- Email: [email protected]
Quaternary ice sheet–ocean interactions and landscape responses
Quaternary Science Reviews 28 (2009) 1570–1572
Contents lists available at ScienceDirect
Quaternary Science Reviews journal homepage: www.elsevier.com/locate/quascirev
Introduction
Quaternary ice sheet–ocean interactions and landscape responses
1. Introduction and scope of this special issue The interplay between ice sheets, oceans and landscape has played a dominant role in shaping our planet over the current Quaternary Period. For this reason it is essential that we develop a better understanding of these phenomena, their driving mechanisms, and their complex array of feedbacks so as to address the environmental challenges we face over the coming decades and centuries. This special issue of Quaternary Science Reviews presents an integrated set of papers that arose from the American Quaternary Association (AMQUA) Biennial Meeting held in June 2008 at Pennsylvania State University. The meeting was further supported by the UNESCO International Geoscience Programme (IGCP) Project 495 ‘‘Quaternary Land–Ocean Interactions: Driving Mechanisms and Coastal Responses’’ and the National Science Foundation (EAR0717364). The volume includes 16 papers grouped by three themes, each presenting new empirical and theoretical findings. The papers are diverse in their topical, spatial and temporal coverage, which reflects the global nature of Quaternary research as well as the intellectual driver to consider linkages between land–ocean processes and landforms. AMQUA is a professional organization of North American scientists, which was founded in 1970 primarily to foster cooperation and communication among the remarkably broad array of disciplines involved in studying the Quaternary Period. AMQUA’s biennial meeting is built around a symposium topic with broad interest to as many constituent groups within AMQUA as possible. IGCP-495 is one of about 400 research programmes supported by a cooperative enterprise of UNESCO and the International Union of Geological Sciences that has been promoting comparative studies in the Earth sciences since 1972. IGCP-495 has a particular interest in improving our understanding of the driving mechanisms responsible for Quaternary land–ocean interactions. IGCP-495 also works closely with the International Union for Quaternary Research (INQUA) Commission on Coastal and Marine Processes, and members from both communities contributed to the papers presented in this special issue. 2. Ice sheet evolution The papers in this section explore the deglaciation and meltwater fluxes of the Laurentide and Greenland ice sheets from modeling and field perspectives, largely since the Last Glacial Maximum (LGM). Further modeling is used to better understand the mass component of the budget of recent global sea-level rise. England et al. (in this issue) present a fundamental revision of North American ice cover during the LGM based on new 0277-3791/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.quascirev.2009.06.014
chronologies of glacial and marine landforms and sediments across the adjacent coastlines of Banks and Melville islands of the western Canadian Arctic Archipelago. An extensive Late Wisconsinan Laurentide Ice Sheet across the western Canadian, in a region previously thought to be too arid to sustain it, has important implications for paleoclimate, ice sheet modeling, Arctic Ocean ice and sediment delivery, and also for clarifying the northeast limit of Beringia. Lowell et al. (in this issue) and Fisher et al. (in this issue) further explore the spatial and temporal patterns of deglaciation of the Laurentide Ice Sheet. Based on radiocarbon control from Thunder Bay, Ontario, Lowell et al. (in this issue) suggest that the rate of deglaciation appears to mimic major climate oscillations of the lateglacial. Their reconstructions would not allow meltwater sourced in the Hudson Basin to drain into the Atlantic basin until after the Younger Dryas. Fisher et al. (in this issue) analyze the age of deglaciation in the broader Fort McMurray, Alberta from the mapping of new moraines. They suggest that deglaciation in this region occurred earlier than previously reported, with the consequence that the associated meltwater could not drain northward to the Arctic Ocean from any source southeast of the Fort McMurray area until approximately 11.8–11.1 ka cal BP. Carlson (in this issue) investigates the contentious issue of the Laurentide Ice Sheet contribution to Meltwater Pulse 1A, which occurred w14.6 ka cal BP and resulted in a w20 m rise in sea-level in less than 500 years. Using planktonic and benthic d18O records and a freshwater runoff-ocean mixing model, Carlson (in this issue) calculates a total Laurentide contribution of less than 5.3 m, suggesting a significant source from the Antarctic Ice Sheet. Compared to the Laurentide Ice Sheet, Greenland’s contribution to global sea-level change since the LGM has been more modest. Nevertheless, as the last major ice sheet in the northern hemisphere and an important contributor to current and future sea-level rise, there is considerable interest in improving our understanding of its Late Quaternary history using field evidence and ice sheet modeling. Simpson et al. (in this issue) investigate the deglaciation of the Greenland Ice sheet from the LGM to present using a glaciological model, which is calibrated to field observations of former sea levels. The study suggests that the retreat of the ice sheet was temporally and spatially variable with a Younger-Dryas readvance in some areas. The maximum retreat of the ice sheet corresponded to the end of the Holocene Thermal Maximum, which was followed in parts of west Greenland by a readvance of up to 100 km during the Neoglacial. Peltier (in this issue) investigates the budget of global sea-level rise derived from modern space-based measurements, specifically inquiring whether the rate of mass addition to the oceans matches the rate at which mass is being removed from the continents. Geophysical modeling demonstrates the
