Seasonal Retreat Research Articles

Seasonal variations of outlet glacier terminus position in Greenland

AbstractMany of Greenland’s marine-terminating outlet glaciers have undergone rapid retreat in the past decade, accompanied by accelerated flow and dynamic thinning. Superimposed on this pattern of retreat, these glaciers undergo seasonal variations in terminus position, corresponding roughly to wintertime advance and summertime retreat. We compiled near-daily time series of terminus position for five of Greenland’s largest outlet glaciers (Daugaard Jensen, Kangerdlugssuaq and Helheim glaciers in East Greenland, and Jakobshavn Isbræ and Rink Isbræ in West Greenland) using Moderate Resolution Imaging Spectroradiometer (MODIS) satellite imagery. There are spatial differences in the timing of the onset of seasonal retreat among all the glaciers in our study, as well as variability in terminus behavior for individual glaciers from year to year. We examine whether this spatial and temporal variability is linked to above-freezing air temperatures or high sea surface temperatures, but find no simple relationship. Instead, we hypothesize that terminus geometry (ice thickness, subglacial topography, fjord bathymetry) exerts an important control on the response of marine-terminating glaciers to climate perturbations. Models for predicting outlet glacier response to climate change need to include this complex interaction between geometry and environmental forcing.

Mitigasi Perubahan Iklim dalam Mempertahankan Produktivitas Tanah Padi Sawah (Studi kasus di Kabupaten Indramayu)

Impact of Climate Change (DPI) in West Java, especially the agricultural sector (food) are strongly influenced by the shift early growing season occurs 2 to 4 weeks since last 5 years. Some areas on the North Coast (North Coast of Java) early season retreat 1 to 2 months. As a result it affects the decline in production and productivity of rice, the price fluctuations of agricultural products and food insecurity disturbing. Purpose of the study looked at the impact of climate change on the productivity of rice paddy fields at the time of drought and floods and how the wisdom of farmers to cope with climate change. The research location Indramayu regency, as it is the central areas of rice-based food production, and the area has the insecurity of the impacts of climate change. The results showed the presence of DPI on the applied local wisdom flooded farmers (a) using the short-lived rice varieties, (b) rice varieties resistant varieties will be flooded and planted in one stretch with monoculture cropping systems. (C) use a pump to remove water . Dry season activities were implemented: (a) promote the planting schedule, (b) create a nursery, (c) use early maturing varieties, (d) cross dams, (e) motion to eradicate rats, (f) spray white butterfly pests (borers rods), (g) irrigation cultivation rationed sleigh, (h) conduct ceremonies (salvation alms earth), (i) and down motion field simultaneously. Productivity of rice under normal conditions GKP 5 tons gkp / ha (R / C 2.21). While the impact of flooded rice productivity on average only up to 3.5 tonnes gkp/ ha (R / C 1.01). Impact of drought rice productivity was only 4 quintals / ha (R / C 0:24). To overcome this required specific technologies and institutional development, and agricultural infrastructure, to support sustainable food self-sufficiency. Keywords: Mitigation. Climate Change, Productivity. wetland

Sea-Ice Distribution in the Bering and Chukchi Seas: Information from Historical Whaleships’ Logbooks and Journals

Satellite data have revealed dramatic losses of Northern Hemisphere sea ice since the end of the 1970s. To place these changes in a longer-term context, we draw on daily observations taken from logbooks and journals of whaling vessels cruising in the Bering and Chukchi seas to investigate sea-ice conditions in this region of the Arctic between 1850 and 1910. We compare these observations to sea-ice data from 1972 to 1982, which predate the majority of the recent changes and cover a period recognized as a relative maximum in recent Bering Sea ice extent. Records from May indicate that end-of-winter sea-ice extent in the Bering Sea during the mid 19th century closely resembled that in the 1972 – 82 data. However, the historical data reveal that sea ice was more extensive during summer, with the greatest difference occurring in July. This pattern indicates a later and more rapid seasonal retreat. These conclusions highlight the value of historical data, which we have far from exhausted in this study.

