Stephen McCarron

Evidence for Heinrich event 1 in the British Isles

In the north Irish Sea basin (ISB), sedimentary successions constrained by AMS 14C dates obtained from marine microfaunas record three major palaeoenvironmental shifts during the last deglacial cycle. (i) Marine muds (Cooley Point Interstadial) dated to between 16.7 and 14.7 14C kyr BP record a major deglaciation of the ISB following the Late Glacial Maximum (LGM). (ii) Terminal outwash and ice-contact landforms (Killard Point Stadial) were deposited during an extensive ice readvance, which occurred after 14.7 14C kyr BP and reached a maximum extent at ca.14 14C kyr BP. At this time the lowlands surrounding the north ISB were drumlinised. Coeval flowlines reconstructed from these bedforms end at prominent moraines (Killard Point, Bride, St Bees) and indicate contemporaneity of drumlinisation from separate ice dispersal centres, substrate erosion by fast ice flow, and subglacial sediment transfer to ice-sheet margins. In north central Ireland bed reorganisation associated with this fast ice-flow phase involved overprinting and drumlinisation of earlier transverse ridges (Rogen-type moraines) by headward erosion along ice streams that exited through tidewater ice margins. This is the first direct terrestrial evidence that the British Ice Sheet (BIS) participated in Heinrich event 1 (H1). (iii) Regional mud drapes, directly overlying drumlins, record high relative sea-level (RSL) with stagnation zone retreat after 13.7 14C kyr BP (Rough Island Interstadial). Elsewhere in lowland areas of northern Britain ice-marginal sediments and morainic belts record millennial-scale oscillations of the BIS, which post-date the LGM advance on to the continental shelf, and pre-date the Loch Lomond Stadial (Younger Dryas) advance in the highlands of western Scotland (ca. 11–10 14C kyr BP). In western, northwestern and northern Ireland, Killard Point Stadial (H1) ice limits are reconstructed from ice-flow lines that are coeval with those in the north ISB and end at prominent moraines. On the Scottish continental shelf possible H1-age ice limits are reconstructed from dated marine muds and associated ice marginal moraines. It is argued that the last major offshore ice expansion from the Scottish mountains post-dated ca. 15 14C kyr BP and is therefore part of the H1 event. In eastern England the stratigraphic significance of the Dimlington silts is re-evaluated because evidence shows that there was only one major ice oscillation post-dating ca.18 14C kyr BP in these lowlands. In a wider context the sequence of deglacial events in the ISB (widespread deglaciation of southern part of the BIS major readvance during H1 ice sheet collapse) is similar to records of ice sheet variability from the southern margins of the Laurentide Ice Sheet (LIS). Well-dated ice-marginal records, however, show that during the Killard Point readvance the BIS was at its maximum position when retreat of the LIS was well underway. This phasing relationship supports the idea that the BIS readvance was a response to North Atlantic cooling induced by collapse of the LIS.

Ice-flow stages and glacial bedforms in north central Ireland: a record of rapid environmental change during the last glacial termination

Satellite imagery is a useful tool to assess large-scale (>103km2) geological patterns. Satellite imagery of north central Ireland shows cross-cut and overprinted subglacial bedform patterns. Bedform lineations, supported by sedimentary evidence, are used to reconstruct four ice-flow stages (named A-D) during the termination of the last (Devensian) glaciation (22 000–13 000 radiocarbon (14C) years BP). Flow stage A relates to southwesterly flow of Scottish ice across eastern Ireland. Flow stage B, during the last glacial maximum (c. 25 000–22 000 14C years BP), records southeasterly ice-flow from dispersal centres in northern parts of Ireland. Transverse subglacial ridges (Rogen moraines) formed during stage B are the largest area of this ridge type in western Europe. Flow stage C records erosional headcutting in the Rogen moraine field and sediment streamlining (drumlinization) by ice streams drawn into the Irish Sea Basin. This flow stage is constrained by AMS radiocarbon dates from marine microfaunas to around 14 500 14C years BP. Flow stage D records drumlinization from an inland centre in the Lough Neagh Basin. Overall bedform patterns can be used to reconstruct ice mass history and evaluate controls on ice activity, including millennial-scale changes in amphi-North Atlantic climate. Field evidence of bedform relationships also casts doubt on current concepts of drumlinization and the role of pervasive sediment deformation in glacial systems.