Introduction / Quaternary Science Reviews 28 (2009) 1570–1572
critical contribution of glacial isostatic adjustment to the mass rate signal over the oceans associated with the process of rotational feedback. Taken as a whole, these papers on ice sheet history demonstrate that many issues remain unanswered. New field evidence, often from areas where little evidence existed previously, requires existing models to be revised. Such revisions provide new targets for the glacio-isostatic and ice sheet modeling communities. They change potential source areas and volumes of water for mass exchange to the oceans. The magnitude, duration and timing of Meltwater Pulse 1A, though advanced by the work presented here, remains unknown. Above all, the research presented by these papers demonstrates the sophisticated nature of the driving mechanisms that link different elements of the Quaternary Earth–Ocean system, a complexity that demands ever more integrated local to global reconstructions and models. 3. Past climatic change and landscape responses The complexity of the climate system requires that we consider not only temperature variations, but also changes in moisture. Despite this requirement, the nature of hydrologic variability in the recent geological past remains poorly understood. Gaining a better understanding of past moisture availability, forcing mechanisms, and ecosystem impacts is critical given that rapid changes in freshwater availability pose significant challenges to societies. Quaternary moisture changes and landscape responses in temperate and tropical environments are examined by three papers in this section. This work provides key insight into the character of millennial to centennial scale hydrologic variability and offers some clues as to potential forcing mechanisms. Further, these papers document significant ecosystem and cultural impacts related to changes in the availability of freshwater that may provide important lessons as we face the prospect of future changes in hydroclimate. Newby et al. (in this issue) investigate the hydroclimate during the Pleistocene/Holocene transition in the typically humid northeastern United States. Lake level records contain evidence for multiple, sub-centennial-to-millennial scale droughts, many of which coincide with meltwater release events or abrupt climate oscillations in the circum North Atlantic. Sedimentary evidence also reveals lower water levels in the 20th century corresponding to regional lower-than-average precipitation, with the most extreme drought in the 1960s corresponding to cool sea surface temperatures in the western North Atlantic. Shuman et al. (in this issue) elucidate the relation between climate and vegetation changes in the northeastern United States from 15 ka cal BP to present. Changes in pollen taxa coincide with isotopic and sedimentary indicators of temperature and moisture balance, which suggest that the interaction of abrupt and slower climate changes determines the regional sequence of vegetation change. Beach et al. (in this issue) also address the Pleistocene–Holocene transition, this time in the Maya Lowlands of Mexico, Belize, and Guatemala. Here, the transition is associated with an increase in rainfall, forests replacing savannas ecosystems and a period of slope instability and wetland aggradation. A second period of landscape instability is recorded in the Maya Preclassic (c. 2000 BC–250 AD) to Classic period (c. 250 AD–900 AD), this time a product of deforestation, land use intensity, and drying. 4. Holocene sea-level change and coastal evolution The papers in this section aim to better understand the driving mechanisms behind sea-level change over a range of spatial (global to local) and temporal (millennia to decadal) scales. These changes in the coastal zone result from external forces, such as climate, sea-
1571
level, tectonics, storm surges and tsunamis, and internal forces including the coastal sedimentary budget, both of which are addressed through hypothesis testing and model building. Further, the papers investigate the interaction of terrestrial and marine processes in controlling lateral changes in shoreline position and marsh elevation. The established methods of data analysis to reconstruct Holocene sea levels were employed by Horton et al. (in this issue) to produce a spatially comprehensive database of sea-level index points from the North Carolina coastline. The observations illustrate relative sea-level rapidly rising during the early and mid-Holocene with no evidence for sea levels higher than present. Predictions from the ICE-5G (VM2) with rotational feedback geophysical model capture the general temporal trend of late-Holocene (last 4000 cal BP) sea-level observations, although there is an apparent misfit for index points older than 2000 cal BP. A comparison of local tide gauge data with the late-Holocene relative sea-level trends implies an additional increase of mean sea-level of greater than 2 mm yr 1 during the latter half of the 20th century. A detailed relative sea-level record is constructed for last 2 ka cal BP by Gonzalez and To¨rnqvist (in this issue) in order to investigate evidence for sea-level oscillations within this time period and explore possible correlations with paleoclimate records. The basal peat sea-level data indicate a possible acceleration in the rate of relative sea-level rise between w1000 and w1200 AD, cautiously correlated with the Medieval Warm Period. Woodroffe and Long (in this issue) develop the first diatom-based transfer functions from salt marshes in Greenland in an effort to bridge the gap between existing millennial-scale