81 results on '"Leng MJ"'
Search Results
2. Dynamics of sediment flux to a bathyal continental margin section through the Paleocene-Eocene Thermal Maximum
- Author
-
Dunkley Jones, T, Manners, HR, Hoggett, M, Turner, SK, Westerhold, T, Leng, MJ, Pancost, RD, Ridgwell, A, Alegret, L, Duller, R, and Grimes, ST
- Subjects
Paleontology ,Physical Geography and Environmental Geoscience - Abstract
The response of the Earth system to greenhouse-gas-driven warming is of critical importance for the future trajectory of our planetary environment. Hyperthermal events - past climate transients with global-scale warming significantly above background climate variability - can provide insights into the nature and magnitude of these responses. The largest hyperthermal of the Cenozoic was the Paleocene-Eocene Thermal Maximum (PETM ∼ 56 Ma). Here we present new high-resolution bulk sediment stable isotope and major element data for the classic PETM section at Zumaia, Spain. With these data we provide a new detailed stratigraphic correlation to other key deep-ocean and terrestrial PETM reference sections. With this new correlation and age model we are able to demonstrate that detrital sediment accumulation rates within the Zumaia continental margin section increased more than 4-fold during the PETM, representing a radical change in regional hydrology that drove dramatic increases in terrestrial-to-marine sediment flux. Most remarkable is that detrital accumulation rates remain high throughout the body of the PETM, and even reach peak values during the recovery phase of the characteristic PETM carbon isotope excursion (CIE). Using a series of Earth system model inversions, driven by the new Zumaia carbon isotope record, we demonstrate that the silicate weathering feedback alone is insufficient to recover the PETM CIE, and that active organic carbon burial is required to match the observed dynamics of the CIE. Further, we demonstrate that the period of maximum organic carbon sequestration coincides with the peak in detrital accumulation rates observed at Zumaia. Based on these results, we hypothesise that orbital-scale variations in subtropical hydro-climates, and their subsequent impact on sediment dynamics, may contribute to the rapid climate and CIE recovery from peak-PETM conditions.
- Published
- 2018
3. In flux: Annual transport and deposition of suspended heavy metals and trace elements in the urbanised, tropical Red River Delta, Vietnam
- Author
-
Roberts, LR, Do, NT, Panizzo, VN, Taylor, S, Watts, M, Hamilton, E, McGowan, Suzanne, Trinh, Duc A, Leng, MJ, Salgado, J, Roberts, LR, Do, NT, Panizzo, VN, Taylor, S, Watts, M, Hamilton, E, McGowan, Suzanne, Trinh, Duc A, Leng, MJ, and Salgado, J
- Abstract
Due to the depositional environment, river deltas are said to act as filters and sinks for pollutants. However, many deltas are also densely populated and rapidly urbanizing, creating new and increased sources of pollutants. These sources pose the risk of tipping these environments from pollution sinks to sources, to the world's oceans. We provide detailed seasonal and annual assessments of metal contaminants in riverine suspended particulate matter (SPM) across the densely populated Red River Delta (RRD), Vietnam. The global contributions of elements from the RRD are all 40) and concentrations of As higher than national regulation limits (>17 mg/Kg) at all sites other than one upstream, agricultural-dominated tributary in the dry season. These ‘hotspots’ are characterised by high inputs of organic matter (e.g. manure fertiliser and urban wastewater), which influences elemental mobility in the particulate and dissolved phases, and are potentially significant sources of pollution downstream. In addition, in the marine and fresh water mixing zone, salinity effects metal complexation with organic matter increasing metals in the particulate phase. Our calculations indicate that the delta is currently acting as a pollutant sink (as determined by high levels of pollutant deposition ∼50%). However, increased in-washing of pollutants and future projected increases in monsoon intensity, saline intrusion, and human activity could shift the delta to become a source of toxic metals. We show the importance of monitoring environmental parameters (primarily dissolved organic matter and salinity) in the RRD to assess the risk of transport and accumulation of toxic metals in the delta sediments, which can lead to net-increases in anthropogenic pollution in the coastal zone and the incorporation of toxic elements in the food chain.
- Published
- 2022
4. Reconstructing postglacial hydrologic and environmental change in the eastern Kenai Peninsula lowlands using proxy data and mass balance modeling
- Author
-
Broadman E, Kaufman DS, Anderson RS, Bogle S, Ford M, Fortin D, Henderson ACG, Lacey JH, Leng MJ, McKay NP, Muñoz SE
- Published
- 2022
- Full Text
- View/download PDF
5. A landscape perspective of Holocene organic carbon cycling in coastal SW Greenland lake-catchments
- Author
-
Anderson, NJ, Leng, MJ, Osburn, CL, Fritz, SC, Law, AC, and McGowan, S
- Subjects
GB ,Global and Planetary Change ,Archaeology ,Geology ,Ecology, Evolution, Behavior and Systematics - Abstract
Arctic organic carbon (OC) stores are substantial and have accumulated over millennia as a function of changes in climate and terrestrial vegetation. Arctic lakes are also important components of the regional C-cycle as they are sites of OC production and CO2 emissions but also store large amounts of OC in their sediments. This sediment OC pool is a mixture derived from terrestrial and aquatic sources, and sediment cores can therefore provide a long-term record of the changing interactions between lakes and their catchments in terms of nutrient and C transfer. Sediment carbon isotope composition (δ13C), C/N ratio and organic C accumulation rates (C AR) of 14C-dated cores covering the last ∼10,000 years from six lakes close to Sisimiut (SW Greenland) are used to determine the extent to which OC dynamics reflect climate relative to lake or catchment characteristics. Sediment δ13C ranges from −19 to −32‰ across all lakes, while C/N ratios are 20 (mean = 12), values that indicate a high proportion of the organic matter is from autochthonous production but with a variable terrestrial component. Temporal trends in δ13C are variable among lakes, with neighbouring lakes showing contrasting profiles, indicative of site-specific OC processing. The response of an individual lake reflects its morphometry (which influences benthic primary production), the catchment:lake ratio, and catchment relief, lakes with steeper catchments sequester more carbon. The multi-site, landscape approach used here highlights the complex response of individual lakes to climate and catchment disturbance, but broad generalisations are possible. Regional Neoglacial cooling (from ∼5000 cal yr BP) influenced the lateral transfer of terrestrial OC to lakes, with three lakes showing clear increases in OC accumulation rate. The lakes likely switched from being autotrophic (i.e. net ecosystem production > ecosystem respiration) in the early Holocene to being heterotrophic after 5000 cal yr BP as terrestrial OC transfer increased.
- Published
- 2018
- Full Text
- View/download PDF
6. Tree height strongly affects estimates of water-use efficiency responses to climate and CO2 using isotopes
- Author
-
Brienen, RJW, Gloor, E, Clerici, S, Newton, R, Arppe, L, Boom, A, Bottrell, S, Callaghan, M, Heaton, T, Helama, S, Helle, G, Leng, MJ, Mielikäinen, K, Oinonen, M, Timonen, M, Finnish Museum of Natural History, and Natural Sciences Unit
- Subjects
1171 Geosciences ,EUROPEAN FORESTS ,Science ,PINUS-SYLVESTRIS ,GROWTH DECLINE ,RAIN-FOREST ,PAST CENTURY ,RING DELTA-C-13 ,FAGUS-SYLVATICA ,C-3 PLANTS ,ATMOSPHERIC CO2 ,1172 Environmental sciences ,CARBON-DIOXIDE CONCENTRATIONS - Abstract
Various studies report substantial increases in intrinsic water-use efficiency (Wi), estimated using carbon isotopes in tree rings, suggesting trees are gaining increasingly more carbon per unit water lost due to increases in atmospheric CO2. Usually, reconstructions do not, however, correct for the effect of intrinsic developmental changes in Wi as trees grow larger. Here we show, by comparingWi across varying tree sizes at one CO2 level, that ignoring such developmental effects can severely affect inferences of trees' Wi. Wi doubled or even tripled over a trees' lifespan in three broadleaf species due to changes in tree height and light availability alone, and there are also weak trends for Pine trees. Developmental trends in broadleaf species are as large as the trends previously assigned to CO2 and climate. Credible future tree ring isotope studies require explicit accounting for species-specific developmental effects before CO2 and climate effects are inferred.
