New research from last week 47/2012
Posted on 26 November 2012 by Ari Jokimäki
This week we have papers on snowfall, rainfall, Arctic vegetation, Arctic sea ice, ozone, Svalbard glaciers, ice cores, ocean waters and others.
Characteristics of ocean waters reaching Greenland's glaciers
Abstract:"Interaction of Greenland's marine-terminating glaciers with the ocean has emerged as a key term in the ice-sheet mass balance and a plausible trigger for their recent acceleration. Our knowledge of the dynamics, however, is limited by scarcity of ocean measurements at the glacier/ocean boundary. Here data collected near six marine-terminating glaciers (79 North, Kangerdlugssuaq, Helheim and Petermann glaciers, Jakobshavn Isbræ, and the combined Sermeq Kujatdleq and Akangnardleq) are compared to investigate the water masses and the circulation at the ice/ocean boundary. Polar Water, of Arctic origin, and Atlantic Water, from the subtropical North Atlantic, are found near all the glaciers. Property analysis indicates melting by Atlantic Water (AW; found at the grounding line depth near all the glaciers) and the influence of subglacial discharge at depth in summer. AW temperatures near the glaciers range from 4.5°C in the southeast, to 0.16°C in northwest Greenland, consistent with the distance from the subtropical North Atlantic and cooling across the continental shelf. A review of its offshore variability suggests that AW temperature changes in the fjords will be largest in southern and smallest in northwest Greenland, consistent with the regional distribution of the recent glacier acceleration."
Citation: Straneo, Fiammetta; Sutherland, David A.; Holland, David; Gladish, Carl; Hamilton, Gordon S.; Johnson, Helen L.; Rignot, Eric; Xu, Yun; Koppes, Michele, Annals of Glaciology, Volume 53, Number 60, November 2012 , pp. 202-210(9), DOI: http://dx.doi.org/10.3189/2012AoG60A059.
Ice core researchers got tired of counting ice layers manually
Abstract:"We present an automated process for determining the annual layer chronology of an ice-core with a strong annual signal, utilising the hydrogen peroxide record from an Antarctic Peninsula ice-core as a test signal on which to count annual cycles and explain the methods. The signal is de-trended and normalised before being split into sections with a deterministic cycle count and those that need more attention. Possible reconstructions for the uncertain sections are determined which could be used as a visual aid for manual counting, and a simple method for assigning probability measures to each reconstruction is discussed. The robustness of this process is explored by applying it to versions of two different chemistry signals from the same stretch of the NGRIP (North Greenland Ice Core Project) ice-core, which shows more variation in annual layer thickness, with and without thinning to mimic poorer quality data. An adapted version of these methods is applied to the more challenging non-sea-salt sulphur signal from the same Antarctic Peninsula core from which the hydrogen peroxide signal was taken. These methods could readily be adapted for use on much longer datasets, thereby reducing manual effort and providing a robust automated layer-counting methodology."
Citation: Wheatley, J. J., Blackwell, P. G., Abram, N. J., McConnell, J. R., Thomas, E. R., and Wolff, E. W.: Automated ice-core layer-counting with strong univariate signals, Clim. Past, 8, 1869-1879, doi:10.5194/cp-8-1869-2012, 2012.
Arctic sea ice limits methane emission from ocean and also absorbs methane from atmosphere
Highlights:► We compared methane fluxes under two conditions, with and without ice cover. ► There is considerable methane potentially storing in central Arctic Ocean. ► Sea ice limits methane emission in Arctic. ► Sea ice absorbs methane in atmosphere potentially related to both photochemical and biochemical oxidation.
Abstract: "Sources and sinks of methane, one of the most important greenhouse gases, have attracted intensive attention due to its role in global warming. We show that sea ice in the Arctic Ocean regulates methane level through two mechanisms, shielding of methane emission from the ocean, and consumption of methane. Using a static chamber technique, we estimated that the methane flux from under-ice water was 0.56 mg(CH4) m−2 d−1on average in central Arctic Ocean, relatively higher than that in other oceans, indicating considerable methane storage in this region under sea ice. Average methane flux on under-ice water was higher than that above sea ice, which suggests that sea ice could limit methane emission. In addition, negative fluxes on sea ice suggest that there are methane consuming processes, which are possibly associated with both photochemical and biochemical oxidation. Our results provide a general understanding about how sea ice in Arctic affects regional and global methane balance."
Citation: Xin He, Liguang Sun, Zhouqing Xie, Wen Huang, Nanye Long, Zheng Li, Guangxi Xing, Atmospheric Environment, Volume 67, March 2013, Pages 8–13, http://dx.doi.org/10.1016/j.atmosenv.2012.10.029.
Strong evidence for warming, wetting and intensified rainfall in South America
Highlights:► Strong evidence for warming, wetting and intensified rainfall in South America ► Cold (warm) extremes are decreasing (increasing) over the 1950–2010 period ► Local trends are spatially more coherent for temperature than for precipitation ► Precipitation is increasing, with SE South America and Amazonia contributing more ► Intensification of heavy rainy events over eastern part of the continent is found.