reconstructions of Holocene sea levels and recent direct observations of ice sheet behavior and associated glacial isostatic responses. They demonstrate that the transfer-function method is applicable in these arctic salt marshes and has the potential to be applied to reconstructing past sea-level change. Preliminary application of the method to a single fossil sequence suggests that from 0.6 to 0.4 ka cal BP sea-level rose at. 2.7 mm yr 1, after which the rate of rise decreased and remained stable until the present day. The theme of Holocene relative sea-level changed is further explored by Shennan (in this issue) in south central Alaska in response to glacial isostatic adjustment and multiple earthquake deformation cycles. The observations of relative sea-level change differ to model predictions for other seismic and non-seismic locations. The stratigraphy reveals buried mud-peat couplets of a great earthquake at 0.9 ka cal BP, including evidence of an associated tsunami. Woodruff et al. (in this issue) infer the driving mechanism of episodic coastal inundation over the last 6.4 ka cal BP from two coastal lakes in southwestern Japan. Periods of barrier breaching ˜ ofrom tropical cyclones are concurrent with an increase in El Nin like conditions. Further, an inverse correlation is observed between tropical cyclone reconstructions from the western North Atlantic and the southwestern Japan, which is consistent with modern climatological relationships of ENSO and tropical cyclones in these regions. Jerolmack (in this issue) considers the influence of Holocene sea-level rise upon changes in channel pattern within deltas. The modeling framework suggests that avulsion and the generation of large scale branches should dominate in the early Holocene under conditions of rapid sea-level rise. However, the subsequent reduction in the rate of sea-level rise in the mid-Holocene allowed progradation, which assisted the growth of smaller scale distributary trees and a reduction in the number of large scale branches. The response of salt marshes to accelerations in the rate of sea-level rise is further considered by Kirwan and Temmerman (in this issue). Numerical models suggest that marsh elevation adjusts in a lagged manner to a step-change in the rate of sea-level rise in w100 years and to a continuous acceleration in the rate of sea-level rise by w20 years. The work could have important implications for
1572
Introduction / Quaternary Science Reviews 28 (2009) 1570–1572
those seeking to infer direct evidence for relative sea-level rise from salt marsh systems that require time to adapt to changes in sealevel forcing. The papers in this section illustrate the importance of high resolution records of Late Quaternary sea-level change and coastal evolution for comparison with geophysical model predictions and paleoenvironmental records from the ice sheets, the oceans and other terrestrial archives. Further research is required to better understand the role of terrestrial and oceanic processes in controlling coastal stratigraphic sequences, sea-level change and coastal evolution. 5. Conclusions A key objective of the AMQUA Biennial Meeting (2008) and of IGCP-495 is to better understand the driving mechanisms responsible for Quaternary ice sheet–ocean interactions and landscape responses. The science of Quaternary environmental change is now well equipped to map change over time although, as the papers here demonstrate, the on-going application of new methods of data collection, often in regions with limited data, will continue to require revision to existing models of ice sheet history, landscape history and land–ocean interaction. A prominent theme is the iterative link between field observation and modeling. This is arguably best demonstrated in the field of glacial isostatic adjustment, where ice sheet reconstructions and relative sea-level observations provide powerful constraints on models that are used to predict meltwater sources and understand how past climate and oceanographic conditions developed. Cross-cutting all of the above is a recognition of the importance of chronology in providing a robust framework for correlation between the different proxies presented. It is noteworthy that radiocarbon dating provides the mainstay of almost all of the papers presented here, with little emphasis on cosmogenic exposure dating or on the opportunities provided by more precise dating techniques such as tephra or annually laminated sediment sequences. These are areas of opportunity for future work. Likewise, the existing models used in these papers are also, to varying degrees, limited by their chronological resolution. Ice sheet model reconstructions are increasingly used to source potential shortlived meltwater pulses, whilst millennial-scale records of ice and water loading are used to provide estimates on current rates of postglacial rebound or ice sheet mass balance. Reconciling model timescales with observational records is an ongoing challenge. Finally, the papers here provide a wonderful insight into the linkages between terrestrial and near-shore environments. However, we note that it is important that we look beyond this, to explore more fully linkages with the ocean realm which are themselves potent driving mechanisms of Quaternary environmental change. Acknowledgements This special issue is a contribution to IGCP Project 495, ‘‘Quaternary Land–Ocean Interactions: Driving Mechanisms and Coastal Responses’’ and to the INQUA Commission on Coastal and Marine Processes. The conference which led to this publication was supported by American Quaternary Association (AMQUA) and the National Science Foundation (Award No. EAR-0717364). We thank the many referees who supported us in the preparation of this special issue, and to Professor Colin Murray-Wallace for sound guidance as journal Editor in Chief.
