Melting Of Ice Sheets Research Articles

The impact of early Holocene Arctic shelf flooding on climate in an atmosphere–ocean–sea–ice model

Abstract. Glacial terminations are characterized by a strong rise in sea level related to melting ice sheets. This rise in sea level is not uniform all over the world, because regional effects (uplift and subsidence of coastal zones) are superimposed on global trends. During the early Holocene the Siberian Shelf became flooded before 7.5 ka BP and the coastline reached modern-day high stands at 5 ka BP. This area is currently known as a sea-ice production area and contributes significantly to the sea-ice exported from the Arctic through the Fram Strait. This leads to the following hypothesis: during times of rising sea levels, shelves become flooded, increasing sea-ice production on these shelves, increasing sea-ice volume and export through the Fram Strait and causing the sea-ice extent to advance in the Nordic Seas, yielding cooler and fresher sea surface conditions. We have tested this hypothesis in an atmosphere–ocean–sea–ice coupled model of intermediate complexity (LOVECLIM). Our experiment on early Holocene Siberian Shelf flooding shows that in our model sea-ice production in the Northern Hemisphere increases (15%) and that sea-ice extent in the Northern Hemisphere increases (14%) but sea-ice export decreases (−15%) contrary to our hypothesis. The reason of this unexpected behaviour has its origin in a weakened polar vortex, induced by the land–ocean changes due to the shelf flooding, and a resulting decrease of zonality in the Nordic Seas pressure regime. Hence the winter Greenland high and the Icelandic low strengthen, yielding stronger winds on both sides of the Nordic Seas. Increased winds along the East Greenland Current support local sea-ice production and transport towards the South, resulting in a wider sea-ice cover and a southward shift of convection areas. The overall strength of the Atlantic meridional overturning circulation is reduced by 4% and the heat transport in the Atlantic basin by 7%, resulting in an annual cooling pattern over the Nordic Seas by up to −4 °C. We find that the flooding of the Siberian shelf resulting from an orbitally induced warming and related glacioeustatic sea level rise causes a Nordic Seas cooling feedback opposed to this warming.

Deep ocean communities impacted by changing climate over 24 y in the abyssal northeast Pacific Ocean

The deep ocean, covering a vast expanse of the globe, relies almost exclusively on a food supply originating from primary production in surface waters. With well-documented warming of oceanic surface waters and conflicting reports of increasing and decreasing primary production trends, questions persist about how such changes impact deep ocean communities. A 24-y time-series study of sinking particulate organic carbon (food) supply and its utilization by the benthic community was conducted in the abyssal northeast Pacific (~4,000-m depth). Here we show that previous findings of food deficits are now punctuated by large episodic surpluses of particulate organic carbon reaching the sea floor, which meet utilization. Changing surface ocean conditions are translated to the deep ocean, where decadal peaks in supply, remineralization, and sequestration of organic carbon have broad implications for global carbon budget projections.

The economic impact of extreme sea-level rise: Ice sheet vulnerability and the social cost of carbon dioxide

The possibility of extreme sea-level rise is one of the commonly cited reasons for concern about climate change. Major increases in sea level would likely be driven by the melting or collapse of major ice sheets. This possibility has implications for the social cost of carbon dioxide, which is a key policy value as well as a useful summary measure of damage caused by greenhouse gas emissions.This paper extends earlier work on the importance of low-probability, high-impact events for the social cost of carbon dioxide to incorporate the possibility of extreme sea-level rise.To estimate its impact, an integrated assessment model is used, which allows a probabilistic assessment of climate change damages based on the linkages between the economic and climate systems. In the model, the generic discontinuity damage is replaced with the possibility of large-scale damage from factors that are taken to be correlated with temperature rise and, crucially for this paper, explicit consideration of extreme sea-level rise.Estimates of the amount of increase in the social cost of carbon dioxide that can be expected from incorporating extreme sea-level rise show that the increase is significant, though not especially large in percentage terms.The paper contributes to the literature of how to represent uncertain climate impacts in integrated assessment models and the associated estimation of the social cost of carbon dioxide.

