Mass transfer from smooth alabaster surfaces in turbulent flows

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/94735/1/grl3757.pd

Sabrina Sea Floor Survey (IN2017-V01) Piston Core Images, Visual Logs and grain size DATA summaries IN2017-V01-A005-PC01

This document presents images, colour description, colour analysis profiles and summary grain size data for individual core sections from piston core IN2017-V01-A005-PC01 collected during the Sabrina Sea Floor Survey on the RV Investigator between January and March 2017. Detail of the survey can be obtained in the post-survey report (Armand et al., 2018).The authors wish to thank the CSIRO Marine National Facility (MNF) for its support in the form of sea time on RV Investigator, support personnel, scientific equipment and data management. All data and samples acquired on the voyage are made publicly available in accordance with MNF Policy. This Project is supported through funding from the Australian Government’s Australian Antarctic Science Grant Program (AAS #4333). We thank the Marine National Facility, the IN2017-V01 scientific party-led by the Chief Scientists L.K. Armand and P. O’Brien, MNF support staff and ASP crew members led by Capt. M. Watson for their help and support on board the RV Investigator. Grain size analyses were carried out by Aziah Williamson at Geoscience Australia. Alix Post publishes with permission of the CEO, Geoscience Australia under creative commons

Sabrina Sea Floor Survey (IN2017-V01) Piston Core Images, Visual Logs and Grain Size Data Summaries IN2017-V01-C012-PC05

This document presents images, colour description, colour analysis profiles and summary grain size data for individual core sections from piston core IN2017-V01-C012-PC05 collected during the Sabrina Sea Floor Survey on the RV Investigator between January and March 2017. Detail of the survey can be obtained in the post-survey report (Armand et al., 2018).The authors wish to thank the CSIRO Marine National Facility (MNF) for its support in the form of sea time on RV Investigator, support personnel, scientific equipment and data management. All data and samples acquired on the voyage are made publicly available in accordance with MNF Policy. This Project is supported through funding from the Australian Government’s Australian Antarctic Science Grant Program (AAS #4333). We thank the Marine National Facility, the IN2017-V01 scientific party-led by the Chief Scientists L.K. Armand and P. O’Brien, MNF support staff and ASP crew members led by Capt. M. Watson for their help and support on board the RV Investigator. Grain size analyses were carried out by Aziah Williamson at Geoscience Australia. Alix Post publishes with permission of the CEO, Geoscience Australia under creative commons

Paleolatitude distribution of Phanerozoic marine ooids and cements

Data on 493 Phanerozoic marine ooid and cement occurrences indicate that the dominance of calcite versus aragonite in tropical marine settings has changed in response to variation in atmospheric CO2 and/or oceanic temperature gradient. Holocene ooid and cement precipitation occurs over similar latitudes, with means centered around 24[deg] and 28[deg], respectively. Aragonite and calcite also display roughly comparable distributions, with average occurrences between 25[deg] and 28[deg]. Surface seawater saturation values requisite for ooid-cement carbonate precipitation are at least 3.8 ([Omega]arg) for aragonite and 3.4 ([Omega]arg) for calcite.Ancient ooid-cement occurrences vary in space and time, with depositional zones generally closer to the equator during continental emergence; greatest extent correlates with periods of maximum transgression. Aragonite formation is favored in more equatorial localities than calcite when cement-ooid distributions are narrow and continents are emergent. Similarity of latitude distribution of marine ooids, cement, and biogenic carbonate suggests that physicochemical processes that control levels of carbonate saturation were more important in predicating sites of limestone accumulation in Phanerozoic seas than biological processes related to net productivity of various carbonate platform communities. Continental position and tropical shelf area available for carbonate accumulation dictates the relative abundance of shallow water inorganic carbonate precipitates in space and time.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/28586/1/0000394.pd

Benthic Foraminiferal response to sea level change in the mixed siliciclastic-carbonate system of southern Ashmore Trough (Gulf of Papua)