While preparing this issue, we learnt of the death of Dr Orson van de Plassche. Orson was an outstanding scientist who was a personal and professional inspiration to many of us researching Quaternary land–ocean interactions and we dedicate this issue to his memory. He will be deeply missed. The testimonial for Orson that appears at the beginning of this special issue was prepared by Alex Wright, Sytze van Heteren and Roland Gehrels. Reference Beach, T., Luzzadder-Beach, S., Dunning, N., Jones, J., Lohse, J., Guderjan, T., Bozarth, S., Millspaugh, S., Bhattacharya, T., 2009. A review of human and natural changes in Maya Lowlands wetlands over the Holocene. Quaternary Science Reviews 28, 1710–1724. Carlson, A.E., 2009. Geochemical constraints on the Laurentide Ice Sheet contribution to Meltwater Pulse 1A. Quaternary Science Reviews 28, 1625–1630. England, J.H., Furze, M.F., Doupe´, J.P., 2009. Revision of the NW Laurentide Ice Sheet: implications for paleoclimatic, the northeast extremity of Beringia, and Arctic Ocean sedimentation. Quaternary Science Reviews 28, 1573–1596. Fisher, T.G., Waterson, N., Lowell, T.V., Hajdas, I., 2009. Deglaciation ages and meltwater routing in the Fort McMurray Region, northeastern Alberta and northwestern Saskatchewan, Canada. Quaternary Science Reviews 28, 1608–1624. Gonzalez, J.L., To¨rnqvist, T.E., 2009. A new late Holocene sea level record from the Mississippi Delta: evidence for a climate/sea level connection? Quaternary Science Reviews 28, 1737–1749. Horton, B.P., Peltier, W.R., Culver, S.J., Drummond, R., Engelhart, S.E., Kemp, A.C., Mallinson, D., Thieler, E.R., Riggs, S.R., Ames, D.V., Thomson, K.H., 2009. Holocene sea-level changes along the North Carolina Coastline and their implications for glacial isostatic adjustment models. Quaternary Science Reviews 28, 1725–1736. Jerolmack, D.J., 2009. Conceptual framework for assessing the response of delta channel networks to Holocene sea level rise. Quaternary Science Reviews 28, 1786–1800. Kirwan, M., Temmerman, S., 2009. Coastal marsh response to historical and future sea level acceleration. Quaternary Science Reviews 28, 1801–1808. Lowell, T.V., Fisher, T.G., Hajdas, I., Glover, K., Loope, H., Henry, T., 2009. Radiocarbon deglaciation chronology of the Thunder Bay, Ontario area and implications for ice sheet retreat patterns. Quaternary Science Reviews 28, 1597–1607. Newby, P.E., Donnelly, J.P., Shuman, B.N., MacDonald, D., 2009. Evidence of centennial-scale drought from southeastern Massachusetts during the Pleistocene/ Holocene transition. Quaternary Science Reviews 28, 1675–1692. Peltier, W.R., 2009. Closure of the budget of global sea level rise over the GRACE era: the importance and magnitudes of the required corrections for global glacial isostatic adjustment. Quaternary Science Reviews 28, 1658–1674. Shennan, I., 2009. Late Quaternary sea-level changes and palaeoseismology of the Bering Glacier region, Alaska. Quaternary Science Reviews 28, 1762–1773. Shuman, B.N., Newby, P., Donnelly, J.P., 2009. Abrupt climate change as an important agent of ecological change in the Northeast U.S. throughout the past 15,000 years. Quaternary Science Reviews 28, 1693–1709. Simpson, M., James, R., Milne, G., Huybrechts, P., Long, A., 2009. Calibrating a glaciological model of the Greenland ice sheet from the last glacial maximum to present-day using field observations of relative sea level and ice extent. Quaternary Science Reviews 28, 1631–1657. Woodruff, J.D., Donnelly, J.P., Okusu, A., 2009. Exploring typhoon variability over the mid-to-late Holocene: evidence of extreme coastal flooding from Kamikoshiki, Japan. Quaternary Science Reviews 28, 1774–1785. Woodroffe, S.A., Long, A., 2009. Salt marshes as archives of recent relative sea level change in West Greenland. Quaternary Science Reviews 28, 1750–1761.
