Paleoclimate research is currently a hot topic in the international debate on how greenhouse-gas emissions affect climate change. Now that the idea of unavoidable global warming by the end of this century is commonly accepted, interest in the early Paleogene climate changes is increasing. During this period, Earths climate experienced episodes of rapid global warming and massive injections of carbon dioxide are linked to these transient temperature anomalies. The Paleocene-Eocene thermal maximum (PETM) at the Paleocene-Eocene (P-E ~55.8 Ma) boundary is the most extreme climate event as it represents a rapid worldwide 5-8 °C warming of Earths surface as well as the deep oceans, associated with large changes in ocean chemistry (ocean acidification). In addition, the PETM is recognized as a critical evolutionary turning point in, which the biosphere was reorganized on a global scale. Unique faunal and floral extinction, radiation and migration patterns are recognized in both terrestrial and marine ecosystems, including a major extinction in deep-sea foraminiferal faunas.In order to establish clear biogeographic patterns of how shallow marine ecosystems responded to the climate changes during the PETM, I studied the benthic foraminiferal distributions in neritic (<200 m water depth) settings in the Northern Hemisphere. During my PhD, I explored the Tunisian Basins and the North Atlantic Coastal Plain in the United States, and compared them to the well-studied Egyptian Basin. I discussed the various aspects of the environmental parameters controlling the benthic foraminiferal distributions and correlated the P-E boundary within the studied basins. The overall result is a synthesis of the short-term biotic response to the PETM.In general, stable latest Paleocene benthic foraminiferal assemblages were in all studied location abruptly replaced by more stress-tolerant faunas during the early stages of the PETM. Our observations indicate that the PETM exerted worldwide environmental stress on benthic foraminiferal communities, triggering prominent transient changes in population structures and biodiversity. Yet the evolutionary impact was minor compared to the deep-sea extinction event. This implies the existence of refugia on the shelves.The increase in abundance of stress-tolerant faunas reflects more stressed dysoxic to anoxic eutrophic marine environments, due to higher nutrient delivery and stratification of the water column. These hypoxic conditions occurred in the early stages of the PETM continually or with high frequencies and evolved towards periodic (seasonal?) oxygen depletion during the later stages of peak warming or initial recovery. The final recovery phase reflects a reoxygenation of the sea floor. These eutrophic conditions remained stable and continued in the aftermath of the PETM and the bottom waters became permanently reoxygenated.Although paleogeographic and climate conditions were different than those of today, the PETM offers insights of how modern regional shelf ecosystems may respond to the massive anthropogenic input of carbon dioxide. This study reveals that benthic foraminifera living on the shelf are not immune to the environmental degradation during global warming and benthic ecosystems will undergo significant transient changes in species composition as global peak warming takes place.<w:latentstyles deflockedstate="false" defunhidewhenused="true" <w:lsdexception="" locked="false" priority="0" semihidden="false"