The use of Dynamic Global Vegetation Models (DGVMs) in paleo-vegetation studies is a practical new approach in paleo-ecology as it allows for process-based investigations within a flexible framework. The goal of this study is to evaluate the applicability of Lund Potsdam Jena (LPJ) – DGVM in a paleo-study of Cretaceous angiosperm spread, while testing several pre-existing theories regarding the spread through model experimentation. I assessed the independent and interactive role of climate variables (temperature, precipitation, atmospheric CO2 concentration, and seasonality), latitudinal light regime, soil structure, and plant characteristics (tree versus grass, and deciduousness) in influencing angiosperm expansion by simulating the response of Cretaceous land cover to changes in each factor. I found that temperature and light were the most influential variables in determining angiosperm success, while plant structure and deciduousness may carry implications for early angiosperm establishment and community competition dynamics. LPJ showed great potential for refinement and effective future use in paleo-applications.

The use of Dynamic Global Vegetation Models (DGVMs) in paleo-vegetation studies is a practical new approach in paleo-ecology as it allows for process-based investigations within a flexible framework. The goal of this study is to evaluate the applicability of Lund Potsdam Jena (LPJ) – DGVM in a paleo-study of Cretaceous angiosperm spread, while testing several pre-existing theories regarding the spread through model experimentation. I assessed the independent and interactive role of climate variables (temperature, precipitation, atmospheric CO2 concentration, and seasonality), latitudinal light regime, soil structure, and plant characteristics (tree versus grass, and deciduousness) in influencing angiosperm expansion by simulating the response of Cretaceous land cover to changes in each factor. I found that temperature and light were the most influential variables in determining angiosperm success, while plant structure and deciduousness may carry implications for early angiosperm establishment and community competition dynamics. LPJ showed great potential for refinement and effective future use in paleo-applications.

During the Late Pliocene, between 3.3 Ma and 2.6 Ma, tectonic events changed ocean basin interactions against a background of shifting orbital forcing mechanisms and a global cooling trend. A climate system that had been locked in a stable, warm state gradually transformed into one typified by the high-amplitude glacial–interglacial fluctuations characteristic of the later Quaternary. The onset of Northern Hemisphere glaciations in the Late Pliocene marks an important step in this transition, due to the role of feedback mechanisms including ice albedo. A crucial factor in this Northern Hemisphere ice sheet expansion is the North Atlantic surface ocean circulation. To evaluate how they are linked, a ca. 200-kyr time slab spanning 2782-2520 ka (Late Pliocene–Early Pleistocene) was analyzed at millennial scale resolution from eastern North Atlantic Deep Sea Drilling Project (DSDP) Site 610 and Integrated Ocean Drilling Program (IODP) Site U1313. The causes of the Plio-Pleistocene climatic turnover are compared to that of the well-documented Marine Isotope Stage (MIS) M2 occurring in the Late Pliocene (3.3 Ma). MIS M2, a severe glacial event seen as a precursor to later Quaternary-style glaciations, was investigated from western North Atlantic DSDP Site 603. Utilizing a same-sample methodology, two paleoceanographic proxies were used: (1) dinocyst assemblages, and (2) foraminiferal geochemistry (δ18O and Mg/Ca). Dinocysts are proven tracers of sea-surface temperature (SST), salinity, nutrient supply, and sea ice cover, and are analyzed here to characterize the overlying water masses at the studied sites. Strong dinocyst assemblage fluctuations attest to variations in the influence of the North Atlantic Current (NAC). Using Mg/Ca ratios for the planktonic foraminifer Globigerina bulloides to determine absolute SSTs allows salinity changes to be reconstructed when combined with stable oxygen isotopes. This study shows a persistent Gulf Stream–NAC in the western North Atlantic during MIS M2, favoring a southern shift of the NAC over a shutdown of the thermohaline circulation. At the newly established Plio-Pleistocene boundary, a profound turnover in dinoflagellate cyst assemblages reveals a shift in ocean mode during MIS 104 (2.6 Ma). Three distinct dinocyst ecozones demonstrate this fundamental reorganization of the North Atlantic circulation.