Ashmore Trough in the western Gulf of Papua (GoP) represents an outstanding modern example of a tropical mixed siliciclastic-carbonate depositional system where significant masses of both river-borne silicates and bank-derived neritic carbonates accumulate. In this study, we examine how benthic foraminiferal populations within Ashmore Trough vary in response to sea level–driven paleoenvironmental changes, particularly organic matter and sediment supply. Two 11.3-m-long piston cores and a trigger core were collected from the slope of Ashmore Trough and dated using radiocarbon and oxygen isotope measurements of planktic foraminifera. Relative abundances, principal component analyses, and cluster analyses of benthic foraminiferal assemblages in sediment samples identify three distinct assemblages whose proportions changed over time. Assemblage 1, with high abundances of Uvigerina peregrina and Bolivina robusta, dominated between ∼83 and 70 ka (early regression); assemblage 2, with high abundances of Globocassidulina subglobosa, dominated between ∼70 and 11 ka (late regression through lowstand and early transgression); and assemblage 3, with high abundances of neritic benthic species such as Planorbulina mediterranensis, dominated from ∼11 ka to the present (late transgression through early highstand). Assemblage 1 represents heightened organic carbon flux or lowered bottom water oxygen concentration, and corresponds to a time of maximum siliciclastic fluxes to the slope with falling sea level. Assemblage 2 reflects lowered organic carbon flux or elevated bottom water oxygen concentration, and corresponds to an interval of lowered siliciclastic fluxes to the slope due to sediment bypass during sea level lowstand. Assemblage 3 signals increased off-shelf delivery of neritic carbonates, likely when carbonate productivity on the outer shelf (Great Barrier Reef) increased significantly when it was reflooded. Benthic foraminiferal assemblages in the sediment sink (slopes of Ashmore Trough) likely respond to the amount and type of sediment supplied from the proximal source (outer GoP shelf)

Sequential changes in ocean circulation and biological export productivity during the last glacial-interglacial cycle: a model-data study

We conduct a model-data analysis of the marine carbon cycle to understand and quantify the drivers of atmospheric CO2 concentration during the last glacial-interglacial cycle. We use a carbon cycle box model, "SCP-M", combined with multiple proxy data for the atmosphere and ocean, to test for variations in ocean circulation and Southern Ocean biological export productivity across marine isotope stages spanning 130 000 years ago to the present. The model is constrained by proxy data associated with a range of environmental conditions including sea surface temperature, salinity, ocean volume, sea-ice cover and shallow-water carbonate production. Model parameters for global ocean circulation, Atlantic meridional overturning circulation and Southern Ocean biological export productivity are optimized in each marine isotope stage against proxy data for atmospheric CO2, delta C-13 and Delta C-14 and deep-ocean delta C-13, Delta C-14 and CO32-. Our model-data results suggest that global overturning circulation weakened during Marine Isotope Stage 5d, coincident with a similar to 25 ppm fall in atmospheric CO2 from the last interglacial period. There was a transient slowdown in Atlantic meridional overturning circulation during Marine Isotope Stage 5b, followed by a more pronounced slowdown and enhanced Southern Ocean biological export productivity during Marine Isotope Stage 4 (similar to -30 ppm). In this model, the Last Glacial Maximum was characterized by relatively weak global ocean and Atlantic meridional overturning circulation and increased Southern Ocean biological export productivity (similar to -20 ppm during MIS 3 and MIS 2). Ocean circulation and Southern Ocean biological export productivity returned to modern values by the Holocene period. The terrestrial biosphere decreased by 385 Pg C in the lead-up to the Last Glacial Maximum, followed by a period of intense regrowth during the last glacial termination and the Holocene (similar to 600 Pg C). Slowing ocean circulation, a colder ocean and to a lesser extent shallow carbonate dissolution contributed similar to -70 ppm to atmospheric CO2 in the similar to 100 000-year leadup to the Last Glacial Maximum, with a further similar to -15 ppm contributed during the glacial maximum. Our model results also suggest that an increase in Southern Ocean biological export productivity was one of the ingredients required to achieve the Last Glacial Maximum atmospheric CO2 level. We find that the incorporation of glacial-interglacial proxy data into a simple quantitative ocean transport model provides useful insights into the timing of past changes in ocean processes, enhancing our understanding of the carbon cycle during the last glacial-interglacial period

Midlatitude Southern Hemisphere Temperature Change at the End of the Eocene Greenhouse Shortly Before Dawn of the Oligocene Icehouse

