Mangrove sediments are valuable archives of paleoenvironmental and relative sea-level changes. Th... more Mangrove sediments are valuable archives of paleoenvironmental and relative sea-level changes. The most widely applied method to obtaining chronologies of past changes in mangrove sediments is radiocarbon dating, because mangroves produce large amounts of organic matter in situ. However, there are many challenges to obtaining reliable radiocarbon chronologies because bioturbation processes from roots and crabs can rework mangrove sediments, resulting in ages that are not in stratigraphic order. Previous studies have suggested that methods that isolate specific sediment size fractions may yield ages closer to the age of the paleo depositional surface by removing younger carbon contamination from fine roots. This study examines which sample types are more likely to yield reliable radiocarbon ages using shallow cores from a mangrove environment on Mahé, Seychelles, in the Indian Ocean. We compare radiocarbon ages from bulk sediment, sieved organic concentrates and above-ground macrofos...
Kenneth G. Miller, Peter J. Sugarman, Scott D. Stanford, James V. Browning, Kimberly Baldwin, Bri... more Kenneth G. Miller, Peter J. Sugarman, Scott D. Stanford, James V. Browning, Kimberly Baldwin, Brian Buttari, Benjamin Dunham, Michael Farazaneh, Rachel Filo, Michael P. Gagliano, Benjamin Horton, Gabrielle Gallegos, Stephen Graham, Christopher S. Johnson, Nicole Khan, Denise K. Kulhanek, Christopher J. Lombardi, Nicole Malerba, Kendra McKoy, Peter P. McLaughlin, Jr., Donald H. Monteverde, J.N. Stanley, and Stella Woodard2
Management and restoration of the Mississippi River Deltaic plain and associated wetlands require... more Management and restoration of the Mississippi River Deltaic plain and associated wetlands requires a quantitative understanding of sediment delivery during large flood events, past and present. Here, we investigate the sedimentary fingerprint of the 2011 Mississippi River flood across a broad expanse of the Louisiana coast (Atchafalaya Delta, Terrebonne, Barataria and Mississippi River Delta basins) to assess spatial patterns of sedimentation and to identify key indicators of sediment provenance. The sediment deposited in wetlands during the 2011 flood event was distinguished from earlier deposits based on biological characteristics, primarily absence of plant roots and increased presence of centric (planktonic) diatoms indicative of Page 2 of 17 riverine origin. By comparison, the lithological (bulk density, organic matter content and grain size) and chemical (stable carbon isotopes of bulk organic matter) properties of flood sediments were nearly identical to the underlying deposit. Flood sediment deposition was greatest in wetlands near the Atchafalaya and Mississippi Rivers and accounted for a substantial portion (35 to 88%) of the annual accretion measured at nearby monitoring stations. The amount of sediment delivered to those basins (1.1 to 1.6 g cm 2) was comparable to that reported previously for hurricane sedimentation along the Louisiana coast (0.8 to 2.1 g cm 2). Our findings not only provide insight into how large-scale river floods influence wetland sedimentation, they lay the groundwork for identifying previous flood events in the stratigraphic record.
We have expanded the previously available quality-controlled database of relative sea-level (RSL)... more We have expanded the previously available quality-controlled database of relative sea-level (RSL) observations for the US Atlantic coast with data from the Atlantic coast of Canada, the Pacific coast of North America and the Caribbean. The Holocene sea-level database for the US Atlantic coast consisted of 836 sea-level indicators. The database documented a decreasing rate of relative sea-level (RSL) rise through time with no evidence of sea level being above present in the middle to late Holocene. The highest rates of rise ...
Geological Society of America Abstracts with Programs, Nov 6, 2012
We have expanded the previously available quality-controlled database of relative sea-level (RSL)... more We have expanded the previously available quality-controlled database of relative sea-level (RSL) observations for the US Atlantic coast with data from the Pacific coast of the USA and Canada, and the Caribbean. The Holocene sea-level database for the US Atlantic coast consisted of 836 sea-level indicators. The database documented a decreasing rate of relative sea-level (RSL) rise through time with no evidence of sea level being above present in the middle to late Holocene. The highest rates of rise were found in the mid-Atlantic ...