Benjamin P. Horton* Department of Earth and Environmental Science, University of Pennsylvania, 240 South 33rd Street, Philadelphia, PA 19104-6316, USA Corresponding author. E-mail address: [email protected] Antony J. Long Department of Geography, Durham University, Durham DH1 3LE, UK Jeffrey P. Donnelly Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA
Contents lists available at ScienceDirect
Quaternary Science Reviews journal homepage: www.elsevier.com/locate/quascirev
Introduction
Quaternary ice sheet–ocean interactions and landscape responses
1. Introduction and scope of this special issue The interplay between ice sheets, oceans and landscape has played a dominant role in shaping our planet over the current Quaternary Period. For this reason it is essential that we develop a better understanding of these phenomena, their driving mechanisms, and their complex array of feedbacks so as to address the environmental challenges we face over the coming decades and centuries. This special issue of Quaternary Science Reviews presents an integrated set of papers that arose from the American Quaternary Association (AMQUA) Biennial Meeting held in June 2008 at Pennsylvania State University. The meeting was further supported by the UNESCO International Geoscience Programme (IGCP) Project 495 ‘‘Quaternary Land–Ocean Interactions: Driving Mechanisms and Coastal Responses’’ and the National Science Foundation (EAR0717364). The volume includes 16 papers grouped by three themes, each presenting new empirical and theoretical findings. The papers are diverse in their topical, spatial and temporal coverage, which reflects the global nature of Quaternary research as well as the intellectual driver to consider linkages between land–ocean processes and landforms. AMQUA is a professional organization of North American scientists, which was founded in 1970 primarily to foster cooperation and communication among the remarkably broad array of disciplines involved in studying the Quaternary Period. AMQUA’s biennial meeting is built around a symposium topic with broad interest to as many constituent groups within AMQUA as possible. IGCP-495 is one of about 400 research programmes supported by a cooperative enterprise of UNESCO and the International Union of Geological Sciences that has been promoting comparative studies in the Earth sciences since 1972. IGCP-495 has a particular interest in improving our understanding of the driving mechanisms responsible for Quaternary land–ocean interactions. IGCP-495 also works closely with the International Union for Quaternary Research (INQUA) Commission on Coastal and Marine Processes, and members from both communities contributed to the papers presented in this special issue. 2. Ice sheet evolution The papers in this section explore the deglaciation and meltwater fluxes of the Laurentide and Greenland ice sheets from modeling and field perspectives, largely since the Last Glacial Maximum (LGM). Further modeling is used to better understand the mass component of the budget of recent global sea-level rise. England et al. (in this issue) present a fundamental revision of North American ice cover during the LGM based on new 0277-3791/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.quascirev.2009.06.014
chronologies of glacial and marine landforms and sediments across the adjacent coastlines of Banks and Melville islands of the western Canadian Arctic Archipelago. An extensive Late Wisconsinan Laurentide Ice Sheet across the western Canadian, in a region previously thought to be too arid to sustain it, has important implications for paleoclimate, ice sheet modeling, Arctic Ocean ice and sediment delivery, and also for clarifying the northeast limit of Beringia. Lowell et al. (in this issue) and Fisher et al. (in this issue) further explore the spatial and temporal patterns of deglaciation of the Laurentide Ice Sheet. Based on radiocarbon control from Thunder Bay, Ontario, Lowell et al. (in this issue) suggest that the rate of deglaciation appears to mimic major climate oscillations of the lateglacial. Their reconstructions would not allow meltwater sourced in the Hudson Basin to drain into the Atlantic basin until after the Younger Dryas. Fisher et al. (in this issue) analyze the age of deglaciation in the broader Fort McMurray, Alberta from the mapping of new moraines. They suggest that deglaciation in this region occurred earlier than previously reported, with the consequence that the associated meltwater could not drain northward to the Arctic Ocean from any source southeast of the Fort McMurray area until approximately 11.8–11.1 ka cal BP. Carlson (in this issue) investigates the contentious issue of the Laurentide Ice Sheet contribution to Meltwater Pulse 1A, which occurred w14.6 ka cal BP and resulted in a w20 m rise in sea-level in less than 500 years. Using planktonic and benthic d18O records and a freshwater runoff-ocean mixing model, Carlson (in this issue) calculates a total Laurentide contribution of less than 5.3 m, suggesting a significant source from the Antarctic Ice Sheet. Compared to the Laurentide Ice Sheet, Greenland’s contribution to global sea-level change since the LGM has been more modest. Nevertheless, as the last major ice sheet in the northern hemisphere and an important contributor to current and future sea-level rise, there is considerable interest in improving our understanding of its Late Quaternary history using field evidence and ice sheet modeling. Simpson et al. (in this issue) investigate the deglaciation of the Greenland Ice sheet from the LGM to present using a glaciological model, which is calibrated to field observations of former sea levels. The study suggests that the retreat of the ice sheet was temporally and spatially variable with a Younger-Dryas readvance in some areas. The maximum retreat of the ice sheet corresponded to the end of the Holocene Thermal Maximum, which was followed in parts of west Greenland by a readvance of up to 100 km during the Neoglacial. Peltier (in this issue) investigates the budget of global sea-level rise derived from modern space-based measurements, specifically inquiring whether the rate of mass addition to the oceans matches the rate at which mass is being removed from the continents. Geophysical modeling demonstrates the
