Changes In Accumulation Rates Research Articles

Geomorphological changes and sediment carbon accumulation at the bare mudflat-saltmarsh interface: The role of typhoons

Blue carbon stored in coastal wetlands can be highly impacted by extreme events, such as typhoons. However, the sediment carbon accumulation capacity in this circumstance, remains unclear. In this study, a field site crossing the bare mudflat-saltmarsh interface was established in Southern Hangzhou Bay, to investigate the geomorphological and subsequent sediment carbon accumulation changes during the typhoon season (2 months) and the succeeding calm weather period (10 months). Surface Elevation Tables (SETs) were used, together with GPS-RTK and UAV-LiDAR surveys, to observe surface elevation changes at different spatial scales. The elevation and sediment organic carbon density data were used to estimate the gain/loss of sediment carbon pool under the impact of two successive typhoons, “In-Fa” and “Chanthu”. This revealed that during the typhoon season, 6.3 cm of surface erosion occurred on the bare mudflat whilst rapid depositions of 6.1 and 12.3 cm occurred in Scirpus mariqueter and Spartina alterniflora habitats, respectively. In the gap between the two typhoon events, the bare mudflat experienced deposition of 4.2 cm, signalling recovery from erosion, but deposition within the saltmarsh front slowed. During the calm weather period, sediment deposition increased landward, with magnitudes of 13.1 cm, 16.4 cm, and 18.2 cm. Sediment carbon budget estimates indicated that during the typhoon season, the bare mudflat lost ~3.4 Mg C ha−1 but saltmarshes gained ~4.9 Mg C ha−1 in their sediment organic carbon pools. These changes in sediment carbon accumulation rates over the typhoon season accounted for >30 % of annual change in the study area, and may be associated with tidal creek dynamics. This study suggests the important role of typhoons in mediating the sediment carbon pool across the mudflat-saltmarsh interface. With future climate change, increasingly frequent catastrophic events could cause considerable changes in coastal blue carbon sequestration capacity.

THE INFLUENCE OF PLANT SPECIES AND PRETREATMENT ON THE 14C AGE OF CAREX-DOMINATED PEAT PLANTS OF A PEAT CORE FROM JINCHUAN MIRE, NE CHINA

ABSTRACT The comparisons among 126 14C dates of Carex samples including separated leaf and root parts with acid (A)-treatment and acid-base-acid (ABA)-treatment, and 48 published 14C dates of bulk peat plants on a 92-cm core from Jinchuan Mire in NE China, indicate old carbon influence (OCI) on the 14C dates. The OCI varies with plant species, pretreatment and peat depth. In vascular peat plants such as Carex, humin fractions (remains after ABA treatment) and humic acids are representative of the original plant precursor, while fulvic acids are regarded as the secondary mobile product which should be removed for 14C dating. ABA- treatment removes both fulvic acids and humic acids, whereas A-treatment gets rid of only fulvic acids. Carex roots uptake more dissolved CO2 in peat water. Carex leaves may use more CO2 (involving degassing CO2) above the peat surface. By removing humic acids throughout ABA treatment, the OCI may vary differently over depth (time). ABA treatment cannot eliminate the fixed OCI in humin fractions of vascular peat plants, instead, this treatment may enhance OCI by removing humic acid which may represent the true age of the plants. In addition, Bacon model results on this core could not show rapid changes in accumulation rate.

Mechanisms of Training-Related Change in Processing Speed: A Drift-Diffusion Model Approach.

Processing speed is a crucial ability that changes over the course of the lifespan. Training interventions on processing speed have shown promising effects and have been associated with improved cognitive functioning. While training-related changes in processing speed are often studied using reaction times (RTs) and error rates, these measures provide limited insight into the mechanisms underlying changes during training. The drift-diffusion model provides estimates of the cognitive processes underlying speeded decision tasks, such as the rate of evidence accumulation (drift rate), response strategies (boundary separation), as well as time for other processes such as stimulus encoding and motor response (non-decision time). In the current study, we analyzed existing data of an extensive multi-session training intervention (von Bastian & Oberauer, 2013) to disentangle changes in drift rate, boundary separation, and non-decision time during training of different speeded choice-RT tasks. During this training intervention, 30 participants performed 20 training sessions over the course of four weeks, completing three tasks each session: a face-matching, a pattern-matching, and a digit-matching task. Our results show that processing speed training increased drift rates throughout training. Boundary separation and non-decision time decreased mostly during the initial parts of training. This pattern of prolonged training-related changes in rate of evidence accumulation as well as early changes in response strategy and non-decision processes was observed across all three tasks. Future research should investigate how these training-related changes relate to improvements in cognitive functioning more broadly.