Relative impacts of insolation changes, meltwater fluxes and ice sheets on African and Asian monsoons during the Holocene

In order to better understand the evolution of the Afro-Asian monsoon in the early Holocene, we investigate the impact on boreal summer monsoon characteristics of (1) a freshwater flux in the North Atlantic from the surrounding melting ice sheets and (2) a remnant ice sheet over North America and Europe. Sensitivity experiments run with the IPSL_CM4 model show that both the meltwater flux and the remnant ice sheets induce a cooling of similar amplitude of the North Atlantic leading to a southward shift of the Inter-Tropical Convergence Zone over the tropical Atlantic and to a reduction of the African monsoon. The two perturbations have different impacts in the Asian sector. The meltwater flux results in a weakening of the Indian monsoon and no change in the East Asian monsoon, whereas the remnant ice sheets induce a strengthening of the Indian monsoon and a strong weakening of the East Asian monsoon. Despite the similar coolings in the Atlantic Ocean, the ocean heat transport is reduced only in the meltwater flux experiment, which induces slight differences between the two experiments in the role of the surface latent heat flux in the tropical energetics. In the meltwater experiment, the southward shift of the subtropical jet acts to cool the upper atmosphere over the Tibetan Plateau and hence to weaken the Indian monsoon. In the ice sheet experiment this effect is overwhelmed by the changes in extratropical stationary waves induced by the ice sheets, which are associated with a larger cooling over the Eurasian continent than in the meltwater experiment. However these sensitivity experiments suggest that insolation is the dominant factor explaining the relative changes of the African, Indian and East Asian monsoons from the early to the mid-Holocene.

Causes of Greenland temperature variability over the past 4000 yr: implications for northern hemispheric temperature changes

Abstract. Precise understanding of Greenland temperature variability is important in two ways. First, Greenland ice sheet melting associated with rising temperature is a major global sea level forcing, potentially affecting large populations in coming centuries. Second, Greenland temperatures are highly affected by North Atlantic Oscillation/Arctic Oscillation (NAO/AO) and Atlantic multidecadal oscillation (AMO). In our earlier study, we found that Greenland temperature deviated negatively (positively) from northern hemispheric (NH) temperature trend during stronger (weaker) solar activity owing to changes in atmospheric/oceanic changes (e.g. NAO/AO) over the past 800 yr (Kobashi et al., 2013). Therefore, a precise Greenland temperature record can provide important constraints on the past atmospheric/oceanic circulation in the region and beyond. Here, we investigated Greenland temperature variability over the past 4000 yr reconstructed from argon and nitrogen isotopes from trapped air in a GISP2 ice core, using a one-dimensional energy balance model with orbital, solar, volcanic, greenhouse gas, and aerosol forcings. The modelled northern Northern Hemisphere (NH) temperature exhibits a cooling trend over the past 4000 yr as observed for the reconstructed Greenland temperature through decreasing annual average insolation. With consideration of the negative influence of solar variability, the modelled and observed Greenland temperatures agree with correlation coefficients of r = 0.34–0.36 (p = 0.1–0.04) in 21 yr running means (RMs) and r = 0.38–0.45 (p = 0.1–0.05) on a centennial timescale (101 yr RMs). Thus, the model can explain 14 to 20% of variance of the observed Greenland temperature in multidecadal to centennial timescales with a 90–96% confidence interval, suggesting that a weak but persistent negative solar influence on Greenland temperature continued over the past 4000 yr. Then, we estimated the distribution of multidecadal NH and northern high-latitude temperatures over the past 4000 yr constrained by the climate model and Greenland temperatures. Estimated northern NH temperature and NH average temperature from the model and the Greenland temperature agree with published multi-proxy temperature records with r = 0.35–0.60 in a 92–99% confidence interval over the past 2000 yr. We found that greenhouse gases played two important roles over the past 4000 yr for the rapid warming during the 20th century and slightly cooler temperature during the early period of the past 4000 yr. Lastly, our analysis indicated that the current average temperature (1990–2010) or higher temperatures occurred at a frequency of 1.3 times per 1000 yr for northern high latitudes and 0.36 times per 4000 yr for NH temperatures, respectively, indicating that the current multidecadal NH temperature (1990–2010) is more likely unprecedented than not (p = 0.36) for the past 4000 yr.