Ce projet porte sur la reconstitution paléo-écologique d'un environnement forestier fossile retrouvé sur un plateau au sud-ouest de l'île Bylot. Il a comme objectifs 1) de préciser la chrono-stratigraphie du site; 2) d’établir une liste et une succession des différents taxons polliniques retrouvés dans les différentes unités stratigraphiques du site; 3) d’estimer leur âge et 4) d’en inférer des conditions climatiques (température et précipitations). Plusieurs coupes stratigraphiques ont été excavées puis échantillonnées afin de réaliser des analyses stratigraphiques, paléomagnétiques et polliniques. Un GPS différentiel fut également utilisé afin de caractériser à petite et grande échelle les unités stratigraphiques associées aux unités organiques fossiles. Les résultats des analyses granulométriques indiquent la séquence de dépôt suivante au sein d’une dépression dans la roche en place (schiste tertiaire) : 1) un diamicton glaciaire local ; 2) un sédiment limoneux d’origine glacio-lacustre ; 3) une unité organique tourbeuse; 4) une unité de type alluvial ; 5) un sédiment fluvio-glaciaire et 6) un diamicton glaciaire d’origine allochtone. Les analyses polliniques suggèrent une végétation similaire à celle présente près de la limite des arbres actuelle, environ 2000 km plus au sud. Les conditions climatiques plus humides et plus chaudes permettaient notamment la croissance du pin (Pinus type strobus et banksiana), de l’épinette (Picea cf. mariana), de l’aulne (type crispa et incana) et du mélèze (Larix, indifférencié). Enfin, les études paléomagnétiques et la présence d’espèces éteintes suggèrent un âge pour les dépôts organiques fossiles situé entre 2,14 et 2,15 Ma ou entre 2,581 et 3,040 Ma. / The project focuses on the paleo-ecological reconstitution of a fossil forest environment found on a plateau on the southwest part of Bylot Island, in the Canadian Arctic. The objectives were 1) to describe the chrono-stratigraphy of the site; 2) to establish a list and the succession of different pollen taxa found in organic and inorganic fossil units of the site; 3) to estimate their age and 4) to infer the past climatic conditions of the site. Several stratigraphic cuts were excavated and sampled for stratigraphic, paleomagnetic and pollen analyses. Also, a differential GPS was used to characterise the stratigraphic units associated with the organic fossil units at a small and large scale. Results of the granulometric analysis suggest the following deposition sequence starting from a depression in the bedrock (tertiary shale): 1) a glacial diamicton with local clasts; 2) a silty sediment of glacio-lacustrine origin; 3) an organic peat unit; 4) an alluvial type unit; 5) a fluvio-glacial sediment and 6) a glacial diamicton of allochtone origin. The pollen analyses suggest vegetation similar to that of the current tree-line limit, situated about 2000 km south of the site. The climatic conditions were warmer and more humid, allowing the local growth of pines (Pinus type strobus and banksiana), spruce (Picea cf. mariana), alder (Alnus type crispa and incana) and larch (Larix, undifferentiated). Paleomagnetic analyses and the presence of extinct species finally suggest an age for the organic fossil deposits of between 2,14 and 2,15 My or most likely between 2,581 and 3,040 My.