Solar and ENSO activity affecting Late Holocene carbon accumulation rates in peatlands from Northeast Asia: Evidence from periodic signal analysis

Peatlands are well developed in large areas of Northeast Asia, where changes in Late Holocene carbon accumulation rate (CAR) have played an important role in influencing the regional carbon cycle. However, the driving mechanisms and periodic signals of these important peatlands have rarely been investigated. The Zhibian peatland is a subalpine peatland, which has a continuous CAR record covering the entire Late Holocene. This peatland is located in Northeast Asia, its carbon dynamics were directly influenced by the East Asian summer monsoon. This peatland recorded direct interactions between the CAR dynamics, solar and El Niño–Southern Oscillation (ENSO) activity. Thus, we selected this peatland as a representative peatland for Northeast Asia. We used spectrum analyses and wavelet analyses to study the periodic signals of CAR dynamics, total solar irradiance (TSI), mean annual precipitation (Pann) and ENSO activity during the Late Holocene. The correlation relationships between the above parameters were investigated to explore the driving mechanisms for CAR dynamics in Northeast Asia peatlands. Our analyses indicate that CAR dynamics show 88a, 210a and 1000a periodicity over the Late Holocene. The potential driving factors, such as the Pann, ENSO and TSI, also indicate similar periodic signals. These relationships further indicate that the Pann, ENSO and TSI played an important role in controlling the CAR variations of Northeast Asia peatlands. Wavelet analyses results suggest that the CAR, Pann and TSI negatively corresponded with the ENSO variations. From the relationship model between these parameters, we concluded that strong solar activity resulted in fewer ENSO events and more precipitation in Northeast Asia. Wet conditions contributed to higher CAR, and vice versa.

Increased erosion in a pre-Alpine region contrasts with a future decrease in precipitation and snowmelt

Climate change is affecting the hydromorphological system. In many places, changes in sediment dynamics are closely correlated to changes in precipitation frequency and magnitude. However, in nivo-pluvial regimes, the hydromorphological response to climate is more challenging to predict as it is not only the amount and occurrence of precipitation that is changing. The changes in precipitation type (i.e., snow or rain), snow accumulation, and snowmelt rates will also have a significant effect on the catchment net precipitation (composed of direct precipitation plus snowmelt contribution), and this may affect overland flow, erosion, stream discharge, sediment transport, and deposition. We investigated the impacts of climate change on hydrology and geomorphology in a small catchment (Emme, 127 km2) located in the Swiss pre-Alps by simulating the difference between the hydromorphological response to net precipitation in the present climate and in three climate scenarios at the end of the century using the CAESAR-Lisflood landscape evolution model. For the most extreme climate scenario (RCP8.5), simulations showed that despite the reduction in net precipitation (by 7 %) and discharge (by 4 %), sediment yield at the outlet of the catchment increased by 6 %. This is not only because precipitation falls more as rain than snow during the cold months, but also because heavy precipitation is expected to intensify. On a seasonal scale, we found that the amount of net precipitation, discharge, and erosion will increase in winter at the end of the century, while it will decrease in spring. In all three climate scenarios, net precipitation is projected to decrease in summer, but sediment yields may both decrease or increase. Autumn is the season with the greatest changes in erosion, while net precipitation remains constant or only slightly increases. Furthermore, we found that erosion and deposition patterns are changing spatially, with more erosion in mid-elevations and more deposition in valleys. Although our results are specific to the study site, we expect similar trends in other catchments of the pre-Alpine region.

High-resolution OSL dating of loess in Adventdalen, Svalbard: Late Holocene dust activity and permafrost development

