107 research outputs found
The composition and characterization of the organic-walled resting cysts of dinoflagellates: Implications for the preservation of organic matte
This cumulative work represents the most comprehensive attempt to characterize the chemical composition of organic-walled dinoflagellate resting cysts (dinocysts) to date. Dinocysts are composed of a refractory biopolymer called dinosporin. The chemical composition of dinosporin, evaluated in three separate studies using micro-Fourier transform infrared spectroscopy, was shown to be variable and may, in fact, be taxon specific. Factors that seemed to exhibit an influence on dinosporin composition include the ecology of the cyst-producing dinoflagellate species, environmental conditions of the upper water column prior to and/or during cyst formation, and post-depositional alteration. The effects of these factors on the dinosporin composition are important to understand for (1) accurate oceanographic and climate reconstructions, as it may influence the preservation potential of dinocysts, and for (2) describing the chemical transformations that organic matter undergoes after deposition, which is a crucial component for a better understanding of the global carbon cycle
Hiddenocysta matsuokae gen. nov. et sp. nov. from the Holocene of Vancouver Island, British Columbia, Canada
A new dinoflagellate cyst genus and species are described here as Hiddenocysta gen. nov. and Hiddenocysta matsuokae sp. nov. from Holocene sediments in a core from the west coast of Vancouver Island (British Columbia, Canada). The genus Hiddenocysta encompasses spherical to ovoid skolochorate cysts, characterized by a gonyaulacoid plate pattern and a 2P precingular archeopyle. The species H. matsuokae is characterized by a granular wall and slender trifurcate processes with heavily perforated process bases. Two end members are described here based on process morphology and number of processes (formas 1 and 2). Cyst wall chemistry is analyzed using micro-Fourier transform infrared (FTIR) spectroscopy and reveals a unique dinosporin composition consistent with a gonyaulacoid autotrophic feeding strategy
Neodymium evidence for increased circumpolar deep water flow to the North Pacific during the Middle Miocene Climate Transition
Low salinity surface water inhibits local deepwater formation in the modern North Pacific.
Instead, southern-sourced Circumpolar Deep Water (CDW) fills the basin, which is the product of water
masses formed from cold sinking centers in the Southern Ocean and North Atlantic. This CDW is responsible
for transporting a significant amount of global heat and dissolved carbon in the deep Pacific Ocean. The
history of its flow and the broader overturning circulation are widely assumed to be sensitive to climate
perturbations. However, insufficient records exist of CDW presence in the deep North Pacific with which to
evaluate its evolution and role in major climate transitions of the past 23 Ma. Here we report sedimentary
coatings and fish teeth neodymium isotope valuesâtracers for water-mass mixingâfrom deepwater
International Ocean Discovery Program Site U1438 (4.7 km water depth) in the Philippine Sea, northwest
Pacific Ocean. Our results indicate the water mass shifted from a North Pacific source in the early Miocene to a
southern source by ~14 Ma. Within the age model and temporal constraints, this major reorganization of
North Pacific water mass structure may have coincided with ice sheet build up on Antarctica and is most
consistent with an increased northward flux ofCDWdue to enhanced sinking of cold water forced by Antarctic
cooling. The northward extent of this flux may have remained relatively constant during much of the past 14Ma
Shore-based X-ray fluorescence core scanning of IODP Expedition 369 (Australia Cretaceous Climate and Tectonics) material
Shore-based X-ray fluorescence core scanning of IODP Expedition 369 (Australia Cretaceous Climate and Tectonics) material
Large igneous province control on ocean anoxia and eutrophication in the North Sea at the Paleocene-Eocene Thermal Maximum
Timing and Pacing of Indonesian Throughflow Restriction and Its Connection to Late Pliocene Climate Shifts
drier conditions. This shift fundamentally reorganized Earth\u27s climate from the Miocene state toward conditions similar to the present. During the Pliocene, the progressive restriction of the Indonesian Throughflow (ITF) is suggested to have enhanced this shift toward stronger meridional thermal gradients. Reduced ITF, caused by the northward movement of Australia and uplift of Indonesia, impeded global thermohaline circulation, also contributing to late Pliocene Northern Hemisphere cooling via atmospheric and oceanographic teleconnections. Here we present an orbitally tuned highâresolution sediment geochemistry, calcareous nannofossil, and Xâray fluorescence record between 3.65 and 2.97 Ma from the northwest shelf of Australia within the Leeuwin Current. International Ocean Discovery Program Site U1463 provides a record of local surface water conditions and Australian climate in relation to changing