I am a physical geographer and environmental scientist with multidisciplinary interests in past climates and environmental change in lakes, oceans and peatlands.
XX INQUA Congress (Jul 2019), Dublin, Ireland., 2019
The Lateglacial period (~14.7 – 11.7 cal. ka BP) eruptive stage of Glacier Peak in the
northern ... more The Lateglacial period (~14.7 – 11.7 cal. ka BP) eruptive stage of Glacier Peak in the
northern Cascade Range deposited a number of ash layers (tephras) in quick
succession, forming visible event-stratigraphic marker layers (isochrons) across much
of western North America. Geochemically distinctive microscopic glass shards from the most explosive eruptions of this stage remain detectible in a ‘cryptotephra’ layer (not visible in stratigraphy to the naked eye) of rhyolitic composition in lake sediments on the NE Atlantic Seaboard, where it is dated to 13.74 – 13.45 cal. ka BP (2σ).
Here, we report the first trans-Atlantic detection of Glacier Peak cryptotephra (set G) in
a Lateglacial lake site in western Scotland, ~7000 km from source. At this location
(Loch Ashik, Isle of Skye), Glacier Peak shares a crowded tephrostratigraphy with two
well-documented cryptotephra layers of likely Icelandic origin: the Borrobol Tephra
(14.19–14.00 cal. ka BP; 2σ) and the geochemically equivalent Penifiler Tephra
(14.06–13.81 cal. ka BP; 2σ) which occur singly or together in a number of terrestrial
Lateglacial sequences in Scotland and Scandinavia.
Previous tephra work at this site, as well as other localities, has not identified shards of
Glacier Peak composition. This may be due to masking of such ultra-distal layers by
the relatively greater concentrations of the closely preceding, and thus stratigraphically
overshadowing, Penifiler and Borrobol tephras which often exhibit reworked post-peak
shard distributions. However, the use of higher resolution 0.5 cm contiguous
stratigraphic sampling and off-peak geochemical analysis in this study resolves
previously unseen shard concentration variations within these distribution tails which
are consistent with additional tephra layers and which are shown to contain a relatively
greater proportion of Glacier Peak composition.
It is likely that other sedimentary sequences with faster accumulation rates will allow
better stratigraphic distinction of the Glacier Peak layer from the Penifiler tephra.
Additionally, Glacier Peak may be present elsewhere in the European tephrostratigraphy in sequences where the Borrobol and Penifiler tephras were not
deposited, and consequently where it will be less obscured.
The introduction of the well-dated Glacier Peak isochron into the regional
tephrostratigraphy of Scotland should aid in constraining local age models. It will also
permit direct trans-Atlantic correlation of sedimentary sequences for the mid-Lateglacial period, which was characterised by abrupt and short-lived climate oscillations. Accurate assessment of the relative timings of such palaeoclimate events is key to determining causal forcing mechanisms throughout the North Atlantic region.
Lakes and bogs in northeastern North America preserve tephra deposits sourced from multiple volca... more Lakes and bogs in northeastern North America preserve tephra deposits sourced from multiple volcanic systems in the Northern Hemisphere. However, most studies of these deposits focus on specific Holocene intervals and the latest Pleistocene, providing snapshots rather than a full picture. We combine new data with previous work, supplemented by a broad review of the characteristics and ages of potential source regions and volcanoes, to develop the first composite tephrostratigraphic framework covering the last 14,000 years for this region. We report new cryptotephra records from three ombrotrophic peat bogsdIrwin Smith (Michigan), Bloomingdale (New York), and Sidney Bog (Maine)das well as new analyses and age models from previously reported sites, Nordan's Pond Bog (Newfoundland) and Thin-Ice Pond (Nova Scotia). A new tephra (Iliinsky) from the NGRIP and GRIP ice cores is also presented as it can be correlated to new data from these terrestrial records and helps validate radiocarbon age models. We identify 21 new tephra in addition to the 15 already known, several of which cover the entire region e the White River Ash east, Newberry Pumice, Ruppert (NDN-230), and Mazama. For the first time we find Mount St. Helens Yn (ca. 3660 cal yr BP) and a set P tephra (~3000e2550 cal yr BP), and confirm the presence of Jala Pumice from Volcan Ceboruco, Mexico, and KS 1 from Ksudach volcano, Kamchatka. We describe new "ultra-distal" tephra, including the early Holocene KS 2 eruption, and propose correlations to volcanoes Iliinsky and Shiveluch of Kamchatka, and Ushishir of the Kurile Islands. Not all of these tephra represent large eruptions, with several plausible correlations to sub-Plinian events. Using Bayesian age-modeling, we present new age estimates for the newly described tephra, for tephra with previously poor age control, and for several proximal correlatives. Overall, we demonstrate northeastern North America's importance for providing transcontinental linkages between paleoenvironmental records and providing insights into ash distribution from different styles and sizes of eruptions.