Holocene climate variations retrieved from Gun Nuur lake-sediment core in the northern Mongolian Plateau

Our pollen-based climate reconstruction shows that both temperature and moisture were low during the early Holocene from ~10,000 to ~8000 cal. a BP and gradually climbed from ~8000 to ~6000 cal. a BP. The last ~6000 years have been generally warm and wet with high-amplitude fluctuations. The high-moisture conditions for the past ~6000 years are not only corroborated by high arboreal pollen/non-arboreal (AP/NAP; trees and shrubs over herbs) pollen ratio and high pollen concentration but also by high organic matter content and diatom data. We suggest that lower winter insolation and remaining ice covers in the early Holocene might have slowed down temperature rise in the continental interiors and that the resulted low temperature might have suppressed regional evaporation that was a major water vapor source for precipitation. At the same time, icemelt-water injection into the North Atlantic Ocean might have also suppressed water vapor supplies to the downwind areas, including the northern Mongolian Plateau. The increase in winter insolation and the final melting of ice sheets, together with the increased atmospheric CO2 concentration and the associated increase in atmospheric water vapor, could be responsible for the higher temperature during the past ~6000 years. The icemelting and the associated rise of sea level during the past ~6000 years might be responsible for the weakening of the winter monsoon in the interior of Asian continent, thus alluring farther eastward penetration of the relatively warm and wet Atlantic air masses and consequently bringing more precipitation to the northern Mongolian Plateau.

Chronological framework of Asian Southwest Monsoon events and variations over the past 24,000 years in Sri Lanka and regional correlations

An accelerator mass spectrometry (AMS- 14C) dated multi-proxy upper montane rainforest record from the Horton Plains, Central Sri Lanka reveals a ~ 24,000 year history of millennial-scale monsoon climate variability since the last glacial maximum (LGM). The vegetation history indicates that post-LGM earliest tropical warming and monsoon initiation preceded the Northern Hemisphere ice-sheet melting by over 3000 years before the Bolling interval, with a significant increase in the precipitation at Termination 1A (event-B in the Horton Plains). This suggests a major early strengthening of the monsoon. Starting ca. 17,600 years before present (yr BP), the rainforest diversity increases in-step with four progressively increasing humid events (A-D) and interrupted by two relatively semi-arid/weak episodes of which the second (Termination 1B) ending ca. 10,400 yr BP may reflect a delayed Younger Dryas event. The optimum rainforest diversification coincides with the Holocene monsoon precipitation maximum ca. 9,200 − 8,800 yr BP (event-D). A disruption to these millennial cycles coincided with a gradual monsoon downturn, precipitation and rainforest decline and aridity between ca. 8,100 − 3,400 yr BP. The conditions became more humid again for rainforest expansions between ca. 3,400 − 1,500 yr BP (event-E). Broadly synchronous millennial-scale climatic records of the Horton Plains, Arabian Sea, Oman, Yemen and India, equatorial West and East Africa, and the North Atlantic regions indicate twoway teleconnections between the tropical Asian Monsoon fluctuations and high latitude events. The above changes reflect vast spatial rearrangements in atmospheric circulation patterns, probably caused by forcing associated with coupled ocean-atmosphere-vegetation feedbacks. There is a remarkably close correlation of the different proxies that has tracked the Southwest Monsoon variations across the region since the LGM. J.Natn.Sci.Foundation Sri Lanka 2013 41 (3): 219-228 DOI: http://dx.doi.org/10.4038/jnsfsr.v41i3.6057

Early Last Interglacial Greenland Ice Sheet melting and a sustained period of meridional overturning weakening: a model analysis of the uncertainties

