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Taylor Valley (taylor + valley)
Selected AbstractsThe balance between photosynthesis and grazing in Antarctic mixotrophic cryptophytes during summerFRESHWATER BIOLOGY, Issue 11 2002William Marshall SUMMARY 1. Grazing and photosynthetic contributions to the carbon balance of planktonic, mixotrophic cryptophytes in Lakes Fryxell and Hoare in the Taylor Valley, Antarctica were measured during November and December 2000. 2. The cryptophytes never became entirely photosynthetic, although carbon derived from grazing decreased in December. Individual grazing rates ranged between 5.28 and 10.08 bacteria cell,1 day,1 in Lake Fryxell and 0.36,11.76 bacteria cell,1 day,1 in Lake Hoare. Grazing rates varied temporally and with depth in the water column. In Lake Fryxell, which is a meromictic lake, highest grazing occurred just above the chemocline. Individual photosynthetic rates ranged from 0.23 to 1.35 pg C cell,1 h,1 in Lake Fryxell and 0.074 to 1.08 pg C cell,1 h,1 in Lake Hoare. 3. Carbon acquisition by the cryptophyte community gained through grazing ranged between 8 and 31% during November in Lake Fryxell, dropping to between 2 and 24% in December. In Lake Hoare grazing contributed 12,21% of the community carbon budget in November and 1,28% in December. Around 4% of the carbon acquired from grazing and photosynthesis was remineralised through respiration. 4. Mixotrophy is probably a major survival strategy for cryptophytes in the extreme lakes of the Dry Valleys, because perennial ice-cover severely limits light penetration to the water column, whereas these phytoflagellates are not normally mixotrophic in lower latitude lakes. The evidence suggests that mixotrophy may be a mechanism for supplementing the carbon budget, as well as a means of acquiring nutrients for growth. [source] The Geologic Basis for a Reconstruction of a Grounded Ice Sheet in McMurdo Sound, Antarctica, at the Last Glacial MaximumGEOGRAFISKA ANNALER SERIES A: PHYSICAL GEOGRAPHY, Issue 2-3 2000George H. Denton A grounded ice sheet fed from the Ross Embayment filled McMurdo Sound at the last glacial maximum (LGM). This sheet deposited the little-weathered Ross Sea drift sheet, with far-traveled Transantarctic Mountains (TAM) erratics, on lower slopes of volcanic islands and peninsulas in the Sound, as well as on coastal forelands along the TAM front. The mapped upper limit of this drift, commonly marked by a distinctive moraine ridge, shows that the ice-sheet surface sloped landward across McMurdo Sound from 710 m elevation at Cape Crozier to 250 m in the eastern foothills of the Royal Society Range. Ice from the Ross Embayment flowed westward into the sound from both north and south of Ross Island. The northern flowlines were dominant, deflecting the southern flowlines toward the foothills of the southern Royal Society Range. Ice of the northern flowlines distributed distinctive kenyte erratics, derived from western Ross Island, in Ross Sea drift along the TAM front between Taylor and Miers Valleys. Lobes from grounded ice in McMurdo Sound blocked the mouths of TAM ice-free valleys, damming extensive proglacial lakes. A floating ice cover on each lake formed a conveyor that transported glacial debris from the grounded ice lobes deep into the valleys to deposit a unique glaciolacustrine facies of Ross Sea drift. The ice sheet in McMurdo Sound became grounded after 26,860 14C yr bp. It remained near its LGM position between 23,800 14C yr bp and 12,700 14C yr bp. Recession was then slow until sometime after 10,794 14C yr bp. Grounded ice lingered in New Harbor in the mouth of Taylor Valley until 8340 14C yr bp. The southward-retreating ice-sheet grounding line had penetrated deep into McMurdo Sound by 6500 14C yr bp. The existence of a thick ice sheet in McMurdo Sound is strong evidence for widespread grounding across the Ross Embayment at the LGM. Otherwise, the ice-sheet surface would not have sloped landward, nor could TAM erratics have been glacially transported westward into McMurdo Sound from farther offshore in the Ross Embayment. [source] Decline in a dominant invertebrate species contributes to altered carbon cycling in a low-diversity soil ecosystemGLOBAL CHANGE BIOLOGY, Issue 8 2008J. E. BARRETT Abstract Low-diversity ecosystems cover large portions of the Earth's land surface, yet studies of climate change on ecosystem functioning typically focus on temperate