LA EVOLUCIÓN DEL LENGUAJE

Jet Stream The simulation results confirm the hypothesis on the from the present differing

LGM jet stream paths. Instead of crossing the British Isles and southern Scandinavia, they ran along the Nordic Seas, between the EIS and the Alps, or over the western Mediterranean. The re- sults confirm the hypothesis on the regionally faster (10 m/s) and narrower LGM jet stream. These LGM jet stream characteristic were most likely caused by the Northern Hemisphere ice sheet ele- vations.

Pressure The LGM NAO and in consequence most likely the westerlies were stronger. This was

confirmed by the simulations that resulted in a larger LGM region affected by the Azores High. Additionally to the present Azores and GIS High, the LIS and the EIS High shaped the LGM cli- mate. Both highs likely caused combined with the ice sheet topographies proglacial northeasters and easterlies. In contrast to the present, low pressure systems prevailed over the subpolar gyre between Newfoundland and Iceland.

Temperature The average LGM temperatures ranged between −45 and 30∘C in the domain, compared with between −35 and 30∘C during the PI. Sea ice likely prevailed in Baffin Bay, on the Labrador, and the Nordic Seas. Permafrost characterized the unglaciated land east of the EIS. Northward heat transport from the low latitudes to the Norwegian Sea by the North Atlantic Cur- rent was likely. The GCM results indicate slightly more warmth than the GLAMAP reconstruc- tion over areas, where heat was transported northward in the oceans. Near the Mauritian coast, the temperature ranges simulated by the GCM (between 15 and 20∘C) and reconstructed from sediment cores (between 14 and 18∘C) agree well. The simulated temperatures are confirmed by Mg/Ca SST reconstructions, foraminifers, and alkenone data for different locations in and near Europe.

Apart from over the ice sheets, the strongest temperature decrease occurred over the Eurasian plains northeast of the Alps (between 8 and 26∘C). In the Mediterranean area, temperatures were between 2 and 6∘C lower and their differences were spatially heterogeneously distributed. For the unglaciated parts of central and eastern Europe, such as western Russia, Ukraine, the Urals, Geor- gia, and Turkey, botanic (pollen) temperature reconstructions validate the simulation-based results. Also, simulated temperature reductions in southern France, Italy, and Greece were confirmed by proxy data. For Iberia, the simulated temperature decrease is lower than the pollen-indicated. This possibly indicates too warm SST in the eastern North Atlantic.

Precipitation The LGM to present climate precipitation similarity indicates a low sensitivity

of precipitation to the glacial conditions. Known present precipitation interaction with other Earth system components, such as precipitation generated during topographic lifting, also shaped the LGM precipitation distribution. This applies particularly to the LGM ice sheet margins; for example, off the east coast of the GIS tip, some of the highest EurAt Domain precipitation rates occurred. Vast LGM sea ice covers hindered and suppressed atmospheric moisture uptake; thereby reducing the fresh water transport to subpolar regions, such as Baffin Bay. Less precipitation over the proglacial central European areas and the North Sea Basin favored their aeolian erosion. This applied also to the unglaciated Eurasian plains east of the EIS, north of 55°N. The agreement between simulation- and botany-based precipitation reconstructions evidences the quality of the simulation-based LGM reconstruction.

5 Atmospheric Variability beyond Climatologies

5.1 Introduction

To reveal the hidden dynamics and to recognize the patterns and interaction of the atmosphere, it is necessary to analyze the atmosphere using appropriate, objective, and reproducible methods. To this aim, the spatiotemporal distributions of the sea level pressure, the near-surface temperatures, and the precipitation rates have been analyzed for the recent climate for distinct regions using combined empirical orthogonal functions126,199,213 (CEOFs). CEOFs are also known as combined principal components126, as joint, as mixed-field, or as extended empirical orthogonal functions. The CEOF analysis extends the empirical orthogonal function (EOF) analysis by combining distinct variables into a single numerical array.