There is considerable uncertainty over the nature and causes of Holocene dust activity in the Arctic, and its links to climatic changes. Loess deposits act as near-source archives of dust deposition and provide a means to address these uncertainties. Here we develop a fully independent age model for a loess core taken in Adventdalen, Svalbard, based on 136 quartz luminescence ages taken at 2 cm intervals. This represents the most detailed luminescence dating analysis undertaken to date on a sedimentary archive. Extensive laboratory tests and stratigraphic consistency indicate that the quartz luminescence ages are reliable. Together with grain size and cryostratigraphic analyses, as well as stratigraphic investigation of an adjacent loess exposure, the exceptional detail of the chronology combined with Bayesian age modelling uniquely allows changes in loess accumulation rates, particle size and permafrost development to be reconstructed over the last 3000 yrs on 101–103 yr timescales. The results show that loess deposition was mostly continuous over this interval, albeit with a short period of reworking or non-aeolian sedimentation during the Little Ice Age. Permafrost development in the loess is dominantly syngenetic, with ice contents increasing with depth. There is considerable variability in loess mass accumulation rate over the late Holocene, with peaks occurring during the last 250 yrs, as well as at 750–900, 1050–1200, 1400–1600, 1900–2450 and possibly 2700–3000 a. These peaks generally coincide with increased coarse silt deposition, potentially suggesting a link with greater wind activity. However, the peaks also seem to coincide with possible warm phases on Svalbard, which would rather imply that temperature-driven sediment availability in glaciofluvial source areas is the main control on dustiness in Adventdalen. In any case, the rates of loess deposition in the Adventdalen core are exceptionally high globally (up to 0.35 cm yr−1/2900 g m−2 yr−1 sedimentation and mass accumulation rates, respectively), and if representative of wider patterns across Svalbard, may suggest that the archipelago is a more important high latitude dust source than previously realised.

A century of human interventions on sediment flux variations in the Danube-Black Sea transition zone

Many deltas around the world have recorded a decreasing sediment input, mostly due to retention in dams constructed on the river or in the river basin. The Danube River has recorded a significant decrease of its sediment supply to the Danube Delta and the NW Black Sea. This study uses 210Pb and 137Cs dating, to investigate the effects of the decreasing sediment flux in lakes, lagoons, delta front and prodelta area. Both the effects of the Iron Gate I and II dams and other local factors are discussed. These results define the period of 1960-1990 as the ‘major anthropic interventions period’ in the Danube Delta. Results show a decrease in siliciclastic flux, especially in lakes, the Sahalin lagoon and the prodelta area and a general increase in the Musura lagoon and the delta front area. Sand content is also shown to decrease in most areas and is replaced by silt. The changes in sediment accumulation rates depend mostly on the hydrological connectivity of the area and the local hydrotechnical works. Overall, the local anthropic interventions in the delta affect sediment flux in the subaerial delta and the delta front, while the prodelta is affected by the overall decrease caused by interventions in the river basin. This study can contribute to improving management strategies in the area and to a better understanding of future research needs in the Danube Delta-Black Sea system.

Vegetation changes and sediment dynamics in the Lake Alaotra region, central Madagascar

Madagascar is known for its high erosion rates in the central highlands, yet the role of human disturbance versus natural processes is not well understood and is a topic of ongoing debate. At present the necessary quantitative data to couple vegetation dynamics and sediment fluxes over time in Madagascar is scarce. This study aims to provide more insight in vegetation changes and sediment transfers over the last millennia in the Lake Alaotra region, and specifically on the role of human disturbances and natural processes. Our vegetation reconstruction is based on pollen records from two lake sediment cores, covering the last 2600 years. Sediment accumulation rates were calculated from cores obtained from the floodplains, from wetlands surrounding the lake, and from Lake Alaotra itself. Our data show an early opening in the landscape, between 2050 and 1700 cal a BP, with a transition from a wooded grassland or woodland/grassland mosaic towards open grassland and an increase in charcoal accumulation rates. (Indirect) human impact is suggested as the main driver for these vegetation changes. Floodplain and wetland sediment accumulation rates only increase in the last 1000 years and peak in the last 400 years. This increased accumulation can mainly be linked to the increased anthropogenic pressure (grazing and farming activities) that triggered increased lavaka (gullies) activity. No changes in accumulation rate were observed in Lake Alaotra, indicating that most sediments are buffered in the floodplains and wetlands. Overall, our pollen and charcoal data suggest an indirect effect of human disturbance on vegetation shifts whilst strong evidence was found for a direct effect of human disturbance on sediment accumulation through intensified use of the grasslands.