Pleistocene glaciations in Ireland

Abstract A literature survey and data from recent investigations are used to reconstruct ice limits in Ireland during the last (Midlandian) and penultimate (Munsterian) cold periods which are correlated with Marine Isotope Stages (MIS) 2-5d (Weichselian) and 6-8 (Saalian) respectively. Evidence for Munsterian ice limits and flow directions is equivocal and based mainly on erratic carriage and the presence of striae and subdued glacial landforms found outside well-marked Midlandian end moraines. Ice extent and flow direction is known only from the late Midlandian (MIS 2; 24-10 kyr BP) although ice may well have been present in the early Midlandian (MIS 3-5d; 24-117 kyr BP). Six late Midlandian glacial stages are identified on the basis of morphosedimentary and dating evidence, and patterns of subglacial bedforms including drumlins and Rogen moraines. Previous late Midlandian glacial models are well-established but are generally based on incomplete and/or erroneous datasets, are not age-constrained, and do not consider time-transgressive sedimentation and landform-shaping events. Recent work shows that repeated ice advance-retreat cycles (oscillations) occurred during the late Midlandian. Oscillations resulted in stratigraphically superimposed, overprinted and cross-cut landform and sediment patterns that record ice activity throughout the glacial cycle. Additionally, subglacial bedforms previously unrecorded in the British Isles, such as flow-transverse ridges (Rogen moraines), are also present. Late Midlandian ice oscillations in Ireland occurred in tempo with millennial-scale changes in North Atlantic climate, suggesting connection to hemispheric shifts of the ice-ocean-atmosphere system.

Cosmogenic 10Be chronology of the last deglaciation of western Ireland, and implications for sensitivity of the Irish Ice Sheet to climate change

Accelerator mass spectrometry (AIMS) C-14 slates of fossiliferous marine mud identify a readvance of the Irish Ice Sheet from the north and central lowlands of Ireland into the northern Irish Sea Basin during the Killard Point Stadial at ca. 16.5 cal k.y. B.P, with subsequent deglaciation occurring by ca. 15.0-15.5 cal k.y. B.P. Killard Point Stadial moraines have been mapped elsewhere in Ireland but have previously remained undated. Here, we report sixteen Be-10 surface exposure dates that constrain the age of retreat of the Killard Point Stadial ice margin from western Ireland. Eight Be-10 dates from the Ox Mountains (13.9-18.1 ka) indicate that final deposition of the moraine occurred at 15.6 +/- 0.5 ka (mean age, standard error). Eight Be-10 dates from Furnace Lough (14.1-17.3 ka, mean age of 15.6 +/- 0.4 ka) are statistically-indistinguishable from the Ox Mountain samples, suggesting that. the moraines were deposited during the same glacial event. Given the agreement between the two age groups, and their common association with a regionally significant moraine system, we combine them sir derive a mean age of 15.6 +/- 0.3 ka (15.6 +/- 1.0 ka with external uncertainty). This age is in excellent agreement with the timing-of deglaciation from the Irish Sea Basin (at or older than 15.3 +/- 0.2 cal k.y. B.P.) and suggests the onset of near-contemporaneous retreat of the Irish Ice Sheet from its maximum Killard Point Stadial limit. A reconstruction of the ice surface indicates that the Irish Ice Sheet reached a maximum surface elevation of similar to 500 m over the central Irish Lowlands during the Killard Point Stadial, suggesting a high sensitivity of the ice sheet to small changes in climate.

Portable X-ray fluorescence as a rapid technique for surveying elemental distributions in soil

ABSTRACT Case studies from two sites demonstrate how concentration distributions of hazardous contaminants can be rapidly measured and visualized using portable XRF (X-ray fluorescence) coupled with geostatistical interpolation tools. In this study, lead is used as an exemplar due to its well-known detrimental effect on human health through long-term exposure. A portable Thermo Scientific NITON X-ray fluorescence (XRF) instrument was used for real-time in-situ concentration measurements, which were linked to GPS coordinates of the sampling locations. A 52 point mixed sampling density survey was performed at a site near Maynooth, Co. Kildare, and a second 58 survey undertaken at Dublin City University (DCU). At Maynooth, high concentrations of Pb (above 110 mg/kg) were found close to the site where a local canal meets a road. At the DCU site, results indicate high Pb concentrations (above 160 mg/kg) near a busy main road. Geostatistical techniques were used to generate concentration prediction and critical threshold contour surfaces for both sites. Linked with GPS coordinates for each sampling location, this technology enables the distribution of multiple elements to be mapped over wide areas in a relatively short time. Supplemental materials are available for this article. Go to the publishers online edition of Spectroscopy Letters to view the supplemental file.

Using gis to map the evolution of the gaeltacht

Abstract This paper describes the results of using digital mapping techniques (Geographic Information Systems ‐ GIS) to facilitate the translation of historical legislative documents into large‐scale (townland level) maps of the Gaeltacht. The boundaries of the Gaeltacht, within the error limits of the digital spatial data, indicate the changing spatial extent of the Gaeltacht from its inception through phases of legislative reform throughout the 20th century. This spatial definition of the Gaeltacht has largely been the basis of protection for the Irish language since independence. Changes in the defining criteria and modification of areas comprising the Gaeltacht have resulted in a discontinuous modern Gaeltacht which lacks definition in any single legislative document. A digital version of the modem Gaeltacht boundary in a GIS readable format will allow its integration with other spatial datasets and gives the administrative region new clarity of definition. This paper does discuss the actual use of Ir...