<p>Rising sea levels in the 21<sup>st</sup... more <p>Rising sea levels in the 21<sup>st</sup> century threaten coastal communities with inundation, yet projecting the relative and global mean sea level response to climate warming is complex. Lack of contemporary analogues for future climate dynamics has turned attention to periods in the geologic past that can illuminate how Earth’s climate system reacts to temperature forcing. Recent evidence suggests the Antarctic and Greenland ice sheets may have retreated inland of their present-day extents during the mid-late Holocene (~8-3 ka), then readvanced until the pre-industrial. These findings have highlighted the utility of the mid-Holocene—when summer temperatures in the northern hemisphere may have neared 4 degrees hotter than preindustrial levels—as a partial analogue for future warming.</p><p>Here we present a new probabilistic estimate of mid-Holocene global mean sea level (GMSL). We construct an ensemble of global ice sheet reconstructions for the last 80 kyr that spans a range of possible mid-Holocene GMSL scenarios. We predict relative sea level from each model accounting for glacial isostatic adjustment and using a range of solid earth structures. We then compare these predictions to 10,733 postglacial sea-level indicators and weigh the GMSL curves from each ice model using data-model fits. The constraints placed on mid-Holocene global mean sea level clarify climate dynamics during this critical interval in Earth’s recent history, and enable new estimates of post-glacial Antarctic ice volume and the likelihood of mid-Holocene West Antarctic ice sheet readvance.</p><p> </p>
Wetlands in the Mississippi River deltaic plain are deteriorating 1 in part because levees and co... more Wetlands in the Mississippi River deltaic plain are deteriorating 1 in part because levees and control structures starve them of sediment 2-4 . In spring 2011 a record-breaking flood brought discharge on the lower Mississippi River to dangerous levels, forcing managers to divert up to 3,500 m 3 s -1 of water to the Atchafalaya River Basin 5 . Here we use fieldcalibrated satellite data to quantify differences in inundation and sediment-plume patterns between the Mississippi and Atchafalaya River. We assess the impact of these extreme outflows on wetland sedimentation, and use in situ data collected during the historic flood to characterize the Mississippi plume's hydrodynamics and suspended sediment. We show that a focused, high-momentum jet emerged from the leveed Mississippi, and delivered sediment far offshore. In contrast, the plume from the Atchafalaya was more diffuse; diverted water inundated a large area, and sediment was trapped within the coastal current. The largest sedimentation, of up to several centimetres, occurred in the Atchafalaya Basin despite the larger sediment load carried by the Mississippi. Sediment accumulation was lowest along the shoreline between the two river sources. We conclude that river-mouth hydrodynamics and wetland sedimentation patterns are mechanistically linked, providing results that are relevant for plans to restore deltaic wetlands using artificial diversions 2-4,6-8 . Protecting and expanding coastal wetlands is vital for ecosystem services of the Mississippi River Delta 9-12 , and harnessing natural processes of wetland building using the Mississippi River and its sediments is an essential component of restoration plans . The only portion of the delta experiencing significant expansion of coastal wetland at present is at the mouth of the Atchafalaya River (Fig. ), where a higher mineral (that is, non-organic) sediment concentration 3 and hydrodynamic factors 8 allow sufficient sediment deposition 6 to outpace subsidence and sea-level rise . The recently released 2012 Coastal Master Plan 14 proposes river diversions and channel realignment to divert sediment and fresh water from the Mississippi River and Atchafalaya River into adjacent basins, to reconnect the river to delta wetlands. Successful design and implementation of such measures require an understanding of diverted sediment movement and deposition, especially during high-water events when the potential sediment load is greatest. The Mississippi River flood of spring 2011 was one of the largest on record 5,15 . Both the Mississippi River and Atchafalaya River