Introduction / Quaternary Science Reviews 28 (2009) 1570–1572
critical contribution of glacial isostatic adjustment to the mass rate signal over the oceans associated with the process of rotational feedback. Taken as a whole, these papers on ice sheet history demonstrate that many issues remain unanswered. New field evidence, often from areas where little evidence existed previously, requires existing models to be revised. Such revisions provide new targets for the glacio-isostatic and ice sheet modeling communities. They change potential source areas and volumes of water for mass exchange to the oceans. The magnitude, duration and timing of Meltwater Pulse 1A, though advanced by the work presented here, remains unknown. Above all, the research presented by these papers demonstrates the sophisticated nature of the driving mechanisms that link different elements of the Quaternary Earth–Ocean system, a complexity that demands ever more integrated local to global reconstructions and models. 3. Past climatic change and landscape responses The complexity of the climate system requires that we consider not only temperature variations, but also changes in moisture. Despite this requirement, the nature of hydrologic variability in the recent geological past remains poorly understood. Gaining a better understanding of past moisture availability, forcing mechanisms, and ecosystem impacts is critical given that rapid changes in freshwater availability pose significant challenges to societies. Quaternary moisture changes and landscape responses in temperate and tropical environments are examined by three papers in this section. This work provides key insight into the character of millennial to centennial scale hydrologic variability and offers some clues as to potential forcing mechanisms. Further, these papers document significant ecosystem and cultural impacts related to changes in the availability of freshwater that may provide important lessons as we face the prospect of future changes in hydroclimate. Newby et al. (in this issue) investigate the hydroclimate during the Pleistocene/Holocene transition in the typically humid northeastern United States. Lake level records contain evidence for multiple, sub-centennial-to-millennial scale droughts, many of which coincide with meltwater release events or abrupt climate oscillations in the circum North Atlantic. Sedimentary evidence also reveals lower water levels in the 20th century corresponding to regional lower-than-average precipitation, with the most extreme drought in the 1960s corresponding to cool sea surface temperatures in the western North Atlantic. Shuman et al. (in this issue) elucidate the relation between climate and vegetation changes in the northeastern United States from 15 ka cal BP to present. Changes in pollen taxa coincide with isotopic and sedimentary indicators of temperature and moisture balance, which suggest that the interaction of abrupt and slower climate changes determines the regional sequence of vegetation change. Beach et al. (in this issue) also address the Pleistocene–Holocene transition, this time in the Maya Lowlands of Mexico, Belize, and Guatemala. Here, the transition is associated with an increase in rainfall, forests replacing savannas ecosystems and a period of slope instability and wetland aggradation. A second period of landscape instability is recorded in the Maya Preclassic (c. 2000 BC–250 AD) to Classic period (c. 250 AD–900 AD), this time a product of deforestation, land use intensity, and drying. 4. Holocene sea-level change and coastal evolution The papers in this section aim to better understand the driving mechanisms behind sea-level change over a range of spatial (global to local) and temporal (millennia to decadal) scales. These changes in the coastal zone result from external forces, such as climate, sea-
1571
level, tectonics, storm surges and tsunamis, and internal forces including the coastal sedimentary budget, both of which are addressed through hypothesis testing and model building. Further, the papers investigate the interaction of terrestrial and marine processes in controlling lateral changes in shoreline position and marsh elevation. The established methods of data analysis to reconstruct Holocene sea levels were employed by Horton et al. (in this issue) to produce a spatially comprehensive database of sea-level index points from the North Carolina coastline. The observations illustrate relative sea-level rapidly rising during the early and mid-Holocene with no evidence for sea levels higher than present. Predictions from the ICE-5G (VM2) with rotational feedback geophysical model capture the general temporal trend of late-Holocene (last 4000 cal BP) sea-level observations, although there is an apparent misfit for index points older than 2000 cal BP. A comparison of local tide gauge data with the late-Holocene relative sea-level trends implies an additional increase of mean sea-level of greater than 2 mm yr 1 during the latter half of the 20th century. A detailed relative sea-level record is constructed for last 2 ka cal BP by Gonzalez and To¨rnqvist (in this issue) in order to investigate evidence for sea-level oscillations within this time period and explore possible correlations with paleoclimate records. The basal peat sea-level data indicate a possible acceleration in the rate of relative sea-level rise between w1000 and w1200 AD, cautiously correlated with the Medieval Warm Period. Woodroffe and Long (in this issue) develop the first diatom-based transfer functions from salt marshes in Greenland in an effort to bridge