Habitat preference, accessibility, and competition limit the global distribution of breeding Black-browed Albatrosses

Telemetry methods and remote sensing now make it possible to record the spatial usage of wide-ranging marine animals and the biophysical characteristics of their pelagic habitats. Furthermore, recent statistical advances mean that such data can be used to test ecological hypotheses and estimate species' distributions. Black-browed Albatrosses Thalassarche melanophrys are highly mobile marine predators with a circumpolar breeding and foraging distribution in the Southern Hemisphere. Although they remain relatively abundant, increased fisheries bycatch has led to their listing as endangered by conservation bodies. We satellite-tracked 163 breeding Black-browed Albatrosses and eight closely related Campbell Albatrosses T. impavida from nine colonies. We then quantified habitat usage, and modeled population-level spatial distribution at spatiotemporal scales >50 km and 1 month, as a function of habitat accessibility, habitat preference, and intraspecific competition, using mixed-effects generalized additive models (GAMM). During incubation, birds foraged over a wider area than in the post-brood chick-rearing period, when they are more time constrained. Throughout breeding, the order of habitat preference of Black-browed Albatrosses was for neritic (0–500 m), shelf-break and upper shelf-slope (500–1000 m), and then oceanic (>1000 m) waters. Black-browed Albatrosses also preferred areas with steeper (>3°) bathymetric relief and, in addition, during incubation, warmer sea surface temperatures (peak preference ∼16°C). Although this suggests specialization in neritic habitats, incubation-stage Black-browed Albatrosses from South Georgia also foraged extensively in oceanic waters, preferring areas with high eddy kinetic energy (>250 cm2/s2), especially the Brazil-Malvinas Confluence, a region of intense mesoscale turbulence. During chick-rearing, this species had a more southerly distribution, and following the seasonal retreat of sea ice, birds from some populations utilized neritic polar waters. Campbell Albatrosses showed similar bathymetric preferences but also preferred positive sea level anomalies. Black-browed Albatross foraging areas were partially spatially segregated with respect to colony and region, with birds preferring locations distant from neighboring colonies, presumably in order to reduce competition between parapatric conspecifics. At the global scale, the greatest concentrations of breeding Black-browed Albatrosses are in southern South American neritic, shelf-break, and shelf-slope waters. These regions also hold large fisheries and should therefore be a priority for introduction of bycatch mitigation measures.

<strong>EFEKTIVITAS PAKET PENGENDALIAN RESIKO PENYIMPANGAN IKLIM DI JAWA TENGAH</strong><br>(THE EFFECTIVENESS OF THE CLIMATE CHANGE RISK MANAGEMENT SCHEME IN CENTRAL JAVA)

This paper is summary report of study on implementation of local government designed strategies to anticipate and manage the climate change risks in Central Java. The basis of information obtained from interviews to farmers. In general, planting patterns follow schedule of water availability; therefore, farmers are more interested in talking about the lack of water compared with the excess water. According to farmers' language, climate change is the rainy season retreat. In this context, almost all respondents stated that the climate changes disrupt their farming activities. These disorders include reduction of production, planting schedule delays, increased costs of irrigation, seeds, pesticides and land management. Local agricultural agencies have been disseminating strategies to anticipate and manage the risks of climate change. Those strategies are planting reschedules, changing varieties or commodities, and improving the water management. Local governments also facilitate the implementation of those strategies, namely distribution of water pumps, and seeds according to climate prediction, and repair or construction of irrigation channels and reservoirs. Most respondents (59%) had never directly followed those socialization activities, and due to limited of the distributed facilities, only 29.87% of respondents enjoyed such facilities. However, the recipient stated that the government facilities effectively assist them in controlling the impact of climate change, and most farmers had committed the management of climate changes impacts in a manner consistent with the recommended strategy. These results show that both government assistance and collective action by farmers had the same important role in anticipating and controlling the impact of climate changes. Therefore, the government should socialize recomended strategies in a more intensive, and improve, and expand the reach of distribution facilities to implement the strategy. These efforts would stimulate farmers self-supporting as a whole, so that the programs in anticipating and controlling the impact of climate changes would be more effective.

Length-Weight Relationships, Maturity, and Reproductive Season of the Fringelip Mullet Crenimugil crenilabis (Forsskål, 1775) from the Arabian Sea Coast of Oman

Fringelip mullet (Crenimugil crenilabis) caught at Al Duqum and Salalah in the Arabian Sea region of Omanwere sampled monthly between January 2001 and December 2002. The total length (TL) of mullet caught with gill- and seine nets ranged from 12 to 54.5 cm (32.4 cm mean ± SD; n = 2445) but <2% of specimens had a TL<24 cm, suggesting gear selectivity. Females dominated samples (1 : 0.36) and reached L at 32.8 cm TL (32.2 cm in males). Length weight relationships were non-linear and conversion factors between TL, fork length (FL) and standard length (SL) were calculated. Proportionately, most females had ripe gonads in September and October, and males in September to November. Both female and male gonadosomatic indices (GSI) peaked in September and October and were lowest between May and August. The peak in reproductive activity coincides with the fall intermonsoon, when the Arabian Sea upwellings caused by the onshore winds of the SW monsoon season (June to August/September) retreat. During this intermonsoon period the inshore water temperatures begin to rise after reaching a minimum in August/September. Some reproductive activity also occurs in other months, particularly February, when water temperatures are seasonally lower.