<p>The Canadian landmass of North America and the Russian Arctic were covered by la... more <p>The Canadian landmass of North America and the Russian Arctic were covered by large ice sheets during the Last Glacial Maximum, and have been key areas for Glacial Isostatic Adjustment (GIA) studies. Previous GIA studies have applied 1D models of Earth’s interior viscoelastic structure; however, seismic tomography, field geology and recent studies reveal the potential importance of 3D models of this structure. Here, using the latest quality-controlled deglacial sea-level databases from North America and the Russian Arctic, we investigate the effects of 3D structure on GIA predictions. We explore scaling factors in the upper mantle (<em>β<sub>UM</sub></em>) and lower mantle (<em>β<sub>LM</sub></em>) and the 1D background viscosity model (<em>η<sub>o</sub></em>) with predictions of of the ICE-6G_C (VM5a) glaciation/deglaciation model of Peltier et al (2015, JGR) in these two regions, and compare with the best fit 3D viscosity structures.</p><p>We compute gravitationally self-consistent relative sea-level histories with time dependent coastlines and rotational feedback using both the Normal Mode Method and Coupled Laplace-Finite Element Method. A subset of 3D GIA models is found that can fit the deglacial sea-level databases for both regions. These databases cover both the near and intermediate field regions. However, North America and Russian Arctic prefer different 3D structures (i.e., combinations of (<em>η<sub>o</sub>, β<sub>UM</sub>, β<sub>LM</sub></em>)) to provide the best fits. The Russian Arctic database prefers a softer background viscosity model (<em>η<sub>o</sub></em>), but larger scaling factors (<em>β<sub>UM</sub>, β<sub>LM</sub></em>) than those preferred by the North America database.</p><p>Outstanding issues include the uncertainty of the history of local glaciation history. For example, preliminary modifications of the ice model in Russian Arctic reveal that the misfits of 1D models can be significantly reduced, but still fit less well than the best fit 3D GIA model.An additional issue concerns the extent to which the 3D models are able to improve both fits in North America and Russian Arctic when compared with 1D internal structure (ICE-6G_C VM5a & ICE-7G VM7), will be assessed in a preliminary fashion.</p>
Rising global sea level, a consequence of climate change, results from an increase in the world o... more Rising global sea level, a consequence of climate change, results from an increase in the world ocean’s water volume and mass. Recent climate warming is responsible for producing the highest rate of global average sea-level rise of the past few millennia, and this rate will accelerate through the 21st century and beyond, exposing low-lying islands and coastal regions to significant flood risks. The flood risks can be compounded or diminished locally because changes in sea level are not uniform. In this review, we briefly discuss ice sheets as drivers of global and local sea levels, and how they could evolve under modern climate change. We underline some of the impacts of sea level change on coastal communities, and emphasize that local sea-level projections can be very different from estimates of the global average.
Holocene relative sea-level (RSL) records exhibit spatial and temporal variability that arises ma... more Holocene relative sea-level (RSL) records exhibit spatial and temporal variability that arises mainly from the interaction of eustatic (land ice volume and thermal expansion) and isostatic (glacio- and hydro-) factors. We fit RSL histories from near-, intermediate-, and far-field locations with noisy-input Gaussian process models to assess rates of RSL change. Records from near-field regions (e.g., Antarctica, Greenland, Canada, Sweden, and Scotland) reveal a complex pattern of RSL fall from a maximum marine limit due to the net effect of eustatic sea-level rise and glacio-isostatic uplift with rates of RSL fall as great as −69 ± 9 m/ka. Intermediate-field regions (e.g., mid-Atlantic and Pacific coasts of the USA, Netherlands, Southern France, St. Croix) display variable rates of RSL rise from the cumulative effect of eustatic and isostatic factors. Fast rates of RSL rise (up to 10 ± 1 m/ka) are found in the early Holocene in regions near the center of forebulge collapse. Far-field ...
