In all other places, the formation of stagnant ice relies on low-gradient slopes and is confined to the terminus region of debris-covered glaciers<!–[if supportFields]> XE “glaciers” <![endif]–><!–[if supportFields]><![endif]–><!–[if supportFields]> XE “glacier” <![endif]–><!–[if supportFields]><![endif]–> with shallow gradients. The authors claim that debris-cover—which is almost always a few centimeters thick—leads to a reduction in melt rates and slows down the glacier’s response to climate change. Debris-cover also influences anthropogenic and natural radiative heat transfer. Thus, the authors conclude that topographic factors, which usually vary with terrain, have significant effects on the glacier’s response to climate change and should be accounted for in future mas-balance calculations.
In large areas of the ablation zone in the south of the GrIS, the melting season had started 50 days earlier than the average melting season (measured from 1979 to 2009) and had ended exceptionally late in 2010. While the increase in surface melting can be positively correlated with the increase in near-surface temperatures, recent studies have shown that the melting of the GrIS also depends on the accumulation, radiation, and refreezing and sublimation conditions. The surface mass balance is also strongly correlated with albedo because when melting increases, the grain size of the snow increases and which consequently, decreases the albedo. In this study, the authors used moderate-resolution imaging spectroradiometer (MODIS) albedo product to study anomalies in albedo; they also used data from automatic weather stations and regional surface and energy models to study the surface mass balance anomalies in 2010. They found the largest negative albedo anomalies occurred in August along the south west coast of the ice sheet; they hypothesized that the reduced amount of snowfall, enhanced melting and increased number of bare ice exposure days could have led to the 2010 albedo anomalies. While the early melt season was triggered by the large increase in near-surface temperatures, the reduced accumulation and albedo were more likely to be responsible for the premature bare ice exposure. Thus, the authors inferred that the anomalously warm conditions reduced the accumulation and albedo, which led to the strongly negative surface mass balance of the GrIS in 2010.
The Fourth Assessment Report of the IPCC predicts that the wastage of glaciers and ice caps will lead to a 0.07 to 0.17 m rise in global sea-levels in the twenty first century. Another study found the accelerating rates of mass loss from the glacier mass balance data between 1995 and 2005; the authors of this study used this model to predict a 0.240±0.128 m rise in sea levels, assuming this rate of acceleration is constant. In order to resolve these discrepancies, Radić & Hock studied the volume changes of mountain glaciers and ice caps in 19 spatially resolved glacierized regions. To quantify future volume changes, the authors developed a calibrated mass balance model to applied it to all the glaciers available in the World Glacier Inventory (WGI-XF). According to their multi-model means, glaciers around the world will cause a 0.124±0.037 m rise in sea-level by 2100. Assuming the GCMs are accurate, the authors predict that there will be a global ice volume loss of 0.124±0.037 m SLE (sea level equivalents) by 2100. The volume loss varies considerably from region to region; the smallest loss was predicted to be in Greenland and High Mountain Asia, and the largest in the European Alps and New Zealand. However, these places are not significant contributors to the future rise in sea-level. The glaciers in Arctic Canada, Alaska and Antarctica are estimated to be the largest contributers to the rise in sea-levels. While there are some uncertainties associated with the rise initial setup of the model, this study reveals the main regional contributers to sea-level rise and pinpoint the areas that are most vulnerable to glacier waste. Thus, if warming continues as expected, glaciers will be a large contributer to sea-level rise around the world.
Degraded coral reefs experience a transition from a dominant reef building community to one overrun by marine macroalgae. This shift affects fish recruitment, coral recruitment, competition, and predation and inevitably leads to an unstable ecosystem. Bahartan et al. studied the algae-coral interactions of the reefs on the coast of Aqaba, Jordan, and the coast of Eilat, Israel. They found that the proliferation of species of red algae as well as the most dominant species of turf-algae, Sphacelaria sp., was not associated with a sudden environmental disturbance, like a mass bleaching event. The red algae do not overcrowd the coral because they grow in spaces that have been vacated by other species. However, since they are fast growing, resistant to most environmental disturbances, and have an increased ability to absorb light in turbid water, the red algae continue to proliferate and grow in the shallow areas of the Eilat. The authors found that the reefs on the Eilat coast had a significantly higher percentage of algal cover in comparison to the reefs on the Aqaba coast. The algae harms coral recruitment and reduces the survival of crustose coralline algae, which contributes significantly to coral calcification and induces larval settlement of corals. The loss of coralline algae could also lead to a weakening of the reef structure and the ecosystem as a whole. Upon further examination, the authors concluded that the reefs on the Eilat coast were degraded, while those on the Aqaba coast were relatively healthy. Thus, the results revealed an algal takeover and a shift in the Eilat reef. Even though the mechanism of the algal takeover is unknown, the authors claim that examination of the coral-algae balance can provide a good indicator of early instabilities in the reef community.
The nature and composition of the algal community is critical in the process of coral reef recovery. Previous studies have shown that different macroalgae have different effects on the rates of coral settlement but these studies have been limited in their approach. Diaz-Pulido et al. studied the effects of eleven species of macroalgae on the settlement of spawning coral Platygyra daedalea, which is found commonly in the Great Barrier Reef and the Indo-Pacific. The authors used discs of Porolithon onkodes as settling agents for the larvae and prepared treatments with different macroalgae in order to compare the differences in larval activity and settlement rates They used plastic algal mimics to study the effects of the physical structure of the macroalgae on the rates of coral settlement. A few days after the treatments, the number of larvae settled on the Porolithon onkodes discs and the number of larvae swimming at the surface of the water were counted. The authors found that 3% of the coral larvae settled in the plastic mimic treatment and 30% of the coral larvae settled in the Porolithon onkodes treatment; these results indicate that calcareous and upright fleshy algae inhibit the settlement of coral larvae while algal turfs and crustose coralline algae enhance the larval settlement. The authors suggested that the larvae might sense the topographical changes in the surface and might try to avoid the upright physical structure of the fleshy macroalgae. Since the Porolithon onkodes has a high deposit of magnesium calcite, it calcifies solidly and provides a good framework for the coral larvae to settle on. Thus, while the upright fleshy algae inhibit Platygyra daedalea settlement, the coralline algae and algal turfs increase the larval settlement and can be used to replenish degraded coral habitats and promote coral recovery.