Particle fluxes and biogeochemical processes in an area influenced by seasonal retreat of the ice margin (northwestern Ross Sea, Antarctica)

Fluxes of biogenic components were determined using time-series sediment trap samples collected at site B (74°01.50′S, 175°05.55′E) in the northern Joides Basin of the Ross Sea from December 1994 to January 1996. In most cases, a great part of the material collected by traps (200 and 540 m depth) was biogenic, opal being the most abundant constituent followed by organic matter. The composition of particles shows a seasonal pattern in the upper trap, which is much less evident at depth. Fluxes showed a marked seasonality due to the presence, in winter, of ice cover. During the sampling period, mass fluxes varied from 0.03 to 120 mg m −2 day −1 and from 24 to 393 mg m −2 day −1 at the upper and bottom level, respectively. Values of 0–64 mg m −2 day −1 of biogenic silica and 0–7.8 mg m −2 day −1 of organic carbon were obtained at 200 m depth. Near-bottom fluxes were almost always much higher: 11–141 and 1.5–19 mg m −2 day −1, respectively. 210Pb fluxes are lower than expected, and this means that particles sink rapidly without reaching an equilibrium with the radiotracer. A mechanism of focusing affects the bottom trap and much more, the seafloor. At site B, we measured particle fluxes that are much lower than those obtained at other locations in the Ross Sea. This can be due to low production and export during the sampling period, and underlies the necessity to further investigate the interannual variability of these processes.

A simple model for the influence of push-morainal banks on the calving and stability of glacial tidewater termini

AbstractPush-morainal banks at the grounding lines of tidewater termini of temperate glaciers are the source of two types of restraining forces operating at the glacier terminus. Horizontal normal forces derive from the lateral support and transport of the bank of sediment at the terminus, whereas a horizontal shear force operates along the base of a bank pushed in front of an advancing glacier. The simple model we present suggests that bank-related restraining forces are significantly larger than the restraining force derived from the hydrostatic pressure of water adjacent to the submerged terminus of a glacier. During glacier advance, restraining forces continually increase, resulting in decreasing flow rates, glacier thickening and the eventual cessation of advance. During retreat, restraining forces continually decrease, resulting in increasing flow rates, glacier thinning and the potential for unstable, rapid, sustained retreat. The normal, seasonal, oscillatory advance retreat cycle of a glacier is moderated by restraining forces associated with push moraines. Unstable retreat is likely initiated when bank-related restraining forces fall below some threshold value during the seasonal retreat cycle. Calving is not a primary cause of glacier retreat, but is more likely a short-term response to increased flow rates. Increased flow rates result in glacier thinning and an approach toward buoyancy, both of which fluctuate seasonally in accordance with bank-related restraining forces.

A simple model for the influence of push-morainal banks on the calving and stability of glacial tidewater termini

AbstractPush-morainal banks at the grounding lines of tidewater termini of temperate glaciers are the source of two types of restraining forces operating at the glacier terminus. Horizontal normal forces derive from the lateral support and transport of the bank of sediment at the terminus, whereas a horizontal shear force operates along the base of a bank pushed in front of an advancing glacier. The simple model we present suggests that bank-related restraining forces are significantly larger than the restraining force derived from the hydrostatic pressure of water adjacent to the submerged terminus of a glacier. During glacier advance, restraining forces continually increase, resulting in decreasing flow rates, glacier thickening and the eventual cessation of advance. During retreat, restraining forces continually decrease, resulting in increasing flow rates, glacier thinning and the potential for unstable, rapid, sustained retreat. The normal, seasonal, oscillatory advance retreat cycle of a glacier is moderated by restraining forces associated with push moraines. Unstable retreat is likely initiated when bank-related restraining forces fall below some threshold value during the seasonal retreat cycle. Calving is not a primary cause of glacier retreat, but is more likely a short-term response to increased flow rates. Increased flow rates result in glacier thinning and an approach toward buoyancy, both of which fluctuate seasonally in accordance with bank-related restraining forces.