Proxy-data suggest that the Last Interglacial (LIG; ~130–116 ka BP) climate was characterized by higher temperatures, a partially melted Greenland Ice Sheet (GIS) and a changed Atlantic meridional overturning circulation (AMOC). Notwithstanding the uncertainties in LIG palaeoclimatic reconstructions, this setting potentially provides an opportunity to evaluate the relation between GIS melt and the AMOC as simulated by climate models. However, first we need to assess the extent to which a causal relation between early LIG GIS melt and the weakened AMOC is plausible. With a series of transient LIG climate simulations with the LOVECLIM earth system model, we quantify the importance of the major known uncertainties involved in early LIG GIS melt scenarios. Based on this we construct a specific scenario that is within the parameter space of uncertainties and show that it is physically consistent that early LIG GIS melting kept the AMOC weakened. Notwithstanding, this scenario is at the extreme end of the parameter space. Assuming that proxy-based reconstructions of early LIG AMOC weakening offer a realistic representation of its past state, this indicates that either (1) the AMOC weakening was caused by other forcings than early LIG GIS melt or (2) the early LIG AMOC was less stable than indicated by our simulations and a small amount of GIS melt was sufficient to keep the AMOC in the weak state of a bi-stable regime. We argue that more intensive research is required because of the high potential of the early LIG to evaluate model performance in relation to the AMOC response to GIS melt.

Short length scale mantle heterogeneity beneath Iceland probed by glacial modulation of melting

Glacial modulation of melting beneath Iceland provides a unique opportunity to better understand both the nature and length scale of mantle heterogeneity. At the end of the last glacial period, ∼13000 yr BP, eruption rates were ∼20–100 times greater than in glacial or late postglacial times and geophysical modeling posits that rapid melting of the large ice sheet covering Iceland caused a transient increase in mantle decompression melting rates. Here we present the first time-series of Sr–Nd–Hf–Pb isotopic data for a full glacial cycle from a spatially confined region of basaltic volcanism in northern Iceland. Basalts and picrites erupted during the early postglacial burst of volcanic activity are systematically offset to more depleted isotopic compositions than those of lavas erupted during glacial or recent (<7 kyr) times. These new isotopic data, coupled with major and trace element data, show that the mantle underneath northern Iceland is heterogeneous on small (<100 km) length scales. The temporal response of the isotopic compositions of the basalts to glacial unloading indicates that the isotopic composition of mantle heterogeneities can be linked to their melting behavior. The present geochemical data can be accounted for by a melting model in which a lithologically heterogeneous mantle source contains an enriched component more fusible than its companion depleted component.

Models find large natural variability in future regional sea level rise

Melting glaciers, ice caps, and ice sheets and thermal expansion of seawater, along with groundwater depletion, have already caused the global ocean to rise at a rate of 1.8 centimeters per decade over the past century. In recent decades the pace has climbed to 3.1 centimeters per decade. As the atmospheric greenhouse gas concentration continues to rise, so will the oceans.

Time-dependent climate sensitivity and the legacy of anthropogenic greenhouse gas emissions

Climate sensitivity measures the response of Earth's surface temperature to changes in forcing. The response depends on various climate processes that feed back on the initial forcing on different timescales. Understanding climate sensitivity is fundamental to reconstructing Earth's climatic history as well as predicting future climate change. On timescales shorter than centuries, only fast climate feedbacks including water vapor, lapse rate, clouds, and snow/sea ice albedo are usually considered. However, on timescales longer than millennia, the generally higher Earth system sensitivity becomes relevant, including changes in ice sheets, vegetation, ocean circulation, biogeochemical cycling, etc. Here, I introduce the time-dependent climate sensitivity, which unifies fast-feedback and Earth system sensitivity. I show that warming projections, which include a time-dependent climate sensitivity, exhibit an enhanced feedback between surface warming and ocean CO2 solubility, which in turn leads to higher atmospheric CO2 levels and further warming. Compared with earlier studies, my results predict a much longer lifetime of human-induced future warming (23,000-165,000 y), which increases the likelihood of large ice sheet melting and major sea level rise. The main point regarding the legacy of anthropogenic greenhouse gas emissions is that, even if the fast-feedback sensitivity is no more than 3 K per CO2 doubling, there will likely be additional long-term warming from slow climate feedbacks. Time-dependent climate sensitivity also helps explaining intense and prolonged warming in response to massive carbon release as documented for past events such as the Paleocene-Eocene Thermal Maximum.