ecosystems, where diversity is high and the effects of individual species on ecosystem functioning are difficult to determine. We show that a climate-induced decline of an invertebrate species in a low-diversity ecosystem could contribute to significant changes in carbon (C) cycling. Recent climate variability in the McMurdo Dry Valleys of Antarctica is associated with changes in hydrology, biological productivity, and community composition of terrestrial and aquatic ecosystems. One of the greatest changes documented in the dry valleys is a 65% decrease in the abundance of the dominant soil invertebrate (Scottnema lindsayae, Nematoda) between 1993 and 2005, illustrating sensitivity of biota in this ecosystem to small changes in temperature. Globally, such declines are expected to have significant influences over ecosystem processes such as C cycling. To determine the implications of this climate-induced decline in nematode abundance on soil C cycling we followed the fate of a 13C tracer added to soils in Taylor Valley, Antarctica. Carbon assimilation by the dry valley nematode community contributed significantly to soil C cycling (2,7% of the heterotrophic C flux). Thus, the influence of a climate-induced decline in abundance of a dominant species may have a significant effect on ecosystem functioning in a low-diversity ecosystem. [source] Snow in the McMurdo Dry Valleys, AntarcticaINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 5 2010Andrew G. Fountain Abstract Snowfall was measured at 11 sites in the McMurdo Dry Valleys to determine its magnitude, its temporal changes, and spatial patterns. Annual values ranged from 3 to 50 mm water equivalent with the highest values nearest the coast and decreasing inland. A particularly strong spatial gradient exists in Taylor Valley, probably resulting from local uplift conditions at the coastal margin and valley topography that limits migration inland. More snow occurs in winter near the coast, whereas inland no seasonal pattern is discernable. This may be due, again, to local uplift conditions, which are common in winter. We find no influence of the distance to the sea ice edge. Katabatic winds play an important role in transporting snow to the valley bottoms and essentially double the precipitation. That much of the snow accumulation sublimates prior to making a hydrologic contribution underscores the notion that the McMurdo Dry Valleys are indeed an extreme polar desert. Copyright © 2009 Royal Meteorological Society [source] Thermal characterisation of active layer across a soil moisture gradient in the McMurdo Dry Valleys, AntarcticaPERMAFROST AND PERIGLACIAL PROCESSES, Issue 1 2009Scott J. Ikard Abstract Heat transport into active layer soils is important to understanding potential responses to changes in surface energy balance, particularly in the context of changing climate. Here we present results of a study to characterise soil thermal properties along a soil moisture gradient adjacent to Lake Fryxell in Taylor Valley, Antarctica. Our goals were to characterise the thermal characteristics of these relatively wet soils (compared to the rest of the McMurdo Dry Valleys landscape), and to assess the response of the active layer to possible increases in soil moisture. We measured subsurface temperatures at depths from 3 to 50,cm at four locations along a natural gradient of wet to dry soils adjacent to Lake Fryxell from January 2006 to January 2007. We used a numerical model to estimate apparent thermal diffusivity (ATD) and simulate observed temperature time series. Calculations of ATD at discrete locations yielded values ranging from 1.0,×,10,9 , 2.4,×,10,5,m2,s,1, and the corresponding range of bulk (i.e. depth averaged at a single surface location) ATD was 2.9,×,10,9,1.2,×,10,7,m2,s,1. Thawed soils had a range of bulk ATD during warming of 2.9,×,10,9,3.8,×,10,8,m2,s,1, and during cooling of 2.9,×,10,9,4.8,×,10,8,m2,s,1. When soils were frozen, however, the range of bulk ATD was 7.6,×,10,9,1.2,×,10,7,m2,s,1 during warming, and 7.8,×,10,9,1.1,×,10,7,m2,s,1 during cooling. Estimated bulk ATD values were consistently greater in locations of enhanced soil moisture, so lakeside soils were more likely to conduct energy into the subsurface. Increased soil moisture across the landscape would likely increase ATD, allowing for greater heat exchange between the atmosphere and the subsurface. Copyright © 2009 John Wiley & Sons, Ltd. [source] | |||||||||||||