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January 12, 2008:
First version
March 5, 2010:
Latest update

Science highlights

On this page, we will be presenting highlights of the research being done within the framework of LUCCI. This can be short reports on fieldwork campaigns, presentations of surprising results, or abstracts of articles published in high-profile international journals.

 
The Chicxulub Asteroid Impact and Mass Extinction at the Cretaceous-Paleogene Boundary
P. Schulte, L. Alegret, I. Arenillas, J.A. Arz, P.J. Barton, P.R. Bown, T.J. Bralower, G.L. Christeson, P. Claeys, C.S. Cockell, G.S. Collins, A. Deutsch, T.J. Goldin, K. Goto, J.M. Grajales-Nishimura, R.A.F. Grieve, S.P.S. Gulick, K.R. Johnson, W. Kiessling, C. Koeberl, D.A. Kring, K.G. MacLeod, T. Matsui, J. Melosh, A. Montanari, J.V. Morgan, C.R. Neal, D.J. Nichols, R.D. Norris, E. Pierazzo, G. Ravizza, M. Rebolledo-Vieyra, W.U. Reimold, E. Robin, T. Salge, R.P. Speijer, A.R. Sweet, J. Urrutia-Fucugauchi, V. Vajda, M.T. Whalen and P.S. Willumsen
Science 327 (2010), 1214-1218; doi: 10.1126/science.1177265
The journal webpage | The article (PDF) | The press release (PDF) | Lund university news (in Swedish)

Abstract:
The Cretaceous-Paleogene boundary ~65.5 million years ago marks one of the three largest mass extinctions in the past 500 million years. The extinction event coincided with a large asteroid impact at Chicxulub, Mexico, and occurred within the time of Deccan flood basalt volcanism in India. Here, we synthesize records of the global stratigraphy across this boundary to assess the proposed causes of the mass extinction. Notably, a single ejecta-rich deposit compositionally linked to the Chicxulub impact is globally distributed at the Cretaceous-Paleogene boundary. The temporal match between the ejecta layer and the onset of the extinctions and the agreement of ecological patterns in the fossil record with modeled environmental perturbations (for example, darkness and cooling) lead us to conclude that the Chicxulub impact triggered the mass extinction.

Correspondence and requests for materials should be addressed to Peter Schulte (e-mail: schulte@geol.uni-erlangen.de) or Vivi Vajda (e-mail: vivi.vajda@geol.lu.se).

 
Half-precessional dynamics of monsoon rainfall near the East African Equator
D. Verschuren, J.S. Sinninghe Damsté, J. Moernaut, I. Kristen, M. Blaauw, M. Fagot, G.H. Haug & CHALLACEA project members (including LUCCI scientist D.J. Conley)
Nature 462 (2009) 637-641; doi:10.1038/nature08520
The journal webpage | The article (PDF) | Press release (PDF)

First paragraph:
External climate forcings - such as long-term changes in solar insolation - generate different climate responses in tropical and high latitude regions. Documenting the spatial and temporal variability of past climates is therefore critical for understanding how such forcings are translated into regional climate variability. In contrast to the data-rich middle and high latitudes, high-quality climate-proxy records from equatorial regions are relatively few, especially from regions experiencing the bimodal seasonal rainfall distribution associated with twice-annual passage of the Intertropical Convergence Zone. Here we present a continuous and well-resolved climate-proxy record of hydrological variability during the past 25,000 years from equatorial East Africa. Our results, based on complementary evidence from seismic-reflection stratigraphy and organic biomarker molecules in the sediment record of Lake Challa near Mount Kilimanjaro, reveal that monsoon rainfall in this region varied at half-precessional (~11,500-year) intervals in phase with orbitally controlled insolation forcing.

Correspondence and requests for materials should be addressed to Dirk Verschuren (e-mail dirk.verschuren@UGent.be) or to Daniel Conley (e-mail Daniel.Conley@geol.lu.se).

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Clean the Air, Heat the Planet?
A. Arneth, N. Unger, M. Kulmala, and M.O. Andreae
Science 326 (2009) 672-673; doi:10.1126/science.1181568
The journal webpage | The article (PDF) | The Lund university press release (in Swedish)

Concluding paragraph:
Like many others in the climate debate, we have focused on surface temperature, but other aspects of climate change - especially the amount, distribution, and intensity of rainfall - are at least as important to human well-being. Changing aerosol burdens may alter local and regional cloud cover and precipitation, change the intensity or timing of the monsoon circulation, and even shift precipitation across national borders. Changes in cloud cover and precipitation will also feed back on the photochemistry and rainout of short-lived species. These issues must be considered if aerosol emissions are to become part of climate policy. Given the toxicity of pollutants, the question is not whether ever stricter air pollution controls will be implemented, but when and where. The jury is out on whether air pollution control will accelerate or mitigate climate change. Still, the studies available to date mostly suggest that air pollution control will accelerate warming in the coming decades. Climate change policies may have to include a "pollution safety margin" in greenhouse gas reduction targets. CO2, indeed, is not the only gas.

Correspondence and requests for materials should be addressed to Almut Arneth (Email: almut.arneth@nateko.lu.se).