the gap between existing millennial-scale reconstructions of Holocene sea levels and recent direct observations of ice sheet behavior and associated glacial isostatic responses. They demonstrate that the transfer-function method is applicable in these arctic salt marshes and has the potential to be applied to reconstructing past sea-level change. Preliminary application of the method to a single fossil sequence suggests that from 0.6 to 0.4 ka cal BP sea-level rose at. 2.7 mm yr 1, after which the rate of rise decreased and remained stable until the present day. The theme of Holocene relative sea-level changed is further explored by Shennan (in this issue) in south central Alaska in response to glacial isostatic adjustment and multiple earthquake deformation cycles. The observations of relative sea-level change differ to model predictions for other seismic and non-seismic locations. The stratigraphy reveals buried mud-peat couplets of a great earthquake at 0.9 ka cal BP, including evidence of an associated tsunami. Woodruff et al. (in this issue) infer the driving mechanism of episodic coastal inundation over the last 6.4 ka cal BP from two coastal lakes in southwestern Japan. Periods of barrier breaching ˜ ofrom tropical cyclones are concurrent with an increase in El Nin like conditions. Further, an inverse correlation is observed between tropical cyclone reconstructions from the western North Atlantic and the southwestern Japan, which is consistent with modern climatological relationships of ENSO and tropical cyclones in these regions. Jerolmack (in this issue) considers the influence of Holocene sea-level rise upon changes in channel pattern within deltas. The modeling framework suggests that avulsion and the generation of large scale branches should dominate in the early Holocene under conditions of rapid sea-level rise. However, the subsequent reduction in the rate of sea-level rise in the mid-Holocene allowed progradation, which assisted the growth of smaller scale distributary trees and a reduction in the number of large scale branches. The response of salt marshes to accelerations in the rate of sea-level rise is further considered by Kirwan and Temmerman (in this issue). Numerical models suggest that marsh elevation adjusts in a lagged manner to a step-change in the rate of sea-level rise in w100 years and to a continuous acceleration in the rate of sea-level rise by w20 years. The work could have important implications for
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Introduction / Quaternary Science Reviews 28 (2009) 1570–1572
those seeking to infer direct evidence for relative sea-level rise from salt marsh systems that require time to adapt to changes in sealevel forcing. The papers in this section illustrate the importance of high resolution records of Late Quaternary sea-level change and coastal evolution for comparison with geophysical model predictions and paleoenvironmental records from the ice sheets, the oceans and other terrestrial archives. Further research is required to better understand the role of terrestrial and oceanic processes in controlling coastal stratigraphic sequences, sea-level change and coastal evolution. 5. Conclusions A key objective of the AMQUA Biennial Meeting (2008) and of IGCP-495 is to better understand the driving mechanisms responsible for Quaternary ice sheet–ocean interactions and landscape responses. The science of Quaternary environmental change is now well equipped to map change over time although, as the papers here demonstrate, the on-going application of new methods of data collection, often in regions with limited data, will continue to require revision to existing models of ice sheet history, landscape history and land–ocean interaction. A prominent theme is the iterative link between field observation and modeling. This is arguably best demonstrated in the field of glacial isostatic adjustment, where ice sheet reconstructions and relative sea-level observations provide powerful constraints on models that are used to predict meltwater sources and understand how past climate and oceanographic conditions developed. Cross-cutting all of the above is a recognition of the importance of chronology in providing a robust framework for correlation between the different proxies presented. It is noteworthy that radiocarbon dating provides the mainstay of almost all of the papers presented here, with little emphasis on cosmogenic exposure dating or on the opportunities provided by more precise dating techniques such as tephra or annually laminated sediment sequences. These are areas of opportunity for future work. Likewise, the existing models used in these papers are also, to varying degrees, limited by their chronological resolution. Ice sheet model reconstructions are increasingly used to source potential shortlived meltwater pulses, whilst millennial-scale records of ice and water loading are used to provide estimates on current rates of postglacial rebound or ice sheet mass balance. Reconciling model timescales with observational records is an ongoing challenge. Finally, the papers here provide a wonderful insight into the linkages between terrestrial and near-shore environments. However, we note that it is important that we look beyond this, to explore more fully linkages with the ocean realm which are themselves potent driving mechanisms of Quaternary environmental change. Acknowledgements This special issue is a contribution to IGCP Project 495, ‘‘Quaternary Land–Ocean Interactions: Driving Mechanisms and Coastal Responses’’ and to the INQUA Commission on Coastal and Marine Processes. The conference which led to this publication was supported by American Quaternary Association (AMQUA) and the National Science Foundation (Award No. EAR-0717364). We thank the many referees who supported us in the preparation of this special issue, and to Professor Colin Murray-Wallace for sound guidance as journal Editor in Chief.