Mangrove sediments are valuable archives of paleoenvironmental and relative sea-level changes. Th... more Mangrove sediments are valuable archives of paleoenvironmental and relative sea-level changes. The most widely applied method to obtaining chronologies of past changes in mangrove sediments is radiocarbon dating, because mangroves produce large amounts of organic matter in situ. However, there are many challenges to obtaining reliable radiocarbon chronologies because bioturbation processes from roots and crabs can rework mangrove sediments, resulting in ages that are not in stratigraphic order. Previous studies have suggested that methods that isolate specific sediment size fractions may yield ages closer to the age of the paleo depositional surface by removing younger carbon contamination from fine roots. This study examines which sample types are more likely to yield reliable radiocarbon ages using shallow cores from a mangrove environment on Mahé, Seychelles, in the Indian Ocean. We compare radiocarbon ages from bulk sediment, sieved organic concentrates and above-ground macrofos...
Kenneth G. Miller, Peter J. Sugarman, Scott D. Stanford, James V. Browning, Kimberly Baldwin, Bri... more Kenneth G. Miller, Peter J. Sugarman, Scott D. Stanford, James V. Browning, Kimberly Baldwin, Brian Buttari, Benjamin Dunham, Michael Farazaneh, Rachel Filo, Michael P. Gagliano, Benjamin Horton, Gabrielle Gallegos, Stephen Graham, Christopher S. Johnson, Nicole Khan, Denise K. Kulhanek, Christopher J. Lombardi, Nicole Malerba, Kendra McKoy, Peter P. McLaughlin, Jr., Donald H. Monteverde, J.N. Stanley, and Stella Woodard2
Management and restoration of the Mississippi River Deltaic plain and associated wetlands require... more Management and restoration of the Mississippi River Deltaic plain and associated wetlands requires a quantitative understanding of sediment delivery during large flood events, past and present. Here, we investigate the sedimentary fingerprint of the 2011 Mississippi River flood across a broad expanse of the Louisiana coast (Atchafalaya Delta, Terrebonne, Barataria and Mississippi River Delta basins) to assess spatial patterns of sedimentation and to identify key indicators of sediment provenance. The sediment deposited in wetlands during the 2011 flood event was distinguished from earlier deposits based on biological characteristics, primarily absence of plant roots and increased presence of centric (planktonic) diatoms indicative of Page 2 of 17 riverine origin. By comparison, the lithological (bulk density, organic matter content and grain size) and chemical (stable carbon isotopes of bulk organic matter) properties of flood sediments were nearly identical to the underlying deposit. Flood sediment deposition was greatest in wetlands near the Atchafalaya and Mississippi Rivers and accounted for a substantial portion (35 to 88%) of the annual accretion measured at nearby monitoring stations. The amount of sediment delivered to those basins (1.1 to 1.6 g cm 2) was comparable to that reported previously for hurricane sedimentation along the Louisiana coast (0.8 to 2.1 g cm 2). Our findings not only provide insight into how large-scale river floods influence wetland sedimentation, they lay the groundwork for identifying previous flood events in the stratigraphic record.
We have expanded the previously available quality-controlled database of relative sea-level (RSL)... more We have expanded the previously available quality-controlled database of relative sea-level (RSL) observations for the US Atlantic coast with data from the Atlantic coast of Canada, the Pacific coast of North America and the Caribbean. The Holocene sea-level database for the US Atlantic coast consisted of 836 sea-level indicators. The database documented a decreasing rate of relative sea-level (RSL) rise through time with no evidence of sea level being above present in the middle to late Holocene. The highest rates of rise ...
Geological Society of America Abstracts with Programs, Nov 6, 2012
We have expanded the previously available quality-controlled database of relative sea-level (RSL)... more We have expanded the previously available quality-controlled database of relative sea-level (RSL) observations for the US Atlantic coast with data from the Pacific coast of the USA and Canada, and the Caribbean. The Holocene sea-level database for the US Atlantic coast consisted of 836 sea-level indicators. The database documented a decreasing rate of relative sea-level (RSL) rise through time with no evidence of sea level being above present in the middle to late Holocene. The highest rates of rise were found in the mid-Atlantic ...