Using sediment accumulation rates in floodplain paleochannel lakes to reconstruct climate-flood relationships on the lower Ohio River

Late Holocene flood frequencies on the lower Ohio River were investigated using 14C-based sedimentation rates from three floodplain lakes located in Illinois (Avery Lake), Kentucky (Grassy Pond), and Indiana (Goose Pond). Changes in sediment accumulation rates were attributed to variability in the delivery of overbank sediment to each site as controlled by the frequency of Ohio River flooding. Sedimentation rates reached their lowest values in all three lakes between 400 and 1230 CE, indicating a regional reduction in flood frequencies on the lower Ohio River during a period that included the Medieval Climate Anomaly (MCA; ca. 950–1250 CE). Sedimentation rates increased after ca. 1230 CE and remained moderately high through the Little Ice Age (LIA; 1350–1820 CE) until the onset of extensive land clearance during the early 1800s CE. After 1820 CE, sedimentation rates increased further and were higher than any other time during the late Holocene. A comparison of regional paleoclimatic proxies with the above floodplain sedimentation records shows that Ohio River flooding during the late Holocene was responsive to mean-state changes in atmospheric circulation. During the MCA, when clockwise mean-state atmospheric circulation advected southerly moisture from the Gulf of Mexico into the Ohio River Valley primarily in the form of convective rainstorms, flooding on the Ohio River was least frequent. During the LIA, meridional mean-state atmospheric circulation increased the proportion of midcontinental moisture that was sourced from the northern Pacific and Arctic and delivered as snowfall, hence increasing flooding on the Ohio River. We attribute the increase in Ohio River flooding during the LIA to an increase in snowpack volume across the Ohio River Valley and the watershed-scale integration of runoff during spring snowmelt. Following Euro-American land clearance in the early 1800s, flood frequencies decoupled from this relationship and the lower Ohio River became susceptible to frequent flooding, despite a return to southerly and clockwise synoptic atmospheric conditions. These modern climate-flood dynamics are fundamentally different than those of the paleo-record and suggest that land-use changes – such as deforestation, tile draining, and landscape conversion to intensive row crop agriculture – have fundamentally altered the modern Midwestern hydrologic cycle.

Gas isotope thermometry in the South Pole and Dome Fuji ice cores provides evidence for seasonal rectification of ice core gas records

Abstract. Gas isotope thermometry using the isotopes of molecular nitrogen and argon has been used extensively to reconstruct past surface temperature change from Greenland ice cores. The gas isotope ratios δ15N and δ40Ar in the ice core are each set by the amount of gravitational and thermal fractionation in the firn. The gravitational component of fractionation is proportional to the firn thickness, and the thermal component is proportional to the temperature difference between the top and bottom of the firn column, which can be related to surface temperature change. Compared to Greenland, Antarctic climate change is typically more gradual and smaller in magnitude, which results in smaller thermal fractionation signals that are harder to detect. This has hampered application of gas isotope thermometry to Antarctic ice cores. Here, we present an analytical method for measuring δ15N and δ40Ar with a precision of 0.002 ‰ per atomic mass unit, a two-fold improvement on previous work. This allows us to reconstruct changes in firn thickness and temperature difference at the South Pole between 30 and 5 kyr BP. We find that variability in firn thickness is controlled in part by changes in snow accumulation rate, which is, in turn, influenced strongly by the along-flowline topography upstream of the ice core site. Variability in our firn temperature difference record cannot be explained by annual-mean processes. We therefore propose that the ice core gas isotopes contain a seasonal bias due to rectification of seasonal signals in the upper firn. The strength of the rectification also appears to be linked to fluctuations in the upstream topography. As further evidence for the existence of rectification, we present new data from the Dome Fuji ice core that are also consistent with a seasonal bias throughout the Holocene. Our findings have important implications for the interpretation of ice core gas records. For example, we show that the effects of upstream topography on ice core records can be significant at flank sites like the South Pole – they are responsible for some of the largest signals in our record. Presumably upstream signals impact other flank-flow ice cores such as EDML, Vostok, and EGRIP similarly. Additionally, future work is required to confirm the existence of seasonal rectification in polar firn, to determine how spatially and temporally widespread rectifier effects are, and to incorporate the relevant physics into firn air models.

Bolt loading effects on the structural integrity assessment of defects in industrial components

Applied loads in bolted geometries of safety critical components can vary with time and operating conditions. Structural integrity and remaining life assessments of such components in aging industrial plants must consider the resultant changes in damage accumulation rates and acceptable defect sizes. Two case studies are presented that demonstrate the effect of bolt pre-load on creep and fatigue lives as well as on the acceptability assessments of defects. In the first case the sensitivity of creep damage accumulation and crack propagation rates to bolt pre-load in high temperature flanged connections are considered. Predicted results were found to compare well with actual damage quantified on a high pressure turbine loop pipe flange connection. It was shown that decreased pre-loads, in this case, leads to an increase the allowable safe defect size during assembly at room temperature. In contrast to this the second case study of corrosion fatigue cracking in a boiler water circulating pump illustrates that an increase in bolt pre-load leads to an increase in fatigue initiation life, a decrease in fatigue crack propagation rate and an increase in the acceptable defect size. Strain gauge measurements of bolt and casing strain, which correlated well with finite element calculations, indicated the necessity for close control of bolt pre-load during assembly to ensure specified levels are attained. In both cases metallurgical analysis and structural integrity assessments of cracked and excavated geometries were conducted which enabled limited continued operation of the components after which repairs and/or replacements will be implemented.

