This paper outlines the evolution of the late Cenozoic mixed carbonate‐siliciclastic depositional system in the Gulf of Papua (GoP), using seismic, gravity, multibeam bathymetry, well data sets, and ...Landsat imagery. The deposition of the mixed sedimentary sequences was influenced by dynamic interplay of tectonics, eustasy, in situ carbonate production, and siliciclastic sediment supply. The roles of these major factors are estimated during different periods of the GoP margin evolution. The Cenozoic mixed system in the GoP formed in distinct phases. The first phase (Late Cretaceous–Paleocene) was mostly driven by tectonics. Rifting created grabens and uplifted structural blocks which served later as pedestals for carbonate edifices. Active neritic carbonate accumulation characterized the second phase (Eocene–middle Miocene). During this phase, mostly eustatic fluctuations controlled the large‐scale sedimentary geometries of the carbonate system. The third phase (late Miocene–early Pliocene) was characterized by extensive demise of the carbonate platforms in the central part of the study area, which can be triggered by one or combination of several factors, such as eustatic sea level fluctuations, increased tectonic subsidence, uplift, sudden influx of siliciclastics, or dramatic changes in environmental conditions and climate. The fourth phase (late Pliocene‐Holocene) was dominated by siliciclastics, which resulted in the burial of drowned and/or active carbonate platforms, although some platforms still remain alive until present‐day.
Understanding changes to the marine nitrogen cycle on millennial and shorter time scales can help determine the influence of rapid climate change on the fixed N pool and its sources and sinks. Rapid ...changes in denitrification have been observed in the eastern tropical North Pacific (ETNP) and Arabian Sea; however, millennial scale δ15N records in regions influenced by N2 fixation are sparse. We present a sedimentary δ15N record from the Cariaco Basin during marine isotope stage (MIS) 3 (~35–55 ka). The δ15N record displays a pattern of millennial scale variability that tracks the Greenland ice core Dansgaard‐Oeschger cycles, with higher values observed during interstadial periods, lower values during stadial periods, and abrupt transitions in between. Conditions during interstadials are similar to those at present in the Cariaco Basin, with the sedimentary δ15N signal reflecting a combination of local processes and an imported regional signal. If interpreted to reflect regional processes, the interstadial δ15N values (average ~5.1‰) support the argument that N2 fixation did not increase in the tropical North Atlantic during the last glacial. The lower δ15N values during stadials, when lower sea level resulted in increased physical isolation of the basin, can be explained primarily by local processes. In spite of the importance of local processes, striking similarity is observed between the Cariaco record and millennial scale δ15N records from the ETNP and Arabian Sea. The apparent synchronicity of changes observed in all three regions suggests an atmospheric teleconnection between the three sites and high‐latitude climate forcing during MIS 3.
Key Points
MIS 3 Cariaco sedimentary δ15N records local and regional N2 fixation changes
Millennial scale changes are synchronous with records of denitrification
Synchronicity suggests atmospheric driver of millennial scale N cycle change
Climate in the tropical North Atlantic is controlled largely by variations in the strength of the trade winds, the position of the Intertropical Convergence Zone, and sea surface temperatures. A ...high-resolution study of Caribbean sediments provides a subdecadally resolved record of tropical upwelling and trade wind variability spanning the past 825 years. These results confirm the importance of a decadal (12- to 13-year) mode of Atlantic variability believed to be driven by coupled tropical ocean-atmosphere dynamics. Although a well-defined interdecadal mode of variability does not appear to be characteristic of the tropical Atlantic, there is evidence that century-scale variability is substantial The tropical Atlantic may also have been involved in a major shift in Northern Hemisphere climate variability that took place about 700 years ago.
Since Last Glacial Maximum (23–19 ka), Earth climate warming and deglaciation occurred in two major steps (Bølling‐Allerød and Preboreal), interrupted by a short cooling interval referred to as the ...Younger Dryas (12.5–11.5 ka B.P.). In this study, three cores (MV‐33, MV‐66, and MD‐40) collected in the central part of Pandora Trough (Gulf of Papua) have been analyzed, and they reveal a detailed sedimentary pattern at millennial timescale. Siliciclastic turbidites disappeared during the Bølling‐Allerød and Preboreal intervals to systematically reoccur during the Younger Dryas interval. Subsequent to the final disappearance of the siliciclastic turbidites a calciturbidite occurred during meltwater pulse 1B. The Holocene interval was characterized by a lack of siliciclastic turbidites, relatively high carbonate content, and fine bank‐derived aragonitic sediment. The observed millennial timescale sedimentary variability can be explained by sea level fluctuations. During the Last Glacial Maximum, siliciclastic turbidites were numerous when the lowstand coastal system was located along the modern shelf edge. Although they did not occur during the intervals of maximum flooding of the shelf (during meltwater pulses 1A and 1B), siliciclastic turbidites reappear briefly during the Younger Dryas, an interval when sea level rise slowed, stopped, or perhaps even fell. The timing of the calciturbidite coincides with the first reflooding of Eastern Fields Reef, an atoll that remained exposed for most of the glacial stages.