<p>Rising sea levels in the 21<sup>st</sup... more <p>Rising sea levels in the 21<sup>st</sup> century threaten coastal communities with inundation, yet projecting the relative and global mean sea level response to climate warming is complex. Lack of contemporary analogues for future climate dynamics has turned attention to periods in the geologic past that can illuminate how Earth’s climate system reacts to temperature forcing. Recent evidence suggests the Antarctic and Greenland ice sheets may have retreated inland of their present-day extents during the mid-late Holocene (~8-3 ka), then readvanced until the pre-industrial. These findings have highlighted the utility of the mid-Holocene—when summer temperatures in the northern hemisphere may have neared 4 degrees hotter than preindustrial levels—as a partial analogue for future warming.</p><p>Here we present a new probabilistic estimate of mid-Holocene global mean sea level (GMSL). We construct an ensemble of global ice sheet reconstructions for the last 80 kyr that spans a range of possible mid-Holocene GMSL scenarios. We predict relative sea level from each model accounting for glacial isostatic adjustment and using a range of solid earth structures. We then compare these predictions to 10,733 postglacial sea-level indicators and weigh the GMSL curves from each ice model using data-model fits. The constraints placed on mid-Holocene global mean sea level clarify climate dynamics during this critical interval in Earth’s recent history, and enable new estimates of post-glacial Antarctic ice volume and the likelihood of mid-Holocene West Antarctic ice sheet readvance.</p><p> </p>
Wetlands in the Mississippi River deltaic plain are deteriorating 1 in part because levees and co... more Wetlands in the Mississippi River deltaic plain are deteriorating 1 in part because levees and control structures starve them of sediment 2-4 . In spring 2011 a record-breaking flood brought discharge on the lower Mississippi River to dangerous levels, forcing managers to divert up to 3,500 m 3 s -1 of water to the Atchafalaya River Basin 5 . Here we use fieldcalibrated satellite data to quantify differences in inundation and sediment-plume patterns between the Mississippi and Atchafalaya River. We assess the impact of these extreme outflows on wetland sedimentation, and use in situ data collected during the historic flood to characterize the Mississippi plume's hydrodynamics and suspended sediment. We show that a focused, high-momentum jet emerged from the leveed Mississippi, and delivered sediment far offshore. In contrast, the plume from the Atchafalaya was more diffuse; diverted water inundated a large area, and sediment was trapped within the coastal current. The largest sedimentation, of up to several centimetres, occurred in the Atchafalaya Basin despite the larger sediment load carried by the Mississippi. Sediment accumulation was lowest along the shoreline between the two river sources. We conclude that river-mouth hydrodynamics and wetland sedimentation patterns are mechanistically linked, providing results that are relevant for plans to restore deltaic wetlands using artificial diversions 2-4,6-8 . Protecting and expanding coastal wetlands is vital for ecosystem services of the Mississippi River Delta 9-12 , and harnessing natural processes of wetland building using the Mississippi River and its sediments is an essential component of restoration plans . The only portion of the delta experiencing significant expansion of coastal wetland at present is at the mouth of the Atchafalaya River (Fig. ), where a higher mineral (that is, non-organic) sediment concentration 3 and hydrodynamic factors 8 allow sufficient sediment deposition 6 to outpace subsidence and sea-level rise . The recently released 2012 Coastal Master Plan 14 proposes river diversions and channel realignment to divert sediment and fresh water from the Mississippi River and Atchafalaya River into adjacent basins, to reconnect the river to delta wetlands. Successful design and implementation of such measures require an understanding of diverted sediment movement and deposition, especially during high-water events when the potential sediment load is greatest. The Mississippi River flood of spring 2011 was one of the largest on record 5,15 . Both the Mississippi River and Atchafalaya River
