The Northwest (NW) Pacific contains a significant, but poorly constrained and poorly understood ice-rafted debris (IRD) belt extending from the subarctic to the mid-latitudes. While these deposits ...point to substantial glacial ice in the Kamchatka-Koryak region during the last glacial period, the timing and dynamics of glacial change are not well constrained. This thesis updates the Late Quaternary marine core record with a high resolution and multi-faceted study of environmental change. The thesis begins with a review of the state of knowledge relating to Late Quaternary glacial and climatic change in the NW Pacific. I present a high resolution, ~175 kyr study of site ODP 1207A (37.79ºN, 162.75ºE), encompassing IRD, 14C dating, benthic δ18O, tephrochronology and planktic foraminifera counts. The southern limit of ice-rafting is revealed to be further south than previously thought. This discovery, in conjunction with a new high resolution age model reveals new information about the scale and timing of large magnitude ice-rafting events from NE Siberia. Ice-rafting does not show synchronicity with other major Northern Hemisphere ice sheets. A second IRD analysis is presented for DSDP 580 (41.37ºN, 153.59ºE) where icebergs are known to have reached. I present an updated age model for DSDP 580 derived from both pre-existing age tie points and new tephrochronological data. Together, these new IRD records reveal periods of widespread glacial collapse and possible synchronous collapse of NE Siberian glacial ice ~40 ka BP. Chapter 6 presents a comprehensive analysis of XRF core scanning data of Late Quaternary sections of nine North Pacific cores. This analysis extracts palaeoenvironmental signals from element intensities and log ratios, which identify episodes of palaeoproductivity change and terrigenous input. The palaeoproductivity indicators Ba and Ca are used to identify inter-core stratigraphic tie-points at multiple N Pacific sites, particularly around the last deglaciation. Chapter 7 presents the results and analysis of coupled climate-iceberg model experiments, which explores the most likely source points for icebergs into the N Pacific. The model experiments are important indicators of IRD provenance and provide a foundation for future geochemical provenance studies.
In this study, we present a Holocene rainfall index based on three high‐resolution speleothem records from the Western Mediterranean, a region under the influence of the westerly winds belt modulated ...by the North Atlantic Oscillation (NAO). On centennial to millennial timescales, we show that the North Atlantic ice‐rafting events were likely associated with negative NAO‐like conditions during the Early Holocene and the Late Holocene. However, our data reveal that this is not clearly the case for the mid‐Holocene ice‐rafting events, during which we also show evidence of positive NAO‐like patterns from other paleo‐oceanographic and paleo‐atmospheric data. Hence, contradictory mechanisms involving prolonged periods of both north and south shifts of the westerly winds belt (resembling positive and negative NAO‐like patterns) might at least partially trigger or amplify the ice‐rafting events and the slowdown of the Atlantic Meridional Overturning Circulation.
Plain Language Summary
During the Holocene, periods of enhanced ice‐rafting, associated with cooling and sea ice expansion in the North Atlantic high latitudes, have been recognized over distant regions. While the causes of these events are still a matter of debate, changes in the atmospheric circulation have been proposed as a potential trigger or amplifier. Here, we use speleothems to establish a precisely dated record of rainfall variability in the Western Mediterranean, a highly sensitive region to the westerly winds belt modulated by the North Atlantic Oscillation. Our results reveal new insights about the dynamics of NAO‐like patterns during the Holocene. On centennial to millennial timescales, prolonged periods of both north and south shifts of the westerly winds belt might trigger or amplify the slowdown of the Atlantic Meridional Overturning Circulation and the North Atlantic ice‐rafting. However, not all ice‐rafting events are associated with either positive or negative NAO‐like conditions.
Key Points
A high‐resolution multi‐speleothem rainfall index describes the Holocene rainfall variability in the Western Mediterranean
On centennial to millennial scales, negative NAO‐like conditions were likely associated with the Early and Late Holocene ice‐rafting events
Different mechanisms involving north and south shifts of the westerly winds belt might contribute to ice‐rafting and the AMOC slowdown
The precipitation strengthened Co-based superalloys show the great potential for the next generation superalloys of aerospace engine, their mechanical properties are associated with the morphology ...stability of L12-γʹ phase under high temperature and loading state. The antiphase boundaries (APBs) formed by different variants of the ordered fcc-L12-γʹ-Co3(Al, W) phase, affect creep morphologies and the high-temperature properties of Co-based superalloys. By coupling with the Kim-Kim-Suzuki (KKS) model and crystal plasticity model, the directional rafting and evolution kinetics of the γʹ phase are studied during the creep of Co–10Al–10W (at.%) superalloy. Creep rafting under high temperature and low stress is a process of stress-induced directional coarsening, rafting is affected by the APBs on hindering the directional element diffusion. In the early stage of creep, the increasing number of APBs leads to a lower creep strain. Higher temperature accelerates the rafting and reduces the γʹ area fraction. Furthermore, under tensile stress and compressive stress, the APBs show the hindering effect on both P-type rafting and N-type rafting. This study reveals the effects of APBs on the rafting behaviors and creep properties, the findings are theoretically important for the microstructure optimization of Co-based superalloys.
