Tropical Southeast Pacific Continent-Ocean-Atmosphere Linkages Since the Pliocene Inferred from Eolian Dust

Paleo-changes in trade-wind strength play a key role in the process of Pliocene and Pleistocene climate reorganization in the tropical oceans. In the Southeast Pacific, knowledge about changes in southeast trade-wind strength is one of the missing links to understand paleo-changes in oceanography and productivity, and associated variations in thermocline depth and upwelling. The area has long been in focus of the paleoclimate studying community due to the warm Pliocene's similarities to modern El-Niño conditions that turned into a dominant La-Niña-like state during the Pleistocene ice ages. Eolian dust is a valuable indicator of paleo-changes in atmospheric circulation and continental aridity. This thesis examines continent-ocean-atmosphere linkages in the tropical Southeast Pacific at selected time intervals during the Pliocene and Pleistocene epochs on the basis of eolian dust as preserved in marine sediments. The main objectives of this study are the reconstruction of changes in (1) southeast trade-wind strength and dust transport, and changes in (2) western South American continental aridity over time

Early Pliocene increase in thermohaline overturning : a precondition for the development of the modern equatorial Pacific cold tongue

Author Posting. © American Geophysical Union, 2010. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Paleoceanography 25 (2010): PA2202, doi:10.1029/2008PA001645.Unraveling the processes responsible for Earth's climate transition from an “El Niño–like state” during the warm early Pliocene into a modern-like “La Niña–dominated state” currently challenges the scientific community. Recently, the Pliocene climate switch has been linked to oceanic thermocline shoaling at ∼3 million years ago along with Earth's final transition into a bipolar icehouse world. Here we present Pliocene proxy data and climate model results, which suggest an earlier timing of the Pliocene climate switch and a different chain of forcing mechanisms. We show that the increase in North Atlantic meridional overturning circulation between 4.8 and 4.0 million years ago, initiated by the progressive closure of the Central American Seaway, triggered overall shoaling of the tropical thermocline. This preconditioned the turnaround from a warm eastern equatorial Pacific to the modern equatorial cold tongue state about 1 million years earlier than previously assumed. Since ∼3.6–3.5 million years ago, the intensification of Northern Hemisphere glaciation resulted in a strengthening of the trade winds, thereby amplifying upwelling and biogenic productivity at low latitudes.Funding for this research was provided by the Deutsche Forschungsgemeinschaft (DFG) through projects Ti 240/7, Ti 240/12 (being part of the DFG Research Unit, FOR 451: Impact of Gateways on Ocean Circulation, Climate, and Evolution at Kiel University), and Ti 240/17 and through the DFG Research Center/Excellence Cluster “The Ocean in the Earth System” at the University of Bremen. A. Timmermann is supported by the Japan Agency for Marine-Earth Science and Technology through its sponsorship of the International Pacific Research Center

Terrigenous proxy record from ODP Site 202-1237 and sediment core RRV9702a-69PC

ODP Site 1237 and sediment core RRV9702a-69PC were investigated for siliciclastic grain-size distributions and changes in geochemical composition to reconstruct southeast trade-wind variability during the past 5 Ma. Because both, working and archive halves of all ODP Site 1237 cores were completely depleted between 3.3 and 8.1 meters composite depths, (mcd), the corresponding sections of pre-site survey core RRV9702A-69PC were sampled and investigated to fill the gap

Die Wechselwirkungen von Kontinent, Ozean und Atmosphäre im Tropischen Südost-Pazifik seit dem Pliozän hergeleitet aus äolischem Staub in marinen Sedimenten

Paleo-changes in trade-wind strength play a key role in the process of Pliocene and Pleistocene climate reorganization in the tropical oceans. In the Southeast Pacific, knowledge about changes in southeast trade-wind strength is one of the missing links to understand paleo-changes in oceanography and productivity, and associated variations in thermocline depth and upwelling. The area has long been in focus of the paleoclimate studying community due to the warm Pliocene's similarities to modern El-Niño conditions that turned into a dominant La-Niña-like state during the Pleistocene ice ages. Eolian dust is a valuable indicator of paleo-changes in atmospheric circulation and continental aridity. This thesis examines continent-ocean-atmosphere linkages in the tropical Southeast Pacific at selected time intervals during the Pliocene and Pleistocene epochs on the basis of eolian dust as preserved in marine sediments. The main objectives of this study are the reconstruction of changes in (1) southeast trade-wind strength and dust transport, and changes in (2) western South American continental aridity over time

Sedimentology on surface samples from the White Sea

In this study, the grain-size and clay-mineral compositions of 73 surface sediment samples collected in a variety of environmental settings in the White Sea are presented to characterize recent sedimentation processes, reconstruct transport pathways, and identify potential source areas of the terrigenous components. Areas >100 m deep are invariably characterized by silty clay, whereas areas <100 m deep exhibit more heterogeneous grain-size compositions plausibly explained by coastal erosion and (re-)distribution mechanisms, particularly tidal currents. The dominance of sand in the estuarine areas of the Onega and Dvina rivers as well as toward Gorlo Strait connecting the White Sea with the Barents Sea, is attributed to increased current speeds. Illite and smectite are the dominant clay minerals in recent sediments of the southwestern and eastern White Sea sectors, respectively. Their distribution patterns largely depend on the geology of the source areas and mirror surface circulation patterns, especially in Dvina Bay. Smectite is a key clay mineral in White Sea surface sediments as it reveals the dominating influence of the Northern Dvina's runoff on sedimentation and water circulation throughout the basin of the sea. In comparison to other Eurasian shelf seas, the White Sea is characterized by a greater diversity of clay-mineral assemblages, which range from illite- to smectite-dominated sectors containing variable amounts of chlorite and kaolinite