Vegetation shifts, human impact and peat bog development in Bassa Nera pond (Central Pyrenees) during the last millennium

High-mountain lakes are suitable ecosystems for studying local environmental shifts driven by large-scale climate changes, with potential applications to predict future scenarios. The precise features in the response of species assemblages are not fully understood, and human pressure may often hide climatic signals. To investigate the origin and impact of past environmental changes in high-mountain ecosystems and apply this palaeoecological knowledge to anticipate future changes, we performed a multi-proxy study of a sediment core from Bassa Nera, a pond located close to montane–subalpine ecotone in the southern central Pyrenees. Combining pollen and diatom analysis at multidecadal resolution, we inferred vegetation shifts and peat bog development during the past millennium. We introduced a montane pollen ratio as a new palaeoecological indicator of altitudinal shifts in vegetation. Our results emphasize the sensitivity of the montane ratio to detect upward migrations of deciduous forest and the presence of the montane belt close to Bassa Nera pond during the Medieval Climate Anomaly. Changes in aquatic taxa allowed to date the onset of the surrounding peat bog which appeared and infilled the coring site around AD 1565. Overall, our results suggest a low-intensity human pressure and changes in management of natural resources during the last millennium, where farming was the main activity from the Medieval Climate Anomaly until AD 1500. Afterwards, people turned to highland livestock raising coinciding with the ‘Little Ice Age’.

Download Full-text

Absence of a Medieval Climate Anomaly, Little Ice Age and twentieth century warming in Skarvsnes, Lützow Holm Bay, East Antarctica

Antarctic Science ◽

10.1017/s0954102014000029 ◽

2014 ◽

Vol 26 (5) ◽

pp. 585-598 ◽

Cited By ~ 11

Author(s):

Ines Tavernier ◽

Elie Verleyen ◽

Dominic A. Hodgson ◽

Katrien Heirman ◽

Stephen J. Roberts ◽

...

Keyword(s):

Twentieth Century ◽

Southern Hemisphere ◽

Northern Hemisphere ◽

Little Ice Age ◽

Environmental Changes ◽

Open Water ◽

Ice Age ◽

Medieval Climate Anomaly ◽

Climate Anomaly ◽

The Past

AbstractPalaeoclimate changes, such as the Medieval Climate Anomaly and the Little Ice Age, are well-defined in the Northern Hemisphere during the past 2000 years. In contrast, these anomalies appear to be either absent, or less well-defined, in high-latitude regions of the Southern Hemisphere. Here, we inferred environmental changes during the past two millennia from proxies in a sediment core from Mago Ike, an East Antarctic lake in Skarvsnes (Lützow Holm Bay). Variations in lake primary production were inferred from fossil pigments, sedimentological and geochemical proxies and combined with absolute diatom counts to infer past diatom productivity and community changes. Three distinct stratigraphic zones were recognized, resulting from a shift from marine to lacustrine conditions with a clear transition zone in between. The presence of open-water marine diatoms indicates a coastal zone seasonally free of sea ice between c. 2120–1500 cal yr bp. Subsequently, the lake became isolated from the ocean due to isostatic uplift. Freshwater conditions were established from c. 1120 cal yr bp onwards after which the proxies are considered highly sensitive to temperature changes. There is no evidence for a Medieval Climate Anomaly, Little Ice Age or twentieth century warming in our lake sediment record suggesting that studies that have imposed Northern Hemisphere climate anomalies onto Southern Hemisphere palaeoclimate records should be treated with caution.

Download Full-text

Interannual climate variability change during the Medieval Climate Anomaly and Little Ice Age in PMIP3 last millennium simulations

Advances in Atmospheric Sciences ◽

10.1007/s00376-016-6075-1 ◽

2017 ◽

Vol 34 (4) ◽

pp. 497-508 ◽

Cited By ~ 6

Author(s):

Kaiqing Yang ◽

Dabang Jiang

Keyword(s):

Climate Variability ◽

Little Ice Age ◽

Ice Age ◽

Last Millennium ◽

Medieval Climate Anomaly ◽

Climate Anomaly ◽

Interannual Climate Variability

Download Full-text

The Medieval Climate Anomaly and the Little Ice Age in the eastern Ecuadorian Andes

Climate of the Past ◽

10.5194/cp-9-307-2013 ◽

2013 ◽

Vol 9 (1) ◽

pp. 307-321 ◽

Cited By ~ 35

Author(s):

M.-P. Ledru ◽

V. Jomelli ◽

P. Samaniego ◽

M. Vuille ◽

S. Hidalgo ◽

...

