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One of the prominent features in sediment sequences formed around the AllerOd-Younger Dryas transition (c. 12.9-12.8 ka bp) in North America is a dark layer of organic-rich material, i.e. the black mat. The black mat sequences in southeast Arizona contain a thin sandy basal layer corresponding to the lower Younger Dryas boundary. Trace element concentrations in the lower Younger Dryas boundary sediments, in the black mat, in the host sediments, and in charcoal from Western Europe and southeast Arizona were studied using LA-ICP-MS. The black mat samples and samples of the underlying host sediments display compositions similar to the average continental crust, while the sediments from the lower Younger Dryas boundary are enriched in rare earth elements, Ni, and Co whereas Ta, Nb, Zr, and Hf are depleted relative to the rare earth elements. Such a difference in compositions between the lower Younger Dryas boundary sediments and other sediments points to a short enigmatic event, which changed conditions of sedimentation just before the onset of the Younger Dryas cooling. The presence of products of biomass burning of still unknown origin is suggested on the basis of trace element features of sediments from the lower Younger Dryas boundary.

In this study, I use 1,163 Paleoindian bifaces from Mississippi to study human behavioral changes in response to the Younger Dryas climate event (12,900 – 11,700 cal yr BP). I use the “organization of technology” as a theoretical approach and a modified version of the marginal value theorem to track changes in Paleoindian lithic technology through time and compare those changes to regional paleoenvironmental data. I find a decrease in absolute point size, increase in rates of resharpening, and expansion of settlement organization and raw material preferences throughout the Younger Dryas. I argue that the organization of hunter gatherer technology abruptly and significantly changed in the shift from fluted to unfluted points during the middle Younger Dryas, and that those changes were coeval with rapid boreal-to-hardwood forest restructuring and fluctuating hunting returns. I conclude that the technological shifts that began during the middle Younger Dryas continued and intensified into the terminal Younger Dryas.

The objective of this study is to investigate the effect of Atlantic meridional overturning circulation (AMOC) changes on tropical coupled ocean-atmosphere system via oceanic and atmospheric processes. A suite of numerical simulations have been conducted and the results show that both oceanic and atmospheric circulation changes induced by AMOC changes can have a profound impact on tropical sea surface temperature (SST) and sea surface salinity (SSS) conditions, but their dominance varies in different parts of the tropical oceans. The oceanic process has a dominant control on SST and SSS response to AMOC changes in the South Tropical Atlantic, while the atmospheric teleconnection is mainly responsible for SST and SSS changes over the North Tropical Atlantic and Pacific Oceans during the period of reduced AMOC. The finding has significant implication for the interpretation of the paleotemperature reconstructions over the southern Caribbean and the western Tropical Atlantic regions during the Younger Dryas. It suggests that the strong spatial inhomogeneity of the SST change revealed by the proxy records in these regions may be attributed to the competing oceanic and atmospheric processes that dominate the SST response. Similar mechanisms may also explain the reconstructed paleo-salinity change in the tropical Atlantic, which shows a basin-wide increase in SSS during the Younger Dryas, according to recent paleo climate studies. Finally, we show that atmospheric teleconnection induced by the surface cooling of the North Atlantic and the North Pacific in response to a weakened AMOC, is a leading physical mechanism that dictates the behavior of El Nino/Southern Oscillation (ENSO) response to AMOC changes. However, depending on its origin, the atmospheric teleconnection can affect ENSO variability in different ways. The atmospheric process associated with the North Atlantic cooling tends to enhance El Nino occurrence with a deepened mean thermocline depth in the eastern Pacific, whereas the atmospheric process associated with the North Pacific cooling tends to produce more La Nina events with a reduced mean thermocline depth in the eastern Pacific. Preliminary analysis suggests that the change in ENSO characteristics is associated with the change in internal atmospheric variability caused by the surface cooling in the North Atlantic and North Pacific. Complex nature of the underlying dynamics concerning the effect of the AMOC on ENSO calls for further investigation into this problem.

This masters thesis investigates the environmental/climatic change that is thought to have brought about the economic shift and transition from Palaeolithic economic system of hunting gathering to Neolithic economic system of agriculture and domestication period around 11.000-10.000 years ago. This study uses the collected animal and plant data of the Natufian culture in the Levant region from the previous zooarchaeological and archaeobotanical literature anlyses. It shows a significant mathematical difference in the zooarchaeological assemblage measures between the Early and Late Natufian sites by calculating Economic value parameters of the Early and the Late Natufian sites, a comparison analysis was made in terms of percentage frequencies of animals site by site and between early-late periods. The result shows a significant animal food supply decrease and change-shift shown during the Younger Dryas climatic crisis times of the whole Late Natufian period sites total and early to late site by site individually, compared to whole Early Natufian period sites. It shows there is a possibility that some big-base camp Late Natufian occupation sites were better able to create coping mechanisms against food crisis/food shortage and more successfully than other Late Natufian sites during the climatic food crisis period. It shows supporting with the animal-plant data and changes in the human bones, burial practices, human teeth, diet changes and anthropological studies evidence, a big social-economic-cultural change and a huge food crisis was highly possible and humans highly possibly lived an economic crisis and an highly connected-related social-cultural crisis during the Younger Dryas in the Late Natufian times human societies.