<p>The Canadian landmass of North America and the Russian Arctic were covered by la... more <p>The Canadian landmass of North America and the Russian Arctic were covered by large ice sheets during the Last Glacial Maximum, and have been key areas for Glacial Isostatic Adjustment (GIA) studies. Previous GIA studies have applied 1D models of Earth’s interior viscoelastic structure; however, seismic tomography, field geology and recent studies reveal the potential importance of 3D models of this structure. Here, using the latest quality-controlled deglacial sea-level databases from North America and the Russian Arctic, we investigate the effects of 3D structure on GIA predictions. We explore scaling factors in the upper mantle (<em>β<sub>UM</sub></em>) and lower mantle (<em>β<sub>LM</sub></em>) and the 1D background viscosity model (<em>η<sub>o</sub></em>) with predictions of of the ICE-6G_C (VM5a) glaciation/deglaciation model of Peltier et al (2015, JGR) in these two regions, and compare with the best fit 3D viscosity structures.</p><p>We compute gravitationally self-consistent relative sea-level histories with time dependent coastlines and rotational feedback using both the Normal Mode Method and Coupled Laplace-Finite Element Method. A subset of 3D GIA models is found that can fit the deglacial sea-level databases for both regions. These databases cover both the near and intermediate field regions. However, North America and Russian Arctic prefer different 3D structures (i.e., combinations of (<em>η<sub>o</sub>, β<sub>UM</sub>, β<sub>LM</sub></em>)) to provide the best fits. The Russian Arctic database prefers a softer background viscosity model (<em>η<sub>o</sub></em>), but larger scaling factors (<em>β<sub>UM</sub>, β<sub>LM</sub></em>) than those preferred by the North America database.</p><p>Outstanding issues include the uncertainty of the history of local glaciation history. For example, preliminary modifications of the ice model in Russian Arctic reveal that the misfits of 1D models can be significantly reduced, but still fit less well than the best fit 3D GIA model.An additional issue concerns the extent to which the 3D models are able to improve both fits in North America and Russian Arctic when compared with 1D internal structure (ICE-6G_C VM5a & ICE-7G VM7), will be assessed in a preliminary fashion.</p>
Rising global sea level, a consequence of climate change, results from an increase in the world o... more Rising global sea level, a consequence of climate change, results from an increase in the world ocean’s water volume and mass. Recent climate warming is responsible for producing the highest rate of global average sea-level rise of the past few millennia, and this rate will accelerate through the 21st century and beyond, exposing low-lying islands and coastal regions to significant flood risks. The flood risks can be compounded or diminished locally because changes in sea level are not uniform. In this review, we briefly discuss ice sheets as drivers of global and local sea levels, and how they could evolve under modern climate change. We underline some of the impacts of sea level change on coastal communities, and emphasize that local sea-level projections can be very different from estimates of the global average.
Holocene relative sea-level (RSL) records exhibit spatial and temporal variability that arises ma... more Holocene relative sea-level (RSL) records exhibit spatial and temporal variability that arises mainly from the interaction of eustatic (land ice volume and thermal expansion) and isostatic (glacio- and hydro-) factors. We fit RSL histories from near-, intermediate-, and far-field locations with noisy-input Gaussian process models to assess rates of RSL change. Records from near-field regions (e.g., Antarctica, Greenland, Canada, Sweden, and Scotland) reveal a complex pattern of RSL fall from a maximum marine limit due to the net effect of eustatic sea-level rise and glacio-isostatic uplift with rates of RSL fall as great as −69 ± 9 m/ka. Intermediate-field regions (e.g., mid-Atlantic and Pacific coasts of the USA, Netherlands, Southern France, St. Croix) display variable rates of RSL rise from the cumulative effect of eustatic and isostatic factors. Fast rates of RSL rise (up to 10 ± 1 m/ka) are found in the early Holocene in regions near the center of forebulge collapse. Far-field ...
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