The Gulf of Papua (GoP) has become a focal point for understanding the deposition and accumulation of siliciclastic and carbonate material along and across a low‐latitude continental margin. Although ...studies have addressed submarine geomorphological features on the inner and middle shelves, as well as processes that may have led to their formation, the seafloor of adjacent slope regions remains poorly documented. This study presents and interprets results from approximately 13,000 line‐km of multibeam bathymetry, 9500 line‐km of 3.5 kHz seismic, and 122 sediment cores that were collected from the GoP shelf edge and slope, primarily on two cruises (PANASH and PECTEN). Bathymetric maps, in conjunction with the seismic profiles and cores, were used to make extensive observations, descriptions, and interpretations of seafloor geomorphology and begin to address several key issues regarding the delivery and accumulation of sediment. This study divided the GoP slope region into physiographic regions including intraslope basins: Ashmore Trough, southern Pandora Trough, northern Pandora Trough, Moresby Trough and intraslope plateaus/platforms: carbonate platforms and atolls and Eastern Plateau. Ashmore Trough contains a very linear northern margin capped by a drowned barrier reef system. This shelf edge is also defined by a broad promontory with channels extending from its apex, interpreted as a relict shelf‐edge delta. Southern Pandora Trough is characterized by pervasive slope channels and slump scars extending down slope to a thick depocenter and an extensive mass‐transport complex. In contrast, northern Pandora Trough has few visible slope channels. Seismic observations reveal a wedge of sediment extending down slope from northern Pandora Trough shelf edge and filling preexisting bathymetry. Large fold‐and‐thrust‐belt ridges are also present on the seafloor in this region and may act to divert and/or catch sediment, depending on sediment transport direction. Moresby Trough contains a large axial submarine channel that extends almost the entire length of the intraslope basin. In addition, an extensive system of canyons lines the NE margin of Moresby Trough. Mass‐transport deposits have been fed from the canyons and in one case deposited a large (∼2000 km2) mass‐transport complex. Fold‐and‐thrust‐belt ridges also extend into Moresby Trough. Here they trend perpendicular to slope and catch gravity flow deposits on their updip side. GoP carbonate platforms/atolls all display very pronounced scalloped‐margin morphology, which may indicate pervasive mass‐wasting processes on carbonate margins. Northwest Eastern Plateau is dominantly carbonate and displays the characteristic scalloped margin morphology; however, most of the plateau is characterized by parallel seismic reflectors. These seismic observations in conjunction with core data indicate that accumulation on Eastern Plateau is primarily mixed pelagic and hemipelagic sediment. Observations and interpretations of the bathymetry have revealed the deep water GoP to contain very diverse geomorphology and suggest it is a dynamic system influenced by a variety of sediment transport processes, particularly mass wasting and other gravity flow processes.
Objective
To update a previously proposed prognostic scoring system that predicts risk of biochemical recurrence (BCR) after salvage radiation therapy (SRT) for recurrent prostate cancer when using ...additional patients and a PSA value of 0.2 ng/mL and rising as the definition of BCR.
Patients and Methods
We included 577 patients who received SRT for a rising PSA after radical prostatectomy in this retrospective cohort study. Clinical, pathological, and SRT characteristics were evaluated for association with BCR using relative risks (RRs) from multivariable Cox regression models.
Results
With a median follow‐up of 5.5 years after SRT, 354 patients (61%) experienced BCR. At 5 years after SRT, 40% of patients were free of BCR. Independent associations with BCR were identified for the PSA level before SRT (RR doubling: 1.25, P < 0.001), pathological tumour stage (RR T3a vs T2 1.21, P = 0.19; RR T3b/T4 vs T2 2.09, P < 0.001; overall P < 0.001), Gleason score (RR 7 vs <7 1.63, P < 0.001; RR 8–10 vs <7 2.28, P < 0.001; overall P < 0.001), and surgical margin status (RR positive vs negative 0.71, P = 0.003). We combined these four variables to create a prognostic scoring system that predicted BCR risk with a c‐index of 0.66. Scores ranged from 0 to 7, and 5‐year freedom from BCR for different levels of the score was as follows: Score = 0–1: 66%, Score = 2: 46%, Score = 3: 28%, Score = 4: 19%, and Score = 5–7: 15%.