This thesis uses geological field data and numerical ice sheet modelling to study the Younger Dryas ice cap in Scotland. The Younger Dryas stadial is important because it represents the most recent period of high-magnitude global climate change, and was marked by the expansion of ice sheets in North America and Scandinavia, and the regrowth of glaciers in the British Isles. An integrated methodology linking field results and modelling is developed and applied here, specifically focussing on the deposits, landforms, and palaeoglaciology of Younger Dryas glaciers in western Scotland. This combined approach enables data of different scales to be compared, and connected, from local sedimentological investigations and empirically derived reconstructions, to regional ice-sheet simulations from a high-resolution numerical model. Previous geological mapping in western Scotland resulted in contradictory views of the thickness and extent of ice during the Younger Dryas, consequently leading to uncertainty about the dynamics of the former ice cap. By using a ‘landsystem’ method to characterise the terrain, it is argued here that geological evidence in the study area implies a relatively thick central ice cap that fed steep outlet glaciers around its margins. These glaciers oscillated throughout the stadial, and during deglaciation produced suites of moraines that marked successive positions of glacier retreat. Widespread preservation of superimposed landforms, and of sediment sequences pre-dating the Younger Dryas, suggest that, despite being active, the Younger Dryas ice cap was not particularly erosive in its central area and only subtly modified its bed. These geological interpretations are supported by high-resolution numerical modelling of the ice cap, which reveals clear spatial variability in the velocity structure, thermal regime, and flow mechanism of the ice cap; patterns that led to local contrasts in basal processes and diversity in the geological imprint. These model experiments also highlight the non-linear relationship between climate forcing and glacier response, identifying evidence of ice sheet hysteresis and climatically decoupled glacier oscillations – concepts as relevant to geological investigations of former ice masses as they are to the prediction of glacier response under future climate changes.

The final stadial of the last glacial - Younger Dryas (12 650 - 11 500 cal yr BP) is relatively well described in sediments of European lakes, however research related to its progress in Central European area is missing. The goal of this thesis was to examine progress of this stadial based on sediment core from Černé Lake at Šumava (Czech Republic). To reconstruct climatic conditions, sub-fossil remains of Chironomidae was used. The air July temperature was estimated using Swiss-Norwegian model. Geochemical analysis was performed to determine intensity of erosion, trophic status of the lake, and sources of its organic matter. To complete information about catchment, pollen analysis was performed. Following climatic events were identified in the sediment: Older Dryas (13 583 - 13 394 cal yr BP), Alleröd (13 394 - 12 383 cal yr BP), Younger Dryas (12 383 - 11 394 cal yr BP) a Early Holocene (11 394 - 11 138 cal yr BP). Presence of two phases of Younger Dryas was not significantly proven, nevertheless, the isotope composition suggests, that the first half of this oscillation was drier. Reconstructed temperature ranged between 8,30 and 10,31řC. The mean temperature for Older Dryas event was 8,92 řC, for Alleröd 9,61 řC, Younger Dryas 9,17 řC and Early Holocene 10,00 řC. Reconstructed temperature...

The rapid rate of global warming currently underway highlights the need for a deeper understanding of abrupt climate change. The Younger Dryas is a Late-Glacial climate event of widespread and unusually rapid change whose study can help us address this need for increased understanding. Reconstructions from the glacial record offer important contributions to our understanding of the Younger Dryas due to (among other things) the direct physical response of glaciers to even minor perturbations in climate. Because the glacier equilibrium line altitude (ELA) provides a more explicit comparison of climate than properties such as glacier length or area, ELA methods lend themselves well to paleoclimate applications and allow for more direct comparisons in space and time. Here we present a physically based ELA model for alpine paleoglacier climate reconstructions that accounts for differences in glacier width, glacier shape, bed topography and ice thickness, and includes error estimates using Monte Carlo simulations. We validate the ELA model with published mass balance measurements from 4 modern glaciers in the Swiss Alps. We then use the ELA model, combined with a temperature index model, to estimate the changes in temperature and precipitation between the Younger Dryas (constrained by 10Be surface exposure ages) and the present day for three glacier systems in the Graubünden Alps. Our results indicate an ELA depression in this area of 320 m ±51 m during the Younger Dryas relative to today. This ELA depression represents annual mean temperatures 2.29 °C ±1.32 °C cooler relative to today in the region, which corresponds to a decrease in mean summer temperatures of 1.47 °C ±0.73 °C. Our results indicate relatively small changes in summer temperature dominate over other climate changes for the Younger Dryas paleoglaciers in the Alps. This ELA-based paleoclimate reconstruction offers a simple, fast, and cost-effective alternative to many other paleoclimate reconstruction methods. Continued application of the ELA model to more regions will lead to an improved understanding of the Younger Dryas in the Alps, and by extension, of rapid climate events generally.