A widespread platinum (Pt) anomaly was recently documented in Greenland ice and 11 North American... more A widespread platinum (Pt) anomaly was recently documented in Greenland ice and 11 North American sedimentary sequences at the onset of the Younger Dryas (YD) event (~12,800 cal yr BP), consistent with the YD Impact Hypothesis. We report high-resolution analyses of a 1-meter section of a lake core from White Pond, South Carolina, USA. After developing a Bayesian age-depth model that brackets the late Pleistocene through early Holocene, we analyzed and quantified the following: (1) Pt and palladium (Pd) abundance, (2) geochemistry of 58 elements, (3) coprophilous spores, (4) sedimentary organic matter (OC and sedaDNA), (5) stable isotopes of C (δ13C) and N (δ15N), (6) soot, (7) aciniform carbon, (8) cryptotephra, (9) mercury (Hg), and (10) magnetic susceptibility. We identified large Pt and Pt/Pd anomalies within a 2-cm section dated to the YD onset (12,785 ± 58 cal yr BP). These anomalies precede a decline in coprophilous spores and correlate with an abrupt peak in soot and C/OC rat...
... c Dryas, Salix, Betula nana, Polytrichum leaves; d ... SPE, Pyne-O&am... more ... c Dryas, Salix, Betula nana, Polytrichum leaves; d ... SPE, Pyne-O'Donnell SDF, Lowe JJ, Matthews IP, Stone A, Pollard AM, Turney CSM, Molyneux E. 2005. A new and less destructive laboratory procedure for the physical separation of distal glass tephra shards from sediments. ...
Holocene palaeoclimate records from the mid and eastern North Atlantic region show a persistent c... more Holocene palaeoclimate records from the mid and eastern North Atlantic region show a persistent cyclical pattern of centennial- to millennial-scale changes in key climate drivers, such as North Atlantic Deep Water formation and the Atlantic Meridional Overturning Circulation. This pattern is relatively well expressed in terrestrial records from Europe; however, the picture differs in the western North Atlantic since this region is proximal to the major discharge routes from the Laurentide Ice Sheet. Here eastern seaboard climates were affected by repeated meltwater discharges into the ocean of varying magnitudes that continued until ca. 6.8 ka BP. The coastal plateau bogs from Maine to northern Newfoundland are well placed to provide detailed palaeoclimate archives describing the impacts of Laurentide deglaciation and the postglacial re-organisation of atmospheric conditions. Terrestrial responses to meltwater-climate-ocean interactions can be clearly expressed in oceanic raised bogs because they are isolated from ground and surface waters, receiving almost all of their water and nutrition from meteoric sources. Specifically, summer precipitation/evapo-transpiration conditions are a major control on bog surface wetness which is in turn a key factor determining the composition of peat-forming communities. The PRECIP project (Palaeo REconstructions of ocean-atmosphere Coupling In Peat) aims to exploit the close coupling between raised bogs and the atmosphere to reconstruct the spatial-temporal pattern of moisture balance changes associated with past variability in the Gulf Stream and the Labrador Current on the eastern seaboard of North America. The reconstructions will be used to test a set of hypotheses concerning the relationships between thermohaline circulation variability, atmospheric circulation and terrestrial responses to climate change. A multi-proxy approach will be used to reconstruct past change in atmospheric moisture balance at multi-decadal to millennial timescales using plant macrofossils and testate amoebae. These reconstructions will be compared with measurements of δ18O and δD in Sphagnum peat cellulose which can be used to determine past changes in precipitation moisture source.