The Eocene‐Oligocene transition (EOT) marked the initiation of large‐scale Antarcticglaciation. This fundamental change in Cenozoic climate state is recorded in deep‐sea sediments by arapid benthic foraminiferalδ18O increase and appearance of ice‐rafted debris in the Southern Ocean.However, we know little about the magnitude of cooling associated with the EOT in shallow waterenvironments, particularly at middle to high latitudes. Here we present new stratigraphic records of theC13r/C13n magnetochron boundary and the EOT in the clay‐rich Blanche Point Formation, SouthAustralia. The Blanche Point Formation was deposited in a shallow shelf setting (water depths of <100 m) ata paleolatitude of ~51°S. We present high‐resolutionδ18O,δ13C, and Mg/Ca records of environmentalchange from well‐preserved benthic foraminifera of latest Eocene age at this site. A marked, negativeδ13Cexcursion occurs immediately before EOT Step 1 and may be a globally representative signal. An ~2°C Ccooling of shallow shelf seawater is evident from benthic foraminiferal Mg/Ca across Step 1. This coolingsignal is both sufficient to account fully for theδ18O increase in our data and is of similar amplitude to thatdocumented in published records for shallow shelf and upper water column open ocean settings, whichsuggests no obvious polar amplification of this cooling signal. Our results strengthen the evidence base forattributing EOT Step 1 to global cooling with little contribution from ice volume growth and contradict themechanism suggested to explain the inferred northward migration of the intertropical convergence zone inthe contemporaneous equatorial Pacific Ocean

Upwelling characteristics and nutrient enrichment of the Kangaroo Island upwelling region, South Australia

An analysis is presented of hydrographic and nutrient data collected over three years for the Kangaroo Island upwelling region, Lincoln Shelf, South Australia, to determine the signature of upwelled water, depth of upwelling and the source water mass being brought onto the shelf. Strong upwelling seasons were recorded during the 2007-2008 and 2009-2010 summers, while the summer of 2008-2009 had only one weak upwelling event. Strong upwelling events during February and March 2008 and February and March 2010 recorded temperatures and salinities as low as 10.44C and 34.85, and NOx and phosphate concentrations as high as 13.35 and 0.94 μmol/L, respectively, at 105 m on the shelf. Upwelled water properties matched slope water properties between 240 and 370 m, indicating water can be upwelled over depths of 200 m or more. Upwelling from these depths sources South Australian Basin Central Water of Southern Ocean origin, which is transported west along the slope by the Flinders Current System. New results for nutrients show average values of NOx and phosphate during months of strong upwelling to be 6.1 times and 4.6 times greater, respectively, than during winter months, and that upwelled water can have nutrient concentrations up to 90 times higher than those in summer surface waters. Strong relationships between temperature and nutrients on the slope can help estimate nutrient concentrations supplied to the shelf during upwelling events. Upwelled water was also low in silicate, a signature of Southern Ocean water masses, which has implications for phytoplankton community structure and diatom abundance on the shelf

Sea level and deep-sea temperature reconstructions suggest quasi-stable states and critical transitions over the past 40 million years

Sea level and deep-sea temperature variations are key indicators of global climate changes. For continuous records over millions of years, deep-sea carbonate microfossil-based 18O (c) records are indispensable because they reflect changes in both deep-sea temperature and seawater 18O (w); the latter are related to ice volume and, thus, to sea level changes. Deep-sea temperature is usually resolved using elemental ratios in the same benthic microfossil shells used for c, with linear scaling of residual w to sea level changes. Uncertainties are large and the linear-scaling assumption remains untested. Here, we present a new process-based approach to assess relationships between changes in sea level, mean ice sheet 18O, and both deep-sea w and temperature and find distinct nonlinearity between sea level and w changes. Application to c records over the past 40 million years suggests that Earth's climate system has complex dynamical behavior, with threshold-like adjustments (critical transitions) that separate quasi-stable deep-sea temperature and ice-volume states

Middle Pleistocene re-organization of Australian Monsoon

The sensitivity of the Australian Monsoon to changing climate boundary conditions remains controversial due to limited understanding of forcing processes and past variability. Here, we reconstruct austral summer monsoonal discharge and wind-driven winter productivity across the Middle Pleistocene Transition (MPT) in a sediment sequence drilled off NW Australia. We show that monsoonal precipitation and runoff primarily responded to precessional insolation forcing until ~0.95 Ma, but exhibited heightened sensitivity to ice volume and pCO2 related feedbacks following intensification of glacial-interglacial cycles. Our records further suggest that summer monsoon variability at the precessional band was closely tied to the thermal evolution of the Indo-Pacific Warm Pool and strength of the Walker circulation over the past ~1.6 Myr. By contrast, productivity proxy records consistently tracked glacial-interglacial variability, reflecting changing rhythms in polar ice fluctuations and Hadley circulation strength. We conclude that the Australian Monsoon underwent a major re-organization across the MPT and that extratropical feedbacks were instrumental in driving short- and long-term variability