During the last deglaciation (ca. 24-10 ka thousand years ago (ka)), the North American Laurentide Ice Sheet (LIS) was a major source of meltwater to the Arctic Ocean, North Atlantic Ocean, and the Gulf of Mexico (GOM), and it is hypothesized that meltwater routing played an important role in regulating Late Quaternary millennial-scale climate variability, via its influence on Atlantic Meridional Overturning Circulation (AMOC). For example, the meltwater routing hypothesis predicts that a rerouting of meltwater from the GOM to the North Atlantic and/or Arctic Oceans resulted in a decrease of North Atlantic Deep Water (NADW) formation and subsequent cooling in the northern North Atlantic region, at the onset of the Younger Dryas (ca. 13 ka). The GOM was an important outlet for meltwater that likely originated from the southern margin of the LIS. Northern GOM sediments document episodic LIS meltwater input via the Mississippi River throughout the last deglaciation, and further study may provide insight to the evolution of LIS deglaciation and the hydrological response of meltwater flux to the marine depositional environment of GOM. Here, a multi-proxy geochemical study, based on marine sediments from Orca Basin, in northern GOM, aims to 1) reconstruct high-resolution records of deglacial (ca. 24-10 ka) LIS melting history to assess linkage between meltwater input to the GOM and deglacial climate change; 2) investigate the relationship between marine-based records of meltwater input and terrestrial evidence for continental deglaciation to reconstruct LIS drainage patterns within the Mississippi River watershed; and 3) reconstruct the redox state of Orca Basin sediments to evaluate the potential role of turbidity flows as a means of meltwater transport into the northern GOM. All data for this study is from core MD02-2550, a 9.09 m long giant box core, recovered from 2248 m water depth from the Orca Basin, approximately 300 km southwest of the modern Mississippi River delta. High sedimentation rates (45 cm/thousand years (kyr)) and 0.5 to 2 cm sampling resolution allow for sub-centennial sampling resolution. An anoxic hypersaline brine lake currently occupies the bottom 200 m of Orca Basin; yet, visible laminations and color changes that suggest episodic suboxic to anoxic sedimentary conditions during deglaciation, possibly related to LIS meltwater input and/or local biologic productivity. In chapter one, paired d18O and Mg/Ca-sea-surface temperature (SST) analyses on two varieties of the surface-dwelling planktic foraminifera Globigerinoides ruber (G. ruber; (white and pink, separately)) are used to reconstruct deglacial changes in GOM seawater d18O (d18Osw). Once corrected for global ice volume, the ice volume-corrected d18Osw (d18Oivc-sw) record is primarily influenced by LIS meltwater. d18Oivc-sw records document negative excursions at ca. 19-18.2, 17.5-16.2, 15.3-14.8, and 13.7-13 ka, interpreted as four LIS melting events, followed by the cessation of meltwater at the onset of the Younger Dryas (12.9 ka). Additionally, LIS melting at ca. 17.5 ka suggests that enhanced seasonality in the North Atlantic produced mild summers sufficient for ice sheet retreat during the Mystery Interval (17.5-14.5 ka) despite extremely cold winters. Because of the inherent difficulties in quantifying meltwater flux using d18Oivc-sw data, foraminiferal (G. ruber) Ba/Ca data are generated in chapter two to assess the influence of LIS meltwater on GOM salinity (a function of meltwater flux) during deglaciation. Ba concentrations in the Mississippi River are elevated relative to GOM seawater and are negatively correlated to sea-surface salinity. Because foraminiferal Ba/Ca (Ba/Caforam) exhibits a predictable relationship to the Ba/Ca of seawater (Ba/Casw), it may be used to calculate changes in salinity arising from deglacial variations in Mississippi River discharge. A complicating factor for Ba/Ca-based salinity interpretations is that Ba concentrations vary spatially throughout the Mississippi River watershed. For example, modern Missouri and Upper Mississippi River Ba concentrations (633 and 436 nM, respectively) are higher than that of the Ohio River (253 nM). Thus, GOM Ba/Ca variability could reflect changes in total Mississippi River input and/or shifts in the dominant region of LIS melting. Applying the modern spatial variability of Ba, we can gain insights into the pattern of ice retreat along the southern margin of the LIS during the last deglaciation. d18Oivc-sw and Ba/Ca results suggest that meltwater, originating from the Great Lakes region, entered the GOM at ca. 19.0 ka and may have contributed to global sea level rise. A melting event at ca. 17.5 ka coincided with Lake Erie Lobe retreat and may have preconditioned the North Atlantic for AMOC instability during the Mystery Interval (ca. 17.5-14.5 ka). Elevated GOM Ba/Ca (ca. 15.6 to 14.0 ka) suggests greater meltwater input from the Ba-rich Missouri and Upper Mississippi River watershed during the second half of the Mystery Interval (ca. 16.1-14.5 ka), when wet climate conditions prevailed in the southwestern United States and Central America. Overall, Ba/Ca and d18Oivc-sw data suggest large variations in the delivery of meltwater to the Mississippi River and GOM during the last deglaciation. In chapter three, a suite of redox sensitive trace metals (Mo, Re, U, Mn) from bulk sediment samples are analyzed to reconstruct the redox state of Orca Basin sediments, from the Last Glacial Maximum through the early Holocene (24-7 ka). Variations in the redox state of Orca Basin sediments during deglaciation may be due to changes in local biologic productivity, sediment transport, and/or regional/global physical oceanography. Laminated sediments enriched with authigenic Mo, Re, and U, suggest suboxic to anoxic conditions coincident with high total organic carbon fluxes and LIS meltwater input at ~17.0 ka. Low authigenic trace element concentrations, high quantities of terrigenous material, and abundant Cretaceous-age nannofossils in a 19-cm homogenous interval indicate a turbidite in Orca Basin at ca. 14.4 ka. This stratigraphic unit correlates with evidence from Pigmy Basin, and the Louisiana Shelf, suggesting increased meltwater flux may reflect LIS contribution to Meltwater pulse 1a (MWP-1a) sea level rise. Trace element records coupled with analyses of Orca Basin sedimentary structures will likely improve understanding of deglacial water column stratification, how meltwater entered the GOM (i.e. as a buoyant cap or at depth via sediment-laden hyperpycnal plumes), and the affects of glacial meltwater on marine biologic productivity.