Conclusion
We developed a scoring system that provides an estimation of the risk of BCR after SRT. These findings will be useful for patients and physicians in decision making for radiation therapy in the salvage setting.
Temporal variations in the atmospheric concentration of radiocarbon sometimes
result in radiocarbon-based age-estimates of biogenic material that do not
agree with true calendar age. This problem is ...particularly severe beyond the
limit of the high-resolution radiocarbon calibration based on tree-ring data,
which stretches back only to, about 11.8 kyr
before present (BP), near the termination of the Younger Dryas cold
period. If a wide range of palaeoclimate records are to be exploited for better
understanding the rates and patterns of environmental change during the last
deglaciation, extending the well-calibrated radiocarbon timescale back further
in time is crucial. Several studies attempting such an extension, using uranium/thorium-dated
corals and laminae counts in varved sediments,
show conflicting results. Here we use radiocarbon data from varved sediments
in the Cariaco basin, in the southern Caribbean Sea, to construct an accurate
and continuous radiocarbon calibration for the period 9 to 14.5 kyr
BP, nearly 3,000 years beyond the tree-ring-based calibration. A simple
model compared to the calculated atmospheric radiocarbon concentration and
palaeoclimate data from the same sediment core suggests that North Atlantic
Deep Water formation shut down during the Younger Dryas period, but was gradually
replaced by an alternative mode of convection, possibly via the formation
of North Atlantic Intermediate Water.
For the last deglaciation and Termination V (the initiation of MIS 11 at around 430 ka) we report high‐resolution sedimentary nitrogen isotope (δ15N) records from Cariaco Basin in the Caribbean Sea. ...During both terminations the previously reported interglacial decrease in δ15N clearly lags local changes such as water column anoxia as well as global increases in denitrification by several thousand years. On top of the glacial‐interglacial change, several δ15N peaks were observed during the last deglaciation. The deglacial signal in Cariaco Basin can be best explained as a combination of (1) local variations in suboxia and water column denitrification as the reason for the millennial‐scale peaks, (2) a deglacial maximum in mean ocean nitrate δ15N, and (3) increasing N2 fixation in response to globally increased denitrification causing the overall deglacial δ15N decrease. In the Holocene, much of the decrease in δ15N occurred between 6 and 3 ka, coinciding with an expected precession‐modulated increase in African dust transport to the tropical North Atlantic and the Caribbean. This begs the hypothesis that N2 fixation in this region increased in response to interglacial maxima in denitrification elsewhere but that this response strengthened with increased mid‐Holocene iron input. It remains to be seen whether the data for MIS 11 support this interpretation.
We investigated sediment and organic‐carbon accumulation rates in two jumbo piston cores (MV‐54, MV‐51) retrieved from the midslope of the northeastern Pandora Trough in the Gulf of Papua, Papua New ...Guinea. Our data provide a first assessment of mass fluxes over the past ∼33,000 14C years B.P. and variations in organic‐carbon sources. Core sediments were analyzed using a suite of physical properties, organic geochemistry, and micropaleontological measurements. MV‐54 and MV‐51 show two periods of rapid sediment accumulation. The first interval is from ∼15,000 to 20,400 Cal. years B.P. (MV‐51: ∼1.09 m ka−1 and ∼81.2 g cm−2 ka−1) and the second occurs at >32,000 14C years B.P. (∼2.70 m ka−1 and ∼244 g cm−2 ka−1). Extremely high accumulation rates (∼3.96 m ka−1; ∼428 g cm−2 ka−1) characterize 15,800−17,700 Cal. years B.P. in MV‐54 and likely correspond to early transgression when rivers delivered sediments much closer to the shelf edge. A benthic foraminiferal assemblage in MV‐51 from ∼18,400 to 20,400 Cal. years B.P. indicates a seasonally variable flux of organic carbon, possibly resulting from enhanced contrast between monsoon seasons. The oldest sediments, >32,000 14C years B.P., contain TOC fluxes >200 g cm2 ka−1, with >50% of it derived from C3 vascular plant matter. Magnetic susceptibility values are 2 to 3 times higher and benthic foraminiferal accumulation rates are 6 times higher during this interval than at any younger time, indicating a greater influence of detrital minerals and labile organic carbon. The MS data suggest more direct dispersal pathways from central and eastern PNG Rivers to the core site.
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