Supervisors: William E.N. Austin Phone: (+44) 01782 733177 Address: School of Physical and Geographical Sciences,
Keele University,
Keele,
Staffordshire,
ST5 5BG,
United Kingdom.
... records can contain Holocene climate records that closely match terrestrial archives such as ... more ... records can contain Holocene climate records that closely match terrestrial archives such as tree-rings and lake varves (Cage & Austin 2010), with the ... 2003; Husum & Hald 2004a, b). New proxies are now being used to estimate temperature, salinity and ice from the Holocene. ...
The sea lochs (fjords) of NW Scotland bridge the land–ocean interface in a region of Europe which... more The sea lochs (fjords) of NW Scotland bridge the land–ocean interface in a region of Europe which is particularly well situated to monitor changes in westerly air streams. Inter-annual atmospheric circulation changes at this latitude are largely governed by the North Atlantic Oscillation (NAO). Comparing two recent extreme NAO years, a two-dimensional model of Loch Sunart, NW Scotland, is used to examine the potential effects of climate oscillations on the magnitude and frequency of deep-water renewal events and the resulting water properties in the fjord basins. In the upper basin of the fjord, meteorological forcing during the high NAO index year (1988–89) resulted in less-frequent deep-water renewal, greater variability in basin salinity and a lower annual-mean salinity (by 0.52) than that predicted for the low NAO index year (1995–96). In the main basin, variations in meteorological forcing had much less effect on basin water properties. In both basins, predicted deep water inflow was significantly greater during the negative phase NAO, with annual inflow to the upper and main basins being respectively 50% and 300% greater during 1995–96 relative to 1988–99. Through a sensitivity analysis, the NAO is shown to affect upper basin water properties through the influence of low-frequency anomalies in the meteorological forcing, particularly the enhanced westerly wind stress associated with positive phases, which inhibits deep water renewal over the winter months. The salinity of the main and upper basins respond differently to the boundary forcing due to differential tidal mixing above the respectively sub- and super-critical entrance sills. Predictions of basin water isotope ratios are made by applying the salinity:δ18Owater mixing line for the region to the salinity results; the combination of the weak dependence of δ18Owater on salinity and the stable salinity predicted for the main basin suggests that some fjord basins may provide ideal sites for palaeotemperature studies.
The first decadal-scale reconstruction of British coastal temperature anomalies spanning the last... more The first decadal-scale reconstruction of British coastal temperature anomalies spanning the last millennium is presented from a sea loch (fjord) basin, Loch Sunart, NW Scotland. Based on modern observation and the results of previous numerical modeling of fjord circulation, benthic foraminiferal oxygen isotope records are interpreted as a record of summer temperature. A significant climate transition, apparently driven by large-scale reorganization of northern Hemisphere atmospheric circulation, occurs in the record around AD 1400. An abrupt, but relatively short-lived climate warming occurs between AD 1540–1610, when the bottom water temperature anomalies are 1.1 °C above the long-term average, which is warmer than most of the 20th century and the late Medieval Warm Period. A long-term cooling occurs throughout the Little Ice Age culminating in the coldest recorded temperature anomalies between the late 1920s and 1940s. The warmest reconstructed temperatures of the past millennium occurred in the last 5 years of the record, which ends in 2006. A replicated post-AD 1900 shift in benthic foraminiferal δ13C of ca −0.6‰ provides evidence of the Oceanic δ13C Suess Effect; this feature provides an independent test of the age model and demonstrates the value of benthic foraminifera as palaeo-proxies in the Loch Sunart record.
Certain marginal marine environments, such as the Scottish fjord systems, contain high-resolution... more Certain marginal marine environments, such as the Scottish fjord systems, contain high-resolution records of palaeoclimatic change in which decadal to centennial climatic events can be resolved. This paper explores the possibilities of using tephrochronology to stratigraphically constrain the timing of such events in the Loch Sunart record (MD04-2831) on the NW coast of Scotland (UK). One tephra horizon (containing both silicic and basaltic shards) is identified within Late Holocene sediment with geochemical analyses of the basaltic shards suggesting an origin in the Veidivötn-Bárðarbunga volcanic system. Radiocarbon age estimates and stratigraphic information suggests that the AD 871 Landnám tephra is the most likely candidate. The shards identified within this horizon appear hydrated and indicate the operation of post-depositional weathering processes possibly influenced by the saline conditions of the fjord environment.
Geological Society, London, Special Publications, 2008
... Foraminiferal shells were gently crushed and rinsed with methanol prior to analysis on either... more ... Foraminiferal shells were gently crushed and rinsed with methanol prior to analysis on either a Finnigan MAT 251 with Kiel device (Bremen University or Bjerknes Centre for Climate Change, Bergen) for large samples (c. 200 µg) or a ThermoFinnigan MAT 253 with Kiel device ...