•Directional diffusion of W is hindered by APBs during creep of Co–Al–W superalloy.•APBs inhibit the rafting of γʹ phase under tensile and compressive creep stress.•APBs improve the creep resistance at the early stage of creep.
Introduction: The development of the tourism sector in Indonesia is so fast, but since the COVID-19 pandemic, tourist visits have decreased. In the new normal era, there is a change in behavior to ...continue to carry out activities by implementing health protocols. Several tourist attractions began operating with the implementation of health protocols. The government issued guidelines for the implementation of Cleanliness, Health, and Safety Environmental Sustainability (CHSE). CHSE rafting tour is guided to meet the needs of tourists for clean, healthy, safe, and environmentally friendly tourism products and services during the COVID-19 pandemic. Payung Rafting Managers try to implement health protocols to the maximum. This study was conducted to determine the extent to which Payung Rafting managers apply the CHSE Guidelines.
Methods: This research is quantitative study with cross sectional design. Analysis of the fulfillment of the CHSE rafting guidelines at the Payung Rafting tourist attraction was carried out, using the CHSE rafting instrument released by the Ministry of Tourism and Creative Economy. This activity has been carried out on August 9, 2021.
Results: The results showed that Payung Rafting was able to meet 69% of the CHSE guidelines, while based on the results of the Pearson Chi-Square test, a value of 0.119 was obtained with a significance value of 0.730 (p> 0.05).
Conclusion: This study statistically shows there is no difference between the CHSE guidelines and implementation in Payung Rafting, but descriptive analysis shows that Payung Rafting can apply 69% of the CHSE guidelines.
There are climatically important ocean flow systems in high latitudes, for example the East and West Greenland and Labrador Currents and Nordic Sea overflows in the North, and Antarctic Circumpolar ...Current in the South, for which it would be useful to know history of flow strength. Most of the sediment records under these flows contain evidence of supply from glacial sources, which has led to the supposition that fine sediment records, which in other settings provide evidence of vigour of flow from the sortable silt proxy, are fatally contaminated by unsorted glacial silt. It is suggested here that if the fine fraction (<63 μm) has been transported and sorted, then it does not matter that it may have been released from icebergs, sea ice or meltwater plumes. Here we show that correlation between sortable silt mean and percentage provides a good indicator of whether a fine sediment record has been sufficiently well current-sorted to provide a reliable flow history. The running downcore correlation (rrun) (5 to 9-point depending on sampling interval) is found to be optimal, and a value of rrun < 0.5 is proposed as an indicator of sufficiently poor sorting to invalidate a section of mean size record. More than 40 grainsize records determined by laser particle sizers from over 30 core sites have been processed and examined for evidence of sorting. As expected, there is a tendency for poor sorting and unreliable records at points where the flow speed has decreased to very low values. There is no consistent relationship between the sorting of the fine fraction and the content of coarse ice-rafted debris (as long as the IRD fraction is not > 50%) because the two are not related. End member (EM) decomposition of several records yields variable results in terms of the relationship between EM ratios and grainsize parameters. Although such an approach can generate fine sediment parameters it does not provide a basis for deciding whether or not a record is acceptably current sorted and thus contains a valid flow speed proxy. Our proposed discrimination between current-sorted and unsorted fine fractions is applicable to all fine grained deposits, not only high-latitude deposits with coarse IRD.
Examples from East Greenland, Faroe Bank Channel, Gardar Drift show mainly well sorted signatures. Amounts of coarse IRD range up to 60% with only those >50% having a consistent impact on sortable silt mean size. With the exception of a Southern Ocean site on the Antarctic continental rise where half the record is poorly sorted, the silt mean data are sufficiently well sorted to provide credible flow speed histories. This bodes well for the extraction of such histories from climatically important high-latitude flows such as the East Greenland Current.