The Holocene thermal maximum in the Nordic Seas: the impact of Greenland Ice Sheet melt and other forcings in a coupled atmosphere–sea-ice–ocean model

Abstract. The relatively warm early Holocene climate in the Nordic Seas, known as the Holocene thermal maximum (HTM), is often associated with an orbitally forced summer insolation maximum at 10 ka BP. The spatial and temporal response recorded in proxy data in the North Atlantic and the Nordic Seas reveals a complex interaction of mechanisms active in the HTM. Previous studies have investigated the impact of the Laurentide Ice Sheet (LIS), as a remnant from the previous glacial period, altering climate conditions with a continuous supply of melt water to the Labrador Sea and adjacent seas and with a downwind cooling effect from the remnant LIS. In our present work we extend this approach by investigating the impact of the Greenland Ice Sheet (GIS) on the early Holocene climate and the HTM. Reconstructions suggest melt rates of 13 mSv for 9 ka BP, which result in our model in an ocean surface cooling of up to 2 K near Greenland. Reconstructed summer SST gradients agree best with our simulation including GIS melt, confirming that the impact of the early Holocene GIS is crucial for understanding the HTM characteristics in the Nordic Seas area. This implies that modern and near-future GIS melt can be expected to play an active role in the climate system in the centuries to come.

Twentieth century sea-level rise inferred from tide gauge, geologically derived and thermosteric sea-level changes

Relative sea-level (RSL) changes at thirteen sites derived from tide gauge and/or salt-marsh sediment sequences, with information for RSL changes during at least the past ∼200 years, are used to infer the rates and causes of the global sea-level rise in the twentieth century (pre-satellite era) by incorporating spatially non-uniform thermosteric sea-level change and recent estimates for the melting of mountain glaciers and both polar ice sheets. The main advantage of the method adopted here is that we can avoid a model-dependence in the GIA (glacial isostatic adjustment) correction and any steady tectonic effect depending on each location can be corrected for. We first estimate the acceleration of sea-level rise in the twentieth century at each RSL observation site, and then evaluate the residuals between the sea-level acceleration and thermosteric sea-level rise. The spatially non-uniform residuals are examined to infer the rates of RSL rise due to the melting of mountain glaciers and polar ice sheets. The comparison between the residuals and the predicted rates for the melting wholly supports the estimates for the melting by the Fourth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC 2007 Report), and does not require a significant melting from the Greenland ice sheet. However, the possible equivalent sea-level rise for mountain glaciers and/or Antarctic ice sheet may be ∼0.3 mm yr−1 larger than the preferred estimate by IPCC 2007 Report (∼0.7 mm yr−1), and the total one is ∼1.0 mm yr−1. The additional melting for ∼0.3 mm yr−1 is due to the comparison mainly for Brest with long tide gauge records of ∼200 years. Also, the present study indicates that the global mean thermosteric sea-level rise before the rapid sea-level acceleration occurred at 1990 is ∼0.3 mm yr−1.

Rapid ice melting drives Earth's pole to the east

Space geodetic observations of polar motion show that around 2005, the average annual pole position began drifting toward the east, an abrupt departure from the drift direction seen over the past century. Satellite gravity measurements from the Gravity Recovery and Climate Experiment (GRACE) show that about 90% of this change is due to accelerated melting of polar ice sheets and mountain glaciers and related sea level rise. The close relationship between long‐term polar motion and climate‐related mass redistribution established using GRACE data indicates that accurately measured polar motion data offer an additional tool for monitoring global‐scale ice melting and sea level rise and should be useful in bridging the anticipated gap between GRACE and follow‐on satellite gravity missions.

