding continental margin.</p>

Antarctic Climate History and Global Climate Changes

2017 ◽  
Author(s):  
Pontus Lurcock ◽  
Fabio Florindo
Keyword(s):  
Ocean Circulation ◽  
Climate Changes ◽  
Numerical Models ◽  
Global Climate ◽  
Sediment Cores ◽  
Ice Sheets ◽  
Global Ocean ◽  
Climate History ◽  
Global Climate Changes ◽  
Planetary Albedo

Antarctic climate changes have been reconstructed from ice and sediment cores and numerical models (which also predict future changes). Major ice sheets first appeared 34 million years ago (Ma) and fluctuated throughout the Oligocene, with an overall cooling trend. Ice volume more than doubled at the Oligocene-Miocene boundary. Fluctuating Miocene temperatures peaked at 17–14 Ma, followed by dramatic cooling. Cooling continued through the Pliocene and Pleistocene, with another major glacial expansion at 3–2 Ma. Several interacting drivers control Antarctic climate. On timescales of 10,000–100,000 years, insolation varies with orbital cycles, causing periodic climate variations. Opening of Southern Ocean gateways produced a circumpolar current that thermally isolated Antarctica. Declining atmospheric CO2 triggered Cenozoic glaciation. Antarctic glaciations affect global climate by lowering sea level, intensifying atmospheric circulation, and increasing planetary albedo. Ice sheets interact with ocean water, forming water masses that play a key role in global ocean circulation.

Shallow-Layers-Detection Ice Sounding Radar for Mapping of Polar Ice Sheets

2021 ◽  
pp. 1-10
Author(s):  
Bo Zhao ◽  
Yueyi Zhang ◽  
Shinan Lang ◽  
Yan Liu ◽  
Feng Zhang ◽  
...  
Keyword(s):  
Ice Sheets ◽  
Polar Ice ◽  
Polar Ice Sheets

scholarly journals Attention Multi-Scale Network for Automatic Layer Extraction of Ice Radar Topological Sequences

2021 ◽  
Vol 13 (12) ◽  
pp. 2425
Author(s):  
Yiheng Cai ◽  
Dan Liu ◽  
Jin Xie ◽  
Jingxian Yang ◽  
Xiangbin Cui ◽  
...  
Keyword(s):  
Deep Learning ◽  
Global Climate ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Sheet Thickness ◽  
Learning Methods ◽  
Convolutional Network ◽  
Multi Scale ◽  
Ice Surface ◽  
Layer Extraction

Analyzing the surface and bedrock locations in radar imagery enables the computation of ice sheet thickness, which is important for the study of ice sheets, their volume and how they may contribute to global climate change. However, the traditional handcrafted methods cannot quickly provide quantitative, objective and reliable extraction of information from radargrams. Most traditional handcrafted methods, designed to detect ice-surface and ice-bed layers from ice sheet radargrams, require complex human involvement and are difficult to apply to large datasets, while deep learning methods can obtain better results in a generalized way. In this study, an end-to-end multi-scale attention network (MsANet) is proposed to realize the estimation and reconstruction of layers in sequences of ice sheet radar tomographic images. First, we use an improved 3D convolutional network, C3D-M, whose first full connection layer is replaced by a convolution unit to better maintain the spatial relativity of ice layer features, as the backbone. Then, an adjustable multi-scale module uses different scale filters to learn scale information to enhance the feature extraction capabilities of the network. Finally, an attention module extended to 3D space removes a redundant bottleneck unit to better fuse and refine ice layer features. Radar sequential images collected by the Center of Remote Sensing of Ice Sheets in 2014 are used as training and testing data. Compared with state-of-the-art deep learning methods, the MsANet shows a 10% reduction (2.14 pixels) on the measurement of average mean absolute column-wise error for detecting the ice-surface and ice-bottom layers, runs faster and uses approximately 12 million fewer parameters.

scholarly journals Last Glacial Maximum and Holocene Climate in CCSM3

2006 ◽  
Vol 19 (11) ◽  
pp. 2526-2544 ◽  
Author(s):  
Bette L. Otto-Bliesner ◽  
Esther C. Brady ◽  
Gabriel Clauzet ◽  
Robert Tomas ◽  
Samuel Levis ◽  
...  
Keyword(s):  
Last Glacial Maximum ◽  
Ice Sheets ◽  
Ocean Model ◽  
Arctic Sea Ice ◽  
Glacial Maximum ◽  
Climate System Model ◽  
Last Glacial ◽  
Global Cooling ◽  
Climate Forcings ◽  
Continental Ice Sheets

Abstract The climate sensitivity of the Community Climate System Model version 3 (CCSM3) is studied for two past climate forcings, the Last Glacial Maximum (LGM) and the mid-Holocene. The LGM, approximately 21 000 yr ago, is a glacial period with large changes in the greenhouse gases, sea level, and ice sheets. The mid-Holocene, approximately 6000 yr ago, occurred during the current interglacial with primary changes in the seasonal solar irradiance. The LGM CCSM3 simulation has a global cooling of 4.5°C compared to preindustrial (PI) conditions with amplification of this cooling at high latitudes and over the continental ice sheets present at LGM. Tropical sea surface temperature (SST) cools by 1.7°C and tropical land temperature cools by 2.6°C on average. Simulations with the CCSM3 slab ocean model suggest that about half of the global cooling is explained by the reduced LGM concentration of atmospheric CO2 (∼50% of present-day concentrations). There is an increase in the Antarctic Circumpolar Current and Antarctic Bottom Water formation, and with increased ocean stratification, somewhat weaker and much shallower North Atlantic Deep Water. The mid-Holocene CCSM3 simulation has a global, annual cooling of less than 0.1°C compared to the PI simulation. Much larger and significant changes occur regionally and seasonally, including a more intense northern African summer monsoon, reduced Arctic sea ice in all months, and weaker ENSO variability.

