Despite small direct changes to radiative forcing, solar sunspot cycles are observed in climate records because of climate system amplification that primarily affects wind and precipitation belts. We ...present a proxy record resolving the dominant sub‐millennial periodicities across the entire Holocene in the Southern Westerly Winds (SWW), whose migrations are linked to ocean‐atmosphere heat and carbon exchange. We use X‐ray fluorescence core scanning to examine a rapidly accumulating sediment record (6 m/kyr) recovered from the Chilean margin, yielding unprecedented <2‐year resolution for the Holocene. We show that variations in terrigenous inputs to the site are linked to precipitation, which is controlled by SWW latitudinal migrations. Superimposed on a long‐term decreasing trend throughout the Holocene, we detect significant centennial cycles in the terrestrial input consistent with solar periodicities. We then propose a mechanism by which southward (northward) SWW movement in response to increasing (decreasing) total solar irradiance cools (warms) Antarctic temperatures.
Plain Language Summary
Solar output has been observed to fluctuate in cycles ranging from 11 to 2,000 years. Although the actual change in solar irradiance reaching the top of Earth's atmosphere is small, solar variability has been observed to impact surface temperature and rainfall. These observations suggest that small solar output variations are magnified by the climate system. A proposed mechanism for signal amplification has been identified and studied in tropical and extratropical wind systems previously, though over short time intervals. Here, we extend the record of Southern Westerly Wind variability over the past 10,000 years at 2‐year resolution to look for evidence of these cycles and to track their evolution across the entirety of the current interglacial period. We find that the dominant solar cyclicity is not constant and changes in line with shifting signal dominance in total solar irradiance. We then connect wind belt migration to variations in Antarctic temperatures.
Key Points
Centennial to millennial scale solar cycles are present in the Southern Westerly Winds (SWW) across the Holocene
Dominant solar cycle period changes between the early and late Holocene
SWW transmit and amplify the total solar irradiance perturbation from the mid‐ to high‐latitudes, impacting Southern Ocean upwelling and Antarctic temperatures
Sediment cores recently collected from the Chilean Margin during D/V JOIDES Resolution Expedition 379T (JR100) document variability in shipboard‐generated records of the green/blue (G/B) ratio. These ...changes show a strong coherence with benthic foraminiferal δ18O, Antarctic ice core records, and sediment lithology (e.g., higher diatom abundances in greener sediment intervals), suggesting a climate‐related control on the G/B. Here, we test the utility of G/B as a proxy for diatom productivity at Sites J1002 and J1007 by calibrating G/B to measured biogenic opal. Strong exponential correlations between measured opal% and the G/B were found at both sites. We use the empirical regressions to generate high‐resolution records of opal contents (opal%) on the Chilean Margin. Higher productivity tends to result in more reducing sedimentary conditions. Redox‐sensitive sedimentary U/Th generally co‐varies with the reconstructed opal% at both sites, supporting the association between sediment color, sedimentary U/Th, and productivity. Lastly, we calculated opal mass accumulation rate (MAR) at Site J1007 over the last ∼150,000 years. The G/B‐derived opal MAR record from Site J1007 largely tracks existing records derived from traditional wet‐alkaline digestion from the south and eastern equatorial Pacific (EEP) Ocean, with a common opal flux peak at ∼50 ka suggesting that increased diatom productivity in the EEP was likely driven by enhanced nutrient supply from the Southern Ocean rather than dust inputs as previously suggested. Collectively, our results identify the G/B ratio as a useful tool with the potential to generate reliable, high‐resolution paleoceanographic records that circumvent the traditionally laborious methodology.
Plain Language Summary
The color of marine sediments often corresponds to oceanic and sedimentary processes that can influence the global climate system. Visual inspection of new sediment cores collected from the Chilean Margin revealed substantial downcore changes in green and blue sediment colors. Greener sediment intervals were usually enriched with diatoms, whereas bluer sediments were rich in clay minerals. A specialized camera was used to scan the cores and enable us to quantitatively describe the core colors using the green/blue (G/B) ratio. The similarity of the downcore G/B ratio with Antarctic ice core records suggests that it may serve as a quick tool to estimate the age of the cores during the cruise. In this paper, we show that changes in the G/B ratio are a function of diatom (biogenic opal) productivity and use a calibrated relationship to calculate a continuous record of opal flux at the Chilean Margin over the last 150,000 years. A distinct opal flux maxima at 50,000 years ago is observed, similar to previous studies in the eastern equatorial Pacific. This common event implies a tight link between the high‐ and low‐latitude eastern Pacific Ocean, potentially attributable to enhanced nutrient supply from the Southern Ocean.