XX INQUA Congress (Jul 2019), Dublin, Ireland., 2019
The Lateglacial period (~14.7 – 11.7 cal. ka BP) eruptive stage of Glacier Peak in the
northern ... more The Lateglacial period (~14.7 – 11.7 cal. ka BP) eruptive stage of Glacier Peak in the
northern Cascade Range deposited a number of ash layers (tephras) in quick
succession, forming visible event-stratigraphic marker layers (isochrons) across much
of western North America. Geochemically distinctive microscopic glass shards from the most explosive eruptions of this stage remain detectible in a ‘cryptotephra’ layer (not visible in stratigraphy to the naked eye) of rhyolitic composition in lake sediments on the NE Atlantic Seaboard, where it is dated to 13.74 – 13.45 cal. ka BP (2σ).
Here, we report the first trans-Atlantic detection of Glacier Peak cryptotephra (set G) in
a Lateglacial lake site in western Scotland, ~7000 km from source. At this location
(Loch Ashik, Isle of Skye), Glacier Peak shares a crowded tephrostratigraphy with two
well-documented cryptotephra layers of likely Icelandic origin: the Borrobol Tephra
(14.19–14.00 cal. ka BP; 2σ) and the geochemically equivalent Penifiler Tephra
(14.06–13.81 cal. ka BP; 2σ) which occur singly or together in a number of terrestrial
Lateglacial sequences in Scotland and Scandinavia.
Previous tephra work at this site, as well as other localities, has not identified shards of
Glacier Peak composition. This may be due to masking of such ultra-distal layers by
the relatively greater concentrations of the closely preceding, and thus stratigraphically
overshadowing, Penifiler and Borrobol tephras which often exhibit reworked post-peak
shard distributions. However, the use of higher resolution 0.5 cm contiguous
stratigraphic sampling and off-peak geochemical analysis in this study resolves
previously unseen shard concentration variations within these distribution tails which
are consistent with additional tephra layers and which are shown to contain a relatively
greater proportion of Glacier Peak composition.
It is likely that other sedimentary sequences with faster accumulation rates will allow
better stratigraphic distinction of the Glacier Peak layer from the Penifiler tephra.
Additionally, Glacier Peak may be present elsewhere in the European tephrostratigraphy in sequences where the Borrobol and Penifiler tephras were not
deposited, and consequently where it will be less obscured.
The introduction of the well-dated Glacier Peak isochron into the regional
tephrostratigraphy of Scotland should aid in constraining local age models. It will also
permit direct trans-Atlantic correlation of sedimentary sequences for the mid-Lateglacial period, which was characterised by abrupt and short-lived climate oscillations. Accurate assessment of the relative timings of such palaeoclimate events is key to determining causal forcing mechanisms throughout the North Atlantic region.
Lakes and bogs in northeastern North America preserve tephra deposits sourced from multiple volca... more Lakes and bogs in northeastern North America preserve tephra deposits sourced from multiple volcanic systems in the Northern Hemisphere. However, most studies of these deposits focus on specific Holocene intervals and the latest Pleistocene, providing snapshots rather than a full picture. We combine new data with previous work, supplemented by a broad review of the characteristics and ages of potential source regions and volcanoes, to develop the first composite tephrostratigraphic framework covering the last 14,000 years for this region. We report new cryptotephra records from three ombrotrophic peat bogsdIrwin Smith (Michigan), Bloomingdale (New York), and Sidney Bog (Maine)das well as new analyses and age models from previously reported sites, Nordan's Pond Bog (Newfoundland) and Thin-Ice Pond (Nova Scotia). A new tephra (Iliinsky) from the NGRIP and GRIP ice cores is also presented as it can be correlated to new data from these terrestrial records and helps validate radiocarbon age models. We identify 21 new tephra in addition to the 15 already known, several of which cover the entire region e the White River Ash east, Newberry Pumice, Ruppert (NDN-230), and Mazama. For the first time we find Mount St. Helens Yn (ca. 3660 cal yr BP) and a set P tephra (~3000e2550 cal yr BP), and confirm the presence of Jala Pumice from Volcan Ceboruco, Mexico, and KS 1 from Ksudach volcano, Kamchatka. We describe new "ultra-distal" tephra, including the early Holocene KS 2 eruption, and propose correlations to volcanoes Iliinsky and Shiveluch of Kamchatka, and Ushishir of the Kurile Islands. Not all of these tephra represent large eruptions, with several plausible correlations to sub-Plinian events. Using Bayesian age-modeling, we present new age estimates for the newly described tephra, for tephra with previously poor age control, and for several proximal correlatives. Overall, we demonstrate northeastern North America's importance for providing transcontinental linkages between paleoenvironmental records and providing insights into ash distribution from different styles and sizes of eruptions.