Late Cenozoic magnetostratigraphy and paleoenvironmental change in the northeastern Tibetan Plateau: Evidence from a drill core in the Wuwei Basin, NW China

• Late Cenozoic sediments sampled by the WW-01 drillhole in the Wuwei basin were depoisted since ca. 11.15 Ma. • The northeastern Tibetan Plateau experienced rapid uplift at 8.25 and 2.58 Ma. • The aridification in NW China was controlled by the tectonic uplift at ca. 8.25 Ma. Basin deposits of the northeastern Tibetan Plateau provide an ideal record for understanding the uplift of the plateau and the history of aridification in NW China. In this study, we present sedimentology, magnetostratigraphy, and paleoenvironmental indexes from the drill core WW-01 in the Wuwei Basin in the northeastern Tibetan Plateau to reconstruct a long depositional–paleoenvironmental history spanning from ca. 11.15 Ma to the present. Firstly, ages of the Fengle Formation, Guoyuan Formation, and Quaternary sediments are precisely defined through the magnetostratigraphy study of the drill core WW-01. Our results show that the upper age limit of Fengle Formation is 8.25 Ma, Guoyuan Fromation ranges from 8.25 to 2.58 Ma, and the Quaternary sediments span the interval from 2.58 Ma to the present. Secondly, detailed analysis of the sedimentology of the drill core reveals that marked changes in sedimentary environment and accumulation rate occurred at ca. 8.25 and 2.58 Ma, respectively. Our results, combined with regional research, indicate that the initial uplift of the northeastern Tibetan Plateau started at ca. 8.25 Ma and that the latest phase of rapid uplift occurred at ca. 2.58 Ma. In addition, the changes of grain size and magnetic susceptibility in the sediments of the drill core combined with knowledge of the regional paleoenvironment evolution show that NW China underwent gradual aridification from the late Miocene (ca. 8.25 Ma), which is consistent with global cooling at that time. However, tectonic uplift of the northeastern Tibetan Plateau may have been the primary driving force of the aridification between ca. 8.25 and 7.14 Ma.

The benthic foraminiferal response to the mid-Maastrichtian event in the NW-European chalk sea of the Maastrichtian type area

Abstract The mid-Maastrichtian carbon isotope event (MME), dated at ∼69 Ma, reflects a perturbation of the global carbon cycle that, in part, correlates with the enigmatic global extinction of ‘true’ (i.e., non-tegulated) inoceramid bivalves. The mechanisms of this extinction event are still debated. While both the inoceramid extirpation and MME have been recorded in a variety of deep-sea sites, little is known about their expression in epicontinental chalk seas. In order to study the shallow-marine signature of the MME in this epicontinental shelf sea, we have generated quantitative foraminiferal assemblage data for two quarries (Hallembaye, NE Belgium; ENCI, SE Netherlands) in the Maastrichtian type area, complemented by a species-specific benthic δ13C record. In contrast to deep-sea records, no significant changes in benthic foraminiferal assemblages and benthic foraminiferal accumulation rates are observed across the MME in the type-Maastrichtian area. At the Hallembaye quarry, the otherwise rare endobenthic species Cuneus trigona reaches a transient peak abundance of 33.3% at the onset of the MME, likely caused by a local transient change in organic matter flux to the seafloor. Nevertheless, high and near-constant species evenness shows that neither oxygen nor organic matter flux was limited across the extinction level or during the MME. Benthic foraminiferal data from the uppermost part of the studied section, above the MME, indicate a significant increase in food supply to the seafloor. Decreased amounts of terrigenous elements across this interval document a lesser riverine or aeolian influx, which means that the increased benthic productivity is linked to a different origin. Potentially, the continuous precipitation of chalk under nutrient-poor conditions in the Late Cretaceous chalk sea was enabled by efficient nutrient recycling in the water column. In shallower depositional settings, nutrient recycling took place closer to the seafloor, which allowed more organic matter to reach the bottom. These results provide insights in the importance of nutrient cycling for biological productivity in the NW-European chalk sea.