- Published
- 2017
7. Statoliths of the whelk Buccinum undatum: a novel age determination tool
- Author
-
Hollyman, PR, primary, Leng, MJ, additional, Chenery, SRN, additional, Laptikhovsky, VV, additional, and Richardson, CA, additional
- Published
- 2018
- Full Text
- View/download PDF
8. Vertical distribution and diurnal migration of atlantid heteropods
- Author
-
Wall-Palmer, D, primary, Metcalfe, B, additional, Leng, MJ, additional, Sloane, HJ, additional, Ganssen, G, additional, Vinayachandran, PN, additional, and Smart, CW, additional
- Published
- 2018
- Full Text
- View/download PDF
9. Atlantic overturning circulation and Agulhas leakage influences on southeast Atlantic upper ocean hydrography during marine isotope stage 11
- Author
-
Dickson, AJ, Leng, MJ, Maslin, MA, Sloane, HJ, Green, J, Bendle, JA, McClymont, EL, and Pancost, RD
- Abstract
Climate dynamics during the marine isotope stage (MIS) 11 interglacial may provide information about how the climate system will evolve under the conditions of low-amplitude orbital forcing that are also found during the late Holocene. New stable isotope and alkenone data are presented from southeast Atlantic Ocean Drilling Program Site 1085, providing detailed information on interglacial climate evolution and the impacts of Atlantic meridional overturning circulation (MOC) and Agulhas leakage on the regional upper ocean hydrography. The data suggest that although warm surface ocean conditions were maintained at approximate Holocene levels for 40,000 years during MIS 11, subsurface temperature and salinity recorded by deeper-dwelling planktonic foraminifera species were maintained at their highest values for only 7000-8000 years. Surface water temperature and salinity data suggest that the interocean exchange of warm, salty waters into the southeast Atlantic Ocean was directly related to changes in the activity of the MOC during the study interval. Specifically, transient regional warming events during periods of weakened overturning circulation may have been amplified by the continuous interocean exchange of warm, salty Indian Ocean waters that primed the MOC for abrupt resumptions into a vigorous mode of operation. Conversely, a peak in interocean exchange at the end of the MIS 11 interglacial optimum may reflect enhanced trade wind forcing of surface waters whose export to the North Atlantic Ocean could have contributed to renewed ice sheet buildup during the MIS 11 to 10 glacial inception. Copyright 2010 by the American Geophysical Union.
- Published
- 2016
10. Mid-depth South Atlantic Ocean circulation and chemical stratification during MIS-10 to 12: Implications for atmospheric CO 2
- Author
-
Dickson, AJ, Leng, MJ, and Maslin, MA
- Abstract
A detailed record of benthic foraminifera carbon isotopes from the intermediate-depth South East Atlantic margin shows little glacial-interglacial variability between MIS-12 to MIS-10, suggesting that Northern Atlantic deep waters consistently penetrated to at least 30°S. Millennial scale increases in either the mass or flux of northern-sourced deep waters over the core site occurred alongside reductions in Lower North Atlantic Deep Water recorded in North Atlantic sediment cores and show that the lower and intermediate limb of the Atlantic deepwater convective cell oscillated in anti-phase during previous glacial periods. In addition, a 500 yr resolution record of the Cape Basin intermediate-deep δ 13C gradient shows that a reduction in deep Southern Ocean ventilation at the end of MIS-11 was consistent with a modeled CO 2 drawdown of ∼21-30 ppm. Further increases in the Southern Ocean chemical divide during the transition into MIS-10 were completed before minimum CO 2 levels were reached, suggesting that other mechanisms such as alkalinity changes were responsible for the remaining ∼45 ppm drawdown. © Author(s) 2008.
- Published
- 2016
11. Low-latitude Holocene hydroclimate derived from lake sediment flux and geochemistry
- Author
-
Parker, AG, Preston, GW, Parton, A, Walkington, H, Jardine, PE, Leng, MJ, and Hodson, MJ
- Subjects
Holocene ,Arabia ,palaeolake ,sediment flux ,humanities ,geochemistry - Abstract
This study investigates hydrological responses to climatic shifts using sediment flux data derived from two dated palaeolake records in southeast (SE) Arabia. Flux values are generally low during the early Holocene humid period (EHHP) (~9.0 to 6.4 k cal a BP) although several short-lived pulses of increased detrital input are recorded, the most prominent of which is dated between ~8.3 and 7.9 k cal a BP. The EHHP is separated from the mid-Holocene humid period (MHHP) (~5.0 to 4.3 k cal a BP) by a phase of increased sediment flux and aridity, which began between ~6.4 and 5.9 k cal a BP and peaked between ~5.2 and 5.0 k cal a BP. The termination of the MHHP is marked by a phase of high detrital sediment flux between ~4.3 and 3.9 k cal a BP. Whilst long-term shifts in climate are most likely linked to changes in the summer position of the Intertropical Convergence Zone (ITCZ) and associated Indian and African monsoon systems, it is noted that the abrupt, short-term phases of aridity observed in both records are coeval with intervals of rapid climate change globally, which triggered non-linear, widespread landscape reconfigurations throughout SE Arabia.
- Published
- 2016
12. Stable isotope signatures reveal small-scale spatial separation in populations of European sea bass
- Author
-
Cambiè, G, primary, Kaiser, MJ, additional, Marriott, AL, additional, Fox, J, additional, Lambert, G, additional, Hiddink, JG, additional, Overy, T, additional, Bennet, SA, additional, Leng, MJ, additional, and McCarthy, ID, additional
- Published
- 2016
- Full Text
- View/download PDF
13. The tempo of Holocene climatic change in the eastern Mediterranean region: new high-resolution crater-lake sediment data from central Turkey
- Author
-
Reed, JM, Leng, MJ, Kuzucuoglu, C, Fontugne, M, Bertaux, J, Bottema, S, Black, S, Hunt, E, Karabiyikoglu, M, Woldring, H., and Groningen Institute of Archaeology
- Subjects
Turkey ,Holocene ,hydrothermalism ,CENTRAL ANATOLIA ,DI-MONTICCHIO ,RECORD ,Mediterranean ,LACUSTRINE ,diatoms ,KONYA BASIN ,crater lake ,pollen ,TOTAL-SAMPLE DISSOLUTION ,SAPROPEL S1 ,RECONSTRUCTION ,VEGETATION ,mineralogy ,isotopes - Abstract
This study presents results from a multi-proxy analysis of cores taken in a crater-lake sequence from Eski Acigol in central Turkey which cover the period from pre-c. 16000 cal. yr BP to the present. The sediments comprise an upper unit of generally non-laminated, banded to massive silts and peats of mid- to late-Holocene age, overlying a laminated unit of late-Pleistocene to early/mid-Holocene age. The laminae, comprising mainly aragonite, amorphous silica (diatom frustules) and organic matter were formed in a relatively deep, dilute, meromictic lake. Pollen data indicate an abrupt replacement of Artemisia-chenopod steppe by grass-oak-terebinth parkland during the period of laminae deposition, marking the start of the Holocene. A gradual increase in tree pollen during the early Holocene came to an end c. 6500 cal. yr BP (U-series and adjusted C-14 timescale), when mesic deciduous taxa declined at the same time as lake levels fell. Human impact on regional vegetation is inferred from a sharp decline in oak around 4500-4000 cal. yr BP. Diatom, isotopic and mineralogical data indicate that during the second half of the Holocene the lake became relatively shallow and oscillated between fresh and brackish/evaporated water conditions. The contrast between wetter early- and drier late-Holocene climatic conditions is matched by other eastern and central Mediterranean proxy climate data. While the Eski Acigol sequence resembles Holocene hydroclimatic changes in the Saharo-Arabian zone and was also apparently linked to orbital forcing, it is unlikely to have had the same direct cause, i.e., an expansion and subsequent retreat of monsoon rainfall.
- Published
- 2001
14. The Potential of Oxygen Isotopes in Diatoms as a Paleoclimate Indicator in Lake Sediments
- Author
-
Lamb, Angela L, primary, Leng, MJ, additional, Barker, PA, additional, and Morley, DW, additional
- Published
- 2004
- Full Text
- View/download PDF
15. Enhanced glacial discharge from the eastern Antarctic Peninsula since the 1700s associated with a positive Southern Annular Mode
- Author
-
Dickens, WA, Kuhn, G, Leng, MJ, Graham, AGC, Dowdeswell, JA, Meredith, MP, Hillenbrand, C-D, Hodgson, DA, Roberts, SJ, Sloane, H, and Smith, JA
- Subjects
13. Climate action ,37 Earth Sciences ,3705 Geology ,3709 Physical Geography and Environmental Geoscience ,3702 Climate Change Science - Abstract
The Antarctic Peninsula Ice Sheet is currently experiencing sustained and accelerating loss of ice. Determining when these changes were initiated and identifying the main drivers is hampered by the short instrumental record (1992 to present). Here we present a 6,250 year record of glacial discharge based on the oxygen isotope composition of diatoms (δ18Odiatom) from a marine core located at the north-eastern tip of the Antarctic Peninsula. We find that glacial discharge - sourced primarily from ice shelf and iceberg melting along the eastern Antarctic Peninsula - remained largely stable between ~6,250 to 1,620 cal. yr BP, with a slight increase in variability until ~720 cal. yr. BP. An increasing trend in glacial discharge occurs after 550 cal. yr BP (A.D. 1400), reaching levels unprecedented during the past 6,250 years after 244 cal. yr BP (A.D. 1706). A marked acceleration in the rate of glacial discharge is also observed in the early part of twentieth century (after A.D. 1912). Enhanced glacial discharge, particularly after the 1700s is linked to a positive Southern Annular Mode (SAM). We argue that a positive SAM drove stronger westerly winds, atmospheric warming and surface ablation on the eastern Antarctic Peninsula whilst simultaneously entraining more warm water into the Weddell Gyre, potentially increasing melting on the undersides of ice shelves. A possible implication of our data is that ice shelves in this region have been thinning for at least ~300 years, potentially predisposing them to collapse under intensified anthropogenic warming.
16. The changing Amazon hydrological cycle – inferences from over 200 years of tree-ring oxygen isotope data
- Author
-
Baker, JCA, Cintra, BBL, Gloor, M, Boom, A, Neill, D, Clerici, S, Leng, MJ, Helle, G, and Brienen, RJW
17. Seasonal variation of trace element and isotopic composition in the shell of a coastal mollusk, Mactra isabelleana
- Author
-
Leng, Mj and Nicholas J G Pearce
18. Investigating the potential of oxygen-isotope records from anthropogenic lakes as tracers of 20th century climate change.
- Author
-
Tindall, JM, Holmes, J, Candy, I, Leng, MJ, Langdon, P, Fonville, T, and Sear, DA
- Subjects
- *
EFFECT of human beings on climate change , *OXYGEN isotopes , *CLIMATE change , *TWENTIETH century , *LAKES , *LAKE sediments - Abstract
Historical climate change in southern England was investigated using ostracod oxygen-isotope (δ18O) records from two anthropogenic lakes in Hampshire, southern England. A strong relationship is observed between δ18Oostracod, δ18Oprecipitation and δ18Olake_water in the contemporary environment and therefore δ18Oostracod from the sedimentary record of these systems has the potential to reflect past climate variability. The possibility of these sites to act as archives of climate change through δ18Oostracod analysis is explored through the study of lake sediment cores that cover the period from the early 20th century onwards. Both lakes showed similar directionality of shifts in δ18Oostracod over this period, suggesting common driving mechanisms. Comparing δ18Oostracod timeseries to meteorological data is challenging in part because of the complexity with which climate parameters are recorded in the δ18Olake_water and consequently within lacustrine carbonates. Our findings highlight the potential of sediments from anthropogenic lakes to act as archives of past climate and indicate they may be an important resource for generating climatic reconstructions across the medieval to instrumental period, which the sediments of many anthropogenic lakes cover. Such climate reconstructions would greatly improve our spatial and temporal understanding of climate variability where instrumental data are unavailable and other natural archives are scarce. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF
19. Oceanic Anoxic Event 2 triggered by Kerguelen volcanism.
- Author
-
Walker-Trivett CA, Kender S, Bogus KA, Littler K, Edvardsen T, Leng MJ, Lacey J, Riding JB, Millar IL, and Wagner D
- Abstract
Large Igneous Provinces (LIPs) are associated with global warming and carbon cycle perturbations during Oceanic Anoxic Event 2 (OAE2, ~94 Ma) and the Mid-Cenomanian Event (MCE, ~96.5 Ma). However, there is still no consensus on the role volcanism played as a trigger, or its source - previously ascribed to the Caribbean LIP or High Arctic LIP. Here, we use Mentelle Basin sedimentary mercury (Hg) concentrations to determine the timing of volcanism, and neodymium (Nd) and strontium (Sr) isotopes for sedimentary provenance. High Hg concentrations compared to Northern Hemisphere records, and a shift to radiogenic Nd isotopes, indicates Kerguelen LIP volcanic activity and plateau uplift occurred in the lead up to and within OAE2. Whilst we find limited evidence that a volcanic event caused the MCE, pulsed Hg spikes before and during OAE2 imply volcanic emissions were key in driving climate and carbon cycle changes and triggering OAE2., (© 2024. The Author(s).)
- Published
- 2024
- Full Text
- View/download PDF
20. Multi-proxy evidence for sea level fall at the onset of the Eocene-Oligocene transition.
- Author
-
De Lira Mota MA, Dunkley Jones T, Sulaiman N, Edgar KM, Yamaguchi T, Leng MJ, Adloff M, Greene SE, Norris R, Warren B, Duffy G, Farrant J, Murayama M, Hall J, and Bendle J
- Abstract
Continental-scale expansion of the East Antarctic Ice Sheet during the Eocene-Oligocene Transition (EOT) is one of the largest non-linear events in Earth's climate history. Declining atmospheric carbon dioxide concentrations and orbital variability triggered glacial expansion and strong feedbacks in the climate system. Prominent among these feedbacks was the repartitioning of biogeochemical cycles between the continental shelves and the deep ocean with falling sea level. Here we present multiple proxies from a shallow shelf location that identify a marked regression and an elevated flux of continental-derived organic matter at the earliest stage of the EOT, a time of deep ocean carbonate dissolution and the extinction of oligotrophic phytoplankton groups. We link these observations using an Earth System model, whereby this first regression delivers a pulse of organic carbon to the oceans that could drive the observed patterns of deep ocean dissolution and acts as a transient negative feedback to climate cooling., (© 2023. Springer Nature Limited.)
- Published
- 2023
- Full Text
- View/download PDF
21. Tracing the impacts of recent rapid sea ice changes and the A68 megaberg on the surface freshwater balance of the Weddell and Scotia Seas.
- Author
-
Meredith MP, Povl Abrahamsen E, Alexander Haumann F, Leng MJ, Arrowsmith C, Barham M, Firing YL, King BA, Brown P, Alexander Brearley J, Meijers AJS, Sallée JB, Akhoudas C, and Tarling GA
- Abstract
The Southern Ocean upper-layer freshwater balance exerts a global climatic influence by modulating density stratification and biological productivity, and hence the exchange of heat and carbon between the atmosphere and the ocean interior. It is thus important to understand and quantify the time-varying freshwater inputs, which is challenging from measurements of salinity alone. Here we use seawater oxygen isotopes from samples collected between 2016 and 2021 along a transect spanning the Scotia and northern Weddell Seas to separate the freshwater contributions from sea ice and meteoric sources. The unprecedented retreat of sea ice in 2016 is evidenced as a strong increase in sea ice melt across the northern Weddell Sea, with surface values increasing approximately two percentage points between 2016 and 2018 and column inventories increasing approximately 1 to 2 m. Surface meteoric water concentrations exceeded 4% in early 2021 close to South Georgia due to meltwater from the A68 megaberg; smaller icebergs may influence meteoric water at other times also. Both these inputs highlight the importance of a changing cryosphere for upper-ocean freshening; potential future sea ice retreats and increases in iceberg calving would enhance the impacts of these freshwater sources on the ocean and climate. This article is part of a discussion meeting issue 'Heat and carbon uptake in the Southern Ocean: the state of the art and future priorities'.
- Published
- 2023
- Full Text
- View/download PDF
22. Finale: impact of the ORCHESTRA/ENCORE programmes on Southern Ocean heat and carbon understanding.
- Author
-
Meijers AJS, Meredith MP, Shuckburgh EF, Kent EC, Munday DR, Firing YL, King B, Smyth TJ, Leng MJ, George Nurser AJ, Hewitt HT, Povl Abrahamsen E, Weiss A, Yang M, Bell TG, Alexander Brearley J, Boland EJD, Jones DC, Josey SA, Owen RP, Grist JP, Blaker AT, Biri S, Yelland MJ, Pimm C, Zhou S, Harle J, and Cornes RC
- Abstract
The 5-year Ocean Regulation of Climate by Heat and Carbon Sequestration and Transports (ORCHESTRA) programme and its 1-year extension ENCORE (ENCORE is the National Capability ORCHESTRA Extension) was an approximately 11-million-pound programme involving seven UK research centres that finished in March 2022. The project sought to radically improve our ability to measure, understand and predict the exchange, storage and export of heat and carbon by the Southern Ocean. It achieved this through a series of milestone observational campaigns in combination with model development and analysis. Twelve cruises in the Weddell Sea and South Atlantic were undertaken, along with mooring, glider and profiler deployments and aircraft missions, all contributing to measurements of internal ocean and air-sea heat and carbon fluxes. Numerous forward and adjoint numerical experiments were developed and supported by the analysis of coupled climate models. The programme has resulted in over 100 peer-reviewed publications to date as well as significant impacts on climate assessments and policy and science coordination groups. Here, we summarize the research highlights of the programme and assess the progress achieved by ORCHESTRA/ENCORE and the questions it raises for the future. This article is part of a discussion meeting issue 'Heat and carbon uptake in the Southern Ocean: the state of the art and future priorities'.
- Published
- 2023
- Full Text
- View/download PDF
23. Improving the routine analysis of siderite for δ 13 C and δ 18 O in environmental change research.
- Author
-
Lacey JH, Sloane HJ, Leng MJ, and Crowley SF
- Abstract
Rationale: The carbon (δ
13 C) and oxygen (δ18 O) isotope composition of siderite (FeCO3 ) is used widely to understand and quantify geochemical processes to reconstruct past climate and environmental change. However, few laboratories follow precisely the same protocol for the preparation and analysis of siderite-bearing materials, which combined with the absence of international reference materials and mineral-specific acid fractionation factors, leads potentially to significant differences in isotope data generated by individual laboratories. Here we examine procedures for the isotope analysis of siderite and discuss factors potentially contributing to inconsistencies in sample measurement data., Methods: Isotope analysis of siderite is first assessed using similar versions of the classical off-line, sealed vessel acid digestion method by comparing data sets obtained from intercomparison materials measured at two participating laboratories. We then compare data from the classical method against those generated using an automated preparation technique using data produced from an independent set of test materials., Results: Measurement of siderite δ13 C is generally both repeatable and reproducible, but measurement of δ18 O may be subject to large (~1‰), method-dependent bias for siderite reacted at differing temperatures (70°C and 100°C) under classical and automated CO2 preparation conditions. The potential for poor oxygen isotope measurement reproducibility is amplified by local differences in sample preparation protocols and procedures used to calibrate measurement data to international reference scales., Conclusions: We offer suggestions for improving the repeatability and reproducibility of δ13 C and δ18 O analysis on siderite. The challenge of producing consistent isotope data from siderite can only be resolved by ensuring the availability of siderite reference materials to facilitate identical treatment as a basis for minimising method-dependent contributions to data inconsistency between laboratories., (© 2022 British Geological Survey (c) UKRI and The Authors. Rapid Communications in Mass Spectrometry published by John Wiley & Sons Ltd.)- Published
- 2023
- Full Text
- View/download PDF
24. In flux: Annual transport and deposition of suspended heavy metals and trace elements in the urbanised, tropical Red River Delta, Vietnam.
- Author
-
Roberts LR, Do NT, Panizzo VN, Taylor S, Watts M, Hamilton E, McGowan S, Trinh DA, Leng MJ, and Salgado J
- Subjects
- Cadmium, Environmental Monitoring, Fertilizers, Geologic Sediments, Humans, Manure, Particulate Matter, Vietnam, Wastewater, Metals, Heavy analysis, Trace Elements analysis, Water Pollutants, Chemical analysis
- Abstract
Due to the depositional environment, river deltas are said to act as filters and sinks for pollutants. However, many deltas are also densely populated and rapidly urbanizing, creating new and increased sources of pollutants. These sources pose the risk of tipping these environments from pollution sinks to sources, to the world's oceans. We provide detailed seasonal and annual assessments of metal contaminants in riverine suspended particulate matter (SPM) across the densely populated Red River Delta (RRD), Vietnam. The global contributions of elements from the RRD are all <0.2% with many elemental fluxes <0.01%, suggesting the RRD is not a major source of elemental pollution to the ocean. However, 'hotspots' of metal pollution due to human activity and the impacts of tropical storm Son Tinh (July 2018) exceed both national level regulations and international measures of toxicity (e.g. enrichment factors). There is widespread 'extreme pollution' of Cd (enrichment factor >40) and concentrations of As higher than national regulation limits (>17 mg/Kg) at all sites other than one upstream, agricultural-dominated tributary in the dry season. These 'hotspots' are characterised by high inputs of organic matter (e.g. manure fertiliser and urban wastewater), which influences elemental mobility in the particulate and dissolved phases, and are potentially significant sources of pollution downstream. In addition, in the marine and fresh water mixing zone, salinity effects metal complexation with organic matter increasing metals in the particulate phase. Our calculations indicate that the delta is currently acting as a pollutant sink (as determined by high levels of pollutant deposition ∼50%). However, increased in-washing of pollutants and future projected increases in monsoon intensity, saline intrusion, and human activity could shift the delta to become a source of toxic metals. We show the importance of monitoring environmental parameters (primarily dissolved organic matter and salinity) in the RRD to assess the risk of transport and accumulation of toxic metals in the delta sediments, which can lead to net-increases in anthropogenic pollution in the coastal zone and the incorporation of toxic elements in the food chain., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 The Author(s). Published by Elsevier Ltd.. All rights reserved.)
- Published
- 2022
- Full Text
- View/download PDF
25. Extensive primary production promoted the recovery of the Ediacaran Shuram excursion.
- Author
-
Cañadas F, Papineau D, Leng MJ, and Li C
- Subjects
- Carbon Isotopes, China, Earth, Planet, Ecosystem, Geologic Sediments analysis, History, Ancient, Nitrogen Isotopes, Oxygen chemistry, Carbon Cycle, Fossils, Geologic Sediments chemistry, Nitrogen Cycle, Seawater chemistry
- Abstract
Member IV of the Ediacaran Doushantuo Formation records the recovery from the most negative carbon isotope excursion in Earth history. However, the main biogeochemical controls that ultimately drove this recovery have yet to be elucidated. Here, we report new carbon and nitrogen isotope and concentration data from the Nanhua Basin (South China), where δ
13 C values of carbonates (δ13 Ccarb ) rise from - 7‰ to -1‰ and δ15 N values decrease from +5.4‰ to +2.3‰. These trends are proposed to arise from a new equilibrium in the C and N cycles where primary production overcomes secondary production as the main source of organic matter in sediments. The enhanced primary production is supported by the coexisting Raman spectral data, which reveal a systematic difference in kerogen structure between depositional environments. Our new observations point to the variable dominance of distinct microbial communities in the late Ediacaran ecosystems, and suggest that blooms of oxygenic phototrophs modulated the recovery from the most negative δ13 Ccarb excursion in Earth history., (© 2022. The Author(s).)- Published
- 2022
- Full Text
- View/download PDF
26. Paleocene/Eocene carbon feedbacks triggered by volcanic activity.
- Author
-
Kender S, Bogus K, Pedersen GK, Dybkjær K, Mather TA, Mariani E, Ridgwell A, Riding JB, Wagner T, Hesselbo SP, and Leng MJ
- Abstract
The Paleocene-Eocene Thermal Maximum (PETM) was a period of geologically-rapid carbon release and global warming ~56 million years ago. Although modelling, outcrop and proxy records suggest volcanic carbon release occurred, it has not yet been possible to identify the PETM trigger, or if multiple reservoirs of carbon were involved. Here we report elevated levels of mercury relative to organic carbon-a proxy for volcanism-directly preceding and within the early PETM from two North Sea sedimentary cores, signifying pulsed volcanism from the North Atlantic Igneous Province likely provided the trigger and subsequently sustained elevated CO
2 . However, the PETM onset coincides with a mercury low, suggesting at least one other carbon reservoir released significant greenhouse gases in response to initial warming. Our results support the existence of 'tipping points' in the Earth system, which can trigger release of additional carbon reservoirs and drive Earth's climate into a hotter state., (© 2021. The Author(s).)- Published
- 2021
- Full Text
- View/download PDF
27. Publisher Correction: Ventilation of the abyss in the Atlantic sector of the Southern Ocean.
- Author
-
Akhoudas CH, Sallée JB, Haumann FA, Meredith MP, Garabato AN, Reverdin G, Jullion L, Aloisi G, Benetti M, Leng MJ, and Arrowsmith C
- Published
- 2021
- Full Text
- View/download PDF
28. A new automated method for high-throughput carbon and hydrogen isotope analysis of gaseous and dissolved methane at atmospheric concentrations.
- Author
-
Smith AC, Welsh S, Atkinson H, Harris D, and Leng MJ
- Abstract
Rationale: The dual isotope ratio analysis, carbon (δ
13 C value) and hydrogen (δ2 H value), of methane (CH4 ) is a valuable tracer tool within a range of areas of scientific investigation, not least wetland ecology, microbiology, CH4 source identification and the tracing of geological leakages of thermogenic CH4 in groundwater. Traditional methods of collecting, purification, separating and analysing CH4 for δ13 C and δ2 H determination are, however, very time consuming, involving offline manual extractions., Methods: Here we describe a new gas chromatography, pyrolysis/combustion, isotope ratio mass spectrometry (IRMS) system for the automated analysis of either dissolved or gaseous CH4 down to ambient atmospheric concentrations (2.0 ppm). Sample introduction is via a traditional XYZ autosampler, allowing either helium (He) purging of gas or sparging of water from a range of suitable, airtight bottles., Results: The system routinely achieves precision of <0.3‰ for δ13 C values and <3.0‰ for δ2 H values, based on long-term replicate analysis of an in-house CH4 /He mix standard (BGS-1), corrected to two externally calibrated reference gases at near atmospheric concentrations of methane. Depending upon CH4 concentration and therefore bottle size, the system runs between 21 (140-mL bottle) and 200 samples (12-mL exetainer) in an unattended run overnight., Conclusions: This represents the first commercially available IRMS system for dual δ13 C and δ2 H analysis of methane at atmospheric concentrations and a step forward for the routine (and high-volume) analysis of CH4 in environmental studies., (© 2021 United Kingdom Research and Innovation, as represented by the British Geological Survey. Rapid Communications in Mass Spectrometry published by John Wiley & Sons Ltd.)- Published
- 2021
- Full Text
- View/download PDF
29. Assessment of bias in carbon isotope composition of organic leaf matter due to pre-analysis milling methods.
- Author
-
Worne S, Lacey JH, Barr C, Schulz C, and Leng MJ
- Abstract
Rationale: Stable isotope analysis of leaf material has many applications including assessment of plant water-use efficiency and palaeoclimatology. To facilitate interpretations of small shifts in the carbon isotope composition (δ
13 C) of leaves, accurate and repeatable results are required. Pre-sample homogenisation is essential to ensure a representative sample is analysed, but can also introduce error., Methods: We investigate how different grinding methods (freezer-milling and ball-milling) affect the carbon content and δ13 C of tree leaves from a wetland in Queensland, Australia, commenting on how increased temperature, sample contamination, sample loss or poor homogenisation may impact results., Results: No alteration of leaf δ13 C is observed due to different milling methods, although there may be a significant increase in %C of samples processed using ball-milling., Conclusions: We suggest %C variability is possibly due to contamination from abraded plastic vials or insufficient homogenisation during ball-milling, with no significant impact on δ13 C. Overall, we suggest that intermittent ball-milling may be the best solution to reduce costs, preparation time and use of liquid nitrogen, aiming to achieve complete homogenisation using the shortest possible duration of milling., (© 2021 The Authors. Rapid Communications in Mass Spectrometry published by John Wiley & Sons Ltd.)- Published
- 2021
- Full Text
- View/download PDF
30. Author Correction: Holocene El Niño-Southern Oscillation variability reflected in subtropical Australian precipitation.
- Author
-
Barr C, Tibby J, Leng MJ, Tyler JJ, Henderson ACG, Overpeck JT, Simpson GL, Cole JE, Phipps SJ, Marshall JC, McGregor GB, Hua Q, and McRobie FH
- Published
- 2021
- Full Text
- View/download PDF
31. Ventilation of the abyss in the Atlantic sector of the Southern Ocean.
- Author
-
Akhoudas CH, Sallée JB, Haumann FA, Meredith MP, Garabato AN, Reverdin G, Jullion L, Aloisi G, Benetti M, Leng MJ, and Arrowsmith C
- Abstract
The Atlantic sector of the Southern Ocean is the world's main production site of Antarctic Bottom Water, a water-mass that is ventilated at the ocean surface before sinking and entraining older water-masses-ultimately replenishing the abyssal global ocean. In recent decades, numerous attempts at estimating the rates of ventilation and overturning of Antarctic Bottom Water in this region have led to a strikingly broad range of results, with water transport-based calculations (8.4-9.7 Sv) yielding larger rates than tracer-based estimates (3.7-4.9 Sv). Here, we reconcile these conflicting views by integrating transport- and tracer-based estimates within a common analytical framework, in which bottom water formation processes are explicitly quantified. We show that the layer of Antarctic Bottom Water denser than 28.36 kg m[Formula: see text] [Formula: see text] is exported northward at a rate of 8.4 ± 0.7 Sv, composed of 4.5 ± 0.3 Sv of well-ventilated Dense Shelf Water, and 3.9 ± 0.5 Sv of old Circumpolar Deep Water entrained into cascading plumes. The majority, but not all, of the Dense Shelf Water (3.4 ± 0.6 Sv) is generated on the continental shelves of the Weddell Sea. Only 55% of AABW exported from the region is well ventilated and thus draws down heat and carbon into the deep ocean. Our findings unify traditionally contrasting views of Antarctic Bottom Water production in the Atlantic sector, and define a baseline, process-discerning target for its realistic representation in climate models.
- Published
- 2021
- Full Text
- View/download PDF
32. Coupled impacts of sea ice variability and North Pacific atmospheric circulation on Holocene hydroclimate in Arctic Alaska.
- Author
-
Broadman E, Kaufman DS, Henderson ACG, Malmierca-Vallet I, Leng MJ, and Lacey JH
- Abstract
Arctic Alaska lies at a climatological crossroads between the Arctic and North Pacific Oceans. The modern hydroclimate of the region is responding to rapidly diminishing sea ice, driven in part by changes in heat flux from the North Pacific. Paleoclimate reconstructions have improved our knowledge of Alaska's hydroclimate, but no studies have examined Holocene sea ice, moisture, and ocean-atmosphere circulation in Arctic Alaska, limiting our understanding of the relationship between these phenomena in the past. Here we present a sedimentary diatom assemblage and diatom isotope dataset from Schrader Pond, located ∼80 km from the Arctic Ocean, which we interpret alongside synthesized regional records of Holocene hydroclimate and sea ice reduction scenarios modeled by the Hadley Centre Coupled Model Version 3 (HadCM3). The paleodata synthesis and model simulations suggest the Early and Middle Holocene in Arctic Alaska were characterized by less sea ice, a greater contribution of isotopically heavy Arctic-derived moisture, and wetter climate. In the Late Holocene, sea ice expanded and regional climate became drier. This climatic transition is coincident with a documented shift in North Pacific circulation involving the Aleutian Low at ∼4 ka, suggesting a Holocene teleconnection between the North Pacific and Arctic. The HadCM3 simulations reveal that reduced sea ice leads to a strengthened Aleutian Low shifted west, potentially increasing transport of warm North Pacific water to the Arctic through the Bering Strait. Our findings demonstrate the interconnectedness of the Arctic and North Pacific on multimillennial timescales, and are consistent with future projections of less sea ice and more precipitation in Arctic Alaska., Competing Interests: The authors declare no competing interest.
- Published
- 2020
- Full Text
- View/download PDF
33. Deep drilling reveals massive shifts in evolutionary dynamics after formation of ancient ecosystem.
- Author
-
Wilke T, Hauffe T, Jovanovska E, Cvetkoska A, Donders T, Ekschmitt K, Francke A, Lacey JH, Levkov Z, Marshall CR, Neubauer TA, Silvestro D, Stelbrink B, Vogel H, Albrecht C, Holtvoeth J, Krastel S, Leicher N, Leng MJ, Lindhorst K, Masi A, Ognjanova-Rumenova N, Panagiotopoulos K, Reed JM, Sadori L, Tofilovska S, Van Bocxlaer B, Wagner-Cremer F, Wesselingh FP, Wolters V, Zanchetta G, Zhang X, and Wagner B
- Subjects
- Biodiversity, Climate Change, Fossils, Lakes, Biological Evolution, Ecosystem
- Abstract
The scarcity of high-resolution empirical data directly tracking diversity over time limits our understanding of speciation and extinction dynamics and the drivers of rate changes. Here, we analyze a continuous species-level fossil record of endemic diatoms from ancient Lake Ohrid, along with environmental and climate indicator time series since lake formation 1.36 million years (Ma) ago. We show that speciation and extinction rates nearly simultaneously decreased in the environmentally dynamic phase after ecosystem formation and stabilized after deep-water conditions established in Lake Ohrid. As the lake deepens, we also see a switch in the macroevolutionary trade-off, resulting in a transition from a volatile assemblage of short-lived endemic species to a stable community of long-lived species. Our results emphasize the importance of the interplay between environmental/climate change, ecosystem stability, and environmental limits to diversity for diversification processes. The study also provides a new understanding of evolutionary dynamics in long-lived ecosystems., (Copyright © 2020 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works. Distributed under a Creative Commons Attribution NonCommercial License 4.0 (CC BY-NC).)
- Published
- 2020
- Full Text
- View/download PDF
34. Human settlement of East Polynesia earlier, incremental, and coincident with prolonged South Pacific drought.
- Author
-
Sear DA, Allen MS, Hassall JD, Maloney AE, Langdon PG, Morrison AE, Henderson ACG, Mackay H, Croudace IW, Clarke C, Sachs JP, Macdonald G, Chiverrell RC, Leng MJ, Cisneros-Dozal LM, Fonville T, and Pearson E
- Subjects
- History, Ancient, Humans, Lakes, Polynesia, Archaeology methods, Droughts, Geologic Sediments analysis, Human Migration history
- Abstract
The timing of human colonization of East Polynesia, a vast area lying between Hawai'i, Rapa Nui, and New Zealand, is much debated and the underlying causes of this great migration have been enigmatic. Our study generates evidence for human dispersal into eastern Polynesia from islands to the west from around AD 900 and contemporaneous paleoclimate data from the likely source region. Lake cores from Atiu, Southern Cook Islands (SCIs) register evidence of pig and/or human occupation on a virgin landscape at this time, followed by changes in lake carbon around AD 1000 and significant anthropogenic disturbance from c. AD 1100. The broader paleoclimate context of these early voyages of exploration are derived from the Atiu lake core and complemented by additional lake cores from Samoa (directly west) and Vanuatu (southwest) and published hydroclimate proxies from the Society Islands (northeast) and Kiribati (north). Algal lipid and leaf wax biomarkers allow for comparisons of changing hydroclimate conditions across the region before, during, and after human arrival in the SCIs. The evidence indicates a prolonged drought in the likely western source region for these colonists, lasting c. 200 to 400 y, contemporaneous with the phasing of human dispersal into the Pacific. We propose that drying climate, coupled with documented social pressures and societal developments, instigated initial eastward exploration, resulting in SCI landfall(s) and return voyaging, with colonization a century or two later. This incremental settlement process likely involved the accumulation of critical maritime knowledge over several generations., Competing Interests: The authors declare no competing interest., (Copyright © 2020 the Author(s). Published by PNAS.)
- Published
- 2020
- Full Text
- View/download PDF
35. Effects of organic removal techniques prior to carbonate stable isotope analysis of lacustrine marls: A case study from palaeo-lake Fucino (central Italy).
- Author
-
Mannella G, Zanchetta G, Regattieri E, Perchiazzi N, Drysdale RN, Giaccio B, Leng MJ, and Wagner B
- Abstract
Rationale: The suitability of organic matter (OM) removal pre-treatments in isotopic studies of lacustrine carbonates is currently under debate. Naturally occurring OM seems to have a negligible effect on the bulk isotopic composition of carbonates compared with changes induced by pre-treatments. This study provides further insights into the possible effects induced by commonly used pre-treatments on natural lacustrine carbonates., Methods: Sixteen samples from the Fucino F1-F3 lacustrine succession (Abruzzo, central Italy) were characterised for their mineralogical and geochemical composition and each was split into three identical aliquots. One aliquot was left untreated while the remaining two were treated with NaOCl and H
2 O2 dilutions. The same treatment was applied to an internal standard consisting of pure Carrara marble. The treated and untreated samples were analysed for their carbon (δ13 C values) and oxygen (δ18 O values) isotope compositions using an Analytical Precision AP2003 isotope ratio mass spectrometer., Results: The samples had variable proportions of endogenic and detrital components, the detrital portion being more (less) abundant during colder (warmer) climate phases. We observed that neither the NaOCl nor the H2 O2 treatment was able to completely remove OM and therefore there was selective removal of compounds within the OM pool. A possible effect of pre-treatment is the loss of carbonates intimately interspersed within the OM, as suggested by the evolution of isotopic ratios towards the local detrital array., Conclusions: Our study highlights sample-specific changes in geochemistry associated with sample pre-treatments; however, such changes do not seem to lead to either systematic and/or predictable isotopic shifts. We suggest that the suitability of NaOCl or H2 O2 pre-treatments for OM removal should be evaluated on a case-by-case basis. In the specific case of lacustrine marls from palaeo-lake Fucino containing relatively low amounts of OM and in which both detrital and endogenic carbonates occur, both pre-treatments should be avoided., (© 2019 John Wiley & Sons, Ltd.)- Published
- 2020
- Full Text
- View/download PDF
36. Orbital pacing and secular evolution of the Early Jurassic carbon cycle.
- Author
-
Storm MS, Hesselbo SP, Jenkyns HC, Ruhl M, Ullmann CV, Xu W, Leng MJ, Riding JB, and Gorbanenko O
- Abstract
Global perturbations to the Early Jurassic environment (∼201 to ∼174 Ma), notably during the Triassic-Jurassic transition and Toarcian Oceanic Anoxic Event, are well studied and largely associated with volcanogenic greenhouse gas emissions released by large igneous provinces. The long-term secular evolution, timing, and pacing of changes in the Early Jurassic carbon cycle that provide context for these events are thus far poorly understood due to a lack of continuous high-resolution δ
13 C data. Here we present a δ13 CTOC record for the uppermost Rhaetian (Triassic) to Pliensbachian (Lower Jurassic), derived from a calcareous mudstone succession of the exceptionally expanded Llanbedr (Mochras Farm) borehole, Cardigan Bay Basin, Wales, United Kingdom. Combined with existing δ13 CTOC data from the Toarcian, the compilation covers the entire Lower Jurassic. The dataset reproduces large-amplitude δ13 CTOC excursions (>3‰) recognized elsewhere, at the Sinemurian-Pliensbachian transition and in the lower Toarcian serpentinum zone, as well as several previously identified medium-amplitude (∼0.5 to 2‰) shifts in the Hettangian to Pliensbachian interval. In addition, multiple hitherto undiscovered isotope shifts of comparable amplitude and stratigraphic extent are recorded, demonstrating that those similar features described earlier from stratigraphically more limited sections are nonunique in a long-term context. These shifts are identified as long-eccentricity (∼405-ky) orbital cycles. Orbital tuning of the δ13 CTOC record provides the basis for an astrochronological duration estimate for the Pliensbachian and Sinemurian, giving implications for the duration of the Hettangian Stage. Overall the chemostratigraphy illustrates particular sensitivity of the marine carbon cycle to long-eccentricity orbital forcing., Competing Interests: The authors declare no competing interest., (Copyright © 2020 the Author(s). Published by PNAS.)- Published
- 2020
- Full Text
- View/download PDF
37. Enhanced glacial discharge from the eastern Antarctic Peninsula since the 1700s associated with a positive Southern Annular Mode.
- Author
-
Dickens WA, Kuhn G, Leng MJ, Graham AGC, Dowdeswell JA, Meredith MP, Hillenbrand CD, Hodgson DA, Roberts SJ, Sloane H, and Smith JA
- Abstract
The Antarctic Peninsula Ice Sheet is currently experiencing sustained and accelerating loss of ice. Determining when these changes were initiated and identifying the main drivers is hampered by the short instrumental record (1992 to present). Here we present a 6,250 year record of glacial discharge based on the oxygen isotope composition of diatoms (δ
18 Odiatom ) from a marine core located at the north-eastern tip of the Antarctic Peninsula. We find that glacial discharge - sourced primarily from ice shelf and iceberg melting along the eastern Antarctic Peninsula - remained largely stable between ~6,250 to 1,620 cal. yr BP, with a slight increase in variability until ~720 cal. yr. BP. An increasing trend in glacial discharge occurs after 550 cal. yr BP (A.D. 1400), reaching levels unprecedented during the past 6,250 years after 244 cal. yr BP (A.D. 1706). A marked acceleration in the rate of glacial discharge is also observed in the early part of twentieth century (after A.D. 1912). Enhanced glacial discharge, particularly after the 1700s is linked to a positive Southern Annular Mode (SAM). We argue that a positive SAM drove stronger westerly winds, atmospheric warming and surface ablation on the eastern Antarctic Peninsula whilst simultaneously entraining more warm water into the Weddell Gyre, potentially increasing melting on the undersides of ice shelves. A possible implication of our data is that ice shelves in this region have been thinning for at least ~300 years, potentially predisposing them to collapse under intensified anthropogenic warming.- Published
- 2019
- Full Text
- View/download PDF
38. Mediterranean winter rainfall in phase with African monsoons during the past 1.36 million years.
- Author
-
Wagner B, Vogel H, Francke A, Friedrich T, Donders T, Lacey JH, Leng MJ, Regattieri E, Sadori L, Wilke T, Zanchetta G, Albrecht C, Bertini A, Combourieu-Nebout N, Cvetkoska A, Giaccio B, Grazhdani A, Hauffe T, Holtvoeth J, Joannin S, Jovanovska E, Just J, Kouli K, Kousis I, Koutsodendris A, Krastel S, Lagos M, Leicher N, Levkov Z, Lindhorst K, Masi A, Melles M, Mercuri AM, Nomade S, Nowaczyk N, Panagiotopoulos K, Peyron O, Reed JM, Sagnotti L, Sinopoli G, Stelbrink B, Sulpizio R, Timmermann A, Tofilovska S, Torri P, Wagner-Cremer F, Wonik T, and Zhang X
- Subjects
- Africa, Mediterranean Region, Models, Theoretical, Climate, Rain, Seasons
- Abstract
Mediterranean climates are characterized by strong seasonal contrasts between dry summers and wet winters. Changes in winter rainfall are critical for regional socioeconomic development, but are difficult to simulate accurately
1 and reconstruct on Quaternary timescales. This is partly because regional hydroclimate records that cover multiple glacial-interglacial cycles2,3 with different orbital geometries, global ice volume and atmospheric greenhouse gas concentrations are scarce. Moreover, the underlying mechanisms of change and their persistence remain unexplored. Here we show that, over the past 1.36 million years, wet winters in the northcentral Mediterranean tend to occur with high contrasts in local, seasonal insolation and a vigorous African summer monsoon. Our proxy time series from Lake Ohrid on the Balkan Peninsula, together with a 784,000-year transient climate model hindcast, suggest that increased sea surface temperatures amplify local cyclone development and refuel North Atlantic low-pressure systems that enter the Mediterranean during phases of low continental ice volume and high concentrations of atmospheric greenhouse gases. A comparison with modern reanalysis data shows that current drivers of the amount of rainfall in the Mediterranean share some similarities to those that drive the reconstructed increases in precipitation. Our data cover multiple insolation maxima and are therefore an important benchmark for testing climate model performance.- Published
- 2019
- Full Text
- View/download PDF
39. Spatial variability of 2 H and 18 O composition of meteoric freshwater lakes in Scotland.
- Author
-
Hoogewerff J, Kemp HF, Leng MJ, and Meier-Augenstein W
- Subjects
- Environmental Monitoring, Scotland, Deuterium analysis, Lakes analysis, Oxygen Isotopes analysis, Rain chemistry
- Abstract
Coastal regions, and in particular islands where precipitation from clouds formed out at sea occurs for the first time, are prime candidates for regions where
2 H and18 O composition of precipitation will deviate significantly from the global mean geographic and physiographic trends of vapour-transport patterns. The results reported here are the outcome of a study that aimed to test this hypothesis by 'isotopographically' mapping the characteristic δ2 H and δ18 O signatures of Scottish freshwaters. The resulting isotope abundance landscapes or 'isoscapes' will underpin studies aiming to authenticate origin of Scottish produce but may also offer a baseline against which environmental changes could be assessed. Between April 2011 and May 2012 freshwater samples were collected from 127 different freshwater lochs and reservoirs across Scotland, and analysis results were compared to precipitation data provided by the British Geological Survey. Here we present the results of the2 H and18 O analyses of these water samples as well as the first detailed Scotland freshwater isoscapes with a grid resolution of about 5 × 5 km (0.05 degrees).- Published
- 2019
- Full Text
- View/download PDF
40. A method for reconstructing temporal changes in vegetation functional trait composition using Holocene pollen assemblages.
- Author
-
Carvalho F, Brown KA, Waller MP, Bunting MJ, Boom A, and Leng MJ
- Subjects
- Biodiversity, Biological Evolution, Biomass, Data Analysis, Ecosystem, England, Models, Theoretical, Phenotype, Plants, Pollen chemistry, Pollen metabolism, Spatio-Temporal Analysis, Wetlands, Data Collection methods, Plant Leaves chemistry, Pollen classification
- Abstract
Methods of reconstructing changes in plant traits over long time scales are needed to understand the impact of changing environmental conditions on ecosystem processes and services. Although Holocene pollen have been extensively used to provide records of vegetation history, few studies have adopted a functional trait approach that is pertinent to changes in ecosystem processes. Here, for woody and herbaceous fen peatland communities, we use modern pollen and vegetation data combined with pollen records from Holocene deposits to reconstruct vegetation functional dynamics. The six traits chosen (measures of leaf area-to-mass ratio and leaf nutrient content) are known to modulate species' fitness and to vary with changes in ecosystem processes. We fitted linear mixed effects models between community weighted mean (CWM) trait values of the modern pollen and vegetation to determine whether traits assigned to pollen types could be used to reconstruct traits found in the vegetation from pollen assemblages. We used relative pollen productivity (RPP) correction factors in an attempt to improve this relationship. For traits showing the best fit between modern pollen and vegetation, we applied the model to dated Holocene pollen sequences from Fenland and Romney Marsh in eastern and southern England and reconstructed temporal changes in trait composition. RPP adjustment did not improve the linear relationship between modern pollen and vegetation. Leaf nutrient traits (leaf C and N) were generally more predictable from pollen data than mass-area traits. We show that inferences about biomass accumulation and decomposition rates can be made using Holocene trait reconstructions. While it is possible to reconstruct community-level trends for some leaf traits from pollen assemblages preserved in sedimentary archives in wetlands, we show the importance of testing methods in modern systems first and encourage further development of this approach to address issues concerning the pollen-plant abundance relationship and pollen source area., Competing Interests: The authors have declared that no competing interests exist.
- Published
- 2019
- Full Text
- View/download PDF
41. Holocene El Niño-Southern Oscillation variability reflected in subtropical Australian precipitation.
- Author
-
Barr C, Tibby J, Leng MJ, Tyler JJ, Henderson ACG, Overpeck JT, Simpson GL, Cole JE, Phipps SJ, Marshall JC, McGregor GB, Hua Q, and McRobie FH
- Abstract
The La Niña and El Niño phases of the El Niño-Southern Oscillation (ENSO) have major impacts on regional rainfall patterns around the globe, with substantial environmental, societal and economic implications. Long-term perspectives on ENSO behaviour, under changing background conditions, are essential to anticipating how ENSO phases may respond under future climate scenarios. Here, we derive a 7700-year, quantitative precipitation record using carbon isotope ratios from a single species of leaf preserved in lake sediments from subtropical eastern Australia. We find a generally wet (more La Niña-like) mid-Holocene that shifted towards drier and more variable climates after 3200 cal. yr BP, primarily driven by increasing frequency and strength of the El Niño phase. Climate model simulations implicate a progressive orbitally-driven weakening of the Pacific Walker Circulation as contributing to this change. At centennial scales, high rainfall characterised the Little Ice Age (~1450-1850 CE) in subtropical eastern Australia, contrasting with oceanic proxies that suggest El Niño-like conditions prevail during this period. Our data provide a new western Pacific perspective on Holocene ENSO variability and highlight the need to address ENSO reconstruction with a geographically diverse network of sites to characterise how both ENSO, and its impacts, vary in a changing climate.
- Published
- 2019
- Full Text
- View/download PDF
42. Closure of the Bering Strait caused Mid-Pleistocene Transition cooling.
- Author
-
Kender S, Ravelo AC, Worne S, Swann GEA, Leng MJ, Asahi H, Becker J, Detlef H, Aiello IW, Andreasen D, and Hall IR
- Abstract
The Mid-Pleistocene Transition (MPT) is characterised by cooling and lengthening glacial cycles from 600-1200 ka, thought to be driven by reductions in glacial CO
2 in particular from ~900 ka onwards. Reduced high latitude upwelling, a process that retains CO2 within the deep ocean over glacials, could have aided drawdown but has so far not been constrained in either hemisphere over the MPT. Here, we find that reduced nutrient upwelling in the Bering Sea, and North Pacific Intermediate Water expansion, coincided with the MPT and became more persistent at ~900 ka. We propose reduced upwelling was controlled by expanding sea ice and North Pacific Intermediate Water formation, which may have been enhanced by closure of the Bering Strait. The regional extent of North Pacific Intermediate Water across the subarctic northwest Pacific would have contributed to lower atmospheric CO2 and global cooling during the MPT.- Published
- 2018
- Full Text
- View/download PDF
43. An early Cambrian greenhouse climate.
- Author
-
Hearing TW, Harvey THP, Williams M, Leng MJ, Lamb AL, Wilby PR, Gabbott SE, Pohl A, and Donnadieu Y
- Subjects
- Biodiversity, Ecosystem, Fossils, Geologic Sediments analysis, Geologic Sediments chemistry, History, Ancient, Oceans and Seas, Oxygen Isotopes analysis, Paleontology, Temperature, Climate, Greenhouse Effect
- Abstract
The oceans of the early Cambrian (~541 to 509 million years ago) were the setting for a marked diversification of animal life. However, sea temperatures-a key component of the early Cambrian marine environment-remain unconstrained, in part because of a substantial time gap in the stable oxygen isotope (δ
18 O) record before the evolution of euconodonts. We show that previously overlooked sources of fossil biogenic phosphate have the potential to fill this gap. Pristine phosphatic microfossils from the Comley Limestones, UK, yield a robust δ18 O signature, suggesting sea surface temperatures of 20° to 25°C at high southern paleolatitudes (~65°S to 70°S) between ~514 and 509 million years ago. These sea temperatures are consistent with the distribution of coeval evaporite and calcrete deposits, peak continental weathering rates, and also our climate model simulations for this interval. Our results support an early Cambrian greenhouse climate comparable to those of the late Mesozoic and early Cenozoic, offering a framework for exploring the interplay between biotic and environmental controls on Cambrian animal diversification.- Published
- 2018
- Full Text
- View/download PDF
44. Groundwater Quality beneath an Asian Megacity on a Delta: Kolkata's (Calcutta's) Disappearing Arsenic and Present Manganese.
- Author
-
McArthur JM, Sikdar PK, Leng MJ, Ghosal U, and Sen I
- Subjects
- Environmental Monitoring, India, Manganese, Arsenic, Groundwater, Water Pollutants, Chemical
- Abstract
Kolkata, the capital city of West Bengal, exploits groundwater for public water-supply. The groundwater has been reported to be widely polluted by arsenic (As). Analysis for As in 280 groundwaters from across Kolkata, failed to detect As concentrations >10 μg/L from natural processes. Arsenic concentrations between 10 and 79 μg/L found in 14 of the 280 groundwaters are remnant from a pollution-plume emanating from a single factory site where Paris Green, an arsenical pesticide, was manufactured between 1965 and 1985. In 45% of groundwaters sampled, concentrations of Mn exceed 0.4 mg/L, a putative health guideline value for drinking water. Sporadic minor hazards are posed by Pb > 10 μg/L introduced into groundwater from well-fittings, from 4% of groundwaters with F concentrations between 0.75 and 1 mg/L, and the 14% of groundwaters containing more than 500 mg/L Na, concentrations that might contribute to excessive daily intake of Na. Compounding hazards from As, F, Mn, Na, and Pb, shows that 64% of public wells and 40% of municipal wells supply groundwater of suspect quality. Groundwaters comply with WHO Guideline Values for drinking water in terms of Cr, Cu, Co, NO
2 , NO3 , Sb, Se, and U. Aesthetic guideline values for Fe, Mn, SO4 , and Cl are exceeded for many groundwaters.- Published
- 2018
- Full Text
- View/download PDF
45. Historical atmospheric pollution trends in Southeast Asia inferred from lake sediment records.
- Author
-
Engels S, Fong LSRZ, Chen Q, Leng MJ, McGowan S, Idris M, Rose NL, Ruslan MS, Taylor D, and Yang H
- Subjects
- Asia, Southeastern, Ecosystem, Fossil Fuels, Humans, Mercury analysis, Metals, Heavy, Soil, Air Pollution, Environmental Monitoring methods, Geologic Sediments chemistry, Lakes
- Abstract
Fossil fuel combustion leads to increased levels of air pollution, which negatively affects human health as well as the environment. Documented data for Southeast Asia (SEA) show a strong increase in fossil fuel consumption since 1980, but information on coal and oil combustion before 1980 is not widely available. Spheroidal carbonaceous particles (SCPs) and heavy metals, such as mercury (Hg), are emitted as by-products of fossil fuel combustion and may accumulate in sediments following atmospheric fallout. Here we use sediment SCP and Hg records from several freshwater lentic ecosystems in SEA (Malaysia, Philippines, Singapore) to reconstruct long-term, region-wide variations in levels of these two key atmospheric pollution indicators. The age-depth models of Philippine sediment cores do not reach back far enough to date first SCP presence, but single SCP occurrences are first observed between 1925 and 1950 for a Malaysian site. Increasing SCP flux is observed at our sites from 1960 onward, although individual sites show minor differences in trends. SCP fluxes show a general decline after 2000 at each of our study sites. While the records show broadly similar temporal trends across SEA, absolute SCP fluxes differ between sites, with a record from Malaysia showing SCP fluxes that are two orders of magnitude lower than records from the Philippines. Similar trends in records from China and Japan represent the emergence of atmospheric pollution as a broadly-based inter-region environmental problem during the 20th century. Hg fluxes were relatively stable from the second half of the 20th century onward. As catchment soils are also contaminated with atmospheric Hg, future soil erosion can be expected to lead to enhanced Hg flux into surface waters., (Copyright © 2018 Elsevier Ltd. All rights reserved.)
- Published
- 2018
- Full Text
- View/download PDF
46. Post-mortem oxygen isotope exchange within cultured diatom silica.
- Author
-
Tyler JJ, Sloane HJ, Rickaby REM, Cox EJ, and Leng MJ
- Subjects
- Diatoms cytology, Hot Temperature, Mass Spectrometry, Oxygen Isotopes analysis, Silicon Dioxide chemistry, Temperature, Diatoms metabolism, Oxygen Isotopes metabolism, Silicon Dioxide metabolism
- Abstract
Rationale: Potential post-mortem alteration to the oxygen isotope composition of biogenic silica is critical to the validity of palaeoclimate reconstructions based on oxygen isotope ratios (δ
18 O values) from sedimentary silica. We calculate the degree of oxygen isotope alteration within freshly cultured diatom biogenic silica in response to heating and storing in the laboratory., Methods: The experiments used freshly cultured diatom silica. Silica samples were either stored in water or dried at temperatures between 20 °C and 80 °C. The mass of affected oxygen and the associated silica-water isotope fractionation during alteration were calculated by conducting parallel experiments using endmember waters with δ18 O values of -6.3 to -5.9 ‰ and -36.3 to -35.0 ‰. Dehydroxylation and subsequent oxygen liberation were achieved by stepwise fluorination with BrF5 . The18 O/16 O ratios were measured using a ThermoFinnigan MAT 253 isotope ratio mass spectrometer., Results: Significant alterations in silica δ18 O values were observed, most notably an increase in the δ18 O values following drying at 40-80 °C. Storage in water for 7 days between 20 and 80 °C also led to significant alteration in δ18 O values. Mass balance calculations suggest that the amount of affected oxygen is positively correlated with temperature. The estimated oxygen isotope fractionation during alteration is an inverse function of temperature, consistent with the extrapolation of models for high-temperature silica-water oxygen isotope fractionation., Conclusions: Routinely used preparatory methods may impart significant alterations to the δ18 O values of biogenic silica, particularly when dealing with modern cultured or field-collected material. The significance of such processes within natural aquatic environments is uncertain; however, there is potential that similar processes also affect sedimentary diatoms, with implications for the interpretation of biogenic silica-hosted δ18 O palaeoclimate records., (© 2017 The Authors. Rapid Communications in Mass Spectrometry Published by John Wiley & Sons Ltd.)- Published
- 2017
- Full Text
- View/download PDF
47. Tree height strongly affects estimates of water-use efficiency responses to climate and CO 2 using isotopes.
- Author
-
Brienen RJW, Gloor E, Clerici S, Newton R, Arppe L, Boom A, Bottrell S, Callaghan M, Heaton T, Helama S, Helle G, Leng MJ, Mielikäinen K, Oinonen M, and Timonen M
- Subjects
- Algorithms, Carbon Isotopes metabolism, Cedrela growth & development, Cedrela metabolism, Fagus growth & development, Fagus metabolism, Models, Theoretical, Pinus growth & development, Pinus metabolism, Quercus growth & development, Quercus metabolism, Species Specificity, Temperature, Time Factors, Trees growth & development, Carbon Dioxide metabolism, Climate, Trees metabolism, Water metabolism
- Abstract
Various studies report substantial increases in intrinsic water-use efficiency (W
i ), estimated using carbon isotopes in tree rings, suggesting trees are gaining increasingly more carbon per unit water lost due to increases in atmospheric CO2 . Usually, reconstructions do not, however, correct for the effect of intrinsic developmental changes in Wi as trees grow larger. Here we show, by comparing Wi across varying tree sizes at one CO2 level, that ignoring such developmental effects can severely affect inferences of trees' Wi . Wi doubled or even tripled over a trees' lifespan in three broadleaf species due to changes in tree height and light availability alone, and there are also weak trends for Pine trees. Developmental trends in broadleaf species are as large as the trends previously assigned to CO2 and climate. Credible future tree ring isotope studies require explicit accounting for species-specific developmental effects before CO2 and climate effects are inferred.Intrinsic water-use efficiency (Wi ) reconstructions using tree rings often disregard developmental changes in Wi as trees age. Here, the authors compare Wi across varying tree sizes at a fixed CO2 level and show that ignoring developmental changes impacts conclusions on trees' Wi responses to CO2 or climate.- Published
- 2017
- Full Text
- View/download PDF
48. Holocene carbon dynamics at the forest-steppe ecotone of southern Siberia.
- Author
-
Mackay AW, Seddon AW, Leng MJ, Heumann G, Morley DW, Piotrowska N, Rioual P, Roberts S, and Swann GE
- Subjects
- Carbon, Climate, Forests, Geologic Sediments, Siberia, Carbon Cycle, Climate Change
- Abstract
The forest-steppe ecotone in southern Siberia is highly sensitive to climate change; global warming is expected to push the ecotone northwards, at the same time resulting in degradation of the underlying permafrost. To gain a deeper understanding of long-term forest-steppe carbon dynamics, we use a highly resolved, multiproxy, palaeolimnological approach, based on sediment records from Lake Baikal. We reconstruct proxies that are relevant to understanding carbon dynamics including carbon mass accumulation rates (CMAR; g C m
-2 yr-1 ) and isotope composition of organic matter (δ13 CTOC ). Forest-steppe dynamics were reconstructed using pollen, and diatom records provided measures of primary production from near- and off-shore communities. We used a generalized additive model (GAM) to identify significant change points in temporal series, and by applying generalized linear least-squares regression modelling to components of the multiproxy data, we address (1) What factors influence carbon dynamics during early Holocene warming and late Holocene cooling? (2) How did carbon dynamics respond to abrupt sub-Milankovitch scale events? and (3) What is the Holocene carbon storage budget for Lake Baikal. CMAR values range between 2.8 and 12.5 g C m-2 yr-1 . Peak burial rates (and greatest variability) occurred during the early Holocene, associated with melting permafrost and retreating glaciers, while lowest burial rates occurred during the neoglacial. Significant shifts in carbon dynamics at 10.3, 4.1 and 2.8 kyr bp provide compelling evidence for the sensitivity of the region to sub-Milankovitch drivers of climate change. We estimate that 1.03 Pg C was buried in Lake Baikal sediments during the Holocene, almost one-quarter of which was buried during the early Holocene alone. Combined, our results highlight the importance of understanding the close linkages between carbon cycling and hydrological processes, not just temperatures, in southern Siberian environments., (© 2016 John Wiley & Sons Ltd.)- Published
- 2017
- Full Text
- View/download PDF
49. Temporal controls on silicic acid utilisation along the West Antarctic Peninsula.
- Author
-
Swann GE, Pike J, Leng MJ, Sloane HJ, and Snelling AM
- Abstract
The impact of climatic change along the Antarctica Peninsula has been widely debated in light of atmospheric/oceanic warming and increases in glacial melt over the past half century. Particular concern exists over the impact of these changes on marine ecosystems, not only on primary producers but also on higher trophic levels. Here we present a record detailing of the historical controls on the biogeochemical cycling of silicic acid [Si(OH)
4 ] on the west Antarctica Peninsula margin, a region in which the modern phytoplankton environment is constrained by seasonal sea ice. We demonstrate that Si(OH)4 cycling through the Holocene alternates between being primarily regulated by sea ice or glacial discharge from the surrounding grounded ice sheet. With further climate-driven change and melting forecast for the twenty-first century, our findings document the potential for biogeochemical cycling and multi-trophic interactions along the peninsula to be increasingly regulated by glacial discharge, altering food-web interactions.- Published
- 2017
- Full Text
- View/download PDF
50. Carbon isotope alteration during the thermal maturation of non-flowering plant species representative of those found within the geological record.
- Author
-
Smith AC, Kendrick CP, Moss-Hayes VL, Vane CH, and Leng MJ
- Abstract
Rationale: The carbon isotope (δ
13 C value) composition of fossil plant material is routinely used as a proxy of past climate and environment change. However, palaeoclimate interpretation requires assumptions about the stability of δ13 C values in plant material during its decomposition and incorporation into sediments. Previous work on modern angiosperm species shows δ13 C changes of several per mille during simulated decomposition experiments. However, no such tests have been undertaken on non-flowering plants, which are found extensively within the geological record. These plants have distinctly different cellulose-to-lignin ratios from those of their angiosperm counterparts, potentially creating hitherto unknown variations in the original to fossil δ13 C signatures., Methods: To test the extent of δ13 C change during decomposition we have subjected a number of plants, representing more basal, non-flowering plant lineages (cycads, ferns, horsetails and dawn redwood), to artificial decay using a hydrothermal maturation technique at two temperatures over periods of up to 273 hours. Subsamples were extracted every 12-16 hours and analysed for their δ13 C and %C values using a Carlo Erba 1500 elemental analyser, and VG TripleTrap and Optima mass spectrometers., Results: The %C values increased for all samples through the maturation process at both temperatures with the largest increases observed within the first 24 hours. Decreases in δ13 C values were observed for all plants at 300°C and for two of the species at the lower temperature (200°C). The maximum shift in the δ13 C value related to experimental decomposition was -0.90‰ (horsetail), indicating a preferential loss of13 C during thermal maturation., Conclusions: The reduction in the δ13 C value potentially suggests a preferential loss of isotopically heavier cellulose in relation to the isotopically lighter lignin component during maturation. The isotopic offset observed here (<0.9‰) means that palaeoclimatic interpretation of δ13 C values from non-flowering plant material within the geological record remains robust, but only where interpretations are based on variations in δ13 C values greater than 1‰. Copyright © 2016 John Wiley & Sons, Ltd., (Copyright © 2016 John Wiley & Sons, Ltd.)- Published
- 2017
- Full Text
- View/download PDF
Catalog
Discovery Service for Jio Institute Digital Library
For full access to our library's resources, please sign in.