Contribution of ice sheet and mountain glacier melt to recent sea level rise

Altimeter data suggest that sea level rose by about 2.4 mm per year from 2005 to 2011, but estimates of the relative contributions of ocean warming and increased ocean mass are equivocal. An analysis of ocean temperature and satellite gravity data suggests that the delivery of meltwater from ice sheets and mountain glaciers contributed 75% of the observed sea-level rise.

The Heinrich and Dansgaard-Oeschger climatic events during Marine Isotopic Stage 3: Searching for appropriate times for human colonization of the Americas

Marine Isotope Stage 3 (MIS 3) was an interstadial stage, a relatively warm climatic period which developed roughly between 60 and 50 and 30 cal. ka BP. Several very cold periods, known as Heinrich (H) events, developed during MIS 3 as a result of partial collapse of the North American ice sheet margins, with formation of huge amounts of icebergs which, after melting in more temperate latitudes, would have inundated the North Atlantic Ocean with low salinity waters which would have impeded the reach of the Gulf Stream into the North Atlantic Ocean. Several paleoclimatic moments with relatively warmer conditions, known as the Dansgaard-Oeschger (D-O) events, took place in between the Heinrich (H) events, throughout MIS 3. These H and D-O cycles would have been very short (perhaps even only around 1 ky each in some cases) and intense, with mean annual temperatures in the area of Beringia ca. 5–8 C° higher than those active at the Last Glacial Maximum (LGM; ca. 24 cal. ka B.P.) and perhaps close to those occurring in past interglacial periods, respectively. Even though climate was warmer, total melting of the continental ice sheets did not take place; thus, global sea level was perhaps still low enough to allow the persistence of the Beringia land bridge between Siberia and North America, without any interruptions throughout the entire MIS 3. The aims of this paper are to present paleoclimatic and paleogeographic information about MIS 3 and to discuss the most favorable chronology for human displacement through Beringia. At the times of MIS 3, there would have been no coalescence between the Laurentide and Cordilleran ice sheets; thus, both the hinterland path from Beringia southwards and the coastal route would have been open and enjoying moderate climate ecosystems, and thus available for humans. In this case, it is now possible to suggest possible moments for human penetration in North America, sometime between ca. 60–50 to 28 cal. ka B.P, during one or more D-O events (most likely sometime between the D-O 16 and D-O 3 events) throughout MIS 3. Other routes of human colonization of the Americas following other routes rather than that of Siberia-Beringia, if they ever existed, are not discussed in this paper.

July 2012 Greenland melt extent enhanced by low-level liquid clouds

Melting of the world's major ice sheets can affect human and environmental conditions by contributing to sea-level rise. In July 2012, an historically rare period of extended surface melting was observed across almost the entire Greenland ice sheet, raising questions about the frequency and spatial extent of such events. Here we show that low-level clouds consisting of liquid water droplets ('liquid clouds'), via their radiative effects, played a key part in this melt event by increasing near-surface temperatures. We used a suite of surface-based observations, remote sensing data, and a surface energy-balance model. At the critical surface melt time, the clouds were optically thick enough and low enough to enhance the downwelling infrared flux at the surface. At the same time they were optically thin enough to allow sufficient solar radiation to penetrate through them and raise surface temperatures above the melting point. Outside this narrow range in cloud optical thickness, the radiative contribution to the surface energy budget would have been diminished, and the spatial extent of this melting event would have been smaller. We further show that these thin, low-level liquid clouds occur frequently, both over Greenland and across the Arctic, being present around 30-50 per cent of the time. Our results may help to explain the difficulties that global climate models have in simulating the Arctic surface energy budget, particularly as models tend to under-predict the formation of optically thin liquid clouds at supercooled temperatures--a process potentially necessary to account fully for temperature feedbacks in a warming Arctic climate.

