Southward migration of the Southern Hemisphere westerly winds corresponds with warming climate over centennial timescales

Recent changes in the strength and location of the Southern Hemisphere westerly winds (SHW) have been linked to continental droughts and wildfires, changes in the Southern Ocean carbon sink, sea ice extent, ocean circulation, and ice shelf stability. Despite their critical role, our ability to predict their impacts under future climates is limited by a lack of data on SHW behaviour over centennial timescales. Here, we present a 700-year record of changes in SHW intensity from sub-Antarctic Marion Island using diatom and geochemical proxies and compare it with paleoclimate records and recent instrumental data. During cool periods, such as the Little Ice Age (c. 1400–1870 CE), the winds weakened and shifted towards the equator, and during warm periods they intensified and migrated poleward. These results imply that changes in the latitudinal temperature gradient drive century-scale SHW migrations, and that intensification of impacts can be anticipated in the coming century

Rapid Lacustrine Response to Recent High Arctic Warming: A Diatom Record from Sawtooth Lake, Ellesmere Island, Nunavut

Diatoms from Sawtooth Lake (79 20\u27N, 81 51\u27W) on the Fosheim Peninsula in Central Ellesmere Island, Canada were analyzed to assess the temporal extent and magnitude of climatic change in the High Arctic during the late Holocene. Diatom results from the sediment cores show an absence of diatoms throughout the last ;2.5 ka (4.6 m) until the 1920s. However, ca. 1926 (5.3-cm depth), a rapid colonization of diatoms in the lake occurred. Within the uppermost section of the core (;1920 to ;1997), the diatom flora shift from a small Fragilaria-dominated assemblage to a more diverse assemblage that is dominated by large planktonic taxa (e.g., Cyclotella bodanica) and large raphid benthic species. The postglacial nature of this assemblage suggests a decrease in ice cover and a concomitant increase in light and nutrient availability for diatom growth over the last ;75 yr. Of particular significance is this absence of diatoms prior to the ;1920s, which indicates that environmental conditions of the last ;75 yr are unlike any of the previous ;2500 yr

The influence of temperature, moisture, and eolian activity on Holocene lake development in West Greenland

Holocene paleolimnological records (diatoms, organic content, spectrally inferred sediment chlorophyll-a) from three West Greenland lakes (~67°N) situated along a transect from the outer coast to a nunatak at the periphery of the Greenland Ice Sheet are used to explore the nature of regional postglacial lake development and its relationship to Holocene climate evolution. The lakes were deglaciated asynchronously by approximately 4 ka (earliest on the coast) and thus their sediment records document different starting points of Holocene ontogeny, both temporally and paleoclimatically. Despite similar time-transgressive characteristics of the diatom stratigraphies, overarching climatic factors, principally effective moisture, and eolian inputs, govern individual lake development. The transition to Neoglaciation between 5.6 and 4 ka BP marks a shift toward a cooler, moister, windier climate from the aridity and higher temperatures of the mid-Holocene (8–6 ka BP). A shift toward increased aridity, windiness, and eolian activity is documented in the interior lakes over the last 500 years. These lake records demonstrate the sensitivity of freshwater lakes in arid regions to changes in effective moisture and highlight the role of wind and eolian activity in Arctic lake environments

Lake Sediments as an Archive of Land use and Environmental Change in the Eastern Settlement, Southwestern Greenland

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Les sédiments lacustres, mémoire du climat et des activités humaines

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Diatom stratigraphy from Lone Spruce Pond.

<p>The figure shows the relative frequency of key diatom taxa, the first and second principal components (PC1 and PC2), the rate of change in the diatom community, and the concentration of diatoms in the sediments.</p

Biogeochemical evidence for hydrologic change during the Holocene in a lake sediment record from southeast Greenland

Holocene paleoclimate records from Greenland help us understand the response of the Greenland Ice Sheet and regional oceanic and atmospheric circulation systems to natural climate variability in order to place recent changes in a longer-term perspective. Here biogeochemical analysis of a lake sediment core from southeast Greenland is used to define changes in moisture balance and runoff during the Holocene in a catchment near the margin of the Greenland Ice Sheet. A 1.6 m sediment core that spans the last 8.8 ka was recovered from Flower Valley Lake on Ammassalik Island. Magnetic susceptibility, diatoms, bulk biogeochemical properties (TOC, C/N, δ13Corg), and lipid biomarkers (n-alkanes; C16–C31) reveal changes in clastic sedimentation and the relative input of terrestrial- and aquatic-derived organic matter. Hydrogen isotope values (δD) of mid- (n-C25) and long-chain (n- C29, n-C31) n-alkanes allow reconstruction of δD of precipitation and summertime evaporation of lake water. Following a period of early lake ontogeny and landscape stabilization after deglaciation from 8.4 to 7.0 ka, the mid Holocene, 8.4–4.1 ka, is characterized by greater evaporative enrichment of the lake water as indicated by δD records. After 4.1 ka, there is a decrease in evaporative enrichment of the lake water. There is also an abrupt transition to more variable sedimentation marked by sharp increases in magnetic susceptibility, C/N, δ13Corg, and the concentration of long-chain n-alkanes, showing periodic delivery of terrestrial organic matter and clastic sediment to the lake. Higher insolation during the mid Holocene resulted in a warmer and drier climate with longer ice-free periods in the summer and enhanced evaporation of lake water. The reduction in insolation and colder temperatures during the late Holocene caused a reduction in evaporation of lake water over the last 4.1 ka and was accompanied by periodic increases in surface runoff, which correspond with intervals of cold Greenland Ice Sheet surface temperatures

A multiproxy evaluation of Holocene environmental change from lake Igaliku, South Greenland

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Retro-observation des interactions hommes-milieux et de leurs conséquences sur l'environnement : le cas de l'agriculture au Groenland.

Quel intérêt pourrait présenter l'étude de l'impact humain sur l'environnement quand on sait que le Groenland fut tardivement peuplé (vers 2500 av. J.-C) par des populations de chasseurs-cueilleurs originaires d'Amérique du Nord ? Des agriculteurs se sont pourtant aventurés dans ces contrées a priori peu hospitalières, pendant les quelques siècles de l'optimum climatique médiéval, puis plus récemment, depuis le début du XXe siècle. L'aventure viking dans le sud du Groenland (qui débute avec Erik le Rouge en 985 et se termine vers 1450) constitue un modèle de référence particulièrement adapté pour l'étude des relations entre une communauté humaine et son environnement, de la conquête à l'abandon. À l'orée du XXe siècle, l'agriculture, pratiquée cette fois par les populations autochtones, est réintroduite sous la forme de l'élevage du mouton. Ce schéma de développement de pratiques agropastorales en deux phases chronologiquement distinctes apparaît alors comme original. Le schéma de la colonisation du Groenland par les agriculteurs est contraint par le climat et se limite à l'élevage. Le scénario groenlandais apparaît alors comme particulièrement bien adapté à un aller-retour entre les deux phases de peuplements. C'est cette " rétro-observation ", particulièrement bien documentée, qui fait l'intérêt du suivi de l'histoire de l'agriculture du Groenland