Keyword(s):

Little Ice Age ◽

Water Storage ◽

Ice Age ◽

Last Millennium ◽

Medieval Climate Anomaly ◽

Climate Anomaly ◽

Abrupt Decrease ◽

Enso Variability ◽

P Index ◽

Poaceae Pollen

Abstract. To better characterize the climate variability of the last millennium in the high Andes, we analyzed the pollen content of a 1150-yr-old sediment core collected in a bog located at 3800 m a.s.l. in the páramo in the eastern Cordillera in Ecuador. An upslope convective index based on the ratio between cloud transported pollen from the Andean forest to the bog (T) and Poaceae pollen frequencies, related to the edaphic moisture of the páramo (P), was defined. This index was used to distinguish changes in the atmospheric moisture from the soil moisture content of the páramo and their associated patterns of interdecadal El Niño–Southern Oscillation (ENSO) variability and South American summer monsoon (SASM) activity. Results show that between 850 and 1250 AD, the Medieval Climate Anomaly interval was warm and moist with a high transported pollen/Poaceae pollen (T/P) index linked to high ENSO variability and weak SASM activity. Between 1250 and 1550 AD, a dry climate prevailed, characterized by an abrupt decrease in the T/P index and therefore no upslope cloud convection, related to lower ENSO variability and with significant impact on the floristic composition of the páramo. During the Little Ice Age, two phases were observed: first, a wet phase between 1550 and 1750 AD linked to low ENSO variability in the Pacific and warm south equatorial Atlantic sea surface temperatures (SSTs) favored the return of a wet páramo, and then a cold and dry phase between 1750 and 1800 AD associated with low ENSO variability and weak SASM activity resulted in drying of the páramo. The current warm period marks the beginning of a climate characterized by high convective activity – the highest in the last millennium – and weaker SASM activity modifying the water storage of the páramo. Our results show that the páramo is progressively losing its capacity for water storage and that the interdecadal variability of both tropical Pacific and Atlantic SSTs matter for Andean climate patterns, although many teleconnection mechanisms are still poorly understood.

Download Full-text

A multi-proxy perspective on millennium-long climate variability in the Southern Pyrenees

Climate of the Past ◽

10.5194/cp-8-683-2012 ◽

2012 ◽

Vol 8 (2) ◽

pp. 683-700 ◽

Cited By ~ 53

Author(s):

M. Morellón ◽

A. Pérez-Sanz ◽

J. P. Corella ◽

U. Büntgen ◽

J. Catalán ◽

...

Keyword(s):

Environmental Changes ◽

Ice Age ◽

Deciduous Tree ◽

Last Millennium ◽

Medieval Climate Anomaly ◽

Cold Temperatures ◽

Significant Development ◽

Arid Conditions ◽

Rainfall Variations ◽

Second Period

Abstract. This paper reviews multi-proxy paleoclimatic reconstructions with robust age-control derived from lacustrine, dendrochronological and geomorphological records and characterizes the main environmental changes that occurred in the Southern Pyrenees during the last millennium. Warmer and relatively arid conditions prevailed during the Medieval Climate Anomaly (MCA, ca. 900–1300 AD), with a significant development of xerophytes and Mediterranean vegetation and limited deciduous tree formations (mesophytes). The Little Ice Age (LIA, 1300–1800 AD) was generally colder and moister, with an expansion of deciduous taxa and cold-adapted montane conifers. Two major phases occurred within this period: (i) a transition MCA–LIA, characterized by fluctuating, moist conditions and relatively cold temperatures (ca. 1300 and 1600 AD); and (ii) a second period, characterized by the coldest and most humid conditions, coinciding with maximum (recent) glacier advances (ca. 1600–1800 AD). Glaciers retreated after the LIA when warmer and more arid conditions dominated, interrupted by a short-living cooling episode during the late 19th to early 20th centuries. Some records suggest a response to solar activity with colder and slightly moister conditions during solar minima. Centennial-scale hydrological fluctuations are in phase with reconstructions of NAO variability, which appears to be one of the main climate mechanisms influencing rainfall variations in the region during the last millennium.

Download Full-text

A multi-proxy perspective on millennium-long climate variability in the Southern Pyrenees

Climate of the Past Discussions ◽

10.5194/cpd-7-3049-2011 ◽

2011 ◽

Vol 7 (5) ◽

pp. 3049-3089 ◽

Cited By ~ 2

Author(s):

M. Morellón ◽

A. Pérez-Sanz ◽

J. P. Corella ◽

U. Büntgen ◽

J. Catalán ◽

...

Keyword(s):

Little Ice Age ◽

Environmental Changes ◽

Ice Age ◽

Deciduous Tree ◽

Last Millennium ◽

Medieval Climate Anomaly ◽

Cold Temperatures ◽

Significant Development ◽

Arid Conditions ◽

Second Period

Abstract. A review of selected, well-dated, multiproxy paleoclimatic records (lacustrine, dendrochronological, geomorphological) characterizes the main environmental changes occurred in the Southern Pyrenees during the last millennium. Warmer and relatively arid conditions prevailed during the Medieval Climate Anomaly (MCA, <1300 AD), with a significant development of xerophytes and Mediterranean vegetation and limited deciduous tree formations (mesophytes). The Little Ice Age (LIA, 1300–1800 AD) was generally colder and moister, with an expansion of deciduous taxa and cold-adapted mountainous conifers. Two major phases occurred within this period: (i) a transition MCA-LIA, characterized by fluctuating, moist conditions and relatively cold temperatures (ca. 1300 and 1600 AD); – (ii) a second period, characterized by coldest conditions and higher humidity, coinciding with maximum (recent) glacier advances (ca. 1600–1850 AD). After the LIA a warming and more arid phase started coinciding with glacier retreat, and interrupted by a short-living cooling episode during the late 19th to early 20th centuries. Some records suggest a response to solar activity with colder and slightly moister conditions during solar minima. Centennial-scale hydrological fluctuations are in phase with reconstructions of NAO variability, which appears to be the main forcing for humidity in the region during the last millennium.