Quantification of the Greenland ice sheet contribution to Last Interglacial sea level rise

Abstract. During the Last Interglacial period (~ 130–115 thousand years ago) the Arctic climate was warmer than today, and global mean sea level was probably more than 6.6 m higher. However, there are large discrepancies in the estimated contributions to this sea level change from various sources (the Greenland and Antarctic ice sheets and smaller ice caps). Here, we determine probabilistically the likely contribution of Greenland ice sheet melt to Last Interglacial sea level rise, taking into account ice sheet model parametric uncertainty. We perform an ensemble of 500 Glimmer ice sheet model simulations forced with climatologies from the climate model HadCM3, and constrain the results with palaeodata from Greenland ice cores. Our results suggest a 90% probability that Greenland ice melt contributed at least 0.6 m, but less than 10% probability that it exceeded 3.5 m, a value which is lower than several recent estimates. Many of these previous estimates, however, did not include a full general circulation climate model that can capture atmospheric circulation and precipitation changes in response to changes in insolation forcing and orographic height. Our combined modelling and palaeodata approach suggests that the Greenland ice sheet is less sensitive to orbital forcing than previously thought, and it implicates Antarctic melt as providing a substantial contribution to Last Interglacial sea level rise. Future work should assess additional uncertainty due to inclusion of basal sliding and the direct effect of insolation on surface melt. In addition, the effect of uncertainty arising from climate model structural design should be taken into account by performing a multi-climate-model comparison.

A latest Carboniferous warming spike recorded by a fusulinid-rich bioherm in Timor Leste: Implications for East Gondwana deglaciation

During the late Paleozoic and early Mesozoic Timor lay in the northern part of the north–south East Gondwana rift system along which the western margin of Australia later developed. Discovery of a latest Gzhelian bioherm in the central highlands of Timor Leste has implications for latest Carboniferous–earliest Permian climate history and deglaciation in basins further south in the rift system.Limestone outcrop of the Maubisse Formation near the village of Kulau is recognized as a bioherm with a massive lower unit, including reef framework at the base, and a bedded grainstone upper unit. The bioherm developed on a basalt substrate in warm shallow-water, as indicated by photozoan assemblages in the massive lower unit. Foraminifera belonging to 17 genera are recorded from the bioherm. These include representatives of the families Biseriamminidae, Biwaellidae, Bradyinidae, Cornuspiridae, Lasiodiscidae, Palaeotextulariidae, Pseudotaxidae, Ozawainellidae, Schubertellidae, Schwagerinidae, Staffellidae and Textrataxidae. Twenty-one species have been referred to known types and 12 species are left in open nomenclature. The assemblage probably belongs within the uppermost Gzhelian Schwagerina robusta–Ultradaixina bosbytauensis Zone although a possible lowest Asselian correlation cannot be excluded. The bioherm is the oldest carbonate unit so far recorded from the Maubisse Formation, and the oldest sedimentary unit biostratigraphically dated in Timor.The dominantly heterozoan composition of the skeletal component of the limestone (except for the basal photozoan assemblage) and the taxonomic diversity of the larger foraminifera suggest a subtropical environment consistent with a paleolatitude of about 40° S. The late Pennsylvanian was a time of glaciation that in Australia is represented by a significant stratigraphic hiatus in basins to the south of Timor in the East Gondwana rift system. The development of the Kulau bioherm during the latest Gzhelian may have coincided with a global warming spike that led to rapid melting of continental ice sheets and a substantial influx of glacigene sediment (alternating diamictite and mudstone) in the southern basins.

Laser eyes spy a big melt in the arctic

Scientists from the U.S. National Oceanic and Atmospheric Administration didn't pull any punches when they released the latest Arctic Report Card in early December. In 2012, levels of snow cover and sea ice were both at record lows, while surface melting of the massive Greenland ice sheet increased, despite temperatures in the region that were "unremarkable relative to the last decade." In short, the Arctic seems to be deteriorating faster than scientists thought it would.