ITF connectivity. Modern analogueâbased interpretations of nannofossil assemblages indicate that ITF configuration culminated ~3.54 Ma. A decrease in warm, oligotrophic taxa such as Umbilicosphaera sibogae, with a shift from Gephyrocapsa sp. to Reticulofenestra sp., and an increase of mesotrophic taxa (e.g., Umbilicosphaera jafari and Helicosphaera spp.) suggest that tropical Pacific ITF sources were replaced by cooler, fresher, northern Pacific waters. This initial tectonic reorganization enhanced the Indian Oceans sensitivity to orbitally forced cooling in the southern high latitudes culminating in the M2 glacial event (~3.3 Ma). After 3.3 Ma the restructured ITF established the boundary conditions for the inception of the SahulâIndian Ocean Bjerknes mechanism and increased the response to glacioâeustatic variability
Indonesian Throughflow drove Australian climate from humid Pliocene to arid Pleistocene
Late Miocene to mid-Pleistocene sedimentary proxy records reveal that northwest Australia underwent an abrupt transition from dry to humid climate conditions at 5.5 million years (Ma), likely receiving year-round rainfall, but after ~3.3 Ma, climate shifted toward an increasingly seasonal precipitation regime. The progressive constriction of the Indonesian Throughflow likely decreased continental humidity and transferred control of northwest Australian climate from the Pacific to the Indian Ocean, leading to drier conditions punctuated by monsoonal precipitation. The northwest dust pathway and fully established seasonal and orbitally controlled precipitation were in place by ~2.4 Ma, well after the intensification of Northern Hemisphere glaciation. The transition from humid to arid conditions was driven by changes in Pacific and Indian Ocean circulation and regional atmospheric moisture transport, influenced by the emerging Maritime Continent. We conclude that the Maritime Continent is the switchboard modulating teleconnections between tropical and high-latitude climate systems
A lower to middle Eocene astrochronology for the Mentelle Basin (Australia) and its implications for the geologic time scale
The geologic time scale for the Cenozoic Era has been notably improved over the last decades by virtue of integrated stratigraphy, combining high-resolution astrochronologies, biostratigraphy and magnetostratigraphy with high-precision radioisotopic dates. However, the middle Eocene remains a weak link. The so-called âEocene time scale gapâ reflects the scarcity of suitable study sections with clear astronomically-forced variations in carbonate content, primarily because large parts of the oceans were starved of carbonate during the Eocene greenhouse. International Ocean Discovery Program (IODP) Expedition 369 cored a carbonate-rich sedimentary sequence of Eocene age in the Mentelle Basin (Site U1514, offshore southwest Australia). The sequence consists of nannofossil chalk and exhibits rhythmic clay content variability. Here, we show that IODP Site U1514 allows for the extraction of an astronomical signal and the construction of an Eocene astrochronology, using 3-cm resolution X-Ray fluorescence (XRF) core scans. The XRF-derived ratio between calcium and iron content (Ca/Fe) tracks the lithologic variability and serves as the basis for our U1514 astrochronology. We present a 16 million-year-long (40-56 Ma) nearly continuous history of Eocene sedimentation with variations paced by eccentricity and obliquity. We supplement the high-resolution XRF data with low-resolution bulk carbon and oxygen isotopes, recording the long-term cooling trend from the Paleocene-Eocene Thermal Maximum (PETM â ca. 56 Ma) into the middle Eocene (ca. 40 Ma). Our early Eocene astrochronology corroborates existing chronologies based on deep-sea sites and Italian land sections. For the middle Eocene, the sedimentological record at U1514 provides a single-site geochemical backbone and thus offers a further step towards a fully integrated Cenozoic geologic time scale at orbital resolution
Paleocene/Eocene carbon feedbacks triggered by volcanic activity
The PaleoceneâEocene Thermal Maximum (PETM) was a period of geologically-rapid carbon release and global warming ~56 million years ago. Although modelling, outcrop and proxy records suggest volcanic carbon release occurred, it has not yet been possible to identify the PETM trigger, or if multiple reservoirs of carbon were involved. Here we report elevated levels of mercury relative to organic carbonâa proxy for volcanismâdirectly preceding and within the early PETM from two North Sea sedimentary cores, signifying pulsed volcanism from the North Atlantic Igneous Province likely provided the trigger and subsequently sustained elevated CO2. However, the PETM onset coincides with a mercury low, suggesting at least one other carbon reservoir released significant greenhouse gases in response to initial warming. Our results support the existence of âtipping pointsâ in the Earth system, which can trigger release of additional carbon reservoirs and drive Earthâs climate into a hotter state
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