A widespread platinum (Pt) anomaly was recently documented in Greenland ice and 11 North American... more A widespread platinum (Pt) anomaly was recently documented in Greenland ice and 11 North American sedimentary sequences at the onset of the Younger Dryas (YD) event (~12,800 cal yr BP), consistent with the YD Impact Hypothesis. We report high-resolution analyses of a 1-meter section of a lake core from White Pond, South Carolina, USA. After developing a Bayesian age-depth model that brackets the late Pleistocene through early Holocene, we analyzed and quantified the following: (1) Pt and palladium (Pd) abundance, (2) geochemistry of 58 elements, (3) coprophilous spores, (4) sedimentary organic matter (OC and sedaDNA), (5) stable isotopes of C (δ13C) and N (δ15N), (6) soot, (7) aciniform carbon, (8) cryptotephra, (9) mercury (Hg), and (10) magnetic susceptibility. We identified large Pt and Pt/Pd anomalies within a 2-cm section dated to the YD onset (12,785 ± 58 cal yr BP). These anomalies precede a decline in coprophilous spores and correlate with an abrupt peak in soot and C/OC rat...
... c Dryas, Salix, Betula nana, Polytrichum leaves; d ... SPE, Pyne-O&am... more ... c Dryas, Salix, Betula nana, Polytrichum leaves; d ... SPE, Pyne-O'Donnell SDF, Lowe JJ, Matthews IP, Stone A, Pollard AM, Turney CSM, Molyneux E. 2005. A new and less destructive laboratory procedure for the physical separation of distal glass tephra shards from sediments. ...
Holocene palaeoclimate records from the mid and eastern North Atlantic region show a persistent c... more Holocene palaeoclimate records from the mid and eastern North Atlantic region show a persistent cyclical pattern of centennial- to millennial-scale changes in key climate drivers, such as North Atlantic Deep Water formation and the Atlantic Meridional Overturning Circulation. This pattern is relatively well expressed in terrestrial records from Europe; however, the picture differs in the western North Atlantic since this region is proximal to the major discharge routes from the Laurentide Ice Sheet. Here eastern seaboard climates were affected by repeated meltwater discharges into the ocean of varying magnitudes that continued until ca. 6.8 ka BP. The coastal plateau bogs from Maine to northern Newfoundland are well placed to provide detailed palaeoclimate archives describing the impacts of Laurentide deglaciation and the postglacial re-organisation of atmospheric conditions. Terrestrial responses to meltwater-climate-ocean interactions can be clearly expressed in oceanic raised bogs because they are isolated from ground and surface waters, receiving almost all of their water and nutrition from meteoric sources. Specifically, summer precipitation/evapo-transpiration conditions are a major control on bog surface wetness which is in turn a key factor determining the composition of peat-forming communities. The PRECIP project (Palaeo REconstructions of ocean-atmosphere Coupling In Peat) aims to exploit the close coupling between raised bogs and the atmosphere to reconstruct the spatial-temporal pattern of moisture balance changes associated with past variability in the Gulf Stream and the Labrador Current on the eastern seaboard of North America. The reconstructions will be used to test a set of hypotheses concerning the relationships between thermohaline circulation variability, atmospheric circulation and terrestrial responses to climate change. A multi-proxy approach will be used to reconstruct past change in atmospheric moisture balance at multi-decadal to millennial timescales using plant macrofossils and testate amoebae. These reconstructions will be compared with measurements of δ18O and δD in Sphagnum peat cellulose which can be used to determine past changes in precipitation moisture source.