During the last deglaciation, Greenland ice core records exhibit multiple, high frequency climate events including the Oldest Dryas, Bølling-Allerød and Younger Dryas, which may be linked to meltwater routing of the Laurentide Ice Sheet (LIS). Previous studies show episodic meltwater input, via the Mississippi River to the Gulf of Mexico (GOM) several thousand years before the onset of the Younger Dryas until ~13.0 kcal (thousand calendar) yrs, when meltwater may have switched to an eastern spillway, reducing thermohaline circulation (THC). Data from laminated Orca Basin in the GOM, constrained by 34 Accelerator Mass Spectrometry (AMS) 14C dates, provide the necessary resolution to assess GOM sea-surface temperature (SST) history and test the meltwater routing hypothesis. Paired Mg/Ca and δ18O data on the Foraminifera species Globigerinoides ruber (pink and white varieties) document the timing of meltwater input and temperature change with decadal resolution. White G. ruber SST results show an early 5°C increase at 17.6-16.0 kcal yrs and several SST decreases, including at 16.0-14.7 kcal yrs during the Oldest Dryas (2°C) and at 12.9-11.7 kcal yrs during the Younger Dryas (2.5°C). While the early deglaciation shows strong similarities to records from Antarctica and Tobago Basin, the late deglaciation displays climate events that coincide with Greenland and Cariaco Basin records, suggesting that GOM SST is linked to both northern and southern hemisphere climate. Isolation of the ice-volume corrected δ18O composition of seawater (δ18OGOM) shows multiple episodes of meltwater at ~16.4-15.7 kcal yrs and ~15.2-13.1 kcal yrs with white G. ruber δ18OGOM values as low as -2.5%0. The raw radiocarbon age of the cessation of meltwater in the GOM (11.375±0.40 14C kcal yrs) is synchronous with large changes in tropical surface water Δ14C, a proxy for THC strength. An early meltwater episode beginning at 16.4 kcal yrs during the Oldest Dryas supports the suggestion of enhanced seasonality in the northern North Atlantic during Greenland stadials. We suggest a corollary to the seasonality hypothesis that in addition to extreme winters during stadials, warm summers allowed for LIS melting, which may have enhanced THC slowdown.