Four decades of radar-echo sounding: The past, present, and future of radar applications for understanding subglacial environments 

2021 ◽  
Author(s):  
Winnie Chu
Keyword(s):  
Ice Sheets ◽  
Ice Sheet ◽  
Thermal Conditions ◽  
Machine Learning Algorithms ◽  
Polar Ice Sheets ◽  
Radar Echo ◽  
Radar Applications ◽  
Bed Roughness ◽  
Subglacial Environments ◽  
Echo Sounding

<p>Airborne radar sounding observations have been instrumental in understanding subglacial environments and basal processes of ice sheets. Since the advent of analog radar-echo sounding (RES) system in the early 1970s, there have been tremendous innovations in both RES hardware and signal processing techniques. These technological advancements have provided high-resolution ice thickness measurements, improved detection and characterization of subglacial hydrology, as well as improved understanding of basal thermal conditions, bed roughness and geomorphology, and other processes that govern the basal boundary of the polar ice sheets. In this talk, I will provide an overview of the recent developments in radar processing approaches and system designs and highlight some of the new understanding of ice sheet subglacial processes that emerge from these breakthroughs. I will end by discussing areas where future radar applications and discoveries may be possible, including the utilization of machine learning algorithms, space-borne radar missions, and ground-based passive radar platforms to provide long-term monitoring of ice sheet subglacial environments.</p>

scholarly journals The response of fabric variations to simple shear and migration recrystallization

2015 ◽  
Vol 61 (227) ◽  
pp. 537-550 ◽  
Author(s):  
Joseph H. Kennedy ◽  
Erin C. Pettit
Keyword(s):  
Thermal Activation ◽  
Nearest Neighbor ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Polar Ice ◽  
Climatic Variations ◽  
Fabric Evolution ◽  
Polar Ice Sheets ◽  
Low Levels ◽  
And Migration

AbstractThe observable microstructures in ice are the result of many dynamic and competing processes. These processes are influenced by climate variables in the firn. Layers deposited in different climate regimes may show variations in fabric which can persist deep into the ice sheet; fabric may ‘remember’ these past climate regimes. We model the evolution of fabric variations below the firn–ice transition and show that the addition of shear to compressive-stress regimes preserves the modeled fabric variations longer than compression-only regimes, because shear drives a positive feedback between crystal rotation and deformation. Even without shear, the modeled ice retains memory of the fabric variation for 200 ka in typical polar ice-sheet conditions. Our model shows that temperature affects how long the fabric variation is preserved, but only affects the strain-integrated fabric evolution profile when comparing results straddling the thermal-activation-energy threshold (∼−10°C). Even at high temperatures, migration recrystallization does not eliminate the modeled fabric’s memory under most conditions. High levels of nearest-neighbor interactions will, however, eliminate the modeled fabric’s memory more quickly than low levels of nearest-neighbor interactions. Ultimately, our model predicts that fabrics will retain memory of past climatic variations when subject to a wide variety of conditions found in polar ice sheets.

scholarly journals Impact of mid-glacial ice sheets on deep ocean circulation and global climate: Role of surface cooling on the AMOC

2020 ◽  
Author(s):  
Sam Sherriff-Tadano ◽  
Ayako Abe-Ouchi ◽  
Akira Oka
Keyword(s):  
North Atlantic ◽  
General Circulation ◽  
Global Climate ◽  
Surface Wind ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Meridional Overturning Circulation ◽  
Strengthening Effect ◽  
Surface Cooling ◽  
Glacial Ice

Abstract. This study explores the effect of southward expansion of mid-glacial ice sheets on the global climate and the Atlantic meridional overturning circulation (AMOC), as well as the processes by which the ice sheets modify the AMOC. For this purpose, simulations of Marine Isotope Stage (MIS) 3 and 5a are performed with an atmosphere-ocean general circulation model. In the MIS3 and MIS5a simulations, the global average temperature decreases by 5.0 °C and 2.2 °C, respectively, compared with the preindustrial climate simulation. The AMOC weakens by 3 % in MIS3, whereas it is enhanced by 16 % in MIS5a, both of which are consistent with a reconstruction. Sensitivity experiments extracting the effect of the expansion of glacial ice sheets from MIS5a to MIS3 show a global cooling of 1.1 °C, contributing to about 40 % of the total surface cooling from MIS5a to MIS3. These experiments also demonstrate that the ice sheet expansion leads to a surface cooling of 2 °C over the Southern Ocean as a result of colder North Atlantic deep water. We find that the southward expansion of the mid-glacial ice sheet exerts a small impact on the AMOC. Partially coupled experiments reveal that the global surface cooling by the glacial ice sheet tends to reduce the AMOC by increasing the sea ice at both poles, and hence compensates for the strengthening effect of the enhanced surface wind over the North Atlantic. Our results show that the total effect of glacial ice sheets on the AMOC is determined by the two competing effects, surface wind and surface cooling. The relative strength of surface wind and surface cooling depends on the ice sheet configuration, and the strength of the surface cooling can be comparable to that of surface wind when changes in the extent of ice sheet are prominent.

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