This paper describes potential methods for reconstructing past marine environmental and climatic ... more This paper describes potential methods for reconstructing past marine environmental and climatic variability in Scottish coastal waters through the investigation of annual growth increments measured from shells of the long-lived marine bivalve Arctica islandica (L.). This is accomplished by using a combination of sclerochronological and dendrochronological techniques which were employed to determine the age of specimens and to create growth chronologies. Using negative exponential detrending methods, a preliminary A. islandica master chronology for the Lynn of Lorn, Scotland has been produced. This chronology indicates highly suppressed growth between the mid 1940s and late 1980s. The growth response of this species to the sea surface temperatures in Scottish coastal waters appears to be complex, most notably during recent decades when land-use changes and marine aquaculture may influence shell growth at this site.
The sea lochs (fjords) of NW Scotland bridge the land-ocean interface in a region of Europe which... more The sea lochs (fjords) of NW Scotland bridge the land-ocean interface in a region of Europe which is particularly well situated to monitor changes in westerly air flow. Inter-annual atmospheric circulation changes at this latitude are largely governed by the North Atlantic Oscillation (NAO), in turn influencing both westerlies and precipitation. Comparing two extreme recent NAO years, circulation modelling results from Loch Sunart, NW Scotland, reveal a clear response to freshwater runoff and wind forcing in both magnitude and rate of deep-water renewal events. Scottish fjords, because of the relatively small impact which salinity has on d18Owater (0.18 % per salinity unit), potentially provide NW Europe's most useful study sites in coastal palaeoclimate research, particularly where palaeotemperature is the primary record of interest. New data from a high-resolution record (7 yr sample resolution), spanning the last two millennia, from the deepest part of the main basin of Loch Sunart illustrate significant multi-decadal to centennial scale variability in the sedimentary and stable isotope record of epibenthic foraminifera Cibicides lobatulus. The long-term pattern in benthic d18O appears to reflect bottom water temperature differences of 1-2§C, resolving climatic periods such as the Medieval Warm Period and the Little Ice Age. Since the core site is connected with shelf waters (i.e. no shallow sill) it seems likely that this paleotemperature reflects changing shelf water, not the exchange process as a function of long-term runoff/wind forcing. Grain size data and XRF data point to catchment-wide responses (weathering and erosion) which appear to show the largest variability during the last millennium, driven either by rainfall and temperature and/or land-use. Pb-isotope data, constraining the modern and industrial period, suggest accelerated sedimentation rates over this interval. On-going work attempts to calibrate proxy data with instrumental historical data.
... records can contain Holocene climate records that closely match terrestrial archives such as ... more ... records can contain Holocene climate records that closely match terrestrial archives such as tree-rings and lake varves (Cage & Austin 2010), with the ... 2003; Husum & Hald 2004a, b). New proxies are now being used to estimate temperature, salinity and ice from the Holocene. ...
The sea lochs (fjords) of NW Scotland bridge the land–ocean interface in a region of Europe which... more The sea lochs (fjords) of NW Scotland bridge the land–ocean interface in a region of Europe which is particularly well situated to monitor changes in westerly air streams. Inter-annual atmospheric circulation changes at this latitude are largely governed by the North Atlantic Oscillation (NAO). Comparing two recent extreme NAO years, a two-dimensional model of Loch Sunart, NW Scotland, is used to examine the potential effects of climate oscillations on the magnitude and frequency of deep-water renewal events and the resulting water properties in the fjord basins. In the upper basin of the fjord, meteorological forcing during the high NAO index year (1988–89) resulted in less-frequent deep-water renewal, greater variability in basin salinity and a lower annual-mean salinity (by 0.52) than that predicted for the low NAO index year (1995–96). In the main basin, variations in meteorological forcing had much less effect on basin water properties. In both basins, predicted deep water inflow was significantly greater during the negative phase NAO, with annual inflow to the upper and main basins being respectively 50% and 300% greater during 1995–96 relative to 1988–99. Through a sensitivity analysis, the NAO is shown to affect upper basin water properties through the influence of low-frequency anomalies in the meteorological forcing, particularly the enhanced westerly wind stress associated with positive phases, which inhibits deep water renewal over the winter months. The salinity of the main and upper basins respond differently to the boundary forcing due to differential tidal mixing above the respectively sub- and super-critical entrance sills. Predictions of basin water isotope ratios are made by applying the salinity:δ18Owater mixing line for the region to the salinity results; the combination of the weak dependence of δ18Owater on salinity and the stable salinity predicted for the main basin suggests that some fjord basins may provide ideal sites for palaeotemperature studies.