Abstract:"Here we show and discuss the results of an assessment of changes in both area-averaged and station-based climate extreme indices over South America (SA) for the 1950–2010 and 1969–2009 periods using high-quality daily maximum and minimum temperature and precipitation series. A weeklong regional workshop in Guayaquil (Ecuador) provided the opportunity to extend the current picture of changes in climate extreme indices over SA. Our results provide evidence of warming and wetting across the whole SA since the mid-20th century onwards. Nighttime (minimum) temperature indices show the largest rates of warming (e.g. for tropical nights, cold and warm nights), while daytime (maximum) temperature indices also point to warming (e.g. for cold days, summer days, the annual lowest daytime temperature), but at lower rates than for minimums. Both tails of night-time temperatures have warmed by a similar magnitude, with cold days (the annual lowest nighttime and daytime temperatures) seeing reductions (increases). Trends are strong and moderate (moderate to weak) for regional-averaged (local) indices, most of them pointing to a less cold SA during the day and warmer night-time temperatures. Regionally-averaged precipitation indices show clear wetting and a signature of intensified heavy rain events over the eastern part of the continent. The annual amounts of rainfall are rising strongly over south-east SA (26.41 mm/decade) and Amazonia (16.09 mm/decade), but north-east Brazil and the western part of SA have experienced non-significant decreases. Very wet and extremely days, the annual maximum 5-day and 1-day precipitation show the largest upward trends, indicating an intensified rainfall signal for SA, particularly over Amazonia and south-east SA. Local trends for precipitation extreme indices are in general less coherent spatially, but with more general spatially coherent upward trends in extremely wet days over all SA."
Citation: María de los Milagros Skansia, Manola Brunet, Javier Sigró, Enric Aguilar, Juan Andrés Arevalo Groening, Oscar J. Bentancur, Yaruska Rosa Castellón Geier, Ruth Leonor Correa Amaya, Homero Jácome, Andrea Malheiros Ramos, Clara Oria Rojas, Alejandro Max Pasten, Sukarni Sallons Mitro, Claudia Villaroel Jiménez, Rodney Martínez, Lisa V. Alexander, P.D. Jones, Global and Planetary Change, http://dx.doi.org/10.1016/j.gloplacha.2012.11.004.
Observations of enhanced thinning in the upper reaches of Svalbard glaciers
Abstract: "Changes in the volume and extent of land ice of the Svalbard archipelago have been the subject of considerable research since their sensitivity to changes in climate was first noted. However, the measurement of these changes is often necessarily based on point or profile measurements which may not be representative if extrapolated to a whole catchment or region. Combining high-resolution elevation data from contemporary laser-altimetry surveys and archived aerial photography makes it possible to measure historical changes across a glacier's surface without the need for extrapolation. Here we present a high spatial resolution time-series for six Arctic glaciers in the Svalbard archipelago spanning 1961 to 2005. We find high variability in thinning rates between sites with prevalent elevation changes at all sites averaging −0.59 ± 0.04 m a−1 between 1961–2005. Prior to 1990, ice surface elevation was changing at an average rate of −0.52 ± 0.09 m a−1 which decreased to −0.76 ± 0.10 m a−1after 1990. Setting the elevation changes against the glaciers' altitude distribution reveals that significant increases in thinning rates are occurring most notably in the glaciers' upper reaches. We find that these changes are coincident with a decrease in winter precipitation at the Longyearbyen meteorological station and could reflect a decrease in albedo or dynamic response to lower accumulation. Further work is required to understand fully the causes of this increase in thinning rates in the glaciers' upper reaches. If on-going and occurring elsewhere in the archipelago, these changes will have a significant effect on the region's future mass balance. Our results highlight the importance of understanding the climatological context of geodetic mass balance measurements and demonstrate the difficulty of using index glaciers to represent regional changes in areas of strong climatological gradients."
Citation: James, T. D., Murray, T., Barrand, N. E., Sykes, H. J., Fox, A. J., and King, M. A.: Observations of enhanced thinning in the upper reaches of Svalbard glaciers, The Cryosphere, 6, 1369-1381, doi:10.5194/tc-6-1369-2012, 2012.