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northern Cascade Range deposited a number of ash layers (tephras) in quick
succession, forming visible event-stratigraphic marker layers (isochrons) across much
of western North America. Geochemically distinctive microscopic glass shards from the most explosive eruptions of this stage remain detectible in a ‘cryptotephra’ layer (not visible in stratigraphy to the naked eye) of rhyolitic composition in lake sediments on the NE Atlantic Seaboard, where it is dated to 13.74 – 13.45 cal. ka BP (2σ).
Here, we report the first trans-Atlantic detection of Glacier Peak cryptotephra (set G) in
a Lateglacial lake site in western Scotland, ~7000 km from source. At this location
(Loch Ashik, Isle of Skye), Glacier Peak shares a crowded tephrostratigraphy with two
well-documented cryptotephra layers of likely Icelandic origin: the Borrobol Tephra
(14.19–14.00 cal. ka BP; 2σ) and the geochemically equivalent Penifiler Tephra
(14.06–13.81 cal. ka BP; 2σ) which occur singly or together in a number of terrestrial
Lateglacial sequences in Scotland and Scandinavia.
Previous tephra work at this site, as well as other localities, has not identified shards of
Glacier Peak composition. This may be due to masking of such ultra-distal layers by
the relatively greater concentrations of the closely preceding, and thus stratigraphically
overshadowing, Penifiler and Borrobol tephras which often exhibit reworked post-peak
shard distributions. However, the use of higher resolution 0.5 cm contiguous
stratigraphic sampling and off-peak geochemical analysis in this study resolves
previously unseen shard concentration variations within these distribution tails which
are consistent with additional tephra layers and which are shown to contain a relatively
greater proportion of Glacier Peak composition.
It is likely that other sedimentary sequences with faster accumulation rates will allow
better stratigraphic distinction of the Glacier Peak layer from the Penifiler tephra.
Additionally, Glacier Peak may be present elsewhere in the European tephrostratigraphy in sequences where the Borrobol and Penifiler tephras were not
deposited, and consequently where it will be less obscured.
The introduction of the well-dated Glacier Peak isochron into the regional
tephrostratigraphy of Scotland should aid in constraining local age models. It will also
permit direct trans-Atlantic correlation of sedimentary sequences for the mid-Lateglacial period, which was characterised by abrupt and short-lived climate oscillations. Accurate assessment of the relative timings of such palaeoclimate events is key to determining causal forcing mechanisms throughout the North Atlantic region.
from Europe; however, the picture differs in the western North Atlantic since this region is proximal to the major discharge routes from the Laurentide Ice Sheet. Here eastern seaboard climates were affected by repeated meltwater discharges into the ocean of varying magnitudes that continued until ca. 6.8 ka BP. The coastal plateau bogs from Maine to northern Newfoundland are well placed to provide detailed palaeoclimate archives describing the impacts of Laurentide deglaciation and the postglacial re-organisation of atmospheric conditions. Terrestrial responses to meltwater-climate-ocean interactions can be clearly expressed in oceanic raised
bogs because they are isolated from ground and surface waters, receiving almost all of their water and nutrition from meteoric sources. Specifically, summer
precipitation/evapo-transpiration conditions are a major control on bog surface wetness which is in turn a key factor determining the composition of peat-forming communities. The PRECIP project (Palaeo REconstructions of ocean-atmosphere Coupling In Peat) aims to exploit the close coupling between raised bogs and the atmosphere to reconstruct the spatial-temporal pattern of moisture balance
changes associated with past variability in the Gulf Stream and the Labrador Current on the eastern seaboard of North America. The reconstructions will be used to test a set of hypotheses concerning the relationships between thermohaline circulation variability, atmospheric circulation and terrestrial responses to climate change.