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Temperature adaptation of soil bacterial communities along an Antarctic climate gradient: predicting responses to climate warming
R. Rinnan, J. Rousk, E. Yergeau, G.A. Kowalchuk and E. Bååth
Global Change Biology (2009) 15, 2615-2625, doi: 10.1111/j.1365-2486.2009.01959.x
The journal webpage | The article (PDF)

Abstract:
Soil microorganisms, the central drivers of terrestrial Antarctic ecosystems, are being confronted with increasing temperatures as parts of the continent experience considerable warming. Here we determined short-term temperature dependencies of Antarctic soil bacterial community growth rates, using the leucine incorporation technique, in order to predict future changes in temperature sensitivity of resident soil bacterial communities. Soil samples were collected along a climate gradient consisting of locations on the Antarctic Peninsula (Anchorage Island, 67°13’40”S, 68°10’80”W), Signy Island (60°14’30”S, 45°13’80”W) and the Falkland Islands (51°17’60”S 59°10’30”W). At each location, experimental plots were subjected to warming by open top chambers (OTCs) and paired with control plots on vegetated and fell-field habitats. The bacterial communities were adapted to the mean annual temperature of their environment, as shown by a significant correlation between the mean annual soil temperature and the minimum temperature for bacterial growth (Tmin). Every 1 °C rise in soil temperature was estimated to increase Tmin> by 0.24-0.38 °C. The optimum temperature for bacterial growth varied less and did not have as clear a relationship with soil temperature. Temperature sensitivity, indicated by Q10 values, increased with mean annual soil temperature, suggesting that bacterial communities from colder regions were less temperature sensitive than those from the warmer regions. The OTC warming (generally <1 °C temperature increases) over 3 years had no effects on temperature relationship of the soil bacterial community. We estimate that the predicted temperature increase of 2.6 °C for the Antarctic Peninsula would increase Tmin> by 0.6-1 °C and Q10> (0-10 °C) by 0.5 units.

Correspondence and requests for materials should be addressed to Riikka Rinnan (Email: riikkar@bio.ku.dk).

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Ecological Dynamics Across the Arctic Associated with Recent Climate Change
Eric Post, Mads C. Forchhammer, M. Syndonia Bret-Harte, Terry V. Callaghan, Torben R. Christensen, Bo Elberling, Anthony D. Fox, Olivier Gilg, David S. Hik, Toke T. Høye, Rolf A. Ims, Erik Jeppesen, David R. Klein, Jesper Madsen, A. David McGuire, Søren Rysgaard, Daniel E. Schindler, Ian Stirling, Mikkel P. Tamstorf, Nicholas J.C. Tyler, Rene van der Wal, Jeffrey Welker, Philip A. Wookey, Niels Martin Schmidt and Peter Aastrup
Science 325, 1355 (2009); doi 10.1126/science.1173113
The journal webpage | The article (PDF) | The Lund university press release (in Swedish)

Abstract:
At the close of the Fourth International Polar Year, we take stock of the ecological consequences of recent climate change in the Arctic, focusing on effects at population, community, and ecosystem scales. Despite the buffering effect of landscape heterogeneity, Arctic ecosystems and the trophic relationships that structure them have been severely perturbed. These rapid changes may be a bellwether of changes to come at lower latitudes and have the potential to affect ecosystem services related to natural resources, food production, climate regulation, and cultural integrity. We highlight areas of ecological research that deserve priority as the Arctic continues to warm.

Correspondence and requests for materials should be addressed to Eric Post (Email: esp10@psu.edu or erp@dmu.dk).

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Large tundra methane burst during onset of freezing
Mikhail Mastepanov, Charlotte Sigsgaard, Edward J. Dlugokencky, Sander Houweling, Lena Ström, Mikkel P. Tamstorf and Torben R. Christensen
Nature Vol 456, 4 December 2008, doi:10.1038/nature07464
The journal | The article (PDF) | The Lund university press release (in Swedish)

First paragraph:
Terrestrial wetland emissions are the largest single source of the greenhouse gas methane. Northern high-latitude wetlands contribute significantly to the overall methane emissions from wetlands, but the relative source distribution between tropical and high-latitude wetlands remains uncertain. As a result, not all the observed spatial and seasonal patterns of atmospheric methane concentrations can be satisfactorily explained, particularly for high northern latitudes. For example, a late-autumn shoulder is consistently observed in the seasonal cycles of atmospheric methane at high-latitude sites, but the sources responsible for these increased methane concentrations remain uncertain. Here we report a data set that extends hourly methane flux measurements from a high Arctic setting into the late autumn and early winter, during the onset of soil freezing. We find that emissions fall to a low steady level after the growing season but then increase significantly during the freeze-in period. The integral of emissions during the freeze-in period is approximately equal to the amount of methane emitted during the entire summer season. Three-dimensional atmospheric chemistry and transport model simulations of global atmospheric methane concentrations indicate that the observed early winter emission burst improves the agreement between the simulated seasonal cycle and atmospheric data from latitudes north of 60° N. Our findings suggest that permafrost-associated freeze-in bursts of methane emissions from tundra regions could be an important and so far unrecognized component of the seasonal distribution of methane emissions from high latitudes.

Correspondence and requests for materials should be addressed to Torben R. Christensen (Email: Torben.Christensen@nateko.lu.se).

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