Browsing by Author "Droxler, André W."

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    Coralgal reef morphology records punctuated sea-level rise during the last deglaciation
    (Springer Nature, 2017) Khanna, Pankaj; Droxler, André W.; Nittrouer, Jeffrey A.; Tunnell, John W. Jr.; Shirley, Thomas C.
    Coralgal reefs preserve the signatures of sea-level fluctuations over Earth’s history, in particular since the Last Glacial Maximum 20,000 years ago, and are used in this study to indicate that punctuated sea-level rise events are more common than previously observed during the last deglaciation. Recognizing the nature of past sea-level rises (i.e., gradual or stepwise) during deglaciation is critical for informing models that predict future vertical behavior of global oceans. Here we present high-resolution bathymetric and seismic sonar data sets of 10 morphologically similar drowned reefs that grew during the last deglaciation and spread 120 km apart along the south Texas shelf edge. Herein, six commonly observed terrace levels are interpreted to be generated by several punctuated sea-level rise events forcing the reefs to shrink and backstep through time. These systematic and common terraces are interpreted to record punctuated sea-level rise events over timescales of decades to centuries during the last deglaciation, previously recognized only during the late Holocene.
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    Progressive shoaling of the equatorial Pacific thermocline over the last eight glacial periods
    (Wiley, 2015) Regoli, Fabienne; de Garidel-Thoron, Thibault; Tachikawa, Kazuyo; Jian, Zhiming; Ye, Liming; Droxler, André W.; Lenoir, Guillaume; Crucifix, Michel; Barbarin, Nicolas; Beaufort, Luc
    The depth of equatorial Pacific thermocline is diagnostic of the main modes of tropical climates. Past estimates of Pacific thermocline dynamics have been reconstructed either for the Last Glacial Maximum or on longer timescales at low resolution. Here we document a new high-resolution set of reconstructed past sea surface and subsurface waters temperatures from the southwestern subequatorial Pacific, core MD05-2930, in the Gulf of Papua, over the last 800 ka. We used two morphotypes of Globigerinoides ruber known to live at different water depths to reconstruct past stratification. We estimated calcification temperature of each morphotypes by Mg/Ca paleothermometry. Our subequatorial Pacific thermocline paleotemperature record indicates a response of the thermocline to both direct orbital forcing and glacial-interglacial changes. Our stratification record shows a systematic shallower glacial thermocline, whereas sea surface temperatures are characterized by precessional forcing. The record is indicative of a progressive long-term shoaling of the thermocline during the glacial stages during the late Pleistocene. The shoaling of the subequatorial Pacific thermocline is consistent with regional estimates. An enhanced South Pacific shallow overturning wind-driven circulation could have driven this progressive shoaling. We speculate that this late Pleistocene glacial shoaling of the thermocline could be related to an increase in the amplitude of the obliquity.
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    Timescale dependent sedimentary record during the past 130 kyr from a tropical mixed siliciclastic–carbonate shelf edge and slope: Ashmore Trough (southern Gulf of Papua)
    (Wiley, 2021) Mallarino, Gianni; Francis, Jason M.; Jorry, Stephan J.; Daniell, James J.; Droxler, André W.; Dickens, Gerald R.; Beaufort, Luc; Bentley, Samuel J.; Opdyke, Bradley N.; Peterson, Larry C.
    In tropical and sub-tropical mixed siliciclastic–carbonate depositional systems, fluvial input and in situ neritic carbonate interact over space and time. Despite being the subject of many studies, controls on partitioning of mixed sediments remains controversial. Mixed sedimentary records, from Ashmore Trough shelf edge and slopes (southern Gulf of Papua), are coupled with global sea-level curves and anchored to Marine Isotope Stage stratigraphy to constrain models of sediment accumulation at two different timescales for the past 130 kyr: (i) 100 kyr scale for last glacial cycle; and (ii) millennial scale for last deglaciation. During the last glacial cycle, carbonate production and accumulation were primarily controlled by sea-level fluctuations. Export of neritic carbonate to the slopes was initiated during re-flooding of previously exposed reefs and continued during Marine Isotope Stage 5e and 1 interglacial sea-level highs. Siliciclastic fluxes to the slope were controlled by interplay of sea level, shelf physiography and oceanic currents. Heterogeneous accumulation of siliciclastic mud on the slope, took place during Marine Isotope Stage 5d to Marine Isotope Stage 3 sea-level fall. Siliciclastics reached adjacent depocentres during Marine Isotope Stage 2. Coralgal reef and oolitic–skeletal sand resumed at the shelf edge during the subsequent stepwise sea-level rise of the last deglaciation. Contemporaneous, abrupt siliciclastic input from increased precipitation and fluvial discharge illustrates that climate controlled deglacial sedimentation. Siliciclastic input persisted until ca 8.5 ka. Carbonate accumulation waned at the shelf edge after ca 14 ka, whereas it increased on the slopes since ca 11.5 ka, when previously exposed reef and bank tops were re-flooded. When comparing the last sea-level cycle sedimentation patterns of the southern Gulf of Papua with other coeval mixed systems, sea level and shelf physiography emerge as primary controls on deposition at the 100 kyr scale. At the millennial scale, siliciclastic input was also controlled by climate change during the unstable atmospheric and oceanic conditions of the last deglaciation.