The first decadal-scale reconstruction of British coastal temperature anomalies spanning the last... more The first decadal-scale reconstruction of British coastal temperature anomalies spanning the last millennium is presented from a sea loch (fjord) basin, Loch Sunart, NW Scotland. Based on modern observation and the results of previous numerical modeling of fjord circulation, benthic foraminiferal oxygen isotope records are interpreted as a record of summer temperature. A significant climate transition, apparently driven by large-scale reorganization of northern Hemisphere atmospheric circulation, occurs in the record around AD 1400. An abrupt, but relatively short-lived climate warming occurs between AD 1540–1610, when the bottom water temperature anomalies are 1.1 °C above the long-term average, which is warmer than most of the 20th century and the late Medieval Warm Period. A long-term cooling occurs throughout the Little Ice Age culminating in the coldest recorded temperature anomalies between the late 1920s and 1940s. The warmest reconstructed temperatures of the past millennium occurred in the last 5 years of the record, which ends in 2006. A replicated post-AD 1900 shift in benthic foraminiferal δ13C of ca −0.6‰ provides evidence of the Oceanic δ13C Suess Effect; this feature provides an independent test of the age model and demonstrates the value of benthic foraminifera as palaeo-proxies in the Loch Sunart record.
Certain marginal marine environments, such as the Scottish fjord systems, contain high-resolution... more Certain marginal marine environments, such as the Scottish fjord systems, contain high-resolution records of palaeoclimatic change in which decadal to centennial climatic events can be resolved. This paper explores the possibilities of using tephrochronology to stratigraphically constrain the timing of such events in the Loch Sunart record (MD04-2831) on the NW coast of Scotland (UK). One tephra horizon (containing both silicic and basaltic shards) is identified within Late Holocene sediment with geochemical analyses of the basaltic shards suggesting an origin in the Veidivötn-Bárðarbunga volcanic system. Radiocarbon age estimates and stratigraphic information suggests that the AD 871 Landnám tephra is the most likely candidate. The shards identified within this horizon appear hydrated and indicate the operation of post-depositional weathering processes possibly influenced by the saline conditions of the fjord environment.
Geological Society, London, Special Publications, 2008
... Foraminiferal shells were gently crushed and rinsed with methanol prior to analysis on either... more ... Foraminiferal shells were gently crushed and rinsed with methanol prior to analysis on either a Finnigan MAT 251 with Kiel device (Bremen University or Bjerknes Centre for Climate Change, Bergen) for large samples (c. 200 µg) or a ThermoFinnigan MAT 253 with Kiel device ...
This paper describes potential methods for reconstructing past marine environmental and climatic ... more This paper describes potential methods for reconstructing past marine environmental and climatic variability in Scottish coastal waters through the investigation of annual growth increments measured from shells of the long-lived marine bivalve Arctica islandica (L.). This is accomplished by using a combination of sclerochronological and dendrochronological techniques which were employed to determine the age of specimens and to create growth chronologies. Using negative exponential detrending methods, a preliminary A. islandica master chronology for the Lynn of Lorn, Scotland has been produced. This chronology indicates highly suppressed growth between the mid 1940s and late 1980s. The growth response of this species to the sea surface temperatures in Scottish coastal waters appears to be complex, most notably during recent decades when land-use changes and marine aquaculture may influence shell growth at this site.
The sea lochs (fjords) of NW Scotland bridge the land-ocean interface in a region of Europe which... more The sea lochs (fjords) of NW Scotland bridge the land-ocean interface in a region of Europe which is particularly well situated to monitor changes in westerly air flow. Inter-annual atmospheric circulation changes at this latitude are largely governed by the North Atlantic Oscillation (NAO), in turn influencing both westerlies and precipitation. Comparing two extreme recent NAO years, circulation modelling results from Loch Sunart, NW Scotland, reveal a clear response to freshwater runoff and wind forcing in both magnitude and rate of deep-water renewal events. Scottish fjords, because of the relatively small impact which salinity has on d18Owater (0.18 % per salinity unit), potentially provide NW Europe's most useful study sites in coastal palaeoclimate research, particularly where palaeotemperature is the primary record of interest. New data from a high-resolution record (7 yr sample resolution), spanning the last two millennia, from the deepest part of the main basin of Loch Sunart illustrate significant multi-decadal to centennial scale variability in the sedimentary and stable isotope record of epibenthic foraminifera Cibicides lobatulus. The long-term pattern in benthic d18O appears to reflect bottom water temperature differences of 1-2§C, resolving climatic periods such as the Medieval Warm Period and the Little Ice Age. Since the core site is connected with shelf waters (i.e. no shallow sill) it seems likely that this paleotemperature reflects changing shelf water, not the exchange process as a function of long-term runoff/wind forcing. Grain size data and XRF data point to catchment-wide responses (weathering and erosion) which appear to show the largest variability during the last millennium, driven either by rainfall and temperature and/or land-use. Pb-isotope data, constraining the modern and industrial period, suggest accelerated sedimentation rates over this interval. On-going work attempts to calibrate proxy data with instrumental historical data.
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Papers by Alix Cage