Ecology and biogeochemistry of the antarctic circumpolar current during austral spring: a summary of southern ocean JGOFS cruise ANT X/6 of R.V. Polarstern

The R.V. Polarstern cruise ANT X/6, part of the international Southern Ocean JGOFS programme, investigated phytoplankton spring bloom development and its biogeochemical effects in different water masses of the Atlantic sector of the Southern Ocean: the Polar Frontal region (PFr), the southern Antarctic Circumpolar Current zone (sACC), its boundary with the Weddell Gyre (AWB) and the marginal ice zone (MIZ). The relative roles of physical stability, iron limitation and grazing pressure in enhancing or constraining phytoplankton biomass accumulation were examined. Three sections were carried out between the PFr and the ice edge along the 6°W meridian from early October to late November 1992. This paper summarises the major findings of the cruise and discusses their implications for our understanding of Southern Ocean ecology and biogeochemistry. A major finding was the negligible build-up of plankton biomass and concomitant absence of CO 2 drawdown associated with seasonal retreat of the ice cover. In striking contrast to this unexpected poverty of both the MIZ and the frontal region of the AWB, distinct phytoplankton blooms, dominated by different diatom species, accumulated in the PFr. Chlorophyll stocks in the sACC remained monotonously low throughout the study. Our findings confirm those of other studies that frontal regions are the major productive sites in the Southern Ocean and that input of meltwater and associated ice algae to the surface layer from a retreating ice edge is by itself an insufficient condition for induction of phytoplankton blooms. The blooms in the PFr developed under conditions of shallow mixing layers, high iron concentrations and relatively low grazing pressure. However, in all three blooms, high biomass extended to deeper than 70 m, which cannot be explained by either in situ growth or sinking out of a part of the population from the upper euphotic zone. Subduction of adjoining, shallower layers to explain depth distribution is invoked. Despite a clear CO 2 drawdown in the Polar Frontal region, the highly variable conditions encountered render reliable estimation of annual CO 2 fluxes in the Southern Ocean difficult.

Injection of dust into the martian atmosphere: Evidence from the viking gas exchange experiment

It is proposed that dust storms on Mars that develop during predawn hours may be triggered by a freeze/thaw dust injection process. The model is based on a phenomenon that was observed during the Viking Gas Exchange experiments on Mars, in which adsorbed gas was catastrophically desorbed from soil samples when exposed to humidification at ∼5°C. Similar conditions may develop at midlatitude locations on Mars near perihelion, and a similar humidification-driven desorption process might occur in the soil column. If soils are dampened during humikification, desorbed gases in confined pore spaces could possibly reach 8.6 bar. Diurnal freezing may possibly cause H 2O to crystallize within the pores, possibly producing cohesive soil failure, release of the trapped gas, and explosive injection of freeze-dried powdery overburden dust into the atmospheric column. The process could potentially occur at 5–20 cm depth, and the freeze/thaw dust injection event may initiate after 10:00 PM local time (20°S lat). Dust would be injected at velocities approaching 450 m sec −1 and it would remain in the atmosphere for several hours before settling out. The plumes could potentially regenerate diurnally until the growing atmospheric dust load produced sufficient dampening of the diurnal thermal wave to prevent freeze/thaw. Seasonal replenishment of H 2O could potentially occur by upward migration from depth during the period between 150 and 475 sols after perihelion. The model was experimentally tested and the results were in good agreement with predictions, although a factor of 14 times more gas evolved from the laboratory samples than from the Viking samples. Most of the characteristics of the predawn storms could possibly be adequately explained by the freeze/thaw injection model, including (1) predawn onsets, (2) postperihelion seasonal occurence, (3) daily recurrence during the initial phases of the storms, and (4) generation of blue clouds (H 2O ice) at the storm sites. The process may possibly occur over widespread locations at midlatitudes during seasonal retreat of “tempofrost” from these latitude belts. Permanent low albedo features in these latitude belts may possibly be regions of preferential humidification-induced dust entrainment and net dust removal. The H 2O injected into the atmosphere may potentially be a major source of H 2SO 4 and HCl aerosols, which may possibly chemically react with the regolith to form soluble sulfate and chloride salts. Mg 2+ may be preferentially depleted from the dust.