EOFs, also known as eigenvectors or as principal components, result from the linear transfor- mation of multidimensional data from one to another reference system. This transformation aims at finding a different set of algebraic basis vectors under the constraint that each vector represents the maximum possible variance that is not yet represented by any of the precedent basis vectors. In some cases, the first few resulting basis vectors are sufficient to represent most of the source data variability. For large multidimensional meteorological fields, the EOF analysis can reveal me- teorological patterns that would otherwise remain invisible. As the EOF decomposition is a purely mathematical tool, any physical meaning of the resulting EOFs is not guaranteed per se. The re- quirement of mutually independent EOFs and maximal variability represented by all subsequent EOF imposes a non-physical restriction on the possible EOF outcomes214.

EOFs have been applied to research numerous meteorological and geoscientifical questions. Their application215–218 to the recent and present-day spatiotemporal distributions of the North Atlantic surface pressure revealed the NAO (North Atlantic Oscillation) as the most significant modern climatological pressure pattern over the North Atlantic. They have also been applied to the sea surface temperature (SST) distribution of the Pacific219, which contributed to reveal the PDO (Pacific Decadal Oscillation), and the ENSO (El Niño Southern Oscillation)220.

The study of the peer-reviewed publications that rely on statistics and multidimensional climate data to analyze the atmospheric dynamics revealed that CEOF results for the EurAt Domain are missing for the LGM. To bridge this gap, the subclimatological dynamics of the LGM and of the recent climate are analyzed and compared in this dissertation by calculating their CEOFs. The CEOFs offer the potential to reveal subclimatological patterns and dynamic relationships between the distinct variables for the LGM and for the recent climate that would otherwise be ignored and remain unknown. The results reveal potential cause-effect mechanisms, dependencies, and feedback between the pressure, temperature, and precipitation dynamics.

Independent climate models208, reconstructions for the recent climate based on measurements199, and LGM climate proxies66 serve to evaluate the obtained CEOF patterns.

5.2 Hypotheses

(1) The cumulative explained variance of the leading CEOFs for the LGM is larger than that for

the PI raising the question whether the atmospheric dynamics of the LGM were characterized by fewer degrees of freedom.

For the Last Glacial Maximum:

(2) Frequent NAO minus phases potentially caused above average temperatures over the

Labrador Sea and the subpolar gyre as well as above average precipitation over Iberia, the northern Mediterranean, the Azores, the Labrador Sea, and the southwestern GIS. Simultaneously, temperatures and precipitation were below average over the EIS coast.

(3) Frequent subclimatological pressure variability created anti-phased pressure dynamics over

the EIS with regard to Baffin Bay, the Labrador Sea, and the Sahara that likely correlated with above average temperatures and precipitation over the eastern GIS and its adjacent areas. Synchronously, below average precipitation likely prevailed over Europe and below average temperatures prevailed over western Asia and the northern Mediterranean.

(4) Frequent anti-phased pressure variability dynamics distinguished France, Spain, and Bermuda

from the Caspian Sea and the low latitude eastern Atlantic; likely correlating with above average temperatures over western Iberia and precipitation over the Azores, the subpolar gyre, western Ice- land, the EIS coast, the Black Sea, Turkey, and the southernmost Mediterranean. Simultaneously, below average temperatures prevailed over central eastern Europe, the Mediterranean, Tunisia, Libya, and the Hoggar Mountains while below average precipitation prevailed over France, west- ern Iberia, Italy, the Bay of Biscay, the southeastern EIS, and the Maghreb coasts.

(5) Compared to the PI, the subclimatological LGM variability was larger over Baffin Bay, Iceland,

southwestern Scandinavia, eastern Germany, and most parts of the Mediterranean. It was similar over central Asia, the Middle East, and northern Africa including the bordering Atlantic. It was smaller over Scotland, the Urals, and southeastern Finland.