Key Points
Sediment green‐to‐blue ratio serves as a novel proxy for changes in diatom productivity on the Chilean Margin
High‐resolution opal mass accumulation rates derived from green‐to‐blue ratio agree with existing records for the last 150 kyr
The green‐to‐blue ratio proxy is potentially applicable in other regions of high diatom productivity with a site‐specific calibration
This study aimed to assess the suitability of the Berkowitz' () social norms approach (SNA) for improving compliance behaviour amongst recreational fishers. A total of 138 recreational shore anglers ...were interviewed in Eastern Cape, South Africa and asked about their compliance, attitudes towards compliance, perceptions of compliance and the attitudes of other anglers. Results indicate that angler compliance for individual regulations was relatively high (75%–90%). Attitudes of anglers towards compliance was positive, with >80% feeling that “breaking any regulation is wrong.” Yet, as predicted by the SNA, interviewees often overestimated the non‐compliance and negative attitudes of other anglers, particularly as their social proximity decreased. Interviewees with the greatest misperceptions were also less compliant. The social norms present in the Eastern Cape rock and surf fishery fulfil the criteria required for the application of the SNA, suggesting that this approach may provide a suitable normative intervention for improving compliance to be used in conjunction with instrumental approaches in recreational fisheries.
Much uncertainty exists about the state of the oceanic and atmospheric circulation in the tropical Pacific over the last glacial cycle. Studies have been hampered by the fact that sediment cores ...suitable for study were concentrated in the western and eastern parts of the tropical Pacific, with little information from the central tropical Pacific. Here we present information from a suite of sediment cores collected from the Line Islands Ridge in the central tropical Pacific, which show sedimentation rates and stratigraphies suitable for paleoceanographic investigations. Based on the radiocarbon and oxygen isotope measurements on the planktonic foraminifera Globigerinoides ruber, we construct preliminary age models for selected cores and show that the gradient in the oxygen isotope ratio of G. ruber between the equator and 8°N is enhanced during glacial stages relative to interglacial stages. This stronger gradient could reflect enhanced equatorial cooling (perhaps reflecting a stronger Walker circulation) or an enhanced salinity gradient (perhaps reflecting increased rainfall in the central tropical Pacific).
Key Points
Central tropical Pacific sediment cores for paleoceanographic study collected
Preliminary stratigraphy established for Line Islands Ridge sediment cores
Enhanced G. ruber oxygen isotope gradient during glacials
The role of risk stratification in normotensive patients with acute pulmonary embolism (PE) is still unclear.
We evaluated, in these patients, the usefulness of six prognostic markers for predicting ...in-hospital adverse events related to PE and 3-month mortality.
Two hundred and one consecutive patients with confirmed acute PE and normal blood pressure, who were administered conventional anticoagulation, were recruited in a multicentre prospective cohort study with 3 months of follow-up. At baseline, they received a comprehensive risk-evaluation including echocardiographic assessment of right ventricular dysfunction, determination of troponin I, brain natriuretic peptide and D-dimer, arterial blood gas analysis and a clinical score. Primary outcome of the study was PE-related in-hospital death or clinical deterioration. Secondary outcomes were in-hospital and 3-month all-cause mortality.
The primary outcome occurred in one patient (0.5%), who died from PE during hospitalization. The in-hospital and 3-month all-cause mortality were 2% and 9%, respectively. None of the prognostic markers was predictive of the primary outcome. Clinical score, troponin I and hypoxemia predicted in-hospital all-cause mortality (P = 0.02, 0.01 and < 0.01, respectively). Clinical score (HR, 4.7; 95% CI, 1.9-12.0), D-dimer (4.8; 1.4-16.3), hypoxemia (5.7; 2.1-15.1) and troponin I (7.5; 2.5-22.7) were predictors of 3-month all-cause mortality on univariate analysis. On multivariate analysis clinical score and troponin I remained independently predictive.
We did not find prognostic markers useful as predictors of in-hospital PE-related adverse events. Clinical score, troponin I and hypoxemia predicted in-hospital all-cause mortality. Clinical score and troponin I independently predicted 3-month all-cause mortality.
Abstract
Submarine groundwater discharge is increasingly recognized as an important component of the oceanic geochemical budget, but knowledge of the distribution of this phenomenon is limited. To ...date, reports of meteoric inputs to marine sediments are typically limited to shallow shelf and coastal environments, whereas contributions of freshwater along deeper sections of tectonically active margins have generally been attributed to silicate diagenesis, mineral dehydration, or methane hydrate dissociation. Here, using geochemical fingerprinting of pore water data from Site J1003 recovered from the Chilean Margin during D/V
JOIDES Resolution
Expedition 379 T, we show that substantial offshore freshening reflects deep and focused contributions of meteorically modified geothermal groundwater, which is likely sourced from a reservoir ~2.8 km deep in the Aysén region of Patagonia and infiltrated marine sediments during or shortly after the last glacial period. Emplacement of fossil groundwaters reflects an apparently ubiquitous phenomenon in margin sediments globally, but our results now identify an unappreciated locus of deep submarine groundwater discharge along active margins with potential implications for coastal biogeochemical processes and tectonic instability.