Stratospheric ozone and temperature simulated from the preindustrial era to the present day
Abstract: "Results from the simulation of a coupled chemistry climate model are presented for the period 1860 to 2005 using the observed greenhouse gas (GHG) and halocarbon concentrations. The model is coupled to a simulated ocean and uniquely includes both detailed tropospheric chemistry and detailed middle atmosphere chemistry, seamlessly from the surface to the model top layer centered at 0.02 hPa. It is found that there is no statistically significant change in simulated stratospheric temperature and ozone prior to the year 1960. As the halocarbon amounts increase after 1970, model stratospheric ozone decreases approximately continuously until about 2000. The steadily increasing GHG concentrations cool the stratosphere from the beginning of the 20th century at a rate which increases with height. During the early period the cooling leads to increased stratospheric ozone. The model results show a strong, albeit temporary, response to volcanic eruptions. While CFC concentrations remain low, the effect of eruptions is shown to increase the amount of HNO3, reducing ozone destruction by the NOx catalytic cycle. In the presence of anthropogenic chlorine, after the eruption of El Chichón and Mt. Pinatubo, chlorine radicals increased and the chlorine reservoirs decreased. The net volcanic effect on nitrogen and chlorine chemistry depends on altitude and, for these two volcanoes, leads to an ozone increase in the middle stratosphere and a decrease in the lower stratosphere. Model lower stratospheric temperatures are also shown to increase during the last three major volcanic eruptions, by about 0.6 K in the global and annual average, consistent with observations."
Citation: John Austin, Larry W. Horowitz, M. Daniel Schwarzkopf, R. John Wilson, and Hiram Levy II, Journal of Climate 2012, doi: http://dx.doi.org/10.1175/JCLI-D-12-00162.1.
Satellite measurements show overall greening in Arctic but also some browning areas
Abstract: "The concern about Arctic greening has grown recently as the phenomenon is thought to have significant influence on global climate via atmospheric carbon emissions. Earlier work on Arctic vegetation highlighted the role of summer sea ice decline in the enhanced warming and greening phenomena observed in the region, but did not contain enough details for spatially characterizing the interactions between sea ice, temperature and vegetation photosynthetic absorption. By using 1 km resolution data from the Moderate Resolution Imaging Spectrometer (MODIS) as a primary data source, this study presents detailed maps of vegetation and temperature trends for the Siberian Arctic region, using the time integrated normalized difference vegetation index (TI-NDVI) and summer warmth index (SWI) calculated for the period 2000–11 to represent vegetation greenness and temperature respectively. Spatio-temporal relationships between the two indices and summer sea ice conditions were investigated with transects at eight locations using sea ice concentration data from the Special Sensor Microwave/Imager (SSM/I). In addition, the derived vegetation and temperature trends were compared among major Arctic vegetation types and bioclimate subzones. The fine resolution trend map produced confirms the overall greening (+1% yr−1) and warming (+0.27% yr−1) of the region, reported in previous studies, but also reveals browning areas. The causes of such local decreases in vegetation, while surrounding areas are experiencing the opposite reaction to changing conditions, are still unclear. Overall correlations between sea ice concentration and SWI as well as TI-NDVI decreased in strength with increasing distance from the coast, with a particularly pronounced pattern in the case of SWI. SWI appears to be driving TI-NDVI in many cases, but not systematically, highlighting the presence of limiting factors other than temperature for plant growth in the region. Further unravelling those limiting factors constitutes a priority in future research. This study demonstrates the use of medium resolution remotely sensed data for studying the complexity of spatio-temporal vegetation dynamics in the Arctic."
Citation: L P Dutrieux, H Bartholomeus, M Herold and J Verbesselt, 2012 Environ. Res. Lett. 7 044028 doi:10.1088/1748-9326/7/4/044028.
Snowfall is projected to decrease in western and central Europe
Abstract:"Large parts of western and central Europe face a 20–50 % future reduction in snowfall on Hellmann days (days with daily-mean temperatures below freezing). This strong reduction occurs in addition to the expected 75 % decrease of the number of Hellmann days near the end of the twenty first century. The result is insensitive to the exact freezing-level threshold, but is in sharp contrast with the winter daily precipitation, which increases under most global warming scenarios. Not only climate model simulations show this. Observational records also reveal that probabilities for precipitation on Hellmann days have been larger in the past. The future reduction is a consequence of the freezing-level threshold becoming a more extreme quantile of the temperature distribution in the future. Only certain circulation types permit these quantiles to be reached, and it is shown that these have intrinsically low precipitation probability."
Citation: Hylke de Vries, Reindert J. Haarsma, Wilco Hazeleger, Climate Dynamics, November 2012, DOI: 10.1007/s00382-012-1583-x.
Other studies from last week
Comparative analysis of the influence of climate change and nitrogen deposition on carbon sequestration in forest ecosystems in European Russia: simulation modelling approach - Komarov & Shanin (2012) [FULL TEXT]
CLASSIC OF THE WEEK: Reid (1895)
Citation: Harry Fielding Reid, The Journal of Geology, Vol. 3, No. 3 (Apr. - May, 1895) (pp. 278-288).
This is a cross-post from AGW Observer. About this series. When each paper is published, it is notified in AGW Observer Facebook page and Twitter page. At least some of these are also retweeted in Skeptical Science Twitter page. Here's the archive for the research papers of previous weeks. If this sort of thing interests you, be sure to check out A Few Things Illconsidered. They also have a weekly posting containing lots of links to new research and other climate related news.