•Correlation between sortable silt parameters is current-sorting index for palaeoflow.•Running downcore correlation <0.5 indicates an invalid size record for flow history.•No consistent relation between fine fraction sorting and coarse IRD content.•End members (EM) do not show whether or not a record is acceptably current sorted.•EMs confuse by combining sediment components having differing depositional origins.
We present a comprehensive record of Holocene (11,590–628 cal. yr BP) climate and hydrographic changes around the Wular Lake located in Kashmir Valley, India. Based on the multi-proxy investigations, ...we have identified three phases of wet climate conditions that prevailed from the commencement of the Holocene Epoch – 9000 cal. yr BP, 8100–6650 cal. yr BP and 6350–5000 cal. yr BP, whereas periods of dry climate were observed during 9000–8100 cal. yr BP, 6650–6350 cal. yr BP and ~5000 to 4000 cal. yr BP. The results also suggested that the lake widened and deepened significantly around 6350–5000 cal. yr BP. The results indicated desiccation and the exposure of the lake margin around 5000–4500 cal. yr BP. The sedimentation rate since 4500–628 cal. yr BP was quite low for detailed paleoclimate interpretations. Oscillations in lake extension and deepening appear to be due to changing intensity of westerly moisture in the region, and we correlate several of the low lake-level phases to the Bond events caused by North Atlantic ice rafting events.
The ln(Zr/Rb) count ratio derived from X‐ray fluorescence (XRF) core scanning holds potential as a high‐resolution tracer for grain‐size variations of glaciomarine sediments, and hence current ...strength. To evaluate this approach, we conducted high‐resolution grain‐size measurements, together with Rb and Zr measurements by XRF core scanning and inductively coupled plasma‐mass spectrometry (ICP‐MS), on a series of sediment cores from different regions of the Southern Ocean. Downcore changes of the ln(Zr/Rb) count ratio from XRF core scanning are consistent with Zr/Rb concentration ratios derived from ICP‐MS analyses, even though Rb and Zr counts deviate significantly from concentrations due to specimen and matrix effects. The ln(Zr/Rb) count ratio displays discrepancies with the bulk mean grain‐size, but correlates well with the mean grain‐size of the sediment fractions that do not include unsorted sand delivered by ice‐rafting. These observations are supported by evidence from a grain‐size separation experiment, which indicates that Zr and Rb are concentrated in different grain‐size fractions. Consistent with its lack of sensitivity to coarse grain‐size fractions derived from ice‐rafting, the ln(Zr/Rb) ratio records similar trends to the sortable silt percent (SS%) and sortable silt mean (SS¯) grain‐size. Universal gradients exist in plots of SS% versus ln(Zr/Rb), and SS¯ versus ln(Zr/Rb), such that the ln(Zr/Rb) ratio provides a convenient way to estimate the magnitude of changes in SS% and SS¯. Overall, our results support the use of the ln(Zr/Rb) ratio as an indicator of bottom current strength in cases where the sediment is current‐sorted.
Key Points
Ln(Zr/Rb) co‐varies with the iceberg rafted debris‐corrected mean grain‐size of glaciomarine sediments from the Southern Ocean
Ln(Zr/Rb) reflects changes in bottom current strength if the sediment is bottom current‐sorted
Constant gradients observed in plots of ln(Zr/Rb) versus SS%, and ln(Zr/Rb) versus SS¯
Throughout the Flinders Ranges of South Australia, the red bed Brachina sequence comprises the lower of two regressive, coarsening-upward successions that together constitute the Ediacaran-aged ...Wilpena Group. Detailed examination of the Brachina sequence has identified evidence of ice-rafting, supporting the contention that frigid climatic conditions continued well after cessation of the Marinoan Glaciation, as well as features postulated to be harbingers of the macroscopic metazoans that occur in abundance higher in the local stratigraphy. Although tuffaceous and lying stratigraphically between deposits of the Marinoan Glaciation and the Acraman Impact/Gaskiers Glaciation, no absolute age dates exist for the sequence. However, through correlation to the global carbon isotope profile, the timespan of Brachina sequence deposition can be constrained to between 635 and 586 Ma, when the regression climaxed with terrestrial deposition upon a local disconformity. The tuffaceous input is timed to have begun at 620 Ma, essentially coincident with initial formation of the passive volcanic continental margin of southeastern Australia and initiation of both the Volyn Large Igneous Province and activity within the Central Iapetus Magmatic Province, all components marking the demise of Rodinia and initial amalgamation of Gondwana.
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