Numerical Study on Vibration Response and Fatigue Damage of Axial Compressor Blade Considering Aerodynamic Excitation

Axial compressor blades with a deformed initial torsion angle caused by aerodynamic excitation resonated at the working speed and changed the rule of fatigue damage accumulation. The fatigue life of a blade has a prediction error, even causing serious flight accidents if the effect of torque causing damage deterioration of the blade fatigue life is neglected. Therefore, in this paper, a uniaxial non-linear fatigue damage model was modified using the equivalent stress with torsional shear stress, and the proposed fatigue model including the torsional moment was used to study the compressor blade fatigue life. Then, the blade numerical simulation model was established to calculate the vibration characteristics under complex loads of airflow excitation and a rotating centrifugal force. Finally, the blade fatigue life under actual working conditions was predicted using the modified fatigue model. The results show that the interaction between centrifugal and aerodynamic loads affects the natural frequency, as the frequencies in modes dominated by bending deformation decreased whereas those dominated by torsional deformation increased. Furthermore, the blade root of the suction surface showed stress concentration, but there is an obvious difference of stress distribution and amplitude between the normal stress and the equivalent stress including torsional shear stress. The additional consideration of the torsional shear stress decreased the predicted fatigue life by 4.5%. The damage accumulation rate changes with the loading cycle, and it accelerates fast for the last 25% of the cycle, when the blade fracture may occur at any time. Thus, the aerodynamic excitation increased the safety factor of blade fatigue life prediction.

Sedimentation and organic content in the mires and other sites of sediment accumulation in the Sydney region, eastern Australia, in the period after the Last Glacial Maximum

This research reports on a synthesis of radiocarbon (14C) dates and the organic content from a variety of depositional sites in a relatively small region in humid eastern Australia centred on Sydney. We focused on basal dates, changes in accumulation rates and the organic content of these sediment records in the period post-dating 21 thousand years ago to make inferences about past environmental conditions, or to infer the timing of past environmental change. We found that low rates of sediment and organic accumulation at the Last Glacial Maximum continued well into the late Pleistocene. The average rate of sediment deposition and organic content increased from about 14.5 calibrated kiloanni before present (cal ka BP), perhaps coincident with Meltwater Pulse 1A, but this was then checked by dry conditions during the Antarctic Climatic Reversal chronozone. An abrupt increase in the average rate of sediment accumulation coincided with the Pleistocene-Holocene boundary (at 11.7 cal ka BP), and this continued until about 9.2 cal ka BP, largely coinciding with the Antarctic thermal maximum, and probably reflecting reduced moisture availability in the Sydney region. Indication of depressed temperature and a more positive moisture availability, from about 9 to 7.6 cal ka BP, witnessed the fastest increase in the number of sites than at any other time. An overall drier early Holocene abruptly altered at about 7.5 cal ka BP and a mid-Holocene ‘optimum’ in moisture availability extended to 6.2 cal ka BP. The compilation of organic contents of the mid-late Holocene suggests environmental variability, but El Niño frequency or strength is not implicated as a driving force. Increased organic productivity, especially after 2.8 cal ka BP, corresponded to a peak in summer insolation, and associated seasonality of insolation and this is likely to have resulted in increased, or more consistent, summer rainfall and easterly air flow into the Sydney region. In contrast to previous generalisations about changes in south-eastern Australia during the Holocene, which have often relied on palaeoenvironmental records from further south, the southward migration of the intertropical convergence zone during the Holocene had vastly different synoptic outcomes in the Sydney region, with the early Holocene drier as continental air dominated, and the late Holocene wetter, as the synoptic conditions saw more tropical and easterly airflow. This work demonstrates the danger in making generalisations across regions and highlights the utility of the compilation of data at a homoclimatic, regional scale.