While preparing this issue, we learnt of the death of Dr Orson van de Plassche. Orson was an outstanding scientist who was a personal and professional inspiration to many of us researching Quaternary land–ocean interactions and we dedicate this issue to his memory. He will be deeply missed. The testimonial for Orson that appears at the beginning of this special issue was prepared by Alex Wright, Sytze van Heteren and Roland Gehrels. Reference Beach, T., Luzzadder-Beach, S., Dunning, N., Jones, J., Lohse, J., Guderjan, T., Bozarth, S., Millspaugh, S., Bhattacharya, T., 2009. A review of human and natural changes in Maya Lowlands wetlands over the Holocene. Quaternary Science Reviews 28, 1710–1724. Carlson, A.E., 2009. Geochemical constraints on the Laurentide Ice Sheet contribution to Meltwater Pulse 1A. Quaternary Science Reviews 28, 1625–1630. England, J.H., Furze, M.F., Doupe´, J.P., 2009. Revision of the NW Laurentide Ice Sheet: implications for paleoclimatic, the northeast extremity of Beringia, and Arctic Ocean sedimentation. Quaternary Science Reviews 28, 1573–1596. Fisher, T.G., Waterson, N., Lowell, T.V., Hajdas, I., 2009. Deglaciation ages and meltwater routing in the Fort McMurray Region, northeastern Alberta and northwestern Saskatchewan, Canada. Quaternary Science Reviews 28, 1608–1624. Gonzalez, J.L., To¨rnqvist, T.E., 2009. A new late Holocene sea level record from the Mississippi Delta: evidence for a climate/sea level connection? Quaternary Science Reviews 28, 1737–1749. Horton, B.P., Peltier, W.R., Culver, S.J., Drummond, R., Engelhart, S.E., Kemp, A.C., Mallinson, D., Thieler, E.R., Riggs, S.R., Ames, D.V., Thomson, K.H., 2009. Holocene sea-level changes along the North Carolina Coastline and their implications for glacial isostatic adjustment models. Quaternary Science Reviews 28, 1725–1736. Jerolmack, D.J., 2009. Conceptual framework for assessing the response of delta channel networks to Holocene sea level rise. Quaternary Science Reviews 28, 1786–1800. Kirwan, M., Temmerman, S., 2009. Coastal marsh response to historical and future sea level acceleration. Quaternary Science Reviews 28, 1801–1808. Lowell, T.V., Fisher, T.G., Hajdas, I., Glover, K., Loope, H., Henry, T., 2009. Radiocarbon deglaciation chronology of the Thunder Bay, Ontario area and implications for ice sheet retreat patterns. Quaternary Science Reviews 28, 1597–1607. Newby, P.E., Donnelly, J.P., Shuman, B.N., MacDonald, D., 2009. Evidence of centennial-scale drought from southeastern Massachusetts during the Pleistocene/ Holocene transition. Quaternary Science Reviews 28, 1675–1692. Peltier, W.R., 2009. Closure of the budget of global sea level rise over the GRACE era: the importance and magnitudes of the required corrections for global glacial isostatic adjustment. Quaternary Science Reviews 28, 1658–1674. Shennan, I., 2009. Late Quaternary sea-level changes and palaeoseismology of the Bering Glacier region, Alaska. Quaternary Science Reviews 28, 1762–1773. Shuman, B.N., Newby, P., Donnelly, J.P., 2009. Abrupt climate change as an important agent of ecological change in the Northeast U.S. throughout the past 15,000 years. Quaternary Science Reviews 28, 1693–1709. Simpson, M., James, R., Milne, G., Huybrechts, P., Long, A., 2009. Calibrating a glaciological model of the Greenland ice sheet from the last glacial maximum to present-day using field observations of relative sea level and ice extent. Quaternary Science Reviews 28, 1631–1657. Woodruff, J.D., Donnelly, J.P., Okusu, A., 2009. Exploring typhoon variability over the mid-to-late Holocene: evidence of extreme coastal flooding from Kamikoshiki, Japan. Quaternary Science Reviews 28, 1774–1785. Woodroffe, S.A., Long, A., 2009. Salt marshes as archives of recent relative sea level change in West Greenland. Quaternary Science Reviews 28, 1750–1761.
Benjamin P. Horton* Department of Earth and Environmental Science, University of Pennsylvania, 240 South 33rd Street, Philadelphia, PA 19104-6316, USA Corresponding author. E-mail address: [email protected] Antony J. Long Department of Geography, Durham University, Durham DH1 3LE, UK Jeffrey P. Donnelly Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA