Hawes Water Research Articles

Climate reconstruction from paired oxygen-isotope analyses of chironomid larval head capsules and endogenic carbonate (Hawes Water, UK) - Potential and problems

Temperature and the oxygen isotopic composition (δ18O) of meteoric water are both important palaeoclimatic variables, but separating their influences on proxies such as the δ18O of lake carbonates is often problematic. The large temperature variations that are known to have occurred in the northern mid-latitudes during the Late Glacial make this interval an excellent test for a novel approach that combines oxygen-isotope analyses of chironomid larval head capsules with co-occurring endogenic carbonate. We apply this approach to a Late Glacial lake sediment sequence from Hawes Water (NW England). Oxygen-isotope values in chironomid head capsules show marked variations during the Late Glacial that are similar to the oxygen isotope record from endogenic carbonate. However, summer temperature reconstructions based on the paired isotope values and fractionation between chironomids and calcite yield values between −20 and −4 °C, which are unrealistic and far lower than reconstructions based on chironomid assemblages at the same site. The composition of a limited number of samples of fossil chironomid larval head capsules determined using Pyrolysis gas-chromatography mass spectrometry indicates the presence of aliphatic geopolymers, suggesting that diagenetic alteration of the head capsules has systematically biased the isotope-derived temperature estimates. However, a similar trend in the isotope records of the two sources suggests that a palaeoclimate signal is still preserved.

Ecological sensitivity of marl lakes to nutrient enrichment: evidence from Hawes Water, UK

Summary Highly calcareous (marl) lakes are infrequent but important freshwater ecosystems, protected under the EU Habitats and Species Directive. Chara lakes have been considered resistant to eutrophication owing to the self‐stabilising properties of charophyte meadows. However, the opposite is suggested by the large‐scale biodiversity declines in marl lake taxa in Europe, and evidence of charophyte sensitivity to eutrophication. We combined contemporary, palaeolimnological and archival methods to investigate the eutrophication of Hawes Water, a shallow marl lake in north‐west England (U.K.). Changes in aquatic macrophyte and invertebrate communities were reconstructed through the analysis of historical macrophyte surveys and sedimentary plant and animal macrofossils in two dated sediment cores from the littoral and deep zones of the lake. In addition, chlorophyll and carotenoid pigments were analysed to track changes in primary production from benthic and pelagic areas. Substantial changes in macrophyte communities were detected over centennial timescales, suggesting high ecosystem sensitivity considering the presently moderate phosphorus concentrations in Hawes Water (mean annual total phosphorus 20 μg L−1). Two apparent periods of threshold‐like change were identified from the sediment record: (i) changes in cyanobacteria (aphanizophyll + myxoxanthophyll to canthaxanthin + zeaxanthin) and potentially in nutrient stoichiometry, reductions in the maximum macrophyte colonisation depth and water clarity, reduced charophyte and Potamogeton diversity, and increases in Nymphaeaceae; and (ii) severe reductions in light availability inferred from subdecadal doubling in phytoplankton abundance, substantial increases in Daphnia abundance and the extinction of charophytes from higher water depths. Further, change in both the littoral and deeper water has confined key marl lake taxa to smaller niches. In the littoral, increasing siltation and reed and Nymphaeaceae densities caused extinction of Littorella uniflora in the early 1900s and have reduced the evenness of Characeae with suspected imminent extinction of two highly localised Chara spp. In the deeper water, upslope creep of maximum colonisation depth has reduced habitat for intermediate‐depth marl lake taxa leading to the loss of four Potamogeton and one Chara species, and replacement of these taxa by Nuphar lutea. The large changes in macrophyte community composition and increased incidences of turbid water have reduced the distinctive and valued marl lake features of Hawes Water, indicating that marl lakes can, as a habitat type, be highly sensitive to eutrophication. The persistence of abundant generalist macrophyte species at considerable water depth may be a feature of high‐alkalinity lakes in clearwater, macrophyte‐dominated states, but is a distinct eutrophication response in marl lakes rather than an indication of resistance to eutrophication.

Controls on lake level in the early to mid Holocene, Hawes Water, Lancashire, UK

This study presents a new interpretation of the evidence for Holocene lake-level changes from Hawes Water in NW England constrained by detailed stratigraphic data, radiocarbon chronology and palaeo-environmental evidence. Lake levels are seen to decline gradually from the start of the Holocene through to 9960 cal. yr BP, in response to lake infilling and the prevailing dry climatic conditions. Low lake levels then persist until 6000 cal. yr BP, punctuated by two transgressive phases. Rising sea levels during the Holocene high-level sea stand are thought to be responsible for a major rise in lake level at 6000 cal. yr BP driven by changes in the local water-table. The rise in lake level is coincident with a rise in anthropogenic activity across the site, possibly reflecting the migration of coastal Mesolithic communities inland in response to rising sea levels.

Early-Holocene temperature variability inferred from chironomid assemblages at Hawes Water, northwest England

This paper presents the first high-resolution chironomid-inferred mean July air temperature (C-IT) reconstruction for the early Holocene from England. The reconstruction is based on a core recovered from a terrestrialised carbonate bench at Hawes Water, a small hard-water lake in northwest England. The record shows that temperatures rose rapidly after the Younger Dryas with temperatures reaching 14.0°C at the beginning of the Holocene. Over millennial timescales, the temperature record points to a slight rise in temperatures towards the top of the sequence at around 8000 years before the year 2000 (b2k). The trend is punctuated by a series of cool oscillations (at 11 200, 11 400, 10 700, 10 400, 9300 and 8300 b2k) and by a short period (11 300 to 10 250 b2k) when temperatures were considerably warmer (up to 14.9°C). The five cool oscillations coincide with temperature reversals found elsewhere in the North Atlantic region and in the Greenland ice core records. These cool events correlate well with both meltwater fluxes from the Laurentide and Scandinavian ice sheets and periods of low solar activity. Two of these oscillations (at 9300 and 8300 b2k) vary significantly from the early-Holocene mean. C-IT shift rapidly during both these events and temperatures fall ~1.6°C below the early-Holocene mean trend for ~ 50—60 years. The results presented here provide an insight into the instability of the early-Holocene climate in the British Isles and demonstrate the sensitivity of chironomids to rapid climatic events during the early Holocene.

Terrestrial impact of abrupt changes in the North Atlantic thermohaline circulation: Early Holocene, UK†

Abrupt cooling events are features of Holocene climate and may recur in the future. We use lake records from Hawes Water, NW England, to quantify the impact of two prominent early Holocene climatic events. Subdecadal oxygen isotope records from sedimentary carbonate (18δOc), dated using thermal ionization mass spectrometry (TIMS) U-series analyses, provide evidence for abrupt cold events, lasting ∼50 and ∼150 yr at 9350 and 8380 yr ago, which correlate with the 9.3 ka and 8.2 ka events recognized in Greenland ice cores. At Hawes Water, mean July air temperatures, inferred from chirono-mid assemblages, decreased by ∼1.6 °C during each event. Calculations show that the isotopic excursions were dominantly caused by decreases in the isotopic composition of meteoric precipitation (18δOp) by ∼1.3‰; this is interpreted as a direct downstream response to cooling and freshening of northeast Atlantic surface water by melting ice sheets. Intermediate in magnitude between events observed in Greenland and central Europe, the effects are consistent with a partial shutdown of the North Atlantic thermohaline circulation.

Determination of Holocene sedimentation rates from a carbonate lake using excess 226Ra profiles

Research on the development of excess 226Ra decay as a novel technique for dating lake sediments has been undertaken on Hawes Water, NW England. Investigation of the behaviour 226Ra and its precursors in the 238U-series in the lake environment supports the theoretical justification for dating carbonate sediments based on the decay of excess 226Ra activity that is transferred from the water column at the time of deposition via calcite coprecipitation. Depth profiles of excess 226Ra activity in bulk and biogenic carbonate phases of the sediment are exponential in form below a surface layer of lake sediment in which enhanced 226Ra influx can be identified. Application of a dating model that assumes a constant rate of supply and no significant post-depositional mobility of 226Ra yields sedimentation rates for the lower parts of two cores of the order of 0.02 g cm − 2 y − 1 that compare well with those obtained from 210Pb dating. Whilst post-depositional redistribution of 226Ra activity is shown to have negligible impact on the down-core profile, the approach is sensitive to changes in the rate of supply and the initial 226Ra activity — both of which can be identified and are confirmed by comparison with the excess 210Pb activity profile.

A Late‐glacial chironomid record from Hawes Water, northwest England

AbstractThis paper presents the results of a high‐resolution Late‐glacial chironomid stratigraphy from Hawes Water, a small carbonate lake in northern Lancashire. The samples were from a core taken from the terrestrialised margin of the present lake, which represents an intermediate depth between the true littoral and the profundal. The chironomid assemblage showed a high degree of sensitivity to both broad‐scale and short‐term temperature changes. Comparison with an existing proxy temperature record (δ18O) for the site confirmed the presence of four temperature inversions within the Late‐glacial Interstadial. A mean July air temperature inference model, derived from acid, soft‐water lakes in Norway and Svalbard, was applied to the data. Despite the absence of carbonate lakes within the Norwegian training set, there was a close similarity between trends in estimated July air temperature and the δ18O trace, with a particularly strong correspondence in the periods of clay deposition. This suggests that this model is highly robust. The inferred maximum Interstadial temperature was 13.4°C, dropping initially to 7.5°C in the Loch Lomond Stadial. Temperatures reach a maximum of nearly 10°C in this period, cool for a short period before rising rapidly to 13.2°C at the start of the Holocene. These temperatures are similar to but slightly higher than those estimated for Whitrig Bog, southeast Scotland, and lower than those inferred from coleopteran‐based models for sites in South Wales. Copyright © 2004 John Wiley & Sons, Ltd.

The use of ultra-sound in the preparation of carbonate and clay sediments for chironomid analysis

Initial investigations of Holocene carbonate sediment from Hawes Water, Northwest England, yielded lower numbers of chironomid head capsules than anticipated. Standard techniques used to prepare sediment for chironomid analysis were ineffective in breaking up the coarse crystalline sediment structure sufficiently. This led to large amounts of sediment being retained and increased sample processing times. The low yield of head capsules also meant that more sediment was needed to produce adequate numbers of head capsules for analysis. The use of ultra-sound as part of the sediment processing was investigated. This technique reduced the amount of sediment left for sorting and yielded significantly more head capsules which were of equivalent structural condition and cleaner than those produced by conventional methods. The technique was extended to clay samples where similar results were obtained although shorter treatment times are recommended. The proportion of Tanytarsini and Tanypodinae heads increased significantly in carbonate and clay samples, respectively; both sediment types showed a significant decline in the proportion of Chironomini. The results indicate that ultra-sonic preparation of samples will yield a more accurate representation of chironomid assemblages in sediments leading to greater sensitivity and reliability in analysing past environmental conditions.

A high resolution Late-Glacial isotopic record from Hawes Water, Northwest England: Climatic oscillations: calibration and comparison of palaeotemperature proxies

Understanding of the impact of past climate change on the terrestrial environment requires the development of quantitative palaeotemperature indicators that can be readily measured at closely spaced stratigraphic intervals. A high resolution oxygen isotopic record from Hawes Water, Lancashire, UK, reveals a degree of climatic instability that is greater than that recognised in previous isotopic studies of sites from the Atlantic margin of Northwest Europe. Four oscillations in the Late-Glacial interstadial before the onset of the Younger Dryas stadial are marked by sharp negative excursions in the δ 18O record of the carbonate sediments and accompanied by marked changes in chironomid populations and the pollen record. The oscillations are interpreted as cold events: they correlate with events recognised in marine and lacustrine temperature proxy records as well as the isotopic record from the Greenland ice-cores. Results suggest that there has been a significant change in lake water composition since the Late-Glacial but it is argued that the Hawes Water isotopic record, constrained by the results of a study of carbonate precipitation in the modern lake, provides a quantitative record of Late-Glacial temperature change. The 7°C maximum temperature difference inferred from the isotopic data, from the Interstadial optimum to the Younger Dryas stadial, and the magnitude of individual oscillations, compare well with estimates from terrestrial (coleopterid) and marine (diatom sea surface temperature) records: all are significantly greater than the, independently calibrated, 4.2°C change documented from a chironomid record from South Scotland. Such differences need to be resolved if the impacts of climatic events are to be fully understood.

A high resolution, multiproxy Late‐glacial record of climate change and intrasystem responses in northwest England

AbstractA lacustrine carbonate sequence from Hawes Water, Lancashire, UK, has been studied using stable isotopic, lithological, pollen and mineral magnetic analysis. The data reveal four abrupt climatic oscillations in the Late‐glacial Interstadial leading up to the onset of the Loch Lomond Stadial. The data also point to climatic warming relatively early within the stadial, ca. 12 500 GRIP yr, prior to the onset of the Holocene. The oxygen isotope record is taken as a signature of climate forcing against which the response of the lake‐system can be monitored. By adopting this approach it is revealed that the response of the biological system to the rapid climatic oscillations is non‐linear and primarily a function of the antecedent conditions. A significant end‐Devensian isotopic excursion (A) is matched by only minor changes in the cold‐adapted floras and faunas. During the warmer interstadial, the response of the biological ecosystem (events B–D) is clearly influenced by thresholds: major changes in the catchment vegetation associated with relatively minor oscillations in the isotopic signature. The stratigraphical patterns reveal significant lag effects between the onset of climate deterioration and resulting changes in vegetation. Copyright © 2002 John Wiley & Sons, Ltd.

Seasonal trends in the uranium-series istopic signatures of lake waters and sediments: Hawes Water, north-west England

Potential seasonal variation in the U-series radioisotopic signatures of lake and input waters was investigated in Hawes Water, north-west England, and the sedimentary record was examined to establish whether any observed seasonality is preserved in the sediment U and Th radioisotopic activity ratios. U-series disequilibrium in the waters is indicative of both surface and shallow sub-surface origins for the dissolved U, and that this supply is influenced by changes in the prevailing hydrological regime. However, the lake is buffered from this seasonality in that the 234U/238U activity ratio remains constant during the year, and the U content undergoes only a marginal decrease during summer. The change in the mechanism of lake sedimentation from allochthonous organic input during winter to autochthonous carbonate formation during summer has a more significant influence on the U-series radioisotopic characteristics of sedimentary record in that the proportion of organic and carbonate material both exhibit a strong control on the234U/238U activity ratio and U content. In addition, significant proportions of ‘sediment’ U and Th are associated with ferromanganese oxyhydroxides. Given this seasonality, it is of some significance that the 234U/238U activity ratios of the bottom sediments preserve a reasonable record of lake U-series disequilibrium and are, therefore, potential indicators of long-term changes in catchment hydrology.

POLLEN‐ANALYTICAL DATA FROM URSWICKTARN AND ELLERSIDE MOSS, NORTH LANCASHIRE

SummaryStratigraphic and pollen‐analytical data from the margin of Urswick Tarn and from the centre of Ellerside Moss are presented and discussed. The diagrams record episodes in the local ecological history from the early part of Post‐glacial pollen zone VI almost up to the present day. It is suggested that at Urswick Tarn there was a phase of lowered lake level during zone VI contemporary with that recorded at Hawes Water in Lonsdale (Oldfield, 1960a). The Ellerside Moss record begins early in pollen zone Vila and at the end of this zone, both diagrams show a clearly marked ‘Elm Decline’separated from a subsequent ‘Landnam’phase (cf. Iversen, 1941; Morrison, 1959; etc.). Above this horizon, most of the pollen‐analytical changes in the diagrams seem to be mainly the result of successive periods of human interference with the local vegetation; the final episode at Urswick Tarn records nineteenth‐century land‐use in the area.