Linking testate amoeba assemblages to paleohydrology and ecosystem function in Holocene peat records from the Hudson Bay Lowlands, Ontario, Canada

Peat cores from boreal bog and fen sites in the Hudson Bay Lowlands of Northern Ontario, Canada, were analysed to calculate Holocene carbon accumulation rates, and to show how testate amoeba taxonomic assemblages, inferred depths to water table, and four morpho-traits that may be linked to function (mixotrophy, aperture size, aperture position, and biovolume) changed since peatland initiation. Carbon accumulation rates were on average higher for the Holocene in the fen record (19.4 g C m−2 yr−1) in comparison with the bog record (15.7 g C m−2 yr−1), which underwent a fen-to-bog transition around 6900 cal yr BP. Changes in rates of carbon accumulation were most strongly driven by changes in rates of peat vertical accretion, with more rapid rates in the fen record. Carbon accumulation rates were highest following peatland initiation when reconstructed water tables were highest, and in the late Holocene, when water table positions were variable. Taxa with larger biovolumes and apertures were generally more abundant when reconstructed water tables were higher, most notably following peatland initiation. Mixotrophic taxa were more prevalent in drier conditions and in the bog record. Changing frequencies of morpho-traits suggest that testate amoebae may occupy a higher trophic position in the microbial food web during wetter periods, signaling the possibility of internal feedbacks between peatland ecohydrology and critical ecosystem functions including long-term carbon accumulation.

210Pb-derived sediment accumulation rates across the Wider Caribbean Region

The Wider Caribbean Region is an important tourist destination where agricultural, industrial and shipping activities are also carried on. Coastal zones are heavily populated and receive a high human pressure; however, few monitoring programmes allow assessing long-term anthropogenic impact trends in these areas, which are especially useful for integrated management programs. Through the support of the International Atomic Energy Agency (project RLA/7/012), sediment core activities of 210Pb and 137Cs were used to evaluate changes in sedimentation rates in 11 relevant coastal areas of the region, where environmental information is scarce, but needed to support national environmental policies. Most 210Pb activity profiles were atypical, attributed to non-steady sedimentation conditions; whereas 137Cs activity profiles, showing very low values, were of little help for 210Pb-dating corroboration. Results evidenced conspicuous changes in mass accumulation rates (MAR), specially through the Anthropocene (i.e. since ~1950s) in most cases, attributed to deforestation and land erosion (one of the clearest indicators of global change), and the input of urban and industrial untreated wastes. The recent MAR decrease in Havana Bay (Cuba) was attributed to the implementation of environmental policies, which showed that 210Pb-derived reconstruction of environmental changes is also useful to verify the effectiveness of management programs to control land-derived erosion and siltation issues. Since siltation can be detrimental to valuable coastal resources around the world, retrospective evaluations of sedimentation rates, based on 210Pb-dated cores, are highly recommended to assist integrated coastal zone management programs in the region and elsewhere.

Holocene evolution of the wave-dominated embayed Moruya coastline, southeastern Australia: Sediment sources, transport rates and alongshore interconnectivity

Sediment budgets on wave-dominated coastlines are important in determining shoreline behaviour and are primarily inherited from geological-scale coastal evolutionary history. Sediment compartments provide a framework to conceptualise and investigate sediment budgets over a range of time and space scales. This study aims to assess the sediment budget for a secondary coastal compartment on the New South Wales (NSW) south coast ∼26 km in length and containing five adjacent but discrete Holocene coastal bay barriers: Barlings Beach, Broulee Beach, Bengello Beach, Moruya Heads Beach and Pedro Beach. Building on earlier morphostratigraphic studies, a new series of Optically Stimulated Luminescence (OSL) ages are presented for foredune ridge sequences at previously un-dated sites. Additional Ground Penetrating Radar (GPR) transects complement earlier stratigraphic datasets, and seamless topographic and bathymetric LiDAR datasets provide insight into subaerial coastal deposits and inner shelf morphology in this region. The results demonstrate that barriers within the compartment have two different sediment sources. The barriers are dominated by shoreface supply of quartz-rich sand transported onshore as shoreface morphology evolved towards equilibrium. Skeletal carbonate sand became an important component of the sediment budget for the northern Barlings and Broulee beaches after ∼3000 years ago. Shoreline progradation at Bengello Beach has been steady throughout the mid-to late- Holocene. Bengello contains the largest volume of Holocene sand and accreted at an average rate of 3.1 m3/m/yr (for the current shoreline length). The other barrier systems have experienced changes in sediment accumulation rate as their shorelines prograded seaward resulting in changes to their alongshore interconnectivity. Rapid filling of the Pedro Beach embayment by ∼4000 years ago initiated headland bypassing and northward sand transport to Moruya Heads Beach which only then commenced progradation. In contrast, as Broulee and Bengello Beaches prograded they converged in the lee of Broulee Island forming a tombolo which led to division of the former continuous shoreline into two. A marked increase in skeletal carbonate content at Broulee occurred after this separation attesting to the restriction of the southern quartz-sand source replaced by local carbonate production. This study emphasises the importance of understanding the long-term temporal variability in sediment budget and embayment interconnectivity in determining shoreline response to changing boundary conditions such as sea level and wave climate as well as contemporary anthropogenic influences.