Download Full-text

Regional Influences of Natural External Forcings on the Transition from the Medieval Climate Anomaly to the Little Ice Age

Journal of Climate ◽

10.1175/jcli-d-15-0599.1 ◽

2016 ◽

Vol 29 (16) ◽

pp. 5779-5800 ◽

Cited By ~ 6

Author(s):

Heather J. Andres ◽

W. R. Peltier

Keyword(s):

Sea Ice ◽

Spectral Resolution ◽

Little Ice Age ◽

Ice Age ◽

Last Millennium ◽

Medieval Climate Anomaly ◽

Volcanic Emissions ◽

Climate Anomaly ◽

Model Simulations ◽

Climate Forcings

Abstract Reconstructions of historical climate changes indicate that surface air temperatures decreased over the preindustrial last millennium. Conflicting explanations have been proposed for the cause of the transition from the Medieval Climate Anomaly (MCA) in the early part of the last millennium to the Little Ice Age (LIA) near its end. The possible causes include volcanic emissions, total solar irradiance (TSI) variations, greenhouse gas concentration fluctuations, and orbital forcing variations. In the present paper, it is demonstrated that all of these climate forcings contribute significantly to simulated surface air temperature (SAT) and sea ice concentration changes over this period. On the other hand, simulated ocean heat content appears to respond significantly only to volcanic and TSI variations. In model simulations at T85 spectral resolution, TSI reductions and volcanic emissions together generate significant increases in sea ice extent in the Barents Sea, which is found to be responsible for most of the temperature reductions over northwestern Europe. TSI appears less important to Arctic sea ice and SAT changes in simulations at T42 spectral resolution, which are weaker than at T85 resolution. Such resolution dependence is attributed to differences in background conditions in the responses to these external climate forcings. Nonlinearities in the forcing responses and sensitivities to background conditions challenge the assumption that sensitivity tests for given forcings can be run independently. Additionally, it is demonstrated that an ensemble of model simulations is required to isolate forcing responses even over a period as long as the last millennium.

Download Full-text

The Medieval Climate Anomaly and the Little Ice Age in the Eastern Ecuadorian Andes

Climate of the Past Discussions ◽

10.5194/cpd-8-4295-2012 ◽

2012 ◽

Vol 8 (5) ◽

pp. 4295-4332 ◽

Cited By ~ 1

Author(s):

M.-P. Ledru ◽

V. Jomelli ◽

P. Samaniego ◽

M. Vuille ◽

S. Hidalgo ◽

...

Keyword(s):

Little Ice Age ◽

Floristic Composition ◽

Ice Age ◽

Last Millennium ◽

Medieval Climate Anomaly ◽

Equatorial Atlantic ◽

Climate Anomaly ◽

Abrupt Decrease ◽

Enso Variability ◽

P Index

Abstract. To better characterize the climate variability of the last millennium in the high Andes, we analysed the pollen content of a 1100-yr-old sediment core collected in a bog located at 3800 m a.s.l. in the páramo in the Eastern Cordillera in Ecuador. An upslope convective index based on the ratio between cloud transported pollen from the andean forest to the bog (T) and Poaceae pollen frequencies, related to the edaphic moisture of the páramo (P), was defined to distinguish the atmospheric moisture from the soil moisture content of the páramo. Results showed that between 900 AD and 1230 AD, the Medieval Climate Anomaly interval was warm and moist with high T/P index linked to a high ENSO variability and a weak South American Summer Monsoon (SASM) activity. Between 1230 and 1650 AD, a dry climate prevailed characterized by an abrupt decrease in the T/P index related to lower ENSO variability with significant impact on the floristic composition of the páramo. During the Little Ice Age, two phases were observed, first a wet phase between 1650 and 1750 AD linked to low ENSO variability in the Pacific and warm south equatorial Atlantic SSTs favored the return of a wet páramo, and a cold and dry phase between 1750 and 1810 AD associated with low ENSO variability and weak SASM activity resulting in drying of the páramo. The Current Warm Period marks the beginning of a climate characterized by high convective activity, the highest in the last millennium, and weaker SASM activity modifying the water stock of the páramo. Our results show that the páramo is progressively loosing its capacity for water storage and that the variability of both tropical Pacific and Atlantic SSTs matters for Andean climate patterns although many teleconnection mechanisms are still poorly understood.

Download Full-text