Ce projet porte sur la reconstitution paléo-écologique d'un environnement forestier fossile retrouvé sur un plateau au sud-ouest de l'île Bylot. Il a comme objectifs 1) de préciser la chrono-stratigraphie du site; 2) d’établir une liste et une succession des différents taxons polliniques retrouvés dans les différentes unités stratigraphiques du site; 3) d’estimer leur âge et 4) d’en inférer des conditions climatiques (température et précipitations). Plusieurs coupes stratigraphiques ont été excavées puis échantillonnées afin de réaliser des analyses stratigraphiques, paléomagnétiques et polliniques. Un GPS différentiel fut également utilisé afin de caractériser à petite et grande échelle les unités stratigraphiques associées aux unités organiques fossiles. Les résultats des analyses granulométriques indiquent la séquence de dépôt suivante au sein d’une dépression dans la roche en place (schiste tertiaire) : 1) un diamicton glaciaire local ; 2) un sédiment limoneux d’origine glacio-lacustre ; 3) une unité organique tourbeuse; 4) une unité de type alluvial ; 5) un sédiment fluvio-glaciaire et 6) un diamicton glaciaire d’origine allochtone. Les analyses polliniques suggèrent une végétation similaire à celle présente près de la limite des arbres actuelle, environ 2000 km plus au sud. Les conditions climatiques plus humides et plus chaudes permettaient notamment la croissance du pin (Pinus type strobus et banksiana), de l’épinette (Picea cf. mariana), de l’aulne (type crispa et incana) et du mélèze (Larix, indifférencié). Enfin, les études paléomagnétiques et la présence d’espèces éteintes suggèrent un âge pour les dépôts organiques fossiles situé entre 2,14 et 2,15 Ma ou entre 2,581 et 3,040 Ma. / The project focuses on the paleo-ecological reconstitution of a fossil forest environment found on a plateau on the southwest part of Bylot Island, in the Canadian Arctic. The objectives were 1) to describe the chrono-stratigraphy of the site; 2) to establish a list and the succession of different pollen taxa found in organic and inorganic fossil units of the site; 3) to estimate their age and 4) to infer the past climatic conditions of the site. Several stratigraphic cuts were excavated and sampled for stratigraphic, paleomagnetic and pollen analyses. Also, a differential GPS was used to characterise the stratigraphic units associated with the organic fossil units at a small and large scale. Results of the granulometric analysis suggest the following deposition sequence starting from a depression in the bedrock (tertiary shale): 1) a glacial diamicton with local clasts; 2) a silty sediment of glacio-lacustrine origin; 3) an organic peat unit; 4) an alluvial type unit; 5) a fluvio-glacial sediment and 6) a glacial diamicton of allochtone origin. The pollen analyses suggest vegetation similar to that of the current tree-line limit, situated about 2000 km south of the site. The climatic conditions were warmer and more humid, allowing the local growth of pines (Pinus type strobus and banksiana), spruce (Picea cf. mariana), alder (Alnus type crispa and incana) and larch (Larix, undifferentiated). Paleomagnetic analyses and the presence of extinct species finally suggest an age for the organic fossil deposits of between 2,14 and 2,15 My or most likely between 2,581 and 3,040 My.

During the Late Pliocene, between 3.3 Ma and 2.6 Ma, tectonic events changed ocean basin interactions against a background of shifting orbital forcing mechanisms and a global cooling trend. A climate system that had been locked in a stable, warm state gradually transformed into one typified by the high-amplitude glacial–interglacial fluctuations characteristic of the later Quaternary. The onset of Northern Hemisphere glaciations in the Late Pliocene marks an important step in this transition, due to the role of feedback mechanisms including ice albedo. A crucial factor in this Northern Hemisphere ice sheet expansion is the North Atlantic surface ocean circulation. To evaluate how they are linked, a ca. 200-kyr time slab spanning 2782-2520 ka (Late Pliocene–Early Pleistocene) was analyzed at millennial scale resolution from eastern North Atlantic Deep Sea Drilling Project (DSDP) Site 610 and Integrated Ocean Drilling Program (IODP) Site U1313. The causes of the Plio-Pleistocene climatic turnover are compared to that of the well-documented Marine Isotope Stage (MIS) M2 occurring in the Late Pliocene (3.3 Ma). MIS M2, a severe glacial event seen as a precursor to later Quaternary-style glaciations, was investigated from western North Atlantic DSDP Site 603. Utilizing a same-sample methodology, two paleoceanographic proxies were used: (1) dinocyst assemblages, and (2) foraminiferal geochemistry (δ18O and Mg/Ca). Dinocysts are proven tracers of sea-surface temperature (SST), salinity, nutrient supply, and sea ice cover, and are analyzed here to characterize the overlying water masses at the studied sites. Strong dinocyst assemblage fluctuations attest to variations in the influence of the North Atlantic Current (NAC). Using Mg/Ca ratios for the planktonic foraminifer Globigerina bulloides to determine absolute SSTs allows salinity changes to be reconstructed when combined with stable oxygen isotopes. This study shows a persistent Gulf Stream–NAC in the western North Atlantic during MIS M2, favoring a southern shift of the NAC over a shutdown of the thermohaline circulation. At the newly established Plio-Pleistocene boundary, a profound turnover in dinoflagellate cyst assemblages reveals a shift in ocean mode during MIS 104 (2.6 Ma). Three distinct dinocyst ecozones demonstrate this fundamental reorganization of the North Atlantic circulation.