Architectural evolution of a mixed-influenced deltaic succession: Lower-to-Middle Ordovician Armorican Quartzite in the southwest Central Iberian Zone, Penha Garcia Formation (Portugal)

Facies stacking patterns and stratigraphic relationships resulting from the interaction of fluvial and wave processes, along with the paleoshoreline orientation and key surfaces, are essential to understand the temporal changes in the rate of change of accommodation space (A) versus sediment supply rate (S). High-frequency sea-level fluctuations in deltaic systems are controlled by changing accommodation and accumulation, which are explained mainly by autocyclic or allocyclic mechanisms. In deltaic systems, changes in the A/S ratio can be showed by significant variations of the internal facies architecture and the external morphology of the delta complex. These criteria have been used to investigate the relationship between autocyclic and allocyclic processes on the architectural evolution of a mixed river- and wave-influenced asymmetrical delta during the Lower-to-Middle Ordovician in the southwest Central Iberian Zone, in Portugal. Relying on the sedimentary and ichnological characteristics, the herein defined Penha Garcia Formation is classified into two main groups of facies associations, which are interpreted as deposited in a mixed asymmetrical delta with a trend of along-strike variations between wave-dominated strandplain (updrift) and river-dominated deltaic settings (downdrift). The vertical stacking arrangements of parasequences led to the identification of five depositional phases (I to V). Detailed analysis of geometry and internal architecture of the depositional phases along depositional strike shows a highly variable number of shallowing-upward cycles and facies thicknesses/heterogeneity on the updrift and downdrift side due to changes in rates of accumulation and hydrodynamic processes. The stratigraphic architectural style of the depositional phases I to V, and the trend of the total regressive ascending shoreline trajectory, are evidences that the deposition of the Penha Garcia Formation likely took place under an increasing rate of accommodation due to long-term relative sea-level rise (allocyclic), and high subsidence rates coupled with an increase in sediment supply, which could have been locally amplified by compaction of the prodelta-related muddy beds (autocyclic). This study suggests that in evaluating the autocyclic mechanisms on deltaic processes in short-time scales, there is a remarkable difference in terms of its impact on the internal variability of the depositional phases, both in the updrift and downdrift regions of mixed-influenced asymmetrical deltas. The most important reasons for the different effects of autocyclic mechanisms can be related to facies-dependent differential compaction or local changes in subsidence pattern, differences in the proximity to the distributary channel system, and differences in the influence of intrinsic processes of storm and wave reworking (wave-sweeping mechanisms).

Demise of the Middle Jurassic carbonate platform: Responses to sea‐level fall in the Qiangtang Basin, Eastern Tethys

Many studies have been focused on the development of carbonate platforms, however, the controlling factors of their evolution are still unclear. The QTKT1 well, drilled in 2016 by the Chengdu Center of the China Geological Survey at the Northern Qiangtang Depression, has allowed further studies of Jurassic environments and resources in the Eastern Tethys. In this study, we investigate variations in spectral gamma‐ray logs and CaCO3 content and perform a cyclostratigraphic analysis in the Xiali mudstones and Buqu limestones and Xiali mudstone to analyse causes for the demise of the Middle Jurassic carbonate platform in the Qiangtang Basin. The concentrations of Th, K, U, and Th/U and Th/K ratios increase suddenly from the Buqu Formation to the Xiali Formation, suggesting increased terrigenous input and/or decreased carbonate production rates. Cyclostratigraphic analysis detects the existence of astronomical cycles and an abrupt change in sediment accumulation rates within the target intervals. Combined with sedimentary facies analysis, our research suggests that the demise of the Middle Jurassic carbonate platform may have been caused by terrigenous detrital inputs into the Qiangtang Basin. High‐frequency sea‐level fluctuations increased terrestrial inputs and carbonate production rates at the orbital scale. The regression happened before the facies change and controlled terrestrial inputs at a larger scale, which resulted in the demise of the carbonate platforms. Contrary to the Western Tethys, a regression took place from the Bathonian to Callovian ages in the Qiangtang Basin, Eastern Tethys, which increased the exposure levels. The large exposure led to significant erosion, accelerated detrital input from the land to the Northern Qiangtang Depression, reduced carbonate production as well as resulted in the demise of the Buqu carbonate platform. The relative sea‐level fall is mainly the result of the regional tectonism during this period.