A multi-proxy approach will be used to reconstruct past change in atmospheric moisture balance at multi-decadal to millennial timescales using plant macrofossils and testate amoebae. These reconstructions will be compared with measurements of δ18O and δD in Sphagnum peat cellulose which can be used to determine past changes in precipitation moisture source.
northern Cascade Range deposited a number of ash layers (tephras) in quick
succession, forming visible event-stratigraphic marker layers (isochrons) across much
of western North America. Geochemically distinctive microscopic glass shards from the most explosive eruptions of this stage remain detectible in a ‘cryptotephra’ layer (not visible in stratigraphy to the naked eye) of rhyolitic composition in lake sediments on the NE Atlantic Seaboard, where it is dated to 13.74 – 13.45 cal. ka BP (2σ).
Here, we report the first trans-Atlantic detection of Glacier Peak cryptotephra (set G) in
a Lateglacial lake site in western Scotland, ~7000 km from source. At this location
(Loch Ashik, Isle of Skye), Glacier Peak shares a crowded tephrostratigraphy with two
well-documented cryptotephra layers of likely Icelandic origin: the Borrobol Tephra
(14.19–14.00 cal. ka BP; 2σ) and the geochemically equivalent Penifiler Tephra
(14.06–13.81 cal. ka BP; 2σ) which occur singly or together in a number of terrestrial
Lateglacial sequences in Scotland and Scandinavia.
Previous tephra work at this site, as well as other localities, has not identified shards of
Glacier Peak composition. This may be due to masking of such ultra-distal layers by
the relatively greater concentrations of the closely preceding, and thus stratigraphically
overshadowing, Penifiler and Borrobol tephras which often exhibit reworked post-peak
shard distributions. However, the use of higher resolution 0.5 cm contiguous
stratigraphic sampling and off-peak geochemical analysis in this study resolves
previously unseen shard concentration variations within these distribution tails which
are consistent with additional tephra layers and which are shown to contain a relatively
greater proportion of Glacier Peak composition.
It is likely that other sedimentary sequences with faster accumulation rates will allow
better stratigraphic distinction of the Glacier Peak layer from the Penifiler tephra.
Additionally, Glacier Peak may be present elsewhere in the European tephrostratigraphy in sequences where the Borrobol and Penifiler tephras were not
deposited, and consequently where it will be less obscured.
The introduction of the well-dated Glacier Peak isochron into the regional
tephrostratigraphy of Scotland should aid in constraining local age models. It will also
permit direct trans-Atlantic correlation of sedimentary sequences for the mid-Lateglacial period, which was characterised by abrupt and short-lived climate oscillations. Accurate assessment of the relative timings of such palaeoclimate events is key to determining causal forcing mechanisms throughout the North Atlantic region.
from Europe; however, the picture differs in the western North Atlantic since this region is proximal to the major discharge routes from the Laurentide Ice Sheet. Here eastern seaboard climates were affected by repeated meltwater discharges into the ocean of varying magnitudes that continued until ca. 6.8 ka BP. The coastal plateau bogs from Maine to northern Newfoundland are well placed to provide detailed palaeoclimate archives describing the impacts of Laurentide deglaciation and the postglacial re-organisation of atmospheric conditions. Terrestrial responses to meltwater-climate-ocean interactions can be clearly expressed in oceanic raised
bogs because they are isolated from ground and surface waters, receiving almost all of their water and nutrition from meteoric sources. Specifically, summer
precipitation/evapo-transpiration conditions are a major control on bog surface wetness which is in turn a key factor determining the composition of peat-forming communities. The PRECIP project (Palaeo REconstructions of ocean-atmosphere Coupling In Peat) aims to exploit the close coupling between raised bogs and the atmosphere to reconstruct the spatial-temporal pattern of moisture balance
changes associated with past variability in the Gulf Stream and the Labrador Current on the eastern seaboard of North America. The reconstructions will be used to test a set of hypotheses concerning the relationships between thermohaline circulation variability, atmospheric circulation and terrestrial responses to climate change.
A multi-proxy approach will be used to reconstruct past change in atmospheric moisture balance at multi-decadal to millennial timescales using plant macrofossils and testate amoebae. These reconstructions will be compared with measurements of δ18O and δD in Sphagnum peat cellulose which can be used to determine past changes in precipitation moisture source.