Seabed geomorphology of the Porcupine Bank, West of Ireland

ABSTRACT A new map of the seabed geomorphology on the Porcupine Bank, located at the western edge of the north-eastern Atlantic shelf west of Ireland, uses high-resolution multibeam bathymetric and backscatter data as well as numerous shallow seismic profiles to identify individual landforms. They are described based on their acoustic signature on the various datasets. The landforms comprise sharp-crested ridges, mounds and outcrops often associated with and expressing underlying bedrock topography; sand waves highlighting modern currents directions; and iceberg scours with strongly preferred orientations. The map is intended as baseline evidence to test models of the palaeoceanographic and palaeoglaciological history of the Porcupine Bank.

Gravity Flow Deposits in the Deep Rockall Trough, Northeast Atlantic

The north-western margin of the Irish Rockall Trough in the Northeast Atlantic is dominated by the scarps of the Rockall Bank Mass Flow (RBMF) which extends towards the centre of the Rockall Trough, whereas the eastern margin is incised by numerous canyons that have no obvious associated fans at the foot of the slope. Terminal lobes associated with the glaciogenic Donegal-Barra Fan extend into the Rockall Trough from the northeast, whereas in the southwest the seafloor is dominated by the Feni Drift, a giant contourite drift formed by ocean bottom currents which was truncated by the sidewalls and depositional lobes of the RBMF. In June 2010 the RV Celtic Explorer cruise CE10008 collected the first comprehensive set of piston cores from the Irish sector of the deep Rockall Trough. Here we report on a sub-set of those cores recovered from across and beyond the bathymetric expression of the RBMF eastern outer limit in order to determine whether gravity flows were released during this event and whether they have traversed across the basin. The cores, taken in water depths of nearly 3,000 m, reveal that significant coarse sediment (up to coarse sand) was emplaced on the deep basin floor by both turbidity currents and bottom currents. We identify several discrete turbidite sand and silt deposits with geochemical signatures that point to different source areas. The youngest two appear to have been generated from the area occupied by the RBMF to the west during the Holocene. The remaining turbidite beds came from an easterly or northeasterly source and tie back to the Donegal-Barra Fan and are probably glacially related. Between the two periods we find a thick (>1.5 m) contouritic sand, possibly formed by bottom current reworking of the Feni Drift.

Advances in Irish Quaternary Studies

Investigation of Ireland’s Quaternary heritage has a long history that extends back prior to the setting up of the Geological Survey of Ireland in 1845. Ireland’s rich Quaternary deposits and land forms have ensured that it continues to be a key location for international research. The publication of The Quaternary History of Ireland in 1985 (Edwards and Warren 1985) has served the Quaternary community extremely well for three decades but it is now timely to review the substantial body of recent research into the Irish Quaternary. This chapter serves to provide a historical context to the syntheses of recent research that are reported in the subsequent chapters of this book. 1 The Background to the Irish Quaternary Investigation of Ireland’s Quaternary heritage has a long history that extends back prior to the setting up of the Geological Survey of Ireland in 1845. Quaternary sections had been extensively described and many were assigned to the classification of ‘drift’ explained at the time by the widely accepted Marine Submergence Theory. The Geological Society of Dublin, founded in 1831, included an address P. Coxon (&) F. Mitchell Trinity College Dublin, Dublin 2, Ireland e-mail: pcoxon@tcd.ie F. Mitchell e-mail: fraser.mitchell@tcd.ie S. McCarron Maynooth University, Maynooth, Kildare, Ireland e-mail: stephen.mccarron@nuim.ie The history of the Geological Survey of Ireland and its early work is interestingly summarized in Herries-Davies’ (1995) book “North From The Hook”. Chapter 8 “Delving the Drift” may be of particular interest to the reader.

Introduction: Advances in Irish Quaternary Studies

Investigation of Ireland’s Quaternary heritage has a long history that extends back prior to the setting up of the Geological Survey of Ireland in 1845. Ireland’s rich Quaternary deposits and land forms have ensured that it continues to be a key location for international research. The publication of The Quaternary History of Ireland in 1985 (Edwards and Warren 1985) has served the Quaternary community extremely well for three decades but it is now timely to review the substantial body of recent research into the Irish Quaternary. This chapter serves to provide a historical context to the syntheses of recent research that are reported in the subsequent chapters of this book.