It is difficult to untangle the mixed influences of high‐ and low‐latitude climate forcing in the eastern equatorial Pacific (EEP). Here we test the hypothesis that the Southern Ocean drove change in ...the EEP via subsurface intermediate waters during the last deglaciation. We use the δ18O signature of benthic foraminifera to reconstruct water density changes during the last 25 kyr at three intermediate water depths (370 m, 600 m, and 1000 m) in the EEP. Carbonate δ18O records a combined signature of temperature and salinity and is therefore more closely related to density than temperature or salinity alone. We find that benthic foraminiferal δ18O values decreased first in the subsurface, simultaneously with rising temperatures over Antarctica, and propagated up to the surface within ~3 kyr. The early subsurface response initiated a rapid decrease in density stratification over the upper water column as indicated by reduced δ18O gradients between surface and intermediate depths. Stratification of the upper water column remained low through the termination, with stratification minima reached during Heinrich Stadial 1 and the Younger Dryas (YD), synchronous with the two‐part deglacial rise in atmospheric CO2. Centennial‐scale shifts toward heavier δ18O signatures at 370 and 600 m during the YD indicate short‐lived shifts in the Subantarctic Mode Water/Antarctic Intermediate Water boundary to shallower intermediate depths. We suggest that decreased density gradients during the deglaciation accelerated vertical mixing across the EEP, and potentially the entire South Pacific subtropical gyre, which enhanced CO2 delivery from depth to the surface ocean and atmosphere.
Key Points
EEP intermediate waters responded to SH climate during the last deglaciation
Early warming in the EEP subsurface altered upper water column stratification
Weak stratification during the YD and HS1 led to enhanced CO2 degassing
Amongst the rivers draining the mountainous islands of the Indonesian Archipelago, the Sepik River of Papua New Guinea is the largest contributor of solute and particulate material to the world ...ocean. Sites U1484 and U1485, drilled during International Ocean Discovery Program (IODP) Expedition 363 provide a continuous, ~555 kyr long, high-resolution record of mainly siliciclastic slope sedimentation on the northern continental margin of PNG, just offshore the mouth of the Sepik River. Sedimentological analysis, based on a combination of smear slide petrography, particle size analysis, high-resolution physical properties track data and visual core description, offers an unprecedented opportunity to investigate the evolution of this major tropical river throughout changing climate and sea-level conditions during the mid- to late Pleistocene. The Sites U1484 and U1485 sediment records exhibit a dramatic lithologic change at ~ 370 ka: the oldest deposits are dominated by pelagic mud, suggesting that the coarser-grained terrigenous discharge from rivers draining the New Guinea Highlands (including a “proto” Sepik River) was captured before reaching the ocean, when the Sepik River basin was an epicontinental sea. The occurrence of coarser-grained, mass-gravity (mainly hybrid) flows after ~370 ka suggests that the epicontinental sea became a more restricted, shallow-water to nonmarine basin, probably due to both basin infilling and the uplift of local coastal ranges. During the last three glacial-interglacial cycles (~300 kyr), this shallow inland basin was strongly affected by global variations in sea level: during sea level lowstands, the Sepik River cut into older sediments and discharged further offshore onto the shallow continental margins, promoting mass-gravity flows. Pelagic mud deposition on the continental margin during the most extreme highstands following deglaciations suggests a return to shallow marine conditions in the Sepik Basin and repositioning of the river mouth further inland, away from the shelf and from the location of the IODP sites. This also indicates that variations in terrigenous fluxes during these extreme highstands were not solely controlled by the intensity of the hydrological cycle and that global sea level variations also influenced sediment deposition. The sequence is interrupted by several massive grain flow deposits, occurring diachronously at Sites U1484 and U1485 and related to a period of intensified tectonic activity between ~280 ka and ~140 ka. The sedimentologic characteristics of these mass-gravity deposits and their lack of correlation between sites are interpreted as resulting from channelized flows along margin-parallel, fault-controlled channels caused by local and regional failures of the continental margins including the area of the Yalingi Canyon, ~50 km north of the sites, where large tsunamigenic events have also occurred in recent years. Time series analyses of magnetic susceptibility and natural gamma radiation (proxies for %sand and %clay content, respectively) indicate that river discharge fluxes were modulated at orbital frequencies (including obliquity-scale cycles), which suggests that precipitation and river discharge were not only linked to precessionally driven shifts in the mean position of the Intertropical Convergence Zone, but also to high-latitude climate change.
•First record of continental margin sedimentation near Sepik River mouth during Pleistocene•<~370ka pelagic mud dominates as river sediments were captured by inner basin•>~370ka alternating mud-sand deposits suggests shoaling and bypass of inner basin•After shoaling of the basin continental margin sedimentation has been strongly affected by global variations in sea level•Higher tectonic activity between ~280–140 ka is recorded by extensive mass-gravity deposition
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